DE1281485B - Adjustable additional delay line in a runtime signal splitting circuit for color television receivers of the PAL type - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

H04n

German class: 21 al - 34/31

Number: 1281485

File number: P 12 81 485.6-31 (L 50146)

Filing date: March 9, 1965

Opening day: October 31, 1968

The invention relates to an adjustable additional delay line in a delay time signal splitter circuit with a fixed delay line of the delay of a line duration for PAL color television receivers, the delay time of the entire delay line at quarter line offset 283.75 ± 0.25 color subcarrier periods amounts to.

Of the known color television transmission systems, only the one that originated in America is so far NTSC system has been put into practical use to a greater extent. However, its main disadvantage is in a high sensitivity to phase errors. There are therefore improved transmission systems, e.g. B. the PAL and the SECAM system, have been developed that retain the basic principle of the NTSC method, but avoid its disadvantages.

The new systems make use of an experience according to which two neighboring Lines of a television picture show almost no differences. For example, in the SECAM process on the transmitter side, in addition to the luminance signal, there is always only one color information from line to Transfer lines alternately. A delay then arises in the receiver in each case a first Color information the simultaneity with the following color information by one line duration.

In contrast to this, with the PAL transmission system, both color information is the same as with the NTSC system transmitted simultaneously and the match between two adjacent lines for Compensation of errors exploited. There is also a delay element here on the receiver side necessary to delay the color information for a line duration.

It is common practice in the PAL color television system as a delay element in the time of flight signal splitting circuit use a fixed delay line, e.g. an ultrasonic delay line, which has an adjustable additional delay line via a transformer to compensate for manufacturing tolerances is downstream. The auxiliary delay line consisting of a spool with a rotating core represents a relatively complicated and expensive switching element.

It is also known to use an all-pass as an additional delay line. Such an all-pass however, it must have the same effect as a wire-wound auxiliary delay line to be able to include a large number of individual elements, so that an extensive circuit is created Matchable

Additional delay line in one
Runtime signal splitting circuit for
PAL type color television receiver

Applicant:

Loewe Opta

Company with limited liability,

1000 Berlin 46, Teltowkanalstrasse. 1-4

Named as inventor:

Dipl.-Ing. Werner Engel, 8621 Gestungshausen;

Hermann Garreis, 8645 Steinwiesen

and considerable adjustment work is also necessary.

The invention is therefore based on the task of replacing the additional delay line used previously to provide a simpler adjustment element.

According to the invention, there is an adjustable additional delay line in a delay time signal splitting circuit with a fixed delay line of the delay of a line duration for PAL color television receivers, where is the delay time of the entire delay line at quarter line offset 283 ± 0.25 color subcarrier periods, such that when the adjustment points the additional delay line for the transit time by ± 1 color subcarrier period to the stated values from an adjustable series inductance and a parallel-connected trimmer capacitor, a There is a setting resistor and a further trimmer capacitor connected in parallel.

A phase-accurate adjustment can thus be carried out again. There can be two Errors occur:

1. The delayed signal can have a maximum of one oscillation compared to the theoretically correct one Value arrive early or late.

2. The bandwidth of the circuit is too small.

The cause of the first error is based on the structure of the PAL system, according to which the Delay line to be provided with exact transit time, which differs from the real duration of a line by ± 0.25 Periods must deviate, 283.5 or 284 periods of the color carrier may be. Commercially available ultrasonic delay lines be with. a delay time of 63.8 ± 0.1 με. In periods

809 629/1133

the color subcarrier frequency of 4.433 MHz are converted for the tolerance range of the delay line at 63.7 μβ 282.4 periods and at 63.9 μβ 283.3 periods.

If the delay line is now allowed to run not only 283.5 and 284 periods, but rather even ± 1 period to these values results in the following running times: 282.5, 283.5, 284.5 or 283, 284, 285 periods with which an adjustment is to be achieved. By this measure of comparison to ± 1 period from the correct values, the color information theoretically loses its resolution. However, since the color information is only transmitted with a maximum bandwidth of 1.5 MHz, is the loss a period with the color subcarrier frequency of 4.433 MHz is meaningless. So it arises several values with an interval of 0.5 periods each, to which a comparison can be made. This is possible with a simple LCÄ element.

The second mistake, namely the limited bandwidth, goes back to the following:

The frequency spacing of the sidebands from the color subcarrier center frequency is 4.433 MHz at Same band operation a maximum of about 0.7 MHz. Used as a variable delay circuit LCR element, the delay time gives way to the sidebands slightly depends on the running time of the center frequency. Phase errors can therefore occur with steep color transitions arise, which, however, can be kept sufficiently small with appropriate dimensioning. A LCÄ element has an amplitude response that differs from the Depends on the delay time, which, however, is controlled by a setting controller in the undelayed transmission branch can be compensated.

When using an LCR delay element, small signal errors occur, but these are not perceptible to the viewer on the screen of a color television receiver. Overall, therefore, the advantages of the new runtime signal splitting circuit predominate, especially in device manufacture. The relatively difficult production of the adjustable additional delay line, of which at least two stages of different basic delay times had to be present up to now, is no longer necessary. In addition, the exact adjustment can be carried out in the simplest possible way using variable inductances and resistors. In addition, there is a further simplification in many cases: The delay element is attenuated at the input by the fixed delay line and at the output by the subsequent circuit. Therefore, in general, part of the additional delay line (phase shift element) can be omitted. The required delay can then be produced simply by adjusting an L or C element. Since the fixed delay line - as already mentioned - has to be adapted to the subsequent circuit by a transformer anyway, a parallel capacitor is sufficient as the only additional component if it is assumed that the inductance of the transformer can be tuned.

The invention is explained in detail with reference to the drawing. The one shown in the drawing Circuit diagram of a time-of-flight signal splitter circuit for a PAL color television receiver containing a transistor 1, at the input of which a color signal flies, which is tapped at the emitter resistor 2 and a fixed one Ultrasonic delay line 3 is supplied. To the fixed delay line 3 is via a Transformer 5 coupled to an additional delay line 4. The additional delay line exists from a phase shift element, which has a secondary winding 6 of the transformer 5, two transverse capacitances 7, 8 (Trimmer capacitors) and a series resistor 9 includes. All elements of the phasing element are designed to be adjustable. From a wiper of the emitter resistor 2, which is designed as a potentiometer leads a connecting line to a primary winding 10 of another transformer 11, its Secondary winding 12 is connected to ground with its center tap 13. One end of the secondary winding 12 has a signal voltage shifted in phase by exactly 180 ° with respect to the other end. Both signal voltages and the delayed signal each influence a resistor matrix 14, 15 or 16.17, their taps 18.19 to one each in the drawing synchronous modulator, not shown, are connected.

Since the phase shifter at the input through the fixed delay line 3 and at the output through the following circuit is attenuated, the setting resistor 9 and the Capacitor 8 is omitted without any disadvantages resulting therefrom.

Claims (3)

Patent claims: 1. Adjustable additional delay line in a delay time signal splitter circuit with a fixed delay line from the delay a line duration for PAL color television receivers, the delay time being the total Delay line at quarter line offset is 283.75 ± 0.25 color subcarrier periods, thereby characterized in that when expanding the adjustment points for the transit time by ± 1 color subcarrier period to the values mentioned the additional delay line (4) from an adjustable series inductance (6) and one to it parallel-connected trimmer capacitor (7), a setting resistor (9) and another there is also a trimmer capacitor (8) connected in parallel. . 2. Adjustable additional delay line according to claim 1, characterized in that the series inductance (6) part of a between the fixed delay line (3) and the additional delay line (4) provided transformer (5) with adjustable inductance. 3. Adjustable additional delay line according to claim 1 or 2, characterized in that that with sufficient attenuation of the additional delay line (4) through the fixed delay line (3) on the one hand and through which at the output of the additional delay line (4) itself subsequent circuit on the other hand, the setting resistor (9) and the capacitor (8) are omitted can. Considered publications:
Funkschau, 1964, no. 23, p. 626;
Telefunken-Zeitung, 1964, no. 1, p. 63;
radio mentor, 1964, no. 2, p. 111. 1 sheet of drawings 809 629/1133 10.68 © Bundesdruckerei Berlin