JPH0614714B2 - Television sound multiplex broadcasting discrimination circuit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television sound multiplex broadcast discrimination circuit used in a television receiver, a video tape recorder, a radio cassette, or the like.

2. Description of the Related Art Audio multiplex broadcasting on television in Japan broadcasts a sub audio signal in addition to a normal audio signal (main audio signal). The sub audio signal is FM-modulated by the sub audio signal. This is a method of superimposing a carrier wave and a pilot signal.

Currently, "2 audio multiplex broadcast" and "stereophonic broadcast" are broadcast in this multiplex broadcast, and a pilot signal 107 as shown in FIG. 7 is added as a signal for judging these on the receiving side. The pilot signal is 922.5Hz in the case of a two-voice multiplex broadcasting pilot signal,
For stereophonic multiplex pilot signals 982.
The carrier is 5 Hz, and each 55.1 kHz carrier is AM-modulated. On the receiving side, the pilot signal is detected and the audio processing circuit is automatically switched to perform a processing operation suitable for the type of broadcast.

In FIG. 8, 100 is an antenna, 101 is a front end part such as a tuner, 102 is an IF (intermediate frequency) circuit, 103 is a voice detection circuit, and 104 is a voice multiplex signal processing circuit. The signal in FIG. 7 is the audio multiplex composite signal generated at point (a) in FIG. 8. In the case of two audio multiplex broadcasting, 105 is the main audio signal, 106 is the sub audio signal, and 107 is the pilot signal. Is. On the other hand, in stereophonic broadcasting, 105 is L + R
A signal, 106 is an L-R signal, and 107 is a pilot signal.
Here, L represents a left channel signal, and R represents a right channel signal. Since 106 is an FM modulated signal with 31.5 kHz as a carrier, it must be further demodulated in the audio multiplex signal processing circuit 104.

Next, with respect to the audio multiplex signal processing circuit 104, a conventional example of the multiplex broadcast discriminating circuit will be described with reference to FIG.
In the figure, the audio multiplex composite signal supplied to the input terminal 110 is passed through the coupling capacitor 111 to the filter group 1
The signals of 105 and 106 shown in FIG. 7 are supplied to a predetermined processing circuit 125 through lines 114 and 115, respectively, while the pilot signal 107 is supplied to an AM detection circuit 116 and detected, and 922.5 It is extracted as a sine wave signal of Hz or 982.5Hz.

Then, this pilot signal is judged by the next PLL circuit 117. The PLL circuit 117 compares the phase of the oscillation signal given from the voltage controlled oscillator 120 via the frequency divider 119 with the pilot signal from the AM detection circuit 116 in the phase comparator 118, and the voltage controlled oscillator 120 Control the oscillation frequency of. The error component (voltage) corresponds to ΔE1 in FIG. 10 when the 922.5 kHz pilot signal is input to the phase comparator 118. Similarly, when a 982.5 Hz pilot signal is input, its error component corresponds to ΔE2 in FIG. Then, the error component is compared with a predetermined value by the comparator 124 to obtain a high-level or low-level output signal, and this output signal is used to determine which of the two pilot signals is the pilot signal. Represent.
The output signal of the comparator 124 is supplied to the processing circuit 125, and controls the processing circuit 125 to perform a processing operation suitable for the type of multiplex broadcasting.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, since this conventional television audio multiplex broadcast discrimination circuit is configured by a PLL circuit, the external capacitor 121 of the voltage controlled oscillator 120 and the frequency of this voltage controlled oscillator circuit 120 are 952.5 kHz. External volume 122 to match
In addition, the number of pins of the IC that constitutes the PLL circuit is large, and the cost is high as a whole, and the oscillation frequency of the voltage control oscillation circuit 120 is 952.
It had to be adjusted to 5 kHz, and there was a drawback that a process for that was required at the time of manufacturing. Furthermore, the capacitor 121, the volume 122, and the loop filter 123
Since the temperature characteristics and changes over time affect the oscillation characteristics, it is also disadvantageous in terms of reliability.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly reliable television audio multiplex broadcast discrimination circuit with a simple configuration.

Means for Solving the Problems In order to achieve the above-mentioned object, the television sound multiplex broadcast discrimination circuit of the present invention uses two of the detected television sound multiplex signals.
Phase processing means for advancing the phase with respect to one of the pilot signals of the kind and delaying the phase with respect to the other signal; first converting means for converting an output signal of the phase processing means into a rectangular wave; Second conversion means for converting the pilot signal into a rectangular wave without passing through the phase processing means, and identification means for identifying the phase relationship between the output waveform of the first conversion means and the output waveform of the second conversion means. And.

In this case, the phase processing means may be constituted by a bandpass filter having a center frequency at a frequency approximately in the middle of the frequencies of the two pilot signals.

Further, the phase processing means may be composed of a state variable bandpass filter using two stages of transconductance amplifiers, and the center frequency thereof may be determined by the constant current of the transconductance amplifiers.

The identifying means may have a data input end, a clock input end, and an output end, and the output state may change only when a clock is input to the clock input end and the data input changes.

Operation According to the above configuration, the phase of the pilot signal that has passed through the phase processing means is delayed or advanced with respect to the output of the second conversion means. Therefore, the type of pilot signal can be identified by identifying whether the phase is delayed or advanced.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the audio multiplex composite signal supplied to the input terminal 1 is input to the filter group 3 through the coupling capacitor 2, and the signals 105 and 106 shown in FIG. 7 are subjected to predetermined processing through the lines 4 and 5, respectively. The pilot signals 107 and 108 are supplied to the circuit 6, while the pilot signals 107 and 108 are supplied to the AM detection circuit 8 to be detected and extracted as a sine wave signal of 922.5 Hz or 982.5 Hz.

Then, the pilot signal is guided to the limiter 10 through the bandpass filter 9 and also to the limiter 11 without passing through the bandpass filter. The bandpass filter 3 has a phase characteristic (A) and an amplitude characteristic (B) as shown in FIG. Therefore, 92
When the 2.5 kHz pilot signal 107 passes through this band pass filter 9, the phase advances and the 982.5 kHz pilot signal 10
When 8 passes, the phase will be delayed.

The bandpass filter 9 is not particularly limited to this, but as shown in FIG. 4, it is configured as a state variable bandpass filter using two trans conductance amplifiers 15 and 19. In addition, capacitors 17, 21 and buffers 18, 22 are provided. In addition, 16 and 20 have shown that it is a current output. The pilot signal is input to the terminal 23 and output from the terminal 24. The capacitors 17 and 21 are formed in the IC. In this state variable bandpass filter, the center frequency changes depending on the conductance gm of the amplifiers 15 and 19, and the conductance gm is determined by the constant current of the amplifiers 15 and 19. As a conclusion, the center frequency fo is proportional to the constant current I.

The filter group 3 shown in FIG.
It has a center frequency of 55.1 kHz, while the bandpass filter 9 has a center frequency of 952.5 Hz as shown in FIG. Therefore, the filter 3 may be similarly configured by a state variable type filter as shown in FIG. 4, and the constant currents of the filter 3 and the bandpass filter 9 may be driven by the same current block. The structure can be made as shown in FIG. 5, for example. In FIG. 5, the constant current source 27 of the filter group 3 is formed by connecting a plurality of transistors in parallel so as to obtain a large current (to increase the center frequency), and the constant current source 28 of the bandpass filter 9 is a small current. It may be formed by one transistor (to lower the center frequency), and these transistors are driven by the drive unit 26 of the current mirror connection. In this case, the variable resistor 7 is used to drive each of the filters 3 and 9. Constant current (hence center frequency)
Can be adjusted in common.

Returning to FIG. 1, the limiters 10 and 11 have the same configuration and serve to convert a sine wave pilot signal into a pulse signal. Reference numerals 12 and 13 are bypass capacitors for bypassing the AC signal. Specifically, as shown in FIG. 6, the base bias of the differential pair transistor Q2 is taken from the base side of the transistor Q1. Signal) on the transistor Q2 side. These capacitors 12 and 13 are externally attached, but even if there are variations, changes over time, temperature characteristics, etc., they can serve as bypass capacitors, so there is no problem and inexpensive capacitors can be used.

The pilot signal pulsed by the limiters 10 and 11 is applied to the next D flip-flop 14 where it is identified. The output of the limiter 10 is given to the data input terminal D, and the output of the limiter 11 is given to the clock terminal C.

Next, the operation of the television sound multiplex broadcast discrimination circuit of FIG. 1 will be described.

Considering the case where the two-voice multiplex broadcast is being received, the pilot signal is 922.5Hz which represents the two-voice multiplex broadcast.
Pilot signal 107 is applied to input terminal 1 in the form of a carrier modulated at 55.1 kHz. This signal passes through the filter 3 and is given to the AM detection circuit 8. Here, the AM detected and extracted pilot signal 107 (FIG. 7) has its phase advanced by the bandpass filter 9 and is pulsed by the next limiter 10, and is shown in (a) of FIG. As shown.
On the other hand, since the output of the limiter 11 is not affected by the phase characteristic action of the bandpass filter 9, its phase is neither delayed nor advanced. The output of this limiter 11 is shown in Fig. 3 (b).
Shown in. The output of the limiter 10 is given to the data input terminal D of the D flip-flop 14, and the output of the limiter 11 is given to the clock terminal C. As a result, the D flip-flop
The output of 14 becomes low level as shown in Fig. 3 (c).

Next, when a stereophonic broadcast is received, the 982.5 Hz pilot signal 107 (Fig. 7) generated at the output of the AM detection circuit 8 passes through the bandpass filter 9 and can be seen from Fig. 2. The phase is delayed, so the limiter
The output of 10 is as shown in Fig. 3 (a '), while the same pilot signal 10 not affected by the bandpass filter 9
The output of the limiter 11 for 8 is as shown in FIG. 3 (b '). As a result, the output of the D flip-flop 14 is shown in FIG.
High level as shown in (c ′).

These low-level and high-level signals are applied to the processing circuit 6, and the processing circuit 6 is controlled so as to perform an operation that matches the received broadcast signal.

EFFECTS OF THE INVENTION As described above, according to the present invention, what is necessary for frequency adjustment of the voltage controlled oscillator is unnecessary as compared with the conventional circuit, and when integrated into an IC, the number of external pins and the number of external components are increased. Can be reduced and cost can be reduced. Further, since the number of externally attached parts is small, it is unlikely to be affected by the change with time or temperature characteristics of the parts, so that the reliability is improved accordingly.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a television sound multiplex broadcasting discrimination circuit embodying the present invention, FIG. 2 is a diagram showing characteristics of the band pass filter, FIG. 3 is a processing waveform diagram of pilot signals, and FIG. Is a circuit diagram showing a configuration example of a bandpass filter, FIG. 5 is a circuit diagram showing a constant current source circuit such as a bandpass filter, and FIG. 6 is a circuit diagram showing a part of a limiter. FIG. 7 is a diagram for explaining a television audio multiplex composite signal, and FIG. 8 is a block circuit diagram showing a schematic configuration of a television audio multiplex signal receiver. FIG. 9 is a block diagram of a conventional example, and FIG. 10 is an explanatory diagram thereof. 3 ... filter, 6 ... processing circuit, 8 ... AM detection circuit, 9 ... bandpass filter, 10,11 ... limiter, 14 ... D flip-flop, 15, 19 ... trans conductance amplifier.

Claims (4)

[Claims] 1. Two out of detected multiple signals of television audio signals.
Phase processing means for advancing the phase with respect to one of the pilot signals of the kind and delaying the phase with respect to the other signal; first converting means for converting an output signal of the phase processing means into a rectangular wave; Second conversion means for converting the pilot signal into a rectangular wave without passing through the phase processing means, and identification means for identifying the phase relationship between the output waveform of the first conversion means and the output waveform of the second conversion means. And a television sound multiplex broadcasting discrimination circuit, characterized by comprising: 2. The television sound multiplex broadcasting discrimination circuit according to claim 1, wherein the phase processing means is a bandpass filter having a center frequency at a frequency substantially intermediate between the frequencies of the two pilot signals. . 3. The phase processing means is a state variable bandpass filter using two stages of transconductance amplifiers, and its center frequency is determined by a constant current of the transconductance amplifier. The television sound multiplex broadcasting discrimination circuit described in. 4. The identifying means has a data input end, a clock input end and an output end, and the output state changes only when a clock is input to the clock input end and the data input changes. The television sound multiplex broadcast discrimination circuit according to claim 1.