| 摘要 |
PURPOSE:To provide a PLL oscillation circuit technique capable of preventing a malfunction and a destruction and making the circuit widely stable in oscillation and low in power consumption by detecting a control voltage to be inputted into a VCO, feedbacking this voltage to the VCO and fixing an output level. CONSTITUTION:This PLL oscillation circuit is incorporated into a semiconductor integrated circuit device such as a single chip microcomputer, and is constituted of a phase comparator 1 comparing the frequencies of an input signal and a feedback signal, a charge pump/low pass filter 2 eliminating high frequency noise components by converting them into the voltage according to the difference of the frequencies and a VCO 3 by which an oscillation frequency changes according to inputs and a voltage detection circuit 4 detecting the voltage level to be inputted in the VCO 3 and controlling the output of the VCO 3. When the error voltage to be detected by this voltage detection circuit 4 deviates from the corresponded voltage within the range of the allowable frequency of an input signal, the output of the VCO 3 is controlled and an output voltage level is fixed. |
