Removing parasitic effects from body impedance measurements with wrist-worn and/or other devices

Abstract

Methods and devices for removing parasitic effects from body impedance measurements. Such parasitic effects can include parasitic coupling(s)/impedance(s) and/or parasitic coupling between the impedance measurement device and the body tissue being measured. In one approach, a drive current is controlled so as to control the voltage of a sense electrode to reduce a parasitic current. In another approach, different known capacitances are added to enable calculation of unknown electrode impedances. In another approach, a positive feedback loop is used to reduce error associated with a parasitic current of a voltage sensor used to measure resulting subject voltage. In another approach, sequential application of drive voltage to each electrode is used and resulting currents through all electrodes are measured and used to calculate body impedance.