Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Ryan Selby
M.S. Final
May 28, 2013, 3:00pm
ECE Conference Room
Low-Power Switched-Capacitor Amplifier and Sigma-Delta Modulator Design for Integrated Biosensor Applications
Neurotransmitters are chemicals present in living
tissue which regulate biological functions. Some
neurotransmitter which are present in the brain,
such as nitric oxide (NO), are believed to play a
role in the process of cellular migration during
development. Today there is no practical way to
measure gradients of neurotransmitters across
pieces of tissue in both the spatial and temporal
domains. Single electrode systems can be used to
determine neurotransmitter concentrations at
specific locations, but do not provide spatial
resolution. Dyes and marking compounds can be used
to locate concentrations of neurotransmitters
across a piece of tissue, but kill the tissue in
the process, thus limiting temporal resolution.
Integrated silicon biosensor arrays have been
proposed as a method for detecting
neurotransmitters in both the spatial and temporal
domains. Using large arrays of microelectrodes
placed at pitches comparable to the size of
individual cells, a high resolution chemical image
of neurotransmitters could be captured in real
time. For such an array, a large number of
electronic components are necessary. Two such
components are high precision amplifiers and
analog-to-digital converters which are necessary
to amplify the extremely small chemical signals
and then convert them to digital values such that
they can be stored and analyzed. These components
must be low power to avoid generating heat, and
small in size in order to limit total silicon
This thesis proposes the design of a low power
switched-capacitor amplifier and Sigma-Delta
modulator for use as an analog-to-digital
converter. The switched-capacitor amplifier
achieves a gain of 40dB with -63.7dB total
harmonic distortion while using 6.82µW and
occupying 0.076mm2 silicon area. The Sigma-Delta
modulator achieves a signal-to-noise ratio of
86.8dB over 2kHz signal bandwidth and uses 9.1µW
while occupying 0.043mm2 silicon area. Both of
these designs were implemented in a 0.18µm CMOS
process with a supply voltage of 900mV and their
functionality verified was in silicon.
Adviser: Dr. Tom Chen
Co-Adviser: N/A
Non-ECE Member: Dr. Stuart Tobet
Member 3: Dr. George Collins
Addional Members: N/A
"A 0.18?m CMOS 2nd Order Sigma-Delta Modulator for Low-Power Biosensor Applications" published in the International Conference on Biomedical Electronics and Devices (Biodevices), Barcelona, Spain 2013.

"A 0.18?m CMOS Switched-Capacitor Amplifier Using Current-Starving Inverter Based Op-Amp for Low-Power Biosensor Applications" published in the Latin American Symposium on Circuits and Systems (LASCAS), Cusco, Peru 2013.
Program of Study: