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AD8227 gain variation in NImultisim


I am trying to model a AD8227 InAmp sensing a differential input from a bridge pressure sensor in NImultisim (see attachments).

I set the gain resistor for the AD8227 to 487ohms and calculated the gain be 169.3. The REF voltage to the InAmp is about 0.481V.

But when I simulate this in NImultisim, the gain seems to vary a lot more than what I expected over my input voltage range of 0 - 25mV - (from <160 to about 168, see spreadsheet).

The CM voltage is about Vcc/2 and input and output voltages are all within range as far as I can tell from the data sheet, and fig 41 quotes a worst case gain non-linearity of about 120ppm.

I do not have any experience using InAmps, so could somebody please tell me if I am doing something wrong or if this is what I could expect to see if I built this circuit, i.e. is this typical behaviour?


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