| 摘要 |
PURPOSE:To control an AFC loop clock frequency digitally by designating a frequency division ratio of a programmable frequency divider to M+ or -P when it is valid to vary the frequency division ratio and designating the frequency division ratio to a normal value N when it is invalid to vary the frequency division ratio. CONSTITUTION:A frequency control variable setting device 103 varies a frequency division ratio of a programmable frequency divider 140 and sets digitally the frequency control variable when a holding time of the said setting value is controlled variably. The programmable frequency divider 104 frequency-divides an AFC basic operation clock 209 outputted from an internal operation basic clock oscillator 105 and generates an AFC output clock Fo. On the other hand, an input clock interruption detector 106 outputs an UP/DOWN count operation stop instruction 210 to an UP/DOWN counter 102 at the interruption of an input clock. Thus, the AFC keeps the frequency state just before the input clock is interrupted. |
