DD152453A5 - TIME CORRECTION DEVICE FOR THE BRIGHTNESS SIGNALS - Google Patents

Abstract

In a two-color (PAL / SECAM) color television receiver, a tagging system provides a mode switching output which automatically switches the color television receiver between the PAL reception mode and the SECAM reception mode, depending on the type of reception Transmission (PAL or SECAM) - enabled. In the SECAM reception mode, a PAL decoder receives the color component output of a SECAM / PAL color decoder; in PAL mode, the PAL decoder receives color signals that bypass the color coder. The brightness channel of the two-standard receiver comprises a switchable brightness signal delay line in cascade with a color component filter circuit. The switchable on or off delay line is controlled by the mode switching output of the identification system so that the delay line is interposed in the brightness signal path only during the SECAM reception mode. The delay caused by the delay line is substantially so large that it corresponds to the difference in the delays to which the color information is exposed during operation in the respective modes. The filter circuit, which causes a delay in the brightness signal that substantially compensates for the delay to which the color information is exposed during the PAL reception mode, includes resonant circuits tuned to the respective upper and lower SECAM inter-frame quiescent frequencies.

Description

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GZ: 1301857

Runtime correction device for the brightness signals Field of application of the invention

The invention relates in general to the circuit design for a brightness channel of a color television and in particular to new circuits for the regulation of the transit time of a received luminance component, which can advantageously be used, for example, in the brightness channel of a combined PAL / SECAM television receiver (two-standard receiver).

Characteristic of the known technical solutions:

In the US-PA No. 001,166 the construction of a combined PAL / SECAM color television is described in which a PAL standard color decoder is used for a) the decoding of a PAL color coded signal in a conventional manner when such a signal is received and b) for color decoding a quasi-PAL signal produced by a SECAM / PAL color coder operating in the general manner described in GB Patent No. 1,358,551 when a SECAM transmission is received. By employing a suitable identification system as described, for example, in co-pending US Pat. No. 5,020,942, the two-standard television receiver can be automatically switched between the SECAM reception, depending on the type of transmission received, namely SECAM or PAL. Mode in which the PAL color decoder receives as input the output of the SECAM / PAL color coder and the PAL reception mode in which the PAL color decoder receives as input signals bypassing the color coder and instead by a corresponding PAL Chroraa band filter go.

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When a television receiver of the type described above operates in the PAL reception mode, the color information of the PAL signal during its conditioning undergoes a certain delay (e.g., due to the interposition of components such as the aforementioned PAL chroma bandpass filter) before it is forwarded in the form of color difference signals to the matrix circuit of the PAL color coder for combination with brightness signals. If such a. However, color television receiver operates in the SECAM receive mode, the color information of the SECAM signal during its processing a certain delay (z, B. due to the interposition of components such as the SECAM-PAL color coder and the SECAM band filter with the bell-shaped Pass-through curve at the input of the color transcoder), which is considerably larger than the delay subjected to the color information of the PAL signal during operation in the PAL reception mode. A solution to this problem of differential delay is to provide the brightness signal path of the television receiver to the color decoder matrix circuits with a compensating delay of a fixed, approximated value (eg, a value midway between the respective delay values used for PAL receive delay compensation and SECAM receive delay compensation are appropriate). However, in an illustrative television receiver construction incorporating the implementation of the color-coded circuits in integrated circuit form, the skew is so large (e.g., about 500 nanoseconds) that unsatisfactory results are achieved when compensating for a delay of a fixed approximated value builds.

Object of the invention:

The object of the invention is to provide an advantageous delay compensation circuit for the luminance signal

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in a color television receiver of the type described above, which automatically provides different amounts of the compensating delay depending on the respective operation of the receiver.

Explanation of the essence of the invention;

In accordance with an illustrative embodiment of the present invention, the brightness channel of the two-color color television receiver comprises a switchable brightness channel delay line in cascade connection with a color component filter circuit. For example, the color component screening circuit includes a pair of screening members tuned to the respective SECAM subcarrier frequency (of 4.250 MHz and 4.40625 MHz), the color component screen being constructed to receive the luminance signals passing therethrough to delay an amount sufficient to compensate for the color information delay incurred when the color television receiver is operating in the PAL reception mode.

The switchable luminance signal delay line is switched by the output of the mode switch of the color television receiver identification system so that the delay line is included in the luminance signal path in cascade with the color component filter circuit only when the receiver operates in the SECAM reception mode. The magnitude of the delay caused by the delay line substantially coincides with the difference in delays experienced by the color information during operation in the respective reception modes, such that when the delay circuit is included, the total delay caused by the delay line and filter circuit in a cascade Size is that

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is sufficient to compensate for the delay of the color information that they are exposed to when the receiver is operating in the SECAM receive mode.

embodiments

In the accompanying drawing, a portion of a two-standard (PAL / SECAM) color television receiver with a luminance signal delay correction device in accordance with an embodiment of the invention is illustrated by the one figure partially schematically and partially in block diagram form.

As shown in the drawing, the BAS signals received from the two-standard (PAL / SECAM) color television receiver appear at an input terminal V and are applied to the inputs of a bell-pass band filter 11 and a PAL chroma band filter 21. The band filter 21 has a pass band including the color signal band of a PAL transmission. The bandpass filter 11 has a passband including the color signal band of a SECAM transmission and has a bell-shaped transmission curve which is conveniently complementary to the curve used for the RF pre-eraphasis of the subcarrier sidebands in SECAM signal conditioning.

The output of the bandpass filter 11 is fed to a SECAM / PAL color converter 13. The color decoder 13 is an example of the general form described in GB-PS No. 1,358,551, in which the respective SECAM subcarriers are successively demodulated by a frequency discriminator and the resulting color difference signals in phase sequence suitable.

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sen of an intermediate carrier of the PAL subcarrier frequency are amplitude modulated. The subcarrier wave input to the color subcoder 13 is supplied from the comparison oscillator of the PAL receiver decoder 19.

For example, to obtain the correct sequence of operation in the color coder 13, a tag system 15 is coupled to the color coder 13 of the type described in the aforementioned US Pat. No. 5,020,942. In the color-coder 13, a flip-flop circuit generates half-line rate control waves for the switching of the master carrier frequency adjustment of the frequency discriminator used for the demodulation of the received SECAM signals. When the output of the flip-flop circuit is brought into phase, the discriminator is tuned to the carrier frequency for demodulating the (RY) SECAM subcarrier (4.40625 MHz) during the picture element of a (RY) line (blanking) gap of the SECAM signal is suitable, as well as tuned to the frequency suitable for the demodulation of the (BY) modulated subcarrier (4.250 MHz) during the picture element of the (BY) line gap of the SECAM signal. Requenz- due to the additional drawing upon Zeilenf and the color burst gaps control waves, however, the timing of the change of the discriminator-rest carrier frequency tuning is so controlled that during the vertical sync pulse pre-equalizing, which the picture elements of both the (RY) - and the (BY) - Precede line gaps, the discriminator's sleep carrier frequency tuning is the same (e.g., tuning to the rest carrier frequency corresponding to the (RY) color carrier). As a result of maintaining the same restraint rf req uence - {(RY) -Framebearers) -Ab Tuning for all color sync gaps appear in the filtered output of the discriminator during the alternating bursts of color sync pulses indicating the subsequent occurrence of a bestie (BY). Characterize a row gap.

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In the tag system 15, the filtered output of a color coder discriminator is connected to a pair of sample and hold circuits. Using the line rate control half-waves of opposite phase coming from the flip-flop, and the common line frequency and burst timing strobes for controlling the sampling times of the respective sample and hold circuits, causes a sample and hold Whereas the other sample-and-hold circuit effects sampling of the filtered discriminator output during the color sync pre-amp introducing the intervening line gaps. A comparison of the outputs of the two sample and hold circuits in a Spannungskotnparator gives an output, aer indicates whether the flip-flop circuit has been brought into the correct phase position or not. If the output indicates that the phase of the flip-flop circuit is not correct, the flip-flop circuit is turned off and then turned on again, so that a new comparison can be made, wherein the process is repeated until the correct Phase angle of the flip-flop circuit has been achieved.

The identification system 15 also generates, via such a voltage comparison, a switching control signal for automatically controlling the operation of the color television receiver depending on the nature of the signals received, i. h, the SECAM or PAL signals. This switching control signal output of the identification system 15 is applied to a control terminal SVV of an electronic switch 17.

The electronic switch 17 comprises a pair of signal

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input terminals A and B and a signal output terminal C. The signal output of the color transcoder 13 is applied to the signal input terminal A of the changeover switch 17, whereas the output of the PAL chroma band filter 21 is applied to the signal input terminal B. The signal output terminal C of the changeover switch 17 is coupled to the input of the PAL decoder 19.

The electronic switch 17 is shown in the drawing in the switching position which it occupies when the switching control signal sets the SECAM reception mode. In this mode, the PAL decoder 19 receives the quasi-PAL signal output of the color converter 13 while being separated from the output of the band filter 21.

The PAL decoder 19 acts on the quasi-PAL signal supplied to the electronic switch 17 in the circumstances shown in a manner as described in the aforementioned British Patent No. 1,358,551 to obtain a set of color difference signals (Fig. RY), (BY) and (GY), which are passed to the matrix circuit 20 to be combined with a Y signal coming from the output terminal L of the color channel television's brightness channel. The output of the matrix circuit 20 comprises a set of color signals R, B and G which can be fed to a conventional color television picture tube for the generation of color images corresponding to the picture information contained in the received SECAM signals.

If the switching control signal applied to the terminal SVV is suitable for the setting of the PAL reception mode of operation, the switching state of the conversion shown in the drawing is

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switch 17 changed accordingly. Under such conditions, the signals coming from the terminal B are supplied to the output C, so that the luminance component of the received PAL signals which are passed through the band pass filter 21 are forwarded to the PAL decoder 19. During the normal PAL decoding operations, color difference information for the generation of color signal outputs is passed to the matrix circuit 20, resulting in the generation of color images corresponding to the image information contained in the received PAL signals.

For the correct generation of the color signals in the outputs of the matrix circuit 20, the brightness information passed from the terminal L to the matrix circuit across the brightness channel of the color television receiver must be subjected to a delay of a size which substantially matches the magnitude of the delay involved in the processing the color component of the received signals appears. However, when the color television receiver operates in the SECAM receive mode, the color component of a SECAM signal is subject to delay during processing (eg, components such as the bandpass filter 11 with the bell-shaped pass and color coder 13), which is substantially larger than that delay which is exposed to the color component of a PAL signal when aer color television receiver is operating in the PAL-reception mode. In accordance with the principles of the present invention, the brightness channel of the color television receiver (which will now be described) comprises a brightness signal delay compensation circuit which automatically effects compensating delays of different magnitudes depending on the mode of operation of the color television receiver.

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The received full image signals appearing at terminal V are applied via a coupling capacitor 31 to a pair of signal paths connected in parallel. In one of these signal paths, the signals are conducted through a resistor 32 in series with a delay line 33 to the base of an npn transistor 40 which operates as an emitter follower whose emitter electrode is directly connected to the input terminal I of a color component filter circuit (described below). connected. In the other of these signal paths signals through a resistor 51 (which a capacitor was connected in parallel 52 for the purpose of high frequency compensation) to the base of an npn transistor 50 is operated as an emitter follower, whose emitter electrode is also connected directly to the terminal I are passed.

The color component filter circuit comprises a pair of parallel resonant circuits (60 and 80) in cascade connection, with an emitter follower (in the form of an npn transistor 70) being interposed as a buffer. The resonant circuit 60 includes a controllable inductor 61 connected between the terminal I and the base electrode of the transistor 70 and the series combination of the capacitors 62 and 63 in parallel with the inductor 61. The resonant circuit 80 includes a controllable inductor 81 connected between the emitter electrode of the transistor 70 and the output terminal 0 of the color component filter circuit, and the series combination of the capacitors 82 and 83 in shunt with the inductor 81. The signals applied to the terminal 0 are connected to the brightness signal conditioning circuits 90 for conventional conditioning to generate the brightness signal input for the matrix 20 at the terminal L.

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The collectors of the emitter follower transistors 40, 50 and 70 are connected directly to the positive terminal of a 12V power supply. A Gs return to the negative terminal (ground) of the power supply to the emitters of transistors 40 and 50 is by means of a resistor 65 connected between the base of transistor 70 and ground. A Gs feedback for the emitter of transistor 70 is provided by a resistor 85 connected between terminal 0 and ground. A resistor 64 is connected between the junction of the capacitors 62 and 63 and ground, and a resistor 84 is connected between the node of the capacitors 82 and 83 ^r and ground.

The parameters of the color component screening circuit are chosen so that the transmitted signals from terminal I to terminal 0 are subject to a delay of one magnitude / so that the color signal input to the matrix 20 is delayed such that the delay involved in preparing the color component of one PAL signal occurs when the color television receiver operates in the PAL reception mode is compensated.

The bias voltage for the base electrode of the transistor 40 is provided by a voltage divider consisting of the resistor 41 connected between the positive terminal of the power supply and the base electrode of the transistor 40 and a resistor 42 connected between the base electrode of the transistor 40 and Earth is connected. The bias voltage for the base electrode of the transistor 50 is made responsible for the mode of operation of the color television receiver by being derived from the output of the mode switch of the identification system 15,

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which is fed into the control terminal SVV of the electronic changeover switch. A pair of resistors 54 and 56 are connected in series between the terminal SW and the base electrode of the transistor 50, and a filter capacitor 55 is connected between the node of the capacitors 54 and 56 and ground.

When the PAL reception mode is set, the mode switching output applied to the terminal SW assumes a relatively high value (eg, up to +12 volts) with respect to the bias potential generated by the voltage divider 41 and 42, so that the Transistor 50 is made conductive and the voltage applied to the terminal I potential is raised to a value which causes the transistor 40 is blocked. Under these circumstances, the signal path including the delay line 33 is effectively turned off and the signals are passed without significant delay from the terminal V to terminal I above a signal path (network 52, 53 and base-emitter path of the transistor 50) connecting the delay line 33 bridged.

When the SECAM reception mode is to be set, the mode switching output applied to the terminal SW decreases with respect to the bias potential generated by the voltage divider 41 and 42, so that the transistor 50 is turned off and the transistor 40 is turned on. Under these circumstances, the signal path bridging the delay line is effectively interrupted and the signals are conducted from terminal V to terminal I via a signal path including delay line 33 (and also resistor 32 and the base-emitter path of transistor 40). The above

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This signal transmitted through the delay line 33 undergoes a delay which is chosen to be substantially equal to the difference between the delays 1) during the processing of the color component of a PAL signal during operation in the PAL reception mode and 2 ) occur during processing of the color component of a SECAM signal during SECAM receive mode operation. In this way, during operation in the SECAM receive mode, as they pass on the signal path including the delay line and through the cascaded color component filter circuit, signals experience a total delay of such magnitude that the delay imposed on the brightness signal input to the array 20 compensates for the magnification that results from the processing of the color component of a SECAM signal.

By means of the controllable induction coils 61 and 81, it is shown how the resonant circuits 60 and 80 of the color component screening circuit can be tuned by setting the coils to a frequency different from the two master carrier frequencies (4.250 MHz and 4.40625 MHz, respectively) of the color subcarrier SECAM standard distinguishes, thus effectively avoiding that in color imaging the dot pattern of the distribution level appears as a consequence of the presence of SECAM color subcarriers during SECAM signal reception. Due to such matching, by means of the color component screening circuit, even during the reception of PAL signals, a considerable attenuation of the PAL subcarrier is effected, which is at a frequency of 4.43361875 MHz and thus slightly higher than the upper SECAM noiseless carrier frequency.

Claims (5)

1) a color television receiver for receiving full color television signals including a luminance component and a color component coded according to the SECAM standard, and for receiving full color television signals including a luminance component and a color component coded according to the PAL standard, the color television receiver A color television receiver comprising: a PAL decoder; a first band pass filter having a passband comprising the frequency band occupied by the color component coded according to the SECAM standard; means responsive to the received signals passed through the first bandpass filter and recoding SECAM color component color components into quasi-PAL format color components; a path for the received signals bypassing the color coder and including a second bandpass filter having a passband comprising the frequency band occupied by the color components coded according to the PAL standard; and a switching system which a) applies the output of the color recoding device to the input of the PAL decoder and separates the output of the Oberbrückungspfades of this when it is in a first switching state, and b) the output of the bridging path to the input of the PAL Decoder and separates the output of the color coder of this when it is in a second switching state; characterized by: a color component screening circuit a delay line a first signal path for the received signals including the delay line a second signal path for the received signals that bypass the delay line - 14 - 2 2 2 6 7 means responsive to the switching state of the switching system and a) enabling the signal path including the delay line while disconnecting the signal line bridging the delay line when the switching system is in the first switching state and b) enabling the signal path bridging the delay line while disconnecting the signal path involving the delay line when the switching system is in the second switching state; means responsive to the results of the color component decoding by the PAL decoder and to the luminance component of the received signals passed through both the enabled one of the two signal paths and the color component screening circuit for forming a plurality of color signals. 2) Runtime correction device according to item 1, characterized in that the delay line exposes the signals passed through it to a delay which is substantially equal to the difference between the delays 1) occurs during the conditioning of the color component of the received signals when the switching system is in the first switching state, and 2) occurs during the conditioning of the color component of the received signals when the switching system is in the second switching state. 2 2 2671 Erfindunpsanspruch: 3) Runtime correction device according to point 2, characterized in that the delay which the signals experience during passage through the color component screen circuit through them is so great that the brightness components -is-- 2 22 67 1 nent, to which the color-signal-forming device responds when the switching system is in the second switching state, experiences a delay that substantially coincides with the delay that occurs in the processing of the color component of the received signals when the switching system is in the second switching state , 4) Runtime correction device according to point 3, characterized in that the first signal path includes a first transistor having a base, emitter and collector electrode, and a circuit for supplying the base electrode with a first bias potential, wherein the first transistor is connected as an emitter follower, the base electrode of which is connected to the output of the delay line for receiving the signals delayed thereby, and whose emitter electrode is connected to the input of the color component filter circuit; in that the second signal path comprises a second transistor having a base, emitter and collector electrode, the second transistor being connected as an emitter follower whose base electrode is connected to the input of the delay line for receiving the relatively little delayed signals and whose emitter electrode is connected directly to the emitter Emitter electrode of the first transistor is connected; and in that the switching state responsive means comprises a circuit which, in the event that the switching oyster is in the first switching state, supplies the base electrode of the second transistor with a second bias potential different from the first bias potential 222671 in the direction differs, so that. causing the blocking of the second transistor and the conduction of the first transistor, and in the event that the switching system is in the second switching state, providing a third bias potential different from the first bias potential in the direction so as to control the conduction of the first second transistor and the blocking of the first transistor causes. 5) Runtime correction device according to item 3, characterized in that the SECAM standard includes the frequency modulation of the subcarrier waves of a first carrier frequency during alternate line gaps and the frequency modulation of the subcarrier waves of a second carrier frequency during the intervening line slits, and in that the color component filter circuit comprises a first resonant circuit, which is tuned to the first sleep carrier frequency of the SECAM standard, and a second resonant circuit, which is tuned to the second sleep carrier frequency of the SECAM standard comprises. See drawings!