AD5933 Configuration Issues

Hello, I am trying to calibrate the AD5933 and even though I have went through all the postings in this site, I am still having trouble getting the correct values.

Measurement range of interest: 1000 ohms to 10 Kohm.

Vdd = 3.3;

Zmin = 1000;

Zmax = 10000;

Vdc_offset = 1.48;  Vpp = 1.98  % Range 1

GAIN = 1;

Vpk = Vdc_offset + Vpp/2;

Vpk = 2.4700

 

Rfb = ((Vdd/2 - 0.2) * Zmin) / (Vpk + Vdd/2 - Vdc_offset) * (1/GAIN)

Rfb = 549.2424

 

Rcal = (Zmax + Zmin) / 3 = 3.6667e+03

 

Then I place a 3.58K resistor (closest value I could get) between Ad5933 pins 5 and 6 so as to run a calibration routine.

 

Ref_Resistor = 3580 ; 

Then I read from AD5933 and get:

 

R=-901

I=1483

 

With these readings I calculate the Gain:

 

Magnitude = sqrt(R^2 + I^2)

Magnitude = 1.7483e+03

 

Gain = (1/Ref_Resistor)/Magnitude

Gain = 1.5977e-07

 

Finally, when trying different resistors so as to check whether the device is measuring correctly I obtain the following for a frequency of 50Khz. I am only interested in measuring bioimpedance at 50 kHz

 

For Z = 3580:

R=-909/I=1496 Phase =-0.00 Mag =1750.51 |Zreal|=-909.00 |Zimag|=1496.00  |Z|=3575.52

For Z = 1k:

R=-2828/I=4610 Phase =-0.00 Mag =5408.30 |Zreal|=-2828.00 |Zimag|=4610.00  |Z|=1157.30

For Z = 10k:

R=-335/I=555 Phase =-0.00 Mag =648.27 |Zreal|=-335.00 |Zimag|=555.00  |Z|=9654.97

I get a considerable error, then I wonder what could be wrong. ?

Thanks in advance for your help.