Patent GB-1117921-A (GB)
Title: Improvements relating to translating apparatus for colour television signals
Inventor: BRUCH WALTER DR
IPC: H04N11/16
Filed: 1965-08-09
Abstract: 1,117,921. Colour television. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 9 Aug., 1965 [8 Aug., 1964; 24 March, 1965; 8 May, 1965], No. 34045/65. Heading H4F. To reduce the phase error in a PAL-type chrominance signal the received chrominance signals are combined with a correction signal of which at least one of the phase and amplitude is a function of the phase error. The thus modified i.e. substantially phase error-free chrominance signals may then be fed to a plurality of receivers which do not have consecutive line electrical averaging means. As shown, Fig. 2, the received conjugate complex chrominance signals F(+#) and #F(+#), both subject to the same phase error +#, corresponding to two lines consecutive in time, and a reference signal of twice the frequency fo of the colour carrier and of constant phase, are applied to a modifier 1. The I and Q signals are used at the transmitter to derive the chrominance signals. The effect of the modifier 1 is to reflect the received chrominance signals in the fixed axis Q which is independent of the error #. As shown in Fig. 3, the received imperfect chrominance signal F(+#) is transformed into the chrominance signal #F(-#) while on the next line #F(+#] is transformed into F(- #). By means of delay line 4, the modified chrominance signals are added in adding stage A to the untransformed chrominance signals of the previous line to form chrominance signals F or F with no phase error # at the correct phase position a, its amplitude being less by a proportion 1-cos # than twice the amplitude of a received chrominance signal. Since at the output of the modifier 1, F is exchanged for F in relation to the signal at the input, the index pulses which adjust the correct switch position of the line frequency change-over switch in the receiver, have to be exchanged, or a synchronizing arrangement in which the synchronizing burst is likewise automatically switched over must be used. In a second embodiment for eliminating the phase error #, Figs. 5 and 6, the error-free chrominance signals F and F are produced from the received chrominance signals #F<SP>1</SP> and F<SP>1</SP> which include the phase error by reflecting them on an axis represented by Q<SP>11</SP> which is shifted in relation to the axis Q by half the angle of error, i.e. #/2. Fig. 6 shows the apparatus for carrying out this reduction in phase error, and the control of modifier 1 i.e. the information at which axis the reflection is to occur, is effected by a reference oscillation applied to the modifier along a line 3. To obtain the reference oscillation line duration delay line 4, 180 degrees phase shifter 5 and adding stages 6, 7 are connected to produce the sum and difference of the conjugate complex chrominance signals obtained on lines consecutive in time. Thus at the output of adding stages 6, 7 the colour carrier frequency signals are freed from phase modulation due to colour information and are dependent only on the angle of phase error #. Frequency doublers e.g. full wave rectifiers, 8 and 9, remove 180 degrees phase jumps that result from modulation with suppressed carrier and by means of phase shifter 10 the signals of twice the colour carrier frequency are brought to the same phase and combined in adding stage 11, at whose output there is produced a signal which, as it is of twice the colour carrier frequency, is modulated in phase with twice the angle of error 2 #. This signal is applied to adding stage 12 together with a signal of twice the colour carrier frequency, but of constant phase, obtained by a quartz crystal controlled oscillator 13 from the colour synchronizing pulses, to produce a reference oscillation of twice the colour carrier frequency which is phase modulated with #. This oscillation which is applied to modifier 1 has the effect that the respective chrominance signal received is reflected on an axis Q<SP>11</SP> at a phase position of half the angle of error # and is thereby transformed into an error-free colour carrier. This reference oscillation may also be produced by applying to a modulator a colour carrier frequency signal without any phase modulation from a quartz oscillator and a colour carrier frequency signal modulated in phase with the angle of error 9 obtained as shown in Fig. 6 by addition or subtraction of the conjugate complex chrominance signals of consecutive lines. In a further embodiment the correction of the colour carrier is effected by adding to the received demodulated television waveform (including the chrominance signal at sub-carrier frequency) a colour carrier frequency correction voltage with a phase depending on the polarity of the angle of error and an amplitude depending on the magnitude of the angle of error such that in the television waveform there is produced a colour carrier freed from the angle of error #. In this embodiment the brightness signal and the chrominance signal may remain together and in correcting the chrominance signal there is no averaging over two lines, this being only necessary for the correction signal. As shown, Fig. 12, the composite colour waveform is applied via terminal 101 and adjustable transit time line 110 to an input adding stage 111. From the composite waveform the chrominance signal with its sidebands is filtered out by filter 112 and passed to subtraction stage 114 directly and by way of modulator 115, which is fed with a voltage of twice the colour carrier frequency, constant amplitude and phase corresponding to the axis Q, and delay line 4. The output of the subtraction stage 114 is connected across an amplitude divider 119 with the factor 2 : 1 to the second input of adding stage 111. In this embodiment, the chrominance signal #F<SP>1</SP> of line 2, Fig. 8, is reflected at the fixed axis Q, so that colour carrier 109 is produced, and by means of delay line 4 the two signals F<SP>1</SP> and 109 are available at the same time and subtracted to produce a colour carrier frequency voltage K with the value 2F sin #. This frequency voltage K is then halved in 119 and added to the erroneous chrominance signal F<SP>1</SP> to produce chrominance signal F with correct phase a but reduced amplitude F cos #. To reduce this amplitude error which occurs as a result of the phase correction of the chrominance signal and to eliminate it at least for two values of the phase error a correction voltage C is produced, Fig. 11, which is equal to the carrier frequency correction voltage K/2 attenuated in amplitude by the factor k, i.e. k.F sin #. This correction voltage C is equal to the ideal correction voltage C<SP>1</SP> i.e. F(1-cos #) for two values of the phase error # i.e. 0 and + #1, and thus the error of amplitude remaining between 0 and + # 1  is only slight. Correction voltage C is produced and applied to the input of adding stage 111, Fig. 12, by passing the colour carrier frequency correction voltage K to a phase shifting filter 120 which feeds a potentiometer 121 whose slider is connected via an inverter 124 to stage 111. By means of the slider of potentiometer 121 the value of the factor K is varied. Inverter 124 reverses the polarity of the correction voltage C when the angle of error # passes through zero and serves to interpret the amount k.F/sin #/. In the path from the slider of potentiometer 121 to the adding stage 111 additional non-linear transmission units e.g. diodes, may be inserted which additionally distort the amplitude of the correction voltage so that exact amplitude correction is obtained over a wide range of phase error.