DE1252731B - Color television receiver for a true color NTSC system - Google Patents

Description

Color television receiver for a true color NTSC system The invention relates to a color television receiver for an NTSC system modified in a known manner.

In the NTSC color television system, the picture carrier is with the luminance signal and the color carrier in the so-called quadrature modulation with two color signals modulated. The amplitude of the color carrier frequencies transmitted with the color carrier suppressed Color signals are a measure of the saturation and the phase position in relation to a co-transferred reference carrier a measure of the hue of the transferred color. Due to phase errors in the transmission path, the phase of the color subcarrier-frequency color signal falsified, so that a wrong color tone at the receiver is reproduced. Differential phase errors that is a phase change of the color subcarrier-frequency color signal as a function of the amplitude of the brightness signal transmitted with the image carrier. Also is the reproduced hue depends on the phase setting of the one restored in the receiver, for demodulating the color carrier-frequency color signal and for separating the color signals necessary reference carrier.

A suggestion has already been made to reduce the impact of these errors has become known, but has not yet found its way into practice (USA patent specification 2 943 1 = t2). Then the phase of the color carrier should be changed by a 130 '' switch one of the two mutually perpendicular modulation axes from the grid to Grid or can be switched from line to line in the transmitter. In the receiver The demodulation axes are then switched over synchronously with the transmitter. To this A unidirectional phase error in the transmission system becomes the way Shift the color in the opposite direction to the target value. The reproduced Color therefore differs z. B. in two consecutive lines in complementary Direction from the true hue. Due to the integrating effect of the eye, the correct hue perceived, while the color saturation changed only slightly is.

The phase change system mentioned has a deficiency. Since the timed consecutive lines spatially consecutive because of the interlace Lines 1, 3, 5 are not immediately adjacent and the eye looks at large phase errors, in which the colors in consecutive lines are strong differ from each other, move a rough line structure in the vertical direction. The invention is based on the object of this line structure through special training of the recipient and thus to improve the mentioned suggestion in such a way that that all practical requirements are met.

The invention thus relates to a color television receiver for a color television system interlaced, in which the color carrier with a first color signal and that of Line to line alternately phase-rotated by + 90 ° and -90 ° color carriers with a second color signal are amplitude-modulated, the transmission with suppressed color carrier takes place and in the receiver for demodulating the carrier-frequency color signals of the carrier added again in the phase positions used in the modulations in the transmitter will. According to the invention, for the electronic compensation of on the transmission path resulting phase errors of each of the two color signals carrier or video frequency with the corresponding color signal delayed by the length of the line for averaging added.

As a delay means in the context of the invention is preferably a Propagation line applied, in which high-frequency signals converted into ultrasound run through the transit time medium (hereinafter referred to as transit time line).

The use of such delay lines delaying by line duration (e.g. 64 gs) is already known in television technology for comparing image signals assigned to points in adjacent lines on top of one another (Electronics, June 1951, p. 122). Another known application of the delay line serves the purpose of releasing the image signals from the influence that the signal that was a line time ago exerts on the pixel sharpness (German Auslegeschrift 1039 S61). In a further known application, the delay line is used to sequentially transmit different types of color signals with line spacing, e.g. B. merge red and blue to produce full color information in the receiver (SECAM system). By the invention: l .; a new application is opened up for the transit time line; it is used in a simultaneous color television system for the electronic averaging of similar color signals transmitted at intervals of the duration of a line. In this way, the known proposal mentioned, on which the invention is based, is decisively improved, in particular in the case of the use of a delay line with a low temperature coefficient. For this purpose was the realization of importance that it is possible using of modern media as a sound conductor to produce delay lines with such a low temperature coefficient (practically to the value zero), that a phase (tetreue delay farbträgerfrequenter Schwingun succeeds g s. The circuit is particularly simple if the delay line is set to the desired phase relationship between the delayed and undelayed color carrier frequency signal.

Embodiments of the invention are shown in FIGS. 2 and 3 shown.

The known color television system from which the invention is based is initially on the basis of FIG. l explains.

Two color carrier vectors 1 and 2 offset by 90 ° (quadrature-modulated) form in FIG. 1 together the resulting color carrier vector T ,, whose phase position to a phase-locked reference carrier 3, which can also be in phase with 2 (NTSC system), is a measure of the hue. Due to a plias error in the transmission path, the color carrier vector T, is shifted by the angle f3 in the positive direction, ie here in the direction of the reference carrier 3, so that the vector T, i; arises and with a modulation according to the axis of the reference carrier 3, an error in the color tone occurs. In the next line, the carrier vector 1 is switched to 180 ″ and forms the carrier vector -1. Since the carrier vector 2 is not switched over, the resulting carrier vector T_ ″, which is again shifted by the angle β in the positive sense due to the phase error mentioned, and the Forms carrier vector T._ß. If, in this second line, the receiver does not demodulate according to axis 1, but rather according to the switchover in the transmitter according to axis -1 , the vector T_j changes to position T @, '. The displacement of the carrier vector T., fl 'is the displacement of the carrier vector T, β with respect to the true position of the carrier vector T, equal and opposite, as in the upper part of FIG. 1 shown. After this switchover, the carrier vector T, ß 'is a mirror image of T = ß in relation to the axis 2 that has not been switched. To switch over the demodulation axis 1 from +1 to -1 in the receiver, only the phase of the reference carrier fed to the synchronous demodulator is expediently rotated by 180 °. Switching is also possible in other stages and in other ways.

In Fig. 2 shows an embodiment of the invention for an electronic compensation of phase errors arising on the transmission path, in which the color carrier-frequency color signals generated by quadrature modulation are first demodulated in known synchronous demodulators, separated from one another and then averaged at video frequency by addition. The received color carrier-frequency color signals are fed from the terminal 25 to the two demodulator groups 26, 27 , each containing two synchronous demodulators, namely the one group 26 without delay and the other group 27 delayed by a line duration via a delay line 5. The demodulator groups 26, 27 are also fed by reference carrier oscillators 28, 29, 28 of which are synchronized by undelayed signals (see arrow above 26) and 29 by signals delayed via the delay line 5 (see arrow below 27). If the delay line 5 is made sufficiently temperature-constant and phase-accurate, which - as mentioned - is possible with the ultrasonic delay line with special glasses, a common reference carrier oscillator can also be used for both demodulator groups 26, 27. The device known from the proposal mentioned for line-frequency 180 ″ switchover of one demodulation axis on the synchronous demodulator (± 90 ° compared to the other demodulation axis) is not shown. If with F, the vector of the carrier-frequency color signal in one line and with F._ the vector of the carrier-frequency color signal in the temporally next line with a switched-over modulation axis, or with I t ' l. " Q ,, Q., the the color signals corresponding to the two modulation axes, the color carrier-frequency signals at the input of the demodulator 26 successively F, F._, F ,, F., and at the input of the demodulator 27 because of the delay r - - F ,, F. " F ,. Accordingly, after demodulation on line 34), the color signals of one type, e.g. B. Q ,, Q. " Q ,, Q_, and on line 33 the signals Q." Q ,, Q_, Q ,. At the inputs of the adder stages 3d, 35 there are always color signals of the same type (Q or 1) assigned to image points which are assigned to one another and which are assigned to one another in successively transmitted lines for comparison. By adding the mean value between I, -mid l., Or Q, and Q_ results: at the output of the adder stages. These signals, in which the color contents of two consecutive lines are combined so that averaging is achieved, are fed to the matrix circuit 36 , at the output of which the color difference signals (BY), (RY), (GY) are available. In this way, the aforementioned interference structure is eliminated.

Instead of an ultrasonic delay line with special glass as the delay medium, which has practically no temperature coefficient, two delay lines with oppositely directed temperature coefficients can also be connected in series. The temperature response can also be regulated by a line from a thermocouple or a phase comparison circuit that can be controlled electrically in terms of its running time. _, In Fig. 3 shows a preferred embodiment of the invention in which the carrier-frequency color signals of the two color signal types (e.g. Q, I) are separated from each other, averaged with respect to successive lines and demodulated with the carrier added again, while evaluating the phase switching of the carrier on the transmitter side will.

The received color carrier-frequency signals are fed from a terminal 4 via a delay line 5 with the delay of the duration of a line, an amplifier 6 canceling the attenuation of the delay line 5 and an adjustable phase rotator 7 to a linear adder 8. The adder 8 is also supplied with the color subcarrier-frequency signals via a line 9 without delay. Amplifier 6 and phase rotator 7 are so set. that in the adder 8 the first color signals transmitted with line spacing add up and the second color signals cancel each other out (cf. FIG. 6 with the associated description). The output signal of the adder 8 arrives via a line 10 at the input of a normal amplitude rectifier 11, at whose output terminal 1: 2 provides the first demodulated color signal (Q). The adder 8 is also supplied by an oscillator 15 for reintroducing the carrier of the reference carriers suppressed in the transmitter via a line 22. The reference carrier oscillator 15 is synchronized by the color synchronizing pulses obtained from the video signal via a line 23 and by the line generator 17 via the line 24. The pulses coming from the line generator 17 via the line 24 removed the color sync pulse from the video signal.

The color carrier frequency signals delayed by a line duration also arrive from the phase rotator 7 to a second linear adder 13, to which the color carrier frequency signals are fed from the terminal 4 via a 180 ° phase rotator 14 . The addition stage 13 is also fed from the reference carrier oscillator 15 via a phase rotator 16 of the reference carrier. The phase rotation of the phase rotator 16 is switched line by line between -I-90 'and -90 ° with meander-shaped pulses 18 coming from the line generator 17. The output of the adder 13 is connected via a line 19 to the input of a normal amplitude rectifier 20 , at whose output terminal 21 the second demodulated color signal (I) is available (see FIGS. 7 and 8 and the associated description).

The mode of operation of the circuit according to FIG. 3 is based on the F i G. 4 to 9 explained.

F i g. .I shows a vector F, composed of the axes I and Q , revolving at a color carrier frequency, in one line. In FIG. 5, the vector F .., revolving at the color subcarrier frequency, is shown for the temporally following line. The axis I is switched to -I , so that the vector F., arises. In the adder 8 , the two vectors F1 and F are added in each line, since the delay line 5 always adds the carrier-frequency circulating vector of a line to that of the preceding line with the same amplitude. This creates a vector diagram according to FIG It can be seen that the vectors 1-I and -l are canceled and only the amplitude-modulated vector Q remains with double amplitude (suppressed carrier). This is true for each row. the ink carrier is added back into the adder 8, so that a normal amplitude-modulated Q-carrier is produced, which is demodulated in a known manner with an amplitude rectifier 11.

In the linear adding stage 13 , the delayed vector F1 of the preceding line, which revolves at a carrier frequency, is added to the vector of the respectively transmitted line, which is phase rotated by 180 °. If, for example, - I is currently being transmitted, the vector image according to FIG. 7 is produced, in which the Q vector is now dropped and the two 1-vectors in phase are added. In the next line in time, + 1 is transmitted, and the vector image according to FIG. 8, in which the Q vector drops out again and the resulting vector - 21 with suppressed carrier is created. Since this resulting vector - # - 2l or -2! is shifted in phase by ± 90 ° compared to the resulting vector + 2Q by the adder 8 , the reference carrier generated in the reference carrier oscillator 15 must also be added with a line-by-line phase change of ± 90 ° for the purpose of demodulation. This is achieved by the phase rotator 16, the phase rotation by a line coming from the generator 17 Schaltm; is switched over iander 18 ± 90 °. After the phase-correct addition of the reference carrier in the adding stage 13, demodulation takes place in a normal amplitude rectifier 20.

The amplifier can also be electronically regulated with a control voltage to the condition - l. = + L._ = O or - Q, + Q: = O. This control voltage is z. B. obtained by briefly only the switched signal is sent at the beginning or end of the line and is regulated in the other demodulator channel to disappearance of this signal.

In fi -. 9 is illustrated with the aid of the block diagram of FIG. 3 and represented by diagrams which color subcarrier-frequency, amplitude-modulated signals appear in successive lines at the outputs of the adder stages 8, 13 . The signals are written at the outputs of these adder stages, specifically for line n, the temporally following, spatially next but one line (n + 2) and the temporally following line (n + 4).

Claims (11)

Claims: 1. Color television receiver for a simultaneous color television system interlaced, in which the color carrier with a first color signal and that of Line to line alternately by +90 'and - 90 ° phase-rotated color carriers with a second color signal are amplitude-modulated, the transmission with suppressed color carrier takes place and in the receiver for demodulating the carrier-frequency color signals of the carrier added again in the phase positions used in the modulations in the transmitter is indicated by the fact that for electronic compensation of the transmission path resulting phase errors of each of the two color signals carrier or video frequency (Fig. 3 or 2) with the corresponding line delayed Color signal is added to averaging. 2. Receiver according to claim 1, characterized in that the carrier-frequency color signals of a first synchronous demodulator group (26 in FIG. 2) are supplied without delay and a second synchronous demodulator group (27) delayed by line duration that the synchronous demodulator groups of the reference carrier in the modulations The phase positions applied in the transmitter are supplied and that the successive lines assigned to each other and corresponding color signals assigned to each other and which are separately available at the outputs of the synchronous demodulator groups are added in adding circuits assigned to them (35 for the first color signal and 34 for the second color signal). 3. Receiver according to claim 2, characterized in that both synchronous demodulator groups have a reference carrier oscillator is assigned jointly and that the delay is in phase. 4. Receiver according to claim 1, characterized in that to obtain the first color signal, the color carrier-frequency color signals of a first adder stage (8 in F i g. 3) are supplied both instantaneously and delayed by line duration in such a way that the color carrier frequencies are added during the addition cancel the second color signals of successive lines and demodulate the added, color carrier-frequency first color signals with the addition of the carrier (reference carrier oscillator 15) , and that to obtain the second color signal, the color carrier-frequency color signals of a second adder (13) are both undelayed and delayed by line duration, however with a phase shift of 180 ° between the undelayed and the delayed signal, are supplied in such a way that during the addition the first color carrier-frequency signals of successive lines cancel each other out and the added second color-carrier-frequency signals are added with the addition of the carrier (Be Tension member oscillator 15, phase rotator 16) are demodulated. 5. Receiver according to claim 4, characterized in that the reference carrier the carrier-frequency first color signal in phase with the color carrier in the transmitter and the carrier-frequency second color signal alternating line frequencies by ± 90 ° is rotated in phase. 6. Receiver according to claim 4, characterized in that the demodulation takes place in the amplitude rectifiers (11, 20) assigned to the two color signals. 7. Receiver according to one of the preceding claims, characterized characterized in that a delay line with a small temperature coefficient for the delay serves. B. Delay line for a receiver according to Claim 7, characterized in that that they point to the desired phase relationship between the delayed and undelayed Signal is set. 9. Receiver according to claim 7, characterized in that in series with the delay line (5) there is an adjustable phase rotator (7). 10. Receiver according to Claim 7, characterized in that instead of a delay line with low temperature coefficients whose two with opposite course of the Temperature coefficients are provided in series. 11. Receiver according to one of the preceding claims, characterized in that the temperature independence of the delay line is produced by electronic means known per se. Documents considered: German Auslegeschrift No. 1 039 56l; U.S. Patent No. 2,943,142 (corresponds to German Patent No. 928,474); Electronics, June 1951, p. 122.