Patent GB-1305635-A (GB)
IPC: H04N9/04
Filed: 1970-05-22
Abstract: 1305635 Colour television SONY CORP 22 May 1970 [31 May 1969] 24847/70 Heading H4F In a television camera employing a vidicon pick-up tube, Fig. 2, the output of the target structure 2 which is supplied to preamplifier 5, is fed back to the cathode via a D.C. restorer circuit 8a, a level adjusting circuit 8b and preferably a gate circuit 7. To avoid beam modulation the signal fed to the cathode 3 is also applied to grid 9a. With this arrangement if image light projected on to the target structure produces a potential Y thereon and a signal aY is fed back to the cathode then upon scanning the target its potential is reduced to aY, a signal Y-aY being derived at output 6 and a signal aY being stored on the target. In this manner a signal component is stored and then picked up as a video signal. By means of gate circuit 7 a desired portion of the output signal is stored on the target structure. In a colour television camera two pickup tubes are used, Fig. 3, tube 1a producing a green video signal and tube 1 which would otherwise produce a red and blue field-sequential video signal (rotating colour filter 11) producing with the aid of the above storage arrangement dotsequential red and blue video signals. Oscillator 12 having a frequency which is an integral number of times as large as the horizontal scanning frequency produces a rectangular sampling signal, Fig. 4A, which is applied to gate 7 via a switching circuit 13 which reverses its phase every field, Figs. 4A and 4B. Output of preamplifier 5 is fed to synchronous detectors 14a and 14b which are supplied with the signals of Figs. 4A and 4B phase switched at field rate. The output of synchronous detector 14a is fed to a switching circuit 15 and to an arithmetic circuit 17 via a T/2 delay circuit 16, T being the period of the switching circuit 13. The output of detector 14b is applied directly to circuit 17 the output of which is applied to circuit 15 which is switched at field frequency to derive red R and blue B dot-sequential signals at outputs 6R and 6B. The red, green and blue signals are matrixed 18 to derive the composite colour television signal.  In operation when the target has initially been exposed via the red filter it has the potential of the red signal as shown in Fig. 5A. Cathode 3 is then supplied with the signal shown in Fig. 5B, level adjusting circuit 8b attenuating the signal by half, and as a result the detectors 14a and 14b are supplied with the signal shown in Fig. 5C and the target potential is altered as shown in Fig. 5B. The target is then exposed with blue light giving it a potential as shown in Fig. 6A. Cathode 3 is then supplied with the signal shown in Fig. 6B, and as a result the detectors 14a and 14b are supplied with the signal shown in Fig. 6C, the target potential being altered as shown in Fig. 6B. From dotsequential signal B+R/2, B/2, B + R/2, B/2,... detector 14a derives signals B/2, 0, B/2, 0... and detector 14b derives signals 0, B + R/2, 0, B + R/2.... The signal from detector 14a is delayed by T/2 and an operation is affected in circuit 17. Thus dot-sequential colour signals B/2, R/2, B/2, R/2,... are obtained at the output of circuit 15. For the next field a similar operation is effected, Fig. 7 (not shown).