A Programmable Bi-phasic Current Stimulator for Implantable Vision Chips

• Main Authors: Ting-You Chen, 陳亭佑
• Other Authors: Ro-Min Weng
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/76824000364048190939

碩士 === 國立東華大學 === 電機工程學系 === 97 === A charge-balance biphasic current pulse of electrical stimulation generated by implantable devices has been reported as an effective approach to partially recover the visual sensation of blind patients caused by retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Epi-retinal prosthesis and sub-retinal prosthesis of the implant chip are two main methods to generate charge-balance bi-phasic current pulse in the retina stimulation system. Electrical stimulation signals provided by the circuits can replace the original signals provided by the retinal cells. The epi-retinal implant prosthesis uses an external camera to captures the image, transmits the data wirelessly to the implant, and converts the data to stimulus parameters. This thesis is focused on the design of an epi-retinal implant chip. A programmable stimulus driver is proposed with low power consumption which is suitable for the high-density retinal prosthesis. The stimulator includes the digital controller and the biphasic current generator. The biphasic current parameter can be varied by a digital controller. The digital controller includes a counter, a pulse width initial setting controller, a pulse width controller, an interphase delay controller, multiplexers, and a decoder. The biphasic current generator includes a high linearity digital-to-analog converter (DAC) which can provide an output swing with large biphasic current and can save chip area by switching in different time. A low power consumption voltage level shifter in the front stage of DAC is designed for the retina stimulator. The proposed voltage level shifter can limit the output swing so as to avoid the damage to the embedded integrated circuits (ICs). The signal of retinal stimulation generated by the stimulus driver is proved through HSPICE simulation. The stimulus driver is implemented by tsmc 0.35μm iii CMOS process. The proposed topology of the retina stimulator can stimulate 8 pixels with ±5V supply voltage. The frequency of input clock is 10KHz. The frequency of current stimulus signals is 39Hz. The maximum amplitude of the biphasic current pulse is 441μA. The pulse width of the interphase delay are 0.1ms~1ms. The impedance of the retinal tissue is around l0kΩ. In the proposed retina stimulation, 6 bit DAC with high linearity has INL and DNL to be 0.2LSB and 0.4 LSB, respectively.