I'm trying to develop a system for bioimpedance measurement with the IC **AD5933**.

*The AD5933 is a high precision impedance converter system that combines a frequency generator with a 12-bit, 1 MSPS, Analog-to-Digital converter. The frequency generator allows an external complex impedance to be excited with a known frequency. The signal in response from the impedance is sampled by the on -board ADC and a discrete Fourier transform (DFT) is done by an on-board DSP engine.*

The DFT algorithm returns both a real (R) and imaginary (I) data-word at each frequency point along the sweep. The impedance magnitude and phase are easily calculated using equations.

To convert this number into impedance, it must be multiplied by a scaling factor called the **gain factor**. The gain factor is calculated during the calibration of the system with a known impedance connected between the VOUT and VIN pins.

The measured **impedance** at the frequency point is given by:

*My problem is that I need to use only the real (Resistance) and imaginary (Reactance) information, rather than the Impedance Magnitude.*

Because the equations of body composition require, for example:

*So, my question is:* *How do I apply the gain factor only in real (Resistance) and imaginary (Reactance) values?*

Another thing, this doubt is very simple:

Is it possible to program the AD5933 to work with a fixed frequency of 50K?

Tks!

Well, the datasheet does not really address operations with complex impedances.

In your case:

Resistance + i* Reactance = 1 / (Gain factor * (Real data register+ i* Imaginary data register)) =

= (Real data register- i* Imaginary data register) / (Gain factor * (Real data register

^{2}+ Imaginary data register^{2})) == Real data register/(Gain factor * (Real data register

^{2}+ Imaginary data register^{2})) -- i* Imaginary data register / (Gain factor * (Real data register

^{2}+ Imaginary data register^{2})),so

Resistance = Real data register/(Gain factor * (Real data register

^{2}+ Imaginary data register^{2}))and

Reactance = - Imaginary data register / (Gain factor * (Real data register

^{2}+ Imaginary data register^{2}))