GB986296A - Television camera apparatus - Google Patents

Abstract

986,296. Television; cathode-ray tube operating circuits; transistor detecter and amplifier Circuits. FERNSEH G.m.b.H. March 7, 1963 [March 7, 1962], No. 9104/63. Headings H3T, H4F and H4T. Television; cathode-ray tube operating circuits.-The invention relates to a television camera arrangement including an imageorthicon tube 1, Fig. 1, the beam of which is suppressed during a part of the scanning flyback period by means of pulse B, Fig. 2, so as to produce in the output signal F derived from the electron multiplier 6 a reference level during the interval t 1 -t 2 which may serve for D.C. restoration purposes in the video channel amplifiers 11 and 12. The operation of an image-orthicon is stated to result in only 50% modulation of the scanning beam which is returned to the electron multiplier with the result that the reference level produced as described above corresponds to about twice peak white. D.C. restoration effected with reference to this level does not therefore stabilize the black and white levels unless the beam current is also maintained substantially constant. According to the invention this is achieved by means of a stabilizing amplifier 13 which is connected to the output of amplifier 11 and produces a control potential by means of a peak rectifier 14, which is applied to the grid 4 of the tube gun via a D.C. amplifier 15. The tube target electrode 2 is driven negatively with respect to cathode 3 by a pulse C for a period exceeding pulse B so causing the whole of the beam current to be returned to the electron multiplier and producing during the interval t 2 -t 3 a signal level (see curve F, Fig. 2) determined by the maximum beam current (see curve G, Fig. 2). The output signal from amplifier 11 thus exhibits periodically repetitive levels representative of minimum and maximum beam currents to which peak rectifier 14 may respond. D.C. restoration is not effected directly on the reference level produced in the interval t 1 -t 2 ; a pulse D is added first during an interval t 1 -t 2 and brings the level down to either peak white or black. The D.C. restoration is effected by clamping circuits included with amplifiers 11, 12 and 13 and operated by pulse E. Transistor detector and amplifier circuits, Fig. 3.-Amplifier 13 comprises a conventional amplifier stage 26 with a clamp stage 29 driven by pulse E connected to the base and an emitter follower stage 33 connected directly to the collector. Peak rectifier 14 comprises diodes 36, 37 in combination with CR circuit 38, 39 and an output emitter follower 40. The resulting output potential is applied directly to the base of transistor 18 which comprises D.C. amplifier 15, the correct operating conditions being established by adjusting the base bias which is determined by a potentiometer 47 connected in a stabilized voltage divider chain including Zener diodes 45, 46.