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有时从组合视频获得CCTV同步 信号时,它们必须保持瞬时保真 度。这方面的一种例子涉及到这样的应用,即几个视频源由一台仪器轮询,而后仪器从视频现场提取测光数据。 本文所描述的电路完全重复输入同步脉冲宽度。这允许精确地箝位在继水平同步电平发生的暗电平上。 组合视频输入端接在电阻器R1上,并由电容器C1交流耦合到运放IC1的倒相输入(见电路图)。由于二极管D1的导通,负电压被IC1倒相,其增益大约为-1。这就把负同步末端箝位在放大器参考电平上。在本例中,参考电平是电路地。当D1不导通时(视频输入为正),放大器输入脚呈现高阻抗,而
Sometimes when CCTV synchronization signals are obtained from a composite video, they must maintain instantaneous fidelity. An example of this is the application where several video sources are polled by one instrument and then the instrument picks up the photometric data from the video scene. The circuit described in this article completely repeat the input sync pulse width. This allows for accurate clamping at dark levels following horizontal sync levels. The combined video input is terminated on resistor R1 and AC coupled by capacitor C1 to the inverting input of op amp IC1 (see circuit diagram). Due to the conduction of diode D1, the negative voltage is inverted by IC1 with a gain of about -1. This clamps the negative sync terminal to the amplifier reference level. In this example, the reference level is circuit ground. When D1 is non-conductive (video input is positive), the amplifier input pin presents a high impedance, whereas