| 摘要 |
PURPOSE:To obtain a variable frequency dividing device which works stably and at a high speed by combining a fixed frequency divider which can work at a high speed with a fixed frequency dividing ratio and a variable frequency divider. CONSTITUTION:A fixed 1/4 frequency divider 1 which can work at a high speed is provided at the preceding stage of a variable frequency divider D. While shift registers R1-R3 consisting of FFs serving as delay elements are connected to the following stages of the divider D. Thus an optional dividing ratio can be set. For instance, the 1/1,000 division is carried out. In this case, comparators C1-C3 are set successively at 0101, 1111 and 0000 respectively by an electronic switch of the divider D. Thus the dividing ratio of the divider D is set at 1/250. Then the divider D is combined with a 1/4 divider 1 to attain the 1/1,000 division. A pulse is obtained at an output S2 of the divider D after a time equivalent to 1,000 pulses of an input clock signal. The signals divided down to 1/1,001, 1/1,002 and 1/1,003 are obtained from output signals S3-S5 obtained via registers R1- R3. Then counters K1-K3 are reset when an output signal S0 is produced through selection of a changeover switch SW1.
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