A sensor is configured for measuring skin conductance. An amplifier is used to convert the skin conductance into an analog output voltage which is then converted into the digital domain by an analog-to-digital converter, so that an increase in the tonic skin conductance and the phasic skin conductance response are obtained in the digital domain. The amplifier has a non-linear logarithmic gain, with a decreasing gain for increasing skin conductance values. The sensor enables detection of increases in both tonic and phasic signals over a wide range of skin conductance. This allows the use of a lower resolution, and therefore lower cost, analog-to-digital converter.