Abstract
Bio-medical field has drawn more and more attention in recent years. Functional electrical stimulation (FES) has been researched and applied to treat neuron disease, repair the physiological function of patients suffering from neuron damage. The stimulator is very close to neuron in all implantable devices, so safety is the critical point. Usually, residual charge on electrode/neuron interface after once stimulation is estimated as safety standard. We wish the residual charge can be reduced as low as possible. Because lower residual charge means the electrode electrolysis probability is smaller. Besides, some researches have proven that the stimulator with asymmetric stimulation output waveform can reduce neuron stimulation threshold charge effectively. However, stimulator with asymmetric output waveform is hard to reduce residual charge because of its difficult calibration through circuit. According to above design hard point, we use an improved current source control signal called sequential switching signal (S.S signal) to achieve lower residual charge when transferring asymmetric waveform. The stimulator has been fabricated using TSMC 0.18μm technology. Simulation result shows that stimulation current is up to 400μA and its residual charge mismatch percentage is less than 0.1%.