DE1963819C - Circuit arrangement for suppressing the color subcarrier contained in a PAL signal - Google Patents

Description

\ IT

is sufficient, where f _{z is} the line frequency, e - 0.25 and η 284.

Di'- lirliiuhiiig refers to a circuit arrangement for the suppression of the video signal in a l-'arb (TÜAS signal) according to the PAL standard contained color signal.

The circuit should therefore use the interlocking frequency spectra of the maturity signal and the color simial separate and suppress the color signal.

Fig.l shows the frequency spectrum of a PAL signal. The components of the luminance signal (K) are integer multiples of the line frequency f _t and can extend into the frequency range of the color subcarrier / ₀ == 4.43 MHz. In the frequency range of the color subcarrier, the components of the color difference signals U, V and the color subcarrier around the K components are grouped - each offset by a quarter line frequency.

ίο With home recipients one is content with this Purpose according to the German Auslegeschnft 1 437 061 with a band pass or a blocking circle in the color carrier area and accepts color disturbances at the edges and in the finer image details. at transcoding, for example a video signal according to the PAL standard into a signal according to the SECAM standard, but small amplitudes at the band limits already result in disruptive interference with the or the SECAM ink carriers.

The filter for filtering out the luminance signal Y would therefore have to be the one shown in FIG. 1 b, which represents the ratio of the output voltage to the input voltage as a function of the frequency, have the frequency response shown. Filters with such a character-

ristics. where the zeros are on the frequency axis repeating it periodically is called a "comb filter". This is generally a direct signal or via a delay line to an adding circuit or a subtracting circuit.

The output voltage depends on the phase shift that the signal experiences through the delay line: If the phase shifts by 180, the result is at the output of the adding circuit (subtracting circuit) a Nullsteüe (maximum), while

with a phase shift of 0 l J ^ r 36O ^r a maximum (zero point) occurs. If the delay time T is measured to be equal to a line period l // _f , then the luminance signal can either be let through or blocked even at high frequencies,

depending on whether the delayed and the undelayed signal are added or subtracted from each other. The German Auslegeschrift 1 266 348 shows an arrangement of this type. If, on the other hand, one of the components U or V of the color difference signal is

filter, the delay time Γ must be greater; it must apply

1/7 U (1 -on).

with PAL e 0.25 and / 1 284 (cf. TeIefunken-Zeitung, vol. 37 11964], issue 2, pp. 115 to 135).

Such comb filters have also been used to separate the color signal. A fundamental one However, the disadvantage of all known circuits of this type is the deterioration in the vertical resolution Direction of the image. This is illustrated below with reference to Fig. 2 explained in more detail:

It is assumed that the brightness changes abruptly from the end of the Zeüo / 1! El. B. 100 ^u / ₀ jumps to 0. This jump in brightness of the signal at the Kamnili input is shown in FIG. 2a as a function of the number of lines (and thus also as a function of time). During the line / 1 - | 1 is the iin-delayed K signal 0; the delayed K signal having a still (from the previous line) the value of H) O ¹ V _0, ^s ° bz.w. that after addition a subtraction of both signals at the output of the chimney

filters results in an average value lying at 50 ° / _{0 of} the previous output signal (cf.Fig. 2b), Since with PAL the signal sometimes even has to be delayed by two lines, such an average value is also obtained during the line η + 2, and only then does the output signal follow the input signal.

Another disadvantage is that, without additional measures, the transmission ranges in each case have the shape of a sine curve (1st half). The Comb filter must be an essential for the K signal have wider passband, as in FIG. Ib shown because the spectrum of the V signal is in contrast to the spectrum of the color signal - unlike in FIG. 1 a shown - in the area of the ink carrier has no sharp lines. It is known from the cited literature that the thin area by means of a suitable feedback from the output of the comb filter to the input ucr delay line can shape the passband in the desired manner. However, this will reduce the resolution in vertical direction even further deteriorated because the delayed signal through the feedback again to the input of the delay line and this, even if weakened, runs through again, so that the output signal of the comb filter does not correspond to the jump of the input signal for many line periods can follow.

In a known circuit (International Electronic Rundschau, 1964, No. 8, especially Fig. 5), this integrating effect of the comb filter, which deteriorates the resolution in the vertical direction, is largely eliminated by the fact that the color video signal is caused by a Hol!, - and a low-pass filter is split ¹ *, with only the high-frequency component containing the color signal being passed to the comb filter. For the division of the color video signal and the subsequent composition of the overall video signal from the low-frequency and the higher-frequency color signal-free component, a precisely dimensioned high- and low-pass filter of the crossover is required for the transit time phtsen and amplitude adjustment, a delay of the low-frequency component by one line period and a correction of the vertical aperture is required, which makes the arrangement complex, error-prone and expensive.

It is the task of the invention. Avoid the described night..Ie. Based on a circuit arrangement to suppress the in a color video signal (FBAS signal) according to the PAL standard contained color signal (F signal) by means of at least one comb filter that has a delay line contains the composite signal or the components lying in the frequency range of the F signal of the composite signal by approximately the period duration the line frequency shifts, i: nd that the delayed signal adds to the undelayed signal or of it subtracted and the sum or difference to which Input of the delay line fed back, this object is achieved according to the invention in that at least the components of the composite signal that are in the frequency range of the F signal are the parallel-sounded ones Inputs of two comb filters are fed, one of which is the delayed and the The instantaneous signal is added while the other subtracts the delayed from the undelayed, and that the signals at the output of the K'imml'ilter by a certain Factor amplified, added and subtracted from the composite signal.

The invention is described below with reference to the exemplary embodiment shown in the drawing explained in more detail. It shows

F i g. 3 a block diagram of the circuit according to the invention,

F i g. 4 the frequency response of the transmission element for the entire composite video signal (4a), the frequency response of the first comb filter (4b), the frequency response of the second comb filter (4c) and the frequency response at the output of the circuit according to the invention (4d),

F i g. 5 shows the time course of the output signal when the input signal changes according to FIG. 2 a changes.

In the case of the in FIG. 3 becomes the Color video signal a ^ indpaß 4 and a delay line 5 zugefüi.rt whose delay time corresponds to the transit time of the signals through the bandpass filter 4. The output of the delay line 5 is connected to a subtraction circuit 3. the Bandpass filter 4 only lets through frequency components of the color video signal that contain color components, and feeds the signals filtered out in this way to the inputs of two comb filters 1 and 2. their output signals amplified by amplifiers 6 or 7, summed and the input of the suir action circuit 3 are supplied, where they \ on subtracted from the FBAS signal arriving via the delay element 5 will.

The bandpass allows the use of simple delay lines with a narrow bandwidth (2 MHz) and limits the integrii'rende which is also present to a lesser extent in the present invention Effect of the comb filler on the higher frequency K components.

The comb filters are essentially constructed identically. They each contain an adder stage U or 21. which adds the delayed and the undelayed signal. The resulting signal is taken from the output of the Adding stage by means of a feedback network 12

(22) to the input of the further adder circuit 13

(23) fed back, which adds the fed back signal and the output signal of the bandpass filter 1 and the The input of the delay line 14 (24), which delays the sign J by the time Γ, where the relationship

l / V --./,(I -ein )

applies, with e 0.25 and η 284.In addition, the amplified signal in the comb filter 2 is rotated by 180 in phase by the inverter 25 and fed to the adder circuit 21 (instead, a subtraction device can be used instead of the Block 21 subtracts the delayed signal from the undelayed signal).

The comb filters described are known per se from the first-mentioned literature slide, in particular FIG. Only the components of the color difference signal U (cam filter 2) or the color difference signal V (comb filter 1) appear at its output. Their effect in connection with the rest of the circuit can be explained with the aid of the sequence shown in Fig. 4:

F i g. 4a, which shows the frequency response of the delay element 5 shows, it can be seen that the entire composite signal enters the SubliaklionssehalUiiuj 3 im reached weakened. F i g. 4h and F i g. 4c show the Frequency response »: of the comb filter 2 or the comb filter

tillers I. which in each case only let the I arbdiffercnzkoniponen- (CIi ('or I' pass. The pass curves are the more acute, the greater the positive feedback. If now the gain of the amplifiers 6 and 7 is measured so that the amplitude The U and K components which the U and K components carry out the subtraction section have the same value as the U and K components contained in the FBAS signal, they stand out from the FBAS signal at the output of the subtraction circuit 3, so that the values shown in F i g. 4d angcdculctc I iUercharaktcristik arises.

Further properties of the contraindication result from a quantitative study.

The output voltage i / ₂ . as far as it lies in the frequency range of the color signal, is calculated as

Ii ₂ Ii, - V ₁ U _x I ₂ I /,;.

Equation (6) shows that for A O the output voltage i / js O will. It's easy to see because the effects of the delay lines 14 and 24 cancel each other out, since once subtracted and once; 'ddicrl will. This means that feedback (A 1 0) is absolutely necessary.

The minima (zeros) of the amount of ι / ₂ / ι / result, as already explained, at

cxp (- 2./irT) I 1.
The maxima are included

cxp (- 2 JItT) ■ - 1.

These values lie exactly in the middle between the minima and thus with the components of the / signal. The amount of the maxima is calculated as follows

Here ι /, the input voltage, u " and, inter alia, the output voltage of the comb filters 1 and 2; the sizes // ,. U ₁ . u " and ιι, ι represent complex voltage amplitudes. v, and \ · ₂ denote the gain factors of the amplifiers 6 and 7.

The voltages i /, and ιι, ι result from the designations given in equations 21 and 22 of the first-mentioned Lilcralur-McIIc

»2

'Ί

2k

A- ²

(for A- > 0).

I '» 1 t exp ( JwT) "1 1 - - A ₁ exp (-jwT) tl, l 1 - cxp ( -./W) "1 1 ί A ₂ cxp (- JhT)

A ₁ and A _{2 are} the (positive) feedback factors (A ₁ , A ₂ <1) of the feedback sensors 12 and 22: ir means the angular frequency. If equations (2) and (3) are inserted into equation (1) and added, then under the assumption V _{1 results}

ν and A, A ₂ A

1I ₂

»Ι

2, 2 A- exp (- 2jwT)
IA ² cxp (- 2j \\ T)

For example, the maximum for A = 0.7 has an as value voi: 0.94. The K components of the output signal Ii ₂ have - as far as they are in the frequency range of the color signal - an _{amplitude 6 ° / 0} lower than the X components in the input signal u, or than the low-frequency ones at the input of the

(2) 30 components of the subtraction circuit

V signals. This slight difference, which becomes smaller, the larger k is. can, if necessary, by subsequent amplification of the high-frequency

(3) K components are repealed.

In the event of a jump in the y (brightness) signal at the input of the circuit from 100 ⁿ / ₀ to 0, as shown in FIG. 2a is indicated, the following results:

The K signal delivered via the delay element 5 or via the bandpass filter 4 is - if you leave it once

4, "the term of the members 4 and 5 ignore - immediately after the jump 0. The delay line 14 (24), however, still storing the existing before the jump value this must because it to J, adds / (subtracted), u. _s (u _d gives the value

(4) 45

- W ₁ {u _d +

If one measures r in such a way that the second term in equation (4) becomes maximally -1 (maxima of this term result in each case at exp ( -2 JwT) + ■ 1). then there are zeros: this must apply:

1 -

The zeros are at the color carriers and the O-Components and the ^ -components, if

MT

is. According to the analysis of equation (5) in equation (4) and corresponding shaping results

All cxp (2 / »7)
I k -exp (2 /.1 /)

to have. The signals originating from the delay lines 14 and 24 result after the addition, exactly as before the jump, iu · 11.1. But since (at A- 0.7) the K component of the signals passing through the comb filter _{only reduces the V component of the signal H 1} by 6 ° / ₀ , only this small portion of the K signal reaches the input and - there yes No more signal comes through the amplifying element 5 - at the output of the subtraction device. At the end of the line period, the feedback to the input of the delay lines 14 or 24 results in a signal weakened by the feedback factor A-, which is further weakened at the end of the next line, etc. However, the values appearing at the output of the subtraction circuits are so small that that they do not disturb.

The circuit behaves in a similar way with one of the rarely occurring vertical arbumps. However, since the U and Γ components passing through the delay line have a large amplitude (10 °, _o

in the signal //, contained U and K components) there is a strong color falsification at the output: ben. This can be done in a known way (see Interionalc Electronic Rundschau, 1969, No. 8, 9 °. Fig. S) by - not in the drawing

- Eliminate the color carrier trap shown. The color carrier trap has a blocking area in a narrow area around the ink carrier, so that most of the Energy contained in the color signal can be suppressed.

1 sheet of drawings

209642/356

Claims (5)

Patent claims: 1.Circuit arrangement for suppressing the color signal (F signal) contained in a color video signal (FBAS signal) according to the PAL standard by means of at least one comb filter that contains a delay line that carries the FBAS signal or that is in the frequency range of the F Signal lying components of the composite signal delayed by approximately the period of the line frequency, and the delayed signal is added to or subtracted from the undelayed signal and the sum or the difference is fed back to the input of the delay line, characterized in that at least the in the frequency range of the! ⁷ signal lying components of the composite signal are fed to the parallel-connected inputs of two comb filters (1,2), of which one (1) adds the delayed and the undelayed signal, while the other (2) subtracts the delayed signal from the undelayed signal , and that the signals at the output of the comb filter are _{amplified by a certain factor (ν, r 2} ), added and subtracted from the composite signal. 2. Circuit arrangement according to claim I, characterized in that the delayed signal in the other comb filter (2) rotated 180 in phase and to the undelayed signal is added. 3. Circuit arrangement according to claim 1, characterized in that the FBAS signal is the The inputs of the comb filter (1, 2) are fed via a bandpass filter (4) which only covers the frequency range lets through, in which there are components of the color signal, and that the composite signal the subtraction device (3) is fed via a delay line (5) which determines the transit time of the bandpass filter (4). 4. Circuit arrangement according to claim 1, characterized in that the signals at the output of the comb filters are amplified by the same factor (v) and that the feedback factors are the same for both comb filters (k) , where the relationship is dij ν Ml - / c ² ) / (2 I 2 k)
holds, with k> 0. 5. Circuit arrangement according to claim 1, characterized in that the transit time (T) of the signals in the delay lines (14, 24) of the comb filter (1.2) of the equation