Outline of the Talk. Retinal Prosthesis Goal. Retinitis Pigmentosa. Human Visual System ISSCC 2004 / SESSION 12 / BIOMICROSYSTEMS / 12.

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1 ISSCC 004 / SESSION / BIOMICROSYSTEMS /.. Retinal Prosthesis Wentai iu, Mark S. Humayun University of California, Santa Cruz, CA University of Southern California, os Angeles, CA A prosthesis device is designed to replace the functionality of defective photoreceptors in patients suffering from Retinitis Pigmentosa and age-related Macula Degeneration. The circuit designs include a telemetry link used for power transmission and a bidirectional data communication bus. The 8.9mm IC dissipates 50mW and is fabricated in.µm technology. Experimental results on human subjects are included. W. iu Outline of the Talk Retinal Prosthesis Background and History Architecture for Epi-Retinal Prosthesis Power and Data Telemetry Microstimulator Results from Human Implants Future Directions and Challenges Conclusions Retinal Prosthesis Goal To bring back OST vision for the bl Gene Therapy Medical Transplantation Microelectronics Approach (our approach) Medicine (ead: Dr. Mark Humayun) Duke University (88-93) Johns Hopkins (93-0) DEI/USC (0-present) Engineering (ead: Prof. Wentai iu) UCSC/NCSU (88 present) Human isual System Epi-Retina 300 um Structure of Human Retina Sub-Retina Human Retina Blness Blness Caused by Diseases Corneal Diseases Cataracts/Glaucoma Retina Diseases Retinitis Pigmentosa (RP- genetic) - in 4000 incidence and 00,000 in USA, million worldwide Age-related Macular Degeneration (AMD) - 700,000 Americans yearly and 0% of them become legally bl Involves only the rods and cones while cells that connect the eye to brain remain healthy (4% of rods/cones, 30% Ganglion cells, and 80% of inner layer remain intact). Optic Nerve Brain Retinitis Pigmentosa See Digest page IEEE International Solid-State Circuits Conference /04/$ IEEE

2 Age Related Macular Degeneration Electrodes in Human Subjects Bi-Phasic Waveform for Electrode Circuit Model isual Prosthesis - Approaches Intraocular Prosthesis Epi-Retinal Prosthesis USC/DEI/UCSC, Harvard/MIT, University of Bonn (Germany), Osaka University (Japan), Tohoku University (Japan), Seoul University (Korea), Sydney University (Australia) Sub-Retinal Prosthesis University of Tubingen (Germany), Optobionics (USA) Prosthesis at Optic Nerve University of ouvain (Belgium) Prosthesis at isual Cortex University of Utah, Dobelle Institute Intraocular Epi-Retinal Prosthesis Surgery Procedures Sixteen Electrodes Twenty-One Electrodes Twenty-Five Electrodes Bi-Directional Telemetry Architecture s Power Back Data Forward Data c 50mW power transfer Mbps forward data rate 3-5Kbps reverse data rate Dual Band Bi-Directional Telemetry Power ink at MHz Optimal Coil Design Minimizing Primary and Secondary osses E & H Field Safety Constraints Class-E Driver ow Battery Supply oltage and High Efficiency Close loop class-e control - immune from circuit component fluctuation Reverse Telemetry Optimal Power Delivery No Excessive Heat Dissipation in Implants Data ink - DPSK (at 5 MHz) Circuit Design Power Transmitter oltage Regulators Algorithms and Modeling Secondary Coil Design Fixation mechanism Surgical Tacks, Bioadhesives, Magnets ong term biocompatibility ery Small R C res C ery arge R res i icres, i i iload icres, i iload cons. Cres ESR load Cres ESR loss i ESR Qs ESR cons., Qs cons. H N loss i ESR R Q p, Q p N Optimums exist for the loss and H-field between two extremes Continued on Page 507 H IEEE / ISSCC 004 ISUAS SUPPEMENT 7

3 ISSCC 004 / PAPER. Continued from page 7 Non-linear model Accurate Can be analyzed only via SPICE Time consuming analysis inear model Coil Design Methodology Semi-automated coil design software using linear model oad specs Coils geometrical specs Carrier frequency Select uctance range for the secondary side Processing data for plotting Selecting secondary uctance based on plots Output Plots Secondary side Conventional New Method Reverse Telemetry Waveform PWM waveform at the secondary side R C res Only valid for specific region Easier to analyze Primary coil: i k Pout R k dd o o Pout Select the uctance range for the primary side Processing data for plotting Selecting primary uctance based on plots Printing system results DONE! Primary side Overlapping envelopes of the Differentially Detected signal at the Primary side Power evel Detection To detect the received power level by sensing the voltage on the storage capacitor Functional Blocks for Adaptive Control oltage sampled at 00Hz using a Flash ADC A zero is added by derivative detection circuitry to increase stability Differential switches to suppress clock feed-through Resolution of the derivative is.4m/ms Reverse Telemetry (secondary side) Closed loop Class-E power transmitter 64 voltage levels through DC-DC controller (95% efficiency) Series regulators provide 3m/ (line) and m/ma (load) regulation Prototype System Testing Results Reverse Telemetry PWM pulses Send power and physiological information back to primary Modulation -- oad Shift Keying No extra physical link is needed! Goal: Recreate the PWM waveform transmitted at the secondary unit and recover NRZ data Pulse mode PWM waveform The load is disconnected by 5us pulses Duty cycle represents digital bit (40% % - ) Storage capacitor provides power during back telemetry Reverse Telemetry (Primary side) PWM NRZ OUT 40% 60% 0 Circuit Blocks: Differential Envelope Detector Toggle Flip-Flop with hysteresis PWM converted to NRZ through atch Comparator 3.3 kbps achieved oad voltage stays at 5 under all loads and changes in coupling distance up to 3cm Settling time is ~00ms, can be reduced by better tuning the system and improving the back telemetry supply Data Telemetry The visual implant requires high quality and efficient perception. - Better BER performance : 6 db better than OOK (or ASK) 3 db better than FSK - Capability of higher data transfer rate - Constant envelope not effected by amplitude variation. DPSK : One differential stage Noncoherent detection Simpler Implementation A modified version of DPSK is employed Digital or sampling DPSK receiver After digitizing the input signal, detection and demodulation is done by means of digital signal processing technique (DSP) High flexibility and controllability. c 7 ISSCC 00 ISUAS SUPPEMENT / IEEE

4 Data Telemetry -Transmitter (NRZI) (DPSK) (Class-C) Receiver Architecture PSK Receiver - Simulation Results Transmitted Data Tran_datain Tran_dataNRZ Retina 3.55 Measurement Results Chip Highlights Two ependent DACs create ependent cathodic and anodic pulses Real-time programmable 60 channels via 60 dedicated drivers (no multiplexing) Each driver is designed to deliver current up to 600uA at.5ua resolution to a load of 0Kohms Charge cancellation Comprehensive digital design with data error detection using CRC and checksum Retina 4 Reduced Area Multibias DAC Multi-bias DAC technique reduces 8-bit DAC area approximately 5% allow more spatial resolution (smaller driver) Tran_DPSK Tran_py Rec_sy Rec_afterHP. mm x. mm. um CMOS Rec_dataNRZI Rec_dataout Received Data S. C. Demarco, W.iu, M. Humayun, et al., An Arbitrary Waveform Stimulus Circuit for isual Prostheses using a ow-area Multibias DAC, JSSC, October 003 Generations of Microstimulator dd Retina 5 Driver Circuitry M60 M3 Current Mirrors Retina- 5x5 photo sensor and signal driver Retina- :5 multiplexing, 4bit resolution 00 Retina-3 (Telemetry unit) channel output stimulator using ASK demodulator with hysteresis single current mirror for each for reliable data recovery. channel Achieving data rates of up to 50kb/s + _ pbias OA OA OA8 A SW9 SW0 SW6 Anodic section PA PA PA8 Output Output Output 8 Cascode Devices Protection Devices ss PC PC PC8 Retina channel stimulator with ependent DACs per each channel creating ependent anodic and cathodic pulses Retina-4 Advanced stimulator with multi bias DAC technique reducing 8-bit DAC area to 5% allowing more spatial resolution Retina-5 New generation low power, high resolution stimulator with charge balance and improved current source, using of high voltage devices in a low voltage process gnd DAC nbias ss SW + _ A M Cathodic section SW SW 8 OC OC OC8 M30 Retina Channel Driver Retina 5 Prototype for 000 Channel Technology Die Size Electrodes Frame Timing resolution Clock Rate Supply Sensitivity Power.um CMOS 5.5mm * 5.5mm 60 unmultiplexed 04 bits 4 clock cycles (/56 frame time).5mhz 6uA / 50mW. mm x. mm.6 um CMOS New driver circuit better linearity, matching, charge balance, power reduction :8 Demultiplexing Reduced headroom using active feedback current mirror Programmable current gain Charge cancellation mechanism IEEE / ISSCC 00 ISUAS SUPPEMENT 73

5 Prosthetic Device - Chronic Implant An implantable prototype (at low resolution 4x4) has been completed and the first clinical chronic trial was conducted on Feb. 00. The nd one was done in Aug. 00. And the 3rd one was done in Mar The chronic trials were conducted at Doheny Eye Institute, University of Southern California. The st generation of implantable prototype was provided by Second Sight C. The patient can read a large letter and identify large objects such as a case, which is directly in front of him. This, for the first time, shows that a completely bl person cannot only follow a light in and out of a room, cannot only tell where a doorway is, but also identify whether objects are directly in front of him or not. Prototypes at higher resolution (8x8,3x3) based on the design presented in the paper are being developed Future Directions and Challenges Goal: 3 x 3 pixels in 5mm x 5mm for facial recognition Integration and miniaturization are the topmost challenges Minimal power dissipation for battery life and safety High voltage devices are needed Global and local device matching are needed Biocompatible material is necessary Hermetic packaging is critical Device/circuit/package reliability and failure analysis More human implants in bl subjects Retinal Prosthesis An Engineering Solution to a Societal Problem The potential benefit to society comes not only from alleviating human suffering, but also by reducing the government resources now directed to assist people with disabilities. First generation of permanent implant (Courtesy of Second Sight C) Even if only 0,000 bl patients were helped for 0 years, an estimated 4 billion federal dollars would be saved!! Conclusions 3 implants in RP patients with bare or no light perception 4x4 electrode array Subjects can sense motion, identify shapes by scanning 74-year old, bl test subject performing Object recognition task. ision Research, 003. A framework for an Implantable Retinal Prosthetic device bridging Engineering and Medicine has been well defined. Dual band telemetry to achieve bi-directionai communication and electrode stimulation have been developed. First-Generation chronic implants in human subjects have yielded promising results towards changing Science Fiction into Technical Reality 3 implants in RP patients with bare or no light perception 4x4 electrode array Subjects can sense motion, identify shapes by scanning 7-year old, bl test subject performing Object location task. 74 ISSCC 00 ISUAS SUPPEMENT / IEEE