Design of a Folded Cascode Operational Amplifier in a 1.2 Micron Silicon-Carbide CMOS Process

This thesis covers the design of a Folded Cascode CMOS Operational Amplifier (Op-Amp) in Raytheon’s 1.2-micron Silicon Carbide (SiC) process. The use of silicon-carbide as a material for integrated circuits (ICs) is gaining popularity due to its ability to function at high temperatures outside the range of typical silicon ICs. The goal of this design was to create an operational amplifier suitable for use in a high temperature analog-to-digital converter application. The amplifier has been designed to have a DC gain of 50dB, a phase margin of 50 degrees, and a bandwidth of 2 MHz. The circuit’s application includes input ranging from 0 volts to 8 volts so a PMOS input differential pair was selected to allow the input range down to the VSS rail. The circuit has been designed to work over a temperature range of 25°C to 300°C

A Manufacturer Design Kit for Multi-Chip Power Module Layout Synthesis

The development of Multi-Chip Power Modules (MCPMs) has been a key factor in recent advancements in power electronics technologies. MCPMs achieve higher power density by combining multiple power semiconductor devices into one package. The work detailed in this thesis is part of an ongoing project to develop a computer-aided design software tool known as PowerSynth for MCPM layout synthesis and optimization. This thesis focuses on the definition and design of a Manufacturer Design Kit (MDK) for PowerSynth, which enables the designer to design an MCPM for a manufacturer’s fabrication process. The MDK is comprised of a layer stack and technology library, design rule checking (DRC), and layout versus schematic checking. File formats have been defined for layer stack and design rule input, and import functions have been written and integrated with the existing user interface and data structures to allow PowerSynth to accept these file formats as a form of input. Finally, an exhaustive DRC function has been implemented to allow the designer to verify that a synthesized layout meets all design rules before committing the design to manufacturing. This function was validated by running DRC on an example layout solution using two different sets of design rules

Compositionally Graded Indium Gallium Nitride Solar Cells

For the past several decades, methods to harvest solar energy have been investigated intensively. A majority of the work done in this field has been on solar cells made with silicon – the most mature semiconductor material. Recent developments in material fabrication and processing techniques have enabled other semiconductor materials to attract practical interest and research effort as well. Indium gallium nitride (InGaN) is one such material. The material properties of InGaN indicate that solar cells made with it have the potential to achieve much higher power density than a standard silicon solar cell. High power density InGaN solar cells could replace silicon cells in applications where size and weight are critical, or in environments where silicon devices cannot survive. This is especially true of space, and most InGaN development has been done with that in mind. However, at high enough power densities, InGaN solar cells could begin to compete with silicon devices in commercial applications. The goal of this research is to investigate the effect a novel growth technique for InGaN – graded layer deposition – has on the power density of an InGaN solar cell. In this research, first a baseline InGaN solar cell was grown, fabricated, and characterized. A standard PiN (P: p-type, i: intrinsic, N: n-type) structure was used for this baseline device. The reference alloy composition was chosen to be 20% indium and 80% gallium (In­0.2Ga0.8N). This sample was grown using molecular beam epitaxy (MBE) under standard conditions for the material. Once the reference crystal was fabricated it was optically and electrically characterized. The material composition was verified through a combination of x-ray diffraction (XRD), photoluminescence (PL), and transmittance/reflectance measurements. The quality of the surface of the crystal was examined using atomic force microscopy (AFM). Once the optical characterization of the material was complete, the crystal was processed for electrical characterization. Individual devices were constructed by etching away much of the p-type and intrinsic layer, leaving behind circular mesas. Each mesa was then given a top and bottom contact, so that it could be connected to test equipment electrically. After the crystal was processed into a solar cell in this way, each device was connected to a test source electrically, and the current-voltage (I-V) curves were taken. This information was used to find the current and power densities of each device. The second step in this work was fabricating and characterizing a graded layer device that was similar to the reference cell. To this end, the graded layer device was chosen to have a starting composition of 25% indium and 75% gallium, with an ending composition of 15% indium and 85% gallium in place of the intrinsic layer. This new crystal was grown under identical conditions as the baseline cell, except for the graded layer, which required a slightly different approach. The graded layer crystal was then characterized and processed consistent with the reference in an attempt to get as accurate of a comparison between the two as possible. The results of this research could significantly affect the field of III-nitride solar cells

POINT PROCESS ALGORITHM FOR THE ESTIMATION OF BI-DIRECTIONAL CARDIORESPIRATORY INTERACTIONS IN PRETERM INFANTS

Cardiorespiratory interactions tend to be frail in the early stages of life, necessitating the further analysis of their existence since this could turn out to be a significant factor in assessing the neurodevelopment of neonates. Strength of cardio-respiratory interactions are presumed to be weak and rapidly fluctuating in neonates. Even with the extensive significant research that have been dedicated to early human development there still isn’t a standard or specific technique to analyze these weak cardio-respiratory fluctuating characteristics in neonates. We employ a mathematical technique that’s based on series of tools that have been outstanding in measurement of significant cardio-respiratory control processes in the adult human being. In our case it has been tailored to capture the physiology of the early human cardiovascular system. We used our technique in the assessment of the cardio-respiratory interactions in 10 preterm infants. The cardio-respiratory interactions were evaluated by employing a specially designed point process model of inter beat interval (RR) of electrocardiogram along with multivariate autoregressive model with respiration as covariate. We computed bi-directional coherence as well as the gain using causal methods between RR and respiration. The technique was used to analyze segments of neonate heart rate during bradycardia (slowness of heart) and segments with regular heart rates, which served as control segments. Our bivariate model captured the presence significantly high coherence values in the low frequency bands and as well as the bands corresponding to respiratory frequency which indicates that both the cardiac system and respiration system work together during a bradycardia episode, to resuscitate the neonate from any life-threatening condition. Our assessment did corroborate the models governing our technique we used in this study and the results established the existence of cardio-respiratory interactions in preterm infants and its influence during a bradycardia event

Design of a Bandgap Voltage Reference

This thesis details the design process of a bandgap voltage reference (BGR) integrated circuit in a 180 nm CMOS process. A BGR provides a constant DC voltage across a range of operating temperatures and supply voltages. By its nature, the circuit is intended as a reference, not to provide current, so the output would be connected to a very high impedance, such as the gate of a transistor. At 27°C, this design provides a 955 mV reference voltage given a nominal VDD of 3 V. From 20°C to 175°C, the output voltage has a variance of 7.2 mV (approximately 0.8%) at the nominal supply voltage. Also, when the supply voltage changes from 2 V to 3.6 V, the output voltage changes by 10.9 mV (approximately 1.1%). CTAT (complimentary to absolute temperature) and PTAT (proportional to absolute temperature) devices placed in series provide stability over temperature variation, and a differential amplifier provides feedback, stabilizing the output over changes in VDD

Ironless, Axial Flux, Electric BLDC Motor for Aircraft Electric Propulsion

3D printing has shown much promise as a method of rapidly manufacturing lightweight ironless motors to meet the growing demand that airlines have for more cost-effective products that reduce emissions and flight prices. 3D-printed ironless, axial flux, electric BLDC motors would meet these needs with both their high efficiency and power density. A Halbach array motor was designed and 3D-printed for the analysis of its magnetic properties to gain more insight about it performance. Fusion 360 was used to design the 3D drawings of the motor parts. The rotor, stator, and stator mount were designed to accommodate the sizes of the available materials. Printing was performed at NCREPT with a Raise3D Pro2 3D printer using ABS for the material. ANSYS Maxwell was used to perform simulated analyses on the magnetic properties of the motor, such as the magnetic flux density, as well as the force and torque on a singular magnet. The torque ranged from -5 N*m to 5 N*m and the force from 100 N to approximately 190 N, both with a period of 20°

Transimpedance Amplification of Optocoupler Output for High Temperature Applications

When looking to the future of electronics, one characteristic is becoming more lucrative: high temperature capabilities. With the goals of not only becoming more efficient electronically, spatially, and cost-wise, adapting electronics for a high temperature environment can potentially be a route to all three of these goals. Not only does it take away the need for a cooling method, but it can also increase the longevity of a product which can make it even more cost effective. In an effort to contribute to the push for high temperature electronics, the University of Arkansas is developing a high temperature power module for use in various extreme environments. This includes the design of a two-stage transimpedance amplifier (TIA) to take input from an optocoupler and convert it to a useable gate drive signal for amplification. The tradeoffs in creating a TIA must be considered: gain and bandwidth, where a larger bandwidth results in less gain and also becomes more complex as more stages are added. Adding a second stage may increase the speed and gain of the amplifier, but this must also be evaluated with the increase in complexity in cost. So long as the cost is not so much more benefits the entire system as a whole, producing a clean gate drive signal for use at room temperature, it may be beneficial to employ this second stage. This can be adapted into high temperature circuitry for integration into the power module and with additional research, supply the signal required at temperatures up to 250 C

Measuring the Electrical Properties of 3D Printed Plastics in the W-Band

3D printers are a method of additive manufacturing that consists of layering material to produce a 3D structure. There are many types of 3D printers as well as many types of materials that are capable of being printed with. The most cost-effective and well documented method of 3D printing is called Fused Deposition Modeling (FDM). FDM printers work by feeding a thin strand of plastic filament through a heated extruder nozzle. This plastic is then deposited on a flat, typically heated, surface called a print bed. The part is then built by depositing thin layers of plastic in the shape of the cross sectional area of the part. The print time of 3D printed parts typically takes anywhere from 15 minutes to a couple days, depending on complexity. FDM printers are capable of printing almost any shape that fits within the print volume of the machine without special tooling. Therefore, 3D printers can be used to rapidly prototype complex designs and are capable as a production method in and of itself. This thesis focuses on the finding the real and imaginary components of the complex permittivity of three common 3D printed plastics in the W-Band (75 GHz - 110 GHz): Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS), and Polyethylene Terephthalate Glycol (PETG). The Free Space System is used to measure the S11, S12, S21, and S22 parameters of a flat sample of the plastics from 75 GHz to 110 GHz. The obtained results demonstrate that the relative permittivity of each sample remains relatively stable across the entire bandwidth of the frequencies tested. PLA has the highest relative permittivity out of all the samples at 2.724 and the PETG has the lowest permittivity at 2.675. The permittivity of these 3D printed materials are slightly higher than that of Teflon which has a real relative permittivity of 2.1. Furthermore, the imaginary part of the permittivity that represents the losses in the material are shown to be small (below 0.045 for all samples) between 75 GHz - 110 GHz