JPH0417571B2 - - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to an audio multiplex broadcast pilot signal identification device, and more particularly, to an audio multiplex broadcast pilot signal identification device for identifying a control signal used for controlling a multiplex demodulation circuit in a TV audio multiplex broadcast receiver. The present invention relates to a pilot signal identification device that generates a pilot signal by identifying a pilot signal.

BACKGROUND ART An audio multiplex signal in TV audio multiplex broadcasting includes a main channel (L+R), a subchannel (L-R), and a pilot signal as signal components. The pilot signal is a carrier wave of approximately 55.125KHz, which is 3.5 times the horizontal synchronization signal, and is amplitude modulated as a single tone (single frequency signal) of 982.5Hz during stereo broadcasting, and 922.5kHz when broadcasting in two languages.
It is amplitude modulated with a single tone of Hz.

Therefore, on the receiving side, the demodulation operation of the multiplex demodulation circuit is performed by discriminating between the two frequency signals of 982.5Hz and 922.5Hz, which are the modulation components of this pilot signal.
It is configured to be performed in response to stereo broadcasting or bilingual broadcasting.

FIG. 3 shows a conventional example of a pilot signal identification device that generates a control signal used for controlling a multiplex demodulation circuit by identifying the pilot signal shown in FIG. In the figure, the audio multiplexed signal is supplied to a BPF (band pass filter) 1, and a carrier wave signal (55.125KHz) that is amplitude modulated (AM) with one of two pilot signals (982.5Hz and 922.5Hz) is extracted. . The output of the BPF 1 is supplied to a first PLL (phase locked loop) circuit 2 and a multiplier 3.

The first PLL circuit 2 locks onto the fundamental wave (carrier wave) output from the BPF 1 and outputs a lock detection signal and a carrier wave signal. Using this carrier signal
A pilot signal is obtained by performing AM detection on the output of BPF1, and this AM detection is performed by multiplier 3 and
This is done using LPF (low pass filter) 4. A.M.
The pilot signal of 982.5 Hz or 922.5 Hz detected by the wave detection is supplied to the second PLL circuit 5.

In the second PLL circuit 5, a phase comparator 50 compares the phase and frequency of the pilot signal with the divided output of a frequency divider 51. The output of this comparison is
After high-frequency components are removed by the LPF 52, it becomes the control voltage V of the VCO (voltage controlled oscillator) 53. According to this control voltage V, the phase and frequency of the output signal of the VCO 53 are controlled. Thereafter, the frequency is divided by a frequency divider 51 to a desired value and becomes the reference input of the phase comparator 50.

This second PLL circuit 5 has a free run frequency (divider output frequency when there is no input to the PLL circuit 5, that is, when there is no pilot signal) that has passed through the frequency divider 51 of the VCO 53, which is equal to the frequency of the two pilot signals. (982.5Hz and 922.5Hz), i.e. 952.5
Hz, and the control voltage V at that time is
Let it be V _O. When the pilot signal is input, the VCO 53 locks to 982.5Hz or 922.5Hz,
The control voltage V at that time changes above or below the control voltage _VO .

This control voltage V becomes a comparison input of comparators 6 and 7. Comparators 6 and 7 have a reference voltage Vref that is approximately equal to the control voltage _VO during free run as a reference input, and when the VCO 53 locks to 982.5Hz, comparator 6 outputs, and when it locks to 922.5Hz, comparator 7 outputs the output. One input each of AND gates 8 and 9 is generated. AND
Gates 8 and 9 receive the lock detection signal from the first PLL circuit 2 as other inputs, and their outputs indicate stereo broadcasting and bilingual broadcasting, respectively, and demodulate the multiplex demodulation circuit (not shown). It becomes a control signal that controls the operation.

Note that the AND gates 8 and 9 are provided to prevent erroneous detection due to malfunction of the comparators 6 and 7 due to noise or the like.

As described above, in the conventional device, the control voltage V when the VCO 53 in the second PLL circuit 5 is locked is
Since the system is configured to obtain a control signal indicating that the audio multiplexed signal is a stereo broadcast or a bilingual broadcast by discrimination, the free run frequency of the PLL circuit 5 must be adjusted. It is extremely difficult to manage drift due to changes in free run frequency over time, temperature changes, etc.
It was difficult to set various parameters, including comparison inputs, and sufficient consideration was required for circuit design, which was a disadvantage, especially when considering IC (integrated circuit) implementation.

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate the drawbacks of the conventional ones as described above, and provides an audio multiplex broadcast pilot signal identification device that enables no adjustment of the circuit and is particularly advantageous for IC implementation. With the goal.

The audio multiplex broadcasting pilot signal identification device according to the present invention extracts a carrier signal whose amplitude has been modulated by one of two pilot signals from an audio multiplex signal, discriminates the pilot signal, and divides the frequency of the extracted carrier wave signal into two. The divided output frequency is compared with the frequency of the discriminated pilot signal, and based on this comparison output, the frequency is divided into values between the respective frequencies of the two pilot signals. The configuration is such that it generates two control signals.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, in which parts equivalent to those in FIG. 3 are designated by the same reference numerals. In the figure, a carrier wave signal extracted by a BPF 1 and a PLL circuit 2 is supplied to a multiplier 3 and also to a 1/58 frequency divider 10. The divided output of this frequency divider 10 is the frequency comparator 1
Two pilot signals (982.5Hz and 922.5Hz) fed to 1 and discriminated by multiplier 3 and LPF 4
The frequency is compared with either one of the two. The comparison output of this frequency comparator 11 becomes one input of an AND gate 13 via an inverter 12, and
It directly becomes one input of the AND gate 14. AND
Gates 13 and 14 have the lock detection signal outputted from PLL circuit 2 as the other input.

Next, the operation of the present invention will be explained.

The operations of extracting the carrier wave modulated by one of the two pilot signals from the audio multiplexed signal and discriminating the AM modulated component as the pilot signal are the same as those of the conventional device shown in Fig. 3. Since the explanation is redundant, it will be omitted here.

Now, as mentioned earlier, the frequency of the carrier wave is
It is specified as 3.5f _H (f _H is the horizontal synchronization frequency),
It is approximately 55.125KHz. This carrier wave is divided into frequency divider 10
If you divide the frequency by 1/58, you will get a divided output of approximately 950Hz, which is equal to the two pilot signal frequencies (982.5
Hz and 922.5Hz). This 950Hz
The frequency comparator 11 uses the divided output of LPF4
By comparing the frequency with the output of the pilot signal, the pilot signal can be identified. The comparison output of the frequency comparator 11 is inverted by the inverter 12.
After passing through the AND gate 13, the audio multiplex signal becomes a control signal OUT1 indicating that it is a stereo broadcast.
Further, a control signal OUT2 indicating that the audio multiplexed signal is a bilingual broadcast is directly passed through an AND gate 14.
becomes.

Note that the AND gates 13 and 14 are provided to prevent erroneous detection due to malfunction of the frequency comparator 11 due to noise or the like.

Frequency comparator 11 that discriminates between two types of frequencies
For example, a digital frequency comparator consisting of a bidirectional shift register as shown in FIG. 2 can be used. The bidirectional shift register consists of four flip-flops 15 to 18 connected in series with each other.
It consists of a flip-flop 1 in the second and third stages.
The comparison output is derived from the input/output terminals 6 and 17, and when the frequency of the right shift clock is higher than that of the left shift clock, a low level output is output, and the frequency of the right shift clock is higher than that of the left shift clock. is low, a high level output is respectively derived. Therefore, the divided output (950Hz) of the frequency divider 10 is used as the left shift clock, and the LPF
By using the output of 4 (982.5Hz or 922.5Hz) as the right shift clock, the pilot signal changes to 982.5Hz.
Hz, low level output, pilot signal
At 922.5 Hz, a high level output is respectively derived and the pilot signal is identified.

By identifying the pilot signal using the frequency comparator 11 in this manner, it is possible to eliminate the need for adjustment of this portion of the circuit, which is particularly advantageous when implemented as an IC.

In the above embodiment, the PLL is used to detect the carrier wave that is AM modulated by either of the two pilot signals.
Circuit 1 was used, but a narrowband circuit was used instead of the PLL circuit.
By using a BPF, a normal envelope detector for AM demodulation, and a normal level detector for detecting the presence or absence of a carrier wave, this part also requires no circuit adjustment, making pilot signal identification extremely easy to handle. The device will be obtained.

Furthermore, in the above embodiment, the carrier wave is frequency-divided by 1/58 to obtain a comparison reference frequency of approximately 950 Hz, but the frequency is not limited to this value, and the resulting divided output frequency is the same as that of the two pilot signals. It is sufficient if the frequency is between the frequencies, and the same effect as in the above embodiment can be obtained.

Effects of the Invention As explained above, the pilot signal identification device according to the present invention is configured to identify the pilot signal by comparing frequencies, so it is possible to eliminate the need for adjusting the circuit, and especially for IC It will be advantageous for the development. Furthermore, since only one PLL circuit is required, lock-in time is shortened and pilot signals can be reliably discriminated.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram showing an example of the frequency comparator shown in FIG. 1, and FIG. 3 is a block diagram showing a conventional example. Explanation of symbols of main parts, 2, 5...PLL circuit,
3... Multiplier, 10... 1/58 frequency divider, 11...
Frequency comparator, 15-18...flip-flop.

Claims (1)

[Claims] 1. An audio multiplex broadcast pilot signal identification device that detects two pilot signals indicating the program contents of an audio multiplex broadcast and generates two control signals according to the contents of each program, which detects the two pilot signals from the audio multiplex signal. an extraction means for extracting a carrier wave signal whose amplitude is modulated by one of the signals; a discrimination means for discriminating the pilot signal from the audio multiplexed signal based on the carrier wave signal; A frequency dividing means for dividing the frequency to a value between the respective frequencies of the two pilot signals, and comparing the divided output frequency of the frequency dividing means and the frequency of the pilot signal discriminated by the discrimination means. 1. A pilot signal identification device for audio multiplex broadcasting, comprising: frequency comparing means, and generating said two control signals based on a comparison output of said frequency comparing means.