Switching Noise Improvement of a Limit-Cycle Amplifier Using a Negative Hysteresis Relay

Limit-cycle or self-oscillating power amplifiers (SOPAs) are seen as an effective and simple option to achieve linear yet efficient power amplification. Unfortunately, they suffer from unfiltered switching noise, also known as ripple, whose amplitude increases for progressively lower self-oscillating frequency. Moreover, such self-oscillating frequency changes with the input signal and its dependency curve, as well as its maximum, are determined by the overall loop delay and by the open-loop filter. To remedy this SOPAs´ pitfall, this paper presents a method to increase the self-oscillation frequency and reduce frequency modulation for a fixed propagation delay and loop filter. This is achieved using a relay that exhibits a novel kind of hysteresis. For that, the theory of its working principle will be discussed in detail, its transfer characteristic will be defined, and an implementation suitable for VLSI will be proposed. To validate the concept, simulations and an experimental prototype were carried out to compare the behavior of existing types of SOPA with the proposed one.