Afstudeerwerken 2009-2010

Programmable current and voltage source for in vivo electrical stimulation of neurons

The Bioelectronic Systems Group works on implants for fine-grain stimulation and recording in deeper brain regions in order to advance therapies for neurological disorders, help pharmacological research, and provide means for fundamental research in neuroscience. We have been developing passive multi-electrode probe technology with micrometer contact dimensions so far for implantation in rodents and are now in the process of increasing the number of electrode contacts significantly (towards 64-128). Electronics functionality close to the electrodes allows for low-noise amplification, signal selection, filtering, and digitization which are essential to handle this large number of signals. Inversely, these electrodes can be used to electrically stimulate neurons using particular current or voltage waveform patterns.

This thesis focuses on the concept and IC design for a two-channel electrical stimulator able to act as current or voltage source with programmable temporal waveforms. The source has to be able to drive a wide range of impedances reflecting range of passive micro-electrodes (about 50-um diameter, different materials like Platinum, Iridium oxide, Titanium nitride) and the permittivity and conductivity differences of solutions and tissue in vitro and implanted in vivo condition. Current signals in the uA-to-mA range are required while voltage signals in the mV-to-V range are used. Stimulation frequencies are comparatively low (< 150 Hz) but typically used waveforms include pulses and ramps requiring decent transmission of higher harmonics into the 10-to-30 kHz range. High-voltage CMOS technologies shall be considered to comply with voltages up to +/-10V. Power consumption and area are optimization criteria for such an implantable device. A first important milestone of the thesis is establishing a high-level functional model of the building block which, in a second step, shall be refined further towards electrical circuit design and estimates for power consumption and component area. Some practical experience with Cadence IC design tools and knowledge in Verilog-A behavioral modeling are a plus.

Student: Charlotte Borremans
Advizors: Prof. Pieter Rombouts, Wolfgang Eberle (IMEC)