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Two-Input Video Fader

Two-Input Video Fader

In some cases it is desirable to adjust amplitude of a video waveform, or cross-fade between two different video sources. This circuit provides a simple means of accomplishing this. The 0V to 2.5V control voltage provides a steering command to a pair of amplifier input sections; at each extreme, one section or the other takes complete control of the output. For intermediate control voltages, the inputs each contribute to the output with a weighting that follows a linear function of control voltage (e.g. at VCONTROL = 1.25V, both inputs contribute at 50%). The feedback network to each input sets the maximum gain in the control range (unity gain is depicted in the example), but depending on the application, other gains or even equalization functions can be voltage controlled.