Apparatus for electrodermal activity measurement with current compensation

An apparatus, comprising:

• a first electrode configured to be in contact with a first portion of tissue;
• a second electrode configured to be in contact with a second portion of the tissue and in electrical communication with the first electrode through the tissue;
• compensation circuitry configured to generate a compensation voltage corresponding to a compensation current;
• and
• processing circuitry operatively coupled to the first and second electrodes and the compensation circuitry, the processing circuitry configured to:
• apply a voltage between the first and second electrodes;
• in response to the application of the voltage, measure a first current flowing between the first and second electrodes;
• obtain a second current by adjusting the first current using the compensation current;
• obtain a first measure of an output voltage by transforming the second current;
• in response to the first measure of the output voltage being outside of a predefined range, adjust the compensation current by adjusting the compensation voltage generated by the compensation circuitry;
• in response to adjusting the compensation current, subsequently obtain a second measure of the output voltage that is within the predefined range and indicative of a phasic level conductance of the tissue;
• and
• determine a tonic level conductance of the tissue, the adjusted compensation voltage being proportional to the tonic level conductance of the tissue.