DE1282063B - Demodulation circuit for PAL color television signals with reduced color saturation errors in the case of suddenly occurring phase errors - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

H04n

German class: 21 al -34/31

Number:
File number:
Registration date:
Display day:

P 12 82 063.2-31 (F 47507)

October 26, 1965

November 7, 1968

The invention relates to a new demodulation circuit for demodulating PAL color television signals. The PAL color television system, described, among other things, in "Nachrichtenentechnische Zeitschrift", Vol. 17, H. 3, March 1964, pp. 109 to 121, has known compared to the NTSC system, the property that in the case of phase errors in the color carrier there are no disruptive Hue errors, only the far less noticeable color saturation errors occur.

To eliminate these color saturation errors that occur as a result of phase fluctuations or phase jumps it is already known to phase synchronously the color subcarrier oscillator for the synchronous demodulators to take part.

Typically, the color subcarrier oscillator is roughly synchronized with the burst, like this is also used with the NTSC method. By the German patent specification 1189124 it is also known, in a PAL system, the received color subcarrier frequency signals after elimination the phase reversal introduced according to the PAL method for fine adjustment of the phase of the oscillator to use. In particular, according to German Auslegeschrift 1196 699, the received multiply conjugate complex color subcarrier components and double the color subcarrier frequency obtained to control the oscillator. Other options are in the German Auslegeschriften 1196700, 1197500 described, after which the oscillator is brought into phase by the conjugate color carrier components and is synchronized by the synchronizing pulses individually or additively in the driving process. Another one Demodulation method in the German Auslegeschrift 1159 011 particularly refers to a SECAM color television broadcast system. A synchronous demodulation method is also used in this circuit used by a carrier-frequency signal obtained from a reference carrier in an adder is added to the individual components and then the mixture is fed to a rectifier will. In the case of rapid phase jumps in the color signal, the readjustment also occurs here because of the inertia of the oscillator falsify the color saturation value.

The invention is based on the fact that the adjustment of the color subcarrier oscillator is always one Requires a certain time, up to which the oscillator has adapted to the readjustment frequency. That means but that especially at sharp edges, at which due to the differential phase error in demodulation circuitry for PAL color television signals large in size to the transmission lines and amplifiers with reduced color saturation error in the event of sudden phase errors

Applicant:

TV G.m.b.H.,

6100 Darmstadt, Am Alten Bahnhof 6

Named as inventor:

Gerhard Krause, 6100 Darmstadt

Phase fluctuations of the color signal and sudden phase jumps occur, the readjustment too sluggish so that clearly visible saturation errors must occur at the edges. The invention pursues therefore a different way in which a readjustment of the color subcarrier oscillator is not necessary.

The demodulation circuit for PAL color television signals, by adding or subtracting the undelayed and the delayed by one line period Color signal the carrier-frequency / '- and ß' signal is obtained and which at suddenly Occurring phase errors of the color subcarrier-frequency color signal have a significantly lower color saturation error provides, is characterized in that according to the invention in the course of the channels for the / '- or Q 'signal components are each provided with an electronic switch actuated in the rhythm of the color subcarrier frequency is that each lets through a half-wave of the components, and that in series with these switches each two parallel peak rectifiers are provided, the two outputs of which with an amount-selective Link are connected, which only that of the two coming from the peak rectifier pair Lets pass signals with the larger amplitude amount.

The advantage obtained with this demodulation circuit is based on the utilization of the fact that in a PAL system the color saturation value through the amplitudes, i. H. so by the maximum value the color signal oscillation is determined. With the specified circuit, this maximum value is now obtained practically independently of the phase, d. H. up to phase errors of approximately 90 °, but which are in rarely occur in practice, and if so, everyone

809 630/573

Make error correction impossible. When rectified signals are output. This Äufman In FIG. 1, the two switching blocks e are satisfied with one that would be sufficient in most cases If the correction range of 45 ° is satisfied, then and / can also be used in the following as amount-selective terms a substantial simplification compared to the syn- are designated. Each of the amount selective Chrondemodulation circuits can be achieved. 5 terms and / should therefore differ when they occur

The invention is now intended to use the outer and opposite amplitudes at its Approximate examples representing figures explained in more detail input only the signal with the larger amplitude will. It shows off its exit. That means,

F i g. 1 the block diagram of the according to the invention that up to a phase error of 90 ° an incorporated Demodulator, ίο clear selection of the maximum amplitude made

Fig. 2a to 2c vibration trains of the color signals.

in front of the counter and behind the counter at over- An example of an amount-selective element is

Carrying without or with phase error of the switch, explained in more detail with reference to FIG. In this figure

F i g. 3 and 4 embodiments for the amount are again D 11 and D12 the two peak equal-selective members, 15 Richter and £ 51 is one electronically controlled

5, 6 and 7 further variants of the switch according to the invention. The actual amount-selective element is converted Circuit. . includes in one branch a 180 ° phase rotation

In Fig. 1, which shows the basic circuit diagram of the new generating element g, which shows as before by a block circuit, the color signal at F is fed. with the sign - 1, further two. Subsequently, ao transistors TrI and Tr2, which work similarly to a by addition and subtraction of the color signal and a self-controlled switch and to this one by a line period, z. B.? «64 μβ for the purpose of a common emitter resistance in the European television standard, delayed television sitting. Due to the well-known transistor characteristic curve signals the carrier-frequency color difference signals Γ, even a very small voltage difference between and Q! won. The arrangement within the as seen from the two bases in order to block one of the two dashed areas largely corresponds to that of a transistor. That from the top-of-the-line PÄL demodulator. The signal coming from the block a reporter D11 is immediately indicated by the number −1, the reversal of the phase to the base of the transistor TrI , the 180 °. In the block, the symbol τ means that from the peak rectifier D12 via a phase delay of the color signal by approximately a 30-rotating member g to the base of the transistor Tr 2nd line period. The addition of the reversed and delayed color signals to the collector resistors of the transistors is carried out in an adder Tz signals or the direct and delayed color signal. reunited, after the phase reversal at g that took place in one of the known demodulator switching channels by a second device, not two synchronous demodulators, which were reversed at k , are present at the output of circles c and d, but have become single. The electronic switch-selective element / for the Q-channel, which closes periodically in terms of amount, is also equipped in the same way. Man ter £ 51 and £ 52. The closing time of the switch is therefore given at the outputs of e and / (Fig. 1) is optimally 180 °, but there are also deviations - a demodulated T or ß 'signal, whose gene to smaller or larger switching phases is permissible, 40 amplitudes influenced by phase fluctuations in this case, however, the working range is switched on. ·

narrowed. The two electronic switches ESi and Another example of an amount-selective

ES 2 are controlled by the ink carrier. The colored link shows Fig. 4. In this circuit are in turn carrier oscillator itself, which is provided by the two transistors TrI and Tr 2 from the color, but the burst signal separated from the signal in the usual way 45 are connected to each other so that they are synchronized with each other is not shown. From this form a Schmitt trigger, the switching point of which is oscillator, the switching impulses are taken and are in relation to ground at OVoIt. Furthermore, a phase different by 0 ° / 180 ° or 90 ° is fed to the further electronic switch ES 3 for selection of switches £ 51 and ES 2. A readjustment of the maximum signal is appropriate, which can be switched by the output voltage of the line generated by or after the phase of the color subcarrier during 50 Schmitt triggers, which is not necessary with the invention. To clarify this connection, however, can also be used. .is a dashed line from the collector of the trans-

The transistor Tr2 appearing at the input of switch £ 51 is pulled to switch £ 53. This signal I is shown in Fig. 2a. If the connected circuit works as follows: If the signal offered is free of phase errors, a signal according to channel (DIl) appears at the value of the rectified voltage in the upper output of switch £ 51, then TrI conducts, while 7V2 Fig. 2 B. If, on the other hand, it is locked with a phase error. If, however, the amount of tension in the subject is, a lower channel appears at the output of £ 51 is larger, is inversely TrI conductive signal shown in FIG. 2c, that is, normally up and TRT, non-conductive. The output voltage of the emerging half-sine wave is switched on at one end, therefore due to the shortened connection and a dashed line at the other end shows the alternating oscillation to negative amplitude, switch £ 53 so that at the center pole of the switch the

The signal shown in Fig. 2b or 2c arrives Q-signal with the larger amount appears, now to the two peak rectifiers DIl and The precedence shown in the circuit diagram of Fig. 3

D12. In the case of a signal according to FIG. 2c, both rectifiers then supply 65 reversal of characters through the phase-rotating element g, an output signal. The output can also take place before the rectifier or even before the output signal of the entire arrangement, but only switch £ 51, as in FIG. 5 or in FIG. 6, if only the larger of the two is shown. In the latter case in particular, this can be

phase-rotating member g can be realized by a transformer. In the case of FIG. 6, the switch ES1 is then replaced by a simultaneously operated double switch.

Another arrangement according to FIG. 3 is shown in FIG. 7. The division into two channels takes place here by a double switch in front of the rectifiers D11 and D12, which, however, in contrast to the previous one Example can be switched out of phase.

In the circuit according to FIG. 3, the elements labeled g and k can also be in the other branch. In this case, pnp transistors must be used. The output signal then appears - / 'or. -ß '.

In principle, instead of according to / 'and Q' , the demodulation can also take place in the direction of the color difference signals or in the direction of other components. The signs of the signals and the directions of the diodes and transistors can of course be reversed accordingly. ao

In the case of PAL operation, it is known that the signal must be reversed by 180 ° from line to line in the / 'channel. In Fig. 1 this is indicated by the symbol 0 ° / 180 ° for the switch ES1 . Instead of the switch ES1 , this reversal of the signal can also be carried out elsewhere in the / 'signal path.

Claims (6)

Patent claims: 1. Demodulation circuit for PAL color television signals, in which the carrier-frequency / '- and Ö' signal is obtained by adding or subtracting the undelayed color signal and the color signal delayed by one line period, with reduced color saturation errors in the case of suddenly occurring phase errors of the color carrier-frequency color signal, characterized that in the course of the channels for the / 'or Ö' signal components an electronic switch (ES1 or ES2) actuated in the rhythm of the color subcarrier frequency is provided, which lets through approximately one half-wave of the components, and that in series with these Switches two parallel peak rectifiers (D 11, D12, D 21, D 22) are provided, the two outputs of which are connected to an amount-selective element (e or f) , which is only that of the two signals coming from the peak rectifier pair with the greater amplitude lets happen. 2. A circuit according to claim 1, characterized in that the peak rectifier each Rectifier pairs are polarized opposite. 3. A circuit according to claim 2, characterized in that the splitting of each of the two color components instead of behind the demodulating electronic switch (ESl) already takes place before the same (F i g. 6), the switch (ESl) being a double-pole, both channels simultaneously The opening electronic switch is that a phase-reversing element (g) is provided in one of these channels in front of the switch, and that both diodes (D 11, D 12) are polarized in the same direction. 4. A circuit according to claim 1, characterized in that the splitting of each of the two color components instead of behind the demodulating electronic switch (ESl) takes place before the same (F i g. 7), a double-pole switch is used as the electronic switch, which the alternately switches both channels, and that both diodes (DU, D 12) are polarized in the same direction. 5. A circuit according to claim 1 or 2, characterized in that the amount-selective element contains a pair of transistors (TrI, Tr 2) with connected emitters, one base of which is the (F i g. 3) from the one peak rectifier (DU) signal coming directly and the other base of which is fed the signal rotated by 180 ° in phase from the peak rectifier (D 12), and that the outputs of the two transistors are added in a summing element (h) after the phase rotation of the rectifier (D 12 ) incoming signal is canceled by another reversing element (k). 6. A circuit according to claim 1 or 2, characterized in that the amount-selective element contains a changeover switch controlled by a Schmitt trigger (ES 3 in FIG. 4). Considered publications:
German Patent Nos. 1189 124, 1196 666, 700, 1197 500;
German Auslegeschrifts No. 1159011,1196699. 1 sheet of drawings 809 630/573 10.68 ® Bundesdruckerei Berlin