FR2479625A1 - Combined SECAM and PAL TV receiver - has two decoders supplying colour signals and colour difference signals to three adding stages - Google Patents

Abstract

The TV receiver which can be operated according to both the SECAM system and the PAL system, uses a double decoder unit in which the colour difference signals for the SECAM system are added to the colour signals for the PAL system. Each module forming the double unit incorporates its own line time delay line. One module is mounted on the other. Each module contains a circuit which automatically blocks the colour channel when its appropriate colour signals are not received. A changeover circuit prevents operation of one decoder when the other colour coder is operating. The SECAM module has inputs for all supplies such as drive voltages, sensing pulses, colour contrast control voltages etc. obtained from the PAL module, which has three adding stages for the two types of signal, providing control signals for the colour tube.

Description

 The present invention relates to a PAL / SECAM multinorm color television receiver. Multinorm color television receivers, which can receive the two standards to be chosen by manual or automatic switching, are known for border areas where it is possible to receive color television broadcasts with different standards, PAL and SECAM for example.

 Since a PAL color television receiver requires a delay line like a SECAM receiver, which introduces a delay equal to the scanning time of a line, efforts are made to use this delay line for both modes of operation.

 In a known arrangement (patent application of the Federal Republic of Germany published under No. 12 79 727), the chrominance subcarriers PAL and SECAM are transmitted on the one hand by the delay line and on the other hand directly to the four inputs of a SECAM permutator. The outputs of this permutator can be connected manually or automatically to the choice of the inputs of a PAL decoder or a SECAM decoder.

 As reception of signals with different standards is only possible in certain border areas, a PAL television is first, within the country, built and marketed first as a PAL television only. Provisions are provided for the transformation, if necessary, of this television set for PAL / SECAM operation. for example, two modules, constituting the color decoder, are replaced by two other modules comprising a PAL / SECAM decoder. The disadvantage of this solution is that the customer has to dismantle modules, replace them and mount new modules. Known PAL / SECAM decoders also require special integrated circuits.

The subject of the invention is a PAL / SECAM decoder for a multinorm color television receiver, which can be produced as a PAL decoder only, but which can be transformed without changing modules for operation.
PAL / SECAM.

According to an essential characteristic of the invention, a first module, containing a PAL decoder and comprising output channels
R, G, B, is connected to a second module containing a SECAM decoder, which receives from the first module the modulated chrominance subcarrier, then returns the chrominance signals (RY), (VY), (BY) which are extracted in the first module, in which they are added to the corresponding signals applied to the output channels R, G, B.

 The invention thus deliberately separates the various functions of the PAL decoder and the SECAM decoder, the SECAM module performing only the typical SECAM functions. Even in SECAM operation, the PAL module advantageously continues to perform all the functions not typical of SECAM. Specific PAL / SECAM integrated circuits are useless, because the PAL module is only typical of PAL and the SECAM module only typical of SECAM. An essential advantage of the invention resides in the fact that it suffices to plug the SECAM module onto the PAL module prepared accordingly. No other operation is necessary, such as opening lines or replacing other modules. The PAL module remains contained in the color television without any modification. The transformation for PAL / SECAM operation is limited to the addition of the SECAM module.

The latter receives all necessary signals only from the module
PAL and also delivers its output signals exclusively to the module
PAL. This is why no other operation than racking in the module
SECAM is not required. The transformation therefore requires no replacement, but simply the purchase of a relatively economical SECAM module and its simple addition. In addition to the technical advantages, there are also commercial advantages for the after-sales service.

 Other characteristics and advantages of the invention will be better understood with the aid of the detailed description below and of the appended drawings in which FIG. 1 represents the block diagram of the assembly according to the invention; Figure 2 shows the block diagram of the receiver for PAL operation; and Figure 3 shows the block diagram of the color television transformed for PAL / SECAM operation.

In FIG. 1, the PAL module 1 contains the delay line Y, the bandpass filter 4 for the modulated chrominance subcarrier, the integrated circuit PAL 5, the delay line PAL 6, introducing an equal delay to the duration of a line and connected to the latter, the video output amplifiers R 7, V 8, B 9, the assembly 10 for adjusting the contrast adjustment, the color contrast and the brightness, and for limiting of the beam current, and the assembly 11 for limiting the peak beam currents. The PAL PAL contains the chrominance subcarrier amplifier, the circuit
CAC, identification for the PAL permutator, the color blocking, the PAL permutator, the reference subcarrier oscillator, the synchronous demodulators, the Y amplifier, the black stage setting circuit, the delivering matrix the color signals R, G,
B, the limitation of the beam current and the necessary suppression circuits.

 The following signals are transmitted to module 1. The composite video signal FBAS is applied to terminal 12. A clock pulse 15 at line frequency is applied to terminal 13 for various uses, such as transmission or suppression of the signal color synchronization and PAL switch synchronization. Terminal 14 transmits the operating voltage U3 to the PAL PAL 5 and to the amplifiers 79. The adjuster H transmits via terminal 16 a voltage to assembly 10 for adjusting the brightness. This assembly acts on the SI PAL so as to allow the brightness to be adjusted on the image tube 17 using the adjuster H. The adjuster K and the assembly 10 transmit a voltage via terminal 18 to the CI PAL 5 for adjusting the image contrast. This voltage controls the amplification of the luminance signal Y. The adjuster FS transmits to the CI PAL, via terminal 19 and the assembly 10, a voltage making it possible to adjust the saturation or the color contrast, by variation of the amplitude of the modulated chrominance subcarrier. The assembly is carried out so that the operation of the adjuster K also varies the color saturation in the desired direction, in order to avoid oversaturation of the colors in the event of a decrease in contrast. The assembly - it measures practically without inertia the current of the beam of one or three outputs R, G, B, and determines the peak currents of the beam exceeding a specified value.

When this value is exceeded, the assembly 11 again reduces the beam current via the assembly 10. The terminal 20 also transmits a regulating variable, which represents the average beam current. When the average beam current exceeds a specified maximum, for example due to an essentially very bright image, the assembly 10 also decreases the beam current. The outputs of amplifiers 7, 8, 9 are connected to the three control electrodes of the color image tube 17, which are attacked by the color signals R, G, B.

 The SECAM 2 module contains the SECAM 2 CI, the correction bell filter 22 and the delay line 23, of delay equal to the duration of a line and connected to the CI 21. The latter contains in particular suppresion circuits, the limiters, the SECAM permutator, the SECAM identification circuit, the FM discriminators and the color blocking.

The television produced for PAL only contains only module 1. The latter then works as described in decoder
PAL and controls picture tube 17 using the composite video signal
FBAS and other signals.

 Module 2 is connected as shown in module 1 when transforming the television set for PAL / SECAM operation. No other arrangement concerning the circuits is necessary.

 The signal flow flowing between the two modules 1, 2 via the connections a-i is described below.

 By connection a, the signal FBAS reaches the input of the filter 22, which transmits the SECAM chrominance subcarrier modulated to the SECAM CI 21. The clock pulse 15, used for transmission and suppression, as well as 'to the synchronization of the SECAM permutator, is applied to the SECAM 21 PCB by connection b. The operating voltage U3 applied to module 1 supplies module 2 via connection c. The connection d transmits a regulating variable which, when the FS adjuster or the K adjuster is operated, acts on the color saturation in the SECAM 2 module. The PAL PAL 5 transmits by the connection e a regulating quantity Us to CI SECAM 21. This regulating variable produces a forced switching, which necessarily disconnects the CI SECAM when the CI PAL 5 is active. The SECAM 2 module is therefore inactive during PAL reception. By the connections g, h, i, the chrominance signals RY, VY, BY are transmitted from module 2 to the inputs of amplifiers 7, 8, 9, or they are added to the signals R, G, B delivered by the output of the IC PAL 5.

 The various operating modes are now described separately.

PAL operation
When receiving a PAL signal, the CI detects the presence of the burst and consequently connects the PAL decoder, that is to say that the color blocking is activated so as not to remove the chrominance subcarrier modulated; module 2 indeed records that no SECAM signal is received as a result of the PAL operation lacking the SECAM identification signal, consisting either of oscillations of the chrominance subcarrier, emitted at the start of each line with a frequency switches from one line to the next, either by the identification signal at the frame frequency. Color blocking therefore disconnects the SECAM decoder. The chrominance signals are therefore all zero on the connections g, h, i and thus have no influence on the signals R, G, B applied to the inputs of amplifiers 7, 8, 9. The module 2 is thus completely inactive during APL reception. Since the PAL and SECAM identification signals are similar, it may happen that disturbed signals however produce the unwanted connection of the SECAM decoder. This is why the forced switching mentioned above by the regulating variable U is provided
s and in any case disconnects the SECAM decoder during reception
PAL, so that it does not deliver any signal to module 1.

SECAM operation
In SECAM operation, the PAL decoder is disconnected by the color lock, due to the absence of the synchronization signal.

PAL color. Only luminance signals are then applied to the outputs R, G, B, because the channel of the luminance signal Y is not interrupted in the CI PAL 5. The translation of the identification signal
SECAM makes the SECAM decoder active in module 2 and thus causes it to deliver the chrominance signals to module 1, via the connections g, h, i.

It can be shown that the desired color signals for controlling the picture tube 17 then reappear on the inputs of the output amplifiers 7, 8, 9. The CI PAL delivers the signals
R, G, B, which can be expressed as follows
R = Y + (RY)
V = Y + (VY)
B = Y + (BY)
The chrominance signals R-Y1 V-Y1 BY according to the SECAM standard are zero in the PAL decoder, because the latter is disconnected as a result of SECAM reception. Only the signal Y is therefore applied to the three inputs of the amplifiers 7, 8, 9. The addition of the chrominance signals of the SECAM 2 module by the connections g, h1 i therefore produces the following signals on the inputs of the amplifiers 7, 8 , 9
Y + (RY) = YY + (VY) = V
Y + (BY) = B.

 It can be seen that the signals desired for controlling the picture tube 17 are again available on the inputs of the three output amplifiers 7, 8, 9. The luminance information comes from the CI PAL 5 and the color information from the SECAM CI 21.

Black and white reception
The PAL decoder and the SECAM decoder are disconnected during black and white reception, so that neither the PAL 5 CI nor the SECAM 21 CI deliver chrominance signals. All the chrominance signals are then zero according to the preceding equations, so that only the luminance signal Y appears as desired on the inputs of the amplifiers 7, 8, 9.

 The module 2 thus advantageously performs only the absolutely essential functions during SECAM reception, in addition to those of PAL reception. Moudle 1 continues to perform all other functions, not typical of SECAM.

 Independently of PAL or SECAM reception, module 1 thus ensures the processing of the luminance signal Y, the limitation of the peak beam current, the limitation of the average beam current, the adjustment of the brightness and the contrast, the additional insertion of R, G, B signals for teletext, etc. possible

 Two delay lines 6 and 23, of delay equal to the duration of a line, are certainly necessary. These lines are however today at a very low price. This additional expense compared to known assemblies is low compared to the resulting advantages, in particular with regard to the possibility of retrofitting.

 In FIG. 2, only the PAL module 1 is plugged into the chassis 24, so that the television can only receive in PAL. The module i is however already provided with connectors 25, 26 which contain the pins a to i according to FIG. I.

 In FIG. 3, the SECAM 2 module is simply plugged into the connectors 25, 26 of the PAL module 1, in the direction of the arrow 27.

The television is thus transformed without any other operation into a PAL / SECAM television.

 Of course, various modifications can be made by those skilled in the art to the principle and to the devices which have just been described only by way of nonlimiting examples, without departing from the scope of the invention.

Claims (7)

Claims 1. PAL / SECAM multinorm color television receiver, characterized in that a first module (1), containing a PAL decoder (5) and comprising output channels R, G, B (7, 8, 9), is connects to a second module (2) containing a SECAM decoder (21), which receives from the first module (1) the modulated chrominance subcarrier (F), then returns the chrominance signals fR-Y), (VY), ( BY) which are extracted from it in the first module (1), in which they are added to the corresponding signals applied to the output channels R, G, B (7-9). 2. Decoder according to claim 1, characterized in that each module (1, 2) contains its own delay line (6, 23), of delay equal to the duration of a line. 3. Decoder according to claim 1, characterized in that the first (1) and the second module (2) each contain an automatic blocking circuit of the color channel, which blocks said channel when the corresponding chrominance signal is not received. 4. Decoder according to claim 3, characterized by forced switching (Us) which, when the decoder of one module (1, 2) is active, switches the decoder of the other module (2, 1) to the inactive state ( connection (e). 5. Decoder according to claim 1, characterized in that the second module (2) receives exclusively from the first module (1) all the necessary voltages, such as modulated chrominance subcarrier (F), operating voltages (U3), pulses clock (15), color contrast adjustment voltage, forced decoder switching, and the like. 6. Decoder according to claim 1, characterized in that the first module (1) comprises three adder stages (7-9), the first three inputs of which are connected to the output channels R, G, B of the PAL decoder (5), whose three second inputs receive the chrominance signals (RY), (VY), (BY) from the output of the second module (2) and whose outputs deliver the signals for controlling the color picture tube (17) in the two modes of operation (PAL, SECAM). 7. Decoder according to claim 1, characterized in that the second module (2) can be plugged into the first (1).