Switching power converter control

1. A controller for a switching power converter of the type comprising one or more power switches, said controller comprising:

a pulse width modulation comparator arranged to output a digital control signal to control the power switches of the switching power converter;

a first input of the pulse width modulation comparator is derived from an output voltage of the switching power converter via a first feedback path;

a second input of the pulse width modulation comparator is derived from the output voltage of the switching power converter via a second feedback path; wherein

one of the feedback paths comprises a signal extractor and a differential amplifier; and

the signal extractor is arranged to filter the output voltage to obtain a first voltage signal in a first frequency range and a second voltage signal in a second frequency range being different from said first frequency range, said first and second voltage signals sharing a common noise component; and to present said first and second voltage signals as respective first and second inputs to the differential amplifier.

2. The controller of claim 1 , wherein the signal extractor comprises:

a first filter network;

a second filter network;

a first coupling network arranged to extract ground noise and couple said extracted ground noise to both of said first and second filter networks; and

a second coupling network is arranged to extract a feedback voltage comprising contributions from the output voltage and ground noise for processing by both of said first and second filter networks.

3. The controller of claim 2 , wherein the first and second filter networks act sequentially on the feedback voltage.

4. The controller of claim 2 , wherein the first and second filter networks are both coupled with the feedback voltage.

5. The controller of claim 2 , wherein the first filter network has a first cut-off frequency and is arranged to high-pass filter the feedback voltage and to low-pass filter the ground noise, and the second filter network has a second cut-off frequency and is arranged to high-pass filter the feedback voltage and to low-pass filter the ground noise.

6. The controller of claim 2 , wherein the first filter network has a first cut-off frequency and is arranged to low-pass filter the feedback voltage and to high-pass filter the ground noise, and the second filter network has a second cut-off frequency and is arranged to low-pass filter the feedback voltage and to high-pass filter the ground noise.

7. The controller of claim 2 , wherein the first coupling network comprises a current source for providing a bias current, and a grounded resistive element; said current source and resistive element being coupled for providing an output with ground noise.

8. The controller of claim 7 , further comprising a second resistive element in series with said grounded resistive element.

9. The controller of claim 8 , wherein the grounded resistive element and/or the second resistive element comprises a diode connected transistor.

10. The controller of claim 2 , wherein the second coupling network comprises a potential divider such that the feedback voltage comprises a scaled output voltage and ground noise.

11. The controller of claim 1 , wherein the differential amplifier is a transconductance amplifier that outputs a current signal that is passed to a reference resistor to generate a voltage ramp that is coupled to the second input of the pulse width modulation comparator.

12. A method of controlling the operation of a switching power converter of the type comprising a pulse width modulation comparator and one or more power switches, said method comprising:

deriving a first PWM input from an output voltage and presenting the input via a first feedback path;

deriving a second PWM input from an output voltage and presenting the input via a second feedback path;

at one of said paths, filtering the output voltage to obtain a first voltage signal in a first frequency range and a second voltage signal in a second frequency range being different from said first frequency range, said first and second voltage signals sharing a common noise component; and

presenting said first and second voltage signals as respective first and second inputs to a differential amplifier.

13. The method of claim 12 , wherein a signal extractor comprises:

a first filter network;

a second filter network;

a first coupling network arranged to extract ground noise and couple said extracted ground noise to both of said first and second filter networks; and

a second coupling network is arranged to extract a feedback voltage comprising contributions from the output voltage and ground noise for processing by both of said first and second filter networks.

14. The method of claim 13 , wherein the first and second filter networks act sequentially on the feedback voltage.

15. The method of claim 13 , wherein the first and second filter networks are both coupled with the feedback voltage.

16. The method of claim 13 , wherein the first filter network has a first cut-off frequency and is arranged to high-pass filter the feedback voltage and to low-pass filter the ground noise, and the second filter network has a second cut-off frequency and is arranged to high-pass filter the feedback voltage and to low-pass filter the ground noise.

17. The method of claim 13 , wherein the first filter network has a first cut-off frequency and is arranged to low-pass filter the feedback voltage and to high-pass filter the ground noise, and the second filter network has a second cut-off frequency and is arranged to low-pass filter the feedback voltage and to high-pass filter the ground noise.

18. The method of claim 13 , wherein the first coupling network comprises a current source for providing a bias current, and a grounded resistive element; said current source and resistive element being coupled for providing an output with ground noise.

19. The method of claim 18 , further comprising a second resistive element in series with said grounded resistive element.

20. The method of claim 19 , wherein the grounded resistive element and/or the second resistive element comprises a diode connected transistor.

21. The method of claim 13 , wherein the second coupling network comprises a potential divider such that the feedback voltage comprises a scaled output voltage and ground noise.

22. The method of claim 12 , wherein the differential amplifier is a transconductance amplifier that outputs a current signal that is passed to a reference resistor to generate a voltage ramp that is coupled to the second input of the pulse width modulation comparator.