| 摘要 |
<p>A frequency synchronous apparatus includes a switch, frequency division circuit, phase comparison circuit, frequency adjustment and calculation circuit, memory, conversion circuit, and voltage-controlled oscillator. The switch selects either one of a highly stable clock output and a reference clock output in accordance with a mode switching signal. The frequency division circuit divides the frequency of the synchronous clock. The phase comparison circuit detects the phase difference between an output clock from the frequency division circuit and an output clock from the switch, and outputs a phase difference value. The frequency adjustment and calculation circuit performs synchronous control so as to adjust the phase difference value output from the phase comparison circuit to 0, and outputs a synchronous control value at this time. The memory holds the synchronous control value output from the frequency adjustment and calculation circuit. The conversion circuit converts the synchronous control value into a control voltage value. The voltage-controlled oscillator outputs a synchronous clock on the basis of the control voltage value. The present invention also provides a frequency synchronous control method. <IMAGE></p> |
