US Patent 7239195 Active power supply rejection using negative current generation loop feedback

A negative current generator for an amplifier circuit including a shunt transistor, first and second mirror transistors, a current bias device, and an amplifier. The amplifier circuit includes a current source transistor having current terminals coupled between a supply terminal and an input node and a control terminal receiving a bias voltage. The shunt transistor is coupled in a shunt configuration with the current source transistor. Each mirror transistor has a control terminal, a first current terminal coupled to the supply terminal and a second terminal coupled to a voltage node. The control terminal of the first mirror transistor receives another bias voltage. The current bias device draws a constant current from the voltage node. The amplifier has a first input receiving a reference voltage, a second input coupled to the voltage node, and an output coupled to the control terminals of the shunt and second mirror transistors.