02-09-2017, 01:05 PM
I wanted to swap to the TVP5150 video decoder and try out some other components so I got a new PCB made up to accommodate them and the Cyclone II board that I am now using. Two photos of the partly populated PCB are attached below, none of the modulator components are fitted yet. The PCB measures 89 X 96 mm.
I have fitted a THS7314D video amp in place of the emitter follower that I was using after the R2R ladder. The THS7314D has 3 amplifiers in one package. Each amp has a fixed gain of X 2 and also a 8.5 MHz low pass filter. I will use one amp for video out and another to feed the modulator.
I am now oversampling the video output at twice pixel frequency, this together with the LPF in the video amp has cleaned up the output nicely.
Photos below of the video output, each photo is of the trailing edge of the sync pulse and the scope is set to 0.1 uS/div . The first is without oversampling. The second is with oversampling, the extra steps are clearly visible. The third is after it has passed through the video amp and LPF.
Frank
I have fitted a THS7314D video amp in place of the emitter follower that I was using after the R2R ladder. The THS7314D has 3 amplifiers in one package. Each amp has a fixed gain of X 2 and also a 8.5 MHz low pass filter. I will use one amp for video out and another to feed the modulator.
I am now oversampling the video output at twice pixel frequency, this together with the LPF in the video amp has cleaned up the output nicely.
Photos below of the video output, each photo is of the trailing edge of the sync pulse and the scope is set to 0.1 uS/div . The first is without oversampling. The second is with oversampling, the extra steps are clearly visible. The third is after it has passed through the video amp and LPF.
Frank