Application of null networks in minimizing thermal noise of Class A power amplifiers

摘要

A filter circuit is described which was designed to shunt 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 analytically in order to obtain maximum signal-to-noise ratio at the operating frequency. The effects of harmonic distortion and noise were analyzed. A circuit has been modeled for use in a system for magnetic resonance spectroscopy. In this simulation, a 200 mu W thermal noise amplitude between pulses of 180-MHz sinewaves was reduced by approximately=40 dB.