Positive and negative values ADC

[MacBam]

Hi,

I want to measure both positive and negative values:

I have two outputs; One I want to measure from 400mV down to -400mV, with 1mV accuracy.

The other output is from -30mV down to -700mV with 1mV accuracy.

Any suggestions ?– currently I am using PSoC5. I have tried voltage divider but the accuracy is not good enough.

 

[danadakk]

The onboard Vref is good to +/- .2%, is it absolute accuracy that is your issue ? If thats
not good enough external Vref in order .....?

Your target accuracy, resolution ? Seems like ~ 10 bits

DelSig, if you bypass input buffer, the inputs can common mode 100 mV outside either
rail. So run the DelSig at 16 bits, and using precision divider on input force input into
the 100 mV outside rail limit ? Dividing input by 8 seems to do the trick, that means
effective res would be 16 bits - 3 bits or 13 bits.

Just a thought.

Alternatively offset the input signal into CM range for inputs, and use a cal routine to remove offsetting R's error.
Could even use onboard DAC to supply cal offset Vdd for the divider, as shown below. There is an ap note
on creating 10 bit DAC.

https://www.cypress.com/file/136326/download

See attached calculator for R values for producing offset for Vin.

Note could use onchip OpAmp as follower to unload divider Z on input signal.

https://www.cypress.com/documentation/application-notes/an84783-accurate-measurement-using-psoc-3-and-psoc-5lp-delta-sigma

https://www.cypress.com/documentation/application-notes/an57821-psocr-3-psoc-4-and-psoc-5lp-mixed-signal-circuit-board

Regards, Dana.