Replica transistor voltage regulator
View Patent ↗A voltage regulator is provided having high accuracy, low PSRR, and no headroom limitation. Generally, the regulator includes: an operational amplifier (OPAMP) having a non-inverting input coupled to a reference voltage; an output source follower coupled to and controlled by an output of the OPAMP, the output source follower including a drain coupled to a voltage source and a source coupled to an output-node of the regulator; a replica source follower coupled to and controlled by the OPAMP, the replica source follower including a drain coupled to the voltage source and a source coupled to circuit ground through a resistor network; and a feedback circuit extending from the output-node through a feedback resistor to the source of the replica source follower and through at least a first resistor of the resistor network to an inverting input of the OPAMP to couple a feedback voltage thereto. Other embodiments are also provided.
1. A voltage regulator comprising:
an operational amplifier (OPAMP) having a non-inverting input coupled to a reference voltage (Vref);
an output source follower coupled to and controlled by an output of the OPAMP, the output source follower including a drain coupled to a voltage source and a source coupled to an output-node of the voltage regulator;
a replica source follower coupled to and controlled by the output of the OPAMP in parallel with the output source follower, the replica source follower including a drain coupled to the voltage source and a source coupled to a circuit ground through a resistor network; and
a feedback circuit extending from the output-node through a feedback resistor to the source of the replica source follower and through at least a first resistor of the resistor network to an inverting input of the OPAMP to couple a feedback voltage (Vfbk) thereto to regulate a voltage (Vout) at the output-node in response to a comparison between Vfbk and Vref.
2. A voltage regulator according to claim 1 , wherein the feedback resistor comprises a resistance equal to or less than about 100 Ohms.
3. A voltage regulator according to claim 1 , wherein the voltage regulator is a replica transistor voltage regulator comprising a replica leg including the replica source follower and the resistor network, and an output leg comprising the output source follower and further comprising a leaker transistor coupled between the source of the output source follower and circuit ground.
4. A voltage regulator according to claim 3 , wherein the leaker transistor comprises a drain coupled to the source of the output source follower and a source coupled to circuit ground, and wherein the leaker transistor is controlled by a bias voltage to leak current from the output-node to provide at least a constant minimum current flow in the output source follower.
5. A voltage regulator according to claim 1 , wherein the voltage regulator has a Vout that varies by 4.5% or less from a predetermined Vout.
6. A voltage regulator according to claim 1 , wherein the voltage regulator has a power supply rejection ratio (PSRR) equal to or less than about −20 decibels (dB).
7. A voltage regulator according to claim 1 , wherein the voltage regulator has maximum headroom of at least 280 millivolts (mV).
8. A voltage regulator according to claim 1 , wherein the voltage regulator utilizes a small area on a substrate on which it is implemented, having an area of less than about 100K microns (μm2).
9. A voltage regulator comprising:
an operational amplifier (OPAMP) having a non-inverting input coupled to a predetermined reference voltage (Vref);
an output source follower coupled to and controlled by an output of the OPAMP, the output source follower including a drain coupled to a voltage source and a source coupled to an output-node of the voltage regulator;
a replica source follower coupled to and controlled by the output of the OPAMP in parallel with the output source follower, the replica source follower including a drain coupled to the voltage source and a source coupled to a circuit ground through a resistor network; and
a feedback circuit extending from the output-node through a feedback transistor to the source of the replica source follower and through at least a first resistor of the resistor network to an inverting input of the OPAMP to couple a feedback voltage (Vfbk) thereto to regulate a voltage (Vout) at the output-node in response to a comparison between Vfbk and Vref.
10. A voltage regulator according to claim 9 , wherein the feedback transistor is controlled by a biasing voltage that can be varied to adjust a magnitude of Vfbk.
11. A voltage regulator according to claim 10 , wherein the feedback transistor is connected as a source follower having a source coupled to the source of the replica source follower and a drain coupled to the source of the output source follower.
12. A voltage regulator according to claim 11 , wherein the feedback transistor further comprises a bulk terminal coupled to the source thereof to improve the stability of the feedback circuit.
13. A voltage regulator according to claim 9 , wherein the voltage regulator is a replica transistor voltage regulator comprising a replica leg including the replica source follower and the resistor network, and an output leg comprising the output source follower and further comprising a leaker transistor coupled between the source of the output source follower and circuit ground to provide at least a constant minimum current flow in the output source follower.
14. A voltage regulator according to claim 9 , wherein the voltage regulator has a Vout that varies by 4.5% or less from a predetermined Vout.
15. A voltage regulator according to claim 9 , wherein the voltage regulator has a power supply rejection ratio (PSRR) equal to or less than about −20 decibels (dB).
16. A voltage regulator according to claim 9 , wherein the voltage regulator has maximum headroom of at least 280 millivolts (mV).
17. A voltage regulator according to claim 9 , wherein the voltage regulator utilizes a small area on a substrate on which it is implemented, having an area of less than about 100K microns (μm2).
18. A method for operating a voltage regulator comprising:
coupling a reference voltage (Vref) to a non-inverting input of an operational amplifier (OPAMP);
controlling with a voltage (Vgate) from an output of the OPAMP an output source follower coupled thereto, the output source follower including a drain coupled to a voltage source and a source coupled to an output-node of the voltage regulator;
controlling with Vgate a replica source follower coupled to the output of the OPAMP in parallel with the output source follower, the replica source follower including a drain coupled to the voltage source and a source coupled to a circuit ground through a resistor network; and
coupling a feedback voltage (Vfbk) from the output-node to an inverting input of the OPAMP through a feedback circuit extending through at least a first resistor of the resistor network to regulate a voltage (Vout) at the output-node in response to a comparison between Vfbk and Vref, wherein the feedback circuit comprises a feedback resistor coupled between the output-node and the source of the replica source follower.
19. A method for operating a voltage regulator comprising:
coupling a reference voltage (Vref) to a non-inverting input of an operational amplifier (OPAMP);
controlling with a voltage (Vgate) from an output of the OPAMP an output source follower coupled thereto, the output source follower including a drain coupled to a voltage source and a source coupled to an output-node of the voltage regulator;
controlling with Vgate a replica source follower coupled to the output of the OPAMP in parallel with the output source follower, the replica source follower including a drain coupled to the voltage source and a source coupled to a circuit ground through a resistor network; and
coupling a feedback voltage (Vfbk) from the output-node to an inverting input of the OPAMP through a feedback circuit extending through at least a first resistor of the resistor network to regulate a voltage (Vout) at the output-node in response to a comparison between Vfbk and Vref, wherein the feedback circuit comprises a feedback transistor coupled between the output-node and the source of the replica source follower and controlled by a biasing voltage that can be varied to adjust a magnitude of Vfbk.