Date of Award

5-2007

Degree Type

Thesis

Degree Name

Master of Science

Major

Electrical Engineering

Major Professor

Benjamin J. Blalock

Committee Members

Charles L. Britton, Syed K. Islam

Abstract

Operational amplifiers (op amps) are key functional blocks that are used in a variety of analog subsystems such as switched-capacitor filters, analog-to-digital converters, digital-to-analog converters, voltage references and regulators, etc. There has been a growing interest in using such circuits for "extreme environment" electronics, in particular for electronics capable of operating down to deep-cryogenic temperatures for lunar and Martian surface explorations.

This thesis presents the design and analysis of a general purpose op amp suited for “extreme environment” applications, with a wide operating temperature range of 93 K to 398 K. The op amp has been implemented using a CMOS architecture to exploit the low temperature operational advantages offered by MOS devices, such as increase in carrier mobility, increased transconductance, and improved switching speeds. The op amp has a two-stage architecture to provide high gain and also incorporates common-mode feedback around the input stage. Tracking compensation has been implemented to provide stable frequency compensation over wide temperature. The op amp has been fabricated in a commercial 0.35-μm 3.3-V SiGe BiCMOS process. The op amp has been tested for the temperature range of 93 K to 398 K and is unity-gain stable and fully functional over this range.

This thesis begins with a study of the impact of temperature on MOS devices and operational amplifiers. Next, the design of the wide temperature general-purpose operational amplifier is presented along with an analysis of the common-mode feedback circuit. The op amp is then characterized using simulation results. Finally, the test setup is presented and the measurement results are compared with those from simulation.

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