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ABSTRACT: The development of a test chip that will be used to evaluate a hermetic and biocompatible package for the driving CMOS circuitry of a retinal prosthesis is described. The package design is estimated to be about 2 × 2 × 0.3 mm<sup>3</sup> and will be formed by conformal layers of parylene and a metal (e.g. titanium) as inner and outer protections, respectively. The test chip has been specifically designed for evaluation of the packaging technology. It consists of many blocks of analog and digital components as well as relative humidity and temperature sensors. The test chip has more probe points than a typical chip, allowing a more thorough evaluation of circuit behavior during the testing. This chip will first be coated in a layer of parylene C and soaked in heated isotonic saline for an extended period of time. Every block in the chip will then be tested for functionality using the surface probe points. The next step is to coat the surface of another test chip with parylene and a metal and repeat these soak tests. The results will then be analyzed and mean time-to-failure for the different samples will then be computed. Using the accelerated testing paradigm, these results will then be extrapolated to mean time-to-failure in the operating intraocular environment. Parylene test structures have already undergone an accelerated lifetime test and results have been analyzed.
Engineering in Medicine and Biology Society, 2004. IEMBS '04. 26th Annual International Conference of the IEEE; 10/2004
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ABSTRACT: This paper describes a closed-loop wireless inductive power transfer system for an implantable retinal prosthetic device. The proposed system is designed to ensure optimal power transfer to the implanted unit despite coil displacements and changes in load current while minimizing the sensitivity to component and process variation. Based on the system modeling, stability constraints are identified and applied to the feedback control system. The model is crucial in determining component values, circuit topology and number of transmitted bits per sampling period required to ensure system stability. In addition, the model significantly reduces design iterations compounded by lengthy circuit simulation. The model is verified by Matlab and SPICE level simulations. The critical analog circuits of the control system have been designed and fabricated through AMI 1.6 μm process.
Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004
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ABSTRACT: This paper presents the design of a highly efficient power link based on class-E driven, inductively coupled coil pair. An optimal power link design for retinal prosthesis and other implants must take into consideration the allowable electric and magnetic field safety limits, which in turn govern the inductances of the primary and secondary coils. In retinal prosthesis, the optimal coil inductances have to deal with the constraints of the coil sizes, the trade-offs between loss, H-field limitation and the DC supply voltage requirement of the class-E driver. Our design starts with the formation of equivalent circuits, followed by the analysis of the loss of rectifier and coils and the H-field for induced voltage and current. Both linear and non-linear models for the analysis are presented. Litz wire is used to reduce the winding losses in our analysis. Based on the procedure, an experimental power link is implemented with an overall efficiency of 67% at the optimal distance of 7 mm between the coils.
Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on; 06/2004
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ABSTRACT: The development of a test chip that will be used to evaluate a hermetic and biocompatible package for the driving CMOS circuitry of a retinal prosthesis is described. The package design is estimated to be about 2 x 2 x 0.3 mm(3) and will be formed by conformal layers of parylene and a metal (e.g. titanium) as inner and outer protections, respectively. The test chip has been specifically designed for evaluation of the packaging technology. It consists of many blocks of analog and digital components as well as relative humidity and temperature sensors. The test chip has more probe points than a typical chip, allowing a more thorough evaluation of circuit behavior during the testing. This chip will first be coated in a layer of parylene C and soaked in heated isotonic saline for an extended period of time. Every block in the chip will then be tested for functionality using the surface probe points. The next step is to coat the surface of another test chip with parylene and a metal and repeat these soak tests. The results will then be analyzed and mean time-to-failure for the different samples will then be computed. Using the accelerated testing paradigm, these results will then be extrapolated to mean time-to-failure in the operating intraocular environment. Parylene test structures have already undergone an accelerated lifetime test and results have been analyzed.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2004; 6:4093-5.
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01/2004
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01/2004
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ABSTRACT: Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are incurable diseases that result in profound vision loss due to degeneration of the light sensing photoreceptors. However, the discovery that direct electrical stimulation of the retinal neurons creates visual sensation has inspired prosthetic devices aimed to restore useful vision in RP/AMD patients. The approach to one such electronic visual prosthesis is described in this article. The prosthesis consists of an external unit and an internal unit. The communication link has three components--power and data transfer from the external to the internal unit, and data transfer from the internal to the external unit. A novel method of integrating power transfer and back telemetry is described here. The goal is to design a stimulator chip with a small area with low power consumption. This chip, capable of stimulating 60 dedicated electrodes, is fabricated using AMI 1.2 microm process technology and the results are presented. Improvements in the design to increase the number of outputs to 1,000 have been discussed. The new circuit is aimed at increasing the circuit density, reducing power per stimulus, and meeting the requirements more closely than the previous designs. The results of the designed chip are presented.
Artificial Organs 12/2003; 27(11):986-95. · 2.00 Impact Factor
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ABSTRACT: This paper describes a smart bi-directional telemetry unit for an implantable retinal prosthetic device. The system is designed to deliver 250 mW to the intra-ocular unit via an inductive link and provide wireless communication capability. A novel dual frequency carrier approach is used to optimize the power link for maximum transfer efficiency and the forward telemetry for high data rates. The power link uses a smart feedback system via reverse telemetry to compensate for instantaneous changes in power level due to coil misalignment and load variations. The system is optimized to minimize the power losses in the analog front-end of the intraocular unit while ensuring proper device operation. Preliminary results are shown in AMI 1.6 μm bulk CMOS process for the reverse telemetry and power feedback system.
Circuits and Systems, 2003. ISCAS '03. Proceedings of the 2003 International Symposium on; 06/2003
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IEEE Engineering in Medicine and Biology Magazine 24(5):66-74. · 2.06 Impact Factor
