Patent GB-1027445-A (GB)
Title: Deflection circuit for cathode ray tubes
IPC: H04N9/09
Filed: 1963-03-06
Abstract: 1,027,445. Colour television; transistor sawtooth circuits. RADIO CORPORATION OF AMERICA. March 6, 1963 [March 27, 1962], No. 8956/63. Headings H3T and H4F. In a deflection system for cathode-ray tubes comprising a deflection coil fed with a sawtooth current waveform having a relatively long flyback period, an auxiliary voltage waveform is added to a saw-tooth voltage waveform derived from the deflection current so that part of the forward stroke of the resulting saw-tooth waveform occurs during the flyback period of the current waveform. The resultant waveform is used for deflection on an electrostatic cathode-ray tube. Optical systems for colour television cameras.- In Fig. 2, a zoom lens 61, mirror 62 and a prism 64, partially silvered at 63, focus an image on the screen of an image orthicon. Two further prisms 66, 67, a field lens 68, dichroic mirrors 71, 73, 76 and lenses 72, 74, 77 distribute the red, green and blue portions of the scene on to three vidicons. Black level clamping in colour television cameras.-A mask 69 provides a vertical dark strip along the edge of the face plate of each vidicon to provide a black reference level. Alternatively, an opaque strip of material may be cemented to each face plate. The image orthicon has magnetic deflection whilst the vidicons use electrostatic deflection. It is arranged that the black strip is scanned by each line sweep during the line flyback period of the image orthicon. Luminance signals from the image orthicon are amplified at 34 (Fig. 1), where horizontal and vertical blanking pulses are added. Spurious signals at the positivegoing (black) side of the composite waveform are clipped off at 36 by clamping to black level during the later part of the horizontal flyback period, the clamping being controlled by differentiated horizontal deflection pulses. The colour output of each vidicon is amplified and clamped at 31, 32, 33 by horizontal drive pulses each time the black strip is scanned. The clamping circuits have short time constant during the clamping period and long time constant at other times. The luminance and colour difference signals are processed in an unspecified manner at 26, after which synchronizing and colour burst signals are added at 27. Saw-tooth circuits; deflection arrangements for colour television cameras.-The horizontal deflection for the image orthicon is produced by passing a saw-tooth current having a conventional flyback time through deflection coils H (Fig. 5). A negative-going voltage of the same waveform is developed across a resistor 44, capacitor CA compensating for self-capacitance of the coils. The waveform is D.C. restored approximately to earth potential by capacitor 81 and diode 82, giving waveform A (Fig. 6), which is fed via resistor 86 to an adding circuit 87, 97. Transistor T1 is normally off but becomes conductive during each horizontal drive pulse B, clamping point C to earth potential, giving waveform C. The horizontal drive pulse is also fed to the base of transistor T2 turning on that transistor and charging capacitor 92. The charge is limited by diode 94, giving waveform D which is added at 87, 97 to waveform C, thus providing a waveform E, having a longer forward stroke and a shorter flyback than waveform A. Waveform E is fed via a pushpull amplifier to the horizontal deflection plates of each vidicon. A voltage having the same waveform as the vertical deflection current of the image orthicon is developed across a variable resistor 41 (Fig. 1), and used to provide vertical deflection on the vidicons.