| 摘要 |
PURPOSE:To obtain a good demodulating signal up to a high band by controlling a loop gain of a PLL circuit by a synchronous detecting output, and making a capture range and a locking range in case of receiving a stereophonic broadcost narrower than those in case of receiving a monaural broadcast. CONSTITUTION:When a PLL circuit 3 is locked to a pilot signal in phase, the pilot signal is detected synchronously by a frequency dividing signal from a 1/2 frequency divider 12 in a phase comparing circuit 13, and it is detected that a stereo is being received, by a stereo-monaural discriminating circuit 14 from a synchronuous detecting output from the circuit 13. As a result, a transistor 16 is turned on, a high level signal is supplied to a connecting switch circuit 21 from an invertor circuit 22, and the circuit 21 is turned on. Also, a series circuit of resistors 20a, 20b operates as a bleeder to a signal from an LPF5, and a cature range and a locking range of the circuit 3 are made narrower than those in case of receiving a monaural broadcast. Accordingly, no distortion is generated in a high band side of demodulating signals of left and right side signals of switching circuits 10L, 10R. |
