I am working on a new PCB with ADUCM350 for bioimpedance tetrapolar measurement, and I have some doubts.
I would know if it's better (and possible) to design a new configuration composed by ADUCM350, AD8226 and Howland circuit insered between the output of the AFE and DUT so I could have the same current reference for every measurement and to maintain the current limit independent of the load resistance, differently from the standard configuration of Evaluation Board .
In attached we can see the howland configuration image:
- HPF for DC voltage removal circuit to avoid polarization effect of tissue impedance;
- VCCS for Howland circuit;
- Instrumenten amplifier like a AD8226;
- AD5933 should be ADuCM350 in this case.
For this new configuration I have some doubts about:
1. insertion of the HPF and VCCS for a correct working;
I suppose that Rlimit will be remove because now I will have the Howland circuit for the current limiting
2. if it's necessary the HPF because inside in the AFE of the ADuCM350 there is already a filter: LPF and the chance for the DAC offset changing (image)
Waiting for good news =)
Thank you for your time