Low noise low-dropout regulator
Representative implementations of devices and techniques provide a regulator having a high regulation speed and low noise across a wide frequency range. A pass through device outputs a regulated voltage based on a control signal output by an error amplifier. The control signal is boosted via a regulated boost signal.
1. An apparatus, comprising:
an amplifier arranged to receive a reference voltage and a feedback voltage and to output a control signal;
a capacitance arranged to receive a boost signal from the amplifier and to increase a magnitude of the control signal based on the boost signal;
a pass through device arranged to output a regulated voltage based on the control signal; and
a boost signal source to provide the boost signal, wherein the boost signal source is arranged to receive a balanced differential signal output at the amplifier, the balanced differential signal comprising a pair of inverted signals with substantially equal magnitudes.
2. The apparatus of claim 1 , wherein the pass through device is to output the regulated voltage based on the control signal at a gate of the pass through device.
3. The apparatus of claim 1 , wherein the amplifier is arranged to output the control signal based on a difference between the reference voltage and the feedback voltage.
4. The apparatus of claim 1 , wherein the boost signal source is arranged to regulate a magnitude of the boost signal.
5. The apparatus of claim 1 , wherein the amplifier comprises a single-stage operational amplifier.
6. The apparatus of claim 1 , wherein the feedback voltage is based on at least a portion of the regulated voltage.
7. The apparatus of claim 1 , wherein the boost signal source comprises an operational amplifier, and differential inputs to the operational amplifier comprise differential outputs of the amplifier.
8. The apparatus of claim 7 , wherein the differential outputs of the amplifier comprise at least a portion of a balanced circuit.
9. A voltage regulator, comprising:
an amplifier having a first input coupled to a reference voltage and a second input coupled to a feedback voltage, an output of the voltage regulator based on a control signal output from the amplifier;
a capacitance coupled to a first output of the amplifier and arranged to increase a magnitude of the control signal based on receiving a boost signal; and
a boost amplifier having a first input coupled to the first output of the amplifier and a second input coupled to a second output of the amplifier, an output of the boost amplifier comprising the boost signal;
wherein a first output signal at the first output of the amplifier is substantially equal in magnitude and opposite in polarity to a second output signal at the second output of the amplifier.
10. The voltage regulator of claim 9 , further comprising a transistor device arranged to receive an input voltage and to output a regulated voltage based on the control signal.
11. The voltage regulator of claim 10 , wherein the transistor device comprises an N-channel pass transistor device.
12. The voltage regulator of claim 9 , further comprising a voltage regulation loop coupled to the second input of the amplifier and arranged to provide the feedback voltage, based on the output of the voltage regulator.
13. The voltage regulator of claim 9 , further comprising a voltage divider arranged to output the feedback voltage.
14. The voltage regulator of claim 9 , wherein a low frequency loop gain of the low drop out voltage regulator comprises a gain of the amplifier multiplied by a gain of the boost amplifier.
15. The voltage regulator of claim 9 , wherein the amplifier comprises a single-stage operational amplifier.
16. The voltage regulator of claim 9 , wherein the boost amplifier comprises an operational amplifier arranged to regulate the boost signal.
17. The voltage regulator of claim 9 , wherein the boost amplifier does not contribute to high frequency thermal noise of the low drop out voltage regulator.
18. The voltage regulator of claim 9 , wherein at least one of the amplifier and the boost amplifier are comprised of a symmetric set of complementary metal-oxide-semiconductor (CMOS) transistor pairs.
19. The voltage regulator of claim 9 , wherein the amplifier and the boost amplifier comprise electrically equivalent devices.
20. A method of controlling a voltage regulator, comprising:
generating a control signal at an amplifier arranged to compare at least a portion of an output of the voltage regulator to a reference signal;
passing a signal through a pass through device based on the control signal;
adjusting a magnitude of the control signal with a boosting voltage applied to the control signal; and
regulating the boosting voltage to output a zero differential voltage at the amplifier.
21. The method of claim 20 , further comprising charging a capacitance with the boosting voltage and applying the boosting voltage to the control signal via the capacitance.
22. The method of claim 20 , further comprising boosting the magnitude of the control signal above a magnitude of an input signal to the pass through device.
23. The method of claim 20 , further comprising boosting the magnitude of the control signal to a value at or above a magnitude of the output of the voltage regulator plus a gate-to-source voltage of the pass through device.
24. The method of claim 20 , further comprising generating the boosting voltage at an operational amplifier, wherein differential inputs of the operational amplifier are coupled to differential outputs of the amplifier, respectively.
25. The method of claim 24 , wherein the differential outputs of the amplifier are set to output a balanced signal.
26. A low dropout voltage regulator, comprising:
an n-channel pass through transistor device arranged to receive an input voltage and to output a regulated voltage based on a control signal applied at a gate of the transistor device;
an error amplifier having a first input coupled to a reference voltage and a second input coupled to a feedback voltage, the error amplifier arranged to output the control signal based on a difference between the reference voltage and the feedback voltage;
a flying capacitance coupled to an output of the error amplifier and arranged to increase a magnitude of the control signal via a boost signal; and
a boost amplifier having a first input coupled to a first output of the error amplifier and a second input coupled to a second output of the error amplifier, the boost amplifier arranged to regulate the boost signal based on a differential output voltage of the error amplifier set to zero.