JPS6349957B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for discriminating SECAM signals, and particularly to a method for discriminating SECAM signals that is extremely stable against uneven characteristics of used parts, aging of used parts, and frequency fluctuations of color subcarriers. This paper relates to a method for discriminating SECAM signals.

It is one of the standard color television systems.
The following method is generally used to distinguish between SECAM color television signals and other color television signals (NTSC or PAL). In other words, in the SECAM method, color subcarriers are alternately used for each horizontal scanning line.
are different (4.25MHz and 4.40625MHz), whereas
Another method of color subcarrier is a method that takes advantage of the fact that the frequency does not change.

In other words, if the color subcarriers of the back porch of the horizontal synchronization signal are gated and extracted using a burst gate pulse, and the frequency of the extracted color subcarriers is discriminated line by line, in the case of the SECAM signal, the color subcarriers are alternately applied line by line. Since the carriers are different, a pulse with a frequency (7.8125KHz) that is half the frequency of the horizontal synchronization signal (15.625KHz) is obtained, whereas in color TV signals of other systems, the frequency of the color subcarrier does not change. It takes advantage of the fact that pulses cannot be obtained.

The present invention also utilizes this method, but first, an example of a conventional SECAM signal discrimination method using the above method will be explained with reference to FIGS. 1 to 3. When a horizontal synchronization signal (pulse) is applied to the first monostable multivibrator 4 via the input terminal 2, the first monostable multivibrator 4
It is triggered by the leading edge of the horizontal synchronization pulse 20 and outputs a pulse 22 (FIG. 3B) having a predetermined pulse width a. The pulse width a of the pulse 22 is determined such that its trailing edge is located at the beginning of the gate pulse that extracts the color subcarrier. The second monostable multivibrator 6 receives the pulse 22 from the first monostable multivibrator 4 and outputs a burst gate pulse 24 triggered at its trailing edge and having a pulse width b. It goes without saying that the pulse width b is determined by considering a width sufficient to extract the color subcarrier 26 (FIG. 3A). That is,
The first monostable multivibrator 4 receives a pulse 22 which determines the start point of extraction of the color subcarrier.
The second monostable multivibrator 6 outputs
Burst gate pulse 24 based on pulse 22
is output and applied to the gate circuit 8. On the other hand, the band pass filter (BPF) 12 is connected to the input terminal 10.
It receives a color television signal (FIG. 3A) through the 3-channel 3D, removes the luminance signal, and outputs a color signal. The color signal output from the BPF 12 is amplitude limited to a desired amplitude by a limiter 14 and applied to the gate circuit 8 at the next stage. The gate circuit 8 is controlled by the burst gate pulse 24 (FIG. 3C) from the second monostable multivibrator 6, extracts only the color subcarrier 26 from the color signal applied from the limiter 14, and adjusts the center frequency. is applied to a ceramic bandpass filter (BPF) 16 of approximately 4.5MHz. As mentioned above,
In the SECAM signal, the frequency of the color subcarrier is alternately 4.25 MHz for each horizontal scan line.
Since it changes to 4.40625MHz, from BPF16,
A pulse with half the frequency (7.8125KHz) of the horizontal sync pulse frequency (15.625KHz) is obtained. On the other hand, in the case of color television signals of other formats, the frequency of the color subcarrier does not change, so
No pulse is generated from BPF16. BPF16
By applying the output of 7.8125 KHz to the frequency discrimination circuit 18, a signal for discriminating the SECAM signal is obtained from the output terminal 19. By the way, since the color subcarrier that performs frequency discrimination is a burst signal, its spectrum has widened sidebands. FIG. 2 shows the spectrum of the fundamental wave of the color subcarrier. In Figure 2, A and B are the spectra of 4.40625MHz and 4.25MHz color subcarrier burst signals, respectively.From Figure 2, it can be seen that the spectrum of A and B overlaps in many parts, so the frequency It turns out that discrimination is difficult. For example, the level difference between A and B at the respective center frequencies of two types of color subcarriers is only about 6 dB. in this way,
Since there is a lot of overlap between the spectra of A and B,
Separation using the BPF 16 is difficult, and the conventional SECAM signal discrimination method shown in FIG. 1 has unstable discrimination operation. Therefore, the object of the first invention of the present application is to focus on the fact that the level ratio of spectra A and B in FIG. 2 is theoretically infinite at the valley of the spectrum, and to It is an object of the present invention to provide a SECAM signal discrimination method capable of performing stable frequency discrimination against fluctuations.

On the other hand, the object of the second invention of the present application is to focus on the fact that the level ratio of spectra A and B in FIG. It is an object of the present invention to provide a SECAM signal discrimination method capable of extremely stable frequency discrimination against carrier frequency fluctuations, uneven characteristics of used parts, aging of used parts, etc.

The first invention of the present application will be explained below with reference to FIGS. 2 to 4. In FIG. 2, at a frequency where one of the two types of spectra A and B has a valley, the level ratio between the spectra A and B is theoretically infinite. Therefore, if the frequency at which the spectrum has a valley is set as the center frequency of a frequency discrimination means such as a bandpass filter, then
SECAM signal discrimination is possible with certainty.

However, in particular, VTR (Video tape)
Since the time width fluctuates during playback of the color subcarrier (that is, the center frequency of the spectrum in FIG. 2). Therefore, at the valley frequency of the spectral distribution
In order to discriminate SECAM signals, it is necessary to remove frequency fluctuation components of color subcarriers.
FIG. 4 shows a block diagram of a circuit for removing frequency fluctuation components of color subcarriers. In FIG. 4, a horizontal synchronizing signal (pulse) containing a frequency variation Δ is applied to a PLL (phase lock loop) multiplier circuit 32 via an input terminal 30.
The PLL multiplier circuit 32 multiplies _H of the horizontal synchronizing pulse (the frequency is 15.625 KHz and is indicated by _H ) by an integer,
Color subcarrier frequency (4.25MHz,
4.40625MHz) and which is synchronized with the horizontal synchronizing pulse and is applied to the frequency converter 34. The output of the PLL multiplier circuit 32 is
It contains a frequency fluctuation component that is equal to the frequency fluctuation component of the color subcarrier. Therefore, as shown in FIG. 4, the frequency of the output of the PLL multiplier circuit 32 is actually 4.25MHz±Δ. On the other hand, an output signal from an oscillator (eg, a crystal oscillator) 36 that generates a reference signal with a reference frequency _S is applied to the frequency converter 34. Note that in this embodiment, _S is set to 4.43MHz. Frequency converter 34
is the frequency of the sum of the frequencies of the signals from the PLL multiplier 32 and the oscillator 36 (4.43MHz + 4.25MHz±△
) is output and applied to another frequency converter 38. The frequency converter 38 has a burst-gated signal via an input terminal 40.
SECAM color subcarrier is applied, but it also includes △, so it is 4.25MHz±△.
A color subcarrier with a frequency of 4.25MHz + _10H ±△ will be applied. Frequency converter 38
is the frequency of the difference between the frequencies of both input signals (4.43MHz
and 4.43MHz + _10H ),
The signal is applied to a band pass filter (BPF) 42 at the next stage. As is clear from the above description, the second signal does not include the frequency variation Δ.

By the way, the second output of the frequency converter 38
Among the frequencies that are the valleys of the signal spectrum distribution,
The frequency of the valley closest to the center frequency of the spectrum is 4.43MHz±1/α or 4.43M, where α is the pulse width of the burst gate pulse that extracts the color subcarrier of the back porch of the horizontal synchronization signal.
Hz+ _10H ±1/α. Therefore, BPF42
If the center frequency of is the frequency of the valley mentioned above,
SECAM signal discrimination is ensured. Furthermore, the second
If the frequency with the largest difference between the two types of spectra obtained from the signal is set as the center frequency of BPF42, the stability of frequency discrimination will be good.
It is common to choose 4.43MHz + 10 _H -1/α.
The output of the BPF 42 (a signal that discriminates the SECAM signal) is sent from the output terminal 44 to an external circuit (not shown).
is applied to

As can be seen from the above description, the first invention of the present application is an integer multiple of the frequency ( _H ) of the horizontal synchronizing signal in the SECAM system in which the frequency of the color subcarrier is alternately different for each horizontal scanning line, and the frequency of the color subcarrier is 2
A first frequency equal to one of the types of color subcarrier frequencies and synchronized with the horizontal synchronization signal.
generating a second signal having a frequency that is the sum of the frequency of the first signal and a reference frequency ( _S );
After removing the frequency fluctuation component of the color subcarrier by calculating the difference between the frequency of the burst-gated color subcarrier and the frequency of the second signal,
A SECAM signal discrimination method characterized in that a third signal having a frequency _S and a fourth signal having a frequency _S + 10 _H are obtained, and the frequency of the trough of the third or fourth signal is set as the center frequency for SECAM signal discrimination. Regarding.

By the way, the center frequency of SECAM signal discrimination is
As mentioned above, it is a function of the pulse width α of the burst gate pulse, so if there are variations in the values of the parts used such as resistors and capacitors that determine the pulse width α, it will be complicated to maintain the pulse width α at a constant value. Adjustments are necessary. Furthermore, since the characteristics of the parts used change due to changes in ambient temperature and changes over time, there is a possibility that the pulse width α changes. In other words, there is a possibility that the discrimination center frequency may vary.

Therefore, the second invention of the present application adds a method to the above-mentioned first invention in which the pulse width α is not affected by irregularities in the characteristics of circuit components, changes over time, etc., and improves the accuracy of frequency discrimination. This article relates to a further improved SECAM signal discrimination method. Hereinafter, the second invention of the present application will be described, but the description of parts that overlap with the first invention will be omitted, and only the generation of burst gate pulses having a constant pulse width will be described.

In FIG. 5, 52 is a phase lock loop (PLL), which is composed of a phase converter 54, a voltage controlled oscillator (VCM) 56, and a 1/ _N0 frequency divider ( _N0 is a positive integer) 58. ing. A phase comparator 54 receives a horizontal synchronization pulse via an input terminal 50;
VCM56 is a frequency synchronized with the horizontal sync pulse
A clock signal of N _{0 H} is applied to NAND gates 60 and 62. Note that the operation of the PLL is well known to those skilled in the art, so the details will be omitted. On the other hand, when a horizontal synchronizing pulse is applied to the set terminal S of the flip-flop (FF) 66 via the input terminal 64,
The output of the output terminal Q of the FF 66 goes high due to the leading edge of the horizontal sync pulse. While the output at output terminal Q of the FF66 is at a high level, the clock signal from the VCM56 is passed through a NAND gate 60 to a 1/ _N1 frequency divider 68 ( _N1 is a positive integer smaller than _N0 ). applied. The frequency divider 68 is FF66
From the point at which the output of output terminal Q of
N ₁ /N ₀ Generates an output signal after _H seconds;
It is applied to the reset terminal R of FF66 and the set terminal S of FF70. Therefore, the output of the output terminal Q of the FF 66 is at a low level, and a pulse corresponding to pulse 22 in FIG. 3B is obtained. On the other hand, FF66
At the same time, the output of the output terminal Q becomes low level,
The output of the output terminal Q of FF70 becomes high level,
This time, through the NAND gate 62, 1/N ₂
A clock signal of frequency N _{0 H} is applied from VCM 56 to frequency divider 72 . After N ₂ /N _{2 H} seconds after the output of the output terminal Q of the FF 70 becomes high level, the frequency divider 72 applies the output signal to the reset terminal of the FF 70 to change the output of the output terminal Q of the FF 70 to a high level. The level is set to low and the gate of Nando gate 62 is closed. Therefore, from the output terminal 74 to C in FIG.
A pulse corresponding to pulse 24 is obtained. The above operation is repeated every time a horizontal synchronizing pulse is applied to the set terminal S of the FF 66. Therefore, output terminal 7 connected to output terminal Q of FF70
By setting the output of 4 as a burst gate pulse, the gate start time can be set from the leading edge of the horizontal sync pulse.
A burst gate pulse is obtained after N ₁ /N _{0 H} seconds and with a pulse width of N ₂ /N _{0 H.} The timing and pulse width of the leading edge of the burst gate pulse obtained from the circuit shown in FIG. 4 are determined by N ₀ , N ₁ , N ₂ , and _H , and are therefore not affected by the components used or the external environment described above. Note that the values of N ₀ , N ₁ , and N ₂ may be determined so that an optimal burst gate pulse can be obtained.

The second invention of the present application can be summarized as follows. That is, in the SECAM system in which the frequency of the color subcarrier is alternately different for each horizontal scanning line, a clock signal is synchronized with the horizontal synchronization signal and has a frequency (N _{0 H} ) that is N ₀ times the frequency ( _H ) of the horizontal synchronization signal. generated using a phase lock loop,
The frequency of the above clock signal is divided by 1/N ₁ , and the start time of the burst gate pulse is set N ₁ /N _{0 H} seconds after the leading edge of the horizontal synchronization signal, and the clock signal is further divided by 1/N _2. A burst gate pulse with a pulse width ( _α ) of N ₂ /N _{0 H} seconds is generated by dividing into generates a first signal having a frequency equal to one of the frequencies and synchronized with the horizontal synchronizing signal, generates a second signal having a frequency equal to the sum of the frequency of the first signal and a reference frequency ( _S ), and After removing the frequency fluctuation component of the color subcarrier by calculating the difference between the frequency of the color subcarrier and the frequency of the second signal, the signal having the frequency _S and the frequency _S
Obtain a signal with +10 _H , _S ±1/α, _S +
10 _H ±1/α is set as the center frequency for SECAM signal discrimination.
This is a SECAM signal discrimination method.

As explained above, according to the present invention, for example, it is not affected by time axis fluctuations during VTR playback, and furthermore, it is almost unaffected by irregularities in the characteristics of the parts used, changes over time of the parts used, etc. extremely stable
SECAM signal discrimination is possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the conventional SECAM signal discrimination method, Fig. 2 is a spectrum of the fundamental frequency of a color subcarrier burst signal, and Fig. 3 is a block diagram of Fig. 1 and the implementation of the present invention. Waveform diagrams for explaining examples, Figures 4 and 5
The figure is a block diagram for explaining an embodiment of the present invention. 32... PLL multiplier circuit, 34, 36... Frequency converter, 42... Band pass filter (BPF), 52... Phase lock loop (PLL), 58... 1/N ₀ frequency divider, 60, 62...
...NAND gate, 66,70...Flip-flop, 68...1/N ₁ frequency divider, 72...1/N ₂ frequency divider.

Claims (1)

[Claims] 1. In the SECAM system in which the frequency of the color subcarrier is alternately different for each horizontal scanning line, the frequency of the color subcarrier is an integral multiple of the frequency ( _H ) of the horizontal synchronizing signal, and 2
A first frequency equal to one of the different color subcarrier frequencies and synchronized with the horizontal synchronization signal.
a second signal having a frequency equal to the sum of the first signal and a reference frequency ( _S ), which is the other subcarrier frequency different from the one subcarrier frequency, and a burst gated color subcarrier; After removing the frequency fluctuation component of the color subcarrier by calculating the difference between the frequency of the second signal and the frequency of the second signal, a third signal having a frequency _S and a fourth signal having a frequency _S + _10H are obtained. Alternatively, a SECAM signal discrimination method characterized in that the frequency of the valley of the frequency spectrum of the fourth signal is set as the center frequency of SECAM signal discrimination. 2 In the SECAM method, in which the frequency of the color subcarrier is alternately different for each horizontal scanning line, a clock signal that is synchronized with the horizontal synchronization signal and has a frequency (N _{0 H} ) that is N ₀ times the frequency ( _H ) of the horizontal synchronization signal is used. The clock signal is divided by 1/N ₁ , and the burst gate pulse starts at N ₁ /N _{0 H} seconds after the leading edge of the horizontal synchronization signal. , the frequency of the above clock signal is divided by 1/N ₂ to generate a burst gate pulse with a pulse width (α) of N ₂ /N _{0 H} seconds, while a burst gate pulse with a pulse width (α) of N 2 /N _{0 H} seconds is generated. A first signal equal to the frequency of one of two color subcarrier frequencies is generated, and a reference frequency (f _S ) which is the other subcarrier frequency different from the one subcarrier frequency and the first signal are generated. generate a second signal having a frequency equal to the sum _of A SECAM signal characterized in that a signal having a frequency _S + 10 _H and a signal having a frequency S + 10 H are obtained, and either one of _S ± 1/α and _S + 10 _H ± 1/α is set as the center frequency for SECAM signal discrimination. Discrimination method.