PLL FREQUENCY SYNTHESIZER TYPE TV RECEIVER

摘要

PURPOSE:To receive a signal by varying a frequency of an AFT circuit so as to shift the frequency up and down the frequency of a correct tuning point. CONSTITUTION:A minute adjusting voltage generating circuit 18 is added to the AFT circuit 8. A voltage applied to a variable capacitor D1 is changed by a VR1 of the circuit 18 to change the resonance frequency of a tuning circuit comprising L1, C1 and D1 of an S-curve generating circuit 81 in the AFT circuit 8. Then an S-curve is generated while a signal fed from a video intermediate frequency amplifier circuit is detected differently to the frequency of the tuning circuit in the circuit 81. When the voltage applied to the variable capacitor D1 is changed, its capacitance is changed and the tuning frequency is changed, then the AFT output voltage is changed. Thus, the tuning point is shifted to the correct tuning point by operating the VR1.