| 摘要 |
Circuit and method for generating a signal for use in locking a second signal on a first signal. The first and second signals have an associated frequency. A first beat note signal (PD1) and a second beat note signal (PD2) are generated from the first and second signals, respectively, when the frequencies of the first and second signals are not equal. The circuit includes a first and second flip-flop and detector circuitry. The first flip-flop (502) is configured to receive the first and second beat note signals for generating a first state signal (S0). The first flip-flop (502) generates the first state signal (S0) by sampling the second beat note signal (PD1) at a first periodic interval of the first beat note signal. The second flip-flop (504) is configured to receive the first and second beat note signals for generating a second state signal (S1). The second flip-flop (504) generates the second state signal (S1) by sampling the second beat note signal at a second periodic interval of the first beat note signal (PD1). The detector circuitry (506, 508) is coupled to receive the first and second state signals from the first and second flip-flops for detecting a polarity of the frequency difference between the first and second signals. The polarity of the frequency difference is defined in a tri-state having a positive state, a negative state, and a zero state.
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