Combining the Composite Sync to the Green Signal
There is a simple, low-cost way to add the composite sync onto the green channel for standard-definition video. The circuit in Figure 1 uses the MAX9589 to add the composite sync to the green channel, and generates the standard RGB signals at each output. For example, consider a 0.7VP-P green signal input and a 0.3V composite SYNC signal input from the video sources that have 75Ω terminations. From Figure 1 the output signal at the green channel after the MAX9589 is 1VP-P. For the 0.7VP-P R and B input signals from the source, the output signals after the MAX9589 are 0.7VP-P.
There is an advantage to using the MAX9589 in this application. The MAX9589 can be used as an anti-aliasing filter in front of the video decoder and, thus, improves the video performance.
Figure 1. Schematic of a sync on green circuit.
Figure 2. Input and output waveforms from the circuit in Figure 1.