JPS622790A - Demodulating device for carrier chrominance components - Google Patents

Abstract

PURPOSE:To develop color instantaneously when the receiving signal level rises by interrupting that the switch circuit is turned off and the output of the amplifier for the PAL signal is supplied to the demodulation circuit for SECAM when the SECAM signal of the weakly electric field comes and the switch circuit is changed over to the PAL side. CONSTITUTION:When the first switch circuit 31 is changed over to an SECAM side, it is discriminated that the third switch circuit 38 is turned on, the output of a delaying circuit 32 is also supplied to a demodulation circuit 28 for SECAM and is an SECAM signal. When the first switch circuit 31 is changed over to a PAL side, the third switch circuit is turned off and the supply of the output of the delaying circuit 32 to the demodulation circuit 28 for the SECAM is interrupted.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

8. Field of industrial application B Summary of the invention C Prior art D Problem to be solved by the invention E Means for solving the problem F Effect G Example H Effect of the invention A Field of industrial application This invention Regarding demodulation devices for carrier color signals of color television receivers that share PAL color video signals and SllICAM color video signals, in particular demodulation circuits for PAL and SECAM
This invention relates to a circuit in which a delay circuit of one horizontal period is shared with the fJja circuit.

B. Summary of the Invention The present invention provides a demodulation device for a carrier color signal of a color television receiver for both PAL and SECAM.
When switching between both methods based on the output that determines whether or not it is an AM signal, if the signal is switched to the SECAM side, the above-mentioned determination is made between the direct signal and the signal delayed by one horizontal period, and the signal is switched to the PAL side. When a weak electric field signal is input, the above-mentioned discrimination is performed only from the direct signal, thereby improving the coloring sensitivity to the SECAM system signal when a weak electric field signal is input.

C. Conventional technology The demodulation circuit for the carrier color signal in the PAL color video signal is
It is configured as shown in the figure.

That is, in FIG. 3, the carrier color signal of the PAL signal extracted through the bandpass amplifier (1) passes through the delay circuit (2) of one horizontal period, and is then sent to the subtraction circuit (3) and the addition circuit (
4), and the signal from the bandpass amplifier (1) is also supplied to the subtraction circuit (3) and addition circuit (4), respectively, without going through the delay circuit (2), and the signal from the subtraction circuit (3) is The component of the red color difference signal RY of the color signal is obtained, and the component of the blue color difference signal B-Y of the carrier color signal is obtained from the addition circuit ((1).
The following components are obtained. These color difference signal R-Y components and B-Y components are sent to t'itm circuits (5) and (6).
), the color difference signals R-Y and B-Y are demodulated and supplied to the matrix circuit (7).

And in this matrix circuit (7), the terminal (8)
The output terminal (9R
), (9G), and (9B), primary color signals R, G, and B of red, green, and blue are taken out.

On the other hand, the demodulation circuit for the carrier color signal of the SECAM color video signal is configured as shown in Fig. 4, and the carrier color signal passed through the bell filter α is directly supplied to the switch circuit (13) via the limiter circuit (11). At the same time, the signal passed through the limiter circuit (11) is transmitted to the delay circuit (12) of one horizontal period.
) is supplied to the other input terminal of this switch circuit (13). This switch circuit (13) is alternately switched to terminals A and B by a switching signal that inverts the state every horizontal section through the terminal (14), and one output terminal of this switch circuit (13) is The carrier color signal component of the red color difference signal R-Y is obtained, and the carrier color signal component of the blue color difference signal B-Y is obtained at the other output terminal.
The signals are supplied to demodulation circuits (15) and (16) for FM demodulation, and color difference signals R-Y and B-Y are extracted, respectively.

These color difference signals are then supplied to the matrix circuit (17) and combined with the luminance signal Y from the terminal (1st).
Primary color signals R, G, and B of red, green, and blue are derived from output terminals (19R), (19G, and 19B).

In this way, both the demodulation circuit for the carrier color signal of the PAL color video signal and the demodulation circuit for the carrier color signal of the SECAM color video signal use a delay circuit of one horizontal period.

For this reason, in the demodulation circuit of the carrier color signal of a color television receiver that can receive both PAL and SECAM color video signals, one delay circuit is shared because this one horizontal period delay circuit is expensive. I try to do that.

In this case, depending on whether the input carrier color signal is a PAL signal or a SECAM signal, the delay circuit for one horizontal period is
It is necessary to determine which of the M demodulation circuits to connect to, but in the past, in order to do this automatically, the input carrier color signal was time-divisionally switched between the PAL demodulation circuit and the SECAM decoupling circuit. At the same time as supplying the signal, the delay circuit for one horizontal period was also switched in a time-division manner.

For this reason, it takes a very long time to determine whether the carrier color signal is a PAL signal or a SECAM signal, and therefore there is a drawback that it takes a long time for the color to appear on the screen. In addition, the configuration for creating timing for time division was extremely complicated. Furthermore, in cases of weak electric fields, PA
When it can be determined that it is either an L signal or a SECAM signal, it is necessary to give priority to demodulating one of them, but the conventional method has had the disadvantage that the procedure for changing the priority is extremely troublesome.

The inventors previously proposed a color demodulation device for PAL and SFICAM that improved the above-mentioned drawbacks (Japanese Patent Application No. 1986-
(See No. 253811).

FIG. 5 shows an example of this PAL/SECAM common color demodulation circuit, in which a signal through an input terminal (21) is supplied to a PAL signal amplifier (22) and also to a SECAM signal amplifier (24). PAL signal amplifier (2
The output signal of 2) is supplied to the PAL demodulation circuit (27) through the S-side input terminals of the switch circuits (25) and (26).

Further, the output signal of the SRCAM signal amplifier (24) is supplied as is to the SECAM demodulation circuit (28).

Furthermore, the output signal of the PAL signal amplifier (22) and the 5BC
A? The output signal of the signal amplifier (24) is sent to the switch circuit (
The output of this switch circuit (31) is supplied to the P input terminals and the S input terminal of the switch circuit (31), respectively, through a delay circuit (32) of one horizontal period to an addition circuit (33) and a subtraction circuit (34).
), and the output signal of the switch circuit (31) is also supplied as is to an addition circuit (33) and a subtraction circuit (34). The output of the addition circuit (33) is supplied to the PAL demodulation circuit (27) through the P-side input terminal 'I of the switch circuit (25), and the output signal from the subtraction circuit (34) is supplied to the switch circuit (26). P through P input terminals of
The signal is supplied to the AL demodulation circuit (27). Furthermore, the output of the delay circuit (32) for one horizontal period is the demodulation circuit for SECAM (
28).

And the red color difference signal (RY) P from the PAL demodulation circuit (27)! The red color difference signal (R-Y) S of the IEcAM demodulation circuit (28) is supplied to the P input terminals and the S input terminal of the switch circuit (29R), which are selectively output to the output terminal by a switching signal described later. (30R). In addition, the blue color difference signal (B-Y) P from the PAL fj[11 circuit (27) and the blue color difference signal (B-Y) S from the SlltCAM demodulation circuit (28) are sent to the switch circuit (29B). They are supplied to the P input terminals and the S input terminal, respectively, and are switched by the same switching signal as the switch circuit (29R) and selectively led out to the output terminal (30B).

A part of the signal from the PAL demodulation circuit (27) is supplied to the PAL killer circuit (35), and the PAL demodulation circuit (27)
), when the PAL signal cannot be demodulated correctly, it is detected by the PAL killer circuit (35).

On the other hand, a part of the signal from the SlICAM demodulation circuit (28) is supplied to the SECAM killer circuit (36), and the SEC
This SECAM killer circuit (36) is used when the SECAM signal cannot be demodulated correctly in the AM demodulation circuit (28).
It is detected in

Then, the output of the PAL killer circuit (35) and the SECAM
(38) The switch circuit (25
) (26) (29R) (29B) and (3
1) can be switched. That is, this switch (37) is a switch for determining whether priority is given to PAL or SECAM.

Therefore, to explain the case where the switch (37) is connected to the P side and PAL is prioritized, if the carrier color signal through the input terminal (21) is a PAL signal, the switch circuit (25) and Regardless of whether (26) is at the S side input terminal or the P input terminal, the PAL demodulation circuit (26)
7), the demodulation operation is performed, and the PAL killer circuit (35) determines that the input carrier color signal is a PAL signal, and the output of this killer circuit (35) is passed through the switch (37) to the switch circuits (25), (26). ), (29R
), (29B) and (31), these switch circuits<25), (26),
(29R), (29B) and (31) are connected to P input terminals. That is, in order to correctly demodulate the PAL signal, a circuit including a delay circuit (32) of one horizontal period is connected to the PAL demodulation circuit (27), and the PALll! Correct demodulation of the sending color signal is performed, and the output terminal (30R)
, (30B) shows the color difference signal output of the PAL signal (
RY)P and (BY)P are obtained.

On the other hand, the carrier color signal through the input terminal (21) is
If it is an M signal, switch circuits (25) and (26)
) is switched to, the PAL demodulation circuit (
27), it is not demodulated, and the PAL killer circuit (35) determines that it is not a PAL signal, and the killer operates, and the switch circuits (25), (26), and (29R).

(29B) and (31) are supplied to the S-side input terminal.

Therefore, the delay circuit (32) is a SECAM demodulation circuit (
28), the SECAM carrier color signal is correctly demodulated, and the color difference signal outputs (R-Y)S and (B-Y)S are obtained at the output terminals (30R) and (30B).

In addition, if the carrier color signal is of a weak electric field and is determined to be either a PAL signal or an SFICAM signal, the switch (37) is connected to the contact P side, so the PAL killer circuit (35) operates. It is determined to be a PAL signal,
Switch circuit (25) (26), (29R)
(29B) and (31) are connected to the P input terminals, and a circuit including a delay circuit (32) is connected to the P A and L demodulation circuit (27) to ensure correct PAL signal demodulation. will be done. In other words, priority is given to PAL.

Next, the switch (37) is connected to the contact S side and the SECA
When priority is given to M, if the input carrier color signal through the child (21) is a PAL signal, the SECAM demodulation circuit (28) cannot demodulate it, so the SRCAM killer circuit (36) cannot demodulate it. is detected and a killer operation is performed, and the output of the killer circuit (36) is transmitted through the switch (37) to the switch circuits (25), (26), (2
9R).

(29B) and (31), and these switch circuits are connected to P input terminals. Therefore, the delay circuit (
32) is connected to the PAL demodulation circuit (27), and the PAL signal is correctly demodulated.

On the other hand, when the signal through the input terminal (21) is an SRCAM carrier color signal, the SECAM demodulation circuit (28)
Since demodulation is possible regardless of the switching operation of the switch circuit (31), the SRCAM killer circuit (36) does not perform a killer operation, and its output causes the switch circuit (25) to perform demodulation.
, (26), (29R), (29B)
and (31) are connected to the S side input terminal. That is, the delay circuit (32) is connected to the SECAM demodulation circuit (28), and the SECAM signal is correctly demodulated.

Furthermore, if the carrier color signal is determined to be either a PAL signal or a 311ICAM signal as described above, the switch (37) is connected to the S side, so the output of the SRCAM killer circuit (36) indicates that it is an SRCAM signal. As a result, the switch circuit (25) is activated.

(26), (29R), (29B) and (
31) is connected to the S-side input terminal, and the SECAM demodulation circuit (28) operates. In other words, priority is given to SfiCAM.

According to the above-described apparatus, it is possible to quickly determine whether the input carrier color signal is PAL or StICAM, and it is also possible to easily switch between PAL priority and SRCAM priority.

In other words, the conventional delay circuit with l horizontal period is replaced by PAL.
Why not connect the JII demodulation circuit and the SECAM demodulation circuit in a time-division manner to determine which method of color video signal is the carrier color signal (to ensure that one of them is determined as having priority)? This has the advantage that the discrimination operation is quick and colors can be quickly applied to the screen.

By the way, in the above case where SRCAM is given priority, it is determined whether the input signal is a SIECAM signal or not using SRCA.
The output of the M signal amplifier (24) itself and the signal passed through the delay circuit (32) are used together, and the switch circuit (13) in Figure 4 is correctly switched in order to synchronize the red and blue color difference signals. Technology for
4-124636)).

That is, in this technique, in the horizontal section in which the modulated color signal DB of the blue color difference signal is inserted, the modulated color signal DR of the red color difference signal with f s = 4.25 MHz is inserted into the SECAM carrier color signal. In the horizontal section fR=4.4062
Since unmodulated carriers Cs and CR of 5 MHz are inserted, these unmodulated carriers are used.

The outline will be described with reference to the time chart shown in FIG.

That is, FIG. 6A shows the input signal DI to the switch circuit (13) of the SIECAM color demodulation circuit shown in FIG. 4, and FIG. 6B shows the input signal DI to the delay circuit (12).
This is the signal DL delayed by.

In addition, C in the figure is the switching signal SW of the switch circuit (13) supplied from the terminal (14), and in this case, the switching point is the end of the modulated color signal DR of the red color difference signal in the input signal DI. This is the time point when the section of the unmodulated carrier at the head position of the modulated color signal DR is divided into two.

Therefore, at one output of the switch circuit (13),
As shown in the sixth diagram, the modulated color signal Da of the blue color difference signal
is the signal followed by the unmodulated carrier C of the input signal DI.
In the first half of the period R, a signal B! in which a non-modulated carrier CR is inserted in place of the original non-modulated carrier CB! is obtained. As shown in the same figure, the other output is a signal followed by the modulated color signal DR of the red color difference signal, but in the first half of the period of the unmodulated carrier CR of the input signal DI, the unmodulated carrier CB is output. An inserted signal RI is obtained in place of the original unmodulated carrier CR. This relationship is expressed in the switch circuit (1
This is the same regardless of whether the switching state in 3) is correct or not.

Then, these signals RI and BI are sent to the demodulation circuit (15)
The demodulation characteristics of the demodulation circuit (15) are shown by the line (100R) in FIG. 7, and the demodulation characteristics of the demodulation circuit (16) are shown by the line in the same figure. (
100B), the demodulated output RO of the demodulating circuit (15) is as shown in Figure 6G, and the demodulated output BO of the demodulating circuit (16) is as shown in Figure 6F. The addition output MO of re-output RO and BO is H in the same figure.
It becomes as shown in .

Therefore, if the first half of each non-modulated carrier section is sampled and held by the sampling pulse SP shown in FIG. 6, a sampling and hold output SH as shown in FIG. 6J can be obtained.

This hold output SH and the switch circuit (13
) is a signal FO indicating the switching state with respect to the input signal DI.
(Fig. 6K) (If the switching state is reversed, the inverted signal FO is used.) From this, it is determined whether the switching state by the switching signal SW of the switch circuit (13) is positive or reversed, and if the switching state is reversed, the switching signal is The states of SW rlJ and rOJ are inverted to achieve the correct switching state.

And the SRC in the SRCAM killer circuit (36)
It can be determined whether the signal is an AM signal or not by monitoring the above-mentioned sampling hold output SH.

In this case, when using the signal DI and its delayed signal DL, the summed output MO of the demodulated outputs RO and BO can be used, and the demodulated output of the unmodulated carrier sampled and held with the sampling pulse SP is as shown in FIG. G, H
As is clear from the above, the level is doubled, and the sensitivity of discrimination is improved.

D Problems to be Solved by the Invention In the demodulator shown in FIG. 5, when a weak electric field SlICAM signal is input, the SECAM killer circuit (36) is activated and the switch circuits (31), (29R),
(29B) may be switched to the PAL side.

In such a case, the signal passing through the PAL signal amplifier (22) is supplied to the delay circuit (32), and the output delayed signal is supplied to the SECAM demodulation circuit (28). Since the input signal is a SECAM signal, when the signal level increases, the switch circuit (31) is activated.

It is desirable that (29R) and (29B) immediately return to the SECAM side.

However, the PAL signal amplifier (22) is a linear amplifier and does not include a limiter circuit like the SECAM signal amplifier (24). Therefore, the large amplitude noise component amplified by the PAL signal amplifier (22) is directly applied to the delay circuit (32), and this large amplitude noise is also applied to the demodulation circuit (28).

Then, the SECAM killer circuit (36) converts the direct signal that has passed through the SIiCAM signal amplifier (24) having a limiter circuit and the delayed signal containing this noise component into the SI
The ECAM signal will be discriminated, but the direct signal will also be disturbed due to the noise component of the delayed signal, so the S
This has the disadvantage that it becomes difficult to distinguish the ECAM signal and it is difficult to color it.

E Means for Solving Problems In this invention, a PAL demodulation circuit (27) and an S
ECAM demodulation circuit (28), one horizontal period delay circuit (32) shared by the re-demodulation circuit, PAL signal amplifier (22), SRCAM signal amplifier (24), and both amplifiers (22) , the first switch circuit (31) selectively supplies the output of (24) to the delay circuit (32), and selects the output of the PAL decoupling circuit (27) and the output of the SECAM demodulation circuit (28). The second switch circuit (29R”), (29B) and the SRCAM
It has a killer circuit (36) and a SIECAM amplifier (
The output of 24) is always the SRCAM signal demodulation circuit (28)
is supplied to the first and second switch circuits (31), (29) by the output of the SRCAM killer circuit (36).
R) and (29B), a switch circuit (38) which is switched in conjunction with the switch circuit (31) is provided between the delay circuit (32) and the SECAM demodulation circuit (28).

F Effect When the first switch circuit (31) is switched to the SECAM side, the third switch circuit (38) is turned on and the output of the delay circuit (32) is also switched to the SECAM demodulation circuit (
28) to determine whether it is an SRCAM signal, and the first switch circuit (31)
When switched to the L side, the third switch circuit (38
) is turned off and the output of the delay circuit (32) is
The supply to the AM demodulation circuit (28) is cut off.

G. Embodiment Figure 2 shows an example of the apparatus of this invention, and this example is an example in which the invention is applied to the example in Figure 5.

That is, in this example, a switch circuit (38) is provided between the output end of the delay circuit (32) and the SECAM demodulation circuit (28).

This switch circuit (38) is switched in conjunction with the switch circuit (31), and in this example, the switch (38) is switched in conjunction with the switch circuit (31).
This switch circuit (38) can also be switched by the output of 7). In this case, when the switch circuit (31) is switched to the input terminal S side, this switch circuit (38) is turned on, and the switch circuit (31)
When the switch is switched to the input terminal P side, this switch circuit (38) is turned off.

In the above configuration, if the switch (37) is switched to the contact S side and the SECAM priority is selected, the SECA
In the electric field where the M signal is stably received, the switch circuit (38) is on, so the operation is exactly the same as the example in FIG. 5.

Then, in the case of a weak electric field, the SECAM signal becomes a noisy signal, and the SECAM killer circuit (36) works, causing the switch circuits (31) and (29R).

When (29B) is switched to the input terminal P side, the switch circuit (38) is turned off, and the supply of the delayed signal to the SECAM demodulation circuit (28) is cut off.

At this time, the SIliCAM demodulation circuit (28) includes S
Direct signal DI (FIG. 2A) L from the ECAM signal amplifier (24) is not supplied. Therefore, the switch circuit (
The signal B■ obtained from one output terminal of 13) is as shown in C in the same figure, and the signal RI obtained from the other output terminal is as shown in the same figure. That is, the signals Bl and R1 are obtained from the modulated color signals DB and DR only every other horizontal period. However, if we look only at the first half of the period of the unmodulated carrier of the signal BI, the unmodulated carrier C
R and CB are obtained alternately every horizontal period.

Therefore, if the demodulated signal BO (E in Figure 2) of this signal BI is sampled and held using the sampling pulse SP (F in Figure 2), the hold output SH' will be the same hold output as described above, as shown in G in Figure 2. is obtained, making it possible to discriminate SECAM signals.

Moreover, this sampling hold output SR' is SRC
It is obtained based only on the direct signal from the AM signal amplifier (24) and is limited. That is, the signal that may contain large amplitude noise that has passed through the PAL signal amplifier (22) and the delay circuit (32) is blocked by the switch circuit (38).
It becomes possible to discriminate SRCAM signals without being affected by the large amplitude noise.

When the switch (37) is connected to the contact P and PAL priority is selected, the switch circuit (31) is on the input end S side and the switch circuit (38) is on when receiving a weak electric field SECAM signal, so the amplifier ( Due to the existence of the limiter (24), large amplitude noise does not appear at the output of the delay circuit (32) and directly affect the signal DI.

H Effects of the invention According to this invention, when demodulating an input signal with SECAM priority, even if a weak electric field SECAM signal arrives and the switch circuit (31) switches to the PAL side, the switch circuit (38) is turned off, and the PAL signal amplifier (22
) is cut off from being supplied to the SECAM demodulation circuit (28) through the delay circuit (32), so that it is not affected by large-amplitude noise and immediately changes color when the received signal level increases. become.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an example of the inventive device, Fig. 2 is a diagram for explaining its operation, Fig. 3 is a block diagram of an example of a PAL color demodulation circuit, and Fig. 4 is an example of a SECAM color demodulation circuit. FIG. 5 is a block diagram of an example of the previously proposed carrier color signal demodulation device, and FIGS. 6 and 7 are diagrams for explaining some of its operations. (21) is an input terminal, (22) is a PAL signal amplifier,
(24) is a SECAM signal amplifier, (25) (2
6) (31) and (38) are switch circuits, (27) is a PAL demodulation circuit, (28) is a SECAM demodulation circuit,
(32) is a delay circuit, and (36) is a S E CAM killer circuit. of··,\,

Claims (1)

[Claims] A demodulation circuit for PAL, a demodulation circuit for SECAM, a delay circuit of one horizontal period shared by both demodulation circuits, an amplifier for PAL signals, an amplifier for SECAM signals, and an output of both amplifiers. a first switch circuit that selectively supplies the delay circuit to the delay circuit; a second switch circuit that selectively takes out the output of the PAL demodulation circuit and the SECAM demodulation circuit;
SECAM killer circuit, the above delay circuit and the above SECA
and a third switch circuit provided between the SECA M demodulation circuit and the SECAM signal amplifier, and the output of the SECAM signal amplifier is always connected to the SECA M demodulation circuit.
Although the first and second switch circuits are switched by the output of the SECAM killer circuit, the third switch circuit is switched in conjunction with the first switch circuit. , when the first switch circuit is switched to the SECAM side, the third switch circuit is turned on and the output of the delay circuit is also supplied to the SECAM demodulation circuit to determine that it is a SECAM signal. At the same time, when the first switch circuit is switched to the PAL side, the third switch circuit is turned off and the supply of the output of the delay circuit to the SECAM demodulation circuit is cut off. A carrier chrominance signal demodulator constructed as described above.