Position: Index >

Composite video signal text adder

2016-09-11 10:17  
Declaration:We aim to transmit more information by carrying articles . We will delete it soon, if we are involved in the problems of article content ,copyright or other problems.

This circuit shows a simple way to add text information to a composite-video signal that might be floating at some indeterminate de level. The text generator and composite-video source must have the same sync signal. The video-input and -output signals share the same terminal. C3 couples the video signal to the output of a rectifier circuit that is based on a subvideo-speed op amp. A faster op amp would clamp on individualsyncpulses rather than on the video waveform`s average value, as is desired.


Rll serves as a pulldown resistor and feedback resistor RlO ensures that TP6 remains at ground level. Emitter follower Ql buffers the text signal, and R5 serves as a gain control. A simple clamp circuit, Q2, is sufficient for regulating amplitude, because the text signal contains no gray-scale levels. Q3 couples the text signal into the op-amp clamp circuit.


Reprinted Url Of This Article: