Design and Implementation of a CMOS Digital Phase Imager for Time-Resolved Luminescence Imaging Applications.
luminescence imaging is a highly selective and sensitive analytical tool that has been
widely used in chemical and biological sensing applications, environment monitoring,
medical diagnosis, and life sciences. Currently the instrumentations for luminescence
lifetime measurement rely heavily on the expensive and bulky Photo-Multiplier Tubes
(PMTs) and the Intensified Ch... read morearge-Coupled Devices (ICCDs); however, there is a great
need nowadays to replace these bulky instruments with low power and highly integrated
devices to facilitate low-cost and portable implementations. An attractive alternative
to the PMTs or ICCDs is the CMOS based image sensors, which have significantly evolved
over the past twenty years to rival CCDs in many fields from consumer electronics,
mobile devices to high-end scientific imaging. CMOS image sensors offer many advantages
over CCDs such as high level system integration, low power consumption, high frame rate,
and flexible chip level signal processing. In this dissertation, we present the first
CMOS image sensor with direct digital phase output for time-resolved luminescence
imaging. A novel Zero-Crossing Detection (ZCD) scheme is implemented to extract the
phase-shift between the intensity modulated excitation signal and the emitted
fluorescence or phosphorescence, generating a time-domain delay that is linearly
proportional to the luminescence lifetime of the target analyte. A time-interpolated
Time-to-Digital Converter (TDC) is subsequently used to quantize the time delay into a
digital representation of the phase-shift for post signal-processing and image
reconstruction. For proof-of-concept, a prototype digital phase imager consisting of a
32 by 32 P+/N-Well/P-Substrate photodiode array, row-level phase readout circuits with
ZCD operation and a global TDC are implemented in an IBM 65nm low-power CMOS technology.
The fabricated chip occupies a 4mm by 4mm silicon area and consumes less than 8.26mW
power from a 1.2V supply. Extensive characterization demonstrates a phase readout
sensitivity of higher than 0.01 degrees at 1.2kHz modulation frequency and 0.1 degrees
at up to 1MHz. The measured TDC resolution is better than 110ps over a 414us temporal
dynamic range. In order to evaluate the complete image sensor performance for
time-resolved imaging applications, a phase image reconstruction is carried out over a
wide range of modulation frequency. Finally the fabricated imager chip is applied to a
sequence of luminescence lifetime imaging experiments, during which a wide field
phosphorescence lifetime imaging of a platinum complex and an oxygen sensing experiment
utilizing a fluorescent ruthenium complex are performed. Compared to the traditional
luminescence lifetime imaging systems, the implemented digital phase imager offers
competitive temporal resolution with significantly lower system cost, reduced size, and
ultra-low power consumption.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Electrical Engineering.
Advisor: Sameer Sonkusale.
Committee: David Walt, Chorng Hwa Chang, Robert White, and Mehmet Dokmeci.
Keyword: Electrical engineering.read less