TELEVISION SYSTEM AUTOMATIC DISCRIMINATING AND SWITCHING DEVICE

摘要

PURPOSE:To perform automatic system discrimination and switching accurately in response to a shift in local frequency of a tuner and an input signal with a weak electric field by using the output signal of the limiter amplifier in a sound demodulating circuit as an input signal for the television system discrimination. CONSTITUTION:A television ratio wave inputted to the tuner 1 is outputted as a video detection output signal (c) through a VIF filter 2, VIF amplifier 3, and video detector 4. Part of this output signal is inputted to a color demodulating circuit 8 and video signal circuit 9 through impedance 5 and the rest is inputted to the sound limiter amplifier 19 through BPFs 17 and 18 and passed through an FM detector 20 to obtain a sound demodulated signal (h). The output (y) of the limiter amplifier 19 is applied to a BPF10 to obtain an automatic switching signal (z) for switching switches 24-27 by a switching driving signal 16 on the basis of the output of the BPF10.