Event
M.S. Thesis Defense: Arindam Mandal
Monday, July 30, 2018
12:30 p.m.
AVW 2328
Maria Hoo
301 405 3681
mch@umd.edu
ANNOUNCEMENT: M.S. Thesis Defense
Name: Arindam Mandal
Committee:
Prof. Robert W. Newcomb (Chair/Advisor)
Prof. Neil Goldsman
Prof. Manoj Franklin
Date & time: Monday, July 30, 2018 at 12:30pm
Place: AVW 2328
Title: Design of a Quasi-Adiabatic Current-Mode Neurostimulator
Integrated Circuit for Deep Brain Stimulation
Abstract:
Electrical stimulation of neural tissues is a valuable tool in the
retinal prosthesis, cardiac pacemakers, and Deep Brain Stimulation
(DBS). DBS is being to treat a growing number of neurological
disorders, such as movement disorder, epilepsy, and Parkinson’s
disease. The role of the electronic stimulator is paramount in such
application, and significant design challenges are to be met to
enhance safety and reliability. A current-source based neurostimulator
can accurately deliver a charge-balanced stimulus maintaining patient
safety.
In this thesis, a general-purpose current-mode neurostimulator (CMS)
based upon a new quasi-adiabatic driving technique is proposed which
can theoretically achieve more than 80% efficiency with the help of a
dynamic high voltage supply (DHVS) as opposed to most conventional
general-purpose CMS having less than 25% efficiency. The high-voltage
supply is required to withstand the voltage seen across the electrodes
(>10V) due to the time-varying impedance presented by the
electrode-tissue interface. The maximum voltage a stimulator can apply
across the electrodes to achieve neural stimulation is defined as its
voltage compliance. The overall efficiency of the designed CMS is
limited by the efficiency of the DHVS.
A DHVS of 12V is implemented from an input voltage (VDD) of 3V, by
cascading five charge pump circuits using the AMI 0.5µm CMOS process.
It can maintain more than 60% efficiency for a wide range of load
current from 25µA to 1.4mA, with peak efficiency at 67% and this is
comparable with existing specific-purpose state-of-the-art
high-voltage supplies used in a current stimulator. The stimulator
designed in this thesis employs a new efficient charge recycling
mechanism to enhance the overall efficiency, compared to the existing
state-of-the-art CMSs. Thus, an overall CMS efficiency up to 60% is
achieved. A current source, programmable by 8-bit digital input, is
also designed which has an output impedance greater than 2MΩ with a
dropout voltage of only 120mV. Measurements show voltage compliance
exceeding +/-12V when driving a biphasic current stimulus of 10µA to
2.5mA through a simplified R-C model of the electrode-tissue
interface.
