Drift free low noise composite amplifier and method of operation thereof

摘要

A composite amplifier includes a discrete active gain element with a feedback circuit that provides for low drift and low offset, but which also has low noise, short settling time and high bandwidth. This is accomplished in part by providing an attenuator in the feedback circuit and by providing a voltage source for the source of the discrete active gain element. The feedback circuit is connected between the gate and the source of the active gain element and is responsive to a change in voltage at the gate to supply a voltage of equal but opposite magnitude to the source. The source has an impedance whose Johnson noise is less than the noise of the active gain element. A differential amplifier in the feedback is constructed in multiple stages with a first stage having lower gain than a second stage.