| 摘要 |
PURPOSE:To convert a channel selecting device into an IC, by providing a lead- in frequency setting circuit which detects that the output of a voltage control oscillator is led into a phase lock loop by the synchronizing signal of the video signal which received the wave detection and then securing the synchronization between the phase of a video carrier wave and the phase of the output of the oscillator. CONSTITUTION:Both the supplied video signal and the signal given from a voltage control local oscillator 2 are applied to a high frequency input part 1 comprising a GaAs device as well as to a mixer 3. Then the synchronous wave detection is given to the video carrier wave, and the conversion of frequency is given to the voice carrier wave. At the same time, the video signal of the part 1 is applied to a mixer 7. The phase of the video carrier wave is synchronized with the output of the oscillator 2 via a PLL comprising the oscillator 2, a 90 deg. phase shifter 6, the signal and PLL low pass filters 8 and 11, a phase comparator 10, etc. Furthermore a PLL lead-in frequency setting circuit is formed with a voltage storage circuit 13, a voltage selection fine adjusting circuit 14, a selection control circuit 20, etc. to detect that the output of the oscillator 2 is led into the PLL by the synchronous signal of the video signal which received the wave detection. Thus a channel selecting device can be easily converted into an IC. |
