Bandwidth improvement of a limit-cycle amplifier using a novel hysteretic relay

Limit-cycle or self-oscillating power amplifiers (SOPAs) are seen as a compact option to achieve efficient yet linear amplification of either complete RF signals or only their base-band envelopes. Unfortunately, one of their undesired drawbacks is that their self-oscillating frequency, and thus available bandwidth, is reduced when a significant propagation delay exists in the feedback loop, typically from the power stage. To remedy this SOPAs´ pitfall, this paper presents a method to increase the self-oscillation frequency 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 is discussed, and a suitable implementation is proposed. To validate the concept, simulations are carried out to compare the behavior of existing types of SOPA with the proposed one.