Switching power amplifier with rate-controlled power supply voltage transitions

• US 9,209,762 B1
• Filed: 10/24/2013
• Issued: 12/08/2015
• Est. Priority Date: 04/01/2013
• Status: Active Grant

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Cirrus Logic Incorporated
• Inventors: Ranjbar, Mohammad, Mortazavi, Yousof, Mashayekhi, Arash
• Primary Examiner(s): Mottola, Steven J
• Assistant Examiner(s): Rahman, Hafizur
• Application Number:
  US14/061,912
• Time in Patent Office: 775 Days
• Field of Search: 330/10, 330/207.A, 330/251, 381/104
• US Class Current: 1/1
• CPC Class Codes: H03F 1/305 in case of switching on or off of a power supply
• CPC Class Codes: H03F 3/185 with field-effect devices H03F3/187 takes precedence
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H03F 3/2175 using analogue-digital or digital-analogue conversion H03F3/2173 takes precedence

Abstract

In a switched-power amplifier that has controlled power supply rails, e.g., when a volume control is implemented by varying the power supply voltages, a rate-controlled power supply control circuit eliminates audible pops that would otherwise occur when a change in input level causes the power supply rail voltages to change. The control circuit generates control signals that control the regulators providing the power supply rails with a controlled rate of change such that asymmetry between the voltages of the power supply rail outputs during changes of the power supply rails is substantially reduced. The controlled rate of change is less than or equal to the slowest rate of change of the power supply outputs that supply the power supply rails of the switched-power amplifier.

Claims

1. A circuit for generating an output signal of varying amplitude, the circuit comprising:

a first low-dropout linear regulator for generating a positive power supply rail output and having a first reference voltage input;

a second low-dropout linear regulator for generating a negative power supply rail output and having a second reference voltage input, wherein a first response of the positive power supply rail output differs from a second response of the negative power supply rail output;

a switching circuit having a first power supply rail input coupled to the positive power supply rail output of the first low-dropout linear regulator and a second power supply rail input coupled to the negative power supply rail output of the second low-dropout linear regulator;

a switching control circuit having an input for receiving an input signal and generating switching control signals for controlling the switching circuit, wherein the switching control circuit comprises a modulator for generating the switching control signals in conformity with a value of the input signal; and

a power supply control circuit having an input for receiving at least one output level control signal and generating at least one power supply control signal supplied to the first reference voltage input of the first low-dropout linear regulator and the second reference voltage input of the second low-dropout linear regulator, wherein the power supply control circuit generates the power supply control signal in conformity with the at least one output level control signal with a controlled rate of change between adjacent steps in the at least one output level control signal, such that asymmetry between the voltages of the positive power supply rail output of the first low-dropout linear regulator and the negative power supply rail output of the second low-dropout linear regulator during changes of the at least one output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of both the first response and the second response such that waveforms of the voltages of the positive power supply output and the negative power supply output are substantially symmetrical when the at least one output level control signal changes.

2. The circuit of claim 1, wherein the first response is a voltage step response of the positive power supply rail output with respect to the at least one output level control signal, and wherein the second response is a voltage step response of the negative power supply rail output with respect to the at least one output level control signal.

3. The circuit of claim 1, wherein the output signal is an audio signal, and wherein the circuit is an audio power amplifier.

4. The circuit of claim 1, wherein the at least one power supply control input signal is a single power supply control input signal that has a controlled rate of change less than or equal to a lesser one of a first slew rate of the first response and a second slew rate of the second response.

5. The circuit of claim 1, wherein the at least one power supply control input signal is modulated to produce the controlled rate of change.

6. The circuit of claim 5, wherein the power supply control circuit includes a delta-sigma modulator for generating the at least one power supply control input signal.

7. The circuit of claim 5, wherein the controlled rate of change is constant, whereby the at least one power supply control input signal has a linear ramp waveshape.

8. A method of controlling a switched-power circuit that generates an output signal of varying amplitude, the method comprising:

generating a pair of symmetric power supply rail outputs using low-dropout linear regulators that control voltages of their respective one of the symmetric power supply rail outputs in conformity with an output level control signal;

controlling voltages of the symmetric power supply rail outputs in conformity with at least one power supply control input signal;

generating the output signal by alternatively switching between the symmetric power supply rail outputs under control of a modulator that controls the switching in conformity with a value of an input signal; and

generating the power supply control input signal in conformity with an output level control signal and with a controlled rate of change between adjacent steps in the output level control signal, so that asymmetry between the voltages of the power supply rail outputs during changes of the output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of responses of both of the power supply rail outputs, such that waveforms of the symmetric power supply rail outputs are substantially symmetrical when the output level control signal changes.

9. The method of claim 8, wherein the responses of the power supply rail outputs are voltage step responses with respect to the output level control signal.

10. The method of claim 8, wherein the output signal is an audio signal, and wherein the circuit is an audio power amplifier.

11. The method of claim 8, wherein the at least one power supply control input signal is a single power supply control input signal that has a controlled rate of change less than or equal to a lesser one of slew rates of the responses of the power supply rail outputs.

12. The method of claim 11, wherein the generating the at least one power supply control input signal modulates the output level control signal to produce the controlled rate of change.

13. The method of claim 12, wherein the generating the at least one power supply control input signal applies delta-sigma modulation to the output level control signal.

14. The method of claim 13, wherein the controlled rate of change is constant, whereby the generating the at least one power supply control input signal generates a linear ramp waveform.

15. A switched-power amplifier circuit, comprising:

a switching output stage for generating an output signal by switching between two symmetric power supply rail voltages according to a modulated input signal;

a pair of low-dropout linear regulators for generating the symmetric power supply rail voltages in conformity with at least one power supply control input signal; and

a power supply control circuit having an input for receiving at least one output level control signal and supplying the at least one power supply control input signal to the controllable power supply, wherein the power supply control circuit generates the power supply control input in conformity with the at least one output level control signal with a controlled rate of change between adjacent steps in the at least one output level control signal, such that asymmetry between the voltages of the power supply rail outputs during changes of the at least one output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of both outputs of the pair of regulators, such that waveforms of the symmetric power supply rail voltages are substantially symmetrical when the output level control signal changes.

16. The circuit of claim 15, wherein the power supply control circuit includes a delta-sigma modulator for generating the at least one power supply control input signal.

17. A method of amplifying an input signal, the method comprising:

switching between a pair of symmetric power supply rail outputs to generate an output signal;

controlling voltages of the symmetric power supply rail outputs in conformity with at least one power supply control input signal using a pair of low-dropout linear regulators; and

generating the power supply control input signal in conformity with an output level control signal and with a controlled rate of change between adjacent steps in the output level control signal, so that asymmetry between the voltages of the power supply rail outputs during changes of the output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of responses of both of the power supply rail outputs, such that waveforms of the symmetric power supply rail voltages are substantially symmetrical when the output level control signal changes.

18. The method of claim 17, wherein the generating the at least one power supply control input signal applies delta-sigma modulation to the output level control signal.

19. A circuit for generating an output signal of varying amplitude, the circuit comprising:

a controllable power supply having power supply rail outputs having symmetric voltages, wherein the voltages are controlled in response to a power supply control input signal, wherein the controllable power supply has a first response corresponding to a first one of the power supply rail outputs and a second response corresponding to a second one of the power supply rail outputs;

a switching circuit having first and second power supply rail inputs coupled to the power supply rail outputs of the controllable power supply;

a switching control circuit having an input for receiving an input signal and generating switching control signals for controlling the switching circuit, wherein the switching control circuit comprises a modulator for generating the switching control signals in conformity with a value of the input signal; and

a power supply control circuit having an input for receiving at least one output level control signal and supplying the at least one power supply control input signal to the controllable power supply, wherein the power supply control circuit generates the power supply control input signal in conformity with the at least one output level control signal with a controlled rate of change between adjacent steps in the at least one output level control signal, wherein the controlled rate of change is less than or equal to a lesser one of a first slew rate of the first response and a second slew rate of the second response, such that asymmetry between the voltages of the power supply rail outputs during changes of the at least one output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of both the first response and the second response of the power supply rail outputs.

20. A method of controlling a switched-power circuit that generates an output signal of varying amplitude, the method comprising:

generating a pair of symmetric power supply rail outputs;

controlling voltages of the symmetric power supply rail outputs in conformity with a power supply control input signal;

generating the output signal by alternatively switching between the symmetric power supply rail outputs under control of a modulator that controls the switching in conformity with a value of an input signal; and

generating the power supply control input signal in conformity with an output level control signal and with a controlled rate of change between adjacent steps in the output level control signal, wherein the controlled rate of change is less than or equal to a lesser one of slew rates of the responses of the power supply rail outputs, so that asymmetry between the voltages of the power supply rail outputs during changes of the output level control signal is substantially reduced by the controlled rate of change being less than or equal to rates of change of responses of both of the power supply rail outputs.