@article{demarco_liu_singh_lazzi_humayun_weiland_2003, title={An arbitrary waveform stimulus circuit for visual prostheses using a low-area multibias DAC}, volume={38}, ISSN={["0018-9200"]}, DOI={10.1109/JSSC.2003.817264}, abstractNote={Attempts are underway to construct a retinal prosthesis to recover limited vision for blind patients with retinitis pigmentosa using implantable electronic devices. These microchips provide electrical stimulation to damaged retinal tissues using an array of stimulus circuits. This paper describes improvements to conventional circuit designs with significantly decreased implementation area and the ability to support arbitrary stimulus waveforms where an array of such stimulus circuits is required. This yields greater spatial resolution in stimulation owing to more stimulus circuits per chip area. Also introduced are digital-to-analog converter gain prescalar and dc-offset circuits which tune the stimulus circuits to an optimally effective range due to variation in retinal degradation. The prototype chip was fabricated by MOSIS in 1.2-/spl mu/m CMOS technology.}, number={10}, journal={IEEE JOURNAL OF SOLID-STATE CIRCUITS}, author={DeMarco, SC and Liu, WT and Singh, PR and Lazzi, G and Humayun, MS and Weiland, JD}, year={2003}, month={Oct}, pages={1679–1690} }
 @article{demarco_lazzi_liu_weiland_humayun_2003, title={Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - Part I: Models and methods}, volume={51}, ISSN={["1558-2221"]}, DOI={10.1109/TAP.2003.816395}, abstractNote={Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Attempts are under way to construct a visual prosthesis to recover a limited sense of vision for these patients with the aid of implantable electronic devices. The function of these microchips is to provide electrical stimulation to existing viable retinal tissues - living ganglion and bipolar cells - using an array of on-chip stimulus circuits, while the dominant mechanism for power and data communication for these implanted devices has been wireless inductive telemetry using coils. This paper describes methods and models used to estimate the heating induced in the human eye and surrounding head tissues subject to the operation of this retinal prosthesis. A two-dimensional 0.25-mm high-resolution human head model has been developed with the aid of a new semiautomatic graphical segmentation algorithm. Finite-difference-based numerical methods for both electromagnetic and thermal modeling have been used to determine the influence of the specific absorption rate (associated with 2-MHz inductive coupling to the implant) and of stimulator integrated circuit (IC) power on tissue heating under different operational conditions and different hypothesis on choroidal blood flow and properties of the complex implanted circuitry. Results, provided in Part II of this paper, show that temperature increases of approximately 0.6 and 0.4/spl deg/C are induced in the midvitreous of the human eye in the absence and presence of choroidal blood flow, respectively, for a 60-electrode retinal prosthesis chip. Correspondent temperature rises of approximately 0.19 and 0.004/spl deg/C on the retina are obtained for these cases. Comparison with in vivo experimental measurements on intraocular heating in dog eyes shows good agreement.}, number={9}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={DeMarco, SC and Lazzi, G and Liu, WT and Weiland, JD and Humayun, MS}, year={2003}, month={Sep}, pages={2274–2285} }
 @article{lazzi_demarco_liu_weiland_humayun_2003, title={Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - Part II: Results}, volume={51}, ISSN={["0018-926X"]}, DOI={10.1109/TAP.2003.816394}, abstractNote={Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Attempts are under way to construct a visual prosthesis to recover a limited sense of vision for these patients with the aid of implantable electronic devices. The function of these microchips is to provide electrical stimulation to existing viable retinal tissues—living ganglion and bipolar cells—using an array of on-chip stimulus circuits, while the dominant mechanism for power and data communication for these implanted devices has been wireless inductive telemetry using coils. This paper describes methods and models used to estimate the heating induced in the human eye and surrounding head tissues subject to the operation of this retinal prosthesis. A two-dimensional 0.25-mm high-resolution human head model has been developed with the aid of a new semiautomatic graphical segmentation algorithm. Finite-difference-based numerical methods for both electromagnetic and thermal modeling have been used to determine the influence of the specific absorption rate (associated with 2-MHz inductive coupling to the implant) and of stimulator integrated circuit (IC) power on tissue heating under different operational conditions and different hypothesis on choroidal blood flow and properties of the complex implanted circuitry. Results, provided in Part II of this paper, show that temperature increases of approximately 0.6 and 0.4 C are induced in the midvitreous of the human eye in the absence and presence of choroidal blood flow, respectively, for a 60-electrode retinal prosthesis chip. Correspondent temperature rises of approximately 0.19 and 0.004C on the retina are obtained for these cases. Comparison with in vivo experimental measurements on intraocular heating in dog eyes shows good agreement.}, number={9}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Lazzi, G and DeMarco, SC and Liu, WT and Weiland, JD and Humayun, MS}, year={2003}, month={Sep}, pages={2286–2295} }
 @article{liu_vichienchom_clements_demarco_hughes_mcgucken_humayun_juan_weiland_greenberg_2000, title={A neuro-stimulus chip with telemetry unit for retinal prosthetic device}, volume={35}, ISSN={["1558-173X"]}, DOI={10.1109/4.871327}, abstractNote={In this retinal prosthesis project, a rehabilitative device is designed to replace the functionality of defective photoreceptors in patients suffering from retinitis pigmentosa (RP) and age-related macular degeneration (AMD). The device consists of an extraocular and an intraocular unit. The implantable component receives power and a data signal via a telemetric inductive link between the two units. The extraocular unit includes a video camera and video processing board, a telemetry protocol encoder chip, and an RF amplifier and primary coil. The intraocular unit consists of a secondary coil, a rectifier and regulator, a retinal chip with a telemetry protocol decoder, a stimulus signal generator, and an electrode array. This paper focuses on the design, fabrication, and testing of a microchip which serves as the telemetry protocol decoder and stimulus signal generator. It is fabricated by MOSIS with 1.2-mm CMOS technology and was demonstrated to provide the desired biphasic current stimulus pulses for an array of 100 retinal electrodes at video frame rates.}, number={10}, journal={IEEE JOURNAL OF SOLID-STATE CIRCUITS}, author={Liu, WT and Vichienchom, K and Clements, M and DeMarco, SC and Hughes, C and McGucken, E and Humayun, MS and Juan, E and Weiland, JD and Greenberg, R}, year={2000}, month={Oct}, pages={1487–1497} }