JPH0354463Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field of the Invention] The present invention relates to a discrimination circuit for a television audio multiplex broadcast receiving device. In particular, it is a discrimination circuit capable of detecting a sub-channel signal of an audio multiplex broadcast signal, determining whether the mode is a monaural broadcast mode or a multiplex broadcast mode, detecting the sub-channel signal, and deriving a detection output. This eliminates the problem of multiple signal discrimination errors.

[Problem that the invention attempts to solve]

As shown in FIG. 4, the spectrum of the television audio multiplex signal is composed of a frequency band consisting of a main channel signal A, a sub-channel signal B, and a control channel signal C. Conventionally, TV audio multiplex broadcast receiving devices used in portable radio receivers, etc. generally use PLL to determine whether the mode is monaural broadcast mode or multiplex broadcast mode by checking the presence or absence of a sub-channel signal of the TV audio multiplex broadcast signal. It is detected by the circuit. The lock range of the PLL circuit that detects this sub-channel signal (the frequency range in which the PLL circuit can maintain lock with the input signal) is adjusted approximately equal to this frequency band, and the capture range of the PLL circuit (the frequency range in which the PLL circuit can maintain lock with the input signal) is adjusted to be approximately equal to this frequency band. Although the frequency band in which the incoming signal and lock can be captured is not limited to this, it is usually set to a value close to this frequency band.

As shown in Figure 3, the spectrum of the FM stereo signal is in the same frequency band as the capture range and lock range of the PLL circuit.
19KHz pilot signal of FM stereo signal (3rd
Due to the existence of Figure A), the 19KHz pilot signal is likely to mix into the PLL circuit of the TV audio multiplex broadcast receiver. For this reason, the conventional discrimination circuit using a PLL circuit in a television audio multiplex broadcast receiving apparatus has a problem in that it incorrectly discriminates the 19 KHz pilot signal as a sub-channel signal. In order to improve these problems, PLL
By strengthening the low-pass filter of the circuit,
In order to _eliminate malfunctions caused by the 19KHz pilot signal, the capture range is narrowed and fixed in advance as shown in C3 in Figure 5, and the lock range _L3 is fixed at 16KHz to 47KHz, which is the frequency band of the sub channel signal. A method has been adopted to eliminate malfunctions by making the PLL circuit insensitive to the 19KHz pilot signal. A TV audio multiplex broadcasting device using such a PLL circuit has the disadvantage that the high frequency region of the detection output is raised, and there are problems such as distortion in sound quality when receiving stereo broadcasts.

Generally, the open transfer function of a PLL circuit has the following relationship.

T(s)=K _T F(s)/s (1) Here, K _T is the total loop gain of the PLL circuit, and F(s) is the transfer function of the low-pass filter.

When a delay filter is used as the low-pass filter of the PLL circuit, F(s) has the following relationship.

F(s)=1/1+sτ [However, τ is the time constant of the low-pass filter] Also, the closed-loop transfer characteristic H(s) of the PLL circuit is:
It can be expressed as follows.

H(s)=T(s)/1+T(s)...(2) [s is a complex frequency. ] As is clear from equations (1) and (2) above, in the high frequency region of the input signal, that is, when the complex frequency s is increased, the frequency characteristics of the detection output of the PLL circuit are as follows.
It will be greatly lifted in the high range. In other words, in the above PLL circuit with a narrowed capture range,
This will cause distortion in the audio output. Therefore,
Attempting to prevent malfunctions by strengthening the PLL circuit's low-pass filter and narrowing the passband to make it insensitive to the 19KHz pilot signal had its limits, and there was room for improvement.

[Purpose of invention]

The present invention has been developed in view of the above, and the main purpose of the present invention is to determine whether the TV audio is in monaural broadcasting mode or multiplex broadcasting mode without causing malfunction, and to output the sub channel signal. An object of the present invention is to provide a discrimination circuit for a television audio multiplex broadcast receiving device that can perform wave detection.

[Summary of the idea]

The discrimination circuit of the television audio multiplex broadcast receiving device of the present invention discriminates between monaural broadcast mode and multiplex broadcast mode, and detects the sub-channel signal of the television audio multiplex signal using a PLL circuit and outputs the detection output. It is equipped with a circuit that sets the capture range and lock range of the PLL circuit narrow in advance, and after the PLL circuit detects the arrival of the sub-channel signal, expands the lock range of the PLL circuit to approximately the frequency band of the sub-channel signal. This eliminates the malfunction of discrimination caused by the 19KHz pilot signal of the FM stereo signal.

[Example of idea]

The discrimination circuit of the television audio multiplex broadcast receiving apparatus of the present invention will be explained based on the embodiment shown in FIG. 1 and the explanatory diagram shown in FIG. 2.

In FIG. 1, a television audio multiplexed signal is supplied to an input terminal 1 and distributed into two systems. One is distributed to the system that derives the main channel signal (FIG. 3A) via the low-pass filter 2, and the other is distributed to the system that derives the main channel signal (FIG. 3A), and the other is distributed to the system that derives the main channel signal (FIG. 3A).
The sub-channel signals are distributed to systems for deriving sub-channel signals through the sub-channel signals, and the output signals from each system are supplied to the matrix circuit 6. Furthermore, the signal that has passed through the bandpass filter 3 is further distributed to determine whether the TV audio multiplexed signal is in monaural broadcasting mode or multiplexed broadcasting mode, and to detect the sub-channel signal and convert it into a stereo signal or sub-audio signal. is supplied to a discriminating circuit 11 that can derive the . Further, the matrix circuit 6 is supplied with the main channel signal from the low-pass filter 2, the sub-channel signal from the discrimination circuit 11, the control signal from the logic circuit 21, and the detection output from the PLL circuit, and performs signal processing. be done. The output from matrix circuit 6 is supplied to speakers 9 and 10 via amplifier circuits 7 and 8.

The discrimination circuit 11 is a circuit mainly composed of a PLL circuit, and after subjecting the sub-channel signal derived through the bandpass filter 3 to waveform processing via the limiter circuit 12, the output signal is supplied to the PLL circuit. and is also distributed to the phase comparator circuit 16.
This is a circuit that determines the arrival of a sub-channel signal, detects it, and derives a stereo signal difference signal (LR) or a sub-sound.

The output from the limiter circuit 12 is supplied to a PLL circuit consisting of a phase comparison circuit 13, a low-pass filter 14, and a voltage-controlled oscillator (VCO) 15, and the output from the low-pass filter 14, that is, detection of the sub-channel signal. The output is supplied to a matrix circuit 6. Also, the pulse-like output from VCO15 is
The signal is supplied to a phase shift circuit 17 that shifts the phase by 90 degrees, and then to a phase comparator circuit 16.
Further, the sub-channel signal is input to the phase comparison circuit 16, and the phase comparison circuit 16 compares the phase difference between the output from the phase shift circuit 17 and the signal from the bandpass filter 3, and calculates the difference between these signals. A DC output corresponding to the phase difference can be obtained. Phase comparison circuit 1
The DC output from 6 is supplied to the hysteresis comparator 19 via the level adjustment circuit 18, and when it is detected that the DC output is above a predetermined level, the arrival of the sub-channel signal is detected, and the indicator light drive circuit 20 is activated and the light emitting diode 24 lights up.

When the arrival of the sub-channel signal is detected, a detection signal is supplied to the logic circuit 21 via the hysteresis comparator 19, and is also supplied to the limiter circuit 12 via the electric line A. Also, logic circuit 2
1 supplies the matrix circuit 6 with a switching signal for selecting a monaural broadcast mode or a multiplex broadcast mode. 22 is a terminal to which a manual switching signal is input, and 23 is a terminal to which a VCO killer signal is input.

The discrimination circuit of the television audio multiplex broadcast receiving apparatus of the present invention controls the amplitude level of the output of the limiter circuit 12 by detecting the sub-channel signal, thereby controlling the capture range of the PLL circuit as shown in FIG. and lock range from C ₁ , L ₁ to C ₂ ,
It automatically moves to the L ₂ range,
That is, before the PLL circuit of the discrimination circuit 11 detects the sub-channel signal, the capture range is narrowed to make it insensitive to the 19KHz pilot signal, and after the sub-channel signal is detected, the lock range of the PLL circuit is reduced to the sub-channel signal. Channel signal frequency band (16K
Hz to 47KHz).

FIG. 6 is a circuit diagram for explaining the essential parts of the discrimination circuit according to the present invention, although it is not intended to limit it, and the discrimination circuit will be explained based on an embodiment embodying an example of the limiter circuit 12. .

Before explaining, the capture range Δω _C of the PLL circuit
and lock range Δω _L will be explained. The capture range Δω _C and the lock range Δω _L are expressed by the following relational expression.

Δω _C = K ₀ K _d A ₁ | F (jΔω _C ) | …(3) Δω _L = K ₀ K _d A ₁ …(4) However, K ₀ indicates the frequency conversion gain with respect to the voltage of the VCO, and K _d is the conversion gain of the phase comparison circuit, and A ₁ is the gain of the DC amplifier of the PLL circuit.

As is clear from equations (3) and (4) above, in order to control the capture range Δω _C and lock range Δω _L of the PLL circuit, the low-pass filter coefficient F
Except for (jΔω _C ), any of K ₀ , K _d , and A ₁ may be controlled.

In the present invention, the conversion gain K _d of the phase comparator circuit is controlled to control the capture range Δω _C and the lock range Δω _L of the PLL circuit, and by controlling the input level of the phase comparator circuit 13, the phase The output of the comparator circuit 13 is controlled to substantially control its conversion gain.

Of the TV audio multiple broadcast signal, a sub-channel signal is derived through the band-pass filter 3 and supplied to the limiter circuit 12, and when the sub-channel signal is detected, a control signal from the hysteresis comparison circuit 19 is supplied to the limiter circuit. and the amplitude of its output is controlled. The amplitude level of the output of the limiter circuit 12 is set small in advance, and when the arrival of the sub-channel signal is detected, the amplitude level of the output of the limiter circuit 12 is adjusted to a large value through the electric line A.

The limiter circuit 12 includes at least one differential amplifier circuit 25 and constant current source circuits 38 and 4 connected to the subsequent stage for adjusting the level of the limiter output.
Current mirror circuits are added from transistors 2 and 28 to 32, transistors 34 and 35, transistors 36 and 37, and transistors 39 and 40, respectively. The on/off of the transistor 41 is controlled by the control signal from the hysteresis comparison circuit 19, and the constant current I _L1 drawn from the transistor 28 by the constant current source circuit 38 is supplied from the constant current source circuit 42. The amplitude level of the output of the limiter circuit 12 is adjusted by adding the constant current I _L2 .

Before the sub-channel signal arrives, the output level of the limiter circuit 12 is kept low, and the capture range _C1 and lock range _L1 of the PLL circuit are set substantially narrow. Phase comparison circuit 15
is usually composed of a differential amplifier circuit, and since the output level of the limiter circuit 12 is kept low, the input level of the differential amplifier circuit is small.
Therefore, the output of the phase comparison circuit 13 also becomes smaller.
This is essentially the same as controlling the gain of the phase comparison circuit 15, and the capture range and lock range of the PLL circuit are controlled.

As mentioned above, by reducing the amplitude level of the output of the limiter circuit 12 in advance, the conversion gain K _d of the phase comparison circuit 13 is reduced, and the capture range Δω _C of the PLL circuit is set to a band insensitive to the 19KHz pilot signal. Set to detect the sub-channel signal. The lock range Δω _L at this time is a band approximate to the capture range Δω _C. Signal from bandpass filter 3 and phase shift circuit 17
is supplied to the phase comparator circuit 16, and if the phase of the signal supplied to the phase comparator circuit 16 is shifted by 90 degrees, the output is zero and the sub-channel signal is being detected, If there is a phase shift, a DC output is generated, which is supplied to the hysteresis comparator 19 via the level adjustment circuit 18, and when it reaches a predetermined level or higher, the transistor 41 of the limiter circuit 12 is turned off. Before the arrival of the sub-channel signal, the transistor 41 is set to the on state, and when the discrimination circuit 11 detects the arrival of the sub-channel signal, the detection signal is supplied to the base of the transistor 41 via the electric path A, and the transistor 41 is turned off. . A current mirror circuit consisting of transistors 39 and 40 operates to generate a constant current from the current source circuit 42.
I _L2 is added to I _L1 and flows as a mirror current of the current mirror circuit 33. Therefore, the amplitude level increases and the limiter output is supplied to the phase comparison circuit 13, and the conversion gain K _d of the phase comparison circuit 13 is substantially increased.
The value of increases, as shown in Figure 2.
The capture range and lock range of the PLL circuit are
It is expanded from C ₁ , L ₁ to C ₂ , L ₂ .

Therefore, in the initial state, it is insensitive to the 19KHz pilot signal, but after detecting the sub-channel signal, both the capture range and lock range are expanded, which causes distortion to the detection output obtained from the sub-channel signal. The signal can be supplied to the matrix circuit 6 without any interference. Of course, there will be no malfunction due to the 19KHz pilot signal of the FM stereo signal.

[Effect of idea]

The discrimination circuit of the television audio multiplex broadcast receiving device of the present invention uses a PLL circuit to detect the sub-channel signal, and the capture range of the PLL circuit is initially set to a dead band with respect to the 19KHz pilot signal. After detection, by expanding the capture range and lock range,
It is possible to provide an extremely effective discrimination circuit for a television audio multiplex broadcast receiving device that eliminates malfunctions for 19KHz pilot signals and does not distort the detected output.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a discrimination circuit of a television audio multiplex broadcast receiving device according to the present invention;
Fig. 2 is a diagram showing the characteristics of the PLL circuit used in the discrimination circuit of the TV audio multiplex broadcast receiving device according to the present invention, Fig. 3 is a diagram showing the spectrum of an FM stereo signal, and Fig. 4 is a diagram showing the TV audio spectrum. Figure 5, a diagram showing the spectrum of a multiplex broadcast signal, shows the conventional PLL.
FIG. 6, which is a diagram showing the characteristics of the circuit, is a circuit showing an embodiment in which a part of the discriminating circuit of the television audio multiplex broadcast receiving apparatus according to the present invention is made concrete for explaining the main part thereof. 1: Input terminal, 2: Low pass filter, 3: Band pass filter, 4: FM detection circuit, 5: Amplifier circuit, 6: Matrix circuit, 7, 8: Amplifier circuit,
9, 10: Speaker, 11: Discrimination circuit, 12: Limiter circuit, 13: Phase comparison circuit, 14: Low pass filter, 15: Voltage controlled oscillator, 16: Phase comparison circuit, 17: Phase shift circuit, 18: Level Adjustment circuit, 19: Hysteresis comparator, 20: Indicator light drive circuit, 21: Logic circuit, 22: Control terminal, 23: VCO killer terminal, 24: Light emitting diode, 25: Differential amplifier circuit, 33: Current mirror circuit, 38, 42: Constant current source circuit.

Claims (1)

[Claims for Utility Model Registration] (1) In a discriminating circuit of a television audio multiplex broadcast receiving device that can detect and derive a sub-channel signal of a television audio multiplex signal using a PLL circuit, the sub-channel signal is derived. a limiter circuit that applies a limiter to the signal that has passed through the bandpass filter, a PLL circuit to which the output from the limiter circuit is supplied, and a capture range of the PLL circuit after detecting the arrival of the sub-channel signal. What is claimed is: 1. A discrimination circuit for a television audio multiplex broadcast receiving device, characterized in that it includes means for expanding the lock range. (2) The means reduces the output level of the limiter circuit before the sub-channel signal arrives.
After the PLL circuit detects the sub-channel signal by narrowing the capture range and lock range of the PLL circuit, increase the output level of the limiter circuit to narrow the capture range and lock range of the PLL circuit to the sub-channel signal. 2. A discriminating circuit for a television audio multiplex broadcast receiving apparatus according to claim 1, characterized in that the discriminating circuit extends to substantially the same frequency bandwidth as the frequency bandwidth of the utility model registration claim 1.