JPS5829677B2 - Irofukuchiyou Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The carrier color signal of a SECAM color television signal is a signal obtained by frequency modulating a subcarrier of f R = 4.40625 MHz with a red color difference signal RY, and f B =
The signals obtained by frequency modulating the 4.25 MHz subcarrier with the blue color difference signal BY are arranged line sequentially, that is, alternately every horizontal section, and the color demodulation circuit of the receiver uses this original signal. The carrier color signal and a signal delayed by one horizontal period are supplied to a switch circuit called a double inch, and this switch circuit uses a color discrimination signal inserted into each vertical retrace interval of the original carrier color signal to detect a color discrimination signal. The inversion state is switched every horizontal section by a switching signal from a controlled flip-flop circuit, and a modulation signal of the red color difference signal R-Y continues from the - output terminal of the switch circuit to the - frequency discriminator. A signal is supplied from the other output end of the switch circuit to the other frequency discriminators, respectively, followed by a modulation signal of the blue color difference signal B-Y, and a red color difference signal is supplied from the - frequency discriminator. Blue color difference signals are obtained from the other frequency discriminators.

However, as mentioned above, in the switch circuit, the switching state relative to the input signal is controlled only by the color discrimination signal inserted in the vertical retrace interval at the beginning of each field. For example, if the horizontal pulse that inverts the flip-flop circuit is missing one after the vertical retrace interval, or if the signal contains noise, the inverted state of the flip-flop circuit and therefore the switching state of the switch circuit may be affected. is incorrect, then from then until the beginning of the next field,
There is a drawback that the erroneous switching state is not corrected and mutually opposite color difference signals are obtained from each frequency discriminator.

In view of this point, the present invention is designed to always obtain the desired color difference signal from each frequency discriminator over the entire field.Hereinafter, an example of the color demodulation circuit according to the present invention will be explained with reference to the drawings. .

In FIG. 1, reference numeral 1 denotes a bandpass filter, which converts the composite color television signal into the original carrier color signal So.
(A in FIG. 2) is separated, and this original carrier color signal So and a signal SD (B in the same figure) obtained by delaying this by one horizontal period in the delay circuit 2 are supplied to the switch circuit 3. C) is supplied as an inversion pulse to the flip-flop circuit 5 through the OR circuit 4, which is inverted every horizontal interval, and the output signal SF of the flip-flop circuit 5 (D in the figure) causes the switch circuit 3 to switch once horizontally. One modulated color signal SR (E in the same figure) is switched alternately for each section, and the other modulated color signal sB (F in the same figure) continues to the other output terminal. The obtained signals are supplied to frequency discriminators 8 and 9 through limiters 6 and 7, respectively, and demodulated.

The frequency discriminator 8 is for obtaining a demodulated output of the red color difference signal, and the frequency discriminator 9 is for obtaining the demodulated output of the blue color difference signal. The correct state is when the state shown in the figure is switched to in the section where the modulation signal of the red color difference signal R-Y is obtained, and conversely, the state shown in the figure is switched to the state shown in the figure in the section where the modulation signal of the blue color difference signal B-Y is obtained from the filter 1. It is an erroneous state when it is switched to a state.

In the present invention, the detection and control of whether the switching state of the switch circuit 3 is correct or incorrect is performed in the following manner. For example, the demodulated output from the frequency discriminator 9 is supplied to the gate circuit 10, while the horizontal pulse PH ( The monostable multi-by-break 11 is triggered by C) in FIG. 2, from which a gate pulse PD is obtained, and this pulse PD is
From this, the demodulated output Bc of the unmodulated carrier inserted at the beginning of each horizontal section is extracted.

Then, whether the switching state of the switch circuit 3 is correct or incorrect is detected based on the demodulated output Bc of this unmodulated carrier.

By the way, the discrimination characteristic of the frequency discriminator 9 is shown by the curve a in FIG.
The demodulation output level of the unmodulated carrier for the red color difference signal is positive at ■R, and the demodulation output level for the blue color difference signal is negative at -vB, but each Since the difference between the frequencies fR and fB of the unmodulated carrier is small, the difference in their respective demodulated output levels is small (see the broken line in FIG. 2G), making it difficult to distinguish between the two.

Therefore, in the present invention, the output PD of the monostable multi-bi break 11 is supplied to the switch circuit 12 provided in the frequency discriminator 9, and this switch circuit 12 is closed only in the section corresponding to the unmodulated carrier portion. , the discrimination characteristic of the frequency discriminator 9 is changed from the state of curve a in FIG. 3 to the curve shown in FIG. be raised up.

Therefore, the demodulated output level of the unmodulated carrier from the frequency discriminator 9 is as high as ■11 for the red color difference signal and =■8' for the blue color difference signal, and the level difference is large enough for discrimination. Become something.

The demodulated output Be (G in FIG. 2) of the unmodulated carrier taken out at a high level in this way is supplied to the integrating circuit 13, and its output SH (K in the same diagram) is supplied to the level comparator 14, and the switch circuit 3 The switching state of the frequency discriminator 9 is correct.
While the modulation signal of the blue color difference signal B-Y is supplied to the demodulated output B of the unmodulated carrier obtained from the gate circuit 10,
O becomes a negative value -vB', and therefore the output shH of the integrating circuit 13 also maintains a negative value.

Then, at time t, when the switching state of the switch circuit 3 becomes incorrect, from this time t1 onwards, the signal SB supplied to the frequency discriminator 9 becomes a modulation signal of the red color difference signal, and from the gate circuit 10 The resulting demodulated output Bc of the unmodulated carrier becomes a positive value ■I, and the output SH of the integrating circuit 13 changes to positive after time t1. For example, when the 10th unmodulated carrier is demodulated from time t, At time t2 when the output is obtained, the reference voltage E8 of the level comparator 14 is exceeded, and at this time t2, the output SL of the level comparator 14 is exceeded.
(H in the figure) is inverted from "1" to "O".

Then, the fall of the output SL from "1" to "0" triggers the monostable multi-by-break 15, which triggers the signal SM with a pulse width shorter than one horizontal period (I
) is obtained, and during this time the charge in the capacitor constituting the integrating circuit 13 is discharged.

And by the trailing edge of this monostable multi-by break 16
is triggered to obtain a narrow pulse width pulse Pc (J in the figure), which is supplied to the flip-flop circuit 5 via the OR circuit 4.

Therefore, if the switch circuit 3 enters an incorrect switching state at time t1, a correction pulse PC is obtained at time t3 in the middle of the 10th horizontal interval counted from this point, and at this time t3, the flip-flop circuit 5 is switched. On the contrary, after this time point t3, the switching state of the switch circuit 3 is set to the proper state, and therefore, the signal S□ supplied to the frequency discriminator 8 becomes a modulation signal of the red color difference signal RY, The signal SB supplied to the frequency discriminator 9 is the one following the modulation signal of the blue color difference signal B-Y.

Note that after time t3, the demodulated output Bc is at time t
As before 1, it becomes a negative value -■B', and the integration circuit 1
The output shH of No. 3 becomes negative f direct.

As described above, in the present invention, the demodulated output of the unmodulated carrier is detected every horizontal interval, and thereby it is determined whether the switching state of the switch circuit 3 is correct or incorrect, so that the switching state is always appropriate. Since control is performed for each horizontal section, even if one horizontal pulse is missing in the middle of a field or the switch circuit 3 is in an incorrect switching state due to noise, etc., this is immediately corrected to the correct switching state. Ru.

Furthermore, in the present invention, the sensitivity of the frequency discriminator is increased only in the section where the unmodulated carrier is inserted, so that the demodulated output level of the unmodulated carrier can be increased, so that the discrimination can be made reliably and stably. The switching state of the circuit 3 is reliably controlled.

In addition, increasing the sensitivity of the frequency discriminator in this way narrows the frequency band of the frequency discriminator, so the S/N with respect to the demodulated output of the unmodulated carrier improves, and malfunctions due to noise can be reduced.

That is, since the noise signal has infinite frequency components, when the noise signal is supplied to a frequency discriminator, a noise demodulation output proportional to the frequency band of the discriminator is generated.

Therefore, the narrower the frequency band of the discriminator, the better the S/N.

Note that when the frequency band is narrowed in this way, the linearity of the discrimination characteristic may deteriorate, but the period during which the frequency band is narrowed is the period of the unmodulated carrier, and this unmodulated carrier has a constant frequency. Therefore, there is no problem as the output that should be obtained at this time only needs to be obtained at a certain level or higher.

Note that, without supplying the demodulated output of the unmodulated carrier to the integrating circuit 13, the levels of the demodulated outputs are compared one by one, and the flip-flop circuit 5 is inverted in the middle of the horizontal section immediately after time t1. You can also do this.

In addition, when obtaining still images from a recording/playback device,
Since the inclination of the scanning trajectory of the head on the tape is different from that during recording, the reproduced transport color signal SPO becomes a modulation signal of the red color difference signal RY at time t1 in the middle of the field, as shown in FIG. 4A. The line-sequential state of the modulation signal of the blue color difference signal B-Y may become discontinuous, and in this case, the reproduced carrier color signal SPO and the signal SPD ( The signals SR and SB (Fig. 1 and E) obtained by switching the switching signal S1 (Fig. However, the present invention can be applied to such a case as well.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of an example of a color demodulation circuit according to the present invention, and FIG.
FIG. 3 is a waveform diagram for explaining the same, FIG. 3 is a characteristic curve diagram for explaining the same, and FIG. 4 is a diagram for explaining the case where the input carrier color signal is special. 1 is a bandpass filter, 2 is a delay circuit that delays one horizontal period, 3 is a switch circuit, 5 is a flip-flop circuit, 8 and 9 are frequency discriminators, 10 is a gate circuit, 11.
15 and 16 are monostable multi-by-breaks, 12 is a switch circuit, 13 is an integration circuit, and 14 is a level comparator.

Claims (1)

[Claims] 1. A first modulated color signal and a second modulated color signal, in which the first and second color signals are frequency-modulated so that their carrier frequencies are different from each other, are arranged in each horizontal section, and are arranged in a corresponding manner. The original carrier color signal in which a non-modulated carrier is inserted into each horizontal interval and the signal obtained by delaying this original carrier color signal by one horizontal period are alternately switched by the switch circuit every horizontal interval, and the switch circuit One continuous modulated color signal is taken out from the first output end of the switch circuit, and the other continuous modulated color signal is taken out from the second output end of the switch circuit, and the one modulated color signal and the other modulated color signal are taken out from the second output end of the switch circuit. The color signals are supplied to first and second frequency discriminators, respectively, and the first and second color signals are demodulated, and the period during which the unmodulated carrier from the first frequency discriminator is inserted is In the color demodulation circuit, the switching state of the switch circuit is controlled by a demodulation output, the non-modulated carrier of the first frequency discriminator is lower in the period in which the non-modulated carrier is inserted than in other periods. A color demodulation circuit in which the demodulation sensitivity at the frequency is increased and the demodulation band is narrowed.