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Entry  Fri Apr 9 20:29:45 2021, Sean Quinn, Spikes/noise sensitive to clock settings? spikes_16MHz.pngspike_period.pngbetter_spikes_15MHz.pngspike_period_15MHz.png
    Reply  Fri Apr 9 21:38:59 2021, Stefan Ritt, Spikes/noise sensitive to clock settings? 
       Reply  Fri Jun 24 09:57:36 2022, LynseyShun, Spikes/noise sensitive to clock settings? 
          Reply  Fri Jul 29 17:23:43 2022, Stefan Ritt, Spikes/noise sensitive to clock settings? 
Message ID: 888     Entry time: Fri Jul 29 17:23:43 2022     In reply to: 885
Author: Stefan Ritt 
Subject: Spikes/noise sensitive to clock settings? 

Look at the DRS4 data sheet, Figure 12. You see there the rising SRCLK pulse which outputs the next analog value. You also see tSAMP which describes the sampling piont (strobe or clock sent to your ADC). The value of tSAMP must be such that the values is sampled at the point where it flattens out, just 2-3 ns BEFORE the next analog sample is clocked out, as written in the text. So you have to phase shift your clock going to SRCLK and the one going to your ADC against each other. This needs adjustment at the ns level, so you need a PLL with fine-valued taps, so you can shift it in fractions of a ns. What you see is that you sample at the BEGINNING of a new value to be output to the chip. Please also note that most ADCs have an internal delay of their clock (usually called 'aperture') which has to be taken into account. So if your SRCLK and your ADC clock come at the same time (not phase shifted), it might happen that the ADC internal aperture delay caues it to sample the analog signal at the BEGINNING of the new value.

Hope this is clearer now.

Best regards,
Stefan

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