We are trying to get a very fast impedance measurement on the Ad5941, with the EVAL-AD5941ELCZ evaluation kit. We will need an impedance output at approximately 1000 Hz. The excitation frequency can unfortunately not be very large, it should be around 4000 Hz.
I modified the BIA 4-wire example for my case (e.g. reduced the DFT_NUM to only 128 samples and increased the BiaODR frequency to 1000). It's fast, but not quite fast enough. I captured the sensor SPI, data-ready interrupt and excitation output in the following plot:
It seems the impedance measurement of the chip is paused during SPI communication. Is there some way to run both simultaneously?
Because each frame of SPI takes up quite some time.
Bonus question: there seems a small lull after each SPI frame. I think this is a very small sleep by the AD5941. Starting from the BIA example, how can I skip any sleep states at all and keep it active?