JPS59229941A - Fm stereophonic demodulator - Google Patents

Abstract

PURPOSE:To improve demodulation when an input level is low by passing a stereophonic composite signal which is not muted through a capacitor, and supplying a signal which is muted to a stereophonic demodulating circuit through a coupling element. CONSTITUTION:When an FM intermediate frequency signal is supplied to an input terminal 14, the FM demodulating circuit 12 outputs the stereophonic composite signal from its 1st output terminal 16 and a level-adjusted composite signal from the other 2nd output terminal 16B. Those signals are supplied to input terminals 36 and 42 of the stereophonic demodulating circuit 32 through the capacitor 30 and coupling element 38 individually. Therefore, stereophonic reproduction is performed at the time of low-level input, and a low-noise stereophonic demodulation output is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM stereo demodulation device, and more particularly to a demodulation device that enables stereo reproduction even in the case of a weak input in an FM stereo receiver.

FIG. 1 shows a conventional FM stereo demodulator. An intermediate frequency signal is applied to the input terminal 2, and after being demodulated by an FMfla circuit 4, the intermediate frequency signal is applied to a stereo demodulation circuit 8 via a capacitor 6. This stereo demodulation circuit 8 detects a pylon (signal) from the stereo composite signal obtained by the FMti modulation circuit 4.
3 8 K Il, which is a multiplied signal of this pilot signal
z switching signal and the stereo composite signal, separate the left and right stereo signals, and output the output terminal 10R1I.
It is designed to be taken out from the office lady.

Conventionally, in the case of such an FM stereo demodulator, noise increases when the input is weak, so in order to improve the S/N ratio, the stereo demodulation was canceled and the playback was forced to play in monaural. There is. That is, the weak input detection signal obtained by the FMiH modulation circuit 4 is sent to the stereo demodulation circuit 8 for stereo,
It is given as a monaural playback control input to cancel stereo playback. Such operations are performed by the FM demodulation circuit 4.
The same thing happens even when soft muting is performed on the frequency.

SUMMARY OF THE INVENTION An object of the present invention is to provide an FM stereo demodulation device that can perform stereo demodulation satisfactorily even when the input is weak.

The present invention provides a first system for individually generating stereo composite signals.
and a second output terminal, and an FM demodulator that directly generates a stereo composite signal obtained by FM demodulation at the first output terminal and generates a stereo composite signal with an adjusted output level at the second output terminal. Install the circuit,
A phase-locked loop for detecting a pilot signal from the stereo composite signal is connected to the first output terminal via a first coupling element, and a multiplied signal of the pilot signal obtained from the phase-locked loop and the output signal are connected to the first output terminal via a first coupling element. A stereo decoder for synthesizing left and right stereo signals and separating left and right stereo signals is connected to the second output terminal via a second coupling element.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the FM stereo abdominal tuning device of the present invention. In the figure, an FM intermediate frequency signal is applied to an input terminal 14 of an FM demodulation circuit B12, and an FM intermediate frequency signal is applied to a first output terminal 1.
An FM7fi tuned stereo composite signal is output from 6A, and the level fJ! is output from the second output terminal 16B. a
The stereo composite signal is configured to be extracted. That is, the FM intermediate frequency signal applied to the input terminal 14 is amplified by the intermediate frequency amplification circuit 18, and then applied to the FM demodulator 2°, and the first output terminal 16A formed in this FMii modulator 2o. A small output teleo composite signal is generated from the FMfJj open output. The FM demodulation circuit 12 also includes a level control circuit 22 for adjusting the level of the stereo composite signal demodulated by the FMi summer sII unit 20.
is installed. That is, the intermediate frequency signal obtained by the intermediate frequency amplification circuit 18 is given to the level signal judgment circuit 24, and the judgment signal obtained by the level signal 11 constant circuit 24 is given to the muting signal generation circuit 26. The muting control signal of the muting signal generation circuit 2G is applied to the electronic volume circuit 28 together with the output of the FM demodulator 20. The level-adjusted output from this electronic volume circuit 28 is taken out to the second output terminal 16B.

The phase-locked loop (PLL (Phase-L) of the stereo demodulation circuit 32 is connected to the first output terminal 16A via a capacitor 3o as a first coupling element.

An input terminal 36 formed in the cked Looρ circuit) 34 is connected. This PLL circuit 34 detects the 19K11z pilot signal from the stereo composite signal applied to the input terminal 36, and detects the 38K11z pilot signal, which is its multiplied signal.
It is configured as a circuit that generates a switching signal of K Ilz and a stereo and monaural display pj power.

Further, the second output terminal 16B is connected to the stereo decoder 4 of the stereo demodulation circuit 32 via the second coupling element 38.
It is connected to an input terminal 42 formed at 0. This stereo decoder 4o is supplied with a 38K Ilz switching signal from the PLL circuit 34 together with the stereo composite signal whose level has been adjusted as described above, and synthesizes the two large sword signals to separate left and right stereo signals. The signal is generated from the output terminal 44R144L.

With the above configuration, the first output terminal 16A of the FM demodulation circuit 12 receives a stereo composite signal that has not been subjected to muting operation, and the other second output terminal 16B receives a signal based on the signal strength. A stereo composite signal with corresponding level, that is, muting control, is generated,
These signals are individually connected to a capacitor 3o or a coupling element 38.
input terminal 36.42 of the stereo i-tone circuit 32 via
given to. . That is, the capacitance of the capacitor 3o is set to such a value that the audio signal component included in the stereo composite signal is sufficiently attenuated, and only the pilot signal component is efficiently passed through <1ill, and the stereo composite signal applied to the input terminal 36 is For example, the operation of the PLL circuit 34 is set in a state that does not disturb the synchronous operation or other operations. In addition, the coupling element 38 is configured with a capacitor or a 19KIIz trap coil, etc. having a capacitance that efficiently passes the audio signal except for the signal component to the pyro 71 for the purpose of the stereo decoder 4o. A composite signal is provided from an input terminal 42. Therefore, with this configuration, even when there is a weak input, stereo playback is possible without canceling stereo playback as in the conventional case, and level adjustment is performed on the Pyro 7J signal and the stereo composite signal. Therefore, it is possible to efficiently obtain a stereo signal without deteriorating stereo separation.

That is, even at the time of weak input, the adverse effect of signal components due to noise can be avoided, and a low-noise stereo reproduction If) output can be obtained.

As explained above, according to the present invention, stereo playback is possible even when the input is weak, and low-noise stereo fi
It is possible to obtain modulation power.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional FM stereo demodulation device, and FIG. 2 is a block diagram showing an embodiment of the FM stereo demodulation device of the present invention. 12... Stereo convergence circuit, 16A... First output terminal, 16B... Second output terminal, 3°... Capacitor as a coupling element, 34... PLL circuit,
38... Second coupling element, 40... Stereo decoder.

Claims (1)

[Claims] forming first and second output terminals that individually generate stereo composite signals;
Installing an FM demodulation circuit that directly generates a stereo composite signal obtained by l tuning and generates a stereo composite signal with an output level fJfiim at a second output terminal,
A phase-locked loop for detecting a biloft signal from the stereo composite signal is connected to the first output terminal via a first coupling element, and a signal multiplied by the pilot signal obtained from the phase-locked loop and the output are connected to the first output terminal via a first coupling element. The second stereo decoder separates left and right stereo signals by combining the left and right stereo signals.
An FM stereo demodulator, characterized in that the FM stereo demodulator is connected to the output terminal of the FM stereo demodulator via a second coupling element.