Asymmetric transient response control

1. A loop controller, comprising:

an error amplifier configured to receive an output of a controlled process and further configured to receive a reference input; and

an asymmetric compensator, including:

a high pass filter configured to receive an amplified version of the reference input and output a filtered reference; and

an asymmetric impedance configured to receive an amplified version of the filtered reference and output a compensation signal;

wherein the error amplifier is further configured to sum the compensation signal and the output of the controlled process, and provide an error signal based on a difference between the sum and the reference input, and wherein the compensation signal includes a first gain for a rising transition of the controlled process output and a second gain for a falling transition of the controlled process output.

2. The loop controller of claim 1 , wherein second gain is greater than the first gain.

3. The loop controller of claim 1 , wherein first gain is greater than the second gain.

4. The loop controller of claim 1 , wherein the second gain compensates for an undershoot of the falling transition.

5. The loop controller of claim 1 , wherein the first gain and the second gain are asymmetric to compensate an asymmetry of the controlled process output.

6. The loop controller of claim 1 , wherein the first gain and the second gain are asymmetric to introduce an asymmetry to the controlled process output.

7. The loop controller of claim 1 , wherein the controlled process output is an output of a power supply.

8. The loop controller of claim 1 , wherein the high pass filter is further configured such that when the reference input changes, a voltage difference appears between terminals of the error amplifier for a duration determined by a time constant of the high pass filter.

9. The loop controller of claim 1 , wherein the asymmetric impedance includes a precision diode circuit.

10. The loop controller of claim 1 , wherein the compensation signal is part of a feed-forward control loop.

11. The loop controller of claim 1 , wherein the compensation signal is part of a feedback control loop.

12. The loop controller of claim 1 , wherein the asymmetric impedance includes at least one of a resistive component and a reactive component.

13. The loop controller of claim 12 , wherein the asymmetric impedance includes a combination of resistive and reactive components.

14. A power supply, comprising:

a regulator;

an error amplifier configured to receive an output of the regulator and further configured to receive a reference input; and

an asymmetric compensator, including:

a high pass filter configured to receive an amplified version of the reference input and output a filtered reference; and

an asymmetric impedance configured to receive an amplified version of the filtered reference and output a compensation signal;

wherein the error amplifier is further configured to sum the compensation signal and the regulator output, and provide an error signal based on a difference between the sum and the reference input, and wherein the compensation signal is part of a feed-forward control loop.

15. The power supply of claim 14 , wherein the asymmetric impedance imparts an asymmetric gain component to the compensation signal.

16. The power supply of claim 15 , wherein the asymmetric gain component includes a first gain for a rising transition of the regulator output and a second gain for a falling transition of the regulator output.

17. The power supply of claim 16 , wherein second gain is greater than the first gain.

18. The power supply of claim 16 , wherein first gain is greater than the second gain.

19. The power supply of claim 16 , wherein the second gain compensates for an undershoot of the falling transition.

20. The power supply of claim 16 , wherein the second gain compensates for an overshoot of the rising transition.

21. The power supply of claim 16 , wherein the first gain and the second gain are asymmetric to compensate an asymmetry of the regulator output.

22. The power supply of claim 16 , wherein the first gain and the second gain are asymmetric to introduce an asymmetry to the regulator output.

23. The power supply of claim 14 , wherein the high pass filter is further configured such that when the reference input changes, a voltage difference appears between terminals of the error amplifier for a duration determined by a time constant of the high pass filter.

24. The power supply of claim 14 , wherein the asymmetric impedance includes a precision diode circuit.

25. The power supply of claim 14 , configured to provide a variable voltage output to an integrated circuit.

26. An apparatus comprising:

a closed loop control system including a controlled process for delivering a controlled process output and a loop controller including an error amplifier and a compensation circuit;

the loop controller being adapted to receive a reference input and a representation of the controlled process output and to produce an error signal for controlling the controlled process;

wherein the loop controller provides a first response characteristic for a perturbation of a first polarity and a second response characteristic for a perturbation of an opposite polarity, the first response characteristic being different than the second response characteristic.

27. The apparatus of claim 26 , wherein the compensation circuit further includes an active network to provide a first gain for the perturbation of the first polarity and a second gain for the perturbation of the opposite polarity.

28. The apparatus of claim 26 , wherein the compensation circuit further includes a linear network and a non-linear network to provide a first impedance for the perturbation of the first polarity and a second impedance for the perturbation of the opposite polarity.

29. The apparatus of claim 28 , wherein the linear network comprises a high pass filter configured to receive an amplified version of the reference input and output a filtered reference.

30. The apparatus of claim 28 , wherein the non-linear network comprises a precision rectifier circuit.

31. The apparatus of claim 28 , wherein the linear network comprises a high pass filter and the non-linear network comprises a unidirectional conduction device.

32. The apparatus of claim 26 , wherein the compensation circuit is connected to an input of the error amplifier.

33. The apparatus of claim 26 , wherein the compensation circuit is connected to an output of the error amplifier.

34. The apparatus of claim 26 , wherein the compensation circuit is connected to an input of the error amplifier and an output of the error amplifier.

35. The apparatus of claim 26 , wherein the error amplifier includes two inputs and the compensation circuit is connected to both inputs of the error amplifier.

36. The apparatus of claim 26 , wherein the compensation circuit provides a first gain for DC signals and a second higher gain for higher frequency signals.

37. The apparatus of claim 26 , wherein the error amplifier is further configured to sum a compensation signal from the compensation circuit and the controlled process output, and provide the error signal based on a difference between the sum and the reference input, and wherein the compensation signal includes a first gain for a rising transition of the controlled process output and a second gain for a falling transition of the controlled process output.

38. The apparatus of claim 26 , wherein the controlled process is a power supply and the controlled process output is an output of the power supply.

39. The apparatus of claim 26 , wherein the compensation circuit is implemented in a digital controller to provide a first gain for the perturbation of the first polarity and a second gain for the perturbation of the opposite polarity.

40. The apparatus of claim 26 , wherein the loop controller is implemented in a digital controller.