Patent ID: 6573787
Filing Date: 2003-06-03
Classification: H03F,H03G

Abstract:
An audio amplifier circuit comprising:a voltage-gain amplifier and a current-gain amplifier in series thereafter between an input node and an output node; power supply lines for supplying power to the audio amplifier circuit; an outer negative feedback loop around the current-gain amplifier and the voltage-gain amplifier; an inner negative feedback loop around the voltage-gain amplifier, the current-gain amplifier being outside the inner negative feedback loop; first switch means for selectively connecting the power supply lines to the current-gain amplifier; second switch means for selectively switching the inner feedback loop or the outer feedback loop to the voltage-gain amplifier; and a control circuit arranged to control the switch means during power supply switching, wherein the control circuit is arranged to control the switch means when power is supplied by: initially opening the first switch means to disconnect the power supply lines from the current-gain amplifier; switching the second switch means to switch the inner negative feedback loop to the voltage-gain amplifier and subsequently, after a delay sufficient to allow the output of the voltage-gain amplifier to stabilise, closing the first switch means to connect the power supply lines to the current-gain amplifier; and switching the second switch means to switch the outer negative feedback loop to the voltage-gain amplifier.