Fig. 1 shows three protection methods against electrolysis
caused by direct current. The approach in Fig 1(a) employs
continuous monitoring of the electrode-tissue impedance [3]
or the stimulus current level [4]. The measured result is
compared with a pre-defined reference value and if the
measured result exceeds the reference, the stimulator output
stage is immediately disabled to prevent nerve damage. The
advantage of this approach is volume saving since the
monitoring circuit can be integrated with the stimulator output
stage circuit. However, the monitoring circuit increases the
stimulator complexity which itself increases the probability of
semiconductor failure.