1. Field
The disclosure relates generally to a voltage regulator and, more particularly, to a low dropout regulator thereof.
2. Description of the Related Art
Low dropout (LDO) regulators are commonly used to regulate internal voltage supplies at lower voltage from higher voltages. Voltage regulation is important where circuits are sensitive to transients, noise and other types of disturbances. The control of the regulated voltage over variations in both semiconductor process variation, and temperature is key to many applications. Additionally, power consumption is also a key design requirement.
A shift resistance RSHIFT increases the current through the resistances RF and shifts up from 1.2V to an arbitrarily value VREG. By setting properly RF, RSHIFT, RPTAT and N, VREG is directly compensated in temperature, but this comes at the cost of two very large resistors RF and an operational amplifier.
The output voltage, VOUT, VOUT=VREG is adjusted by the operational amplifier OA1340 such that its fraction R4/(R3+R4) matches ˜1.25V. Then it is possible to optimize only the left part (bandgap part) to compensate it in temperature, and so the same compensation will also result for VOUT=VREG.
The disadvantage of this circuit topology is the sensitivity to the regulated voltage VREG. If the regulated voltage, VREG, has noise, it is amplified because applied on the gate-to-source voltage of the MPLOOP.
The PTAT effect is done by matching the current in Q2545A (N elements) with the current in Q1535 (1 element) through the VREG loop. VREG is adjusted for this matching and {R2570, R3580} allow to adjust the value of VREG. This implementation has the following disadvantages and drawbacks:
U.S. Pat. No. 6,995,587 to Xi, describes a method for generating a bandgap reference current. The method for generating a band gap reference current includes the steps for mirroring the bandgap reference current, summing the mirrored currents, and modulating and outputting a bandgap reference voltage from the sum. Representative preferred embodiments are disclosed in which the methods of the invention are used in providing under-voltage protection and in providing a regulated output voltage. Preferred embodiments of the invention include a bandgap under-voltage detection circuit using a comparator and a voltage regulator circuit having a regulated voltage output capability.
U.S. Pat. No. 6,512,398 to Sonoyama describes a circuit device with improved reliability by minimizing the fluctuations of the detection level of the supply voltage. In the circuit device comprises a differential amplifier circuit that amplifies the differential voltage representing the difference between the reference voltage VREF generated by a reference voltage generating section and the detection voltage obtained by dividing a supply voltage. The reference voltage generating section generates reference voltage VREF from the base-emitter voltage of a bipolar transistor.
A bandgap voltage reference is discussed in the Analog Devices data sheet for AD580. The AD580 Data Sheet discloses a 3-terminal, low cost, temperature-compensated, bandgap voltage reference, which provides a fixed 2.5V output for inputs between 4.5V and 30V. A unique combination of advanced circuit design and thin film resistors provide the AD580 with an initial tolerance of ±0.4%, a temperature stability of better than 10 ppm/° C., and long-term stability of better than 250 μV.
In these prior art embodiments, the solution to establish a utilized various alternative solutions.
It is desirable to provide a solution to address an efficient voltage regulator with minimal power consumption.
A principal object of the present disclosure is to provide a circuit with a loop gain VCTL with a ground reference for better power supply rejection ratio (PSRR) and noise immunity.
Another further object of the present disclosure is to provide a circuit that utilized field effect transistors that are voltage tolerant to high voltage.
Another further object of the present disclosure is to provide a circuit that utilizes high voltage field effect transistors to avoid series-cascode of the bipolar junction transistors.
In summary, a circuit providing a temperature compensated voltage comprising a voltage regulator circuit configured to provide a regulator voltage, a voltage reference circuit configured to provide a reference voltage a startup circuit configured to provide a control voltage VCTL, and an operational amplifier configured to provide amplification and coupling to said startup circuit.
In addition, a method is disclosed in accordance with the embodiment of the disclosure. A method of providing a temperature compensated high voltage comprising the steps of a first step, providing a circuit on a semiconductor chip, the circuit comprising a voltage reference generator, and a voltage regulator generator; a second step, establishing a current in transistor QN; a third step, copying the current onto transistor QN1; a fourth step, copying the current back to current mirror {MP1, MPN}; a fifth step, comparing the current in transistor Q1 to current in transistor QN to establish a voltage VCTL; a sixth step, driving the current-mode operational amplifier {MNOA, MPOA, and MP}; and, a seventh step, adjusting a regulator voltage VREG to match currents in transistor Q1 and QN.
Other advantages will be recognized by those of ordinary skill in the art.
The present disclosure and the corresponding advantages and features provided thereby will be best understood and appreciated upon review of the following detailed description of the disclosure, taken in conjunction with the following drawings, where like numerals represent like elements, in which:
The regulator voltage, VREG, is adjusted such that the signal voltage VCTL drives a given current through n-channel transistor MNOA 640; this allows prevention of signal clipping of the signal VCTL. (e.g. VCTL is not clipping up nor down). The regulator voltage VREG is adjusted to match the currents in bipolar transistor Q1650 and bipolar transistor QN 645A. This method emulates a PTAT, with the advantage that the regulation voltage itself is referenced to the ground VSS 620.
The derivation of the regulation voltage VREG is illustrated in the following equations. First, equating the currents of transistor QN 645A, and transistor Q1650 where IQN=IQ1. This can be expressed as
The regulation voltage, VREG and can expressed as
The regulation voltage can be expressed as a ratios of the resistors RPTAT 660, resistor RUP 670, and RSHIFT 680
This equation is made of a base-emitter voltage, VBE1 term that decreases with temperature, and a ΔVBE term that increases with temperature. By calculating properly RUP, RPTAT, RSHIFT and N (that is embedded in ΔVBE), the value of VREG can be chosen and also compensate it in temperature.
In the circuit 700, the collector-to-emitter current in bipolar transistor QN 745A is mirrored onto bipolar transistor QN1745B with the ratio N:1. Using a current mirror {QN 745A, QN 745B} limits the current consumption. The current is then copied back to the p-channel current mirror MPN 732A and MP 1732B where the 1:N ratio restores the previous N:1 scaling. Thus, the current in bipolar transistor Q1750 is compared to the current to QN 745 and the result pushes or pulls the signal line voltage VCTL. This establishes a drive current which establishes the current-mode operational amplifier formed from n-channel MOSFET MNOA 740, and current mirror p-channel MOSFET MPOA 730B and p-channel MOSFET MP 730A, where the ratio MPOA:MP can be very large to be able to inject more current to the output. Additionally, the implementation in general does not have to restore exactly the ratio N:1 to 1:N. An implementation when the ratio is not restored to 1:1, but to 1:M or M:1, where M is. As long as this ratio remains constant (using mirror ratios), a PTAT behaviour can also be implemented. For example, this can lead to current IQ1 different from current IQN, but ratio well controlled between both.
The regulator voltage, VREG, is adjusted such that the signal voltage VCTL drives a given current through n-channel transistor MNOA 740; this allows prevention of signal clipping of the signal VCTL. (e.g. VCTL is not clipping up nor down). The regulator voltage VREG is adjusted to match the currents in bipolar transistor Q1750 and bipolar transistor QN 745A. This method emulates a PTAT, with the advantage that the regulation voltage itself is referenced to the ground VSS 720.
A startup function system includes a p-channel MOSFET 785A, a p-channel MOSFET 785B, and startup resistance 790. The gate of p-channel MOSFET 785 is electrically connected to the drain of p-channel MOSFET 785B, providing a startup signal GPSTART. The gate of p-channel MOSFET 785B is connected to the p-channel current mirror {MP 730A, and MPOA 730B}. The p-channel MOSFET 785B drain is electrically connected to the resistance RSTARTUP 790.
In this embodiment, the PTAT requires a p-channel MOSFET current mirror referenced to the supply from the current mirror MPN 732A and MP1732B; this can use the rail OUT=VREG. For example, the sources of the p-channel MOSFET current mirror are connected to the battery BAT instead of VREG.
The start-up system components, GPSTART is initially discharged as long as no current flows through the amplifier. This allows the supply to connect to OUT using the “Startup MS” PMOS 785A. Once current starts flowing, GPSTART goes up to the supply and deactivates MS.
The resistance RSTARTUP 790 can be a passive or active element. For example, the resistance RSTARTUP 790 can be a source-drain resistance of a MOSFET or plurality of MOSFETs. In this embodiment, a very large startup resistance RSTARTUP 790 is desired to activate the regulator.
Other equivalent circuit embodiments can be utilized. High-voltage transistors can replace the low-voltage transistor components within the circuit embodiment. For example, the transistor MNOA 740 can be a high-voltage transistor to drive the transistors MPOA 730B, and transistor MP 730A in a high voltage domain. Additionally, other equivalent circuit embodiments also can be utilized. It is worth noting that all the bipolar NPN transistors may be replaced by NMOS in weak inversion, to eliminate the base-current errors and to reduce the total size.
In the method in accordance with the embodiment, the third step 830, the current in QN is copied onto QN1 with the ratio N:1 (to limit the consumption).
In the method in accordance with the embodiment, the fourth step 840 the current is copied back to {MP1, MPN} where the 1:N ratio restores the previous N:1 scaling.
In the method in accordance with the embodiment, the fifth step 850 the current in Q1 is compared to the current to QN and the result pushes or pulls the line VCTL.
In the sixth step 860, this drives the current mode operational amplifier {MNOA, MPOA and MP} where the ratio MPOA:MP can be very large to be able to inject more current to the output.
In the seventh step 870, VREG is adjusted such that VCTL drives a given current through MNOA, and this means VCTL is not clipping up nor down: in other words VREG is adjusted to match the currents in Q1 and QN. We have thus emulated a PTAT, with the advantage compared to prior art that the regulation itself is referenced to the ground.
In the method in accordance with the embodiment, this can be further described from the equation from the equating of the current through transistor QN and the transistor Q1, starting with IQN=IQ1. This means:
In the method in accordance with the embodiment, the derivation of the regulated voltage VREG can be derived according to VREG:
This equation is made of a VBE1 term that decreases with temperature, and a ΔVBE term that increases with temperature. By calculating properly RUP, RPTAT, RSHIFT and N (that is embedded in ΔVBE), we can choose both the value of VREG and also compensate it in temperature.
Other equivalent circuit embodiments are also can be utilized. Equivalent reference voltage and voltage regulator generators can be merged to provide temperature compensation at voltages above 1.2 V.
It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the proposed methods and systems and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
Other advantages will be recognized by those of ordinary skill in the art. The above detailed description of the disclosure, and the examples described therein, has been presented for the purposes of illustration and description. While the principles of the disclosure have been described above in connection with a specific device, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the disclosure.
Number | Date | Country | Kind |
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14178436.3 | Jul 2014 | EP | regional |