Energy-efficient personal audio device output stage with signal polarity-dependent power supply update rate

Abstract

A charge pump power supply may comprise a plurality of capacitors and a switching circuit for switching the capacitors to provide a first voltage or a second voltage in accordance with the select input. The charge pump power supply may have a signal polarity input for indicating a polarity of an output audio signal. Switches for switching one or more capacitors providing a first polarity voltage in a then-current operating mode may be configured to switch at a greater frequency than switches for switching one or more capacitors providing a second polarity voltage responsive to the signal polarity input indicating a positive polarity of the output audio signal. Switches for switching one or more capacitors providing the first polarity voltage in a then-current operating mode are configured to switch at a lesser frequency than switches for switching one or more capacitors providing the second polarity voltage responsive to the signal polarity input indicating a negative polarity of the output audio signal.

1 . An audio amplifier circuit for providing an output signal to an audio transducer, the audio amplifier circuit comprising:
 a power amplifier having an audio input for receiving an audio input signal, an audio output for providing the output signal, and a power supply input; and   a charge pump power supply for providing a power supply voltage to the power supply input, wherein the power supply voltage has a first polarity voltage relative to a common-mode voltage and a second polarity voltage relative to the common-mode voltage such that the power supply voltage equals a difference between the first polarity voltage and the second polarity voltage, wherein:
 the charge pump power supply has a signal polarity input for indicating a polarity of the output signal; and 
 switches for switching one or more capacitors providing the first polarity voltage are configured to switch in a first sequence such that electrical charge is transferred from the one or more capacitors providing the first polarity voltage at a greater rate than a rate of transfer of electrical charge from the one or more capacitors providing the second polarity voltage. 
   
     
     
         2 . The audio amplifier circuit of  claim 1 , further comprising a control circuit for generating the signal polarity input based on the polarity of the output signal. 
     
     
         3 . The audio amplifier circuit of  claim 2 , wherein the control circuit determines the polarity of the output signal based on a sign bit of a digital audio input signal. 
     
     
         4 . The audio amplifier circuit of  claim 2 , wherein:
 the power amplifier further comprises at least one driving device for generating the output signal based on the audio input signal; and   the control circuit determines the polarity of the output signal based on a ratio of load current to quiescent current in the at least one driving device.   
     
     
         5 . The audio amplifier circuit of  claim 2 , wherein:
 the charge pump power supply further comprises an input for receiving a source voltage; and   the control circuit determines the polarity of the output signal based on a voltage difference between the power supply voltage and the source voltage.   
     
     
         6 . (canceled) 
     
     
         7 . The audio amplifier circuit of  claim 1 , wherein:
 responsive to a magnitude of a difference between the output signal and the first polarity voltage being less than a predetermined threshold, the charge pump power supply operates the switches for switching one or more capacitors providing the first polarity voltage at a first frequency; and   responsive to the magnitude of the difference between the output signal and the first polarity voltage being greater than the predetermined threshold, the charge pump power supply operates the switches for switching one or more capacitors providing the first polarity voltage at a second frequency less than the first frequency.   
     
     
         8 . The audio amplifier circuit of  claim 1 , wherein:
 responsive to a magnitude of a difference between the output signal and the second polarity voltage being less than a predetermined threshold, the charge pump power supply operates the switches for switching one or more capacitors providing the second polarity voltage at a first frequency; and   responsive to the magnitude of the difference between the output signal and the second polarity voltage being greater than the predetermined threshold, the charge pump power supply operates the switches for switching one or more capacitors providing the second polarity voltage at a second frequency less than the first frequency.   
     
     
         9 . The audio amplifier circuit of  claim 1 , wherein:
 the power amplifier includes at least one switching device for generating a first polarity of the output signal and at least one switching device for generating a second polarity of the output signal based on the audio input signal;   responsive to the signal polarity input indicating a positive polarity of the output signal, the at least one switching device for providing the first polarity voltage operates at a first current; and   responsive to the signal polarity input indicating a negative polarity of the output signal, the at least one switching device for providing the first polarity voltage operates at a second current less than the first current.   
     
     
         10 . The audio amplifier circuit of  claim 1 , wherein:
 the power amplifier includes at least one switching device for generating a first polarity of the output signal and at least one switching device for generating a second polarity of the output signal based on the audio input signal;   responsive to the signal polarity input indicating a negative polarity of the output signal, the at least one switching device for providing the second polarity voltage operates at a first current; and   responsive to the signal polarity input indicating a positive polarity of the output signal, the at least one switching device for providing the second polarity voltage operates at a second current less than the first current.   
     
     
         11 . The audio circuit of  claim 1 , wherein the power supply voltage is a single-ended voltage referenced to a ground voltage in which the common-mode voltage is equal to one-half of a maximum power supply voltage and the second polarity voltage has a minimum equal to the ground voltage. 
     
     
         12 . The audio circuit of  claim 1 , wherein the power supply voltage is a differential voltage in which the common-mode voltage is equal to a mean of a maximum first polarity voltage and a minimum second polarity voltage. 
     
     
         13 . A method for providing an output signal to an audio transducer, comprising:
 providing by a charge pump power supply a power supply voltage to a power supply input of a power amplifier having an audio input for receiving an audio input signal and an audio output for providing the output signal, wherein:
 the power supply voltage has a first polarity voltage relative to a common-mode voltage and a second polarity voltage relative to the common-mode voltage such that the power supply voltage equals a difference between the first polarity voltage and the second polarity voltage, wherein: 
 the charge pump comprises a plurality of capacitors and a switching circuit for switching the capacitors to provide the first voltage or the second voltage in accordance with the select input; and 
 the charge pump power supply has a signal polarity input for indicating a polarity of the output signal; and 
   switching switches for switching one or more capacitors providing the first polarity voltage in a first sequence such that electrical charge is transferred from the one or more capacitors providing the first polarity voltage at a greater rate than a rate of transfer of electrical charge from the one or more capacitors providing the second polarity voltage.   
     
     
         14 . The method of  claim 13 , further comprising generating the signal polarity input based on the polarity of the output signal. 
     
     
         15 . The method of  claim 14 , further comprising determining the polarity of the output signal based on a sign bit of a digital audio input signal. 
     
     
         16 . The method of  claim 14 , wherein:
 the power amplifier further comprises at least one driving device for generating the output signal based on the audio input signal; and   determining the polarity of the output signal further comprises determining the polarity based on a ratio of load current to quiescent current in the at least one driving device.   
     
     
         17 . The method of  claim 14 , wherein:
 the charge pump power supply further comprises an input for receiving a source voltage; and   determining the polarity of the output signal further comprises determining the polarity based on a voltage difference between the power supply voltage and the source voltage.   
     
     
         18 . (canceled) 
     
     
         19 . The method of  claim 13 , further comprising:
 responsive to a magnitude of a difference between the output signal and the first polarity voltage being less than a predetermined threshold, operating the switches for switching one or more capacitors providing the first polarity voltage at a first frequency; and   responsive to the magnitude of the difference between the output signal and the first polarity voltage being greater than the predetermined threshold, operating the switches for switching one or more capacitors providing the first polarity voltage at the second frequency less than a first frequency.   
     
     
         20 . The method of  claim 13 , further comprising:
 responsive to a magnitude of a difference between the output signal and the second polarity voltage being less than a predetermined threshold, operating the switches for switching one or more capacitors providing the second polarity voltage at a first frequency; and   responsive to the magnitude of the difference between the output signal and the second polarity voltage being greater than the predetermined threshold, operating the switches for switching one or more capacitors providing the second polarity voltage at the second frequency less than a first frequency.   
     
     
         21 . The method of  claim 13 , further comprising:
 responsive to the signal polarity input indicating a positive polarity of the output signal, operating the at least one switching device for providing the first polarity voltage at a first current; and   responsive to the signal polarity input indicating a negative polarity of the output signal, operating the at least one switching device for providing the first polarity voltage at a second current less than the first current.   
     
     
         22 . The method of  claim 13 , further comprising:
 responsive to the signal polarity input indicating a negative polarity of the output signal, operating the at least one switching device for providing the second polarity voltage at a first current; and   responsive to the signal polarity input indicating a positive polarity of the output signal, operating the at least one switching device for providing the second polarity voltage at a second current less than the first current.   
     
     
         23 . The method of  claim 13 , wherein the power supply voltage is a single-ended voltage referenced to a ground voltage in which the common-mode voltage is equal to one-half of a maximum power supply voltage and the second polarity voltage has a minimum equal to the ground voltage. 
     
     
         24 . The method of  claim 13 , wherein the power supply voltage is a differential voltage in which the common-mode voltage is equal to a mean of a maximum first polarity voltage and a minimum second polarity voltage. 
     
     
         25 . The method of  claim 13 , further comprising switching switches for switching one or more capacitors providing the first polarity voltage in the first sequence responsive to the signal polarity input indicating a positive polarity of the output signal. 
     
     
         26 . The method of  claim 13 , further comprising switching the switches for switching the one or more capacitors providing the first polarity voltage in a second sequence such that electrical charge is transferred from the one or more capacitors providing the first polarity voltage at a lesser rate than the rate of transfer of electrical charge from the one or more capacitors providing the second polarity voltage. 
     
     
         27 . The method of  claim 16 , further comprising:
 switching the switches for switching the one or more capacitors providing the first polarity voltage in the first sequence responsive to the signal polarity input indicating a positive polarity of the output signal; and   switching the switches for switching the one or more capacitors providing the first polarity voltage in the second sequence responsive to the signal polarity input indicating a negative polarity of the output signal.   
     
     
         28 . The audio amplifier circuit of  claim 1 , wherein the switches for switching one or more capacitors providing the first polarity voltage are configured to switch in the first sequence responsive to the signal polarity input indicating a positive polarity of the output signal. 
     
     
         29 . The audio amplifier circuit of  claim 1 , wherein the switches for switching the one or more capacitors providing the first polarity voltage are configured to switch in a second sequence such that electrical charge is transferred from the one or more capacitors providing the first polarity voltage at a lesser rate than the rate of transfer of electrical charge from the one or more capacitors providing the second polarity voltage. 
     
     
         30 . The audio amplifier circuit of  claim 29 , wherein:
 the switches for switching the one or more capacitors providing the first polarity voltage are configured to switch in the first sequence responsive to the signal polarity input indicating a positive polarity of the output signal; and   the switches for switching the one or more capacitors providing the first polarity voltage are configured to switch in the second sequence responsive to the signal polarity input indicating a negative polarity of the output signal.   
     
     
         31 . An audio amplifier circuit for providing an output signal to an audio transducer, the audio amplifier circuit comprising:
 a power amplifier having an audio input for receiving an audio input signal, an audio output for providing the output signal, and a power supply input; and   a charge pump power supply for providing a power supply voltage to the power supply input, wherein the power supply voltage has a first terminal with a first polarity voltage relative to a common-mode voltage and a second terminal with a second polarity voltage relative to the common-mode voltage such that the power supply voltage equals a difference between the first polarity voltage and the second polarity voltage, wherein:
 the charge pump comprises a plurality of capacitors and a switching circuit comprising a plurality of switches for switching the capacitors to provide the power supply voltage; 
 switches for switching one or more capacitors providing the first polarity voltage to the first terminal are configured to switch with a first switching sequence and at a first frequency based on a first current drawn by the power amplifier from the first terminal; and 
 switches for switching one or more capacitors providing the second polarity voltage to the second terminal are configured to switch with a second switching sequence and at a second frequency based on a second current drawn by the power amplifier from the second terminal. 
   
     
     
         32 . The audio amplifier circuit of  claim 31 , wherein:
 the charge pump power supply has a signal polarity input for indicating a polarity of the output signal; and   the charge pump power supply is configured to output a first polarity voltage and a second polarity voltage such that:
 when the polarity of the output signal is of a first polarity, a magnitude of difference between the first polarity voltage and the common-mode voltage is greater than a magnitude of difference between the second polarity voltage and the common-mode voltage; and 
 when the polarity of the output signal is of a second polarity, a magnitude of difference between the first polarity voltage and the common-mode voltage is lesser than a magnitude of difference between the second polarity voltage and the common-mode voltage. 
   
     
     
         33 . A method for providing an output signal to an audio transducer, comprising:
 providing by a charge pump power supply a power supply voltage to a power supply input of a power amplifier having an audio input for receiving an audio input signal and an audio output for providing the output signal, wherein the power supply voltage has a first polarity voltage relative to a common-mode voltage and a second polarity voltage relative to the common-mode voltage such that the power supply voltage equals a difference between the first polarity voltage and the second polarity voltage, and wherein the charge pump comprises a plurality of capacitors and a switching circuit comprising a plurality of switches for switching the capacitors to provide the power supply voltage;   switching switches for switching one or more capacitors providing the first polarity voltage with a first switching sequence and at a first frequency based on a first current drawn by the power amplifier from the first terminal; and   switching switches for switching one or more capacitors providing the first polarity voltage with a second switching sequence and at a second frequency based on a second current drawn by the power amplifier from the second terminal.   
     
     
         34 . The method of  claim 33 , wherein the charge pump power supply has a signal polarity input for indicating a polarity of the output signal and further comprising outputting the first polarity voltage and the second polarity voltage by the charge pump power supply such that:
 when the polarity of the output signal is of a first polarity, a magnitude of difference between the first polarity voltage and the common-mode voltage is greater than a magnitude of difference between the second polarity voltage and the common-mode voltage; and   when the polarity of the output signal is of a second polarity, a magnitude of difference between the first polarity voltage and the common-mode voltage is lesser than a magnitude of difference between the second polarity voltage and the common-mode voltage.