Low-power switched-capcitor amplifier and Sigma-Delta modulator design for integrated biosensor applications
Date
2013
Authors
Selby, Ryan, author
Chen, Tom, advisor
Collins, George, committee member
Tobet, Stuart, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Neurotransmitters are chemicals present in living tissue which regulate biological functions. Some neurotransmitters 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 area. 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.