Patent ID: 6580315
Filing Date: 2003-06-17
Classification: H03F

Abstract:
A circuit for maintaining a substantially constant amplifier common-mode output voltage comprising:an amplifier having an input and further having an output connected to a load resistor; an amplifier switch operational to selectively connect the load resistor to a supply voltage when the amplifier switch is closed and disconnect the load resistor from the supply voltage when the amplifier switch is open; a high current source configured to be turned-on to provide a high level current after the amplifier switch is closed and further configured to be turned-off before the amplifier switch is opened; a low current source configured to be continuously powered-on, and further configured to provide a low level current substantially lower in magnitude than the high level current; a voltage reference operational to provide a reference voltage dependent on the high level current and the low level current; a voltage reference switch operational to disconnect the voltage reference from the amplifier after the amplifier switch is closed and high current source is turned on, and further operational to connect the voltage reference to the amplifier before the amplifier switch is opened and high current source is turned off; and a low impedance device configured to couple the reference voltage to the amplifier output when the voltage reference switch is closed such that the amplifier common-mode output voltage remains substantially constant regardless of whether the amplifier is on or off, wherein the low current source provides a low level DC current flow through the low impedance device when the amplifier is turned off to maintain a low power level when the amplifier is turned off.