Hi Sharat, The plot you provided has no labels or units so I will assume the x-axis represents time in samples and the y-axis represents signed 8-bit sample values. I'm not sure why there is such a negative bias but perhaps that's particular to your instrument.
Please, at the very least, run the MMCM calibration described at https://github.com/sma-wideband/adc_tests to reduce glitches on the interface. I believe Jack also has a more sophisticated approach which adjusts the IODELAY for each individual data line; sadly I don't have a link handy for that. Although you may not see these glitches with a sine wave, a noise-like signal will cause more transitions on each bit and thus more glitches with an uncalibrated interface. Thanks, Rurik On Tue, Sep 1, 2015 at 2:54 AM, sharat varma <va...@hku.hk> wrote: > Hi Jack, > > Thanks for the reply. > > I did not run mmcm calibration. Actually, we checked the ADC by feeding it > a low frequency sine wave from a function generator and it works fine. > > The problem with spikes occurs when we feed the ADC with the > photo-detector output. > > Regards, > Sharat > > > On 1 September 2015 at 13:52, Jack Hickish <jackhick...@gmail.com> wrote: > >> Hi Sharat, >> >> Are you running the adc mmcm calibration routine after programming your >> roach? >> >> Cheers, >> Jack >> >> On 31 August 2015 at 22:41, sharat varma <va...@hku.hk> wrote: >> >>> >>> Hi Casper, >>> >>> I am working as a post-doc working under guidance of Dr. Hayden So at >>> The University of Hong Kong. >>> >>> We are using ROACH2 to capture data from optical cytometry. We are >>> using ASIAA ADC5G ADC to capture data at 4 to 5 Gsps. >>> >>> We basically use the following parameters. >>> >>> Block parameter: two-channel, ZDOK0, demux 1:1 . >>> System: roach2, clock source:adc0_clk, clock rate: 300 MHz. >>> >>> We are connecting the output of a photo-detector 1544-B from Newport >>> Corp (the spec is attached) to the ADC input using SMA. >>> We find that noisy spikes are introduced when we capture the data >>> through the ADC (see attached fig). We double checked if the source had >>> problems using a oscilloscope, but on the oscilloscope we do not see any of >>> these spikes. >>> >>> We would be grateful if you could let us know if we are doing anything >>> wrong. >>> >>> Rgards, >>> Sharat >>> >>> >>> >> >
