JPH0652937B2 - Television audio multiplex signal demodulator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television audio multiplex signal demodulation device.

2. Description of the Related Art In recent years, as a television audio multiplex signal demodulating device, various demodulating devices have been developed with an increase in television audio multiplex broadcasting stations.

A conventional television audio multiplex signal demodulator will be described below with reference to the drawings.

First, the frequency spectra of FM stereo broadcasting and television audio multiplex signals (during stereo broadcasting) are shown in FIGS. 2 and 3, respectively.

In FIG. 2, a is an FM stereo main signal (L + R), b is a pilot signal, and c is an FM stereo sub signal (LR) component, which is composed of a carrier suppression AM modulated wave of 38 KHz. In FIG. 3, a is a television stereo main signal (L + R), and b is a television stereo sub signal (L-).
In R), FM modulation is performed with a carrier frequency of 31.5 KHz. Reference numeral c is a control signal, which is AM-modulated at 98.25 Hz using 55.125 KHz as a carrier. This is distinct from bilingual broadcasting (922.5Hz for bilingual broadcasting)
It is made up of

This FM stereo signal and television audio multiplex signal demodulation device will be described below as a conventional example.

FIG. 4 is a block diagram of a conventional television audio multiplex signal demodulator, in which an FM stereo signal and a television audio multiplex signal are input from an input terminal 5. Reference numeral 1 denotes an FM stereo signal demodulation device, which is composed of a phase locked loop (hereinafter abbreviated as PLL) synchronized with a pilot signal of 19 KHz, a sub audio signal (LR component) demodulator, and a matrix. Further, when the PLL is locked to the pilot signal, the indicator light emitting diode 3 is connected to the power supply terminal 6
It is designed to light up more via the power supply. 7 is PL
This is a terminal for stopping the voltage-controlled oscillator of L and used when switching to monaural broadcasting.

The FM stereo signal demodulator 1 outputs the signal as it is without operating the internal demodulator when it is other than the FM stereo signal (excluding the pilot signal of 19 kHz), and is input to the television audio multiplex signal demodulator 2 of the next stage. It This television audio multiplex demodulation device is composed of an amplifier, a sub-signal demodulation device (including an indicator lighting circuit), and a matrix.

It should be noted that the television audio multiplex demodulation device 2 also operates as a mere amplifier when the television audio multiplex signal is not input, like the FM stereo signal demodulation device 1.

Since it is possible that there are two types of television audio multiplex signals, stereo broadcast and bilingual broadcast (or multiplex broadcast), switching terminals 8a and 8b for content selection are provided, and a demodulation signal terminal is provided depending on the input state. Demodulated signals corresponding to the signal contents are obtained in 9a and 9b.

It should be noted that the indicator LED 4 is configured to illuminate via the power supply terminal 6 by the internal detection circuit when the television audio multiplex signal is input. In other words, by these two systems of demodulation devices, the FM stereo signal demodulation device 1 is input when the FM stereo signal (when the pilot signal is 19 kHz) is input, and the FM stereo signal demodulation device 1 is input when the television audio multiplex signal is input. The television sound multiplex demodulation device 2 operates via the.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above-described configuration, the FM stereo signal demodulating device 1 is always used to demodulate the FM stereo signal.
It is necessary to operate the PLL, and the voltage control oscillator in the PLL is also operating, and high-frequency components with the free-running oscillation frequency of about 19 KHz as the fundamental wave appear, and those signals are transmitted to the television sound multiplex signal device. Is entered. In other words, the beat frequency of 6.5 K is obtained by the difference between the second harmonic component of 38 KHz and the sub signal component of the television audio multiplex signal of 31.5 KHz.
A new component of Hz is generated, and this signal component is demodulated and output 9
a) and 9b, and had various problems such as S / N ratio and deterioration of distortion.

In view of the above problems, the present invention provides an excellent television audio multiplex signal demodulation device capable of demodulating a television audio multiplex signal with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention includes an FM stereo signal and a television audio multiplex signal including a phase locked loop having a voltage controlled oscillator stop terminal.
In a television audio multiplex signal demodulation device, which is connected to the output side of a stereo signal demodulation device and has an indicator output terminal for outputting a signal for displaying the input when the audio multiplex signal is input, an indicator output terminal Connected to the voltage-controlled oscillator stop terminal, and sends the display signal output generated at the indicator output terminal to the voltage-controlled oscillator stop terminal when the audio multiplex signal is input, and stops the oscillation of the voltage-controlled oscillator of the phase-locked loop. It has the structure provided with the coupling circuit for.

Effect of the Invention With the above-described structure, the present invention prevents the beat damage caused by the harmonic component of the voltage controlled oscillator of the FM stereo signal demodulating device and the carrier component of the sub signal in the television audio multiplex signal, which has been a problem from the conventional PLL. Since the voltage-controlled oscillator of No. 1 is stopped by the detection output of the television audio multiplex signal, it does not occur at all, and the S / N ratio, distortion, etc. can be further improved.

Embodiment Hereinafter, a television sound multiplex signal demodulation device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a television audio multiplex signal demodulating device of the present invention, wherein 1 is an FM stereo signal demodulating device, 2 is a television audio multiplex signal demodulating device,
3 is an LED for FM stereo signal indicator, 4 is a LED for television audio multiple signal indicator, 5 is a signal input terminal, 7 is a voltage controlled oscillator stop terminal of PLL, 8
a and 8b are content selection terminals for the television audio multiplex signal,
Denoted at 9a and 9b are demodulated signal output terminals, and their operations are exactly the same as those of the conventional example.

The present invention is newly connected to the voltage controlled oscillator stop terminal of the PLL via the delay circuit 10 from the television audio multiple signal indicator output terminal.

Here, consider the case where a television sound multiplex signal is input. At this time, the detection circuit of the television sound multiplex signal demodulator 2 operates, and the television sound multiplex indicator 4 lights up via the indicator output terminal. That is, the cathode of the LED is pulled to the low level. Also,
This indicator output terminal is connected to the PL via the delay circuit 10.
Since it is connected to the stop terminal 7 of the voltage-controlled oscillator of L, the oscillation is stopped when the television audio multiplex signal is input (when the indicator LED 4 is lit), and the auxiliary signal component of the television audio multiplex signal is generated. , Beats due to harmonics of the free-running frequency of the voltage controlled oscillator of the PLL do not occur.

In addition, the delay circuit 10 is provided to always operate the FM stereo signal demodulating device with priority in order to prevent the FM stereo signal demodulating device 1 and the television audio multiple signal demodulating device 2 from operating at the same time. is there.

As described above, according to this embodiment, when the television audio multiplex signal is input, the PLL of the FM stereo signal demodulating device is stopped by the audio multiplex signal detection output.
Since the harmonic component of the L voltage controlled oscillator is eliminated, it is possible to easily eliminate the beat trouble with the sub-signal component in the television sound multiplex signal.

EFFECTS OF THE INVENTION As described above, the present invention is based on
The demodulation output of the stereo demodulator is added to the input of the television audio multiplex signal demodulator, and when the television audio multiplex signal is input, the phase-locked loop of the FM stereo signal demodulator is stopped by the audio multiplex signal detection output, Further, since a delay circuit is provided in the detection output so that the demodulators of two systems do not operate at the same time, a harmonic component of 19 KHz generated from the PLL of the FM stereo signal demodulator, which has been a problem in the past, is generated. The present invention provides a television audio multiplex signal demodulation device which eliminates beat interference due to the difference between the carrier frequency of a sub signal in the television audio multiplex signal, improves the S / N ratio, and reduces distortion.

[Brief description of drawings]

FIG. 1 is a block diagram of a television audio multiplex signal demodulator according to an embodiment of the present invention, FIG. 2 is a frequency spectrum diagram of an FM stereo signal, FIG. 3 is a frequency spectrum diagram of a television audio multiplex signal, and FIG. The figure is a block diagram of a conventional television audio multiplex signal demodulator. 1 ... FM stereo signal demodulator, 2 ... Television audio multiple signal demodulator, 3 ... FM stereo signal indicator LED, 4 ... Television audio multiple signal indicator, 5 ... Signal input terminal, 6 ... Power supply terminal,
7 ... Voltage-controlled oscillator stop terminal, 8a, 8b ... Television audio multiplex signal demodulation output selection terminal, 9a, 9b.
Demodulation output terminal, 10 ... Delay circuit.

Claims (2)

[Claims] 1. An audio stereo signal is connected to the output side of an FM stereo signal demodulation device which includes a phase locked loop having a voltage controlled oscillator stop terminal and receives an FM stereo signal and a television audio multiplex signal. In a television audio multiplex signal demodulating device having an indicator output terminal for outputting a signal for displaying its input, when the audio multiplex is connected between the indicator output terminal and the voltage controlled oscillator stop terminal, A television sound multiplex signal having a coupling circuit for sending a display signal output generated at the indicator output terminal when a signal is input to the voltage controlled oscillator stop terminal to stop the oscillation of the voltage controlled oscillator of the phase locked loop. Demodulator. 2. The television audio multiple signal demodulation device according to claim 1, wherein the coupling circuit is a delay circuit.