Triple cascode high output impedance current stimulator with dynamic element matching for retinal prostheses

This paper reports a triple cascode high output impedance current stimulator with dynamic element matching (DEM) for retinal prostheses. In the artificial retinal prostheses system, the current stimulator is a key building block. The proposed stimulator can reduce the residual charge by using the DEM circuit even under process variation condition, thus can prevent the damage of the stimulating electrodes by charge accumulation between tissue-electrode interfaces. The output current of the stimulator can be affected by the impedance variation of the electrodes and the retinal tissues. The triple cascode structure can achieve the high output impedance, thus can supply the consistent stimulation current to retinal cell. The maximum stimulation current of the proposed stimulator is 57.3 µA. The stimulation current variation of the stimulator with the load impedance from 1 kΩ to 60 kΩ is 0.023 %, while the variations of the conventional stimulator and cascode stimulator are 11.47 % and 1.21 %, respectively. The residual charge is decreased to 2.13 % by adopting DEM technique in comparison with conventional stimulator.