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PCB with ADUCM350 and Howland circuit

Question asked by jackforin on Jun 13, 2017
Latest reply on Jul 8, 2017 by jackforin

Hello everyone, 

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

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