Summary form only given. This talk describes the efforts at MIT and the Massachusetts Eye and Ear Infirmary over the past 15 years to develop a chronically implantable retinal prosthesis. The goal is to restore some useful level of vision to patients suffering from outer retinal diseases, primarily retinitis pigmentosa and macular degeneration. We initially planned to build an intraocular implant, wirelessly supplied with signal and power, to stimulate the surviving cells of the retina. In this design electrical stimulation is applied through an epiretinal microelectrode array attached to the inner (front) surface of the retina. We have carried out a series of six acute surgical trials on human volunteers (five of whom were blind with retinitis pigmentosa and one with normal vision and cancer of the orbit) to assess electrical thresholds and the perceptions resulting from epiretinal retinal stimulation. The reported perceptions often corresponded poorly to the spatial pattern of the stimulated electrodes. In particular, no patient correctly recognized a letter. We hope that chronically implanted patients will adapt over time to better interpret the abnormal stimuli supplied by such a prosthesis. Experiences with both animals and humans exposed surgical, biocompatibility, thermal and packaging difficulties with this epiretinal approach. Two years ago we altered our approach to a subretinal design which will, we believe, reduce these difficulties. Our current design places essentially the entire bulk of the implant on the temporal outer wall of the eye, with only a tiny sliver of the 10 micron thick microelectrode array inserted through a scleral flap beneath the retina. In this design the entire implant lies in a sterile area behind the conjunctiva. We plan to have a wireless prototype version of this design ready for chronic animal implantation this Spring
Two methods for extending the definition of reactive power beyond the sinusoidal steady state are presented. Reactive power concepts are created that can be useful in the state-space analysis of nonlinear or nonperiodic systems. All definitions and results are given purely in the time domain without using Fourier analysis or other orthogonal function expansions.< >
The above paper[1] proposes basic definitions and conventi which are not appropriate for nonlinear networks in general, although I may be appropriate for the class of networks to which the paper addressed. Since the paper[1] does not make this distinction clear, this l is written in the hope that these concepts will be subjected to crit scrutiny before adoption elsewhere in the literature. The new res appearing in the paper[1] are not affected by this discussion of fundamen
In the analog VLSI implementation of neural systems, it is sometimes convenient to build lateral inhibition networks by using a locally connected on-chip resistive grid to interconnect active elements. A serious problem of unwanted spontaneous oscillation often arises with these circuits and renders them unusable in practice. This paper reports on criteria that guarantee these and certain other systems will be stable, even though the values of designed elements in the resistive grid may be imprecise and the location and values of parasitic elements may be unknown. The method is based on a rigorous, somewhat novel mathematical analysis using Tellegen's theorem (Penfield et al. 1970) from electrical circuits and the idea of a Popov multiplier (Vidyasagar 1978; Desoer and Vidya sagar 1975) from control theory. The criteria are local in that no overall analysis of the interconnected system is required for their use, empirical in that they involve only measurable frequency response data on the individual cells, and robust in that they are insensitive to network topology and to unmodelled parasitic resistances and capacitances in the interconnect network. Certain results are robust in the additional sense that specified nonlinear elements in the grid do not affect the stability criteria. The results are designed to be applicable, with further development, to complex and incompletely modeled living neural systems.
A new formula for the sensitivity of a vertically matched CMOS sense amplifier, of the type used in DRAMs, to threshold voltage mismatch, parasitic capacitance mismatch, transconductance mismatch, and bitline load capacitance mismatch is derived. The mathematical methods used in the derivation of the formula are described in detail. The formula yields insight on the DRAM sensing operation. The perturbation approach used is novel and rigorous and yields an explicit closed-form solution. The formula agrees well with simulations. It is inherently slightly conservative and thus appropriate for use in design.< >
An effort was made to produce fast, but accurate, estimates of best and worst-case delay for on-chip emitter-coupled logic (ECL) nets. The effort consisted of two major parts: (1) macromodeling of ECL logic gates acting as both sources and loads; and (2) delay estimation for individual nets using the gate macromodel parameters and RC tree models for metal interconnect. Both of these functions have been extensively tested on an industrial ECL process and cell (i.e., logic gate) library. It is noted that the success of a macromodeling approach relies on repetitive use of members of a library of modeled cells. A fixed computational cost (several CPU hours per cell) is paid to obtain simplified macromodel parameter values. Resultant timing estimates are typically within 5-10% of SPICE and are obtained roughly three orders of magnitude more quickly than SPICE.< >
This paper addresses the frequency-domain characterization of stochastic signals in linear time-invariant distributed networks. A new general relation is derived. The average power flow at each frequency from one source to another through a lossless coupling network is shown to obey an inequality related to the second law of thermodynamics. The sources can be essentially any stationary random signal or noise processes; in particular, they need not represent thermal noise. In this sense the inequality is quite general. Proofs are based on standard techniques from the theory of linear circuits and random signals: thermodynamic concepts are used only for motivation and interpretation.
