Cohn filters for minimizing thermal noise of Class A amplifiers

A Cohn filter circuit was designed to bypass the white noise generated by the thermal properties of a 150-W, 300-MHz class-A amplifier. The optimum values of the network components were derived, and the effects of harmonic distortion and noise were analyzed. A circuit has been developed for use in a system for magnetic resonance spectroscopy. The circuit was designed to reduce the thermal noise floor of the amplifier, measured at 200 mu W (between pulses), by approximately=40 dbs.<
>