| 摘要 |
PROBLEM TO BE SOLVED: To control a logic circuit by a DC level decision circuit means and to automatically select an oscillation circuit having a needed oscillation characteristic by allowing the DC level deciding means to control the logic circuit during the fly-back period of a vertical synchronizing signal and automatically selecting the oscillation circuit. SOLUTION: A logic circuit 2 of a PLL circuit 2 selects an N type oscillation circuit 3 included in the PLL circuit 1 according to control data transmitted from a DC level decision circuit 8. A frequency division circuit 4 performs frequency division of a clock outputted from the oscillation circuit 3, and a phase comparator 5 performs phase comparison of a horizontal synchronizing signal with the clock frequency divided by the circuit 4. A charge pump circuit 6 charges up or discharges a phase difference component outputted from the comparator 5 to a loop filter on the next stage as a DC level. The circuit 8 decides a DC level obtained by a loop filter 7 which eliminates harmonic components or decides the dynamic characteristics of the PLL circuit 1. |
