Hello!

I created the circuit for impedance measurement with using AD5933.

It works very good.

But something isn't clear.

Some words from the Datasheet AD5933.pdf, page 15:

" A DFT is calculated for each frequency point in the sweep. The AD5933 DFT algorithm is presented by formula ... "

Could you explain me please, in detail, how ad5933 gets the real and imaginary parts of the measured admittance at the Frequency Point.

Thank you very much

Serg01

Hi Sergey,

I'm not an expert in DFT but all I can say is that the formula is being carried by the a DSP logic inside the DDS. This DFT processing can extract the complex data as captured by the ADC. With the presumption of having a single tone frequency, one can derive the amplitude and phase of the signal. The resistance and reactance can be deduced by considering the amplitude(sqrt(R^2 + I^2)) of the received signal, and simultaneously including the phase information (tan-1(I/R)). In most DFT processing, the phase information is ambiguous, but since the DFT processing is synchronous to the DDS it can calculate the phase information accurately. Every time the DDS changes frequency, AD5933 conducts an independent DFT calculation which makes it possible to derive the R+jX on each point within the frequency range that you desired.

Best Regards

Louijie