| 摘要 |
PURPOSE:To ensure the variation of the reference frequency by an extremely small amount, by divinding the frequency of the crystal oscillator to obtain plural numbers of frequencies and then compounding these frequencies to secure a digital change of reference frequency. CONSTITUTION:The output frequency f1 of the crystal oscillator 21 is divided to 1/2 through the fixed frequency divider 22 to obtain frequency f2. And when the set signal has no agreement with the frequency f2, the switch gate circuit 23 gives a passing to the frequency f2. And this output is counted up by the counter 24. And when the count value coincides with the preset signal, the circuit 23 gives a passing to the f1 via the coincident detecting circuit 25. The fixed frequency divider 27 is connected to the rear stage of the oscillator 21, and thus the signal using the fixed time T as one cycle is delivered. Then the frequency f1 is counted up to the time T. At the time T, both the circuit 25 and the counter 24 are reset, and the counter 24 starts counting of the frequency f2. |
