JPH0628466B2 - Signal playback device - Google Patents

Description

The present invention relates to a signal reproducing apparatus, for example, when recording a color signal of a color video signal on a recording medium by a line-sequential method and then reproducing the same, each horizontal scanning is performed. It is possible to discriminate which of the two types of color signals, for example, the two types of color difference signals of RY and BY, without delay, and to mix them from the line-sequential color difference signals without intermingling with each other. The present invention relates to a technique for extracting two types of color difference signals in parallel.

<Prior Art> In France and the like, a line-sequential television system called a SECAM system has been standardized. In this SECAM method, two color difference signals BY and RY are alternately switched for each horizontal scanning period, and each of them has a slightly different frequency.
A carrier video signal is formed by frequency-modulating with one subcarrier and superimposing it on the luminance signal. Therefore, in the demodulation system of the carrier video signal, the color difference signals R-Y and B-Y which are lost for each horizontal scanning period are obtained by extracting the signal delayed for one horizontal scanning period and the signal other than that in parallel. Two independently continuous color difference signals R-Y and BY are obtained by supplementing the color difference signals R-Y and BY before one horizontal scanning period. Therefore, the demodulation system is provided with a switch for alternately extracting a signal delayed by one horizontal scanning period and a signal not so. Extracting two types of color signals in parallel in this way is called synchronization, and a switch therefor is called a synchronization switch.

The synchronization switch in the SECAM system is switched as follows. That is, two color difference signals R-Y,
When a line-sequential color signal is obtained from BY, the frequency of the sub-carrier for each horizontal scanning period is made different, and the demodulation system determines which of the color difference signals RY or BY based on the frequency difference. A signal for discrimination is created, and the synchronization switch is switched by this discrimination signal.

In the case of making a discrimination signal from the frequency difference of subcarriers, conventionally, a discrimination signal is produced by passing a burst signal in parallel through two narrow band bandpass filters and detecting the magnitude of the filter output.

<Problems to be Solved by the Invention> In this case, the band of the bandpass filter must be made as narrow as possible in order to extract each subcarrier accurately and separately from each other without being affected by noise or the like.

However, as the band is narrowed, the output of the filter is significantly delayed, so that the switching timing of the synchronization is delayed and the other color difference signal enters the next in the middle of one color difference signal. Occurs.

Such a problem is not limited to the television system by SECAM, and two color difference signals are line-sequentially and two sub-carriers having slightly different frequencies are FM-modulated by the respective color difference signals. Of course also occurs in the case of frequency-division-multiplexing (FDM) with an FM luminance signal obtained by FM-modulating the main carrier wave with the luminance signal, and recording and then reproducing.

The present invention solves the problems caused by the above-described filtering, provides a device that can determine the types of color signals with almost no delay and can simultaneously synchronize two types of color signals from line-sequential color signals without mutual mixing. The purpose is to do.

<Means for Solving the Problems> [I] The signal reproducing apparatus according to the first aspect of the present invention synchronizes all modulated line-sequential color signals in general, and two types of color signals form one horizontal scanning period. A single demodulation means for demodulating a line-sequential color signal which is alternately selected for each time and is modulated such that the potentials in the horizontal blanking period after demodulation are different between the two types of color signals; Line-sequential color signal is input, the signal level in the horizontal blanking period is detected to determine the type of color signal, and the demodulated line is detected according to the determination result of the line-sequential determination means. And a synchronization unit that sequentially outputs color signals by dividing them into two signals.

[II] A signal reproducing device according to the second invention is intended for synchronizing modulated line-sequential color signals which are frequency-multiplexed with a modulated luminance signal and recorded on a recording medium. And the line-sequential color signal in which the potentials in the horizontal blanking period after demodulation are modulated so as to be different from each other. Means for reproducing the recording medium on which the frequency signal and the recorded luminance signal are frequency-multiplexed, separating means for separating the modulated line-sequential color signal from the reproduced signal, and demodulating the separated line-sequential color signal. Single demodulation means, input the demodulated line-sequential color signal, and detect the signal level in the horizontal blanking period to determine the type of color signal, and line-sequential determination means Depending on the result, demodulated line-sequential color Characterized in that it comprises a and a synchronizing means for outputting in two signal No..

[III] As an example of an embodiment of the line-sequential discriminating means, first and second sample-hold circuits for inputting a demodulated line-sequential color signal, and a pulse given every horizontal scanning period And a sampling circuit that divides the frequency by 2 and outputs a sampling pulse that is triggered in synchronization with the rising timing of the output signal of the frequency divider circuit and that activates the first sample and hold circuit within the horizontal blanking period. First to do
Second sampling pulse generating circuit and a second sampling pulse which is triggered in synchronization with the falling timing of the output signal of the frequency dividing circuit to output a sampling pulse for operating the second sample and hold circuit within the horizontal blanking period.
Sampling pulse generator circuit, a comparator for comparing the magnitude of the output signals of the first and second sample and hold circuits, and the exclusive OR of the output signal of the comparator and the output signal of the frequency divider circuit, And an exclusive OR gate for activating the synchronization means by the output signal of the calculation result.

[IV] As another example of an embodiment of the line-sequential determining means, a reset terminal is provided, and a pulse given every one horizontal scanning period is divided into two, and the synchronizing means is divided by the divided output signal. The frequency divider circuit to be operated, the clamp pulse generator circuit that is triggered in synchronization with either the rising or falling edge of the output signal of the frequency divider circuit, and outputs the clamp pulse within the horizontal blanking period, and the demodulation circuit. The clamp circuit that clamps the generated line-sequential color signal to a predetermined potential when a clamp pulse is input, and the clamped line-sequential color signal is used for at least the clamped horizontal blanking period of each horizontal blanking period. Immediately after, the sampling circuit that performs sampling in the horizontal blanking period and the sampling value obtained by the sampling circuit are compared with the reference value, and the sample value is larger than the reference value. If squid small or of a predetermined one condition is satisfied, there is one having a reset pulse generating circuit for outputting a reset pulse to the reset terminal of the frequency divider circuit, the.

[V] Further, as an example of the reset pulse generating circuit in the line-sequential discriminating means of the above [IV], a differential amplifier that differentially amplifies the output signal of the sampling circuit and the first signal of a constant level, and a difference amplifier A switch that alternately selects the output signal of the dynamic amplifier and the second signal of a constant level at a timing that coincides with the sampling pulse of the sampling circuit, and the output signal of this switch or a signal proportional to this output signal as the sample value. And a comparator that compares with a reference value.

[VI] Furthermore, as an example of the sampling circuit in the line-sequential discriminating means of the above [IV], the sampling pulse and the clamp pulse generation circuit triggers at the rising or falling timing of the output signal of the frequency dividing circuit. There is a sampling pulse generating circuit that outputs a pulse for operating the sampling switch within the horizontal blanking period immediately after the clamped horizontal blanking period, which is triggered in synchronization with the timing of the non-driving. In this case, the reset pulse generation circuit may have a comparator that compares the value of the sampling pulse period with the reference value.

<Operation> In the first invention, when the modulated line-sequential color signal is demodulated by the single demodulating means, the potential of the demodulated line-sequential color signal in each horizontal blanking period and the type of the color signal are changed. Different.
Therefore, by detecting the signal level in the horizontal blanking period, the SECAM using the narrow band bandpass filter is obtained.
Compared with the method, the type of color signal can be discriminated with almost no delay, and the synchronizing means operates according to the discrimination result to prevent the color signals from being mixed with each other.

In the second invention, since the modulated luminance signal and the modulated line-sequential color signal are frequency-multiplexed and recorded on the recording medium, the modulated line-sequential color signal is separated from the reproduction signal of the recording medium. After that, this is demodulated by a single demodulation means. The subsequent operation is the same as that of the first invention.

As can be seen from the above description, the modulation system may be either the FM modulation system or the PM modulation system, and in the demodulated line-sequential color signal, the potentials in each horizontal blanking period are different between the two types of color signals. If applicable, it can be applied. Also, 2
The type of color signal is not limited to the RY and BY color difference signals. Further, the present invention can be applied not only to the television system but also to various recording systems such as a VTR and a rotary disc device.

<Examples> Hereinafter, the present invention will be described with reference to the drawings. It is to be noted that FIG. 1 shows an example of a simplified configuration of a line-sequential magnetic recording system for reference, FIG. 2 shows an example of the simplified configuration of the reproducing system for reference, and FIG. Examples are given for reference along with related signals and these are briefly described in advance.

In FIG. 1, as an example of a magnetic recording system, 1 is an input terminal for a luminance signal Y, 2 is an input terminal for one color signal, for example, RY, and 3 is an input terminal for the other color signal, for example, BY. Is an FM modulator whose carrier wave is about 7 MHz, 5 is a 1.2 MHz carrier wave
FM modulator, 6 is an FM modulator whose carrier wave is 1.3 MHz, 7
Is a line-sequential switch, 8 is an adder circuit, 9 is a recording amplifier, 10 is a recording head, and 11 is an input terminal for a switch control signal. The switch control signal is generated based on a horizontal drive signal (a so-called HD pulse) generated at each horizontal scanning period, that is, at each start edge of 1H, and is an on / off signal that repeats rising and falling every 1H, that is, 1 / 2f _H Signal (f _H is a horizontal scanning frequency).

As an example of a reproducing system, in FIG. 2, 12 is a reproducing head, 13 is a head amplifier, 14 is a high-pass filter for separating FM luminance signals, 15 is an FM demodulator for luminance signals, and 1
6 is a low-pass filter for FM line sequential color difference signal separation, 1
7 is a single FM demodulator for line-sequential color difference signals, 18 is 1H
A delay line, 19 is a synchronization switch, and 20 is an input terminal for the discrimination signal ID.

Now, the demodulated line-sequential color difference signal LSS repeats RY and BY in the order shown in FIG. 3 (a), and in BY, the potential V _{H of the} horizontal blanking period HBLK _BY. Is higher than the potential _VL of the horizontal blanking period HBLK _R-Y of _RY . It is also assumed that the level of the discrimination signal ID changes to, for example, "0" or "1" in response to the repetition of BY and RY as shown in FIG. 3 (b). Then, Fig. 3
As shown in (c) and (d), the contacts 19a, 19b, 1 of the synchronization switch 19 are associated with "0" and "1" of the discrimination signal ID.
By turning on / off 9c and 19d, two continuous color difference signals in which RY and BY are separated from each other can be obtained. However, the change point of the discrimination signal is the same as the change point during recording.

<First Embodiment> An embodiment of the present invention will be described with reference to FIGS. 11, 12, and 13.

FIG. 11 shows a line-sequential discriminating circuit according to an embodiment of the present invention. In the figure, reference numeral 21 is an input terminal of the demodulated line-sequential color difference signal LSS, which inputs the output signal of the FM demodulator 17 shown in FIG. 28 is an input terminal for a pulse generated in the horizontal blanking period for every 1H, for example, an HD pulse, 50 and 51 are sample and hold circuits, 52 is a frequency dividing circuit that divides the input pulse HD by 2, 53 and 54 are sampling pulse generation A circuit, 55 is a comparator, and 56 is an exclusive OR gate. The hold time of the two sample and hold circuits 50 and 51 is set to 2H, and the sampling pulses SP _a and SP _b are supplied to the sampling pulse generation circuits 53 and 53, respectively.
Each time it is input from 54, the line-sequential color difference signal LSS is sampled and held for 2H. The sampling pulse generating circuits 53 and 54 generate sampling pulses SP _a and SP _b by the output pulse of the frequency dividing circuit 52. This frequency dividing circuit 52 does not need a reset function, and it is sufficient to simply divide the HD pulse by two. Therefore, the two sampling pulse generating circuits 53 and 54 alternately sample the sampling pulses SP _a and SP every 1 H in each horizontal blanking period.
_b is generated. As both circuits 53 and 54, here, a rising trigger monostable multivibrator and a falling trigger monostable multivibrator are used, and both are triggered by the terminal output of the frequency dividing circuit 52. The comparator 55 inputs the output of one sample-hold circuit 50 to the plus input terminal and the output of the other sample-hold circuit 51 to the minus input terminal, compares the magnitudes of both signals, and the voltage at the plus input terminal is Outputs "1" when it is larger than the minus input terminal,
In the opposite case, "0" is output. The exclusive OR gate 56 performs an exclusive OR operation between the output of the comparator 55 and the output of the frequency divider circuit 52, and outputs the logical result as a discrimination signal ID to the terminal 29 to output the synchronization switch shown in FIG. 19
Operate.

Here, the line-sequential color-difference signal LSS is one in which two types of color-difference signals R-Y and B-Y are alternately selected based on the HD pulse, and in B-Y, the horizontal blanking period H thereof is selected.
BLK _B-Y potential V _H is R-Y horizontal blanking period H
It is assumed that it is higher than the potential V _L of BLK _R−Y . The output of the frequency dividing circuit 52 is an inverted output of the HD pulse divided by 2, and the "1" level period of this output corresponds to the RY signal and the "0" level period corresponds to the BY signal. There are two states, that is, the case where the output "0" level period corresponds to the RY signal and the case where the output "1" level period corresponds to the RY signal, and the correspondence relationship is not always constant. . On the other hand, for the discrimination signal ID, the synchronization switch is operated to convert the line-sequential color difference signal LSS into two color difference signals R-Y and BY.
Is to be separated without being mixed in the
The "1" level period of the discrimination signal ID always corresponds to the RY signal, and the "0" level period always corresponds to the BY signal.

In FIG. 12, assuming that the line-sequential color difference signal LSS and the terminal output of the frequency dividing circuit 52 have a correspondence relationship shown in FIGS. 12 (a) and 12 (b), two sampling pulses SP _a ,
The correspondence between SP _b and the line-sequential color difference signal LSS is shown in the same figure.
It becomes like (c) and (d). According to this sampling, R
If towards the potential V _L towards -Y is lower than the potential V _H towards B-Y, always lower voltages towards R-Y is inputted to the positive input terminal of the comparator 55, the opposite Since the higher voltage of BY is always input to the minus input terminal, the output of the comparator 55 is always "0". Therefore, the exclusive OR of the output of the comparator 55 and the terminal output of the frequency dividing circuit 52 gives the signal of FIG. This signal is the discrimination signal ID. As can be seen from the comparison of FIGS. 12 (a) and 12 (e), when the discrimination signal ID is "1", it corresponds to the RY signal, and when it is "0", it is B-. Corresponds to the Y signal.

On the other hand, as shown in FIG. 13, for some reason, for example, noise causes the timing of synchronization to change, and the correspondence relationship between the line-sequential color difference signal LSS and the terminal output of the frequency dividing circuit 52 is shown in FIGS. Let us consider a case in which it is reversed from b) and becomes as shown in FIGS. 13 (a) and 13 (b). If left as it is, the output of the synchronization switch 19 is switched between the RY color difference signal and the BY color difference signal. However, according to the present invention, in this case, the correspondence relationship between the two sampling pulses SP _a and SP _b and the line-sequential color difference signal LSS is also reversed as shown in FIGS. 13 (c) and 13 (d). Therefore, the output of the comparator 55 is always "1". Therefore, if the exclusive OR of the output of the comparator 55 and the terminal output of the frequency dividing circuit 52 is taken, the 13th
The signal shown in FIG. 6E is obtained from the gate 56 as the discrimination signal ID. Comparing FIGS. 13 (a) and 13 (e), when the discrimination signal ID is "1", it corresponds to the RY signal, and when the discrimination signal ID is "0", it corresponds to the BY signal. . This correspondence is the same as in the case of FIGS. 12 (a) and 12 (e).

That is, the output of the exclusive OR gate 56 can be used as a determination signal for activating the synchronization switch 19 shown in FIG. Incidentally, instead of the terminal output of the frequency dividing circuit 52, its Q terminal output is given to the exclusive OR gate 56,
The same can be said when the sampling pulse generating circuits 53 and 54 are applied, and the determination signals "1" and "0" and the RY and BY signals are maintained in a fixed correspondence relationship.

In the embodiment described above, the types of color difference signals are discriminated by mutually comparing the potentials in the respective horizontal blanking periods. Therefore, there is almost no delay in the discrimination, as compared with the case of discriminating based on the frequency difference using a filter.

<Second Embodiment> Next, a line-sequential discriminating circuit according to another embodiment of the present invention will be described with reference to FIG.

In FIG. 4, reference numeral 21 denotes a demodulated line-sequential color difference signal L.
SS input terminal, 22 clamp circuit, 23 sampling switch, 24 sampling pulse SP input terminal, 25 reset pulse generating circuit, 26 reference voltage V
A setting terminal of _ref , 27 is a frequency dividing circuit using a flip-flop F / F, 28 is an input terminal of a pulse given every 1H, for example, an HD pulse, 29 is an output terminal of a discrimination signal ID, and 30 is a monostable multivibrator M. It is a clamp pulse generation circuit using / M.

The operation of the line-sequential discriminating circuit shown in FIG. 4 will be described. now,
The line-sequential color difference signal LSS entering the clamp circuit 22 is shown in FIG.
As shown in (a), it starts from the RY color difference signal and
It is assumed that the potential V _H during the horizontal blanking period of the BY color difference signal is higher than the potential V _L during the horizontal blanking period of the −Y color difference signal, and is also shown in FIG. It is assumed that the HD pulse generated in the horizontal blanking period is input to the frequency dividing circuit 27. Further, when the first color difference signal R-Y ₁ is input and the first pulse HD ₁ is input, the terminal output of the frequency dividing circuit 27 happens to rise to “1” as shown in FIG. 5 (d), Clamp pulse generation circuit 3 by this terminal output
Suppose 0 is triggered. Then, by appropriately selecting the time constant, the clamp pulse CP ₁ is output to the Q terminal of the clamp pulse generating circuit 30 within the horizontal blanking period as shown in FIG. 5 (e). As a result, the potential of the first horizontal blanking period HBLK ₁ is not always the clamp potential V
_cp . On the other hand, the sampling pulse SP is shown in FIG.
If given every 1H as in (c), the sample value obtained by the first sampling pulse SP ₁ is the clamp potential V _{cp as} shown in FIG. 5 (f). Also,
For simplicity, the reset pulse generation circuit 25 outputs the reset pulse by directly comparing the input voltage with the reference voltage V _ref, and outputs the reset pulse only when V _ref <input voltage (Equation (1)). Set it. Therefore, by setting the clamp potential so that V _cp <V _ref (Equation (2)),
There is no reset pulse in the first sampling. Therefore, even if the second pulse HD ₂ is input to the frequency dividing circuit 27, the terminal output only falls and the clamp pulse is not output. Regarding the potential of the next horizontal blanking period HBLK ₂ , the potential V _H during the horizontal blanking period of BY is R− as described above.
Y and it was higher than the potential _{V L} in the horizontal blanking period, since clamping the HBLK ₁ corresponding with the clamp potential _{V cp} for the first color difference signal _{R-Y 1,} HBLK
_It becomes higher than the clamp potential V _{cp of 1} . Therefore, since the sample value obtained by the _second sampling pulse SP ₂ is V _cp + (V _H −V _L ), reset so that V _ref <V _cp + V _H −V _L (Equation (3)) is also satisfied. By setting the reference voltage V _ref of the pulse generation circuit 25, when the sampling switch 23 is turned on, the reset pulse RP is output as shown in FIG. 5 (g). When this reset pulse is output, the terminal output of the frequency dividing circuit 27 immediately rises. As a result, the second clamp pulse CP ₂
Occurs and the potential of HBLK ₂ is clamped. Next, even if the third pulse HD ₃ is input to the frequency dividing circuit 27, the terminal output only falls and the clamp pulse is not output.
The potential of LK ₃ is not clamped. However, sample values obtained by the third sampling pulse SP ₃ from which the potential of the HBLK ₂ immediately before is clamped to _{V cp,} V cp - a _(V H -V _L). Since V _H > V _L and the formula (2), V _cp −V _H + V _L <V _ref ... Formula (4) is established, so that the reset pulse is not generated this time. Next, when the fourth pulse HD ₄ is input to the frequency dividing circuit 27, the terminal output rises, the clamp pulse CP ₃ is generated, and the potential of HBLK ₄ which is the color difference signal of BY is clamped. In this state, the sampling switch 23 is turned on and the reset pulse generating circuit 25 receives the clamp potential V
_{Even if cp} is input, the reset pulse does not occur because V _cp <V _ref . After that, the same thing is repeated,
The type of color difference signal and the level of the terminal output of the frequency dividing circuit 27 completely correspond to each other after BY- ₂ . Therefore, by inputting the Q terminal output of the frequency dividing circuit 27 shown in FIG. 5 (h) to the discrimination signal input terminal 20 of FIG. 2, when the first color difference signal is input, the correspondence relationship with the type of color difference signal is obtained. No. does not match and the output of the frequency dividing circuit 27 is either "1" or "0", the discrimination signal ID corresponding to the line-sequential color difference signal shown in FIG. 3B is obtained after 2H. . Further, even if a dropout occurs during the continuation of the determination, the determination signal ID correctly corresponds to the line-sequential color difference signal after the end 2H of the dropout.

In the above description of the operation, the reset pulse generation circuit is assumed to directly compare the input sample value with the reference potential V _ref and to output the reset pulse when the expression (1) is satisfied. The relationship of (3) became necessary.
However, if the input voltage <V _ref ... Equation (5) is used as the condition for reset pulse generation instead of Equation (1), If it is set so that the relationship between the terminal output of the frequency dividing circuit 27 and the type of color difference signal is reversed from the case described above. Further, even if the setting of the magnitude relation of the potentials in each horizontal blanking period is reversed, the relation between the terminal output of the frequency dividing circuit 27 and the type of the color difference signal only reverses to the case described above. Furthermore, it is not always necessary to directly compare the sampled value with the reference potential, and usually an amplifier etc. is inserted in the middle,
In many cases, a voltage or current proportional to the sample value is compared with a reference value.

<Third Embodiment> As an application of the embodiment of FIG. 4, an embodiment in which a current proportional to a sample value is compared with a reference value will be described with reference to FIGS. 6 and 7. The clamp pulse CP may be output during the horizontal blanking period, so the frequency dividing circuit 2
The clamp pulse generating circuit 30 may be triggered in synchronization with the falling timing of the terminal output of No. 7. Further, instead of the terminal output of the frequency dividing circuit 27, it is possible to trigger with the Q terminal output, and it is also possible to output the discrimination signal ID from the terminal.

In FIG. 6, a differential amplifier 31, a changeover switch 32,
The constant current circuit 33, the current mirror circuit 34, the comparator 35, and the current detecting resistor R form a reset pulse generating circuit 25. Others are the same as the circuit of FIG. The operation will be described with reference to FIG. However,
In contrast to FIG. 5, FIG. 7 shows that the waveform of FIG.
It is different from the one in Fig. (F), but for the sake of simplicity of explanation, the other two diagrams (a), (b), (c), (d), (e), (g) ) And (h) are the same. That is, it is assumed that V _H > V _L and that the terminal output of the frequency dividing circuit 27 happens to rise to “1” when the color difference signal of RY ₁ is input. Therefore,
The potential of the first horizontal blanking period HBLK ₁ is clamped to V _cp . On the other hand, the sampled signal is applied to the input terminal of the differential amplifier 31. The output of the differential amplifier 31 is given to one contact A of the changeover switch 32, and is supplied to the current mirror circuit 34 through this switch 32 only during the sampling period. The constant current circuit 33 is connected to the other contact B of the changeover switch 32, and the constant current circuit 33 is connected to the current mirror circuit 34 except during the sampling period. The current mirror circuit 3 is provided in the comparator 35.
The terminal voltage E _R of the resistor R connected to the output of No. 4 is given and compared in magnitude with the reference voltage V _ref . If V _ref voltage _{E R} due to the resistance R than small, the reset pulse RP is output from the comparator 35. by the way,
A constant voltage E _b is applied to the other input terminal of the differential amplifier 31, and even if the clamp potential V _cp is sampled and input, it is slightly less than the constant current circuit 33, but almost the same amount from the current mirror circuit 34. It can absorb electric current. Therefore, even if the potential of HBLK ₁ clamped by the first clamp pulse CP ₁ is sampled, the inter-terminal voltage E _R of the resistor R hardly decreases and the bias voltage is set to be sufficiently higher than the reference voltage V _ref. E _b
And the reference voltage V _ref are selected. As a result, no reset pulse is generated. Therefore, no clamp pulse is output even if the _second pulse HD ₂ is input to the frequency dividing circuit 27. Therefore, when the sample value V _cp + (V _H −V _L ) obtained by the second sampling pulse SP ₂ is applied to the differential amplifier 31, the output current is greatly reduced and the terminal voltage ER of the resistor _R is more than V _ref . The bias voltage E _b and the reference voltage V _ref are further selected so as to be sufficiently small. If E _b and V _ref are selected in this way, a reset pulse is generated in the second sampling, and HBLK ₂
Potential is clamped. Then the third pulse HD ₃
Is not clamped because the terminal output falls even when it enters the frequency dividing circuit 27. The potential of HBLK ₃ is V _cp − (V
_Since it is ( _H - _VL ), no reset pulse is issued. When the fourth pulse HD ₄ enters the frequency dividing circuit 27, the potential of HBLK ₄ is clamped and the reset pulse is not issued. The same applies thereafter, and the Q terminal output or terminal output of the frequency dividing circuit 27 can be used as the discrimination signal ID. Since the current mirror circuit 34 is used for expanding the dynamic range, it is basically unnecessary.

<Fourth Embodiment> FIG. 8 shows a more specific embodiment of the circuit of FIG.
In FIG. 8, the transistors 36 and 41 and the capacitor 48 form the clamp circuit 22. Transistor 3
Reference numeral 9 corresponds to the sampling switch 23, and the transistors 39 and 40 are turned on / off in reverse, and correspond to the changeover switch 32. Further, the transistors 41 and 42 form the differential amplifier 31, and the transistors 44 and 45 form the current mirror circuit 34.
The three resistors 46, 47 and 38 provide the differential amplifier 31 with an appropriate bias voltage E _b . In addition, as an example, the constant current circuit 33 flows 2 mA, the current detection resistor R is 2 KΩ, and the inter-terminal voltage E _R of this resistor R drops from the steady state of 4 V to 2 V at the second sampling. Has become. In FIG. 8, the capacitor 48 is for cutting direct current.

<Fifth Embodiment> The sampling pulse may be generated at a timing opposite to that of the clamp pulse generating circuit 30. For example, if the clamp pulse is generated at the rising edge of the output signal of the frequency dividing circuit 27, the sampling pulse may be generated at the falling edge of the same signal. An example of such an arrangement is shown in FIG. In FIG. 9, 21 is an input terminal for the line-sequential color difference signal LSS, 22 is a clamp circuit, 23 is a sampling switch, 25 is a reset pulse generating circuit, 27 is a frequency dividing circuit, 28 is an HD pulse input terminal, and 29 is a discrimination. Signal ID
Is a clamp pulse generating circuit, and 49 is a sampling pulse generating circuit. The clamp pulse generating circuit 30 uses a monostable multivibrator that is triggered by the rising edge of the terminal output of the frequency dividing circuit 27, while the sampling pulse generating circuit 49 uses the frequency dividing circuit 27.
It uses a monostable multivibrator that is triggered by the falling edge of the terminal output. Of course, frequency divider 2
It is also equivalent to use a monostable multivibrator triggered by the rising edge of the Q terminal output of 7. Note that the sampling pulse must not be so wide as to exceed the horizontal blanking period. The output of the sampling switch 23 is given to the comparator 35. So comparator 3
5, the reset pulse RP can be obtained only by comparing the output level when the sampling switch 23 is turned on with the reference voltage V _ref . Other points of the circuit operation are the same as those in FIGS. 4, 6 and 8. First
FIG. 0 shows the operation waveform of each part in FIG.

In each of the embodiments shown in FIGS. 4, 6, 8 and 9 described above, the potential in the horizontal blanking period immediately after the clamped horizontal blanking period is directly or indirectly compared with the reference value. By doing so, the type of color difference signal is determined. This method has an advantage that an extremely accurate determination can be performed regardless of the pattern by clamping the potential in the horizontal blanking period immediately before the determination. Of course, since the determination is performed by using the potential in the horizontal blanking period, it can be said that there is almost no delay in the determination as compared with the case where the frequency difference is determined using a filter.

<Effects of the Invention> As described above in detail, according to the present invention, the potential of the demodulated line-sequential color signal in each horizontal blanking period differs depending on the type of color signal. Since the color signal is discriminated by detecting the potential, the color signal can be discriminated correctly without delay.

[Brief description of drawings]

FIG. 1 is a simplified block diagram of a magnetic recording system shown as an example of a line-sequential system, FIG. 2 is a simplified block diagram of its reproducing system, FIG. 3 is an operation explanatory diagram of each part in FIG. 2, and FIG. FIG. 5 is a circuit diagram of one embodiment (second embodiment) of the invention, FIG. 5 is an operation explanatory diagram of each part in FIG. 4, and FIG. 6 is a circuit showing one embodiment (third embodiment) of a reset pulse generation circuit. FIG. 7 is a diagram for explaining the operation of each part in FIG. 6, and FIG. 8 is a more specific example of FIG.
FIG. 9 is a circuit diagram of another embodiment (fifth embodiment), and FIG. 10 is an operation explanatory view of each part in FIG.
FIG. 11 is a circuit diagram showing an embodiment (first embodiment) of the present invention, and FIGS. 12 and 13 are operation explanatory views of respective parts of FIG. In the drawing, 22 is a clamp circuit, 23 is a sampling switch, 25 is a reset pulse generation circuit, 27 is a frequency divider circuit with a reset terminal, 30 is a clamp pulse generation circuit, 31 is a differential amplifier, 32 is a changeover switch, and 33 is a constant switch. A current source, 35 is a comparator, 49 is a sampling pulse generating circuit, 50 and 51 are sample and hold circuits, 52 is a frequency dividing circuit, 53 and 54 are sampling pulse generating circuits, 55 is a comparator, and 56 is an exclusive OR gate. is there.

Claims (6)

[Claims] 1. Two types of color signals are alternately selected every horizontal scanning period, and the potential is 2 during the horizontal blanking period after demodulation.
A single demodulation unit that demodulates line-sequential color signals that are modulated differently among different types of color signals, and the demodulated line-sequential color signal is input, and the signal level during the horizontal blanking period is detected. And a line-sequential discriminating means for discriminating the type of the color signal, and a synchronizing means for dividing the demodulated line-sequential color signal into two signals and outputting the signals according to the discrimination result of the line-sequential discriminating means. Signal reproduction device. 2. The signal reproducing apparatus according to claim 1, wherein the line-sequential discriminating means includes first and second sample-hold circuits for inputting demodulated line-sequential color signals. It is triggered in synchronization with the rising timing of the output signal of the frequency dividing circuit and the frequency dividing circuit which inputs the pulse given every horizontal scanning period, and the first sample 1st which outputs the sampling pulse which operates a hold circuit
Second sampling pulse generating circuit and a second sampling pulse which is triggered in synchronization with the falling timing of the output signal of the frequency dividing circuit to output a sampling pulse for operating the second sample and hold circuit within the horizontal blanking period.
Sampling pulse generator circuit, a comparator for comparing the magnitude of the output signals of the first and second sample and hold circuits, and the exclusive OR of the output signal of the comparator and the output signal of the frequency divider circuit, An exclusive OR gate for activating the synchronization means by an output signal of a calculation result, and a signal reproducing device. 3. A signal reproducing apparatus according to claim 1, wherein the line sequential discriminating means has a reset terminal, and divides a pulse given every one horizontal scanning period by two and divides the divided output. The frequency divider circuit for activating the synchronizing means by a signal and the output signal of the frequency divider circuit are triggered in synchronization with either rising or falling timing, and a clamp pulse is output within the horizontal blanking period. A clamp pulse generation circuit, a clamp circuit that clamps the demodulated line-sequential color signal to a predetermined potential when a clamp pulse is input, and the clamped line-sequential color signal is clamped at least during each horizontal blanking period. The sampling circuit that performs sampling in the horizontal blanking period immediately after the horizontal blanking period and the sampling value obtained by the sampling circuit as the reference value. And a reset pulse generation circuit that outputs a reset pulse to the reset terminal of the frequency divider circuit when the sample value satisfies one of the predetermined conditions, that is, the sample value is larger or smaller than the reference value. Signal reproduction device. 4. The differential amplifier according to claim 3, wherein the reset pulse generating circuit differentially amplifies an output signal of the sampling circuit and a first signal of a constant level, and the differential amplifier. Switch and the second signal of constant level are alternately selected at the timing matching the sampling pulse of the sampling circuit, and the output value of this switch or a signal proportional to this output signal is used as the reference value as the sample value. A signal reproducing apparatus comprising: a comparator for comparing with. 5. The sampling circuit according to claim 3, wherein, in the sampling circuit and the timing of the rising or falling of the output signal of the frequency dividing circuit, the one in which the clamp pulse generating circuit is not triggered. And a sampling pulse generating circuit that outputs a pulse for operating a sampling switch within a horizontal blanking period immediately after the clamped horizontal blanking period, which is triggered in synchronization with timing, and the reset pulse generating circuit A signal reproduction device having a comparator for comparing the value of the sampling pulse period with a reference value. 6. Two kinds of color signals are alternately selected every horizontal scanning period, and the potential is 2 during the horizontal blanking period after demodulation.
A line-sequential chrominance signal, which is modulated differently between different types of chrominance signals, and a means for reproducing a recording medium in which the modulated luminance signal is frequency-multiplexed, and the reproduced signal is modulated. Separation means for separating the line-sequential color signal, single demodulation means for demodulating the separated line-sequential color signal, and inputting the demodulated line-sequential color signal, the signal level in the horizontal blanking period A line-sequential discriminating means for detecting and discriminating the type of the color signal; and a synchronizing means for dividing and outputting the demodulated line-sequential color signal into two signals according to the discrimination result of the line-sequential discriminating means. Signal reproduction device.