Ultra-low power bias current generation and utilization in current and voltage source and regulator devices

Abstract

A bias current topology with embodiments in current source, current reference, (pseudo bandgap) voltage reference, and bandgap voltage reference that operate at ultra low currents and low power supply voltages which may use main stream standard digital Complementary Metal-Oxide-Semiconductor (CMOS) processes. The bias current topology uses chiefly a self cascode (SC), whose active resistor MOSFET is paced in series with the gate input of the MOSFETs that help generate the proportional to absolute temperature (PTAT) voltage that is applied to the active resistor MOSFET to produce a bias current.

Description

FIELD OF THE INVENTION

This invention relates to improvements in bias current generation for use in analog and mixed signal integrated circuits (ICs), such as current and voltage references and others.

BACKGROUND

Bias current generation is a core requirement for any integrated circuits (IC), including for higher order functions such as references, regulators, amplifiers, filters, clocks, analog to digital converter (ADC), digital to analog converter (DAC) and other key building blocks in any analog, mixed mode electronic system, or system on a chip (SOC). The bias current should be relatively stable under varying power supply and temperature conditions. Ideally it may further have the capability to operate with low power consumption.

SUMMARY OF THE INVENTION

Aspects of the embodiments disclosed herein include that they can often be fabricated in standard digital complementary metal-oxide semiconductor (CMOS) (e.g., for low cost and high volume applications); they may be resistor less (for ultra low power battery powered and emerging batteryless applications, and small size applications); their performance is mostly independent of metal-oxide-semiconductor field effect transistor's (MOSFET's) threshold voltage or V_TH (e.g., for tight performance despite wide manufacturing variations of V_TH); and the embodiments typically operate MOSFETs in subthreshold (e.g., for low current and low supply voltage consumption applications). Also, by scaling and operating MOSFET pairs in the subthreshold region a pseudo thermal voltage or V_T may be generated which has proportional to absolute temperature (PTAT) voltage characteristics.

Other aspects of the embodiments disclosed herein may be a ‘current source’ comprising: a self cascode (SC) and an amplification function (in conjunction with PTAT voltage generation) whereby the PTAT signal is generated which is mostly dependent on thermal voltage (V_T). Also, a complementary to absolute temperature (CTAT) signal is generated which is mostly dependent on MOSFET's mobility (μ) so that a relatively temperature and V_TH independent bias current (I_BIAS) source may be produced. This may be done in part by applying the PTAT voltage (V_PTAT) and supplying the I_BIAS) at the gate and not the source of the reference current mirror or loop amplifier. In this way, the active MOS resistor (and the generation of the V_PTAT) is effectively placed in series with the gate terminals (instead of the source terminal) of the current mirror or loop amplifier. This topology provides the option and flexibility for employing differential source followers (or differential voltage followers) in unity gain before the amplification function. This option can help in generating a higher amplitude V_PTAT so to improve performance and die yield. The temperature coefficient (TC) of the current source can receive adjustments (through program or predetermination by topology with different MOSFET's aspect ratios) to exhibit approximately flat or positive or negative TC depending on electronics system's requirements.

Other aspects of the embodiments disclosed herein are a method of creating a ‘current reference’: two bias current sources (with same functional topology as the first disclosure above) I_TCa and I_TCb with same polarity TCs that are set by W/L ratios to yield differing slopes, and subsequently be ratioed and subtracted from each other to form a stable TC current reference (I_REF). Alternatively, depending on an application, the topology has the flexibility to deliver positive TC or negative TC I_REF that can also receive adjustments by programming or setting different MOSFET W/Ls. In each of the two bias current sources, the amplifier's built-in offsets are forced across MOSFETs contained in self-cascodes (SC) to make the I_TCa and I_TCb. The magnitudes of I_TCa and I_TCb are set partially independently from their TCs via MOSFET's aspect ratios. To generate an I_REF with stable TC, a current scalar and subtraction circuit then scales I_TCa to S_a.I_TCa whose value changes by the same amount as S_b. I_TCb over an objective temperature span. This resultant S_a.I_TCa current is then subtracted from S_b.I_TCb to yield an I_REF. S_a and S_b are abbreviated formulaic representations (as a function of MOSFET W/L ratios and CMOS device constants).

Other aspects of the embodiments disclosed herein are a ‘voltage reference’ (V_REF) circuit comprising: resistor free voltage reference with an output voltage V_REF, which can be a pseudo bandgap voltage, V_BG. Here, CTAT signal voltage (V_CTAT) is generated by V_BE of a parasitic bipolar junction transistor (BJT) in CMOS, and its PTAT signal voltage V_PTAT is generated by summing K of pseudo thermal voltage, V_T×ln(g), terms generated via K series (or chain) of scaled p-channel MOSFET (PMOSFET) self-cascodes (SC), whose operating conditions are provided through a bias current generator with substantially similar functional block diagram as the first and second disclosures above. Similarly, the TC of this V_REF can be set (by programming or predetermination by topology with different MOSFET's aspect ratios) to exhibit approximately flat or positive or negative TC, depending on electronics system's need.

Other aspects of the embodiments disclosed herein include a method of generating a bandgap voltage reference, V_BG. In the general category of conventional bandgaps, a voltage reference is comprised of a V_PTAT that is gained up by the ratios of two passive resistors and then added to a V_CTAT (e.g., V_BE) to produce V_BG. Passive resistors are generally prohibitive, in size or cost, for ultra low power applications based in standard digital CMOS. This embodiments herein generally eliminate the need for passive resistors. Instead, this disclosure consists of a network of composite active MOS resistors whose operating conditions (e.g., current) are supplied via the substantially similar bias current functional topology. Here, the central bias current generation and the bandgap loop circuitries, independently apply V_PTAT across functionally similar composite MOS resistors (i.e., R_M802 and R_M826r) to generate their respective operating currents (i.e., as a multiple or ratio of I_bias). The resultant V_PTAT is subsequently added to a V_CTAT (e.g., V_EB) to generate a V_BG. Again, the TC of this reference can be set (via programming or predetermination by topology with different MOSFET's aspect ratios) to exhibit approximately flat (for V_BG) or positive or negative TC output V_REF, depending on electronics system's requirement. Note that operations of: R_BIAS and I_BIAS in the SC of the bias generation circuit, the composite active MOS resistor circuit (i.e., R_BS), the chain or series of the same composite active MOS resistor (i.e., p.R_BG), and the bandgap's PTAT loop follow substantially similar operating mechanisms over process, temperature, and power supply variations. This embodiment which combines the bias current circuit, active resistor circuit, and bandgap PTAT loop circuit not only may avoid passive resistors (for ultra low current and low cost), but also it can enhance bandgap's overall performance by enabling tracking of operating conditions over process, temperature, and supply voltage variations.

Further aspects of the embodiments disclosed herein include: a method of generating a bias current by using a first active resistor metal-oxide-semiconductor field effect transistor (MOSFET) operating in the linear region that is in series with gate input terminals of a proportional to absolute temperature (PTAT) voltage generator.

Further aspects of the embodiments disclosed herein include: a system comprising: a means for generating a bias current is in series with gate input terminals of a proportional to absolute temperature (PTAT) voltage generator.

Further aspects of the embodiments disclosed herein include: a bias current generator system comprising: a first current generator comprising: a first amplifier having a built in offset voltage tracking a proportional to first absolute temperature (PTAT) voltage (V_PTAT); a first bias resistor metal-oxide-semiconductor field effect transistor (MOSFET) operating in the linear region and forming a first bias resistor, wherein the gate input terminals of the amplifier carrying the V_PTAT are in series with source-drain terminals of the first bias resistor MOSFET; and wherein a first bias current is generated as a ratio of the first V_PTAT over the resistance of the first bias resistor MOSFET and where adjustments can be made to the amplitude and temperature coefficient (TC) of the first bias current.

Further aspects of the embodiments disclosed herein include: a bias current generator system comprising: a MOSFET resistor operating in the linear region which is in series with a V_PTAT; and a means for generating said V_PTAT voltage and a bias current by feeding back the bias current into the MOSFET resistor. The MOSFET resistor may be part of MOSFET self-cascode or a current mirror.

Further aspects of the embodiments disclosed herein include: a bias current generator system comprising: a first current generator comprising: a first amplifier having inputs connected to the output of a first differential voltage follower, wherein the first differential voltage follower has a built in offset voltage tracking a proportional to first absolute temperature (PTAT) voltage (V_PTAT); a first bias resistor metal-oxide-semiconductor field effect transistor (MOSFET) operating in the linear region and forming a first bias resistor, wherein the gate input terminals of the first differential voltage follower carrying the V_PTAT are in series with source-drain terminals of the first bias resistor MOSFET; wherein the first amplifier output generates the bias current which flows through the source-drain of the bias resistor MOSFET until the amplifier input voltages are substantially equalized; and wherein a first bias current is generated as a ratio of the first V_PTAT over the resistance of the first bias resistor MOSFET and where adjustments can be made to the amplitude and temperature coefficient (TC) of the first bias current.

Further aspects of the embodiments disclosed herein include: a bias current generator system comprising: a MOSFET resistor operating in the linear region which is in series with a V_PTAT; a means for generating a V_PTAT; and a means for generating a bias current by feeding back the bias current into the MOSFET resistor. The MOSFET resistor may be part of MOSFET self-cascode or a current mirror.

Further aspects of the embodiments disclosed herein include: a method of generating a reference current comprising: generating first and second bias currents such that the first and second bias currents have the same polarity of temperature coefficient (TC) and different TC slopes; and wherein the first and second bias currents are then scaled and subtracted from one another to yield stable TC reference current over an objective temperature range.

Further aspects of the embodiments disclosed herein include: a system of generating a reference current comprising: a MOSFET resistor operating in the linear region; and a means for generating two bias currents with the same temperature coefficients (TC) polarity but different TC slope and different amplitudes which are subsequently subtracted from one another to form the reference current.

Further aspects of the embodiments disclosed herein include: a method of using a composite active metal-oxide-semiconductor field effect transistor (MOSFET) resistors in bandgap voltage reference comprising: developing a proportional to absolute temperature voltage (V_PTAT) across a composite active MOSFET resistors and subsequently adding the V_PTAT to a complementary to absolute temperature voltage (V_CTAT) to generate the band gap voltage.

Further aspects of the embodiments disclosed herein include: a system comprising: an active MOSFET resistor which has a V_PTAT placed across it to generate a bias current; and a means for generating a floating resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a system and method of generating ‘bias current’.

FIG. 2 is an alternative embodiment of FIG. 1 having a functional block diagram of the system and method of generating ‘bias current’.

FIG. 3 is another alternative embodiment FIGS. 1 and 2 having functional block diagrams of the system and method of generating ‘bias current’.

FIG. 4 is a schematic circuit diagram of the embodiment illustrating a bias current source, or regulator, or generator utilizing FIG. 1.

FIG. 5 is a schematic circuit diagram of the embodiment illustrating a current reference, or source, or regulator, or generator utilizing FIG. 2.

FIG. 6 is a schematic circuit diagram of the embodiment illustrating a voltage reference, or regulator, or bandgap voltage utilizing FIG. 2.

FIG. 7 is a schematic circuit diagram of the embodiment illustrating a bandgap voltage reference or regulator utilizing FIGS. 3, 8, and 9.

FIG. 8 is a schematic circuit diagram of the embodiment illustrating a bias current source, regulator, or generator utilized in embodiment of FIG. 7.

FIG. 9 is a schematic circuit diagram of the embodiment illustrating an active MOS resistor, a composite active MOS resistor or MOS resistor utilized in embodiment of FIG. 7 in conjunction with embodiment of FIG. 8.

FIG. 10 is a schematic circuit diagram of an embodiment illustrating a prior art bandgap voltage reference.

FIG. 11 is a schematic circuit diagram of an embodiment illustrating a prior art current source.

FIG. 12 is a schematic circuit diagram of an embodiment illustrating another prior art current source.

DETAILED DESCRIPTION

The following description has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Many modifications and variations are possible in light of the teachings disclosed herein. The embodiments were chosen and described to explain principles of operation and their practical applications. However, the scope of the invention is to be defined by the claims.

Battery operated or batteryless electronic systems benefit from integrated circuits and electronic components that consume minimal power, which can withstand and perform to specifications down to the lowest power supply levels over a wide span of temperatures, as well as ones that can provide stable Alternating Current (AC) and non-jittery transient power up and power down characteristics. For higher order analog functions (e.g., references, regulators, amplifiers, converters, voltage controlled oscillators, phased locked loops, clock chips, etc) and systems (e.g., mixed mode system on a chip (SOC)), higher performance of the bias generation function can facilitate a more rugged system topology and lower cost systems solutions when such functions can be fabricated in standard digital mainstream Complementary Metal-Oxide Semiconductor (CMOS) technologies. While battery operation would benefit from low current consuming electronics, however, for next generation batteryless electronics (e.g., batteryless Internet of Things, energy harvesting, biometrics electronics, etc.), ultra low power consuming electronics is a not a ‘nice to have’ but a ‘must have’.

Generally, ultra low power analog and mixed signal electronic systems require large value resistors that may occupy large die sizes. Otherwise, they would require special and additional fabrication layers (which are costly) to deposit high ohm per square resistive material on silicon wafers which makes the use of passive resistors very costly. In order for the new and emerging applications (e.g., energy harvesting, biometrics, consumer medical electronics) to realize their full market size and reach potential expediently, resistor free electronics in small die size are key, and being based in main stream digital CMOS fabrication process manufacturing (that is proven) would be required. Such proven manufacturing platforms help achieve low cost and reduce manufacturing risk so as to facilitate and expedite serving such emerging applications, especially those that require passing regulatory tests (that favor proven manufacturing platforms) such as bio-electronics and consumer bio-metrics applications.

Definitions, Acronyms and Abbreviations

The following terms, definitions, acronyms, term usages and abbreviations are explained below and used throughout this detailed description:

TERMS                            DESCRIPTION
Bias current, reference current  Used interchangeably
circuit, and current source
CMOS                             Complementary Metal Oxide
                                 Semiconductor (may be operated in
                                 subthreshold or normal regions)
MOSFET                           Metal Oxide Semiconductor Field
                                 Effect Transistors (may be operated in
                                 subthreshold or normal regions)
CMOS, PMOS, NMOS and             Used interchangeably
CMOSFET, PMOSFET,
NMOSFET
Gate, source, drain and gate     Used interchangeably
terminal, source terminal, and
drain terminal
W/L of a MOSFET                  Width over length ratio (aspect ratio)
                                 of MOSFETs
W/L of a MOSFET, scale factors,  Used interchangeably
and aspect ratios
Ohms per square or Ω/square      Resistivity of material per square area
Terms applied to the W/L of      Used interchangeably
MOSFETs such as predetermined,
or programmed, or set
A                                Ampere
V                                Volt
N                                Nano or 10−9 (e.g., nA = nano ampere
                                 or 10−9 A
BJT                              Bipolar Junction Transistor
PTAT                             Proportional to Absolute Temperature
CTAT                             Complementary to Absolute
                                 Temperature
VPTAT                            Proportional to Absolute Temperature
                                 Voltage
VCTAT                            Complementary to Absolute
                                 Temperature Voltage
PTAT signal, CTAT signal,        May be used interchangeably
VPTAT signal and VCTAT signal
VREF                             Reference voltage
VBG                              Bandgap voltage
IREF                             Reference current
IBIAS                            Bias current
RBIAS                            Bias resistor
RBG                              Bandgap resistor
VEB or VBE                       May be used interchangeably as the
                                 base emitter voltage of a BJT
M                                MOSFET carrier mobility
VT                               Thermal voltage
COX                              Gate oxide capacitance
VTH                              Threshold voltage of a MOSFET
M                                To show MOSFET mobility exponent
                                 factor used in device equations
N                                To MOSFET gain factor correction
                                 used in device equations
VOFS                             Offset voltage between MOSFETs
VDS                              Drain to source voltage of a MOSFET
IDS, ID or IDMxxx                Drain to source current of a MOSFET
VGS                              Gate to source voltage of a MOSFET
TC                               Temperature coefficient
VC                               Voltage coefficient
PSRR                             Power supply rejection ratio
‘a’ through ‘z’                  To show the ratio of MOSFET W/Ls
                                 or their aspect ratios used in a circuit
                                 design
Ki (e.g., Ka or Kb) or           To show formulaic constants as a
Sj (e.g., Sa or Sb)              function of either set MOSFET scale
                                 factor, or process fabrications
                                 constants, or both
SC                               MOSFET Self-cascode
MOSFET's linear, triode,         Used interchangeably
resistive regions of operations
Subthreshold                     MOSFET's Subthreshold region of
                                 operation
Differential source follower,    Used interchangeably
differential voltage follower,
differential DC level shifters,
unity gain buffers, and
differential voltage buffers
VPTAT, VBIAS, built in offset voltage Used interchangeably
Resistance and impedance         Used interchangeably

Here is a brief introduction of the bias current generator block diagram functions (FIGS. 1, 2, and 3). The proposed bias current generation circuit belongs to a class of circuits that uses thermal voltage (V_T) as a PTAT signal that work in concert with MOSFET's mobility (μ) as a CTAT signal to generate a current that can be set (predetermined and programmed via MOSFET's W/L ratios, which can be controlled most accurately in fabrication process manufacturing) to be approximately stable with temperature (i.e., have a stable TC) or have a positive or negative TC, depending on the electronics systems need.

The majority of circuit implementations (in the prior art in this category of bias current generation) derail in their current regulation at high temperatures. When operating at ultra low currents, amongst other factors, the MOSFET's small leakage currents (e.g., MOSFET source, drain, body junction diode's leakage) may no longer be ignored, when compared to that of the (also very small) circuit's operating currents. Leakage current especially mounts at hot temperatures and as such they can interfere and derail performance. Although, operating at ultra low currents generally narrows the temperature span due, in part, to standard digital CMOS device leakages, but circuits may be more or less sensitive to leakage depending on topology. For example, in the prior art implementations, where the bias resistors are in series with the source of the current mirror or loop amplifier circuit, such implementations are accompanied with asymmetries induced by mismatched MOFET W/Ls in order to generate the PTAT signal in current mirrors, loop amplifiers, and or self-cascode cells. Therefore, high temperature operation may, in part, be hindered due to MOSFET source drain body junction diode leakage imbalances. For example, in asymmetric junction diode areas in drain or source terminal's leakage currents pile on (which are hard to match and cancel) as they double every 10 degrees Celsius (10 C)—in a thin ice circuit environment so to speak—where each transistor is already operating in ultra low currents (approximately five to tens of nanoamperes (e.g., more than approximately 5 nA and less than approximately 100 nA).

In order for the leakage current imbalances present in ‘signal paths’ of current mirror's, or loop amplifier's, or self-cascode's to be contained for a majority of bias current circuit implementations in the prior art, MOSFET aspect ratios need to be somewhat restricted, which limits the magnitude of the V_PTAT signal that can be generated. In the subthreshold region (for ultra low current operation), MOSFET's mismatches are dominated by V_TH mismatches. The implementation of most of the prior art systems, generally limits the magnitude of the V_PTAT signal (to contain leakage), which then makes the topology more sensitive to MOSFET's V_TH mismatches. As such, the V_TH mismatches become a large part of the intended V_PTAT magnitude, which worsens the current source's die yield to specifications. Moreover, in the general cases of the prior art (e.g., when using a self-cascode structure to generate the PTAT signal) the positive TC of V_T term and negative TC of V_GS (V_TH) can push the self-cascode stack off to the edge of the triode-saturation region and derail accuracy of the current reference at min-max temperatures. In the next sections, the proposed embodiments are described along with their benefits.

Suitable for ultra low power and high volume applications, the proposed ‘bias current generator’ IC belongs to a resistor-free category of CMOS circuits that combines a proportional to absolute temperature (PTAT) signal dependent mostly on pseudo thermal voltage (V_T) and a complementary to absolute temperature (CTAT) signal dependent mostly on MOSFET's mobility (μ) to generate a relatively temperature and MOSFET threshold voltage (V_TH) independent current source, although the embodiments disclosed here can be set to deliver positive or negative TC depending on application need.

First, a brief description of the general embodiments are provided where the ‘bias current generator’ block diagrams contain 2 basic functions: amplification function (in combination with some V_PTAT as a built in offset voltage generation function) and self cascode (SC) function. A subset of variations of the bias current generator's functional block diagrams are depicted in FIGS. 1 and 2 which demonstrate using either NMOS or PMOS self cascode (SC) with respect to a voltage source V_B (e.g., negative power supply). Other variations knowable to those skilled in the art, could include, but not limited to, using n-type metal-oxide-semiconductor field effect transistor (NMOSFET) or p-type metal-oxide-semiconductor field effect transistor (PMOSFET) SC with respect to a positive power supply as well.

Functional block diagram of FIG. 1 is utilized in bias current source embodiment of FIG. 4. Functional block diagram of FIG. 2 is utilized in embodiment of FIG. 5 (current reference), and FIG. 6 (voltage reference, which can be a pseudo bandgap voltage reference). Functional block diagram of FIG. 3 is utilized in embodiment of FIG. 7 (bandgap voltage reference). The specific embodiments of each of the FIGS. 4, 5, 6, and 7 will be described below in detail.

The simplified block diagrams in FIGS. 1, 2, and 3 could contain elements such as amplifiers. The amplifier is defined herein broadly. For example, it could be a voltage output or current output amplifier, or have voltage output combined with voltage controlled current source or VCCS. Such an amplifier, could also contain differential buffers (e.g., differential source followers, DC level shifters, voltage offset generators in series with its differential inputs). Other elements contained here could be voltage followers, DC level shifters, voltage offset generators, independent Voltage Controlled Current Sources (VCCS), current mirrors, bias current or current generator circuits, self-cascodes, and MOS transistors (e.g., MOS transistors can be configured to function as an active resistor, or VCCS, current mirrors, current sources or active resistors or can be paired in the input of an amplifier or buffer or DC level shifter—with differing scale factors—to generate offset voltage).

In FIGS. 1, 2, and 3, the amplifiers A_200n, and A_400p, and A_800p (respectively) combined with or embed offset voltage (i.e., multiple of V_T or V_PTAT) generation circuits. Note that although V_T is generally thermal voltage associated with BJTs. However, when operating multiple MOSFETs (which are scaled differently or are operated at different quiescent currents) in a subthreshold region, a pseudo V_T term may be realized as a function of their gate terminal to source terminals voltage (V_GS) differences which is what is done here. The described amplifiers, generate and force the I_BIAS current (i.e., ID_M202n, ID_M402p, ID_M802p) through the self cascode MOSFETs (i.e., M_200n-M_202n, M_400p-M_402p, M_800p-M_802p) until the inputs of said amplifiers are substantially equalized with some amplitude of V_PTAT that can be set by W/L of input MOSFETs (e.g., combining the V_PTAT generation and amplification circuits). Note that the I_BIAS can be set to generate a positive, negative, or stable TC depending on settings of MOSFET's W/L ratios. The PTAT signal is mostly contributed via pseudo thermal voltage, or pseudo V_T, derived from the built in or programmed offset voltages that can be generated by subthreshold MOSFET of the differential inputs, at their gates (e.g., of either the amplifier or voltage followers or combination thereof). The CTAT signal is mostly contributed via μ of the resistive MOSFET that is contained in the self-cascode.

Node description of FIG. 1 is as follows: node 200n is connected to the output of A_200n, drain and gate of M_200n, and gate of M_202n. Node 202n is connected to sources and body of M_200n, drain of M_202n, and input of A_200n. Node V_B is connected to voltage source, the other input of A_200n, and source and body of M_202n.

Node description of FIG. 2 is as follows: node 400p is connected to the output of A_400p, drain and gate of M_400p, and gate of M_402p. Node 402p is connected to sources and body of M_400p, drain of M_402p, and input of A_400p. Node V_B is connected to voltage source V_B, the other input of A_400p, and source and body of M_402p.

Node description of FIG. 3 is as follows: node 800p is connected to the output of A_800p, drain and gate of M_800p, and gate of M_802p. Node 802p is connected to sources and body of M_800p, drain of M_802p, and input of A_800p. Node 1p is connected to voltage source V_A, the other input of A_800p, and source and body of M_802p.

In FIGS. 1, 2, and 3, the MOSFET aspect ratios p₁, p₂, n₁, and n₂ can be predetermined or programmed from approximately 0.1 to approximately 20. Note that there are other variations of this embodiment. For example, self cascodes (SC) can be NMOS or PMOS types with their body terminal shorted to the sources or to voltage sources (e.g., a supply voltage), and the SC's operating current can be supplied with I_BIAS via a VCCS from the positive or negative supply or other voltage source terminals. The amplifier block (i.e., A_200n, A_400p, and A_800p) can be a voltage output or current output (e.g., trans conductance amplifier) or an amplifier with a built in offset, or series combination of an amplifier with no built offset plus source followers (or DC level shifters) with built in offsets that generates a V_PTAT signal.

In summary, the higher performance of the bias current generator shown in block diagrams of FIGS. 1, 2, and 3 or their other variations are achieved in part by sensing the V_PTAT and forcing the I_BIAS at the ‘gate’ and not the ‘source’ terminal of the reference current mirror or loop amplifier. In effect, the V_PTAT is generated and applied at the gate of the current mirror or loop amplifier. In such a configuration, the active MOS resistor (R_BIAS) in series with the gate of the current mirror or loop amplifier, and the I_BIAS is flowing through the active MOS resistor drain to source terminals. There are additional benefits in this bias current generator, such as more flexibility, enhanced AC and transient response, less leakage, more rugged topology for manufacturability, which will be discussed in more details herein. Moreover, there are extended and combinational benefits when utilizing this bias generator function in combination with other higher level analog functions such as a current reference (i.e., FIGS. 4 and 5) and voltage reference (i.e., FIGS. 6 and 7), which will be also described in more detail in subsequent sections.

Placing the MOSFET of self cascode that establishes the R_BIAS (i.e., M_202n, M_402p, M_802p) in ‘gate’ and not the ‘source’ terminal of the current mirror or loop amplifier, effectively places the R_BIAS function into the feedback loop of the current mirror amplifier signal path. One benefit of this feature is that, in effect, the open loop amplification in effect reduces the impedance effect of the R_BIAS (which is in the mega ohms level for ultra low currents) at output and input nodes of the current mirror or loop amplifier.

These implementations allows for the flexibility and having the option of employing differential source followers to generate a larger V_PTAT (instead of prior art use of either asymmetric current mirror's or loop amplifier's source terminal connected to R_BIAS or scaled self-cascode, which in part can limit optimal amplitude for the V_PTAT signal). This method's flexibility allows for larger V_PTAT which helps desensitize I_BIAS from offsets (e.g., due to normal manufacturing V_TH and W/L mismatches associated with transistors in current mirror and loop amplifier). Therefore the I_BIAS could be more insensitive to standard digital CMOS process fabrication variations and mismatches.

Source drain junctions of MOSFETs have leakage current that double with every 10 C rise in temperature. The proposed bias current generator topology allows for reduction of the impact of asymmetric aspect ratios for MOSFETs, and the narrowing their undesirable impact of their associated source drain junction leakages, for example in the cascoded current mirrors, in the I_BIAS current mirror or current loop amplifier.

This bias current generation scheme provides the option of utilizing NMOSFET or PMOSFET self cascodes where with respect to either the positive and negative power supply. For example, this is demonstrated in FIG. 1 with NMOSFET SC and FIG. 2 with PMOSFET SC, where both implementations are with respect to V_B which can be a negative power supply. However, in FIG. 3, a PMOSFET SC is implemented with respect to V_A, which can be a positive power supply. This feature can have several benefits, including but not limited to, more power supply head room, higher PSRR, and more system topology flexibility in setting the bias current with respect to either positive or negative power supplies.

Another benefit of this bias current generation scheme is that it allows for negative power or V_SS and ground potential (GND) to be same, as well as allowing for decoupling of negative power or V_SS from ground (GND), where technically V_SS can run at a lower voltage than the ground potential. As a result, the bias current value may be set relative to either GND or V_SS depending on electronics system requirement, which provides for more system topology flexibility.

In summary, the benefits of the bias current generation circuit may include: the proposed topology can deliver current consumption in the tens of nanoamperes (nA) range (i.e., more than approximately 10 nA and less than approximately 100 nA) operate with sub 1 volt supply voltage in a small die size that is 4 to 50 times smaller in size, compared to prior art current references in its category. Benefits of this current reference may include: low cost, higher temperature span, low voltage coefficient (VC), wider TC and V_DD span. The impact of source-drain junction leakages is reduced and hot temperature span of the bias current generator is extended. Low power supply operation at ultra low current can be achieved in part because of the flexibility of the bias current generation scheme. Power supply rejection ratio (PSRR) and other AC performance are enhanced. The overall benefit of this class of bias current generators is retained, including for example, that it can operate in sub-threshold, which keeps current consumption low and enables lower V_DD operation. Moreover, the impact of process fabrication variation on performance is contained and controlled given the significantly less sensitivity of the bias current generation to V_TH and dependence on μ, which is more tightly controlled in fabrication process. Moreover, low cost is also achieved because in part the proposed topology does not require any passive resistors. Low cost is also achieved by proposed topology's small die size that may be based in standard digital CMOS, making the topology portable to multiple digital standard CMOS fabrication facilities. Also, basing the topology on standard digital CMOS fabrication process (without any custom or special devices) facilitates process portability which should help speeding up regulatory bodies qualification of new products (i.e., biometric ICs) who view standard manufacturing ICs much more favorably.

Description of the FIG. 4 Embodiment in a ‘Bias Current Source’

The first utilization of the functional block diagram of FIG. 1 (bias current generation) is embodied in the ‘bias current source’ that is depicted in FIG. 4 which can contain elements such as amplifiers. The amplifier is defined here broadly, which could be a voltage output or current output, or have voltage output combined with voltage controlled current source or VCCS. Such an amplifier could also contain differential buffers (e.g., differential source followers, DC level shifters, voltage offset generators in series with its differential inputs). Other elements contained here could be independent voltage followers, DC level shifters, voltage offset generators, voltage controlled current source (VCCS), current mirrors, bias current or current generator circuits, self-cascodes, and MOS transistors (e.g., MOS transistors can be configured to function as an active resistor, or VCCS, current mirrors, current sources or active resistors or can be paired in the input of an amplifier or buffer or DC level shifter—with differing scale factors—to generate offset voltages).

Here is a brief summary of the description and benefits of the embodiment of FIG. 4, which flow from functional block diagram of the embodiment shown in Figure (and its various benefits that were just summarized in the previous section).

Suitable for ultra low power applications, including energy harvesting, the proposed ‘bias current source’ embodiment belongs to a resistor-free category of CMOS circuits that combines a PTAT signal dependent mostly on V_T and CTAT signal dependent mostly on MOSFET's μ to generate a relatively temperature and V_TH independent current source. The proposed topology consumes ultra lower currents (e.g., 50 nA to 500 nA) and can operate with sub-1V V_DD. The simplicity of the topology, in part, enables its small size, compared to prior art current references in its category. It has the potential for wider temperature compared to its alternatives. Higher temperature span may be achieved by the following. First, sensing the PTAT voltage and forcing the I_BIAS at the gate and not the source of the reference current mirror or loop amplifier. In effect this topology, places the R_BIAS (and the development of V_BIAS) in series with the gate as opposed to in series with the source of the current mirror or loop amplifier. Second, having the option of using differential source followers to generate a larger PTAT voltage instead of prior art use of either asymmetric MOSFETs in the current mirror or current loop amplifier and or scaled self-cascode. Third, using donut shaped equal W/L transistors in a circuit layout to minimize the drain size for less leakage current.

This embodiment allows for larger PTAT voltage, which helps desensitize I_BIAS from error contributions of normal mismatches and offset and fabrication process variations (e.g., V_TH and W/L mismatches associated with transistors in current mirror and loop amplifier). The proposed topology allows for minimization or elimination of the impact of asymmetric transistors and cascoded current mirrors in the current reference (I_REF or I_R or I_r) loop. As a result, compact die size is realized, the impact of source-drain junction leakages is reduced substantially, and hot temperature span is extended.

In FIG. 4, the signal loop that generates the operating current, or I_BIAS, of the circuit consist of M₂₀₂ (which makes the active CMOS resistor, R_BIAS or R_M202), source followers M₂₀₄ and M₂₀₆, voltage amplifier A₂₀₀, and PMOS transistors M₂₁₀-M₂₁₆. Note that all transistors used in this embodiment of FIG. 4 circuitry operate in the subthreshold region to keep the power supply headroom and current consumption low, but this topology is not limited to subthreshold operation. The active resistor MOSFET, M₂₀₀, operating in triode, takes a small die size but can generate high value resistor (R_M202) needed for ultra low power applications. As noted earlier, this would otherwise be impractical (due to large size or high cost of additional thin film resistor layer) with the available passive resistor in standard digital CMOS fabrication. Transistors M₂₁₄ and M₂₁₆ (where aspect ratio or W/L_M216 over W/L_M214 is ‘d’) function as current sources for the source follower differential pairs composed of M₂₀₄ (biased by ID_M214) and M₂₀₆ (biased by ID_M216) that have a built in offset voltage (set by aspect ratios of M₂₀₄ over M₂₀₆ that is ‘b’) which help generate the PTAT term V_T.ln(b×d) or V_BIAS or V_PTAT. Note that the active MOS resistor, M₂₀₂, which is the R_BIAS, is in series with the gates of source followers, M₂₀₄ and M₂₀₆, that feed the inputs of the current loop amplifier, A₂₀₀. This in effect, places the R_BIAS and generation of the V_BIAS (or V_PTAT) applied to the gate of loop amplifier, A₂₀₀. The amplifier A₂₀₀ substantially equalizes its inputs which are the source terminals voltages of M₂₀₄ and M₂₀₆ by forcing the gate voltages of transistors M₂₁₀ and M₂₁₂ (which operate as a voltage controlled current source (VCCS)). Accordingly, operating currents ID_M210 and ID_M212 flow through R_M202 whose operating current scales in proportion with I_BIAS. The value of R_M202 or R_BIAS is a function of I_BIAS as well as being set in part by the SC₂₀₀ (composed of M₂₀₀ and M₂₀₂) W/Ls and MOSFETs mobility (μ), which helps generate the CTAT term. Note that in FIG. 4 the scale factors a, b, c, and d are the ratios of transistor's width over length (W/L or scale factors or aspect ratios) that may be programmed or predetermined from approximately 0.1 to approximately 50 (but for ‘c’ that can be zero that is eliminating M₂₁₂) depending on such considerations as die size and various operating specifications, including but not limited to current consumption, temperature coefficients, and power supply range objectives.

The connections of the elements in FIG. 4 are described as follows. Node 1 is the positive supply voltage terminal or V_DD. Node 2 is the negative supply voltage terminal or V_SS (which can also be set as the zero voltage terminal or ground). The source and body terminals of transistors M₂₁₀, M₂₁₂, M₂₁₄, and M₂₁₆ are connected to node 1. Node 2 is connected to source and bodies of M₂₀₂, M₂₀₄, and M₂₀₆, as well as the body of M₂₀₀. Transistors M₂₀₀ and M₂₀₂ form the self cascode, where the diode connected M₂₀₀ is cascoded with M₂₀₂. Node 200 is connected to the gate and drain terminals of M₂₀₀ as well as to the gate of M₂₀₂ plus drain of M₂₁₀. Node 202 is connected to the source terminal of M₂₀₀, and drain terminal of M₂₀₂, and gate of M₂₀₄, and drain of M₂₁₂. Note that the body terminal of M₂₀₀ can be connected to either its source at node 202 or to node 2, depending on the process fabrication. In this embodiment, the body terminals of M₂₀₀ and M₂₀₂ are connected to node 2. Moreover, here the PTAT voltage is generated by using two source followers with a built in offset voltage, which is formed by transistors M₂₀₄ and M₂₀₆ combined with current sources supplied by M₂₁₄ and M₂₁₆. Node 204 is connected to the source and body of M₂₀₄, drain of M₂₁₄ and positive input of A₂₀₀. Node 206 is connected to body and source of M₂₀₆, drain of M₂₁₆, and negative input of A₂₀₀. Note that M₂₁₀, M₂₁₂, M₂₁₄, and M₂₁₆ function as current mirrors. Node 208 is connected to the output terminal of amplifier A₂₀₀, and it is connected to the gates of transistors M₂₁₀, M₂₁₂, M₂₁₄, and M₂₁₆. The drain current or I_D of M₂₀₈ constitutes the bias current of the circuit or reference current, I_BIAS.

In FIG. 4 there is the first voltage loop consisting of M₂₀₂, M₂₀₄, A₂₀₀, and M₂₀₆ produce a PTAT signal as a function of V_T which is forced upon the V_DS of M₂₀₂ by the operation of the M₂₀₄ and M₂₀₆ source followers (which carry the built in offset as a function of PTAT signal), the current source's loop amplifier A₂₀₀, and current mirrors M₂₁₈, M₂₁₄, M₂₁₂, and M₂₁₀ on the self cascade SC₂₀₀. There is also a second voltage loop consisting of M₂₀₀ and M₂₀₂ where M₂₀₀ operates in saturation and M₂₀₂ operates in the triode region (i.e., that is acting as an active MOS resistor of R_M202=R_BIAS for this current source). The active MOS resistor, while functioning as the current source's resistor, contributes to a CTAT signal being mostly a function of μ. Application of PTAT signal via V_T while interacting with CTAT signal via μ whose combination (using different MOSFET aspect ratios) can facilitate making a positive TC, or negative TC, as well as a stable TC for the I_BIAS. Note that for demonstrative clarity of the proceeding formulations, second order effects—including but not limited to—early voltage, body effect, and subthreshold slope factor TC are ignored:VGS_M202−VGS_M200=VDS_M202;R_BIAS=R_M202≈[μ.C_OX.(W/L)_M202(VGS_M202−V_THn−VDS_M202/2)]⁻¹;VGS_M202≈[2I_BIAS/μ.C_OX.(W/L)_M200]^1/2+V_THn;VGS_M206−VGS_M204=[V_T.ln(d×b)]=VDS_M202;VDS_M202≈I_BIAS(c+1)×R_M202≈[V_T.ln(d×b)];μ.C_OX.(W/L)_M202×[I_BIAS/μ.C_OX.(W/L)_M200]^1/2≈I_BIAS(c+1)×[V_T.ln(d×b)]⁻¹; andI_BIAS≈f(S₂₀₂,μ,V_T).

It can be noticed that V_TH term is canceled out in both the first loop (M₂₀₄, A₂₀₀, M₂₀₆) and the second loop (M₂₀₀, M₂₀₂). This trait can significantly reduce I_BIAS's sensitivity to V_TH, where V_TH has substantial variations in process fabrication and manufacturing (e.g., V_TH nominal at 0.4V with +/−50% variation). As it is the case with this class of current sources, I_BIAS is primarily a function of C_OX, V_T, and u. Here C_OX is a function of gate oxide thickness which has a very low temperature coefficient, V_T has a positive TC (PTAT like) and μ has a negative TC (CTAT like). Therefore, the TC of I_BIAS can be positive or negative or approximately flat depending on the abbreviated formulaic constant (scalar), S₂₀₂, which is function of MOSFET's aspect ratios a, b, and d as well as MOSFET device constants.

In this section some of the benefits of the utilization of the embodiment of FIG. 1 that is embodied in FIG. 4 are described. As noted earlier, the PTAT voltage or V_PTAT or V_BIAS of the current source is applied across an active resistor, R_BIAS at the gate terminal compared to the prior art (see FIG. 11 and FIG. 12) that does it at MOSFET's source terminal of the PTAT voltage generation circuit.

In both prior art examples depicted in FIG. 11 and FIG. 12, M_802sc or M_802cm which are the active MOSFET resistor (forming the R_BIAS) are placed in series with the source terminal of M_804sc or M_804cm, that are part of the M_804sc-M_806sc or M_804cm-M_806cm which is part of the circuit that generates the PTAT voltage (or V_BIAS or V_PTAT) that is applied across R_BIAS to make the I_BIAS (=V_BIAS/R_BIAS).

However, in this invention shown in FIG. 1 (or its equivalent variations FIG. 2 and FIG. 3) embodied in FIG. 4, the active MOSFET resistor M₂₀₂ which forms the R_BIAS (where the V_PTAT or V_BIAS or V_PTAT signal is applied) is placed in series with the gate of M₂₀₄ that is part of the M₂₀₄-M₂₀₆, which is part of the circuit that generates the V_PTAT or V_BIAS, which makes the I_BIAS (=V_BIAS/R_BIAS). Placing the R_BIAS with the gate terminal of the PTAT signal generation circuit has many benefits, some of which are explained below.

In the FIG. 4 embodiment, a larger V_PTAT can be generated via M₂₀₄ and M₂₀₈ differential source followers with larger asymmetric W/L ratios to make a larger built in offset voltage. The drains of the followers M₂₀₄ and M₂₀₆ are shorted to ground, which shorts their junction leakages also to ground. Donut shaped (in layout) M204 and M206 also help reduce the junction areas and their associated leakages. In this manner the V_PTAT generation function (i.e., the built in offset of the differential source followers) is separated from the function of current mirror or loop amplifier. As such, a current mirror or current loop amplifier can be constructed with complete symmetry (i.e., equal W/L ratios). Therefore, the bias current's high temperature regulation span is widened via minimizing current leakage in key signal paths because asymmetries in the current mirror or loop amplifiers associated with prior art implementations can be eliminated or reduced, and more of the drain or source junctions areas and their associated leakage currents are shorted to power supplies. As noted earlier, most prior art implementations, employ asymmetries by scaling-in offsets in current mirrors, loop amplifiers, and or self-cascade cells for V_T generation. As such, high temperature operation is in part hindered due to imbalances in asymmetric junction diode areas in drain or source terminals (which are hard to match and cancel out) and whose leakage currents pile on and double every 10 C—in a thin ice circuit environment so to speak—where each transistor is already operating in ultra low currents (five to tens of nano amperes).

For some of prior art implementations, it could be that in order for current mirror's, or loop amplifier's, or self-cascode's leakages to be contained (and ultimately its hot temperature performance less hindered), the MI (or area) of pertinent MOSFETs had to be somewhat restricted, which limits the allowed amplitude of V_PTAT that can be generated (e.g., approximately 50 mV versus 150 mV). Note again that Voltage Proportional to Absolute Temperature (V_PTAT) is generally generated via the difference in V_GS of two MOSFETs that operate in subthreshold, but whose W/L and or quiescent currents are scaled differently. A circuit topology for reliable manufacturing would benefit from a V_PTAT whose amount is set by W/L ratios and V_T (which are accurately controlled) as opposed to being dominated from example by V_TH mismatch between the two pair of MOSFETS. The prior art is restricted to smaller amount of V_PTAT (e.g., 50 mV) which is a disadvantage because it would increase the impact of normal process fabrication mismatches and offsets on controlling the value of I_BIAS to specifications in manufacturing, and ultimately the yield of I_BIAS to the target specifications. For example, a contribution of 5 mV of V_OFS (mismatch between two MOSFETs) to a 50 mV of V_PTAT is 10% offset error contribution to V_PTAT which is the case with some of the prior art. However, 5 mV of V_OFS over 150 mV V_PTAT is 3% offset error contribution to V_PTAT which can be the case with this embodiment's topology. In the embodiment of FIG. 4, by having the option of using source followers to generate the PTAT terms, the drain junction and their associated leakage are shorted to the negative supply which helps higher temperature span. An additional benefit of this embodiment besides the (some relief) greater freedom from derailment of hot performance due to drain or source junction current leakages, the differential source follower in FIG. 4 can be constructed for higher value V_PTAT (e.g., M₂₀₄ and M₂₀₆ aspect ratios >approximately 16× vs. prior art equivalent PTAT generator aspect ratio ˜4-6×). As such, V_TH mismatch (of the loop amplifier or current mirror) within the current loop equation becomes a smaller percent contributor to I_BIAS overall (in)accuracy. This in turn allows for using smaller transistors that would leak less and hence help extend the temperature span.

Note also that in the general cases of prior art (where a self-cascode structure is employed to generate the PTAT term) the positive TC of V_T.ln(b×d) and negative TC of V_GS (or V_TH) can push the self-cascode stack off to the edge of triode-saturation region and derail accuracy of current reference at min-max temperatures. Also, in the FIG. 4 embodiment, employing source follower (that also function as voltage buffers) to drive the input terminals of the loop amplifier, A₂₀₀, would help loop stability and enhance AC and transient response of this current source topology. This topology places the R_BIAS in the input-output feedback loop of the current mirror amplification function, which helps its DC and AC performance (e.g., the impact of the ultra high resistance value of R_BIAS, needed for ultra low current operation, can be attenuated by the gain of the current mirror loop amplifier). Another benefit of the FIG. 4 embodiment is that by establishing the I_BIAS via R_BIAS in the gate of current mirror loop (via amplifier A₂₀₀), it provides more flexibility for scaling (via scale factor c) M₂₁₀ and M₂₁₂ to set the value VDS_M202 and hence the value of I_BIAS. Moreover, this move also helps with balancing VDS_M202 across PMOSFETs non-cascade current source M₂₁₀, M₂₁₂, M₂₁₄, and M₂₁₆ pairs, which eliminates the need to use cascoded current mirrors (otherwise needed to avoid MOSFET's early voltage induced current mismatch). Moreover, another advantage of FIG. 4 embodiment is that, in part, due to balanced V_DS across M₂₁₀, M₂₁₂, M₂₁₄, and M₂₁₆, the VC, PSRR, and TC performance is not compromised despite smaller but equal sized W/L transistors (e.g., L=1 micron for all NMOS and PMOS). Additionally, another advantage of the embodiment of FIG. 4 is that the prior art's use of cascoded current mirrors with unequal source-drain junction areas (and their respective junction leakages which double with every 10 C increase in temperature) are avoided, which in turn helps with higher temperature span of this embodiment. Retaining the benefits of the class of bias current sources to which it belong, an advantage of the embodiment of FIG. 4 is it allows operation of MOS transistors in subthreshold, which enables low power supply and ultra low power consumption. Also, as noted earlier, the embodiment of FIG. 4 is substantially independent of V_TH and mostly depended on μ, which is better controlled in process fabrication, hence the overall power consumption of the bias current source is more tightly controlled over process variations. Having the flexibility of using NMOS or PMOS SC (self cascade) with respect to either of positive or negative power suppliers, another benefit of the embodiment of FIG. 4 is using such flexibility for the bias current source to operate with sub 1V power supply (i.e., minimum V_DD is limited to only subthreshold V_GS 2V_DS). Another benefit of the FIG. 4 embodiment is that V_SS (negative power supply) and the ground connection (GND) may be the same of separated, depending on system requirements, which allows I_BIAS to be set in value independent of the ground potential.

Description of the FIG. 5 Embodiment in a ‘Current Reference’

Employing the functional block diagram of FIG. 2 (which is a variation of that of FIG. 1) is utilized in the embodiment of a current reference that is depicted in FIG. 5. The embodiment of FIG. 5 includes current generator I_TCa, current generator I_TCb, and current scalar and subtractor which outputs the ‘current reference’, I_REF. One of the goals of utilizing the embodiment of FIG. 2 in the embodiment of FIG. 5 is to make current reference that is ultra low power, resistor free, whose operating condition are mostly independent of V_TH, based in CMOS process fabrication, where there is greater level of flexibility in programming or predetermining MOSFET's W/L sizes or ratios, to make a high performance I_REF with positive, negative, or stable TC.

The following is a description of the embodiment of FIG. 5. Typical reference topologies add two currents with opposing temperature coefficient (TC) polarities to generate a stable TC current, whereas this reference generates two currents (I_TCa and I_TCb) with same polarity TCs that are scaled with differing slopes, and subsequently scaled and subtracted from each other to form a positive or negative TC as well as a stable TC I_REF. Here is how: in FIG. 5, the two currents, I_TCa and I_TCb are generated across two PMOSFETs, M₄₀₂, and M_402b, as part of a pair of self-cascodes, SC_400a and SC_400b Loop amplifiers A_400a and A_400b operating in conjunction with the SCs force VDS_M402a and VDS_M402b to equal V_T.ln(c×d) and V_T.ln(f×g), respectively, which are the built-in offset voltages of A_400a and A_400b, respectively. Note here that the V_PTAT signal is not generated via the source followers or DC level shifters (which was the case with the functional block diagram of FIG. 1 when utilized in the embodiment of FIG. 4). Instead, the V_PTAT signal is initiated via a built in offset voltages that is generated by scaling (and or operating their quiescent current) differently the amplifier's input MOSFETs, which operate in the subthreshold region. The TC and magnitude of I_TCa=VDS_M402a/R_M402a and I_TCb=VDS_M402b/R_M402b can be sloped differently via (mostly by) adjustments in setting the ratio of W/Ls of M_400a-M_402a (i.e., mostly set by ‘a’) different from M_400b-M_402b (i.e., mostly set by ‘b’) while adhering to matching considerations by using the same narrow W and long L (i.e., Y) for M_400a-M_402a and M_400b-M_402b. Here the TC_a of R_402a in the denominator of I_TCa (with equally sized M_400a-M_402a in SC_400a) is sloped differently from TC_b of R_402b in the denominator of I_TCb (with differently sized M_400b-M_402b in SC_400b) by sizing b>a. Hence, apples-to-apples, there is less R_M402a contraction in resistance via increasing VGS_M400a at higher temperatures, since VGS_M402a−VGS_M400a=VDS_M402a=VT.ln(c×d).

As noted earlier, the proposed topology allows for magnitude and TC of I_TCa and I_TCb be set with some independence from one another using device aspect ratios, while it employs substantially identical topology mechanisms to generate I_TCa and I_TCb—which improves performance over power supply, temperature, and fabrication process variations. Concurrently, I_TCa and I_TCb (whose TCs and amplitudes are set partially independently from one another by adjustments to their MOSFET's aspect ratios) are fed into a current scalar and subtraction circuit, which scales (K_400a.I_TCa) to S₄₀₀. (K_400a.I_TCa) whose value changes by the same amount as K_400b.I_TCb over an objective temperature span. This resultant current or S₄₀₀.(K_400a.I_TCa) and K_400b.I_TCb are subtracted from each other to yield an I_REF. All generated currents are mostly independent of V_TH and primarily a function of MOSFET's μ and V_T, thus helping stable specifications of I_REF over fabrication process variations. Note that I_REF can also be programmed to have a negative or positive TC via wider flexibility in choosing different MOSFET's W/L ratios in the generation of I_TCa, I_TCb, and the scalar factor (e.g., S₄₀₀, K_400a and K_400b, which is a formulaic representation of MOSFET W/L ratios as well as MOSFET's device parameter constants) in the current scalar subtraction circuit.

This second utilization of the embodiment of FIG. 2 in the embodiment depicted in FIG. 5 includes elements such as amplifiers. The amplifier could be a voltage output or current output or have voltage output combined with voltage controlled current source or VCCS. Such amplifier, could also contain differential buffers (e.g., differential source followers, DC level shifters, voltage offset generators in series with its differential inputs). Other elements contained here could be voltage followers, DC level shifters, voltage offset generators, current mirrors, voltage controlled current source (VCCS), bias current or current generator circuits with differing TC, self-cascodes, current scale and subtractor circuit, and MOS transistors (e.g., MOS transistors can be configured to function as a VCCS, current mirror, current sources or active resistors or can be paired in the input of an amplifier or buffer or DC level shifter—with differing scale factors—to generate offset voltage).

As noted earlier, the same principles of this embodiments of the functional block diagram of FIG. 1 or its variation FIG. 2 can be utilized in the embodiment of FIG. 5. Here two independent bias current generators are utilized. For each of bias current generator, the R_BIASa,b (R_M402a,b) remains in the feedback loop of the current loop amplifier, and it is connected to the gate and not the source of the loop amplifier (V_BIAS which is the V_PTAT signal is not applied in series with the source terminal of the current mirror loop or loop amplifier). Note that other variations where a bias current generator (of FIG. 1 or FIG. 2) with R_BIASa is connected to the gate, and can be combined with a bias current generators where R_BIASb is connected to the source, which can offer a different cost performance characteristic. Another variation can be to have R_BIASa be based on an NMOS active resistor (as in FIG. 1), and the other R_BIASb be based on a PMOS active resistor (as in FIG. 2), where the process variations and relations between NMOS and PMOS can offer other cost performance traits. The embodiments shown in FIGS. 1 and 2 provide the flexibility to generate currents of I_TCa and I_TCb with two different TCs before they are scaled and subtracted from one another to generate the I_REF of interest. Also, note that all transistors used in this embodiment of FIG. 5 circuitry operate in the subthreshold region, but this topology is not limited to subthreshold operation.

Firstly, here are more details describing how current generator I_TCa yields a current with TC_a. The signal loop that generates I_TCa includes M_402a, which makes the active CMOS resistor, R_M402a (i.e. R_BIASa). The active transistor M_402a, operating in deep triode, makes the small size but high value resistor, R_M402a, which helps in keeping the die size small while current at ultra low levels. The signal loop is also composed of amplifier A_400a (consisting of M_404b-M_416a) with a built in offset determined by W/L ratios of M_404a to M_406a and M_410a to M_408a, which are c and d, respectively. Input stage of A_400a helps generate the PTAT term of about V_T.ln(c×d). The amplifier A_400a, substantially equalizes the V_DS of M_402a to the PTAT term of about V_T.ln(c×d). This is accomplished in part via forcing the gate voltages of transistors M_418a, which operate as a voltage controlled current source (VCCS) to bias M_402a and M_400a which set R_M402a and whose operating current scales in proportion with I_TCa. The value of R_M402a or R_BIAS-400a is set in part by the SC_400a composed of M_400a and M_402a scale factors and MOSFET's mobility which helps generate the CTAT term. The I_TCa is made of V_T.ln(c×d) divided by R_M402a. Note that in FIG. 5, the scale factors ‘a’ through ‘j’ are the ratios of transistor's width over length (W/L or scale factors or aspect ratios) that may be set depending on such considerations as die size and various operating specifications, including but not limited to current consumption, temperature coefficients, and power supply range objectives. The scale factors ‘a’ through ‘j’ shown in FIG. 5 can be between approximately 0.1 and 50.

Secondly, and similar to the above description to I_TCb generation, applying the same principle to the embodiment of FIG. 5, this is how current generator I_TCb outputs a current with TC_b. The signal loop that generates I_TCb includes M_402b, which makes the active CMOS resistor, R_M402b (i.e., R_BIASb). The active transistor M_402b, operating in deep triode, makes the small size but high value resistor, R_M402b, which helps in keeping the die size small while current at ultra low levels. The signal loop is also composed of amplifier A_400b (consisting of M_404b-M_416b) with a built in offset determined by W/L ratios of M_404b to M_406b and M_410b to M_408b, which are f and g, respectively. Input stage of A_400b helps generate the PTAT term of about V_T.ln(f×g). The amplifier A_400b, substantially equalizes the V_DS of M_402b to the PTAT term of about V_T.ln(f×g). This is accomplished in part via forcing the gate voltages of transistors M_418b, which operates a voltage controlled current source (VCCS) to bias M_402b and M_400b which set R_M402b and whose operating current scales in proportion with I_TCb. The value of R_M402b or R_BIAS-400b is set in part by the SC_400b composed of M_400b and M_402b scale factors and MOSFET's mobility which helps generate the CTAT term. The I_TCb is made of V_T.ln(f×g) divided by R_M402b.

Thirdly and lastly, the current I_TCb is scaled and mirrored via M_418b and M_420b (by 1/h.X) and fed into M_422b which is scaled (by j.X) and mirrored onto M_422a. Concurrently, the current I_TCa is scaled and mirrored via M_418a and M_420a (by 1/e.X) and fed into drain of M_422a. Here the final I_REF is generated which is a function of K_400b. I_TCb−S₄₀₀. (K_400a. I_TCa), where K_400a, K_400b, S₄₀₀ are formulaic representations and approximately a function of MOSFET's W/L ratios and MOSFET's (device) fabrication process constants. Also note that other variations of this circuit topology knowable by those skilled in the art can include, but not limited to, for example generating I_TCb using the prior art circuits such as the ones shown in FIG. 11 and FIG. 12, which is then scaled and subtracted from I_TCa generated by this invention topologies (e.g., FIG. 1, or 2, or 3) to yield an I_REF.

The connections of the elements in FIG. 5 are described as follows. As noted earlier, node 1 is the positive supply voltage terminal or V_DD. Similarly, node 2 is the negative supply voltage terminal or V_SS (which can also be set as the zero voltage terminal or ground). The source and body terminals of M_414a, M_416a, M_418a, M_420b, and M_414b, M_416b, M_418b, M_420b are connected to node 1, which is the positive power supply terminal. Note that M_414a and M_414b sets the bias voltage for the MOSFETs and M_416a, M_418a, M_420b, and M_416b, M_418b, M_420b, respectively. Here, M_414a, M_416a, M_418a, and M_420b are current mirrors, as well as M_414b, M_416b, M_418b, and M_420b all of which also function as current sources to set bias currents for I_TCa and I_TCb circuitries. The source and body terminals of M_408a, M_410a, M_412a, M_422a, and M_408b, M_410b, M_412b, M_422b are connected to node 2, which is the negative or ground power supply terminal. Gates and drains of M_400a and M_400b (both of which is part of the self cascade circuits together with M_402a and M_402b) are shorted to each other and connected to the node 2. Source and body of M_400b are connected to drain of M_402b and connected to node 402b, which is also connected to gate of M_406b. Source and body of M_402b are connected to drain of M_418b and gate of M_404b and connected to node 400b. Source and body of M_404b, and source and body of M_406b and drain of M_416b are connected to node 406b. Drain of M_404b and drain of M_408b and gate of M_412b are connected to node 408b. Gate and drain of M_410b and drain of M_406b are connected to node 410b. Drain of M_412b and gate and drain of M_414b are connected to node 404b. Gate terminals of M_416b, M_418b, and M_420b are connected to node 404b. Drain of M_420b and gate and drain terminals of M_422b are connected to node 412b. Note that M_404b, M_406b, M_408b, M_410b, M_412b, and M_414b form an amplifier (A_400b) with M_404b and M_406b gates at nodes 400b and 402b as A_400b's input terminal and gate and drain of M_414b as its output terminal. Also, as is the case with the FIG. 5 embodiment, note that offset voltage generation and amplifier function can be accomplished in one shot by scaling differing the sizes of M_404b, M_406b and scaling differing currents through them via scaling differing the sizes M_408b and M_410b.

Source and body of M_400a are connected to drain of M_402a and connected to node 402a, which is also connected to gate of M_406a. Source and body of M_402a are connected to drain of M_418a and gate of M_404a and connected to node 400a. Source and body of M_404a, and source and body of M_406a and drain of M_416a are connected to node 406a. Drain of M_404a and drain of M_408a and gate of M_412a are connected to node 408a. gate and drain of M_410a and drain of M_406a are connected to node 410a. Drain of M_412a and gate and drain of M_414a are connected to node 404a. Gate terminals of M_416a, M_418a, and M_420a are connected to node 404a. Drain of M_420a and gate and drain terminals of M_422a are connected to node 412a, which is the I_REF terminal. Note that M_404a, M_406a, M_408a, M_410a, M_412a, and M_414a form an amplifier (A_400a) with M_404a and M_406a gates at nodes 400a and 402a as A_400a's input terminal and gate and drain of M_414a as its output terminal. Also, as is the case with the FIG. 5 embodiment, note that offset voltage generation and amplifier function can be accomplished in the amplifiers A_400a (and A_400b) by scaling differing the sizes of M_404a, M_406a and scaling differing currents through them via scaling differing the sizes M_408a and M_410a (as well as M_404b, M_406b and scaling differing currents through them via scaling differing the sizes M_408b and M_410b). Note also that transistor pairs M_402b-M_400b and M_402b-M_400b form the self cascades, SC_400a and SC_400b, respectively where R_M402b (or R_BIAS-400b) and R_M402a (or R_BIAS-400a), play into the equation that sets the value of I_TCb and I_TCa currents.

Drain of M_420a is connected to gate and drain of M_422b as well as gate of M_422a at node 412b. Drain of M_422a and drain of M_420a are connected to node 412a, as well as the I_REF output terminal. Note that M_420a, M_422a, and M_420b, M_422b constitute one of many possible embodiments (a simple one used here for descriptive simplicity and clarity) for the current scalar and subtractor function, but there are other higher performance variations of current scalar and subtractor function available and covered in prior art (e.g., Ledesma, F. et al, “Comparison of new and conventional low voltage current mirrors,” Circuits and Systems, 2002. MWSCAS-2002, which is hereby incorporated by reference in its entirety).

In summary, current generator I_TCa includes M_400a-M_418a, and current generator I_TCb includes M_400b-M_418b, where I_TCa and I_TCb have differing TCs which are set by the circuit's MOSFET's scale factors (as well as a factor of MOSFET device parameter constants) so to generate an I_REF with positive TC, or negative TC, or a near zero TC, which will be explained below.

Here is a more detailed explanation of the embodiment of FIG. 5. The circuit is composed of two current generator making I_TCa and I_TCb whose respective magnitude and TC can be set partially independently from one another so to be scaled and subtracted from each other to generate an I_REF with near zero TC. Each current generator is composed of a CMOS amplifier (A_400a and A_400b) and self-cascode (SC_400a and SC_400b). Amplifier A_400a's input includes M_404a, M_406a, M_408a, and M_410a and has a built-in offset voltage roughly equal to V_T.ln(c×d) which is forced across M_402a of SC_400a (with its diode connected counterpart M_400a) so to generate a current I_TCa via M_418a that has a temperature coefficient of TC_a:I_TCa=IDS_M418a=IDS_M402a=IDS_M400a=VDS_M402a/R_M402a;VGS_M406a−VGS_M404a≈V_T.ln(c×d)=VDS_M402a;R_M402a≈[μ.C_OX.(W/L)_M402a(VGS_M402a−V_THp−VDS_M402a/2)]⁻¹;VGS_M402a≈[2I_TCa/μ.C_OX.(W/L)_M400a]^1/2+V_THp;μ.C_OX.(W/L)_M402a×[I_TCa/μ.C_OX.(W/L)_M400a]^1/2≈I_TCa.[V_T.ln(d×c)]⁻¹.I_TCa≈f(K_400a,μ,V_T);Where K_400a is set approximately by MOSFET's device parameter constants and the W/L sizes of MOSFETs in the I_TCa's current generator circuitry.

Similar operations hold for the A_400b and SC_400b loops that generate the I_TCb. Amplifier A_400b's input includes M_404b, M_408b, M_408b, M_410b that has a built-in offset voltage roughly equal to V_T.ln(f×g) which is forced across M_402b of SC_400b (with its diode connected counterpart M_400b) so to generate a current I_TCa via M_418a that has a temperature coefficient of TC_b:I_TCb=IDS_M418b=IDS_M402b=IDS_M400b=VDS_M402b/R_M402b;VGS_M406b−VGS_M404b≈V_T.ln(g×f)=VDS_M402b;R_M402b≈[μ.C_OX.(W/L)_M402b(VGS_M402b−V_THp−VDS_M402b/2)]⁻¹;VGS_M402b≈[2I_TCb/μ.C_OX.(W/L)_M400b]^1/2+V_THp;μ.C_OX.(W/L)_M402b×[I_TCb/μ.C_OX.(W/L)_M400b]^1/2≈I_TCb.[V_T.ln(g×f)]⁻¹;I_TCb≈f(K_400b,μ,V_T),where K_400b is set approximately by the W/L sizes of MOSFETs in the I_TCb's current generator circuitry;

In the current scalar and subtractor circuit there is: I_REF=K_400b. I_TCb−S₄₀₀. (K_400a I_TCa). As noted earlier, If a near zero TC current reference (I_REF), then magnitude of I_TCa can be scaled with MOSFET's W/L ratios such that a current S₄₀₀. (K_400a. I_TCa) whose value changes near equally to that of K_400b I_TCb over an objective temperature range.

In the embodiment of FIG. 5, similar to the embodiment of FIG. 4, it can be noticed in the I_TCa and I_TCb equations that V_TH term is canceled out in both the first loop (M_404a, M_406a as well as M_404b, M_406b) and the second loop (M_400a, M_402a as well as M_400b, M_402b) which desensitizes I_TCa and I_Tcb value from V_TH variations in process fabrication. As it is the case with this class of current sources, I_TCa and I_TCb, and thereby I_REF which is a byproduct of them to be primarily a function of C_OX, V_T, and μ. Here C_OX is a function of gate oxide thickness which has a very low TC, V_T has a positive TC (PTAT like) and u has a negative TC (CTAT like). Therefore, the TC of I_TCA and I_TCB (and hence TC of I_REF which is a function I_TCA and I_TCB) can be positive or negative or approximately flat depending on S₄₀₀, K_400a, and K_400b which are predetermined or programmed (depending on circuit need) by the MOSFET device constants, and W/L sizes by setting scale factors ‘a’ through ‘j’, in FIG. 5. Note also that other variations of the proposed topology could include, but not be limited to, operating MOSFETs in SC_400a and SC_400b at different scaled currents (instead of PMOS), utilizing NMOS self-cascode or conventional current mirrors (triode MOS plus saturation diode connected MOS), or using source followers or diode level shifters or NMOS input (instead of PMOS) A_400a and A_400b with built-in offset voltages in order to achieve different specifications trades-offs (e.g., sub-1V operations).

In this section some of the benefits of the embodiment depicted in FIG. 5 are described: as noted earlier, typical reference topologies add two currents with opposing TC polarities to generate a stable TC current reference, whereas this reference generates two currents (I_TCa and I_TCb) with same polarity TCs that are scaled with differing slopes, and subsequently scaled and subtracted from each other to form a very stable TC I_REF which provides a the benefit of more flexibility in generating I_REF with different amplitude and TC. One of these flexibilities includes, but not limited to, programming an I_REF with wider range of positive, negative, or very stable TC.

Also, while adhering to matching considerations by using the same exact narrow W and long L in the two independent self cascades (SC_400a and SC_400b), the TC and magnitude of I_TCa and I_TCb can be programmed differently via (mostly by) setting the ratio of W/Ls of MOSFETs aspect ratios, which can be made accurate with respect to topology targets because they are most independent of fabrication process variation.

In effect, the embodiment of FIG. 5 uses substantially similar functional blocks of the embodiment of FIG. 2 two times. Using different MOSFET aspect ratios (which are tightly controllable in process), the first instance of bias current generation (i.e., I_TCa) produces certain amplitude and TC that is different from that of the one produced in the second instance of bias current generation (i.e., I_TCb), while both I_TCa and I_TCb are subject to the same process fabrication, power supply, and temperature variations. As such, an advantage of the embodiment of FIG. 5 is to generate I_TCa and I_TCb by using the same configuration and same CMOS W/Ls in amplifiers (A_400a and A_400b), same CMOS W/Ls in self cascades (SC₄₀₀, and SC_400b), and same CMOS W/Ls in current mirrors (VCCS_400a and VCCS_400b). And because of this, the second order errors due to process, temperature, and power supply variations track each other and some of them are cancelled out, which helps both DC and AC performance of the current reference.

Similar to the embodiment of FIG. 4, for this embodiment of FIG. 5, the V_PTAT is sensed and current is forced across an active resistor, R_M4002a and R_M402b, at the gate terminal instead of the prior art that does it at the source terminal of the current mirror loop amplifier. However, the embodiment of FIG. 4 used an NMOS resistor, an independent PMOS source follower (i.e., unity gain buffer with a built in offset voltage as a function of pseudo V_T) function for built offset voltage (or V_PTAT) generation, and a separate loop amplifier function for amplification. Instead, here in FIG. 5, the function of built in offset voltage (or V_PTAT) generation and amplification are both preformed in MOS amplifiers which save some area and current, where additionally both active MOSFET resistors and MOSFET amplifier inputs are of the same type (i.e., PMOS) enabling better fabrication process tracking and lower noise (since PMOS has lower noise than NMOS).

As just noted for the embodiment of FIG. 5, the sensing and forcing of signal takes place at the gate terminal instead of the prior art that does it at the source terminal. As a result, another benefit of this embodiment is that one input of the loop amplifier is biased via an MOS that is diode connected (gate and source shorted) in SC and the other input of the loop amplifier is biased via the other MOS in SC that (is the resistor and sets the operating current) is in the feedback loop of the amplifier. As a consequence, the active MOS impedance (e.g., R_BIASa,b) is lowered by the gain of the current mirror loop or current loop amplifier. Also, beside improvements in AC performance due to lower impendence here, the junction leakage asymmetries associated with generation of V_T (in prior art implementations) are also separated from the SC operation, which helps wider temperature span (e.g., improving 0-70 C temperature span to 0-100 C) of this embodiment.

Moreover, embodiment of FIG. 5 is benefited for less dependence on process parameter variation because it eliminates some of the second order device's second order effects, including but not limited to, for example the elimination of NMOS body effect in M₂₀₀ that was present in the embodiment of FIG. 4. Also, keeping the benefits of the category of circuits to which it belongs, the embodiment of FIG. 5 is substantially independent of V_TH and mostly depended on μ, which is better controlled in process fabrication, hence the overall power consumption of the current reference is more tightly controlled over process variations. Also, the embodiment of FIG. 5 can operate MOSFET in the subthreshold region, which enables low power supply and ultra low power consumption. Another benefit of the FIG. 5 embodiment is that V_SS (negative power supply) and the ground potential (GND) may be the same of separated, providing flexibility to system topology, which allows I_TCa, I_TCb and I_REF to be set in value independent of the ground potential.

Description of the FIG. 6 Embodiment in a ‘Voltage Reference’

The embodiment shown in FIG. 5 is utilized in the embodiment depicted in FIG. 6, which is a ‘voltage reference’ that can also generate a pseudo bandgap reference voltage. This third embodiment in FIG. 6 includes elements such as amplifiers. The amplifier is defined here broadly, which could be a voltage output or current output, or have voltage output combined with voltage controlled current source or VCCS. Such an amplifier, could also contain differential buffers (e.g., differential source followers, DC level shifters, voltage offset generators in series with its differential inputs). Other elements contained here could be a voltage buffer or followers or DC level shifters, voltage offset generators, current mirrors, voltage controlled current source (VCCS), self-cascodes, and MOSFETs (e.g., MOS transistors can be configured to function as a VCCS, current mirror, current sources or an active resistors or MOSFETs that can be paired in the input of an amplifier or buffer or DC level shifter—with differing scale factors—to generate offset voltage).

The embodiment in FIG. 6 is a voltage reference, which includes current bias generator section or I_BIAS section, MOS self cascode (SC) series section (that sums a number V_PTATs to establish the PTAT term of the voltage reference), and V_BE generator (that establishes the CTAT term) combined with an output voltage amplifier section, yielding the voltage reference output, V_REF. The embodiment of FIG. 6 may be used to make a low cost (small die size), ultra low power, resistor free, CMOS pseudo bandgap voltage reference, where by programming or predetermining MOSFET's W/L sizes or ratios, an V_REF equal to bandgap voltage (about 1.2V) of V_BG with a stable TC may be realized. Different adjustments in MOSFET aspect ratios in this topology also allows for the option of generating a V_REF that exhibits positive or negative TC.

Here is a description of the embodiment of FIG. 6 and some of its benefits. The proposed circuit belongs to a class of resistor free bandgap voltage references (V_REF or V_BG) whose CTAT voltage (V_CTAT) is generated by V_EB of a parasitic BJT available in standard CMOS fabrication process. This reference's PTAT voltage V_PTAT is generated via summation, where the PTAT term is generated by adding K of the V_T.ln (g) terms that are generated via K plurality of scaled MOS self-cascodes (SC) whose each of resistive MOFET's source-drain terminals are in series with one another while they all operate in subthreshold. All the SCs are concurrently biased by the bias current circuit of that is the embodiment of functional block diagram depicted in FIG. 2. Here K is the number of SC put in series with one another in the PTAT segment of the circuit. The embodiment of FIG. 6 shows K=4, but K can be a number as low as 2 or as high as 20. This circuit's contributions may include the following. The topology employs SCs in a manner to generate both the bandgap's I_BIAS and V_PTAT segments of the circuitry so that their operating conditions track over power supply, temperature, and supply variations, thereby aiding V_REF's specifications. AC, transient performances are benefited because V_PTAT and V_CTAT signal paths are made in independent signal paths from one another, avoiding the simultaneous positive and negative V_PTAT loops inherent in conventional bandgaps. Also, the die yield, attributed to impact of random non-ideal terms in the V_PTAT's signal path, is comparatively attenuated since V_PTAT is generated via summation instead of the multiplication that is operant in conventional bandgaps.

Operating in subthreshold, the MOS bias current generator segment includes the SC's M₆₀₂ and M₆₀₀. In the bias current generator segment of FIG. 6, by utilizing the built in offset voltage of V_PTAT˜V_T.ln(b×c) that is set by scaling M₆₀₄-M₆₀₆ and M₆₀₈-M₆₁₀ within the bias amplifier A₆₀₂ (composed of M₆₀₄, M₆₀₆, M₆₀₈, M₆₁₀, M₆₁₂, M₆₁₄, and M₆₁₆), a V_PTAT is forced across VDS_M602. Note that I_BIAS flowing through the bias current generator's SC (M₆₀₀-M₆₀₂) is also fed into the SC series of the PTAT segment of the V_REF circuit (M_i-M_it where ‘i’ is even numbers 624 to 630, such as M₆₂₆-M_626t or M₆₂₄-M_624t). It is of note that I_BIAS can be configured such that its operating currents can be set to have a positive, negative, or near zero TC, depending on V_REF circuit performance requirements and process parameters. Similar to I_BIAS generation of FIG. 4 and that of FIG. 5, here in embodiment of FIG. 6 the I_BIAS value over fabrication process variations is primarily a function of V_T and μ (mobility of MOSFETs) and not V_TH. Here the TC of I_BIAS operating conditions which employs SC, mimics a similar mechanisms in the chain of SCs (M_i-M_it SCs) used in the PTAT section. The W/L of MOSFETs in the chain of SCs of the V_PTAT section and in the SC of the I_BIAS section may be made identical. Since I_BIAS that is fed to SCs of the V_PTAT section (M₆₂₄, M₆₂₆, M₆₂₈, and M₆₃₀) is mirrored from the I_BIAS that resulted from forcing a PTAT voltage or ˜V_T.ln(b×c) across SC in the bias circuit (V_DS of M₆₀₂), therefore a (multiple or fraction of) PTAT voltage can be developed across the drain to source terminals of each of the resistive MOSFETs M₆₂₄, M₆₂₆, M₆₂₈, and M₆₃₀ of SCs of the cumulative V_PTAT section. A voltage reference output or V_REF, with respect to V_DD is hence generated via the summation (series combination or accumulation) of each of such PTAT voltages developed across drain to source terminals of each of the resistive MOSFETs of series of SCs, whose cumulative voltage (e.g., K×V_PTAT) is subsequently added to a V_CTAT, generated via the BJT Q₆₂₂, which is configured in unity gain with a DC shift of V_BE.

Note that in FIG. 6, the scale factors ‘a’ through ‘h’ are the ratios of transistor's width over length (W/L or scale factors or aspect ratios) that may be set depending on such considerations as die size and various operating specifications, including but not limited to current consumption, temperature coefficients, and power supply range objectives. The scale factors ‘a’ through ‘h’ can be in the range of approximately 0.1 to approximately 50.

The connections of the elements in FIG. 6 are described as follows. Similar to the bias current generators utilized in FIGS. 5 and 6, the embodiment in FIG. 6 also employs a bias current generator. Node 1 is the positive power supply, V_DD, which is connected to the following terminals: source and body of M₆₁₈, source and body of M₆₁₆, source and body of M₆₁₄, source and body of M₆₃₀, and source and body of M₆₂₀. Node 2 is the negative power supply, V_SS, which can also be the ground potential depending on system requirements. Node 2 is connected to the following terminals: gate of M₆₀₂, gate and drain of M₆₀₀, body and source of M₆₁₀, body and source of M₆₀₈, body and source of M₆₁₂, body and source of M_630i, body and source of M_628i, body and source of M_626i, body and source of M_624i, and collector of Q₆₂₂.

In the current bias generator section, which biases up the voltage reference, the source and body of M₆₀₀ are connected to drain of M₆₀₂ and connected to node 602, which is also connected to gate of M₆₀₄. Source and body of M₆₀₂ are connected to drain of M₆₁₈ and gate of M₆₀₆ and connected to node 600. Source and body of M₆₀₄, and source and body of M₆₀₆ and drain of M₆₁₆ are connected to node 606. Drain of M₆₀₆ and drain of M₆₁₀ and gate of M₆₁₂ are connected to node 608. Gate and drain of M₆₀₈ and drain of M₆₀₄ are connected to node 610. Drain of M₆₁₂ and gate and drain of M₆₁₄ are connected to node 604. Gate terminals of M₆₁₆, M₆₁₈, and M₆₂₀ are connected to node 604. Note that M₆₀₄, M₆₀₆, M₆₀₈, M₆₁₀, M₆₁₂, and M₆₁₄ form a voltage amplifier (A₆₀₂) with M₆₀₄ and M₆₀₆ gates at nodes 600 and 602 as A₆₀₂'s input terminal, and gate and drain of M₆₁₄ as the amplifier output terminal. Also, similar to the embodiment of FIG. 5, in the embodiment of FIG. 6 note that offset voltage generation and amplifier function can be accomplished in one shot by scaling differing the sizes of M₆₀₄ M₆₀₆ and scaling differing currents through them via scaling differing the sizes M₆₀₈ and M₆₁₀. MOSFETs M₆₁₄, M₆₁₆, M₆₁₈, and M₆₂₀ form current mirrors whose value is scaled via ‘d’ with respect to the bias level established by M₆₁₄, and here also M₆₁₈ functions as the VCCS₆₀₀ that feeds the bias current for the self cascode (SC₆₀₀) composed of M₆₀₂ and M₆₀₀.

The PTAT signal (with respect to V_DD) is generated via a series of MOS SCs, whose node's connectivity is as follows: node 628 is connected to drain of M₆₃₀ and to the body and source of M_630t and to the source and body of M₆₂₈. Node 624 is connected to drain of M₆₂₈ and to the body and source of M_628t and to the source and body of M₆₂₆. Node 620 is connected to drain of M₆₂₆ and to the body and source of M_626t and to the source and body of M₆₂₄. Node 616 is connected to drain of M₆₂₄ and to the body and source of M_624t and to the positive input terminal of output amplifier, A₆₀₀. Node 630 is connected to gate of M₆₃₀ and gate plus drain of M_630t and drain of M_630i. Node 626 is connected to gate of M₆₂₈ and gate plus drain of M_628t and drain of M_628i. Node 622 is connected to gate of M₆₂₆ and gate plus drain of M_626t and drain of M_626i. Node 618 is connected to gate of M₆₂₄ and gate plus drain of M_624t and drain of M_624i. Gates of M_630i, M_628i, M_626i, and M_624i are connected to gate of M₆₁₂ at note 608. In FIG. 602, the MOSFET pairs whose W/L's are scaled by the ratio ‘g’ are M₆₂₄-M_624t, M₆₂₆-M_626t, M₆₂₈-M_628t, and M₆₃₀-M_630t make the self cascode SC₆₀₀, SC₆₀₂, SC₆₀₄, and SC₆₀₆, respectively. M_630i, M_628i, M_626i, and M_624i provide the bias current for the SCs whose currents are mirrors of one another and are scaled by ‘d’ biased via M₆₁₂ (from the bias generation section). Note that for ease and clarity of describing the embodiment of FIG. 6, only four SCs are shown. But the SC series could contain different number of SCs and bias currents (e.g., between 2 to 12) depending on fabrication process and V_REF's specification requirements. Moreover and also for demonstrative clarity a simple current bias and mirror circuitry is shown in FIG. 6. But bias current circuits could be looped differently and or cascoded (e.g., desensitize the impact of MOS's V_A) to improve bandgap's specifications, including but not limited to its' VC. The CTAT signal generation in FIG. 6 containing the V_EB DC level shift and output amplifier section has the following nodes: node 612 is connected to the negative terminal of A₆₀₀ which is also connected to emitter of Q₆₂₂ and drain of M₆₂₀. Output of A₆₀₀ is connected to node 614 which is also connected to the base of Q₆₂₂.

The following is a more detailed description of FIG. 6. V_BG is composed on V_PTAT with a positive TC and V_CTAT with a negative TC whose addition generates a near zero TC output voltage of V_BG. The V_PTAT generator is made by K series of SC PMOSFETs, M_i-M_it (also operating in the subthreshold region) sized with ‘1/g’ ratio. The SC's PMOSFETs generate K×[V_T.ln(g)+V_e]. Here V_e is approximated as the average DC equivalent of error terms (i.e., offset, drift, noise, etc) in the V_PTAT signal path. The random contribution of V_e to die yield should be roughly the square root of sum of V_e² or about K^1/2.Ve versus for conventional bandgaps where V_e equivalent term (dominated by the PTAT loop amplifier) is multiplied by PTAT loop gain or about K. V_e. The bandgap's CTAT is generated by V_EB of parasitic vPNP with Q₆₂₂ that DC shifts the output of the unity gain amplifier. The bandgap voltage V_BG accounting for random impact of V_e to yield, is about: V_BG˜V_EB+K.[V_T.ln(g)(K^1/2+1)×1)×V_e].

As noted earlier in this section, the embodiment in FIG. 6 employs SCs in a manner to generate both the bandgap's I_BIAS and V_PTAT circuitry so that their operating conditions track over power supply, temperature, and supply variations, thereby aiding bandgap's specifications. Hence similar to the embodiments in FIGS. 4 and 5, here in FIG. 6 there is the first voltage loop consisting of M₆₀₂, M₆₀₄, A₆₀₂, and M₆₀₆ produce a PTAT signal as a function of V_T which is forced upon the V_DS of M₆₀₂ by the operation of the loop. There is also a second voltage loop consisting of M₆₀₀ and M₆₀₂ where M₆₀₀ operates in saturation and M₆₀₂ operates in the triode region (i.e., that is acting as an active resistor of R_M602=R_BIAS for this current source). This active resistor, while functioning as the current source's resistor, contributes to a CTAT signal into the I_BIAS being mostly a function of μ. In the bias section, the application of PTAT signal via V_T while interacting with CTAT signal via μ enables setting the objective TC (positive, negative, or neutral, or in between them) for I_BIAS. This same I_BIAS is applied to the SC series. Note that for demonstrative clarity of the proceeding formulations, second order effects—including but not limited to—early voltage, body effect, subthreshold slope factor TC are ignored:VGS_M602−VGS_M600=VDS_M602:R_BIAS=R_M602≈[μ.C_OX.(W/L)_M602(VGS_M602−V_THp−VDS_M602/2)]⁻¹;VGS_M602≈[2I_BIAS/μ.C_OX.(W/L)_M600]^1/2+V_THp;VGS_M604−VGS_M606=[V_T.ln(c×b)]=VDS_M602; andμ.C_OX.(W/L)_M602×[I_BIAS/μ.C_OX.(W/L)_M600]^1/2≈I_BIAS.[V_T.ln(c×b)]⁻¹;I_BIAS≈f(S₆₀₀,μ,V_T).

As just noted above, this same I_BIAS is applied to the SC series, where:VDS_M630=VGS_M630−VGS_M630t;VDS_M628=VGS_M628−VGS_M628t;VDS_M626=VGS_M626−VGS_M626t; andVDS_M624=VGS_M24−VGS_M624t.

Given that the bias circuit employs a similar mechanism (i.e., VGS_M602−VGS_M600=VDS_M602) to generate both the bandgap's I_BIAS and V_PTAT sections, hence their operating conditions track over power supply, temperature, and supply variations, thereby aiding bandgap's specifications.

Before turning to more details about the benefits of the FIG. 6 embodiment, it can be noticed that V_TH term is canceled out in both the first loop (M₆₀₄, A₆₀₂, M₆₀₆) and the second loop (M₆₀₀, M₆₀₂) as well as in the SC series (M₆₃₀-M_630t, M₆₂₈-M_628t, M_626t, and M₆₂₄-M_624t) which desensitizes I_BIAS and the V_PTAT terms (as well as the V_REF or V_BG) from V_TH variations in process fabrication.

Some of the benefits of the embodiment of FIG. 6 are summarized here. First, low cost due to small die size with no passive resistor in standard digital CMOS fabrication with ease of process node portability besides smaller die size keeping the cost low. Moreover, in order to serve some of the medical applications of this topology, a very small die size is necessary for small incisions (e.g., or inside a crown). Second, ultra low power consumption over temperature span. Ultra low current consumption is key in some applications for example because replacement of micro-batteries or use of noisy magnetic micro-harvesters for power transfers may be impractical or unsafe. Third, superior VC, PSRR, and transient performance. For example, there could be mission critical biomedical batteryless systems may require uninterrupted monitoring and measurements while the IC's power supply is being charged via multiple micro-harvesters or being subjected to disorderly patterns. Fourth, avoiding big decoupling capacitors may be key for voltage references in some applications. For example, a large decoupling capacitor (typically isolated from power storage supercapacitor with a Schottky diode) can burden the scarce power of micro-energy harvester reserves, especially during power up and power down transients. As such, a voltage references such as the embodiment in FIG. 6 with superior VC, PSRR, and AC performance (or requiring much smaller decoupling capacitors) can be significantly more critical for micro-energy harvesting ICs. Fifth, another benefit of the FIG. 602 embodiment is that V_SS (negative power supply) and the ground potential (GND) may be the same of separated, providing some flexibility to system topology. Sixth, also note that a challenge with ultra low current and MOSFETs is high noise. Apples-to-apples the embodiment of FIG. 6 is architecturally equipped to enhance noise performance compared to prior art because: (a) as noted above, the contribution of noise within the V_PTAT generation circuit is (noise)×K^1/2 because of the operation of summation instead of multiplication in the conventional bandgap of FIG. 2 where operation of multiplication or K (noise)×K gains up the loop amplifier A1's noise; (b) PMOSFET SCs may be used to build up to the V_PTAT along the SC string, PMOSFETs may be used in the SC and the amplifier of the bias current generation circuit, as well as in the output amplifier differential input pairs, which should reduce the contribution of 1/f noise to the V_BG output; and (c) bandgap reference's noise can be materially band pass filtered out by placing a capacitor at the end of the SC string or the high impedance node of output amplifier but in accordance with consideration for power up and down settling time requirements.

In addition to the synthesis of the aforementioned contributions of the embodiment of FIG. 6, as noted earlier, aims to improve upon the broader benefits attributable to the category of bandgap references to which it belongs. Some of such benefits are: (1) the PTAT and CTAT signal paths are independent, and hence the positive and negative feedback loops inherent in conventional bandgap PTAT loops are avoided, thus helping transient and power-up and down responses of the bandgap; (2) the non-idealities attributed to random DC offsets and noise that impact V_BG are attenuated, due to operations of summation compared to multiplication for conventional bandgaps; and (3) tight performance tolerance over standard CMOS manufacturing process variations. Bandgap's I_BIAS is made independent of CMOS V_TH and instead primarily depends on V_T and μ, which is more tightly controllable in manufacturing.

Description of the FIG. 9 Embodiment in a Bandgap Voltage Reference Along with FIGS. 3, 7, and 8

This fourth embodiment shown in FIG. 7, along with FIGS. 3, 8, and 9, includes elements such as amplifiers. The amplifier is defined here broadly, which could be a voltage output or current output, or have voltage output combined with voltage controlled current source or VCCS. Such an amplifier, could also contain differential buffers (e.g., differential source followers, DC level shifters, voltage offset generators in series with its differential inputs). Other elements contained here could be voltage buffer or followers or DC level shifters, voltage offset generators, current sources, current mirrors, voltage controlled current sources (VCCS), self-cascodes, bipolar transistors or BJTs (including parasitic vertical BJT) and MOSFETs (e.g., MOS transistors can be configured to function as an active resistor, or a VCCS, current mirror, current sources or MOSFETs that can be paired in the input of an amplifier or buffer or DC level shifter—with differing scale factors—to generate offset voltage).

The embodiment in FIG. 7 is a voltage reference, which consists of current bias generator I_BIAS, MOS active resistors (that establishes the PTAT signal in the bandgap), and V_EB generator (that establishes the CTAT signal in the bandgap) plus output amplifier delivering the voltage reference output, V_REF or V_BG.

The goal here is for the functional block shown in FIG. 3 to be used in an embodiment of a bandgap voltage reference depicted in FIG. 7 so as to make an ultra low power, resistor free, CMOS bandgap voltage reference. By setting MOSFET's W/L ratios in FIG. 7, a V_REF equal to bandgap voltage (about 1.2V) or V_BG with a stable TC may be realized, although a V_REF with positive, or negative TC is possible with the topology.

Here is a summary description and some of the benefits of the embodiment of FIG. 7. The proposed circuit belongs to a conventional class of bandgap voltage references that adds a PTAT and a CTAT signal to yield a near zero TC, as depicted in prior art FIG. 10. In FIG. 10, a V_PTAT (as a multiple of V_T) signal is placed across R₈₀₀ (or R_BG). As a consequence, the current through R_BG flows through R₈₀₂ (p.R_BG), which amplifies the V_PTAT such that the sum of VEB_Q802 (which is the CTAT signal) and [p+1]×V_PTAT yields the V_REF or V_BG with a stable TC. Conventional bandgap voltage reference, such as the one shown in FIG. 10, can be attractive because for high volume markets, bandgap voltage references may be viewed in a more favorable light in manufacturing due to the predictable V_BE and V_T terms that constitute the V_BG.

However, prior arts bandgaps of this category require passive resistors (e.g., R₈₀₀ and R₈₀₂), which makes their implementation in small form factor, low-cost, and ultra low power applications, such as energy harvesting impossible or impractical. Therefore, a resistorless CMOS bandgap embodied of FIG. 7 employs the bias current generator (functional block shown in FIG. 3) that is utilized in FIG. 8.

A new composite active MOS resistor is proposed, depicted in FIG. 9, which has a small size and high resistance. A network of active resistors using this composite active resistor cell (FIG. 9) replace the function of R_GB for R₈₀₀ plus ‘p’ times of R_GB for R₈₀₂. The composite active resistor of FIG. 9, working in concert with the bias current circuit of FIG. 804, is embodied in the bandgap circuit (FIG. 7).

The bias circuit of FIG. 8, makes possible the creation of the active resistor (FIG. 9), which enables keeping both the reliability benefits of conventional bandgap topology as well as eliminating the bandgap's need for passive resistors, which consequently enables making an ultra low power bandgap of FIG. 7 possible in standard digital CMOS. In the I_BIAS generator of FIG. 8, a V_PTAT (in the M₈₀₄-A₈₀₀-M₈₀₆ loop making VT.ln [b×c]) is forced upon the active resistors R_M802. Similarly, in the bandgap voltage reference circuit of FIG. 7, a V_PTAT (in the Q₈₀₄-A₈₀₀-Q₈₀₆ loop making VT.ln [g×i])]) is forced upon the active resistors R_M826r. The I_BIAS generator circuit of FIG. 8 and the bandgap loop circuitries of FIG. 7 independently apply PTAT voltages across functionally similar composite MOS resistors, namely R_M802 and R_M826r to generate their respective operating currents ID_M802 and ID_M826r.

Note also that in the SC loop in the I_BIAS generator circuit of FIG. 8, VGS_M800−VGS_M802=VDS_M802, where M₈₀₂ is the MOS resistor of I_BIAS circuit. Similarly, note that in the active MOS resistor of FIG. 9, ignoring the V_OFFSET of amplifier A₈₂₄ for now, VGS_M824b−VGS_M824r=VDS_M824r, where M_824r is the MOS resistor of active resistor circuit. This topology uses substantially similar functional conditions between the operations of M₈₀₂-M₈₀₀ loop in the I_BIAS generator circuit of FIG. 8, and that of each of the MOS resistors of FIG. 9 that is utilized in the bandgap circuit of FIG. 7 (i.e., M_826b-A₈₂₆-M_826r loop, M_828b-A₈₂₈-M_828r loop, M_830b-A₈₃₀-M_830r loop, M_834b-A₈₃₄-M_836r loop). Therefore, the operating conditions of the I_BIAS generator of FIG. 8, the active MOS resistor of FIG. 9, and bandgap circuit of FIG. 7 substantially track each other over fabrication process and temperature and power supply variations, and able to approximate a PTAT like behavior over temperature.

The combination of the I_BIAS generator of FIG. 8, the active MOS resistor of FIG. 9, and bandgap circuit of FIG. 7 enable the bandgap's power consumption to be mostly independent of MOSFET's V_TH and chiefly a function of mobility, μ, that benefits manufacturability and yield because μ, is more tightly controllable (compared to poly resistance or V_TH, for example). Such trait not only yields a more stable bandgap voltage reference, but also one that delivers ultra low power which has a narrower range of variation over temperature and fabrication process corners.

Another advantage of combining I_BIAS generator of FIG. 8, the active MOS resistor of FIG. 9, and bandgap circuit of FIG. 7, is that the bandgap circuit can be more stable in AC and transient response. For example, wireless and batteryless electronic systems, in general, may be subject to less orderly power supply patterns. To guard band against disorderly power supply and start-up patterns, especially for instance in mission critical bioelectronics applications, the positive feedback loop associated with prior art FIG. 10 which uses a conventional bandgap's PTAT amplifier (that is vulnerable to transients) is eliminated in bandgap circuit of FIG. 7. This is done without denting bandgap's accuracy since the overall bandgap's operating current is compensated by topology with ID_M802 and ID_M824 tracking each other (also because of combining I_BIAS generator of FIG. 8, the active MOS resistor of FIG. 9, and bandgap circuit of FIG. 7). Although other variations are possible depending on different performance trade-offs, note that for the embodiment of FIG. 7, PMOS transistors are used in all of bandgap's key signal paths (i.e., amplifiers, composite MOS resistor, etc.) which should enhance the topology for manufacturability, provide some immunity against SOC's substrate (digital) jitters, and be less (1/f) noisy. Note that in FIGS. 3, 7, 8, and 9 the scale factors ‘a’ through are the ratios of transistor's width over length (W/L or scale factors or aspect ratios) that may be set depending on such considerations as die size and various operating specifications, including but not limited to current consumption, temperature coefficients, and power supply range objectives. As such, for FIGS. 3, 7, 8, and 9 the scale factors ‘a’ through can be predetermined or programmed to be between approximately 0.1 to approximately 50. Similar to the bias current generators utilized in FIGS. 1, 2, and 3, the embodiment in FIG. 7 also employs a bias current generator, which is depicted in FIG. 3.

The connections of the elements in the embodiment of FIG. 8 are described as follows: node 1 is the positive supply voltage terminal or V_DD. Node 2 is the negative supply voltage terminal or V_SS (which can also be set as the zero voltage terminal or ground). Source and body of M₈₀₂, M₈₂₂, and M₈₂₀ are connected to node 1. Source and body of M₈₁₀, M₈₁₂, M₈₁₄, M₈₁₆, and M₈₁₈ are connected to node 2. Transistors M₈₀₀ and M₈₀₂ form the self cascode, where the diode connected M₈₀₀ is cascoded with M₈₀₂. Node 800 is connected to gate and drain f M₈₀₀, gate of M₈₀₂, and drain of M₈₁₀. Node 802 is connected to source and body of M₈₀₀, drain of M₈₀₂, drain of M₈₁₂, drain of M₈₂₂, and source and body of M₈₀₄. Note that the body terminal of M₈₀₀ can be connected to either its source at node 802 or to node 1, depending on performance objectives and the process fabrication. Moreover, here the PTAT Voltage is generated by using two DC level shifters (diode connected V_GS followers) with a build in offset voltage, which is formed by diode connected MOSFETs M₈₀₄ and M₈₀₆ combined with current sources supplied by M₈₂₂, M₈₁₄ and M₂₁₆. Node 804 is connected to gate and drain of M₈₀₄, drain of M₈₁₄, and inverting input of amplifier A₈₀₀. Node 806 is connected to the non-inverting input of A₈₀₀, drain of M₈₁₆, and gate and drain of M₈₀₆. Node 808 is connected to the gates of M₈₁₀, M₈₁₂, M₈₁₄, M₈₁₆, and M₈₁₈. Node 810 is connected to the drain of M₈₁₈, and gate and drain of M₈₂₀. Note that M₈₂₀ and M₈₂₂, and M₈₁₀, M₈₁₂, M₈₁₄, M₈₁₆ and M₈₁₈ function as current mirrors, as well as VCCS whose gate voltage varies by the output of A₈₀₀. The drain current or I_D of M₈₁₀ or that of M₈₁₈ constitutes the bias current of the circuit or reference current, I_BIAS.

The connections of the elements in FIG. 9 are described as follows: node 1 is the positive supply voltage terminal or V_DD. Node 2 is the negative supply voltage terminal or V_SS (which can also be set as the zero voltage terminal or ground). Source and body of M_824i are connected to node 1. Drain of M_824b is connected to node 2. Node 826 is connected to drain of M_824i, body and source of M_824b, and the inverting input of A₈₂₄. M_824i functions as the current source whose current is mirrored from (VBISA) node 810 to establish the operating current for M_824b. Node 824 is connected to gate of M_824b and the output of A₈₂₄. Node 822 is connected to non-inverting node of A₈₂₄ and drain of M_824r. Node 820 is connected to source ad body of M_824r. Single, series or parallel combinations of M_824r can be as the resistor cell that is used in the bandgap (e.g., R800 and R802 of FIG. 10).

The connections of the elements in FIG. 7 are described as follows: node 1 is the positive supply voltage terminal or V_DD. Node 2 is the negative supply voltage terminal or V_SS (which can also be set as the zero voltage terminal or ground). Source and body of M_836i, M_834i, M_832i, M_830i, M_828i, and M_826i are connected to node 1. Node 2 is connected to drains of M_834b, M_832b, M_830b, M_828b, and M_826b as well as collectors of Q₈₀₆ and Q₈₀₄. Node 3 is V_MID, which can also be connected to the ground or zero potential, and is connected to the base of Q₈₀₄ and Q₈₀₆. Node 828 is connected to emitter of Q₈₀₄, positive input of A₈₃₆, and drain of M₈₃₆. Node 830 is connected to emitter of Q₈₀₆, positive input of A₈₂₆, and drain of M_826r. Node 832 is connected to gates of M_826r and M_826b and output of A₈₂₆. Node 834 is connected to source and body of M_826b, drain of M_826i, and negative input of A₈₂₆. Node 836 is connected to the source and body of M_826r, positive input of A₈₂₈, drain of M_828r, and negative input of A₈₃₆. Node 838 is connected to gates of M_828r and M_828b and output of A₈₂₈. Node 840 is connected to source and body of M_828b, drain of M_828i, and negative input of A₈₂₈. Node 842 is connected to the source and body of M_828r, positive input of A₈₃₀, drain of M_830r. Node 844 is connected to gates of M_830r and M_830b and output of A₈₃₀. Node 846 is connected to source and body of M_830b, drain of M_830i, and negative input of A₈₃₀. Node 848 is connected to the source and body of M_830r, positive input of A₈₃₂, drain of M_832r. Node 850 is connected to gates of M_832r and M_832b and output of A₈₃₂. Node 852 is connected to source and body of M_832b, drain of M_832i, and negative input of A₈₃₂. Node 854 is connected to the source and body of M_832r, positive input of A₈₃₄, drain of M_834r. Node 856 is connected to gates of M_834r and M_834b and output of A₈₃₄. Node 858 is connected to source and body of M_834b, drain of M_834b and negative input of A₈₃₄. Node 860 is the V_REF of V_BG connected to body and source of M_834r, and output of A₈₃₆.

The connections of the elements in the prior art FIG. 10 are described as follows: node 1 is the positive supply voltage terminal or V_DD. Node 0 is the ground or zero voltage terminal. Node 1 is connected to body and source of M_800a and M_802a as well as output of A₈₀₂. Node 0 or ground is connected to base and collector of Q₈₀₀ and Q₈₀₂. Node 804a is connected to emitter of Q₈₀₂ and one side of R₈₀₀. Node 802a is connected to the other side of R₈₀₀ and one side of R₈₀₂ and the positive input of A₈₀₂. Node 808a is the V_REF or V_BG output that is connected to the other side of R₈₀₂ and the drain of M_820a. Node 806a is connected to the gates of M_802a and M_800a and the output of A₈₀₂. Node 800a is connected to emitter of Q₈₀₀, drain of M_800a, and negative input of A₈₀₂.

As noted earlier, the proposed circuit belongs to the general category of bandgap voltage references in standard digital CMOS that operate in subthreshold (see FIG. 7). One part of the proposed bandgap is the I_BIAS generation circuit that is shown in simplified FIG. 8 (which is the embodiment of the functional block diagram of bias current generation shown in FIG. 3, which is also a variation of the functional block diagrams of the bias current generation embodiments shown in FIG. 1 and FIG. 2).

In FIG. 8 there is the first voltage loop consisting of M₈₀₂, M₈₀₄, A₈₀₀, and M₈₀₆ produce a PTAT signal as a function of V_T, which is forced upon the V_DS of M₈₀₂ by the operation of the loop. There is also a second voltage loop consisting of M₈₀₀ and M₈₀₂ where M₈₀₀ operates in saturation and M₈₀₂ operates in the triode region (i.e., that is acting as an active resistor of R_M802=R_BIAS for this current source). The active resistor, while functioning as the current source's resistor, contributes to a CTAT signal being mostly a function of μ. Application of PTAT signal via V_T while interacting with CTAT signal via μ whose combination (using different MOSFET aspect ratios) can facilitate making a positive TC, or negative TC, as well as a stable one for some temperature compensation for the I_BIAS. Note that for demonstrative clarity of the proceeding formulations, second order effects—including but not limited to—early voltage, body effect, subthreshold slope factor TC are ignored:VGS_M802−VGS_M800=VDS_M802;R_BIAS=R_M802≈[μ.C_OX.(W/L)_M802(VGS_M802−V_TH−VDS_M802/2)]⁻¹;VGS_M802≈[2I_BIAS/μ.C_OX.(W/L)_M800]^1/2+V_TH;VGS_M806−VGS_M804=[V_T.ln(d×b)]=VDS_M802;VDS_M802≈I_BIAS(e+1)×R_M802[V_T.ln(c×b)];μ.C_OX.(W/L)_M202×[I_BIAS/μ.C_OX.(W/L)_M200]^1/2≈I_BIAS(e+1)×[V_T.ln(c×b)]⁻¹;I_BIAS≈f(S₈₀₀,V_T).

This I_BIAS, mostly a function of S₈₀₀ (which is formulaic representation consisting of MOSFET W/L ratios and MOSFET's device constants) as well as μ, and V_T.

The composite active MOS resistor of FIG. 9 is formed via the loop composed of A₈₂₄, M_824b (saturation mode), and M_824r (in linear mode). In FIG. 9, M_824r replaces and performs the role of bandgap resistor, R_BG in FIG. 10.

The equivalent of R_BG of FIG. 10 is the composite active MOS resistor R_M826r, which is utilized in the PTAT loop composed of Q₈₀₆, Q₈₀₄, and A₈₃₆ shown in the bandgap circuit of FIG. 7. Ignoring non-idealities (e.g., V_OFS) for now, the concurrent operation of the active MOS resistor composed of A₈₂₆-M_826r-M_826b voltage loop (depicted in FIG. 7) which is utilized in the bandgap in combination with the Q₈₀₆-Q₈₀₄-A₈₃₆ voltage loop roughly yields:VDS_M826r˜V_T.ln(n₁×g);VGS_826b−VGS_826r˜VDS_826r˜V_T.ln(n₁×g);IDS_M826r˜V_T.ln(n₁×g)/R_M826r;IDS_M826i˜IDS_M826b˜f(S.μ,V_T).

As such, IDS_M826r (and the composite MOS's resistance) is mostly a function of V_T and μ and is independent of MOSFET's V_TH. Here, the dependence of R_BA's network (of active resistance and its operating current) on μ and V_T and their approximate independence from V_TH can help enhance manufacturability and enable performance optimization, including efficient trimming to attain higher accuracy in this bandgap. To simplify description of this circuit's operations and it benefits, the composite active MOS resistors are approximated as: R_BG as a lump sum ‘resistor’ in series with a lump sum ‘voltage source’ (which encapsulates the offset mismatch due to V_GS terms of MOSFETs as well as the amplifier in the composite active resistor circuit of FIG. 9). In such a model the ‘voltage source’ is an offset voltage (V_OFSR) between the composite active MOS resistors in the bandgap PTAT loop. Note that the V_OFSR the systematic offsets are cancelled out: R₈₀₂/R₈₀₀˜(R_M828r+R_M830r+R_M832r+R_M834r)/R_M826r.

ΔV_OFSR is configured as the random mismatch between VOFS_M828r, VOFS_M830r, VOFS_M832r, VOFS_M834r, VOFS_M826r of each of the composite MOS resistors. Here ΔV_OFSR should induce an additional offset error term (statistical contribution) to V_BG output of roughly (G+1)^1/2×ΔV_OFSR where ‘G’ is set by the (number active MOS resistor in series in the feedback loop of the bandgap circuit) ratio of string of composite active MOS resistors in the PTAT loop to satisfy the functional equivalent R₈₀₂/R₈₀₀ ratio (in FIG. 10) requirement for a near zero TC V_BG. Given that MOSFETs operate in subthreshold, V_TH mismatches dominate the differential pairs (i.e., input amplifiers, etc.) offset terms, and ΔV_OFSR˜f(V_T) that tracks the PTAT term in V_BG and can be roughly trimmed out for more precision.

To guard band for start-up and transient response A₈₃₆'s output does not drive both the operating currents that feed Q₈₀₄ and Q₈₀₆ in order to eliminate the positive feedback in the PTAT loop. But accuracy of the V_BG is not compromise. This is because the proposed embodiment of FIG. 7 enables I_BIAS, which feeds Q₈₀₄ and the strings of composite MOS resistors with the bandgap's PTAT loop that operate in a substantially (formulaically) similar manner, tracking each other over fabrication process, and temperature variations. Moreover, the same single pole CMOS amplifier is utilized throughout the bandgap which offers better transient, AC, and PSRR performance. Excluding the impact of random mismatch between amplifier offsets, the systematic higher V_OFSA, which is the offset voltage associated with single pole amplifiers (A₈₃₆), is roughly canceled out, and hence approximately:V_BG˜V_EB+(G+1)[V_T.ln(n₁×g)+V_OFSA]+(G+1)^1/2.ΔV_OFSR.

Although other variations of this topology are possible, the embodiment in FIG. 7 utilizes (but for substrate vertical PNPs in the PTAT section of the bandgap) PMOSFETs in the key signal paths (i.e., MOS resistors, bandgap amplifier, composite resistor amplifier, bias circuit MOS resistors and amplifier) that dictate bandgaps DC, AC, and transient performance. This use should further enhance manufacturability since most of the bandgap's performance would depend on fewer device parameters. This move should also improve the AC response of the bandgap, better 1/f noise performance, as well as provide some immunity against transient substrate noise when the bandgap is in a noisy SOC.

In summary the benefits of the embodiment in FIG. 7 are as follows. First, this is a voltage reference is based in standard digital CMOS fabrication. References are considered a key and critical electronics functions needed around actuators, sensors, and other access points circuits (for energy harvesting and wireless and batteryless Internet of things applications) must be small, low cost, and manufacturable to make it to high volume. As such, main stream digital CMOS processes can produce the smallest and be the lowest cost manufacturing platforms, assuming that circuit solutions here neither require any additional steps (i.e., no separate n-wells and p-wells or depletion mode MOSFETs) nor impose any non-standard device configuration (i.e., no lateral PNP, DMOST, or MOS body). Second, this is an ultra low power bandgap reference that could only require for example under approximately 250 nano ampere of current. Energy harvesting, wearable and next generation implantable bio-medical electronics are but a few examples of emerging wire-less-battery-less (WLBL) Internet of Things (IoT) applications with large total available market (TAM) potentials that require such ultra-low power and very small form-factor solutions. A voltage or current reference is a fundamental building block in systems, including in WLBL electronics that for example have to monitor, measure report on referenced levels of carbon monoxide, toxicity, acidity, sugar or salt levels, blood pressure, temperature, or a heart pulse, just to name a few.

As noted above, for WLBL electronics market potential to materialize, it is imperative that circuits ought to operate with ultra low currents. Hence the use of passive resistors are nonviable for several reasons: higher resistance obviously means prohibitively large die area (e.g., V_PTAT of 700 mV at 10 nA requires 70MΩ poly resistor). Mainstream digital CMOS foundries generally do not guarantee resistance specifications, including for higher Ω/square poly resistors. Compared to lower Ω/square layer 1 poly resistors, the layer 2 higher Ω/square ones typically exhibit higher mismatch, worst non-linearity, and inferior TCs, in part because of less fabrication process control for the less critical process layers (i.e., ploy 2 and higher layers, especially highly doped ones). High Ω/square diffusion resistors are also impractical here due to unfavorable leakage, VC, and TC characteristics. Therefore, predominant research on ultra low power configurations, based on digital standard CMOS, has produced (non-conventional) non-bandgap topologies to generate voltage references, that are generally not as rugged as bandgaps.

In order to guard band for long-term production continuity, utilizing the kind of circuit topologies that can be ported to multiple process nodes with minimal challenge are obviously favored. In this regards, conventional bandgap topologies could generally be viewed on a more positive light because of manufacturing's familiarity and experience with the more predictable and controllable BJT parameters such as V_BE and V_T that constitute V_BG. This embodiment retains the benefit of the class of bandgap voltage references to which it belongs.

This embodiment provides a composite active CMOS resistor (FIG. 9) that is small in size, consumes ultra low power (eliminates the need for passive resistors), and works in combination with the I_BIAS generator (FIG. 8 which is the embodiment of the functional block diagram of FIG. 3), and in combination with bandgap circuit (FIG. 7) in such a way that the active MOS resistors' and I_BIAS generator's and bandgap's circuits operating conditions track each other. As such more stable and reliable performance is achievable over process, temperature, and power supply variations. Given that the circuit current consumption is approximately in depended of MOSFET's V_TH, mainly a function of V_T and μ, which are more tightly controllable, hence manufacturability and performance specification can be improved. Combination of the features of I_BIAS circuit and active MOS circuit enables, segregating the positive and negative feedback loops of the bandgap circuit, without materially denting its DC performance. Instead, the AC and transient performance of this circuit is improved. For example, batteryless energy harvesting or IoT applications could receive their power from single type (e.g., single or series of solar diodes) or multiple energy harvester types (e.g., solar diodes in the light, and magnetic harvesters in the dark in conjunction with super capacitors to store voltage). The V_DD power-on and power-off patterns may be jittery and not follow a predictable or orderly pattern, and hence the AC and transient response of the references are as critical as their DC accuracy. Feeding the output of PTAT loop amplifier via MOSFETs back to its positive and negative inputs are avoided in this topology because they can pose start-up and transient risks (inherent in typical bandgap reference topologies). Another benefit of the FIG. 7 embodiment is that V_SS (negative power supply) and the ground potential (GND) may be the same of separated, providing flexibility to system embodiments. Also note that a challenge with ultra low current and MOSFETs is high noise. In FIG. 7, the bandgap reference's noise can be materially band pass filtered out by placing a capacitor in the end amplifier (A₈₃₄ that is used to form the composite active resistor) high impedance node of output amplifier but in accordance with consideration for power up and down settling time requirements. Additionally, PMOSFETs are used in the composite active resistors as well as in the output amplifier which should reduce the contribution of 1/f noise to the V_BG output.

In summary, disclosed above are bias current topologies with embodiments in current source, current reference, (pseudo bandgap) voltage reference, and bandgap voltage reference that operate at ultra low currents and low power supply voltages which may use main stream standard digital Complementary Metal-Oxide-Semiconductor (CMOS) processes. The bias current topology uses chiefly a self cascode (SC) and PTAT offset generation with loop signal amplification to produce a bias current. The bias current circuit, senses and forces the PTAT signal (mostly as a function thermal voltage V_T) at the gates of its loop amplification circuit, which in combination with a CTAT signal (mostly as a function of mobility of MOSFETS, μ) provides the flexibility of setting a negative, positive, or stable temperature coefficient (TC) bias current generator circuit, depending on an application's need. This circuit retains the benefits of the class of bias current circuits, whose current variations are approximately independent of threshold voltage (V_TH) and mostly a function μ. Hence die yields and performance over process and temperature spans are improved. Embodiments of the bias current topology (FIG. 1) in a current source (FIG. 4) is provided which offers wider temperature span, in part, due to lower leakage associated with the bias current topology. Also bias current topology (FIG. 1) is utilized in the embodiment of a current references (FIG. 5) that combines multiple bias current source, with the capability of setting the current's TC and amplitude approximately independently from one another. This trait enables greater flexibility and making a higher performance and more stable current reference over process, temperature, and power supply variations. Moreover, the bias current topology when combined with series of SCs (FIG. 6) that make a summation of pseudo V_T's that can be added to a V_BE of a parasitic BJT available in digital CMOS, to generate a pseudo bandgap voltage. Lastly, the bias current topology when combined with a composite active MOS resistor enables making a conventional bandgap reference. A PTAT voltage is applied across the active MOS resistor, which is gained up using the strong of the same active MOS resistor to generate the required V_PTAT that is added to V_BE of parasitic BJT in digital CMOS to generate the V_BG. The bias generation, active MOS resistor, and bandgap circuits use substantially similar functionality, which enables their operating conditions to track and hence enhancing their performance of the bandgap over process, temperature, and power supply variations. Moreover, the topology not only delivers ultra low power but also one whose current consumption is approximately independent of V_TH, which can improve performance and die yield. All such embodiments enable making ultra low power, low cost (base on standard digital CMOS fabrication that are portable across multiple fabrications), with optimized yields (due in part to independence from V_TH).

A number of embodiments are described in the present application, and are presented for illustrative purposes only. The described embodiments are not, and are not intended to be, limiting in any sense. One of ordinary skill in the art will recognize that the disclosed embodiment(s) may be practiced with various modifications and alterations, such as structural, logical, software, and electrical modifications. Although particular features of the disclosed invention(s) may be described with reference to one or more particular embodiments and/or drawings, it should be understood that such features are not limited to usage in the one or more particular embodiments or drawings with reference to which they are described, unless expressly specified otherwise.

Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Therefore, any given numerical range shall include whole and fractions of numbers within the range. For example, the range “1 to 10” shall be interpreted to specifically include whole numbers between 1 and (e.g., 1, 2, 3, . . . 9) and non-whole numbers (e.g., 1.1, 1.2, . . . 1.9).

The present disclosure is not a literal description of all embodiments of the invention(s). Also, the present disclosure is not a listing of features of the invention(s) which must be present in all embodiments. A description of an embodiment with several components or features does not imply that all or even any of such components/features are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the present invention(s).

Although process (or method) steps may be described or claimed in a particular sequential order, such processes may be configured to work in different orders. In other words, any sequence or order of steps that may be explicitly described or claimed does not necessarily indicate a requirement that the steps be performed in that order. The steps of processes described herein may be performed in any order possible. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, does not imply that the illustrated process or any of its steps are necessary to the invention(s), and does not imply that the illustrated process is preferred. Although a process may be described as including a plurality of steps, that does not imply that all or any of the steps are preferred, essential or required. Various other embodiments within the scope of the described invention(s) include other processes that omit some or all of the described steps.

Although a product or system may be described as including a plurality of components, aspects, steps, qualities, characteristics and/or features, that does not indicate that any or all of the plurality are preferred, essential or required. Various other embodiments within the scope of the described invention(s) include other products that omit some or all of the described plurality.

Claims

1. A method of generating a reference current comprising: a first p-channel metal-oxide-semiconductor field effect transistor (PMOSFET), operating in the triode region, to make a first PMOSFET resistor;a second PMOSFET, operating in the triode region, to make a second PMOSFET resistor;the first PMOSFET resistor utilized to generate a first bias current;the second PMOSFET utilized to generate a second bias current;wherein the first bias current and the second bias current have the same polarity of temperature coefficient (TC) and different TC slopes; andwherein the first and second bias currents are scaled and subtracted from one another to yield stable TC reference current over an objective temperature range.

2. A method of generating a reference current comprising: a first N-channel metal-oxide-semiconductor field effect transistor (NMOSFET), operating in the triode region, to make a first NMOSFET resistor;a second NMOSFET, operating in the triode region, to make a second NMOSFET resistor;the first NMOSFET resistor utilized to generate first bias current;the second NMOSFET utilized to generate second bias current;wherein first bias current and second bias current have the same polarity of temperature coefficient (TC) and different TC slopes; andwherein the first and second bias currents are scaled and subtracted from one another to yield stable TC reference current over an objective temperature range.