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AD7793 linearity in Ain(+) to Ain(-) voltage near zero voltage.

Question asked by m-kun on Nov 16, 2017
Latest reply on Nov 17, 2017 by JellenieR

Hi 

I have question about AD7793 evaluation board .

Condition:

AVDD=3.3V

VREF=2.5V (external)

Ain(+)= Ain(-)± 150mV (1mV-step)

Ain(-)=0.9V

Buffer on

SPS=39.2Hz

Gain=1,4,8,16

 

Result:

Gain=1

linearity is ok.

 

Gain=4

Usual data step is  13356/mV

But -66mV to -67mV and 66mV to 67mV 

data step is 13135/mV.(non-linearity point)

 

Gain=8

Usual data step is  26807/mV

But -32mV to -33mV and 32mV to 33mV 

data step is 26500/mV.(non-linearity point)

 

Gain=16

Usual data step is  53633/mV

But -15mV to -16mV and 15mV to 16mV 

data step is 53296/mV.(non-linearity point)

 

Gain =4, 8, 16 have non-linearity point .

The bigger gain value is ,the smaller non-linearity voltage.

 

Are there any special characteristics about In-Amp or other in non-linearity point ?

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