An implantable medical device which has a sensor that provides a waveform to an energy accumulator, such as a capacitor. The waveform is representative of electrical activity from a nerve. The implantable medical device further includes a threshold detector which provides a discrete output signal when the energy in the signal energy accumulator exceeds a threshold. The signal energy accumulator can be periodically discharged and then recharged during the time period that electrical activity is being sensed from the nerve thereby generating a number of discrete output signals each time the recharged energy accumulator exceeds the threshold. The frequency and number of pulsed outputs is indicative of the sensed electrical activity.