JP3514897B2 - L-SECAM method discrimination circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an L-SECAM system discriminating circuit suitable for use in VTR reproduction processing.

[0002]

2. Description of the Related Art There are three color transmission systems for TV signals that are broadcast worldwide, PAL / NTSC / SECAM. In the SECAM system, color signals are transmitted by carriers of different frequencies for each line. , FM modulation and superimposing on the luminance signal is adopted.

There are currently two methods for recording this SECAM video signal on a VTR. One is SECAM
A method of dividing a chroma signal into four to convert it to a low frequency chroma signal, which is called an L-SECAM method, and another is a method for processing a SEAL image signal in a PAL VTR recording process. It is called a method. The former is the VTR standard, and the latter is a derivative system for processing by the PAL system VTR.

Therefore, as a method of recording in the VTR, PAL / NTSC / L-SECAM / ME-SEC
There are four types of AM. In the PAL and NTSC systems, the originally broadcast signal is AM modulation, and when converting to low frequency chroma in the VTR, a frequency conversion system is adopted.

In a VTR corresponding to a plurality of such methods, it is necessary to determine which method should be used when reproducing a recorded signal. As mentioned above,
Since the L-SECAM system performs signal processing unique to other systems, the signal processing circuit is also independent of those for PAL and NTSC. Therefore, when the recorded signal is reproduced, whether or not it is the L-SECAM system is performed in the L-SECAM signal processing circuit and is output to a processing circuit that manages the entire system such as a microcomputer. In some cases, the L-SECAM signal processing circuit and the discrimination circuit are separated as a separate chip IC, but even at that time, it is suitable to input the output signal of the L-SECAM processing to the discrimination circuit.
Consider it as an AM playback processing system.

An unmodulated carrier signal inserted for each line is used as the SECAM type discrimination signal. SE
As for the CAM signal, the carrier signal foB on the BY line is 4.
At 25 MHz, the carrier signal foR of the RY line is FM-modulated at 4.40625 MHz, and the unmodulated signal of each line is superimposed on the back porch portion of the video signal. This signal is called the ident signal.

FIG. 8 shows a conventional example of a discrimination circuit of such an L-SECAM signal processing circuit. A signal reproduced by a VTR reproducing circuit (not shown) is input from the L-SECAM signal input terminal 1. The playback processing system of the L-SECAM system is
It is composed of a bell filter, a limiter, a quadruple multiplication circuit, an inverse bell filter and various band pass filters. Here, the quadruple multiplication circuit 2 is shown as a representative. Quadrupling circuit 2
The chroma signal whose frequency is converted to the high frequency range is input to one of the 90-degree phase shifter 10 and the mixer circuit 12,
The output of the 0 ° phase shifter 10 is supplied to the other input of the mixer circuit 12. The mixer circuit 12 inputs the gate pulse GP for punching out the period of the identification signal from the terminal 5, and activates the operation of the mixer circuit 12 only during that period. Further, the mixer circuit 12 has a function of inverting the polarity of mixing the two input signals, and inverts the polarity for each line by the polarity switching 1 / 2fH signal from the terminal 11. The output of the mixer circuit 12 is connected to the constant current source I via the switch 6. Switch 6 is a gate pulse G
Close only for P period. Further, the output of the mixer circuit 12 is connected to the capacitor C and one input of the comparator 8. A constant voltage source 7 having a comparison voltage Vth is connected to the other input terminal of the comparator 8. The output of the comparator 8 is connected to the output terminal 9 as a discrimination signal.

The characteristics of the 90-degree phase shift circuit 10 are shown in FIG.
Specifically, it is a discriminator such as LC resonance. The input / output amplitude characteristic of the phase shift circuit 10 is as shown in (a), and the phase characteristic is as shown in (b). foB and foR
On the other hand, since the phase shift characteristic as shown in (b) is obtained, when the mixer circuit 12 detects the original signal, a positive f is obtained in foB.
With oR, the output is negative.

Further description will be given with reference to FIG. Now, only the identification signal part of the input signal is shown in (a). Only three lines are extracted, in the order foB, foR, foB. At this time, the gate pulse GP is a pulse capable of extracting the identification signal portion as shown in (b),
According to the polarities in FIG. 9, the output current of the mixer circuit 12 is as shown in (c). In (c), the convex represents the charging current for the capacitor C and the concave represents the discharging current. Mixer circuit 1
The 1 / 2fH signal that inverts the polarity of 2 becomes as shown in (d), and the polarity of the mixer circuit 12 is inverted at the concave discharge current portion, so that charging occurs, and the current flowing through the capacitor C eventually becomes as shown in (e). Like The current of the constant current source I also flows into the capacitor C by the gate pulse GP, and the state is shown in (f). As a result, the voltage of the capacitor C gradually rises as shown in (g), and the discrimination signal (h) becomes Hi when the voltage exceeds the comparison voltage Vth of the comparator 8.

The 1 / 2fH signal is composed of a simple flip-flop and may not match the line polarity of the chroma signal. In this case, it is necessary to restore the correct polarity, but at that time, the flip-flop is reset by using a separate error detection circuit.

The operation will be briefly described. When the line polarity of the flip-flop is inverted, the output current of the mixer circuit 12 flows in the line discharge direction.
Contrary to FIG. 10G, the voltage decreases. Another comparator is provided to detect when the voltage drops below a certain level,
Hold the flip-flop only for one line period.
Since the polarity becomes correct from the next line, the detected voltage starts to rise. The operation of this circuit is described in JP-A-3-2.
Since detailed description is given in Japanese Patent No. 10892, the description thereof is omitted here.

If the above circuit is used, the L-SEC
The reproduced signal that has passed through the AM system reproduction processing system is SECA.
It is possible to determine whether or not it is the M method, and it is possible to construct a determination system for a VTR system that supports multiple methods.

The conventional L-SECAM discriminating circuit has a problem that it tends to malfunction due to signals of other systems. Especially ME
-The SECAM signal is recorded by the processing circuit of the PAL system, and the frequency is different for each line. That is, the low frequency conversion frequency is about 812 KHz for the BY line and about 656 KHz for the RY line. In the conventional system, it is easy to detect a signal having a different frequency pattern for each line, and it is easy to make an erroneous determination.

Further, when the signals recorded in the long-time recording mode (EP, LP) are cueed and the special reproduction of the review is performed,
When the magnetic head traces and crosses tracks, the line arrangement of the previous track and the line arrangement of the next track may be reversed. If this skew phenomenon occurs, the line phase of 1/2 fH and the line phase of the input chroma signal are reversed in the conventional discriminating circuit, and it may be impossible to discriminate.

[0015]

DISCLOSURE OF THE INVENTION The above-mentioned conventional L-S
In the ECAM discrimination circuit, not only the signals of other systems are apt to malfunction, but also when the signal recorded in the long-time recording mode is subjected to the cue and special reproduction of the review, a skew phenomenon may occur and the discrimination may be impossible.

The present invention prevents an erroneous operation when a signal recorded by another method is reproduced and also enables an erroneous determination operation for a skew phenomenon to be prevented.
An M type discriminating circuit is provided.

[0017]

In order to solve the above problems, in the L-SECAM system discrimination circuit of the present invention,
Input video signal containing at least low-pass converted chroma signal
Signal is converted to high frequency and output as a video signal containing the original chroma signal.
And 4 multiplication circuit to force converted video signal the high frequency is input
The original chroma signal and the center frequency of the original chroma signal.
A bandpass filter that passes the phase rotation as 0 degree and outputs it, and the highpass- converted video signal and the output signal of the bandpass filter . Belief
A detecting means for obtaining a detection output corresponding to the phase difference of the item, based on the level of the detection output of each obtained by the detection means, the input video signal determination means for determining whether a L-SECAM system It is characterized by including.

By taking such means, L-S
Playback signal of ECAM system and playback signal of other system are LS
When signal processing is performed by the ECAM signal processing circuit, the difference in frequency is remarkable, and by using a bandpass filter that allows the chroma signal to pass at a 0-degree phase that results in synchronous detection at the L-SECAM frequency, L- It is possible to determine the SECAM method.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an input terminal to which a recording signal reproduced by a magnetic head (not shown) and a reproducing system are supplied, and the input terminal 1 inputs the signal to the L-SECAM signal processing circuit. The L-SECAM signal processing circuit includes a bell filter, a limiter circuit, a quadrupling circuit, an inverse bell filter, and various band pass filters. Here, these are described here for the sake of simplicity as in the conventional description. Is represented by a quadruple multiplication circuit 2. The chroma signal supplied to the input terminal 1 is a low-pass converted chroma signal whose frequency is about 1.063 MHz on the BY line.
It becomes 1.102 MHz on the RY line. When these signals are multiplied by 4 and converted to the original chroma signal in the high frequency range, their frequencies are 4.25 MHz and 4.40625 MHz, respectively.
become.

The high-frequency converted signal is input to one input terminal of the bandpass filter 3 and the mixer circuit 4. The output signal of the bandpass filter 3 is connected to the other input terminal of the mixer circuit. A gate pulse GP indicating a detection period is input from the terminal 5 to the mixer circuit 4, and the detection operation is activated only when the gate pulse GP is at the H level. The output of the mixer circuit 4 is connected to the constant current source I via the switch 6. The switch 6 is controlled by the gate pulse GP, and is closed while the gate pulse GP is at the H level. To the output of the mixer circuit 4, the other capacitor C and one input terminal of the comparator 8 are connected. A constant voltage source 7 having a comparison voltage Vth is connected to the other input terminal of the comparator 8. The output of the comparator 8 is taken out from the output terminal 9 as a discrimination signal.

An example of the characteristics of the bandpass filter 3 is shown in FIG. 2, and the description will be continued further. The bandpass filter 3 here has a quadratic function. The amplitude characteristic is (a) and the phase characteristic is (b). The center frequency fo of the bandpass filter 3 is set between the two carrier signals foB and foR of the SECAM chroma frequency. Phase is fo
Since it becomes 0 degrees at, the positive phase rotation occurs at foB and the negative phase rotation occurs at foR. The amount of rotation is less than 90 degrees.

The detection operation will be described with reference to FIG. First, it is assumed that anident signal as shown in FIG. This shows only the identification signal in the 3-line period.
The order is foB, foR, and foB. This identification signal is punched out by the gate pulse GP shown in (b), and detection is performed only during the required identification signal period. Mixer circuit 4
Then, the input / output signal of the bandpass filter 3 is multiplied, but since the phase signal in the range of 0 ° ± 90 ° and the original signal are multiplied in both lines, the synchronous detection direction is obtained, and the positive detection current, that is, the charging current is Output. This is shown in (c). At this time, the constant current source I also flows during the H level period of the gate pulse GP, as shown in (d). The constant current source I is a discharging current, and a difference from the charging current from the mixer circuit 4 flows in the capacitor C. When the current of the mixer circuit 4 is set to be sufficiently larger than that of the constant current source I, the line voltage is charged and the capacitance voltage gradually rises as shown in (e). When the capacitance voltage exceeds the comparison voltage Vth, the comparison output is inverted and the discrimination output becomes Hi as shown in (f).

Next, the prevention of malfunctions with respect to signals of other systems will be described. First, when the recorded method is PAL or NTSC, the chroma signal frequency reproduced by the magnetic head is about 630 KHz, and the L-S
Even if the signal enters the ECAM signal processing circuit and is multiplied by 4, it reaches the bandpass filter 3 at about 2.5 MHz. L-
The frequency is 1.8 MHz lower than that of the SECAM recording signal. In addition, the signal frequency recorded by the ME-SECAM system is different for each line, and as described above, 812/656.
It becomes KHz. When this is subjected to signal processing in the L-SECAM signal processing circuit, it becomes 3.2 / 2.6 MH after being multiplied by 4.
However, it is still lower than the signal of the L-SECAM system by about 1 MHz.

If the filter characteristics of the bandpass filter 3 are set so as not to pass the signals of these other systems, only the L-SECAM signal will be responded, and no malfunction will occur. There are two aspects to the characteristic setting of the bandpass filter 3. One is to increase the Q of the bandpass filter 3 to suppress other system signals in terms of amplitude characteristics, and the other is to set the phase characteristics to 90 degrees at other system signal reproduction frequencies. It is a direction to set the phase shift characteristic. Since Q is also involved in this, by setting Q to an appropriate value as the setting, the ability to eliminate other methods is determined. The higher the Q is, the higher the removal capability is. However, if the Q is too high, the phase shift at the time of reproducing the L-SECAM signal approaches 90 degrees from 0 degree, so that the discrimination sensitivity decreases. Therefore, it is necessary to set Q that balances both. Experimentally, a Q value of about 10 to 16 was good.

As described above, the amplitude and phase characteristics of the bandpass filter 3 prevent the signals of the systems other than L-SECAM from being discriminated, and the L-S which does not discriminate in practical use.
An ECAM discrimination circuit can be constructed. Furthermore, since it is only necessary to detect whether or not there is a signal within the frequency band, it is not necessary to input a 1/2 fH pulse to the mixer circuit 4 and there is no need to invert the detection polarity. To do. Since it is not necessary to detect the pattern of alternating frequencies and invert the polarity for each line, it is possible to perform good method discrimination even in a special situation such as skew.

In the above description, the center frequency fo is L-
Although it has been described that the SECAM signal is multiplied by 4 and set between the two carrier signals foB and foR, all other system signals have low frequencies. Therefore, the frequency of fo is increased to increase the margin for malfunction. Is also possible.

FIG. 4 shows the discrimination sensitivity on the frequency axis.
As shown in. The sensitivity is highest at the center frequency fo of the bandpass filter 3, and the sensitivity decreases as the frequency becomes more peripheral. The sensitivity is zero at frequencies well separated. In actual use, the characteristic that the sensitivity converges to zero may be a problem, so this will be described below.

Now, it is assumed that not the L-SECAM signal but the no-chroma signal is reproduced (raw tape, monochrome recording, etc.). Ignoring luminance signal leakage in the chroma band, L-S
All the noise generated in the ECAM signal processing circuit passes through to the bandpass filter 3. The L-SECAM signal processing circuit includes various band pass filters, and the noise band is almost equal to the chroma band. If this noise level is too high, this may be mistakenly recognized as a chroma signal and L-SECAM discrimination may be performed. In order to avoid this, the constant current source I may be increased to increase the discharge current and reduce erroneous discrimination at the time of noise input.

Another embodiment of the present invention in which the malfunction caused by the noise is improved will be described with reference to FIG. This embodiment shows only the bandpass filter of FIG. 1, and the other configurations are all the same as those of the embodiment of FIG. The bandpass filter 3 is configured by a two-stage cascade connection of secondary bandpass filters 3a and 3b.

FIG. 6 shows the characteristics of a fourth-order bandpass filter that is a combination of the bandpass filters 3a and 3b. The amplitude characteristic is (a) and the phase characteristic is as shown in (b). Although the second-order band-pass filter is described in FIG. 2, the amplitude suppression effect is steep because of the fourth-order in FIG. Further, the phase characteristic also rotates 180 degrees in FIG.
Then rotate 360 degrees. In any case, the center frequency fo
Signal is passed at 0 degrees, and the phase shift amount is 0 to less than 90 degrees at the frequencies of the carrier signals foB and foR.

As described above, the operation for discriminating the L-SECAM recording signal is not changed at all, and the discrimination sensitivity for the signal outside the L-SECAM chroma band can be lowered. FIG. 7 shows the detection sensitivity on the frequency axis. Figure 4
In FIG. 7, it converges to zero as the distance from the center frequency fo increases, but in FIG. 7, it is possible to obtain a negative sensitivity for discriminating that it is not L-SECAM. At a signal frequency sufficiently separated from the center frequency fo, the phase is 1 as shown in FIG. 6 (b).
Since it rotates by 80 degrees, the output of the mixer circuit 4 becomes negative synchronous detection and a discharge current is output.

Therefore, the capacitance voltage decreases and L-SECA
It operates in the direction not discriminated as M. In the case of this embodiment, since the mixer circuit 4 itself supplies the discharge current to the out-of-band signal, the current of the constant current source I may be small and can be deleted.

This operation does not cause a malfunction with respect to other system signals, and the detection band can be made narrower than that in FIG. 1, so that the malfunction is prevented even with noise. The bandpass filters 3a and 3b may have different Qs. One has a high Q of about 10 to 16 in order to set the phase characteristics near fo, and the other has a low Q of about 2 to 5 to contribute only to rotate the out-of-band phase. If set,
Performance can be defined concisely. Further, the center frequency f of the low Q band pass filter and the high Q band pass filter is
It is also possible to shift by setting o.

As described above, if the phase rotation around fo is set by the high-Q bandpass filter, it is desirable that the center frequency fo is set between the carrier signals foB and foR as described above. In a low-Q bandpass filter, assuming that a malfunction suppression range for noise and other system signals is set, the carrier signal fo has a direction superior to other systems, that is, the carrier signal f.
It should be set to a frequency higher than the middle between oB and foR.

By the way, the quadratic type has the smallest circuit configuration of the bandpass filter, and the quadratic type is superior in cost. By connecting these in cascade connection in multiple stages, the characteristics of the bandpass filter can be changed in various ways, which is convenient in terms of variations. Although the fourth-order bandpass filter is used as an example in the embodiment of FIG. 5,
The present invention is not limited to this, and can be realized by using a higher-order bandpass filter by connecting more stages.

[0036]

As described above, the L-S of the present invention is
By using the ECAM system discriminating circuit, not only the malfunction can be prevented even when the signal recorded by another system is reproduced, but also the mis-discriminating operation for the skew phenomenon can be prevented.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of the present invention.

FIG. 2 is a characteristic diagram for explaining a characteristic example of the bandpass filter in FIG.

FIG. 3 is a signal waveform diagram for explaining the operation of FIG.

FIG. 4 is an explanatory diagram for explaining sensitivity characteristics of the circuit of FIG. 1.

FIG. 5 is a circuit configuration diagram for explaining another embodiment of the present invention.

6 is a characteristic diagram for explaining a characteristic example of the fourth-order bandpass filter in FIG.

FIG. 7 is an explanatory diagram for explaining sensitivity characteristics when the circuit of FIG. 5 is used.

FIG. 8 is a circuit configuration diagram for performing system discrimination of a conventional L-SECAM system.

9 is an explanatory diagram for explaining a characteristic example of the 90-degree phase shift circuit in FIG. 8;

10 is a signal waveform diagram for explaining the operation of FIG.

[Explanation of symbols]

1 ... Input terminal, 2 ... 4 multiplication circuit, 3, 3a, 3b ... Band pass filter, 4 ... Mixer circuit, 5 ... Terminal, 6 ... Switch, 7 ... Constant voltage source, 8 ... Comparator, 9 ... Output terminal, I
… Constant current source, C… Capacitor.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04N 9/44-9/898

Claims (4)

(57) [Claims] 1. An L-SECAM system discrimination circuit in a signal processing circuit for performing L-SECAM system signal processing.
The input video signal containing at least the low-pass converted chroma signal.
Signal is converted to high frequency and output as a video signal containing the original chroma signal.
And 4 multiplication circuit to force converted video signal the high frequency is input, the original chroma
The signal is phase rotated at the center frequency of the original chroma signal.
Bandpass filter for passing and outputting as 0 degree , high-pass converted video signal, and bandpass filter
Detection means for obtaining a detection output according to the phase difference of each signal multiplied by the output signal of the output signal and the level of each detection output obtained by the detection means. An L-SECAM system discriminating circuit comprising: a discriminating means for discriminating whether or not the system is the L-SECAM system. Wherein said band-pass filter is a second order band pass filter, the center frequency 4.25M
It is higher than Hz, L-S according to claim 1.
ECAM system discrimination circuit. 3. The L-SECAM system discriminating circuit according to claim 1, wherein the bandpass filter is a bandpass filter group in which secondary bandpass filters are connected in cascade. 4. The L-SECAM system discrimination circuit according to claim 3, wherein the Q and the center frequency of each of the second-order bandpass filters are set to different values.