Improving Vadc quality of AD5933

JanuFift said:

the voltage signal that I should expect to be received in the Vadc of the AD5933 should be within 0V to VDD with its center at VDD/2?

Yes, this is correct and also Vadc should be a pure sine wave free of any distortions, otherwise the built-in DFT produces incorrect results in the the Re and Im output registers.

While the ADI folks are looking at the potential AD8220 model issues, the thing to also consider would be the asymmetry of the AD8220 INAMP common mode input voltage as a function of gain and output voltage, see Fg. 30 in the AD8220 datasheet. Same voltages as in the model you posted, but the INAMP gain is 1 instead of a 100 and that could be an issue. The model should reasonably reflect the behaviour of the INAMP, so perhaps it would make sense to tweak the parameters in the model, like reducing excitation voltage while increasing the INAMP gain to see if it would be possible to get the INAMP to output undistorted voltage sine wave of the desired amplitude.

JanuFift said:

the voltage signal that I should expect to be received in the Vadc of the AD5933 should be within 0V to VDD with its center at VDD/2?

Yes, this is correct and also Vadc should be a pure sine wave free of any distortions, otherwise the built-in DFT produces incorrect results in the the Re and Im output registers.

While the ADI folks are looking at the potential AD8220 model issues, the thing to also consider would be the asymmetry of the AD8220 INAMP common mode input voltage as a function of gain and output voltage, see Fg. 30 in the AD8220 datasheet. Same voltages as in the model you posted, but the INAMP gain is 1 instead of a 100 and that could be an issue. The model should reasonably reflect the behaviour of the INAMP, so perhaps it would make sense to tweak the parameters in the model, like reducing excitation voltage while increasing the INAMP gain to see if it would be possible to get the INAMP to output undistorted voltage sine wave of the desired amplitude.