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Title: Transient Electrothermal Modeling of Digital and Radio Frequency Circuits.
Authors: Luniya, Sonali R.
Advisors: Dr. Michael B. Steer, Committee Chair
Dr. Kevin G. Gard, Committee Member
Dr. Paul D. Franzon, Committee Member
Dr. Rhett Davis, Committee Member
Keywords: electrothermal modeling
high dynamic range transient circuit analysis
Issue Date: 24-Aug-2006
Degree: PhD
Discipline: Electrical Engineering
Abstract: Simulator technology for the high dynamic range, electrothermal modeling of electronic circuits is developed and applied to digital, radio frequency (RF) and microwave circuits. High-dynamic range is achieved using a combination of device models based on state-variables and utilizing automatic differentiation, precise error determination, and time step control. State-variables enable simpler and faster development of models less prone to implementation error. Automatic differentiation yields error free evaluation of the derivatives of circuit quantities with respect to each other and so removes any uncertainty in establishing the precise circuit condition. In transient analysis precise error determination and time step control is achieved by comparing two nonlinear solutions at each time point. A two-tone test of an X-band GaAs MESFET MMIC (Gallium Arsenide, Metal Semiconductor Field Effect Transistor Monolithic Microwave Integrated Circuit) was used to investigate and validate dynamic range. In the determination of the third-order intermodulation product in a two tone test a dynamic range of 165 dB was demonstrated. This high dynamic range was achieved through precise evaluation of the derivatives, accurate time step control and the circuit state, which is important in long electrothermal transient simulations. This minimization of accumulated numerical error is especially important in long electrothermal transient simulations. The 3D compact thermal models of the X-band MMIC LNA developed were verified with thermal images of the MMIC LNA taken with an infra red camera. The thermal models predict the temperature rise on various spots of the MMIC with less than 5% error. To perform an coupled electrothermal simulation at RF frequencies, a linear RC network based thermal macromodel of the MMIC was developed. The high dynamic range capability helped detect the small changes in the output voltage of the MMIC, at elevated temperatures. This thermal macromodel was applied to electrothermal simulations of an 3D thermal test chip designed with a 0.18 um Fully Depleted Silicon on Insulator (FDSOI) MOSFET (Metal Oxide Semiconductor Field Effect Transistor) technology. An experimentally validated state-variable based electrothermal model of a 0.18 um FDSOI MOSFET is implemented.
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