JPH07123340A - Discrimination system for television audio multiplex broadcasting - Google Patents

Abstract

PURPOSE:To eliminate adjustment and to reduce cost. CONSTITUTION:This system is provided with a band pass filter 2a for extracting a pilot signal PL from a television multiplex audio signal, PLL circuit 3 equipped with a voltage controlled oscillator (VCO) 33 setting its own running frequency at the same frequency as that of the pilot signal PL, demodulation circuit 5 for synchronously detecting the pilot signal PL based on a control signal fo from the PLL circuit 3, PLL circuit 8 equipped with a VCO 83 setting its own running frequency at the same frequency as the sub carrier frequency of a sub channel audio signal and equipped with the same characteristics as the VCO 33, and low-pass filter 9 for obtaining a DC control voltage vd1' (t) by smoothing a control voltage vd1 (t) of the VCO 83 and corresponding to the DC control voltage vd1' (t), the VCO 33 is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television sound multiplex broadcast discrimination system.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing a frequency spectrum and a frequency deviation of an audio multiplex signal of a known television audio multiplex broadcast. The audio multiplexed signal is the main channel audio signal MA.
IN (stereo L + R) and sub channel audio signal SUB
The pilot signal P _L is added to (stereo L-R).

The main channel audio signal MAIN is about 15
Occupies a band of kHz. Sub channel audio signal SUB
Is FM-modulated with a center frequency fc = 31.5 kHz as a subcarrier and occupies a band of about 16 kHz to about 47 kHz.

The pilot signal P _L is AM-modulated by a multiplex control signal of 922.5 Hz for bilingual broadcasting and AM by a multiplex control signal of 982.5 Hz for stereo broadcasting.
Although modulated, it is set to an extremely low level as compared with audio signals such as the main channel audio signal MAIN and the sub channel audio signal SUB.

FIG. 3 is a block diagram showing a configuration of an example of a conventional television sound multiplex broadcast discrimination system.

The bandpass filter 2 has a center frequency of 5
It is set to 5.125 kHz, and the pilot signal P including the sideband is included in the audio multiplexed signal from the input terminal 1.
_Take out _L.

The integrated PLL circuit 3 is supplied with the comparison reference frequency from the CR oscillation circuit 4, generates an output oscillation frequency fo having the same frequency and the same phase as the pilot signal P _L , and outputs it to the demodulation circuit 5. . The comparison reference frequency of the CR oscillation circuit 4 is variably adjusted by adjusting the value of the semi-fixed resistor R, for example.

The demodulation circuit 5 outputs an output oscillation frequency which is a control signal.
Pilot signal P based on the number fo _LSynchronously detect
It consists of 55.125kHz second harmonic,
The multiple control signal depending on the mode of the
Generate the detection output.

The low-pass filter 6 has a cutoff of 10 kHz.
The detected output is filtered at about z to block the second harmonic and a multiplex control signal of 922.5 Hz or 982.5 Hz is extracted. Based on this multiplex control signal, it is determined whether it is a bilingual broadcast or a stereo broadcast.

[0010]

However, in the above-described conventional television sound multiplex broadcast discrimination system, P
Since the output oscillation frequency fo of the LL circuit 3 fluctuates by ± 30%, it is necessary to adjust the value of the semi-fixed resistor R to correct this fluctuation within 55.125 ± 3 kHz.

Alternatively, it was necessary to construct an oscillation circuit using a Ceralock oscillator having a frequency accuracy of ± 2%. If any of these measures is not taken, the output oscillation frequency fo may be synchronized with the band of the sub-channel audio signal SUB.

However, the former method requires an adjustment step, and the latter method has a problem that the number of parts increases and the cost increases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a television sound multiplex broadcast discrimination system which solves the above problems.

[0014]

[Means for Solving the Problems] The above problems can be solved by the following constitution.

That is, a filter for extracting a pilot signal from a television audio multiplex signal including a main channel audio signal, a sub-channel audio signal and a pilot signal, and a free-running frequency set to be the same as the frequency of the pilot signal. PLL with one voltage controlled oscillator
In a television audio multiplex broadcast discrimination system including a circuit and a demodulation circuit for synchronously detecting a pilot signal based on a control signal from the first PLL circuit, the free-running frequency is the same as the subcarrier frequency of the sub-channel audio signal. And a second PLL circuit having a second voltage controlled oscillator having the same characteristics as the first voltage controlled oscillator, and smoothing the control voltage of the second voltage controlled oscillator to generate a DC control voltage. The second PLL circuit is locked to the subcarrier frequency of the subchannel audio signal by controlling the first voltage controlled oscillator by the DC control voltage. The solution is that the circuit locks to the frequency of the pilot signal and outputs a control signal.

[0016]

According to the present invention having the above structure, the sub-channel audio signal has a signal level higher than that of the pilot signal as is well known, and the second PLL circuit sets the free-running frequency to the same as the sub-carrier frequency of the sub-channel audio signal. Since it is set, it acts so as to easily lock to the subcarrier frequency of the subchannel audio signal.

Furthermore, when the second PLL circuit locks to the subcarrier frequency of the subchannel audio signal, the first PLL circuit
Since the PLL circuit of 1 locks to the frequency of the pilot signal, the first PLL circuit acts so that the control signal locked to the frequency of the pilot signal is easily output.

As a result of the synchronous detection of the pilot signal by the demodulation circuit based on this control signal, it is determined whether it is a bilingual broadcast or a stereo broadcast.

[0019]

1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, the same components as those in FIG. 3 are designated by the same reference numerals.

That is, the television audio multiplex broadcasting discrimination system shown in FIG. 1 has the CR oscillation circuit 4 shown in FIG.
And the semi-fixed resistor R are deleted, a PLL circuit 8 and a low pass filter 9 are additionally provided, and the band pass filter 2 is replaced with a voltage control type band pass filter 2a.

The PLL circuit 8 includes a phase comparator 81, a low pass filter 82, a voltage controlled oscillator (VCO; Voltage Co).
ntrolled oscillator 83 is a well-known configuration. The PLL circuit 3 described above has a well-known configuration including a phase comparator 31, a low-pass filter 32, and a voltage-controlled oscillator 33, like the PLL circuit 8.

Both low-pass filters 32 and 82 have a nitride film capacitance and are integrated into an IC. Further, the low-pass filter 9 as the smoothing means is composed of a CR integrator circuit,
In the circuit shown in FIG. 1, only the capacitor of the low pass filter 9 is an external discrete component. As this capacitor, for example, an aluminum electrolytic capacitor of about 0.1 μF is used.

Since each circuit is integrated, the voltage controlled oscillator 33 of the PLL circuit 3 and the voltage controlled oscillator 83 of the PLL circuit 8 have the same characteristic that they oscillate at the free-running frequency when the same control voltage is applied. ing.

However, the free running frequency of the voltage controlled oscillator 33 is set to 55.125 kHz, and the free running frequency of the voltage controlled oscillator 83 is set to 31.5 kHz. Therefore, when the control voltage changes, the oscillation frequency changes at a relatively constant rate. Therefore, variations in IC characteristics are relatively absorbed.

The voice multiplexed signal from the input terminal 1 is supplied to the bandpass filter 2a and the phase comparator 81 of the PLL circuit 8. The free running frequency of the voltage controlled oscillator 83 is 31.
It is set to 5 kHz, and the subcarrier frequency of the sub-channel audio signal SUB in the audio multiplex signal is 31.5 kHz.
z has a large level as compared with the pilot signal P _L = 55.125 kHz.

Therefore, the PLL circuit 8 has a subcarrier frequency of the subchannel audio signal SUB = 31.5 kHz.
It can be easily locked to z. That is, the control voltage vd ₁ (t) of the voltage controlled oscillator 83 is set to a predetermined voltage including a pulsating flow synchronized with 31.5 kHz.

The PLL circuit 8 is connected to the sub-channel audio signal SU.
Another reason for locking the B sub-carrier frequency = 31.5 kHz is that the band of the sub-channel audio signal SUB is as wide as 16 to 47 kHz as compared with the case of directly locking the pilot signal P _L. This is because even if there is a variation in the oscillation frequency of, it can be sufficiently absorbed.

The bandpass filter 2a has its center frequency controlled by the control voltage vd ₁ (t), and the center frequency when the PLL circuit 8 is locked is 55.125 kHz.
It is said that As a result, the pilot signal including the sideband is extracted from the television sound multiplex signal.

On the other hand, the control voltage vd ₁ (t) is supplied to the low-pass filter 9 to be a DC control voltage vd ₁ ′ (t) with the pulsating flow of 31.5 kHz smoothed and removed. The DC control voltage vd ₁ '(t) controls the oscillation of the voltage controlled oscillator 33 of the PLL circuit 3.

Therefore, since the DC control voltage vd ₁ '(t) is equal to the average value of the control voltage vd ₁ (t), the PLL circuit 8 locks at 31.5 kHz, so that the PLL circuit 3 outputs the output oscillation frequency fo = 55. Since it locks at .125 kHz, it becomes possible to easily lock to the pilot signal frequency.

The pilot signal P _L and the same frequency, the pilot signal P _L by the demodulation circuit 5 on the basis of the output oscillation frequency fo, which is the same phase is synchronously detected, are cut off unnecessary high frequency from the detection frequency by the low-pass filter 6, A multiplex control signal of 922.5 Hz or 982.5 Hz is taken out from the output terminal 7. 2 based on this multiplex control signal
It is determined whether it is a national language broadcast or a stereo broadcast.

As described above, according to this embodiment, since the PLL circuit 8 easily locks at 31.5 kHz, the PLL circuit 3 locks at 55.125 kHz.
The pilot signal P _L is synchronously detected without increasing the number of parts and increasing the cost because it does not require an adjusting process unlike the one using a conventional CR oscillating circuit and does not require a reference oscillator such as a CERALOCK. Then, it is possible to determine whether the type of broadcasting is bilingual broadcasting or stereo broadcasting.

[0033]

As described above, according to the present invention, the second PL
The L circuit sets the free-running frequency to be the same as the subcarrier frequency of the subchannel audio signal and easily locks to the subcarrier frequency of the subchannel audio signal having a signal level higher than that of the pilot signal. Furthermore, at this time, the first PLL circuit locks to the frequency of the pilot signal, and the control signal locked to the frequency of the pilot signal is easily output from the first PLL circuit. Based on this control signal, the demodulation circuit Since the pilot signal is synchronously detected by the method, there is a feature that the adjustment process is not required, and the type of broadcast can be determined without increasing the number of parts and increasing the cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a frequency spectrum and a frequency shift of a voice multiplexed signal.

FIG. 3 is a block diagram showing a configuration of an example of a conventional television sound multiplex broadcast discrimination system.

[Explanation of symbols]

 2,2a band pass filter 3,8 PLL circuit 5 demodulation circuit 6,9,32,82 low pass filter 31,81 phase comparator 33,83 voltage controlled oscillator

Claims (3)

[Claims] 1. A filter for extracting the pilot signal from a television audio multiplex signal including a main channel audio signal, a sub-channel audio signal and a pilot signal, and a free-running frequency set to be the same as the frequency of the pilot signal. In a television sound multiplex broadcasting discrimination system including a first PLL circuit having a first voltage controlled oscillator, and a demodulation circuit for synchronously detecting the pilot signal based on a control signal from the first PLL circuit. A second voltage-controlled oscillator having a free-running frequency set to be the same as the sub-carrier frequency of the sub-channel audio signal and having the same characteristics as the first voltage-controlled oscillator.
A PLL circuit and smoothing means for smoothing the control voltage of the second voltage controlled oscillator to obtain a DC control voltage, and controlling the first voltage controlled oscillator by the DC control voltage. Then, when the second PLL circuit locks to the subcarrier frequency of the subchannel audio signal, the first PLL circuit locks to the signal frequency of the pilot and outputs the control signal. Television audio multiplex broadcast discrimination system. 2. The first PLL circuit and the second PL circuit
2. The television sound multiplex broadcasting discrimination system according to claim 1, wherein the L circuits are each formed on the same semiconductor chip. 3. The television sound multiplex broadcasting discrimination system according to claim 1, wherein said filter has a center frequency controlled by a control voltage of said second voltage controlled oscillator.