DK145790B - CONTROL CONNECTION FOR A PAL COLOR REMOTE VIEWS - Google Patents

Description

in 145790

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a control circuit for a PAL color television converter which produces a modified color information signal by alternating each other of the original color infrared components and its delayed color information by means of line delay circuits and line periodic switching circuits.

In the PAL system, a composite color television signal comprises two color signal components, usually as color difference signals containing color information, which are simultaneously encoded by cross-phase amplitude modulation with a suppressed carrier on the color subcarrier within the video frequency band, of the color signal components is turned 180 ° for each line period. Ie the color television signal according to the PAL system has two different types of oscillation alternating for successive line periods.

For demodulation of such a composite color television signal, various systems have been proposed in the past, e.g. the so-called simple PAL system and the standard PAL-20 system. However, these common systems demodulate the PAL signals with poor quality of the rendered image or with a significant increase in the complex nature of the system.

The description of Danish patent application No. 6612/70 discloses a new system for the conversion of the PAL signals in such a way that some of the limitations of the existing PAL converter systems are avoided. The new system is theoretically also capable of receiving signals transmitted either by the PAL system or by the so-called NTSC system, although the current color subcarrier frequencies used in these two television systems make it difficult to take advantage of this latter property.

The transducer of this patent application comprises a switching circuit arrangement and associated delay means for receiving the incoming color information signal. This color information signal is first transmitted directly to demodulators in one line time interval, and then the same information is delayed one line time interval by the delay means again through the switching circuit to the demodulators in the next line time interval. The color information transmitted by the television station during the second line interval is not utilized by the receiver. The signal transmitted during the third line interval goes without delay to the demodulators and is repeated in delayed form during the time line of the fourth line. The result is that the color information signal, in which both modulation axes of two color signal components are held in fixed phase relationships during all the line intervals, is received and applied to the demodulators. In this case, it is necessary that the phases of the two modulation axes in the color information signal supplied to the demodulators for proper demodulation, respectively, have the same phases as the phases of the corresponding reference sub-wave signals coming from a local oscillator that is phase controlled hold.to a color synchronous signal contained in the composite color television signal and used for demodulation of the two color signal components. One of the ways to accomplish this is to detect the phases of the color information signal modulation axes, in other words, to detect the type of color information signal and to control the switching circuit connected to receive the incoming color information signal so that the color information signal is transmitted with the correct type. to the demodulator, or to control the phase of the reference subcarrier signal from the local oscillator.

The color information signal transmitted in accordance with the PAL system contains a color synchronization signal which occupies two phase positions alternately offset 90 ^ relative to each other for each line interval. These two synchronization phases are used alternately according to the phase of the one modulation axis which is turned 180 ° for each line period.

In the PAL system, the color synchronization signals are 90 ° phase-shifted in two consecutive line intervals, as mentioned above, but there is an off period for the color synchronization signal covering e.g. nine line intervals (9H), at each transition between consecutive frames. The color synchronization signal off period consists of a vertical synchronization signal period covering two and a half line intervals (2.5H) at the beginning of each frame as well as equalization pulse periods before and after 10. In the color television receiver, the color synchronization signal is used to control the phase of a reference subcarrier for color demodulation. In order to avoid bad influence from the absence of the color synchronization signal during the extinguishing period, a last color synchronization signal is applied in a sub picture immediately before the extinguishing period and a first color synchronization signal in a sub picture immediately after the extinguishing period in the same phase, which causes the last and the last first color sync signals in each frame are all in the same phase. This is commonly called a color synchronization arrangement in the PAL signal. The phase of the color synchronization signal corresponds to that of the two modulation axes in the color information signal, which is turned 180 ° for each line period. Thus, the color information signals in the line intervals in which the first and last color synchronization signals are present in the respective sub-images are all of the same type. Furthermore, the location of the color synchronization off period is shifted relative to the beginning of each frame one after another for a period of four 30 frames. Accordingly, the first and last color synchronization signals in each frame are of the same phase, but their locations are periodically shifted relative to one another for a period of four frames.

The object of the present invention is to provide a control coupler which ensures, with simple construction, that the incoming color information signal is always supplied to a demodulator in such a way that the modulation axes of the color information signal have a proper phase relative to a sub carrier signal.

This is achieved with the control coupling according to the invention, characterized in that, for establishing the correct phase relationship to the reference carrier, it detects at least once after four consecutive sub-frame periods the first occurring color synchronization signal and, as a function of this, emits a control signal for the switching circuit.

By detecting the first color synchronization signal 10 in at least one of four sub-frames, determination of the type of the color information signal as well as the time of operation of the switching circuit is achieved.

Advantageous embodiments of the control coupling according to the invention are set out in the subclaims.

Other advantages of the invention will become apparent from the following description with reference to the accompanying drawings, in which: FIG. 1 and 2 show vector diagrams for explaining the PAL color television signal; 3 are graphs for explaining the PAL color television signal; FIG. 4 is a block diagram of an embodiment of the invention; FIG. 5 and 6 are graphs for explaining the example of FIG. 4, FIG. 7 is a block diagram of a modified embodiment of the invention; and FIG. 8 shows a series of graphs for explaining the example of FIG. 7th

The distinctiveness of the PAL color television system lies in the phase relationship between the two color difference signals modulated on a common subcarrier to form the color information signal. This phase relationship is shown in FIG. 1. One of the color information components, Eg-Ey, contains information about blue components in the television picture. The second, ER-EY, contains information related to red components. Both of these color information components are modulated on the same carrier or, more specifically, the same sub carrier, but the modulation is carried out separately and in such a way that for a given time interval corresponding to one line nine the color television image, the color information component ER-Ey is modulated on the carrier. with a modulation axis of the phase φο · In the same time interval, the second color information component Eq-E ^ is modulated on the carrier by a modulation axis of the phase IT φ-j. It is therefore the color information component (ΕΒ-Εγ) η which represents blue information in the given line interval n is shown as a horizontal arrow, and the red color information component (ΕΕ - ΕΕ) in the same line interval n is shown as a vertical arrow. The vector sum of these two color information components gives a resultant signal F, which is a complex voltage that can be determined by the term; (Wn + 3'Wn-

The phase relationship of the following line n + 1 is also shown in FIG. 1. In this case, the color information component (Εβ-Εγ) n + - ^ on the carrier is also modulated by the modulation axis with the phase φ - 5, and hence the color information component U 4 (ΕΒ ~ Εγ) η + 1 for the line n + 1 is shown. in the same direction as the component (E_-E „). However, the color information component Et, -Ev is modulated in accordance with the PAL system on the carrier 25 by a modulation axis having a phase Φ0-7Γ (= “Φ0)” i.e. phase inversion with respect to the preceding line n, and therefore the color information component (ER-EY) n + ^ for the line n + 1 is shown in the opposite direction of the component (ER-EY) n * The signal Fn + ^ can therefore be determined by the expression (EB -Ey) n + 1-j w. «· 30 The color information signal comprises a color synchronization signal which occupies different phases in the two signals Fn and Fn +] _ · ie. as shown in FIG. 2, the phase of the color synchronization signal in the signal Fn is 45 ° ahead of the phase Φο, which is shown as B +, and the phase of the color synchronization signal 35 in the signal Fn + -j_ is 45 ° backwards for the phase φQ-π (= - φQ), which is shown as B-.

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FIG. 3 shows portions of successive sub-images in the PAL signal with the color synchronization signal off periods and adjacent portions thereof. In the PAL signal shown, one image consists of 625 line periods, and the signal contains at the transition part between consecutive subparagraphs an off period Bg for the color synchronization signal at nine line intervals (9H), which consists of a period of a vertical synchronization signal Vg which at the beginning of each frame appears in two-and-a-half line intervals 10 (2.5H), and of periods of prior and subsequent equalization pulses and ET occurring before and after the vertical synchronization signal Vg. The color synchronization signal off period is shifted incrementally

D

time in the four frames, and in the fifth frame 15 returns to the position in the first frame. Namely, the off period ignβ of the color synchronization signal is shifted over a period of four frames. The first color synchronization signal in each frame immediately after the off period Ββ is a color synchronization signal B +, which is always 135 ° ahead of phase relative to the axis BY, as indicated by an upward arrow, and the last color synchronization signal immediately before the off period Ββ is also a color synchronization signal B +, which is also 135 ° ahead of phase relative to the axis BY. The extinguishing period Ββ is always followed by a line signal, hereinafter referred to as a plus line signal, which in a horizontal extinguishing period contains the color synchronization signal B + with the phase 45 ° before the axis φ, and in which the phase of the red color difference signal modulation axis is Φο The plus line signal is followed by a line signal, hereinafter referred to as a minus line signal, which contains a color synchronization signal B-, whose phase is 45 ° posterior to the axis -φ, and in which line signal the phase of the modulation axis of the red color difference signal is - φ. Then the plus and minus 35 signals follow alternately. As shown in FIG. 3, accordingly, the location of the first color synchronization signal B + relative to the vertical synchronization signal V is shifted periodically over a period of four sub-

P

Pictures. The figures in FIG. 3 indicates the line number of each image.

FIG. 4 shows an example of the control coupling according to the invention. Reference numeral 1 denotes a bandpass amplifier from which the color information signal is separated from the composite color television signal. The color information signal separated by the band-pass amplifier 1 is continuously applied to an input terminal 9a on a switching circuit 9 and at the same time to another input terminal 9b through a delay line 10, of which the color information signal is delayed one horizontal 10 period. The switching circuit 9 is switched alternately for each horizontal line period, as described later, by alternating signals from output terminals 11a and 11b on a multivibrator 11 which is triggered during each horizontal line period, and the output of the switching circuit 9 is applied to demodulators 2 and 3. Accordingly, demodulators 2 and 3 are supplied to the line so that only the color information signal in the plus line or in the minus line signal is applied to them.

Furthermore, the color information signal from the bandpass amplifier 1 is applied to an opening circuit 4 for therefrom to derive the color synchronization signals B + and B- alternately in the plus and minus lines signals. The color synchronization signals B + and B- are applied to a carrier generator 5 with a quartz crystal to produce a continuous carrier signal having a phase coinciding with the axis - (BY) precisely in the middle of the signals B + and B-, and the carrier signal thus obtained is fed through a local wave signal 6. 7 to derive therefrom a reference subcarrier signal having a phase coinciding with the axis BY, i.e. φ- which is supplied to one demodulator 2. Furthermore, the subcarrier signal derived from the local oscillator 7 is applied to the other demodulator 3 through a 90 ° phase shift circuit 8. The vertical synchronization signal Vg is applied e.g. a monostable multivibrator.14 to produce a signal of 35 rectangular waveform of about 5H, as shown in FIG. 5B, where the signal S- ^ sinks at the leading edge of the vertical synchronization signal Vg and rises immediately before the time of the first color synchronization signal B + in the third sub-frame, as indicated in FIG. 5A. The rectangular signal thus obtained is applied to an opening signal generator 15 to produce an opening signal S2 / as shown in FIG. 5C and having a pulse width sufficient to enclose the first color synchronization signal B + in the third sub-frame. The aperture signal S2 is emitted to one of a transistor 17 which forms a "and" circuit 10. At the same time, the color synchronization signal from the aperture circuit 4 is applied to a color synchronization amplifier 18, from which the output signal is applied to an automatic gain control, a so-called AGC circuit 19. the output signal therefrom is controlled by the gain of the color synchronization amplifier 18 and the color synchronization signal thereof is defective by a detector circuit 20 and the detected output signal is applied to the base of the transistor 17 forming the "and" circuit 16. The output signal of the "and" circuit , ie the collector signal on the transistor 17, is applied through a diode 21 to the one output terminal 11a of the bistable multivibrator 11. Furthermore, e.g. a horizontal synchronization pulse 22 as a trigger signal to the multi vibrator 11. In this case, the transistor 17 is sized not to trigger when only the aperture signal S2 is applied to its emitter.

Therefore, as the first color synchronization signal B + appears in the third sub-frame, the opening signal S2 is applied to the emitter in the transistor 17 constituting the "and" circuit 16, and at the same time the first color synchronization signal B + detected output signal Sg, as shown. in FIG. 5D, applied to the base of the transistor 17. This causes the transistor 17 to become conductive and on its collector produces a control pulse S 1, as shown in FIG. 5E, which is an "and" signal of signals S2 and Sg. The control pulse is applied to the output clamp 11a of the multivibrator 11 to control it. Namely, the multivibrator 11 is always brought to a predetermined state by the control pulse, ie. in such a state, where its one transistor 23 is conductive and the other transistor 24 is non-conductive, regardless of the state of the multivibrator 11 before the control pulse appears, and the switching circuit 9 is brought to such state where diode 12 is conductive and 5 diode 13 not conductive. Accordingly, upon receiving the plus line signal with the first color synchronization signal B + in each sub-frame, the multivibrator 11 in the state of the transistor 23 is conductive and the transistor 24 is non-conductive, and since the switching circuit is therefore in a state where diode 12 10 is conductive and diode 13 becomes non-conductive. receiving the incoming color information signal, as is, the demodulators 2 and 3. Upon receiving the subsequent minus line signal with the color synchronization signal B-, the multivibrator 11 is brought by the horizontal synchronization pulse 22 15 in the second state where the transistor 24 becomes conductive and transistor 23 nonconductive. the switching circuit 9 is changed to such a state where the diode 13 is conductive and diode 12 is non-conductive, so that the demodulators 2 and 3 are applied to the plus line signal from the previous line period 20 through the delay line 10. The minus line signal is replaced by the plus line signal from the previous line period and demodulate. the ears 2 and 3 are always fed to the plus line signal. Since the fixed phase reference subcarrier is always applied to demodulators 2 and 3, as explained above, a modulated predetermined signal will always be demodulated by the predetermined phase subcarrier to derive predetermined, demodulated color signals from demodulators 2 and 3 .

It is also possible to supply the demodulators 2 and 3 minus the line signal by reversing the switching mode of the switching circuit 9, but in this case the demodulator 3 must be supplied with a sub-carrier signal with the phase -φ.

In the foregoing, the control signal is only received in the third frame, ie. in the first frame of the image with even number 35, and the triggering function of the multivibrator 11 is controlled in every four frames. However, it is also possible to control the triggering of the multivibrator 11 twice for every four frames by obtaining an opening signal S2, as shown in FIG.

5F, and having a pulse width capable of recording the first color synchronization signal B + in the third and second sub-frames and obtaining control pulses simultaneously with recording of the first color synchronization signal Bf-in the second and third sub-images. . Also, in the case of controlling the triggering of the multivibrator 11 once for every four frames, the control pulse can be obtained at the time when the first color synchronization signal 10 B + is received in the second frame.

In the above example of the circuit according to the invention, even if the triggering of the multivibrator 11 is reversed in a partial image to bring the switching circuit 9 in the wrong switching state, so that the minus line signal is applied to the demulators 2 and 3 instead of the plus line signal, the triggering of the multivibrator 11 controlled once or twice for every four sub-frames, and consequently the switching circuit 9 will immediately return to its proper switching state. This ensures that a modulated predetermined signal is always demodulated by a predetermined subcarrier signal to produce a predetermined demodulated color signal at all times. In the event that the synchronization amplifier 18 is subject to automatic gain control, as in the example described, and the time constant of the AGC circuit 19 is selected extremely small, the gain of the synchronization amplifier 18 will be at a strong field in which noise is immaterial. be large the moment the first color synchronization signal in each frame is received, as shown in FIG. 6A, whereby the output signal detected from the 30 color synchronization signal and thus the control pulse is secured. In the case of a weak field in which noise is noticeable, the gain of the color synchronization amplifier 18 upon receiving the first color synchronization signal in each sub-frame becomes relatively small, as shown in FIG. 6B so that noise is not recorded as a control signal by the aperture signal S2, thereby reducing the influence of the noise.

11

1657 9 O.

Although in the example shown, the multivibrator 11 is driven by the horizontal synchronization pulse, it can also be driven by the output signal or the like detected by the color synchronization signal, which is synchronized with the horizontal synchronization signal.

FIG. 7 shows another example of the control circuit according to the invention which is different in the circuit structure in which the control pulse for controlling the multivibrator is produced. The color information signal separated from the bandpass amplifier 1 is applied to the demodulators 2 and 3 through the switching circuit 9. Furthermore, the color information signal from the bandpass amplifier 1 is applied to the opening circuit 4 to derive the color synchronization signals B + and B - alternately shown as 8A. The color synchronization signals B + and B- are applied to a filter 26 with a low Q quartz crystal 25 to produce a continuous carrier signal Sn, the amplitude of which is gradually attenuated during the extinguishing period Ββ of the color synchronization signal, as shown in FIG. 8B, and signal S11 is applied to an amplifier 29 20 consisting of transistors 27 and 28. The output of the collector of transistor 27 is applied to the local oscillator 7.

Since the carrier signal from filter 26 has a phase coinciding with the axis - (BY) precisely in the middle of the color synchronization signals B + and B-, the signal Sq of the transistor 27 is phase-shifted to derive a reference sub-signal from the oscillator 7 whose phase coincides with the axis. BY, ie φ - The subcarrier signal thus obtained is applied to one demodulator 2. In addition, the subcarrier signal is applied to the other demodulator 3 through a 90 ° phase shift circuit 8.

At the same time, the carrier signal from the amplifier 29 is applied to a detector circuit 31 to produce a detected output signal S 2 / as shown in FIG. 8C and applied to a differentiation circuit 30 to obtain a differentiated pulse S13 for each color synchronization signal, as shown in FIG. 8D. In this case, the carrier signal from the low Q quartz crystal 25 of low Q is designed as indicated in FIG. 8B, so that the differential pulse S1 obtained by the first color synchronization signal B + in each subpage immediately after the off period BB is at the highest level. The differential pulse S ^ 3 is applied to the 5 base of the transistor 16 constituting the "and" circuit 17. Furthermore, the vertical synchronization signal Vg is applied, for example, to the monostable multivibrator 14 to derive a rectangular signal of about 5H, as shown. in Figure 8E, which sinks at the leading edge of the vertical synchronization signal V and rises immediately before the time O 'the first color synchronization signal B + appears in the third sub-frame, as shown in Figure 3. The rectangular signal S - ^ is applied to the aperture signal generator 15 to produce an aperture signal S1, as shown in Fig. 8F, and having a pulse width capable of enclosing the first color synchronization signal B + in the third sub-frame, and the aperture signal is applied to the emitter in transistor 16 constituting "and" circuit 17. Thereafter, the output signal from "and" circuit 17, i.e., the collector output signal 20 on transistor 16, is applied as a control pulse through diode 21 to one output. terminal 11a of the multivibrator 11. In this case, the transistor 16 is arranged not to respond when only its emitter is applied to the opening signal S1.

With the structure described above, the carrier signal Sllf as shown in FIG. 8B, from the filter 26 before and after the off period Ββ, and the differential pulse is generated by recording the color synchronization signal in each frame, but just at the time when the first color synchronization signal B + in the third frame is received, the opening signal is applied to the emitter 16 constituting the "and" circuit 17, and at the same time, the high-level differential pulse is applied to the base of the transistor 16, so that the transistor 16 at this point becomes conductive and produces on its collector a control pulse S FIG. 8G, which is an "and" output signal for signals S15 and S13 · Although the multivibrator 11 is in any state before the control pulse S1 g is recorded, the multivibrator 11 is always brought by the control pulse S16 into its predetermined state. The following functions are the same as those described in connection with FIG. 4th

Ie the multivibrator 11 is brought to such a state that one transistor 23 is conductive and the other transistor 24 5 is non-conductive, and the switching circuit 9 is thereby brought to such state where diode 12 is conductive and diode 13 is non-conductive. In a horizontal line interval in which the first color synchronization signal B + is obtained, the plus line signal is passed through the diode 12 to the demodulator 2. In the 10 horizontal line interval, in which the next color synchronization signal B- is received, the multivibrator 11 is switched to the second state of the horizontal pulse 22, i.e. the transistor 23 is non-conductive and the transistor 24 is conductive, and the switching circuit 9 is thereby changed to such a state where the diode 12 is non-conductive and the diode 13 is conductive, whereby the delayed plus line signal is transmitted to demodulator 3 through diode 13.

In accordance with the present example, the control pulse is obtained on the basis of the signal produced by applying the color synchronization signal to the filter with the quartz crystal, so that the influence of noise is diminished and a stable function can be expected. Furthermore, since the quartz crystal can be used as a carrier generator for controlling the color synchronization oscillator, the circuit structure can become extremely simple.

Claims (5)

1. Control switching (14,15,16,21) for a PAL color television transmitter which, by means of line delay circuits and line periodic switching circuits, generates a modified color information signal in which each other of the original color information components and the alternate color information components are utilized alternately. characterized in that, for establishing the correct phase relationship to the reference carrier, it detects, at least once after 10 consecutive frame periods, the first occurring color synchronization signal and, as a function of this, outputs a control signal (S 1) to the switching circuit (9). Control circuit according to claim 1, characterized in that the switching circuit (9) is controlled by the output of a bistable multivibrator (11). Control coupling according to claim 2, characterized in that the bistable multivibrator (11) is controlled by the output signal (S4) from the control coupling (14,15,16). Control circuit according to claim 1, characterized in that it comprises a color synchronization signal detector (20) for detecting all color synchronization signals in the color information signal, an impulse generator (14,15) for generating an opening pulse (S2) as a function of a a vertical synchronization signal (Vg) as well as a color synchronization opening circuit (4) for deriving a particular color synchronization signal of the detected color synchronization signals by the opening pulse. Control circuit according to claim 4, characterized in that the pulse generator (14,15) is applied to the vertical synchronization signal (Vg) and produces the opening pulse (S2) at a time different from the time of the vertical synchronization signal (Vg) with a predetermined time interval.