Electrical and Electronic Engineering - Theses
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ItemA highly flexible stimulator for a high acuity retinal prosthesis implemented in 65 nm CMOS process( 2011)This thesis presents a design of a flexible stimulator in 65 nm Complementary Metal Oxide Semiconductor (CMOS) as part of a 1024-electrode epiretinal prosthesis to restore partial vision in patients suffering from eye diseases such as retinitis pigmentosa (RP) and age-related macular degradation (AMD). The stimulator design is to support as many different stimulation strategies as possible. In particular, a wide variety of current amplitudes and stimulation frequencies is called for. Bipolar as well as monopolar stimulation strategies are also catered for. The selection of electrodes is fully flexible where any electrodes and any number of them can be selected as active or return at any time slice. The separation of image data update rate and stimulation refresh rate helps reduce data bandwidth by a half, which is very beneficial because the bandwidth for the data receiver of the stimulator chip is limited to 300 kHz in Medical Implant Communication Service (MICS) band. A distributed design where data is mainly processed at the local controller of every electrode driver simplifies signal routing, which is critical when the number of electrodes goes up to 1024. Global controlling circuits which help realizing some of the flexibility were designed, fabricated and tested with good performance. A novel electrode driver topology was proposed. Each electrode is controlled by its own driver, which helps selecting electrodes independently. The proposed electrode driver allows its electrode to act as active or return. The novel electrode driver operates in an alternately push-pull manner where only one current sink or source works at a time when doing stimulation. This results in a reduction of headroom voltage by a half, or equivalently more voltage can be used for stimulation, which is extremely advantageous as the maximum supply voltage of the implemented 65 nm CMOS process is limited to 3.3V. In order to verify the feasibility of the flexibility in terms of the ability of circuit implementation and power consumption, a prototype stimulator with 64 outputs was designed, fabricated, and tested. This prototype stimulator supports all the targeted stimulation flexibility. The verification of this prototype stimulator is a very useful and important preparation stage in designing a fully integrated high acuity epiretinal stimulator. The prototype stimulator was extensively tested and expected performance has been achieved. The power consumption of the prototype stimulator is 400 µW excluding the stimulus power, which makes the power consumption of the ultimate 1024-electrode stimulator just a few mW.