JPS6150437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a line discrimination circuit for SECAM color video signals.

In the SECAM color video signal, the carrier color signal is a 4.40625MHz subcarrier with a red color difference signal.
The modulated signal and the signal obtained by FM modulating the 4.25MHz subcarrier with the blue color difference signal are arranged alternately for each line (one horizontal period), and the vertical synchronization signal within each vertical blanking period is In the latter nine lines, a color discrimination signal in which a trapezoidal pulse is FM-modulated to different frequencies for the line corresponding to the red color difference signal and the line corresponding to the blue color difference signal is inserted, and a vertical feedback signal is inserted. In each line except for some lines within the line period, the red color difference signal line is 4.40625MHz, and the blue color difference signal line is 4.40625MHz.
A 4.25MHz unmodulated carrier is inserted.

The color demodulation circuit of the receiver that receives the SECAM color video signal needs to determine whether the line is a red color difference signal line or a blue color difference signal line. In devices that correct the time axis of SECAM color video signals, it is still necessary to determine whether the line is a red color difference signal line or a blue color difference signal line.

One method for this determination is to utilize the color discrimination signal inserted within the above-mentioned vertical retrace period. However, this method has the drawback that if an incorrect determination is made in the middle of a vertical scanning period, a correct determination will not be made until the next vertical retrace period. There is also the idea of using the vertical retrace period for other purposes such as inserting test signals, and it is also possible that color discrimination signals will not be inserted in the future, in which case this method will no longer be usable.

On the other hand, there is also a method of using a non-modulated carrier inserted into each line. In this case, conventionally, the difference between the frequency _R of the unmodulated carrier C _R in the red color difference signal line and the frequency _B of the unmodulated carrier C _B in the blue color difference signal line is used to 1. Supply it to a band-pass filter or the like with the characteristics shown in Figure A, create a level difference between unmodulated carriers C _R and C _B as shown in Figure B, and convert this to a constant reference voltage V _O Both lines are discriminated by comparing them. However, with this method of simply comparing with a fixed reference level, incorrect judgments may be made if the input level of the unmodulated carrier changes, its wave number changes, or if the reference level is improperly set. There are some shortcomings, and stable discrimination cannot be made.

This invention uses a non-modulated carrier to discriminate between lines, and in particular, it is designed to ensure correct discrimination even when the input level of the non-modulated carrier changes or the wave number changes. This is what I did.

FIG. 2 shows an example of the circuit of the present invention, in which the input terminal 1
The horizontal synchronizing pulse from the D flip-flop circuit 2 or the pulse synchronized with this pulse R _H (Fig. 3A)
as a clock input. This D flip-flop circuit 2 has its output as its D input, so the Q output _O.sub.X and the output _O.sub.Y are inverted at every trailing edge, that is, every rise, of the pulse _PH . Q of this D flip-flop circuit 2
The output O _X is taken out as the final discrimination output.

Pulse P _H is supplied as a clock input to another D flip-flop circuit 3. This D flip-flop circuit 3 is always supplied with a positive voltage as its D input.

On the other hand, the carrier color signal of the SECAM color video signal from the input terminal 4 is supplied to the gate circuit 5, and the pulse P _H is supplied to the gate pulse generation circuit 6 to obtain a gate pulse for extracting the unmodulated carrier portion. It is supplied to the gate circuit 5, from which the unmodulated carrier S _O in each line is
(Fig. 3B) is taken out. Then, this input unmodulated carrier S _O is supplied to a bandpass filter ₇ having characteristics as shown in FIG. A level difference is provided between the unmodulated carriers C _B in the filter 7, and unmodulated carriers S _F (FIG. 3C) having a level difference for each line from the filter 7 are supplied to the level comparator 8. . A reference voltage is supplied to the level comparator 8 as described later, and the output signal S _C of the level comparator 8 is supplied to the above-mentioned D flip-flop circuit 3 as a clear input. The output Q _Y of the D flip-flop circuit 3 is supplied to an integrating circuit 9 and smoothed, and the smoothed voltage is supplied to a level comparator 8 as a reference voltage.

Furthermore, the output Q of the D flip-flop circuit 3
_Y is supplied as a clock input to a counter 10, the output P _C of this counter 10 is supplied as a reset input to the above-mentioned D flip-flop circuit 2, and the Q output O _X to the D flip-flop circuit 2 is supplied as a clear input to the counter 10. Ru.

As shown in FIG. 3G, the Q output O _X of the D flip-flop circuit 2 is "0" on the red color difference signal line, that is, the carrier C _R line, and "0" on the blue color difference signal line, that is, the carrier C _B line. 1"
In the state where the correct discrimination output is obtained, conversely, as shown in _the same figure G', the Q _{output O} A state in which the line becomes "0" is a state in which an erroneous discrimination output is obtained.

The reference voltage V _O applied to the level comparator 8 is between the level of the carrier C R and the level of the carrier C _B of the unmodulated carrier S _F obtained by the filter 7, as shown by the broken line in FIG. _3C . As _shown in _FIG .
is cleared. Therefore, the Q output Q _X of the D flip-flop circuit 3 is as shown in FIG.
At the trailing edge, that is, the rising edge, of the pulse P _H , the state becomes "1", and at the time of the carrier C _R , it is inverted to "0", and the output Q _Y has the opposite polarity as shown in F in the same figure. Become. Then, this output Q _Y is smoothed by an integrating circuit 9, and the average value of the voltage is applied to the level comparator 8 as the above-mentioned reference voltage V _O.

Then, in the counter 10, the Q output O of the D flip-flop circuit 2 at the time when the output Q _Y of the D flip-flop circuit 3 rises.
When the state of _X is read _, that is, when the discrimination output O _X is in the correct state as shown in FIG. _3G , the discrimination output O Without counting the rising edge of Q _Y , the output P _C of counter 10 is G in the same figure.
As shown in , it is always in the state of "1", so the D flip-flop circuit 2 is not reset;
The discrimination output _O.sub.X remains in its correct state.

On _the other hand, when _the discrimination output _O The rising edge of _Y is counted. In the figure, when the rising edge of the output Q _Y is counted up to, for example, "15", the output P _C of the counter 10 changes from "1" to "0".
The falling edge resets the D flip-flop circuit 2, inverting its Q output _O.sub.X to "0" and its output _O.sub.Y to "1". Therefore, from this, the discrimination output O _X is determined to be in the correct state. In addition, in this way, the discrimination output O
After _X is in the correct state, a negative signal is obtained as the output _SC of the level comparator 8 during the period of "0", and the output Q of the D flip-flop circuit 3
When _Y rises, the output P _C of the counter 10 is returned to the original "1".

The reason why the erroneous state is corrected after it continues for a certain number of lines is to prevent malfunctions during the vertical retrace period.

As the input level increases, that is, the level of the unmodulated carrier S _O obtained by the gate circuit 5 increases, and as shown in _{FIG .}
When the levels of _B are both greater than the reference voltage V _O ,
As shown in the figure, a negative signal is obtained on each line as the output _SC of the level comparator 8. Therefore, D
The output of the flip-flop circuit 3, Q _Y , falls at the trailing edge of the pulse P _H on each line,
It starts to rise immediately after the non-modulated carrier, and its duty factor becomes large. Therefore, the smoothed voltage obtained from the integrating circuit 9, that is, the reference voltage V _O of the level comparator 8, follows the fluctuation of the input level. The correct level comparison as shown in FIG. 3 can be made.

Conversely, the input level becomes smaller, that is, the level of the unmodulated carrier S _O obtained from the gate circuit 5 becomes smaller, and as shown in FIG.
When the levels of the carriers C _R and C _B of the unmodulated carrier S _F obtained from the above are both lower than the reference voltage V _O , a negative signal cannot be obtained as the output S _C of the level comparator 8, as shown in the figure. Therefore, D
The output Q _Y of the flip-flop circuit 3 is always "0", so the reference voltage V _O of the level comparator 8 is lowered to follow the fluctuation of the input level, and the correct level comparison as shown in FIG. Become what is done.

Note that a frequency discriminator may be provided in place of the bandpass filter 7, and its discrimination output may be supplied to the level comparator 8.

As described above, according to the present invention, even if the input level of the unmodulated carrier changes or the wave number changes, the reference voltage of the level comparator is controlled in a feedback manner, so that the level comparison can always be made correctly. was done,
This ensures that correct discrimination output is obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention, FIG. 2 is a system diagram of an example of the circuit of the present invention, and FIGS. 3 to 5 are waveform diagrams for explaining its operation. 3 is a D flip-flop circuit as a comparison circuit, 5 is a gate circuit, 7 is a bandpass filter,
8 is a level comparator, and 9 is an integrating circuit.

Claims (1)

[Claims] 1 Corresponding to the difference in frequency between the line in which one modulated color signal of the unmodulated carriers in each line of the SECAM color video signal is inserted and the line in which the other modulated color signal is inserted. A circuit that extracts a signal having a level difference for each line, a level comparator to which a signal having a level difference for each line from this circuit is supplied, and a horizontal synchronizing pulse or a pulse synchronized with this to extract a signal having a level difference for each line. a comparator circuit that is set to one state and set to another state by the output signal of the level comparator, a circuit that smoothes the output signal of the comparator circuit and supplies it as a reference voltage to the level comparator, and a horizontal synchronizing pulse or the like. A line discrimination circuit for a SECAM color video signal, comprising a circuit whose state is inverted by a pulse synchronized with a pulse, generates a discrimination output, and controls the discrimination output based on the output of the comparison circuit.