JP2000069393A - Audio if signal identification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a device to automatically discriminate the kinds of an SIF signal, from a composite video signal detected by the inter-carrier system. SOLUTION: This audio IF signal identification device that identifiers plural audio IF signals with different frequencies is provided with an extract means 6 that extracts an audio IF signal for a period, when no chroma signal exists, an FM detector 7 that applies FM detection to the audio IF signal from the extract means 6, and an oscillator 4 that oscillates at a prescribed frequency, and plural audio IF signals are identified, depending on the comparison result between the FM detection result of the audio IF signal and the FM detection result of the oscillator 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a TV receiver and a VT
The present invention relates to an audio IF signal identification device incorporated in R or the like to detect and identify the frequency of a PAL audio IF signal, and more particularly to an audio IF signal identification device suitable for use in an intercarrier video detector.

[0002]

2. Description of the Related Art The detection method of a video intermediate frequency (hereinafter referred to as VIF) includes an intercarrier method (a method of detecting a mixture of a video IF signal and an audio IF signal at the time of video detection) and a split method (a video IF A signal and an audio IF signal are first separated and detected separately). In the case of an intercarrier, the SIF carrier is output together with a video detection output. This is called a composite video signal. SI included in this composite video signal
The F carrier is FM-modulated. The sound is demodulated by performing FM detection on the SIF signal on which the FM modulation is performed.

[0003] There are various frequencies in PIF SIF carriers. In the PAL M system / N system, the audio IF signal frequency is fs = 4.5 MHz and PAL B
In the System / G system, the audio IF signal frequency is fs = 5.
5 MHz, the audio IF signal frequency is fs = 6.0 MHz in the PAL I system, and the audio IF signal frequency is Fs = 6.5 MHz in the PARD system / K system. In general, the SIF signal is identified manually by a TV set manufacturer or the like.

[0004]

However, it is time-consuming to perform manually. Since the SIF signal has a different frequency, FM detection may be performed to identify the SIF signal. However, in the case of the above-mentioned intercarrier, the SIF signal mixed in the composite video signal is
Even if an attempt is made to make a determination by inputting the signal to a detector, it is difficult to make a good determination because the luminance signal and the chroma signal become interference waves.

FIG. 2A is a waveform diagram of a composite video signal detected by the intercarrier system. The composite video signal includes a luminance signal (constituting a synchronization signal), a chroma signal, and an audio IF signal.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is an audio IF signal identification apparatus for identifying a plurality of audio IF signals having different audio IF signal frequencies. , The sound I during the period when no chroma signal exists
Extracting means for extracting the F signal, and voice I from the extracting means
An FM detector for FM-detecting the F signal and an oscillator for oscillating at a constant frequency are provided, and a plurality of audio IF signals are identified according to a comparison between the FM detection result of the audio IF signal and the FM detection result of the oscillator. It is characterized by doing so.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An audio IF signal discriminating apparatus according to the present invention will be described with reference to FIG.

In FIG. 1, reference numeral 1 denotes an antenna for receiving a PAL TV broadcast, reference numeral 2 denotes an RF amplifier for amplifying an RF (radio frequency) signal from the antenna 1, and reference numeral 3 denotes an IF (intermediate frequency) signal from an RF amplifier 2. Frequency), an IF signal is amplified, an IF signal is amplified, and an IF detection circuit for inter-carrier detection of the IF signal is further provided. 4 is an oscillator oscillating at 4.0 MHz, and 5 is a horizontal synchronizing signal from a luminance signal from the IF detection circuit 3. Synchronization separation circuit for separation, 6 is synchronization separation circuit 5
When the horizontal synchronization signal is applied to the switch, the switch is switched to the a side, and in the other periods, the switch is switched to the b side. A first sample-and-hold circuit that samples and holds the detection result of the oscillation output signal of the oscillator 4, 9
Is the SIF in the horizontal synchronization signal period detected by the FM detector 7
A second sample and hold circuit that samples and holds the detection result of the signal is a resistor that divides the output voltage of the first sample and hold circuit 8 and creates a plurality of reference voltages for identifying the FM detection voltage. A comparator for comparing the level of the reference voltage generated by the resistors 10 to 13 with the output voltage of the second sample and hold circuit 9;
Numerals 19 to 19 denote output terminals for deriving the type of the incoming SIF signal at 3-bit "H" level and "L" level.

FIG. 2A is a waveform diagram of a composite video signal detected by the inter-carrier method. FIG.
FIG. 2B shows the SIF signal included in FIG.
The SIF signal exists continuously in the composite video signal. FIG. 2A shows that many of the periods are mixed with other AC signals (such as a chroma signal, a burst signal, and a luminance signal). Due to the influence of other AC signals, S
FM detection of the IF signal has become difficult.

Therefore, in the present invention, detection is performed using a horizontal synchronizing signal period in which the influence of other AC signals is minimal and the detection period can be easily set. This period is shown in FIG.
As shown in (a), there is only a horizontal synchronization signal which is a DC component, and there is no other AC signal. The horizontal sync signal can be easily obtained using the existing sync separation circuit,
A pulse indicating the detection period can be easily obtained.
Although the horizontal synchronizing signal period is used in the embodiment of FIG. 1, it may be a vertical synchronizing signal period. The operation of FIG. 1 will be described.

A PAL TV broadcast is received by an antenna 1 and amplified by an RF amplifier that amplifies an RF (radio frequency) signal. The RF signal from the RF amplifier 2 is converted to an IF (intermediate frequency) signal by the IF detection circuit 3 and amplified. Then, the IF signal is further inter-carrier detected by the IF detection circuit 3. The composite video signal detected by the intercarrier detection is applied to a terminal a of the switch 6 and the sync separation circuit 5. The synchronization separation circuit 5 is configured as shown in FIG.
When the horizontal synchronizing signal is separated as shown in (c), it is applied to the switch 6 and the second sample and hold circuit 9. Then, the switch 6 switches to the terminal a only during the period of generation of the horizontal synchronizing signal, and the SIF signal as shown in FIG.
Applied to the detector 7.

FIG. 3 is a characteristic diagram showing the relationship between the input signal frequency of the FM detector 7 and the detection output voltage. The detection output voltage decreases as the input signal frequency increases. now,
Assuming that the SIF signal of the PAL B system / G system has arrived and its frequency is fs = 5.5 MHz, 2.7 V
A detection voltage is generated. The detected voltage of 2.7 V is held in the second sample and hold circuit 9. The held detection voltage of 2.7 V is applied to the negative input terminals of the comparators 14 to 16.

On the other hand, the FM detector 7 outputs 4.0M
The FM signal of HZ is applied, and as shown in FIG. 3, a DC voltage of 4.0 V is generated. For this reason, the detection output signal of the FM detector 7 has a horizontal synchronizing signal period of 2.7 V as shown in FIG.
It becomes 4.0V in other periods. The sampling pulse shown in FIG. 2F is applied to the first sample hold circuit 8. Therefore, the first sample and hold circuit 8
Applies a DC voltage of 4.0 V to the resistors 10 to 13.

SIF of PAL M system / N system
(Fs = 4.5 MHz), the SIF of the PAL B system / G system (fs = 5.5 MHz) is 2.7 V, and the SIF of the PAL I system (fs = 6.0 MHz).
The voltage is 2.2 V when z) is applied, and 1.7 V when the SIF (fs = 6.5 MHz) of the PARD system / K system is applied.

Therefore, the intermediate value of each SIF detection voltage is used as a judgment threshold value in the comparator. For example, by applying 3.15 V (corresponding to 5 MZ of the input signal frequency) to the comparator 14, it is possible to distinguish between the M system / N system and the other system. Similarly, 2.45 V and 1.95 V are supplied to comparators 15 and 16.

The detection characteristics of the FM detector shown in FIG. 3 are not always the characteristics indicated by the solid line due to variations in the circuit. Therefore, if the thresholds of the comparators 14 to 16 are fixed values, it is not possible to cope with a change in the input signal value. Therefore, in the present invention, the threshold values of the comparators 14 to 16 are set as relative values. That is, the thresholds of the comparators 14 to 16 are created based on the voltage (4.0 V) obtained by detecting the output signal of the oscillator 4. Then, if the detection voltage of the FM detector changes, the threshold value also changes. Therefore, the relation between the relative detection voltage and the threshold does not change.

The detected voltage of 2.7 V held in the second sample-and-hold circuit 9 is compared with the comparators 14 to 16
Is applied to the negative input terminal. As a result, output terminal 1
“H, L, L” occurs in 7 to 19, and the B system /
Identify it as a G system.

Similarly, different 3-bit digital data is obtained at the output terminals 17 to 19 in accordance with the frequency of each SIF signal.

Therefore, according to the apparatus shown in FIG. 1, the composite video signal detected by the inter-carrier method
The type of the F signal can be determined.

[0020]

According to the present invention, the type of the SIF signal can be automatically determined from the composite video signal detected by the intercarrier method.

Further, according to the present invention, frequency detection can be easily performed because FM detection is performed during a period in which no chroma signal exists, such as a horizontal synchronizing signal period.

Further, according to the present invention, since the reference voltage for determination is created using a fixed oscillator, the relation between the relative detection voltage and the threshold value does not change, and stable determination is always performed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an audio IF signal identification device of the present invention.

FIG. 2 is a waveform diagram for describing the present invention.

FIG. 3 is a characteristic diagram for describing the present invention.

[Explanation of symbols]

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C026 DA01 DA04 DA24 DA28 5C066 BA03 CA13 DC08 GA04 GA06 GA12 GB07 HA05 JA09 KD02 KD04 KG01 KG08 LA02

Claims (2)

[Claims] 1. An audio IF signal discriminating apparatus for identifying a plurality of audio IF signals having different frequencies of an audio IF signal, comprising: extracting means for extracting an audio IF signal in a period in which no chroma signal is present; An FM detector for FM-detecting the audio IF signal of the above, and an oscillator oscillating at a constant frequency, wherein a plurality of audio IF signals are provided in accordance with a comparison result between the FM detection result of the audio IF signal and the FM detection result of the oscillator. An audio IF signal identification device characterized in that the audio IF signal identification device is configured to identify 2. An audio IF signal identification device for identifying a plurality of audio IF signals having different frequencies of an audio IF signal, comprising: extracting means for extracting an audio IF signal in a period in which no chroma signal is present; An FM detector for FM detection of the audio IF signal of the above, an oscillator oscillating at a constant frequency, a first sample and hold circuit for sampling and holding the FM detection result of the audio IF signal, and a sample and hold for the FM detection result of the oscillator Second
And a plurality of sound I / Os corresponding to the output voltages of the first and second sample and hold circuits.
An audio IF characterized by identifying an F signal.
Signal identification device.