Bugbee, Martin Bryan; (2000) An Implantable Stimulator for Selective Stimulation of Nerves. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Acute experimentation performed at many centres over the last twenty years has shown techniques which allow small neurones to be stimulated without large, the reverse of the normal recruitment order usually encountered during electrical stimulation; one-way excitation of neurones; and excitation of only a region of a nerve. These techniques should improve neural prosthesis by, for example: avoiding pain during stimulation and requiring electrode sites and therefore fewer incisions. To enable chronic clinical experiments of these advanced methods, there is a need for a specialised chronically-implantable stimulator, which can control either dipolar, tripolar or pentapolar nerve cuff electrodes. This thesis is concerned with the design and development of such a stimulator and, in particular, a fully customised analogue integrated circuit that converts incoming digital words into corresponding stimulation currents. A binary word is transmitted to the implant, which defines the current waveform parameters for the electrodes. This word is loaded into a shift register at the input. Part of the word is presented to a digital to analogue converter, to specify stimulation amplitude, and a pulse generator, which generates either a quasi-trapezoidal, or a square shaped stimulation waveforms. Four novel low offset linear transconductors provide the stimulation currents that are switched to the desired outputs. The charge balancing of the stimulation waveform is realised by a very long time-constant switched capacitor integrator. The major difficulties in the design of the analogue full custom IC proved to be the linear transconductor stages and the integrator. Results for the test ICs are presented and the design of a complete stimulator system is described.

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