Patent ID: 7157942

Claim:
A frequency difference detector for detecting the frequency difference between first and second signals, comprising: a first input for receiving said first signal; a second input for receiving said second signal; a first counter configured to count pulses of the first input signal; a second counter configured to count pulses of the second input signal, said second counter being capable of a higher bit count than said first counter; a first memory for storing a logic value indicating that said second counter has overflowed out of a first bit position in response to said second counter overflowing out of said first bit position; a second memory for storing a logic value indicating that said second counter has overflowed out of a second bit position in response to said second counter overflowing out of said second bit position; and a logic circuit effective for responding to said first counter overflowing out of its corresponding first bit position, by examining the current bit value of the second counter and the stored logic values said first and second memories and determining from theses examined values if said first signal has a higher frequency than said second signal.