ADS1284: Low frequency noise peaks in shorted-input noise spectrum

Gman

Part Number: ADS1284
Other Parts Discussed in Thread: LM27762, REF6250

We are evaluating ADS1284 and during our tests, on our prototype board, we have noticed that while we achieve very similar SNR (RMS noise) numbers to the datasheet, we are seeing a few low-frequency (~3 Hz, ~6 Hz) monochromatic noise peaks in the shorted-input data spectrum.

We do not think it is the power supply or reference, but with the noise being monochromatic, the power system would be my first guess. We run 4 ADS1284's all off the same +/- 2.5V analogue supplies and use the REF6250 reference. The +/- 2.5V supplies are generated from a 3.3V SMPS ---> LM27762 ---> +/- 2.5V ---> (REF6250) ---> ADS1284

over 4 years ago

0 Christopher Hall over 4 years ago

TI__Mastermind 44640 points

Hi Gman,

What you're describing sounds like it could be the modulator idle tones that are very low amplitude tones that are observable at very small input amplitudes.

By chance have you tired enabling the internal offset function to see if this has any effect effect on these tones (see https://www.ti.com/lit/ds/symlink/ads1284.pdf#page=24 for a description of this feature). Generally, increasing the input amplitude (or enabling the internal offset) will push these tones out of the digital filter passband.

0 Gman over 4 years ago in reply to Christopher Hall

Prodigy 40 points

Thanks Chris. That appeared to be the issue.

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ADS1284: Low frequency noise peaks in shorted-input noise spectrum