THESIS
2013
xvii, 142 pages : illustrations ; 30 cm
Abstract
With the problems of aging moving to center stage in many countries, there is an
emerging demand for novel point-of-care diagnostic testing (POCT) with
portable/wearable/implantable devices. Among the widespread chronic diseases, the brain-related
diseases (neurodegenerative diseases, neural disorders, etc.) have raised significant
attention due to their large patient populations and the lack of effective diagnostic methods
for long-term monitoring at the early stages.
Real-time diagnosis and mechanism study of brain-related diseases requires the
recording of electrophysiological/electrochemical neural signaling at the cellular level.
Besides the clinical EEG and traditional patch-clamp methods, integrated with electronics, the
microelectrode array (MEA) platform provides anoth...[
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With the problems of aging moving to center stage in many countries, there is an
emerging demand for novel point-of-care diagnostic testing (POCT) with
portable/wearable/implantable devices. Among the widespread chronic diseases, the brain-related
diseases (neurodegenerative diseases, neural disorders, etc.) have raised significant
attention due to their large patient populations and the lack of effective diagnostic methods
for long-term monitoring at the early stages.
Real-time diagnosis and mechanism study of brain-related diseases requires the
recording of electrophysiological/electrochemical neural signaling at the cellular level.
Besides the clinical EEG and traditional patch-clamp methods, integrated with electronics, the
microelectrode array (MEA) platform provides another viable method of diagnosis with great
benefits that the other methods do not afford: high spatial/temporal resolution, high
throughput and being less invasive.
Although MEA devices have been widely studied, great technical challenges exist for
future POCT applications. The integration of the MEA device and the acquisition IC for high-resolution
recording is a major constraint at the moment. The performance of existing
acquisition ICs is not suitable for POCT devices, which limits the POCT applications greatly.
Therefore, the design of acquisition ICs has to be altered for the technology to advance.
This thesis focuses on developing a set of novel acquisition IC designs for different
modes of neural signals, which include neural potentials and neurotransmitters, as well as
neuron-electrode adhesion. In the research scope of this thesis, two chips have been
developed with voltage channels for sensing of neural potentials, current channels for sensing
of neurotransmitter release and impedance channels for monitoring the adhesion. Novel
circuit techniques to reduce the noise and improve the power efficiency, the linearity and the processing dynamic range techniques are developed.
The first chip is designed to capture dual-band neural potentials, which include the
local-field potential (LFP, 0.1-200Hz) and the spike potential (SP, 200-10kH). To achieve high sensitivity and avoid the cross-talk between dual-band signals, the acquisition IC uses a
continuous-time (CT) front-end with chopping to suppress the flicker noise in the LFP band
and a discrete-time (DT) back-end to achieve good linearity. A new feedback loop is also
proposed to linearize the chopped low-noise amplifier (LNA) in the front-end.
The second chip is designed to record the chemical neurotransmitter release and
electrical neural potentials simultaneously for high-density MEA. As the MEA technology is
migrating to more electrodes (up to tens of thousands), power and area constraints are
becoming the bottleneck of the acquisition IC design. Under the constraints of noise, linearity
and settling performance, this design enables the most efficient usage of power and area. The
current channel for chemical sensing saves power and lowers the noise with a novel current
buffer biased in the discrete-time (DT) before a TIA (trans-impedance amplifier). The voltage
channel for electrical sensing maximizes its power and area efficiency with a new
methodology proposed to optimize the major noise sources.
Impedance is another important signal from biosensors. This thesis also presents the
development of a novel impedance channel for fast electrochemical impedance spectroscopy
(EIS) with the best power efficiency. The design implements heterodyne conversion for the
first time. It allows multiple input frequencies with the FFT methods for fast response, and it
preserves the amplitude and phase, which can be extracted simultaneously without another
quadrature channel. The impedance front-end is designed with low noise, low settling power
and minimal interference.
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