| 摘要 |
PURPOSE:To obtain a digital subtraction system which eliminates the necessity of manual offset adjustment before the photographing of an X-ray TV device by installing an automatic zero compensating circuit to an amplifier itself, or to the front and the rear of a logarithmic amplifier. CONSTITUTION:At the digital subtraction system of the X-ray TV device, a video signal from a TV camera is introduced to an A/D converter via a transmission line selected by means of a switch SW1 out of two transmission lines. Switches SW3-5 of each automatic zero compensating circuit fitted to each amplifier 20', 22', and 24' are turned on the (b) side before the X-ray is irradiated and, when the offset voltage of the amplifiers are held and a video signal is inputted into the switch SW1, the switches SW3-5 are turned on the (a) side to compensate a voltage variation. After the input of the video signal is terminated, an FET is turned on by a control signal CL and the electric charge of a capacitor is discharged. Since the offset is compensated in this way, the manual adjustment before an inspection becomes unnecessary. |
