Hi All, I have a question regarding the ADC16x250-8 coax rev 2 running in demux by 4 mode. When I terminate the inputs with a 50 ohm connector and collect data using a basic snapshot block design, I get a little bit of noise on the LSB. I export the data to a csv file and find that it is a collection of 0's and -1's, indicating that the level being converted by the adc is sitting between these two values and there is some sort of internal noise causing us to jump between values. What is alarming is that when I collected 2^18 samples and run spectral analysis I see large spikes at intervals of FS/16 (See Attached, pwelch(x,1024,256,[],800)).
I am running the ADC at 800MHZ and the FPGA at 200MHZ. I am using one of the more recent casper builds after the bitslipping commit on Mar 25th. I also tried to use the ruby script located at https://github.com/jack-h/casper_adc16/tree/master/ruby/lib. I run the bof file with "adc16_init.rb --reg=0x3a=0x0202,0x3b=0x0202 -d 4 roach_ip boffile", where I change the ic inputs. We only connected 8 of the 16 coax cables to the board and I had to switch off the default. Has anyone else had a similar experience or ideas? ---------------------------------------------------- Adam Schoenwald ----------------------------------------------------
