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PSoC 5, 3 & 1 MCU

New Contributor II

I am having some issues with non-linear and inconsistent readings off the Sigma Delta converter.


My circuit uses a resistor ladder to attenuate a high DC voltage. That is buffered with an INA217 amplifier. The readings off the amplfier measure in a near linear fashion.


I am having a problem with the converter. It always reads a few milliviolts below what my meter reads. This variation changes with different voltage readings, especially over a large range.


The amplifier circuit is pretty linear, so it is safe to say the problem is the converter.


I read about a similar problem on another thread regarding analog routing and the voltage reference. I have the converter set:


Range 0-1.024V


Internal 1.024V reference.


16 bits at 48ksps.


What is going on?

1 Reply
Esteemed Contributor

Your LSB is ~ 15.7 uV. Look at supply rails with DSO on infinite persistence


to get a handle on pk-pk noise.




The following may help -






            AN57821     AN61290     AN58827






Use bypass the reference option.




What is in the signal path between sensor and A/D ? Lot of CM in design,


if so are you using differential conversion ?




Look at CM range, see below.




Regards, Dana.