The technology described in this patent document relates generally to voltage reference circuits and methods.
Voltage references are circuits that are commonly used as functional blocks in mixed-mode and analog integrated circuits (ICs) such as data converters, phase lock-loops (PLLs), oscillators, power management circuits, dynamic random access memory (DRAM), flash memory, and much more. A voltage reference is preferred to be nominally independent of temperature, power supply, and load variations.
To help compensate for variations in temperature, known voltage reference circuits include temperature compensation circuits that utilize bipolar junction transistor (BJT) technology. In evolving technologies, such as low voltage reference circuits, the performance of BJT-based temperature compensation circuits may be constrained, for example due to BJT or diode cut-in voltages. There is therefore a need for a voltage reference circuit that provides a high accuracy, low temperature coefficient (TC) regulated voltage using metal-oxide semiconductor (MOS) based technology.
Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures.
The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Various embodiments in accordance with this disclosure relate generally to IC (integrated circuit) devices, and more specifically, provide circuits and methods of producing circuits for process-invariant and temperature-independent voltage reference circuits in low-voltage applications. High temperature generally changes the characteristics of IC devices in ways that adversely impact their operating speed and reliability, therefore low-cost and temperature-independent devices are desired, particularly for modern portable and IoT (Internet-of-things) devices. IoT devices are usually untethered and require components with low power consumption. Sensing devices for IoT applications such as pressure, temperature, or humidity sensors, use ADC (analog-to-digital converter) and DAC (digital-to-analog converter) components that are temperature-independent and operate under low bias voltage. Voltage reference circuits in accordance with this disclosure are integral and vital parts for the above-mentioned low-power IoT applications, or power supply systems, such as low dropout (LDO) regulators.
Voltage reference circuit 100 is a substantially temperature-independent voltage reference circuit, in which a positive temperature dependency of the PTAT circuit 104 is cancelled by a negative temperature dependency of the CTAT circuit 102, thus resulting in a stable output voltage (Vref) 108 at a reference temperature. In the PTAT circuit 104, the variation in output voltage is proportional to temperature, i.e., increasing and decreasing as temperature increases and decreases, respectively. In the CTAT circuit 102, the variation in output voltage is complementary to temperature, i.e., decreasing and increasing as temperature increases and decreases, respectively. In operation, the PTAT circuit 104 generates output voltage VP and current IP, and the CTAT circuit 102 generates output voltage VC and current IC. Output currents generated by CTAT 102 and PTAT 104 circuits are combined to generate the reference voltage (Vref) 108. Reference voltage (Vref) 108 is substantially insensitive to changes in temperature or power supply.
The current bias circuit 204 is configured to generate a constant bias current 212 in response to a supply voltage (VDD) 214 input. An example of a current bias circuit 204 is described below with reference to
The temperature compensation circuit 202 includes a proportional-to-absolute temperature (PTAT) circuit and a complementary-to-absolute temperature (CTAT) circuit that share a common metal-oxide-semiconductor field-effect transistor (MOSFET) (M2) 216. The PTAT and CTAT circuits collectively generate the substantially temperature-independent reference voltage (Vref) 210 in response to the regulated current input (I1) 208. The PTAT circuit includes a first MOSFET (M1) 218 and the common MOSFET (M2) 216, and produces an increase in magnitude of the reference voltage (Vref) 210 with an increase of temperature. The CTAT circuit includes a first resistor (R1) 220, a second resistor (R2) 222, and the common MOSFET (M2) 216, and produces a decrease in magnitude of the reference voltage (Vref) 210 with the increase of temperature. Thus, an increase in magnitude of the reference voltage (Vref) 210 produced by the PTAT circuit is at least partially offset by a decrease in magnitude of the reference voltage (Vref) produced by the CTAT circuit, and vice versa.
In the PTAT circuit, a source terminal of the first MOSFET (M1) 218 and a gate terminal of the first MOSFET (M1) 218 are coupled to an input node (Va) 224 of the temperature compensation circuit 202, a drain terminal of the first MOSFET (M1) 218 is coupled to a source terminal of the common MOSFET (M2) 216 at the output node (Vref) 226 of the temperature compensation circuit 202, and a drain terminal of the common MOSFET (M2) 216 is coupled to a ground potential. In the CTAT circuit, the first resistor (R1) 220 is coupled between the gate terminal of the first MOSFET (M1) 218 and a gate terminal of the common MOSFET (M2) 216, and the second resistor (R2) 222 is coupled between the gate terminal of the common MOSFET (M2) 216 and the ground potential.
The sizes of the MOSFETs (M1 and M2) 218, 216 and the values of the resistors (R1 and R2) 220, 222 may be selected in order to tune the temperature coefficient (TC) of the temperature compensation circuit 202 such that the reference voltage output (Vref) 210 is accurate and substantially temperature-independent (i.e., achieving a low TC) even for low VDD operations. For example, in an embodiment, MOSFETs M1 and M2 (218, 216) may be sized in a ratio of N:1, and values for M1, M2, R1, and R2 may be selected based on the following equations:
Va=Vref+VgSM1,
where Va is the voltage at node 224, Vref is the reference voltage at node 226, and VgsM1 is the gate-source voltage of M1 218. Using voltage divider rules:
Vref=(VgSM2−VgsM1)+(R1/R2)*VgSM2,
where VgsM2 is the gate-source voltage of M2 216. M1 and M2 (218, 216) are biased in a subthreshold condition. In subthreshold condition, MOS Vgs is as follows:
Vgs˜Vth+η*(VT)*(Id/(W/L·μ·VT2)),
VT=k·T/q,
where k is the Bolzmann constant, T is absolute temperature, q is the charge in eV, Vth is the MOSFET threshold voltage, η=subthreshold swing, Id=current W/L=width/length of MOS μ=mobility. Thus,
(Vgs2−Vgs1)˜(Vth2−Vth1)+η*(VT)*ln[(Id/W/L·μ·VT2)/Id/N*W/L·μ·VT2],
(Vgs2−Vgs1)˜η*(VT)*ln(N),
where Vth/μ is the same for both transistors (M1 and M2); Id is the same in this topology, only W/L of M1˜N*W·L of M2. The operation of the PTAT and CTAT circuits may therefore be expressed as follows:
Vref˜{η*(kT/q)*ln(N)}+{(R1/R2)*VgsM2},
where {η*(kT/q)*ln(N)} represents operation of the PTAT circuit, and {(R1/R2)*VgsM2} represents the operation of the CTAT circuit.
Vref˜η(kT/q)*ln(N)+(R1/R2)*VgSM2
Vref˜η(kT/q)*ln(N)+(R1/R2)*VgSM2
The example current bias circuit 900 shown in
It should be understood that other current mirror and/or current bias circuit configurations may also be used in the voltage reference circuits shown in
With reference first to
In one example, a temperature compensation circuit includes a proportional-to-absolute temperature (PTAT) circuit, and a complementary-to-absolute temperature (CTAT) circuit. The PTAT circuit and the CTAT circuit include at least one common metal-oxide-semiconductor field-effect transistor (MOSFET) and are configured to collectively generate a reference voltage in response to a regulated current input. The PTAT circuit is configured to produce an increase in magnitude of the reference voltage with an increase of temperature, and the CTAT circuit is configured to generated a decrease in magnitude of the reference voltage with the increase of temperature, wherein the increase in magnitude of the reference voltage produced by the PTAT circuit is at least partially offset by the decrease in magnitude of the reference voltage produced by the CTAT circuit.
In one example, a voltage reference circuit includes a temperature compensation circuit that receives a regulated current input at an input node and generates a reference voltage at an output node, the temperature compensation circuit comprising a proportional-to-absolute temperature (PTAT) circuit and a complementary-to-absolute temperature (CTAT) circuit that share at least one common metal-oxide-semiconductor field-effect transistor (MOSFET) and that collectively generate the reference voltage in response to the regulated current input. The PTAT circuit is configured to produce an increase in magnitude of the reference voltage with an increase of temperature, and the CTAT circuit configured to generated a decrease in magnitude of the reference voltage with the increase of temperature, wherein the increase in magnitude of the reference voltage produced by the PTAT circuit is at least partially offset by the decrease in magnitude of the reference voltage produced by the CTAT circuit. In embodiments, the voltage reference circuit may further include a current bias circuit that generates a reference current, and a current mirror circuit that generates the reference current input responsive to the reference current.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.
The application claims priority to U.S. Provisional Application No. 63/156,402, titled “High Accuracy Low Temperature Coefficient MOS Voltage Reference Circuit,” filed on Mar. 4, 2021, the entirety of which is incorporated herein by reference.
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5034626 | Pirez | Jul 1991 | A |
5059890 | Yoshikawa | Oct 1991 | A |
5818294 | Ashmore, Jr. | Oct 1998 | A |
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Number | Date | Country | |
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20220283601 A1 | Sep 2022 | US |
Number | Date | Country | |
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63156402 | Mar 2021 | US |