Amplifier circuit and methods of operation thereof

Abstract

A signal amplifying circuit and associated methods and apparatuses, the circuit comprising: a signal path extending from an input terminal to an output terminal, a gain controller arranged to control the gain applied along the signal path in response to a control signal; an output stage within the signal path for generating the output signal, the output stage having a gain that is substantially independent of its supply voltage, and a variable voltage power supply comprising a charge pump for providing positive and negative output voltages, the charge pump comprising a network of switches that is operable in a number of different states and a controller for operating the switches in a sequence of the states so as to generate positive and negative output voltages together spanning a voltage approximately equal to the input voltage.

1 - 40 . (canceled) 
   
   
       41 . A method of amplifying an input signal, the method comprising:
 receiving an input signal with a multi-stage amplifier;   receiving a mixed set of voltage rails, wherein each amplification stage of the multi-stage amplifier receives a set of the voltage rails and at least one member of one set of the voltage rails is a variable voltage rail; and   amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.   
   
   
       42 . The method of  claim 41  wherein the set of voltage rails received by a last stage of the multi-stage amplifier comprises two variable voltage rails. 
   
   
       43 . The method of  claim 42  wherein the set of voltage rails for each of the stages of the multi-stage amplifier includes one of the variable voltage rails received by the last stage of the multi-stage amplifier and the set of voltage rails received by each of the stages of the multi-stage amplifier except the last stage also includes a fixed voltage rail. 
   
   
       44 . The method of  claim 41  wherein the input signal comprises an audio signal, the method further comprising:
 providing the amplified input signal to at least one speaker.   
   
   
       45 . The method of  claim 41  further comprising:
 for each amplification stage, generating an output signal;   for each amplification stage, except an initial amplification stage, receiving the output signal of a preceding amplification stage; and   receiving the variable voltage rail with one of the amplification stages, wherein the variable voltage rail received by the amplification stage varies in response to the output signal received by the amplification stage to increase efficiency of the amplification stage.   
   
   
       46 . The method of  claim 41  wherein the mixed set of voltage rails comprises fixed voltage rails and the variable voltage rail. 
   
   
       47 . A signal processing device comprising:
 a multi-stage amplifier, the amplifier comprising:
 a first amplification stage having an output node and first and second power supply nodes, wherein during operation the first and second power supply nodes of the first amplification stage are coupled to respective first and second voltage rails; and 
 a second amplification stage, coupled to the output node of the first amplification stage, having first and second power supply nodes, wherein during operation the first and second power supply nodes of the second amplification stage are respectively coupled to a variable voltage rail and to a third voltage rail, and the first voltage rail is greater than the variable voltage rail. 
   
   
   
       48 . The signal processing system of  claim 47  wherein during operation of the multi-stage amplifier, the second voltage rail is equal to the third voltage rail. 
   
   
       49 . The signal processing system of  claim 47  wherein, during operation of the multi-stage amplifier, the first voltage rail has a fixed voltage and the second and third voltage rails vary over time. 
   
   
       50 . The signal processing system of  claim 47  wherein the multi-stage amplifier further comprises:
 a third amplification stage, coupled between the first and second amplification stages, having first and second power supply nodes, wherein during operation the first and second power supply nodes of the third amplification stage are coupled respectively to the first and second voltage rails.   
   
   
       51 . The signal processing system of  claim 47  wherein the multi-stage amplifier further comprises at least one input terminal to receive an audio input signal and at least one output terminal to supply an amplified version of the audio input signal. 
   
   
       52 . The signal processing system of  claim 47  wherein the multi-stage amplifier further comprises at least one input terminal to receive an audio input signal and at least one output terminal to supply an amplified version of the audio input signal, the system further comprising:
 an input source of the audio input signal coupled to the input terminal to supply the audio input signal to the multi-stage amplifier; and   at least one speaker coupled to the output terminal of the multi-stage amplifier.   
   
   
       53 . The signal processing system of  claim 47  further comprising:
 a first power supply coupled to the first power supply node of the first amplification stage; and   a second power supply coupled to the second power supply node of the first amplification stage and to the first and second power supply nodes of the second amplification stage.   
   
   
       54 . The signal processing system of  claim 47  wherein the multi-stage amplifier comprises integrated circuit components. 
   
   
       55 . A method of amplifying an input signal, the method comprising:
 receiving first and second power supply voltages with a first amplification stage of a multi-stage amplifier;   receiving third and fourth power supply voltages with a second amplification stage of the multi-stage amplifier, wherein the first power supply voltage is greater than the third power supply voltage, the third power supply voltage varies over time during operation of the multi-stage amplifier and the first and third power supply voltages are more positive than respective second and fourth power supply voltages;   receiving an input signal with the multi-stage amplifier; and   amplifying the input signal using the multi-stage amplifier to generate an amplified input signal.   
   
   
       56 . The method of  claim 55  wherein the second power supply voltage equals the third power supply voltage. 
   
   
       57 . The method of  claim 55  wherein the second power supply voltage and the third power supply voltage vary over time during operation of the multi-stage amplifier, and the first power supply voltage is fixed. 
   
   
       58 . The method of  claim 55  further comprising:
 supplying the first and second power supply voltages to a third amplification stage of the multi-stage amplifier, wherein the third amplification stage is an intermediary amplification stage.   
   
   
       59 . The method of  claim 55  further comprising:
 providing the amplified input signal to at least one speaker.   
   
   
       60 . A signal processing system comprising:
 a first amplification stage, wherein during operation the first amplification stage receives a fixed supply voltage and a first variable supply voltage, and the fixed supply voltage is greater than the first variable supply voltage;   a second amplification stage, coupled to an output of the first amplification stage, wherein during operation the second amplification stage receives the fixed supply voltage and the variable supply voltage; and   a third amplification stage, coupled to an output of the second amplification stage, wherein during operation the third amplification stage receives a second variable supply voltage and the first variable supply voltage, wherein the fixed supply voltage is greater than a maximum second variable supply voltage.   
   
   
       61 . The signal processing system of  claim 60  further comprising:
 an audio input signal generator, coupled to an input of the first amplification stage; and   at least one speaker coupled to an output of the third amplification stage.   
   
   
       62 . The signal processing system of  claim 61  further comprising:
 a first power supply coupled to the first amplification stage to provide the fixed supply voltage; and   a second power supply coupled to the second and third amplification stages to provide the first and second variable supply voltages.