Hi,
We are having a problem with high gains (8 to 24) in the ADS1299 and we don't know what can be causing it.
We have made a software where the data received by the ADS1299 is normalized and then plotted. That is, if we adjust the gain to 12, we convert the data received to volts and then we divide by the gain, in this case 12. So if we apply a 1mVpp sine wave to the input we should be getting in our graph 1mVpp independent of the gain we use but for higher gains we receive lower values than what we should. When using the internally generated test signal this doesn't occur and we get the expected values for each gain.
We have made a test to make it more clear.
We've set up a channel to measure a sinusoidal wave comming from a function generator and we get the following values for each gain. This is raw data (difference) straight from the ADS1299:
Gain 1: 7152
Gain 2: 14276
Gain 4: 28375
Gain 6: 39584
Gain 8: 44100
Gain 12: 48476
Gain 24: 51532
As you can see the last gains don't correspond with the expected values. For example Gain 24 should give us 6 times what we get with gain 4 (170250) , and we don't.
The input circuitry only has a low pass RC filter made with a 4.99K and a 4.7nF capacitor. The same as the one used in Dev Kit.
What can be causing this?
Thank you.
