Analysis and Measurement of Noise Suppression in a Nonlinear Regenerative Amplifier

This paper analyzes the ability to suppress in-band noise power of a regenerative amplifier (RA) operating in the nonlinear regime in response to a continuous wave (CW) input tone. As opposed to the linear regime where a CW tone and the noise floor experience the same transfer function, it is shown that the non-linear saturation behavior of an RA yields different transfer characteristics between a CW tone and noise, ultimately leading to an improvement in the output carrier-to-noise ratio (CNR). This is all thanks to the high gain, narrow bandwidth, and the compressive third-order nonlinearity of the RA. This non-linear noise suppression is first analyzed mathematically using single tones in the frequency domain to represent the signal and the noise. Then, simulation of an RA circuit model is shown to be in excellent agreement with the analytical results. Lastly, a discrete RA has been implemented to experimentally verify the noise-suppression phenomenon. The measurement results clearly demonstrate noise suppression and show an output CNR improvement of up to 3 dB. Potential applications of the RA with noise suppression are also discussed.