AM/FM TELEVISION PICTURE RECEIVER

摘要

PURPOSE:To perform both the AM and FM wave detections with a simple constitution, by combining an AM wave detecting circuit with a PLL type FM demodulating circuit. CONSTITUTION:The FM modulated intermediate frequency TV signal given from a tuner 3 and the AM modulated intermediate frequency TV signal given from a tuner 7 are supplied to a common intermediate frequency amplifying circuit 10 via a changeover switch 13. The output of the circuit 10 is supplied to a PLL type AN/FM wave detecting circuit comprising an AM wave detecting circuit 14 and a PLL type FM wave detecting circuit 15. The intermediate frequency signal given from the circuit 10 and the oscillating signal given from an oscillator 27 are compared with each other through a phase comparator 28. Then an FM wave detecting output is obtained from the output of an amplifier 30. The signal obtained by giving a 90 deg. phase shift to the oscillating signal of the oscillator 27 is compared with the signal of the amplifier 10 through a comparator 18. Then an AM wave detecting output is obtained from the comparator 18.