Patent GB-1280049-A (GB)
Title: Television camera system
IPC: H04N5/073
Filed: 1969-11-04
Abstract: 1280049 Television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 4 Nov 1969 [7 Nov 1968] 53990/69 Heading H4F In a television camera system comprising a camera connected to a control unit by a transmission path, video signals from the camera and sync. pulses from the control unit are transmitted in opposite directions along the transmission path by frequency multiplexing, and digital signals for controlling the camera unit circuit functions are inserted into the back porches of the sync. pulses. The control unit, Fig. 2, comprises a source 40 of analogue control signals and a source 41 of digital control signals, the signals benig selected in sequence by means of electronic cross-bar switches 55, 56 under control of a selector circuit 60. When an analogue signal is selected it is converted to digital form in A : D converter 59. The selected digital or converted analogue signal is applied to a store 58. The selector circuit 60 is driven by sync. pulses from a generator 42 so that sixty analogue and two digital signals are selected in turn during successive lines of a television picture, the sequence being repeated so that each control signal is selected four times during each frame. A synchronizing pulse, camera identification bits and a parity bit are also inserted in store 58 the contents of which are sequentially read out under control of the selector 60 by means of colour subcarrier frequency pulses obtained from generator 58. These coded control pulses are timed so that they occur in the back porch of a horizontal sync. pulse with which they are combined in an adder 61 the output of which is modulated (in 16) on a carrier and applied to the transmission path. Audio signals from a source 46 are frequency modulated in modulator 72, added to audio signals from a second source 45 and amplitude modulated on to the subcarrier which is applied to adder 61 via a gate 75 which is opened during the picture intervals. Signal components which might interfere with the modulated colour subcarrier signals are removed from a video signal from source 44 by a filter 76 and the remaining signal also applied to adder 61. The output of adder 61 therefore contains a composite video signal having coded control signals inserted into the back porches of the horizontal sync. pulses and a colour subcarrier signal modulated with two audio signals. The control unit also contains a filter 25 to select video signals from the camera unit which are applied to detector 26 and then to sync. stripper 87. The picture signal is applied to adder 90 together with sync. pulses and a colour burst signal to provide a composite video signal at its output terminal. The phase of the sync. pulses of the received signal is compared with the output of generator 42 in comparator 87 the output of which is transmitted to the camera via the digital control signal channel. Monitor signals from the camera are selected by filter 29 and applied to detector 30. A D.C. supply 84 may also be connected to the transmission line. The camera unit, Fig. 4, comprises a colour camera 13 with signal processing circuits 21 the output of which is modulated in modulator 22 and transmitted to the control unit over the transmission path. The signal from the control unit is selected by filter 19 and detected in 20, and the video signal is applied to the viewfinder 126 when selected by the camera operator instead of the signal from processing circuits 21. The colour subcarrier signal is selected by filter 101 and demodulated in detector 120, the audio signal from source 45 in the control unit being obtained by filter 121 and the audio signal from source 46 in the control signal being obtained by filter 122 and FM detector 123. The received colour subcarrier signal is also applied to a limiter 102 the output of which is used to phase lock a colour subcarrier oscillator 103. The colour subcarrier is applied to a chain of frequency multipliers and dividers 104 to 108 to generate the horizontal and vertical sync. signals. The coded control signals are selected from the received signal by gate 110 and stored in a processor 111 from which they are read out in parallel and steered by cross-bar switch 112 under control of selector 115 to appropriate output channels, the digital signals being applied to decoder 113 and the digitally coded analogue signals being applied to D : A converter 114. One of the digital control signals (originating from comparator 87 in the control unit), is utilized to adjust the division ratio of divider 105 to maintain the phase relationship of the sync. pulses. The control signals are applied to the signal processing circuits 21. The signals at various parts of the processing circuits are selected by generator 15 modulated on a carrier and transmitted to the control. These signals are not provided with conventional sync. pulses but pulse width modulation signals are inserted by means of which an audio signal is transmitted to the control unit. Means are provided for selecting a signal from one colour channel or all three channels on a line sequential or framesequential basis the mode of operation being indicated by the insertion of appropriate colour burst signals. Selected picture lines may be replaced by wide pulses indicating the presence or absence of various voltages in the camera. The camera unit also includes a power supply unit 130 using D.C.-D.C. converters. The camera signal processing circuits, Fig. 7, comprise red, green and blue pickup tubes 220 to 222, the signals from which are applied to preamplifiers 224 to 226, blanking and black level control circuits 230 to 232, amplifiers 237 to 239, black level shading circuits 245, and gain shading circuit 250 to correct the signals as a function of the position in the raster. The green signal is applied to a contour control circuit 261 and then together with the red and blue signals to a linear matrix 260. The outputs of the matrix 260 are connected via white clipping circuits 300 to 302 to encoder 262 which produces the composite video signal. Each circuit unit is provided with one or more control terminals to which are applied the decoded control signals transmitted from the control unit. The monitor signals are taken from the terminals 315 to 323. The matrix 260 may comprise a first fixed matrix for deriving M (luminance), R-M, and B-M signals, a second variable matrix using four controllable gain amplifiers (280 to 283) having control terminals (273 to 276), and a further fixed matrix (272) to derive R<SP>1</SP>, G<SP>1</SP> and B<SP>1</SP> signals. A further control terminal (291) is provided to control the operation of a switch (290) by means of which the matrix may be by-passed if desired, Fig. 8 (not shown). Although the transmission path between the control unit and camera is shown as a coaxial cable it may be a radio link.