Circuit and method for demodulating frequency shift keyed (FSK) signals

摘要

The circuit includes an antenna (16) which receives the FSK signal transmitted from the transponder (14) as a sinusoidal waveform. Digital circuitry converts the received signal into count values. an adaptive reference count value is determined by averaging the duration of received pulses during the preamble of the transmission. The reference count represents either the high or low logic level. The count occurring during the coded signal part is compared with the adaptive reference count. A digital level output signal based on whether the count is within a predetermined range from the adaptive reference count. The predetermined range corresponds to either a valid low logic or valid high logic.