A design of the retina chip for artificial eye

• Main Authors: Yu-Wei Chang, 張育維
• Other Authors: Yin Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/51490340203578967694

碩士 === 國立陽明大學 === 生醫光電工程研究所 === 92 === Eyes, known as the window of the soul, are the important medium for getting information from the world. Life becomes extremely inconvenient if one loses his/her eyesight. Fortunately, researchers found that some eye diseases could be cured in the foreseeable future, particularly for the blindness which was caused by the damaged photoreceptors. Hence, by implanting the microelectrodes into the retina and effectively stimulating the bipolar or ganglion cells of the eyes, the sight could be restored. Up to now, there are two main ways of the visual prosthesis: sub-retinal, and epi-retinal approaches. Each of them, however, has its merits and demerits, thus it is difficult to tell which one is better. In order to improve the overall performance, we have brought up a new idea—the sandwich-type approach, which is surpassing for its high resolution and low power consumption. We hereby name the implantable visual prosthesis “retina chip,” and the whole system “artificial eye.” An artificial eye contains imaging sensor, wireless transmitter, retinal chip, and microelectrodes. The retinal chip, as the theme of this thesis, is made up of two parts. Stimulus waveform controller is the first part, which is implemented by CPLD(Complex Programmable Logic Devices), whose code is composed of amplitude controller, timing parameter, biphasic logic, and scanning controller. Biphasic current stimulator, the second part, is implemented by ASIC(Application-Specific Integrated Circuit), whose circuit is composed of digital to analog converter, cascoded current mirror, demultiplexer, and biphasic controller. The considerations of this design are safety, effectiveness, economy, and practicability. The experimental results have met the desired specifications. With 1 KΩ retinal load, the retina chip can generate the programmed stimulus waveform, operating at the frequency up to 5 MHz with good linearity. The differential nonlinearity is less than 0.6 LSB and the integral nonlinearity is less than 2.1 LSB. The maximum output of the biphasic current is 620 uA with 20 uA step. It can also sequentially stimulate 16 channels to make up frames. Compared to the other related reports, we find that the sandwich-type approach has better resolution and lower power consumption, thus the overall performance can be improved.