Ultra low noise optical receiver

Abstract

An amplifier topology for receiving signals output from a fiber optic rotation sensor and producing voltages that may be processed to determine the rotation rate includes a photodiode for receiving an optical signal and producing a corresponding electrical photodiode output signal. An ultra low noise and ultra low capacitance differential input stage is connected to receive the photodiode output signal. An operational amplifier having low noise and ultra-wide bandwidth is connected to the ultra low capacitance differential input stage to receive the output signal therefrom as a driving signal and to produce a low noise output signal. The differential input stage comprises a first amplifier circuit that includes a first transistor connected to the photodetector to act as a first buffer having low noise, low capacitance and unity gain. The first amplifier circuit also includes a second transistor configured as a first voltage follower connected between the output of the first buffer and the operational amplifier to isolate the output of the first buffer from parasitic capacitive loading from a biasing network. The differential input stage further comprises a second a second amplifier circuit that includes a third transistor having an input connected to a reference potential, the third transistor acting as a second buffer having low noise, low capacitance and unity gain. The second amplifier circuit also includes a fourth transistor configured as a second voltage follower connected between the output of the second buffer and the operational amplifier.