Super-regenerative Receiver

Integrated Circuit (IC) designers have the luxury of taking for granted that the incremental cost of a transistor is essentially zero, which has given liberty to the large device count circuits that are prevailing today. This is a recent development, but it really was not all that long ago when the economics of circuit design were fundamentally based on the number of device counts, and often the designer was restricted by the relatively expensive active device to try to get blood (or at least rectification) from a stone.

It is amazing that in the early 1920s, Edwin Armstrong devised a super-regenerative receiver circuit using few components that trade log of gain for bandwidth, contrary to the conventional wisdom that gain and bandwidth should trade off more or less directly. The reduction of the number of the device components is not only cost-effective, but also improves reliability.

The characteristics of the super-regenerative receiver to generate large-signal gain at very low bias currents and the ability to operate above the cut-off frequency (fT) of the RF device make it attractive and the preferred architecture for integrated ultra-low power wireless receivers. Figure 1 depicts a 1940’s 500 MHz SRR, which is bulky and require manual calibration, but the circuit operates above the device fT, which was an astonishing accomplishments in those days.

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