Chip design for retinal stimulation of artificial eye

• Main Authors: Bo-Jun Zhao, 趙博鈞
• Other Authors: Yin Chang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/73832570426253870320

碩士 === 國立陽明大學 === 醫學工程研究所 === 96 === Objective：Age-related macular degeneration (AMD) and retinitis pigmentosa (RP) are two of the leading causes of blindness due to the degeneration of retinal photoreceptors. Artificial eye is one of the ways which may restore sight for the people who are blind caused these diseases. Studies showed that proper visual signals may be restored by effectively stimulating bipolar or ganglion cells through implanted electrodes in retina. Method：There are two major approaches of retinal stimulation in the visual prosthesis: sub-retinal and epi-retinal configurations. Each of them has its advantages and bottlenecks in performance. That leads us to bring out a new idea which may overcome the defects that have been existed in these two types of prosthesis and improve the overall performance: the sandwich-type approach. According to the structural algorithm, the sandwich-type should provide higher image resolution and lower power consumption than the two previous configurations. This research is focused on the parameters setting associated with the stimuli of current amplitude and duration for what we need in the sandwich-type approach. Thus to achieve this purpose the type of the retinal chip should equip with photo-sensitive device on it. This main structure of the retinal chip can be divided into several parts which contain photodiode, signal processing circuits and electrodes. The mechanism of this testing chip is that using photodiode as light sensor which transfers light intensity to current amplitude so that it can reflect the gray level of an image. Incorporated with the followed control circuit in the chip, which the stimulus parameters are preset, the light intensity in the form of current amplitude is delivered to the designed particular electrode of the electrode-array. Then the bipolar or ganglion cells in retina can be properly stimulated for the purpose of vision restoration. Result：Two generations of retinal chips had been designed with single and double power supply individually in this study. Linearity test of current output showed with pretty good results for the two chips. The maximum output current for the first chip is 496�嫀 with LSB of 16�嫀, and 88�嫀 with LSB of 2.8�嫀 for the second one. Conclusion：In this study the designated chip was using the process of TSMC 0.35�慆 Mixed-Signal 2P4M CMOS to implement the functions which the parameters of the output biphasic currents containing amplitude, pulse width, duration, period, frequency of stimulation in a period and selection of the electrode can be programmable. In the future, if the photodiode can be replaced by a form of high density array, the system design of this kind of chip might become more complex, but it should be more fulfilled with the physiological function in the reality of biology. Keywords：artificial eye、retina chip、micro-stimulator