Mark E. Halpern

A Complete 256-Electrode Retinal Prosthesis Chip

This paper presents a complete 256-electrode retinal prosthesis chip, which is small and ready for packaging and implantation. It contains 256 separate programmable drivers dedicated to 256 electrodes for flexible stimulation. A 4-wire interface is employed for power and data transmission between the chip and a driving unit. Power and forward data are recovered from a 600 kHz differential signal, while backward data are sent at 100 kbps rate simultaneously. The stimulator possesses many stimulation features, supporting various stimulation strategies. Many safety features are included such as real-time monitoring of voltage compliance and temperature, electrode self-locking in the event of out-of-compliance, and ESD protection circuit at every electrode. The chip is fabricated in a 65 nm CMOS process. The electrode driver pitch is 150 μm, and total chip area is 8 mm 2 . The chip has been extensively tested and all the requirements have been successfully verified. The measured DC current error for single driver stimulation without electrode shorting is 20 nA. The average power consumption per electrode with typical stimulus pulse parameters and full-scale output current is 129 μW, inclusive of all standby power. The chip overall power efficiency is 70% with 23 mW of power delivered to load.

Current Waveforms for Neural Stimulation-Charge Delivery With Reduced Maximum Electrode Voltage

This paper contains results on the design of electrical signals for delivering charge through electrodes to achieve neural stimulation while reducing the peak electrode voltage. A generalization of the usual constant current stimulation phase to a stepped current waveform is presented. Techniques based on optimization and linear dynamic system theory are then applied to design the magnitude of each current segment in such a way as to minimize the maximum electrode voltage, while transferring a designated quantity of charge in a specified time. Experimental results are provided which validate the approach in saline and in neural tissue.

A fully flexible stimulator using 65 nm cmos process for 1024-electrode epi-retinal prosthesis

This paper presents a fully flexible stimulator using 65 nm CMOS process for a 1024-electrode epi-retinal prosthesis. The stimulator can select any number of electrodes at any time and also supports both mono-polar and multi-polar stimulation. Furthermore, the stimulator supports a wide range of stimulus parameters. A novel feature is that the electrode driver operates in an alternately pull-push manner, which helps reduce headroom voltage while guaranteeing charge balance at the active electrode. The use of positive supplies instead of both positive and negative supplies simplifies CMOS circuit design. The current distribution between two nearby simultaneously active electrode groups was investigated and measurement result showed a maximum current crosstalk of 8%.

Wireless power delivery for retinal prostheses

Delivering power to an implanted device located deep inside the body is not trivial. This problem is made more challenging if the implanted device is in constant motion. This paper describes two methods of transferring power wirelessly by means of magnetic induction coupling. In the first method, a pair of transmit and receive coils is used for power transfer over a large distance (compared to their diameter). In the second method, an intermediate pair of coils is inserted in between transmit and receive coils. Comparison between the power transfer efficiency with and without the intermediate coils shows power transfer efficiency to be 11.5 % and 8.8 %, respectively. The latter method is especially suitable for powering implanted devices in the eye due to immunity to movements of the eye and ease of surgery. Using this method, we have demonstrated wireless power delivery into an animal eye.

Optimal pole placement design for SISO discrete-time systems

In this paper, we incorporate the placement of one real closed-loop pole into a compensator design framework based upon the Youla parameterization, duality theory, and linear programming. This framework has been used to design discrete-time compensators to solve the l/sub 1/ controller design problem as well as other related time-domain optimization problems. Previous work on these problems has focused on deadbeat systems. It is known that these can require high-order controllers. Part of the motivation for this work is to improve the tradeoff between controller order and performance over that, using deadbeat control.

A prototype 64-electrode stimulator in 65 nm CMOS process towards a high density epi-retinal prosthesis

This paper presents a highly flexible 64-electrode stimulator using 65 nm CMOS process fabricated as a stage towards a 1024-electrode epi-retinal prosthesis, which aims to restore partial vision in patients suffering from eye diseases such as retinitis pigmentosa (RP) and age-related macular degradation (AMD). The stimulator drives 64 electrodes with many flexible features, which are necessary before making a complete 1024-electrode implant chip. Each electrode driver can provide a bi-phasic stimulus current with fully programmable parameters such as amplitude, pulse duration, inter-phase gap, and stimulation rate. The electrode driver operates in an alternately pull-push manner with only one current source working at a time, which helps reduce headroom voltage while controlling charge balance at the active electrode. The stimulator varies both stimulus current amplitude and stimulation rate to represent phosphene brightness. The stimulus current amplitude starts from the tissue depolarization threshold with 64 different levels. The selection of active and return electrodes is arbitrary, any electrodes and any number of them can be selected at any time. The power consumption of the stimulator is 400 μW excluding the stimulus power. Measurement results verify correct operation. The stimulator is easily scaled up to drive 1024 electrodes.

Optimal Tuning of Inductive Wireless Power Links: Limits of Performance

This paper shows how to choose compensation capacitors for optimal performance in two-coil fixed-frequency inductive wireless power links having a series-parallel (SP) configuration. First, for the SP circuit with given coils, coupling and sinusoidal input voltage, it is shown how to calculate nonnegative valued capacitors to maximize power delivered to a given resistive load. Exact conditions for such a compensated system to deliver the maximum power obtainable from a circuit with the same resistances and an ideal transformer with optimal turns ratio are presented. The second main contribution is a method for selecting compensation capacitors to maximize a weighted sum of efficiency and delivered power to obtain a trade-off between these two quantities. This can allow flexible performance with a given set of coils. All of this can be implemented without numerical optimization software. The results are illustrated by numerical examples and supported by experimental measurements.

High-Q flexible spiral inductive coils

A limitation on the optimal design of inductive coils for wireless power transfer is its physical size. We investigated the effect of varying width and spacing of conductive trace of spiral inductive coils in order to improve its quality factor and hence power transfer efficiency between two coils. These spiral coils have inner and outer diameter of 23 mm and 36.5 mm, respectively. We found that for the same number of turns, quality factor Q increases with an increase in spacing. This is attributed to proximity effects in adjacent conductive tracks of the coil. An increase of Q at 6.78 MHz by 121% from the minimum value was achieved by systematically varying the different topologies. We conclude that an optimal topology of choice for a spiral coil is larger spacing and smaller number of turns.

A super low power MICS band receiver in 65 nm CMOS for high resolution epi-retinal prosthesis

We report a super low power MICS band receiver for a high resolution epi-retinal prosthesis (BionicEye). The FSK receiver consumes less than 1.5 mW power with 1 V supply. It can achieve a maximum data rate of 400 kb/s. In this paper, we present the research work carried out on designing a fully-integrated sub-threshold receiver fabricated on a 65nm CMOS chip. In order to achieve super low power consumption, more than 90% of the transistors in all analog building blocks are operated in sub-threshold region. System level issues, such as required receiver architecture and specifications are also addressed1.

Robust stability and design of linear discrete-time SISO systems under l/sub 1/ uncertainties

Shows how value sets and the zero exclusion principle can be used to obtain results on the robust stability and design of controllers against a special infinite-dimensional l/sub 1/ norm bounded parametric uncertainty in both numerator and denominator of scalar discrete-time plants. This parametric uncertainty has properties of both parametric and unstructured uncertainty and allows standard H/sup /spl infin// design tools to be used without conservatism.