DE2142899C3 - Circuit arrangement for decoding color television signals according to SECAM. system - Google Patents

Description

r result in a frequency demodulator signal in front of the transit time memory.

; is arranged. The object of the invention is to provide a circuit

In the SECAM color television system, orders are used to decode color television signals

: known to indicate two color signals line by line alternating according to the SECAM system, in which

by means of a frequency-modulated color subcarrier, the circuit complexity is significantly reduced for

wear. During the decoding, the storage time makes the transit time memory an inexpensive, but qualitative one

use a high-quality clock sonic delay line for line duration by means of a delay line

a color signal is repeated in the lines, in which it can be detected and interferences caused by echo

which it is not transmitted, so that before and after signals do not have a visible effect,

the transit time memory both color signals at the same time 35 The circuit arrangement for decoding of

available. After the transit time memory is a color television signals according to the SECAM system with

Electronic switch required, which has a runtime memory and a switch for

two color signals to the associated channels - conversion of the sequential to simultaneous color

arranges. signals, whereby in the signal path before the runtime storage

Up to now it has been customary for a frequency demodulator to be arranged in front of the transit time memory * s

only one carrier-frequency equalization stage and according to the invention characterized in that between

to provide a limiter. The two color channels see the frequency demodulator and the transit time memory

after the switch, a low-pass filter, a keyed video equalizer stage and

and each contained a second limiter, an amplitude modulator and thatC

Frequency demodulator, a low-pass filter and one for each of the two color signals R-Y "and B-K

groped video tarer level. The decoded, video amplitude demodulator in the signal path after

Frequent output signals RY and BY were provided with changeover switches.

Then the dematrix to form the control signals for From the German Auslegeschrift 1 044 154 it is

fed to the picture tube. Although already known, amplitude demodulators before

This known circuit is relatively complex because it is to be arranged in this way or behind the transit time memory. These

however, for each of the two color signals other than its own known circuit refers to one of

Demodulator also requires the SECAM system of today's standard type required for demodulation.

auxiliary equipment such as limiter and escapes of the SECAM-AM color television system

zerrer, had to be provided twice. which does not require frequency demodulation

Also step through the new on the market 55 dig is.

reflection delay lines that have come in The circuit according to the invention has the advantage the known circuit multiple-t-echo interference that by using only one frequency demodulation (in particular 3-T echo interference), which has a lators, a low-pass filter and a video equalizer stage considerable loss of quality of the decoded output for the two color signals and not just the effort common signals. These interfering signals are significantly reduced, but also significantly In the case of the frequency-modulated signals, they are less particularly sensitive to interference from foreign carriers from the fact that between the delayed and the multiply sensitive functional levels are present. A delayed, frequency-modulated color subcarriers Inter- Another advantage is to be seen in the fact that through the References arise. This has a Störphasenmodu- alternating transmission of the color signals via the lation result that after demodulation and 65 the same demodulation channel for both color signals Obtaining the control signals for the picture tube on completely identical transmission properties before The screen is visibly disruptive. lie. In addition, multiple t-echo these have an effect Disturbances »are therefore very noticeable, since disturbances in the reflection delay line are visible

3 4

not off, as both signals (delayed and multiple gatesU or 14 are frequency-modulated

delayed signal) on the same carrier - signals demodulated To eliminate color

are modulated, and thus no interferences between carrier elements then passes through each video

rule carriers of different frequencies and frequency color signals each have a low-pass filter 16 and 17, respectively.

Phasing can occur. This means that 5 In keyed video equalizer stages 18 and 19 are required

also no high demands on the reflection video frequency made in the SECAM coder

delay line compensated for the accuracy of the predistortion of the color signals

Term to be asked. Another advantage is outputs 21 and 22 of the B&H decoder

there is little adjustment effort for amplitudes - the two color signals RY and BY are now available

modulation and demodulation. "> available and can then be sent to the dematrix

When a color saturation setting is used, the formation of the control signals for the picture tube is supplied

The best synchronization between the two signals will be achieved.

ensures that there is only one electronic control circuit in the circuit arrangement according to the invention

must be used, compared to two control switch according to Fig. 2, the SECAM color television signal

with the known circuit. 15 as well as in FIG. 1 via terminal 1 of the

The invention is now to be supplied with reference to FIGS. 1 and 2 zerrerstufe2 and the limiter}. There-

are explained in more detail, with only the explanation after it is demodulated in the frequency demodulator 23

the parts necessary for the invention are shown. lates. After demodulation, 24

The same parts appearing in both figures are still present carrier-frequency components.

provided with the same reference numerals. It shows ao presses. The one made in the SECAM coder

Fig. I the block diagram of the known deco video-frequency predistortion is in the video encoder for color television signal after the SECAM distortion circuit 25 reversed The on the AusSystem, step 25 occurring sequential color

F i g. 2 the block diagram of the signals according to the invention are shown in the following amplitude modulus Decoder for color television signal after the SECAM- 15 lator 26 modulated onto a carrier whose frequency System. quenz z. B. is about 4.43 MHz (center frequency In the known decoder according to FIG. 1 arrives in the pass band of the reflection delay line

the SECAM color television signal via a terminal 1 device). The one with the sequential color signals

to an equalizer stage 2, which on the one hand becomes the amplitude-modulated carrier that is separated off directly

the FM component of the overall signal, 30 and once via the transit time memory 4 to the cross

on the other hand, the switch 6 made in the SECAM coder is supplied, so that the two signals on the

reverses carrier-frequency predistortion. At output 7 or 8 are present simultaneously and the

then the modulated color carrier is assigned to the respective channels RY and BY

an amplitude limiter 3. The limited fre- can. A certain amplitude of the is used here

frequency-modulated color signals are once directly _3S carrier (achromatic signal) as a reference voltage for

and once via a run-out memory 4, the amplitude demodulators. After the atnpli-

Changeover switch 6, the so-called cross switch, to- tude demodulation in demodulator 28 for the purpose

guided. In the transit time memory 4, the signals Ä-V-Kanal and in the demodulator 29 for the BY-

by the duration of a line of e.g. B. 64 μ5ε! Ί delayed. Channel can use the videofrequentcn color signals such as

As a result, a color signal in lines _{40 is} usually fed to the inputs of the dematrix.

repeats in which it is not transmitted, so the.

that at the connections 7 and 8 the two color In the decoder according to the invention the signals are alternating line by line, but simultaneously before multiple t-echo disturbances of the reflection delay. The electronic changeover switch 6 also switches the line, but the two color signals are now line-frequented on the channels associated with the amplitude-modulated color, in which the demodulation differential signals are such that there is only a reduction in the frequency-modulated, carrier-frequency colors Total amplitude of the respective color difference signals is made. Each of the two channels results in signals. This can be by a larger Verenthält a second limiter 11 and 12, slightly in strengthening in the respective channel out which the delayed and the undelayed equalized be exceeded _50th Disturbances in the form of lighter and lighter carrier-frequency color signal on the same ampli-darker reproduced line groups on the tuden. The frequency demodula screen does not occur here.

For this purpose 2 sheets of drawings

Claims (1)

Stanzas of six lines in two up * claim: be played einanderfolgendsa partial images of light and dark \ ^T. The formation of ZeUen circuit arrangement for decoding groups of six lines each over two fields provides color television signals according to the SECAM system 5 in connection with the type of connection of the two SECAM-ter selected in the SECAM process with a transit time memory and a switchover for converting the sequential in simul- color carriers. A certain reduction in these errors - tan color signals, with a frequency demodulator in the signal path in front of the delay time memory according to the conventional decoding methods - only by increasing the degree of limitation of the fet, characterized, io downstream limiter possible, but it succeeds between frequency demodulator (23) and it is not possible to achieve a reduction to below the visual transit time memory (4), a low-pass filter (24), a availability limit. sampled video user stage (25) and an amplification modulator (26) are arranged, and that it is furthermore already known, the frequency for the two color signals {RY, BY) each a 15 demodulator in the signal path before the transit time memory Amplitude demodulator (28 or 29) to be arranged in the signal. In this known circuit are provided away after the changeover switch (C). However, the two color signals are low-frequency, delayed, which means that the effort for the run time ■ memory is very large. Because a low frequency This transit time memory for color signals would then have to The invention relates to a circuit arrangement, for example, a much more expensive and, moreover, one »Ur decoding of color television signals after the more extensive cable delay line or also • SECAM system with a runtime memory and an equally expensive so-called charge-coupled system - Be a switch for converting the sequential memory chain circuit, which also has a len into simultaneous color signals, with a strong deterioration in the quality of the delayed signal path as