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Entry  Thu Dec 8 15:32:04 2016, Gabriele, Electronics, Configuration, Timing issue: is it a DAC issue? 6x
    Reply  Mon Dec 12 14:15:53 2016, Gabriele, Electronics, Configuration, Timing issue: is it a DAC issue? dac_spectra.png
    Reply  Sat Dec 17 06:29:15 2016, rana, Electronics, Configuration, Timing issue: is it a DAC issue? 
Message ID: 240     Entry time: Mon Dec 12 14:15:53 2016     In reply to: 237
Author: Gabriele 
Type: Electronics 
Category: Configuration 
Subject: Timing issue: is it a DAC issue? 

I swapped the DAC with another one, but I see the same behavior in the output signal. Here's a spectrum of the DAC output, with and without output.


My previous test showed that the timing drift was somehow related to the output of the signal generator being connected to the DAC.

Some more findings follow. When the CyMAC is powered down, the timing sent to the DAC is highly distorted. It stays the same even when I power the CyMAC up again, and it gets better only after the IOP process is started. My guess is this has something to do with the DAC board initialization. In the following: first trace is the timing signal with CyMAC off; second with the CyMAC powering on, but IOP not yet started; third when the IOP process is running.

A small residual distortion around the transitions is visible. This is not present on the original signal, or even if the ADC only is connected to the timing.

To try to debug the problem, I set up a second signal generator (not locked to the first one) and used it to provide the DAC timing. In this way ADC and DAC get their timing from two different signal generators.

I still see the same small distortion on the DAC timing. More important, I noticed that the signals generated by the DAC (here a 1kHz sinusoid) are very noisy: there is a very large glitch at every clock transition. Is this a sign that tha DAC is malfunctioning? I don't recall seeing anything like that in any other case. In both screeshots, the purple trace is the DAC output (1 kHz sinusoid) and in the second screenshot the blue trace is the DAC timing. It's clear that there is a glitch every time the clock signal transitions.


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