Closed loop power controller

• US 5,352,986 A
• Filed: 01/22/1993
• Issued: 10/04/1994
• Est. Priority Date: 01/22/1993
• Status: Expired due to Fees

• Current Assignee: Digital Fidelity Limited
• Original Assignee: Digital Fidelity Limited
• Inventors: Nelson, Robert G., Modgil, Onkar S., Reif, Margaret S.
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US08/007,521
• Time in Patent Office: 620 Days
• Field of Search: 330/10, 330/207 A, 330/251, 330/107, 330/109
• US Class Current: 330/10
• CPC Class Codes: H03F 1/083 in transistor amplifiers H03F1/10 - H03F1/22 take precedence
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03M 3/432 the quantiser being a pulse width modulation type analogue/digital converter, i.e. differential pulse width modulation
• CPC Class Codes: H03M 3/438 the modulator having a higher order loop filter in the feedforward path

Abstract

A power controller includes a closed-loop system having a summer to sum an input signal with a derived output signal to produce a difference signal. A comparator compares the difference signal with a reference signal to produce a digital signal representative of the polarity difference between the difference signal and the reference signal. Two switching networks respond to the digital signal to produce high energy outputs representative of the digital signal which are used to reduce the level of the difference signal in a frequency band of interest at the comparator. A low pass filter between the high energy outputs and the comparator attenuates high-frequency noise. A low-pass filter of at least the third order, connected in the closed loop, enhances the signal-to-noise ratio. In a specific application the power controller is a power amplifier and the input signal is in the audio frequency range.

Claims

1. A closed-loop system, having an input and an output, for controlling power comprising, means to sum an input signal with a derived output signal to produce a difference signal representative of the polarity of the difference between said input signal and said derived output signal,

means for producing an asynchronous digital signal representative of the polarity of said difference signal, at least two switching networks, said switching networks having high energy outputs and being responsive to said asynchronous digital signal to reduce the level of said difference signal in a frequency band of interest at said means of producing the said asynchronous digital signal;

and

a low-pass filter at least of the third order between said high energy outputs and said means of producing the said asynchronous digital signal to attenuate high-frequency noise, said low-pass filter being in said closed loop to enhance the signal-to-noise ratio at said output of said closed-loop system and modified to maintain loop stability.

3. A closed-loop system as set forth in claim 2 or 1 in which said switching networks are responsive to said digital signal synchronous with a clock producing pulses at a rate significantly higher than the frequencies of the input signal.

4. A closed-loop system as set forth in claim 1 wherein said low-pass filter is underdamped.

10. A closed-loop system as set forth in claim 1, 2, 3, 4 or 5 wherein said low-pass filter of at least the third order has more than 180 degrees of phase lag at certain frequencies.

12. A closed-loop system as set forth in claim 10 including means for reducing the phase lag below 180 degrees.

15. A closed-loop system as set forth in claim 1, 2, 3, 4, 5, 6, or 7, wherein the closed loop system is a power amplifier and the input signal is in the audio frequency range.

19. A closed-loop system as set forth in claim 10 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

20. A closed-loop system as set forth in claim 12 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

21. A closed-loop system as set forth in claim 12 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

2. A closed-loop system, having an input and an analog output, for controlling power comprising,

means to sum a signal applied to the input with a signal derived from the analog output to produce a difference signal representative of the polarity of the difference between said input signal and said derived output signal,

means for producing a digital signal representative of the polarity of said difference signal,

at least two switching networks, said switching networks having high energy outputs and being responsive to said digital signals, to reduce the level of said difference signal in the frequency band of interest at the means for producing the said digital signals,

a low-pass filter between said high energy outputs and the said analog output to attenuate high-frequency noise, and

a low-pass filter at least of the third order in said closed loop to enhance the signal-to-noise ratio at said output of said closed-loop system, said low-pass filter at least of the third order modified to maintain loop stability.

5. A closed-loop system as set forth in claim 2 wherein said low-pass filter in the closed-loop is underdamped.

6. A closed-loop system, having an input and an output, for controlling power comprising,

means to sum a signal applied to the input with a signal derived from the output to produce a difference signal,

means for generating a reference signal, comparison means for comparing said difference signal with said reference signal to produce a digital signal representative of the polarity difference between said difference signal and said reference signal,

at least two switching networks, said switching networks having high energy outputs representative of said digital signal, to reduce the level of said difference signal in the frequency band of interest at the means for producing the said digital signal,

a low-pass filter between said high energy outputs and said means for producing the said digital signal to attenuate high-frequency noise, and a low-pass filter of at least the third order in the closed loop to enhance the signal-to-noise ratio and modified to maintain loop stability.

7. A closed-loop system as set forth in claim 6 in which said low-pass filter of at least the third order is underdamped.

8. A closed-loop system as set forth in claim 6 or 7 wherein the closed-loop system includes a pulse-width modulator.

9. A closed-loop system as set forth in claim 6 or 7, wherein said low-pass filter of at least the third order has more than 180 degrees of phase lag at certain frequencies.

11. A closed-loop system as set forth in claim 8 wherein said low-pass filter of at least the third order has more than 180 degrees of phase lag at certain frequencies.

13. A closed-loop system as set forth in claim 11 including means for reducing the phase lag below 180 degrees.

14. A closed-loop system as set forth in claim 9 including means for reducing the phase lag below 180 degrees.

16. A closed-loop system as set forth in claim 8 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

17. A closed-loop system as set forth in claim 9 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

18. A closed-loop system as set forth in claim 14 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.

22. A closed-loop system as set forth in claim 13 wherein the closed-loop system is a power amplifier and the input signal is in the audio frequency range.