Document Type

Honors Thesis

Major

Electrical Engineering

Advisor(s)

Nuri W. Emanetoglu

Committee Members

Mauricio Pereira Da Cunha, Melissa Ladenheim, Andy Sheaff

Graduation Year

May 2023

Publication Date

Spring 2023

Abstract

A high-temperature Pierce oscillator circuit was designed, analyzed, simulated, built and tested. The oscillator was designed as part of a high-temperature sensor system for monitoring the condition of equipment operating in harsh environments. The oscillator was designed using a silicon carbide (SiC) metal-oxide-semiconductor field effect transistor (MOSFET) common source amplifier with an LC tank resonant circuit. It was manufactured using gold paste on alumina with 1 mil gold wire bonded between components. All components needed to be capable of operating at temperatures up to 400°C. To this end, high-temperature spiral planar inductors were designed and fabricated. These were found to be within 15% of their designed values. Commercially available high-temperature capacitors, resistors, and MOSFETs were purchased. The oscillator was simulated to determine its output characteristics with temperature varying from room temperature to 350 . This was done by deriving the circuit’s open loop transfer function, which was simulated in both MATLAB and Microcap. These simulations predicted room temperature oscillation frequencies of 3.93 and 3.81MHz respectively. Sensitivity analysis was done on the MATLAB transfer function to predict which components would affect the oscillation frequency the most. Two copies of the oscillator circuit were built and tested. The first produced an oscillation frequency of 3.45MHz at 350°C with an amplitude of 5Vpp­ off of a 5V input, reduced from 7.36Vpp at room temperature. The discrepancy in oscillation frequency compared to simulated values was found to be caused by loading from transmission cables. It was tested further until the MOSFET failed for reasons which are still being investigated. The second copy of the circuit was modified to address cable loading and a small choke in the first and oscillated at 3.68MHz at 100°C with an amplitude of 5.68Vpp for a 5V input, reduced from 6.56Vpp at room temperature. The oscillation frequency of the second oscillator was within 10% of the designed oscillation frequency in both MATLAB and Microcap. Simulations of amplitude change with temperature in the first circuit were all accurate within 5% as well. The second circuit is planned to be tested at higher temperatures and more analysis of the first circuit’s MOSFET failure is planned.

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