| 摘要 |
PURPOSE:To always ensure an accurate control of the white balance, by mixing the output signal of a photodetector with the input signal of a gain control circuit in a chrominance signal circuit of a TV camera and controlling the level of the output signal to a necessary level. CONSTITUTION:The transistors 31-33 of a photodetector 30 are made to condudct with the vertical flyback line signal VBLK to charge capacitors 37-39. Photoconductive elements 34-36 have the spectral characteristics approximate to the red, blue and luminance signals and vary their internal resistance by the volume of received light. Thus the voltage is reduced gradually for the capacitors 37-39. The minimum voltage discharged by these capacitors is held at rectifying circuits 50- 52. Then the output signal of an oscillator 55 is modulated by the output signals of the circuits 51 and 52 to be mixed with the blue and red modulated signals of a pickup tube 1 through mixers 56 and 57. Gate circuits 58 and 61 extract the signals mixed within a horizontal flyback time, and these signals are smoothed by rectifying circuits 59 and 62. Comparators 60 and 63 give a comparison among the output signals of circuits 59, 62 and 50 each, and give a control to gain control circuits 4 and 12 so as to obtain a coincidence between two output signals. |
