JPS6057268B2 - Audio multiplex broadcast pilot signal identification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pilot signal identification circuit for generating a control signal used to control a multiplex demodulation circuit in a television audio multiplex broadcast receiver.

'■The main channel (L) is the signal component of multiplex broadcasting.
+R), a subchannel (L-R), and a pilot signal, and this pilot signal is about 55.
125KH2 carrier wave is 982.5 when broadcasting in stereo
AM is modulated with a single tone of H2, while when broadcasting in two languages, AM is modulated with a single tone of 922.5H2.
It is modulated.

Therefore, on the receiving side, control is performed to discriminate between the two frequency signals of 982.5H2 and 922.5H2, which are the modulation components of this pilot signal, and to cause the multiplex demodulation circuit to perform the demodulation operation in stereo or in accordance with two languages. is configured to do so. FIG. 2 is a block diagram showing a conventional example of a pilot signal discrimination circuit for detecting the pilot signal shown in FIG. 1 and generating a control signal for a demodulation circuit.

In the figure, a pilot signal having a carrier frequency of 55.125KH2 that is AM modulated with either 982.5H2 or 922.5H2 is detected by an AM detector 1, and sent to read filters 3 and 4 via a buffer circuit 2, respectively. applied. 9 in lead filters 3 and 4
Either 82.5H2 or 922.5H2 is identified, and the respective outputs are rectified by rectifier circuits 7 and 8 via amplifiers 7 and 8, respectively, and then control signals A and B are output. In the figure, the vibrations and shocks of the device may cause
- The reed filters 3 and 4 vibrate, resulting in the reed filter malfunctioning.

Therefore, there is a drawback that the multiplex switching circuit of the demodulation circuit (not shown) malfunctions, resulting in so-called shock noise. SUMMARY OF THE INVENTION An object of the present invention is to provide a highly reliable audio multiplex broadcast pilot signal identification circuit that does not use a lead filter that is susceptible to shocks.

The pilot signal identification circuit of the present invention includes a VCO (voltage controlled oscillator) whose oscillation frequency is controlled by a predetermined control voltage;
The phase of the oscillation signal based on the output of this VCO and the detected output of the pilot signal is compared, and the VCO is adjusted according to this phase difference.
The present invention is characterized in that it includes a phase comparison means for generating a control voltage of 1, and an identification means for identifying program contents according to the level of the control voltage.

The present invention will be described below with reference to the accompanying drawings.

FIG. 2 is a schematic block diagram showing an embodiment of the present invention,
Components equivalent to those in FIG. 1 are designated by the same reference numerals.

In the figure, A that has been detected by AM and passed through the buffer circuit 2
M detection signal (982.5 or 922.5Hz) is PLL
(Phase lock loop) is input to the circuit 10. That is, the AM detection signal is applied to one input of the phase comparator circuit 11 and compared with the output signal of the frequency dividing circuit 12 in terms of phase and frequency. The output of this comparator circuit 11 has high frequency components removed by LPFl3, and after DC amplification, the control voltage V of VCOl4
becomes. According to this control voltage V, the phase and frequency of the output signal of VCO14 are controlled. After that, the frequency is divided by 1/n and becomes the external power of the phase comparator circuit 11,
A well-known PLL circuit 10 is configured. The output voltage V of LPFl3 is also compared with a reference voltage V8 in a voltage comparator 15. It is assumed that the comparison signal output C of the voltage comparator 15 is configured to be at a high or low level when the control voltage V is larger or smaller than the reference voltage (R), respectively. ), the free-running frequency that passes through the frequency divider 12 of the VCOl4 (the frequency divider output frequency when there is no input signal to the PU7 circuit 10, that is, when there is no pilot signal) is 922.5.
Hz<5982.5Hz, the level of the control voltage V at that time is set as Vf, and ■CO is 922.5Hz.
The control voltage levels when locked to 5Hz and 982.5Hz are VM and VS, respectively, and V and 〉V.
If M is set, ■ku■, and the relationship V,〉■r〉VM is established. Therefore, voltage comparator 15
By setting the reference voltage VR to ■, the comparison signal output C has a high level at 982.5 Hz (stereo) and a low level at 922.5 Hz (two languages).

Therefore, it is clear that the identification signal can be generated based on this comparison signal C, and in the example of FIG. 2, the pilot signal detection circuit 20
and the stereo control signal A using the identification signal generation circuit 30.
and a two-language control signal B is obtained.

In other words, the comparison signal C is directly connected to the 1 input of the AND gate 16.
AND gate and becomes one input of AND gate 18.

On the other hand, the output of the buffer circuit 2 is amplified by an amplifier 19 and applied to an LPF 2l that removes high-frequency noise components.
There, the 982.5 or 922.5 Hz component is detected and becomes one input to the gate 22. In this case, an output signal is generated in the LPF 2l only when a pilot signal exists and either 982.5 or 922.5 Hz exists, and the gate 2 is configured to output this output as a high-level detection signal.
A gate voltage (+B) is applied to the second external power. The output of the gate 22 is applied to the other power of the AND gates 16 and 18, and therefore the output of the AND gates 16 and 18
is in an open (activated) state only when the output of the gate 22 is at a high level, that is, when an input signal is present, and the control signals corresponding to the level applied to one input of each gate 16 and 18 are respectively activated. It will be derived from the outputs of gates 16 and 18. It goes without saying that the gate 22 of the input signal detection circuit 20 may be replaced by a waveform shaping circuit that amplifies and shapes the output of the LPF 2l. With this configuration, PlJ. Malfunction of the circuit can be completely prevented by adding the input signal detection circuit 20 and activating the identification signal generation circuit 30 only while the detection signal is being generated.

As described above, according to the present invention, since a PLL circuit is used instead of a reed filter, it is resistant to shock noise caused by vibration and impact, and is useful for preventing malfunctions in multiple switching.

Furthermore, it is possible to completely prevent the adverse effects of bass sound caused by video signal components unique to television. Further, it goes without saying that the input signal detection circuit 20, PU circuit 10, and identification signal generation circuit 30 in the above embodiments are not limited to the configurations shown in the drawings, and can be modified in various ways.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional pilot signal identification circuit.
FIG. 2 is a block diagram showing an embodiment of the present invention. Explanation of symbols of main parts, 1...AM detector, 1
0...PLLllll...phase comparator,
14... ■COll5... Voltage comparator, 30...
...Identification signal generation circuit.

Claims (1)

[Claims] 1. A pilot signal identification device that detects a pilot signal indicating the program content of audio multiplex broadcasting and generates an identification signal according to each program content, comprising a detection means for detecting a display signal of the program content from the pilot signal. , a voltage-controlled oscillator whose oscillation frequency is controlled by a predetermined control voltage, and a frequency and phase comparison between an oscillation signal based on the output of the voltage-controlled oscillator and a detection signal of the detection means, and according to this phase difference, the phase comparison means for generating a predetermined control voltage; identification means for detecting the level of the predetermined control voltage and identifying the display signal of the program content based on this level; and gate means for deriving an output.