Low noise tuned amplifier

摘要

A bandpass amplifier employing a field effect transistor amplifier first stage (10) with a resistive load (R2) either a.c. or directly coupled to the non-inverting input of an operational amplifier second stage (20) which is loaded in a Wien Bridge configuration. The bandpass amplifier may be operated with a signal injected into the gate terminal (G) of the field effect transistor and the signal output taken from the output terminal of the operational amplifier. The operational amplifier stage appears as an inductive reactance, capacitive reactance and negative resistance at the non-inverting input of the operational amplifier, all of which appear in parallel with the resistive load (R2) of the field effect transistor.