ADS1211 evaluation: a bit of shielding goes a long way…

Following-up on earlier analysis, the ADC performance observed at small decimation (like 1 s averages, with 60 Hz data rate – 60x decimation) left something to be desired – quite a few bits lost due to mains (and/or other) sinusoidal noise.

Look at 1 hour worth of data (60x decimated; each sample: 1 s worth of data), at higher magnification than before – ticks every 15 minutes:
ads1211 zero dec=60 noise

Obiously, there are some bursts. And these are almost certainly not related to the ADC or anything internal to the circuit. Maybe the power supply, but added quite a few decoupling capacitors…

So, if the noise source is external, a bit of shielding might help – great to have a little metal box (even a steel box) at hand!

ads1211 in shielded box

Note the 2 BNC cables – rather than one – feeding the test signals from a fully-differential source, to avoid ground loops.

ads1211 zero shielded noise

Well, not much to add! Amazing what a little metal box can do!

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