Patent GB-1207358-A (GB)
Title: Improvements in or relating to chrominance signal amplitude controls
Inventor: DILLENBURGER WOLFGANG
IPC: H04N9/793
Filed: 1967-10-19
Abstract: 1,207,358. Colour television. FERNSEH G.m.b.H. 19 Oct., 1967 [19 Oct., 1966], No. 47640/67. Heading H4F. In a circuit arrangement for automatically controlling the amplitude of the chrominance signal is a colour television signal played back from a magnetic tape scanned in tracks inclined to the length of the tape by transducer heads carried upon a rotating head-wheel, a control voltage corresponding with the difference between the amplitude of the colour synchronizing signal (burst) in the signal component developed by an individual transducer head and the mean value of the amplitudes of the colour synchronizing signals in the signal components from all the transducer heads is derived, and is applied to control the gain or the frequency response of the signal path including said individual transducer head in such a manner as to reduce any difference in the amplitude of the compared signals. In Fig. 1 the signal components from transducer heads 11-14 are individually amplified and equalized 15-18 and applied to transducer head change-over switch 19 which combines the signal components into a continuous television signal. The colour synchronizing signal (burst) is separated 21 from the videofrequency signal, rectified 23 e.g. peak rectification, and applied to a difference amplifier 25 directly and via an integrating circuit comprising resistor 28 and capacitor 29, the signal appearing across which represents the mean value of the output of rectifier 23. The voltage at the output of difference amplifier 25 which represents the difference at any time between the amplitude of the colour television signal of the signal path then in use and the mean value of all the colour synchronizing signals, is then distributed to the four amplifiers and equalizers 15-18 by means of switch 31. Equalizers 15-18 contain controllable frequency-response correctors e.g. cosine correctors, the degree of correction being adjustable by an applied control voltage. The resistance controlling the amount of correction in the cosine corrector may comprise a photo-sensitive resistance which is illuminated by a light source of which the intensity is varied by the applied control voltage. The amplitude of the mean value signal applied to input 27 may be adjusted by means of an adjustable gain amplifier. A change-over switch 46 allows input 27 of difference amplifier 25 to be connected to a constant, adjustable voltage source represented by lead 47, by means of which the amplitude of the chrominance signal, and thus the colour saturation in the reproduced picture may be altered. In a second embodiment, Fig. 2, the video frequency colour television signal from demodulator 20, Fig. 1, is separated 41 into a luminance component and a chrominance component, each of which are amplified 42, 43, the gain of the chrominance amplifier 43 being adjustable by means of a control voltage. The corrected colour signal is applied to a gating stage 21 wherein by means of a gating impulse from impulse generator 45 the colour synchronizing signal is separated. This signal is rectified 23 and applied to a difference amplifier directly and via an integrating circuit 28, 29 as in Fig. 1. Gain control of the chrominance amplifier 43 is carried out in the manner of a gated gain control, the control voltage being stored in capacitor 46 which is charged only when the control voltage pulse appears at the output of difference amplifier 25 by means of switch 47.