Patent ID: 7532064

Claim:
A demodulator circuit for demodulating a signal modulated by frequency shift keying (FSK), comprising: a frequency discriminator for discriminating frequencies of the signal modulated by frequency shift keying to generate demodulated data; a correlator for correlating the demodulated data with a predetermined synchronization word to obtain a correlation signal; a synchronization detector that detects the synchronization word when the correlation signal indicates that the demodulated data match the synchronization word, and also detects the synchronization word when the correlation signal indicates that the demodulated data are complementary to the synchronization word; a decision circuit for storing a decision signal when the synchronization detector detects the synchronization word, the decision signal having a first value indicating that the demodulated data match the synchronization word and a second value indicating that the demodulated data are complementary to the synchronization word; and an output circuit for outputting the demodulated data if the stored decision signal has the first value, and for inverting the demodulated data to obtain complementary data and outputting the complementary data if the stored decision signal has the second value.