| 摘要 |
PROBLEM TO BE SOLVED: To provide a phase locked loop oscillation circuit which is incorporated with a loop filter composed of an external resistor, a capacitor, etc., and can secure the characteristics of filters respectively having optimum cutoff frequencies even when the input frequency fluctuates by finely adjusting the characteristics of the filters. SOLUTION: A phase locked loop oscillation circuit is constituted to control the frequency of the oscillating signal of a voltage-controlled oscillation circuit 6 based on the control signal corresponding to a compared-result signal obtained by comparing the M frequency dividing signal (M=2, 3,...) of inputs signals with the N frequency dividing signal (N=2, 3,...) of the oscillating signal of the circuit 6 by means of a comparator circuit 2, to change the cut-off frequency of the signal corresponding to the compared-result signal by means of a programmable low-pass filter circuit 5 which is provided to make the phase and frequency of the N frequency dividing signal can become coincident with those of the M frequency dividing signal, and to output the control signal. |
