Abstract: A signal processing circuit can be used to select between a high bias current and good noise performance or a low bias current and poorer noise performance. The circuit comprises an input device having high impedance and low noise characteristics. A first current source provides a minimal current level through the input device. Additional current sources provide additional current through the input device to improve noise performance of the circuit. The additional current sources can be switched into the circuit when improved noise performance is required, and switched out of the circuit to conserve power when improved noise performance is not required.