A 2.6V Silicon-on Sapphire CMOS current imbalance sensing circuit for neurostimulation applications

The occurrence of charge imbalance during the electrical stimulation of neurons has potential for destroying electrodes and damaging cells, which may lead ultimately to the stimulator explantation. In a measurement approach, imbalance can be treated as a DC component of the stimulation current. In this paper, we introduce a circuit solution suitable for measuring DC components associated with stimulation imbalances when voltage swings over three or more times the maximum voltage supply for the technology (3.3V). The proposed topology uses a current mirror connected in series to the stimulator to charge sampling capacitors, isolating the readout input from the high voltage (HV) stimulator output. The circuit was designed for Silanna Silicon-on-Sapphire 0.5μm/FC process, and has two operation modes: continuous integration (or charge sensing, for low stimulation currents), or instant error sampling. Simulation results indicates that the technique is suitable for detecting imbalances <;100nA for a milliampere stimulation current.