| 摘要 |
PURPOSE:To prevent the malfunction of stereophonic demodulation during TV sound multiplex demodulation and to obtain a demodulation state by discriminating on a demodulation mode on the basis of the output of an FM stereophonic demodulating circuit, and setting the operation mode of the FM stereophonic demodulating circuit with the discrimination signal. CONSTITUTION:The 1st and the 2nd outputs obtained by the FM stereophonic demodulating circuit 2 are applied to input terminals 26 and 28 of a TV sound multiplex demodulating circuit 20 from output terminal 12 and 14. A multiplex composite signal applied to a terminal 26 as the 1st output is separated by a band-pass filter (BPF)30 into a subchannel signal and a control channel signal, which are applied to a sound multiplex demodulation mode discrimination circuit 40A to generate the discrimination signal according to whether the sound subcarrier of the subchannel signal or control subcarrier (55.125Hz) of the control channel signal is detected or not. This discrimination signal is applied from a discrimination output terminal 40 to the switch circuit 11 of an FM stereophonic demodulating circuit 11 as a switching control signal and switching operation is stopped in TV multiplex demodulation to place a stereophonic decoder 8 in a monaural state forcibly. |
