Patent ID: 7714660

Claim:
A signal amplifying circuit comprising: an input for receiving an input signal; an output for outputting an output signal; a signal path extending from the input to the output; a gain controller arranged to control the gain applied along said signal path in response to a control signal; an output stage coupled to the gain controller within said signal path for generating said output signal; and a variable voltage power supply comprising a charge pump circuit for providing a positive output voltage and a negative output voltage for supplying the output stage, the charge pump circuit comprising: a supply input node and a common node for connection to an input voltage supply; first and second supply output nodes for connection to first and second reservoir capacitors, said first and second supply output nodes outputting said positive and negative output voltages; at most first and second flying capacitor nodes; a network of switches for interconnecting said nodes; a controller for operating said switches; and a control signal input for receiving said control signal; wherein said variable voltage power supply, employing said charge pump circuit with said at most first and second flying capacitor nodes, is arranged for generating either first positive and negative output voltages or second positive and negative output voltages in response to said control signal, wherein said first positive and negative output voltages are each substantially equal in magnitude to the voltage of said input voltage supply and said second positive and negative output voltages are each substantially equal in magnitude to half the voltage of said input voltage supply.