I need a reference circuit for 4_wire the impedance measurement using AD5934, range 50 to 250 ohm.

Question

I saw the reference design file CN0349 and CN0217, I think both are 2-wire implementation of the AD5P3x family IC. Can I get the circuit reference for the 4-wire implementation, with impedance range of 50 to 250 ohm. 
 Help will be highly appreciated.

Snorlax · Accepted Answer

Congrats, your simulation works! You have probably noticed that the model gets stuck, when the U4 output approaches certain amplitude (about 0.65V) when reducing R4 to give U4 larger gain - this is likely indication that signal hits the boundaries of that "box" on Fig, 28 in the AD8220 datasheet or rather the unknown boundaries of that "box" at the off-spec 3.3V power voltage. 
 Some general remarks regarding your model: 1. What does R12 represent? If this is the internal impedance of the AD5933 VOUT source, its value should be taken form Table 5. "Voltage Levels Respective Bias Levels for 3.3 V" on p. 13 of the AD5933 datasheet 2 . What does R11 represent? It seems to have no function in this schematic and should be removed 3. What would be the function of C2 - it only reduces the signal and shifts its phase, perhaps should be removed 4. R8 and R9 are probably unnecessary, at least one of them or both should be removed 
 What would you want to do next? Tune this model to work with the AD5933? Try some different instrumentation amplifier? Some additional gain should be added to the AD5933 input OPAMP to obtain the amplitude of Vdd/2 - 0.2V = 1.45V for optimal use of the ADC input dynamic range.)

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I need a reference circuit for 4_wire the impedance measurement using AD5934, range 50 to 250 ohm.