DD206521A3 - CIRCUIT ARRANGEMENT FOR REDUCING INTERFERENCE IN THE COLOR CHANNEL IN VIDEO STORAGE DEVICES, ESPECIALLY FOR SECAM SIGNALS - Google Patents

Abstract

The invention relates to a switching arrangement for the reduction of disturbances in the color channel by compensation of the components of dust by means of a comb filter which consists of a delay line and summing stage in video memory devices, and to a further reduction of these disturbances and thus a further improvement of the picture quality. THEREFORE, A COMPENSATION OF THE STOERANTS FOR ANY STATISTICAL SIGNALING COMPONENT SHOULD BE ACHIEVED. According to the invention, in parallel to the summation stage of the comb filter on the basis of its delay line, a summing stage is provided, and the summing stage and the sub-step are connected, respectively, to a nonlinear amplification stage connected to a final summing stage.

Description

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Circuit arrangement for reducing interference in the color channel in video memory devices, in particular for Secam signals

Verwesadungs.zweCk ₁₁ of Erfindunß

The invention relates to a circuit arrangement for reducing disturbances which occur in the case of video storage devices as a result of insufficient crosstalk attenuation of adjacent magnetic tracks and, in particular, result in undesirable deteriorations of the picture quality in the color signal.

The invention relates in particular to the treatment of SECAM color signals by way of reproduction by comb filtering.

State of the art

In Videoaufseichnungsgeräten it is common to split the composite color video signal in a brightness signal and in a carrier-frequency color signal · The brightness signal] is frequency-limited and modulates a carrier in the frequency. The color signal is transposed into a frequency range which is below the range for the frequency-modulated luminance signal. It is customary to record the magnetic tracks close to each other without gaps and for the purpose of reducing the crosstalk components from adjacent tracks which are not entirely avoidable by tracking errors or magnetic scattering two mutually scanning magnetic heads in such a way that their! head gaps differ

19.10.81 -G966158

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Take an angle based on the orientation of the track.

However, this slanted tilt position, which is referred to as the azimuth offset, only acts for higher frequencies, ie. h "for the frequency-modulated luminance signal" For the color signal recorded at low frequencies, the slit skew only has a small effect, therefore it is necessary to provide further measures to suppress unwanted crosstalk.

It is therefore usually switched when recording in a certain line frequency rhythm, the phase of the color signal. The rhythm becomes track geometry, i. the assignment of certain pixels on the magnetic track and the ITorm of the image signal to be stored with two, four or eight lines selected. During playback, the rhythmic phase change made during recording is reversed and the color signal is then passed through a comb filter in which the disturbing crosstalk components are suppressed. These for all fixed carrier operating color television systems z. B. PAL and NTSC well-functioning arrangement fails if the reference carrier for the color information is not constant or the coloring information itself as a frequency modulation such. B. is used in the SECAM horm.

Since in SECAM color television signals, the two color difference signals are transmitted line sequentially, so in the rhythm of two line periods abut each similar color signals, the comb filter is to be formed over a delay line for two lines. FIG. 1 shows a conventional arrangement for a comb filter. From an input 1, the signal is once fed directly to a summation stage and once via a delay line 3 for two lines of the same summation stage 2. At an output 4, the comb filtered color signal is available. Such a filter can only work properly with SECAM signals if

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the color content of the two mutually added signals can not be, different "Step in the vertical direction Farbübei transitions, so there is color distortion ·

In the DB-AS 29 11 927 a solution is given how color interference in SECAM signals are avoided at vertical transitions.

The specified solution is shown in FIG. 2. The comb filter is formed as in FIG. 1 from the delay line 3 for two lines and the summing stage 2, but a switch 5 is provided which switches off the delayed channel when phase deviations occur between the direct and the delayed signal. The switching criterion is obtained in a phase comparator 6 from the comparison of the phases and converted to the switching voltage after an amplitude evaluation in a threshold amplifier 7. In the invention description, it is emphasized that the error signal arising during the phase comparison provides a direct measure of the similarity of the color signals in the two periods len. However, it can be easily deduced that this criterion is not sufficient by itself, because even with completely coincident signals, the phase difference of the compared signals at a fixed predetermined delay time frequency dependent.

To illustrate the dependence of the phase between input and output of the delay line, the following consideration is given:

The following apply:

"C s delay time

f = signal frequency

T = ^ r ss period

The number of signal periods delayed in the delay line is

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η S

Itur for the Pall that the Vsrzogerinigsiaeit f is a whole multiple of the signal period T, there is equality in output and Eingangsphaae (ns whole) »If η is not an integer and then 2 η an odd number _s then the phase difference between input and output 180 ·

At the usual delay times of 2 line period durations

t s 2 · 64 / US s 128, us

and the usual signal frequencies of about * 4 MHz corresponding to T = O ₉ 25 / üs

η & 500.

If the input signals present in chronological order are not different in frequency, the phase difference between the input and the output of the delay line is different from the ratio "?" dependent and can not be used as a criterion for the shutdown of the delayed channel.

The actual effect of the known arrangement is limited to the work area, in which the condition for phase equilibrium η = integer is maintained or largely approximated. Judging from the particular when SECAM signals legitimate statistical distribution of the instantaneous _frequencies} then, this applies only for a small fraction of the operating states, so that image interference.

Object of the invention

The invention aims to further reduce the interference in the color channel caused by crosstalk between adjacent magnetic tracks in video storage devices.

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Dar1e ^ mi ^ the essence of the invention

The invention has for its object to provide a Schaltungsanordn, which achieves a compensation of the interference components on comb filters for oede statistically occurring signal component.

This object is achieved with a circuit arrangement for reducing disturbances in the color channel by compensation of the interference components by means of a delay line and Sutnmierstufe comb filter according to the invention that parallel to the summation after the delay line a Subtrahie stage is provided and that the summation and the Subtrahie stage with each connected to a non-linear amplitude transmission stage, which are connected to a final summation.

An expedient embodiment of the invention provides that the non-linear amplitude transmission stages are designed zero-point-symmetrical. Also, the summing and subtracting can be connected to a switch-controlling amplitude Auswertestufe and the switches with the final summing, the switches can also be designed as a continuous arbe tend actuators.

Ausführunssbeispiel

The features of the invention will be illustrated in an embodiment.

In Fig. 3 of an input 1, the color signal of the delay line 3 is supplied. The delayed signal is fed to the summation stage and to a subtraction stage 8 and added or subtracted with the direct signal supplied by input 1. In subtraction, it is advantageous to subtract the delayed signal from the undelayed signal. The sum signal becomes one

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Nonlinear Amplitudenüberfcragungsstufe 9 »and the difference signal is a nonlinear Amplittidenübertragungsstufe 10 performed. The output signals of these two distortion stages are combined additively in a final summation stage 11 "the signal freed from crosstalk components is available at the output 4",

As a characteristic of the characteristic of the two non-linear stages 9 and 10 preferably zero-point-symmetrical arrangements are provided, as described for. B * with arrangements according to Pig. 4 as antiparallel connected diodes 12 can be realized in conjunction with a load resistor 13.

Level conditions and characteristic curve are to be chosen so that in at least one branch of the non-linear stages 9 and 10, a signal component is transmitted.

In the case of the phase equality between the input and output of the delay line 3, the output of the summing stage 2 has a maximum, and at the output of the subtracting 8, a minimum occurs. At the output 4 are mainly transmitted from the non-linear stage 9 signal components, while the signal components from the subtracting 8 due to the non-linear characteristic of the stage 10 are not transmitted.

In the case of the phase difference of 180 ° between the input and output of the delay line of the branch with the non-linear stage 10 is signal leading. There is thus automatically a selection of sum or difference signal, with a suitable adaptation of the level to the characteristics of the non-linear stages, a continuous transition from the sum signal to differential signal can be achieved.

In a variation of the circuit arrangement, the amplitude of the signal present at the output of the summation stage 2 or / and at the output of the subtraction stage δ is evaluated and used for switching

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used the two branches. As an example, Figure 5 shows a possible arrangement. With otherwise the same structure as in Figure 4, a Amplitudenauswertestufe 14 is provided in which from the output signals of the summing 2 and / baw. the subtracting stage 8, the switching voltages for the operation of the switches 15 and 16 are obtained · The switching criteria are chosen so that in each case the greater level signal is switched through. Instead of the switches 15 and 16, it is also possible to use continuous actuators which run in opposite directions; speed of the existing levels each transmit the higher amplitude signal in the manner of the known diversity method.

Claims (4)

E urface Circuit arrangement for reducing disturbances in the color channel of video reading devices by compensating the interference components by means of a comb filter consisting of delay line and summing stage, characterized in that a subtraction stage (8) is provided parallel to the summing stage (2) after the delay line (3) and the Sumtnierstufe (2) and the subtracting stage (8) are each connected to a nonlinear Amplituübübrtragungsstufe (9 or · 10), which are connected to a final summation stage (11) « 2. Circuit arrangement according to item 1, characterized in that the non-linear amplitude transmission stages (9 »10) are formed zero-point-symmetrical · 3 · Circuit arrangement according to items 1 and 2, characterized in that the summing stage (2) and the subtracting stage (8) with an amplitude evaluation stage (14) controlling a switch (15, 16) and via the switches (15> 16) with the final summing stage (11) are connected. 4. Circuit arrangement according to item 1 to 3i, characterized in that the switches (15, 16) are designed as continuously acting actuators « For this 3 sheets of drawings