| 摘要 |
PURPOSE:To reduce a response time inexpensively with simple constitution without using a DA converter by providing a control circuit comparing levels of signals fed respectively to two circuits and controlling the level of the signal fed to the circuits. CONSTITUTION:A control circuit 40 receives a control signal SA of a voltage controlled oscillator(VCO) 1 included in a 1st phase locked loop(PLL) and a control signal SB of a VCO 2 included in a 2nd PLL. The control circuit 40 has a function comparing levels of both the control signals and supplying a level signal in response to the signal SA from the VCO 1 to an input terminal of the VCO 6 for a period when the level difference between the signals SA and SB is a set voltage or over. Thus, an expensive DA converter is not required and if the shift in an output frequency f2 is large, the control voltage of the VCO 1 with a fast response is used to apply pre-tuning to the VCO 6 thereby moving the operating state forcibly into the vicinity of the designated frequency. Thus, the whole circuit can attain fast speed response. |
