| 摘要 |
A frequency comparison circuit for determining, at least within certain limits of accuracy, whether the frequency of a received signal is equal or not to a frequency F. Generating means produce first and second reference signals at frequency F, in phase quadrature. A logic circuit periodically compares the signs m, p and q of the received signal and of the two reference signals and according to the results of these comparisons (m, p and q alike, or m different from p and q, or q different from m and p and p different from m and q) applies a pulse to the plus or minus input of a first bidirectional counter or to the plus or minus input of a second bidirectional counter, one of the two counters overflowing when the frequency of the received signal is sufficiently close to F. In a variant embodiment the second reference signal has a frequency 2F. |
