17-11-2018, 01:06 PM
I have started trying build a system A modulator within a FPGA and this is as far as I have got. I am using a EP4CE10 Cyclone IV FPGA and a AD9744 DAC chip. The DTO clock frequency is pixel frequency X 20 = 174.96 MHz.
The AD9744 that I received from a reputable source was faulty. It has a differential output and one side is completely dead. I had thought that because one side was down the other wouldn't work either but there is a sensible output from the other side which I am using.
All the photos below is of a 51.75 MHz carrier. The first photo is the output of the DAC and the second is after feeding it through a low pass filter. The filter is a C-L-C-L-C Butterworth with a cutoff frequency of around 70 MHz. The next is it modulated with a grey scale and then Test card C. Test card C looks a lot worse in the photo that it actually is.
It works OK'ish but it's dirty or slightly foggy looking, not as crisp as it should be.
The last photo is of the unmodulated carrier with the trigger control carefully adjusted it can be seen that the carrier's amplitude is not stable and I believe that it is this that is causing the fogginess.
Frank
The AD9744 that I received from a reputable source was faulty. It has a differential output and one side is completely dead. I had thought that because one side was down the other wouldn't work either but there is a sensible output from the other side which I am using.
All the photos below is of a 51.75 MHz carrier. The first photo is the output of the DAC and the second is after feeding it through a low pass filter. The filter is a C-L-C-L-C Butterworth with a cutoff frequency of around 70 MHz. The next is it modulated with a grey scale and then Test card C. Test card C looks a lot worse in the photo that it actually is.
It works OK'ish but it's dirty or slightly foggy looking, not as crisp as it should be.
The last photo is of the unmodulated carrier with the trigger control carefully adjusted it can be seen that the carrier's amplitude is not stable and I believe that it is this that is causing the fogginess.
Frank