| 摘要 |
PURPOSE:To prevent malfunction of mode discrimination at a weak electric field, by providing a means detecting the presence/absence of carrier wave of a sub-channel signal, in an audio multiplex broadcast. CONSTITUTION:An audio composite signal is applied to input terminals T20 and T30 of a sub-carrier wave detection circuit 80. When an audio sub-carrier wave is detected, a voltage level at a terminal P80 is higher, and if not detected, the voltage level is lower. A carrier control signal in the audio multiplex composite signal is applied to a pilot signal detection circuit 10, a limiter circuit 20, and a phase comparison circuit 30 from a terminal T10. The circuit 10, a constant current circuit 50 and a Schmitt trigger circuit 60 constitute a PLL circuit, and the output of the circuit 30 is compared at a voltage comparison circuit 70 to discriminate bilingual broadcast and stereo broadcast. The output of circuits 70 and 80 is applied to a mode discriminating circuit 90, and the mode discrimination is made with logical operation by the circuit 90. |
