AD5933 4-Electrode configuration for human body thoracic impedance measurement(0-60 ohm)

Question

1.Please suggest the circuit diagram for 4-electrode configuration for human body thoracic impedance measurement range 0-60 ohm using ad5933 
 2.I want inject ac current 200uA at 100khz ...please suggest the Resistor and capacitor value in the circuit diagram 
 3.Two electrodes for injecting the current and another two electrodes for sensing the voltage 
 4.I want operate the circuit at single power supply 
 5.I have referred the link: AD5933 4 Wire Configuration for low impedence (< 50 ohm) but there is no clarity in the diagram.Please suggest the circuit diagram for 4-electrode configuration for human body thoracic impedance measurement range

isantos · Accepted Answer

Hi Sanjay, 
 DC Block capacitor (transmit stage) = 22 nF 
 Yes you are right, Rcal value = 20 Ohms will be for 1-60 Ohm impedance range 
 INAMP: you may use AD8220 for this. 
 Use Vdd/2 as reference for AD8220 
 Set the input resistor value and the gain resistor value to 2kOhm. Other values are shown below: 
 
 Cheers, 
 Ivan)

isantos · Answer

Hi Sanjay, 
 
 I do not think you can measure thoracic impedance and perform ECG measurements simultaneously since the current source from the impedance measuring circuit will act as a source of disturbance to the ECG circuitry which might explain why ECG waveform characteristics are not seen. 
 
 We advise you to consider taking a look at ADAS1000 as front end ECG and for thoracic impedance measurement . 
 
 Cheers, 
 Ivan

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AD5933 4-Electrode configuration for human body thoracic impedance measurement(0-60 ohm)