AD5933 in 4-electrodes configuration

Hi,

I would like to design analog front end for the AD5933 to be able to measure bioimpedance. Thus, I need to have 4-electrodes measurement. I have previous experience and fully-operating AD5933-based device in 2-electrode configuration. Does anyone have idea how to implement Howland-circuit or similar current source?

John

I'm not sure I can help, but when I used to do thin film resistivity measurements. Force and sense could be arbitrarily arranged I+, V+, I-, V- Around the bulk material. The probes were electrically rotated and an I-V curve generated again. With perfect symmetry and homoginity, the lines would lie on top of one another, A formula was applied and the ohms/square was derived. Some wierd function was applied if the curves were way off. It's some paper for measuring resistivity using a 4 probe method. Units were ohms/square.

Not sure how to get a force sense using your chip. Resistivity required the thickness.

An inline method could be used too with 4 probes. I on the outside and measured V on the inside, Polarity was reversed as a check. probe distances and currents were designed so that the result was ohms/square Look for 4 point probe for measuring sheet resistance.