| 摘要 |
A digitally controlled frequency generator is provided having a selectively variable output frequency with crystal controlled accuracy and stability. Should the desired output frequency drift, however, a phase comparator detects the drift and compares the phase thereof with a provided reference signal. The resultant error signal is then fed into the frequency generator to shift the frequency back to its original value. In addition, should it be desired to change the output frequency of the frequency generator, a new program is applied to a variable program counter which produces an electronic response representative of the new program. This response is sensed by both the phase comparator and an acquisition circuit, the acquisition circuit providing signals to the phase comparator to achieve a "lock-in" of the system at the new desired frequency.
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