ADS1294: Channel 1 noise much different than other channels

Matt Gaidica1

Part Number: ADS1294

I realize that THD and INL are different for channel 1, but I'm not sure if that can explain my observation that channel 1, when input shorted OR measuring real signals, is different by a factor of 1,000. I've read back the CHnSet for each channel to make sure my gains are all matching—they are. I've also inspected the raw data on the ADS1294 side, and indeed, ch1 values are just much smaller (it's not a conversion issue). I can capture a heart rhythm on all channels with the same, really clean looking waveform, so I'm likely not dropping bits or something in reading from the ADS. Thanks for the help,

over 3 years ago

0 TCT over 3 years ago

TI__Genius 11550 points

Hi Matt,

The noise data on your mobile apps for all channels seem to be much smaller than the device channel's noise performance. Are these data taken with the channel input shorted internally? Are you able to get similar input-referred noise performance shown in Table 1 to 4 in the datasheet when the channel input is shorted internally?

Thanks.

-TC

0 Matt Gaidica1 over 3 years ago in reply to TCT

Expert 1540 points

Ch2-4 are consistent with the data sheet. I must be dropping the MSB over SPI, because Ch1 has both lower noise and lower signal, effectively compensating for each other. I'll have to dig into that.

0 Matt Gaidica1 over 3 years ago in reply to Matt Gaidica1

Expert 1540 points

Ugh an outdated multiplier in my code. Thanks for the reassurance to *keep looking* TC.

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ADS1294: Channel 1 noise much different than other channels