University of Colorado Students Learn Microwave Office Software With Ease
Most graduate-level engineering students with a consummate interest in “fields and waves” have designed and possibly even fabricated numerous hybrid microwave circuits. Few engineering schools, however, provide graduate students with the opportunity to not only design microwave monolithic integrated circuits (MMICs), but to transfer their designs to a foundry, obtain working devices, and evaluate their actual performance against simulated results. Thanks to an innovative program begun in 2008 between the University of Colorado, NI (formerly AWR Corporation), and Qorvo (formerly TriQuint Semiconductor), this real-world experience has become a reality for students in the computer-aided, active microwave circuit design course taught by Prof. Zoya Popovic. Dr. Popovic, the Hudson Moore Jr. chaired professor in the Department of Electrical, Computer and Energy Engineering, is an IEEE Fellow and respected authority on applied electromagnetic (EM) and microwave engineering. Prof. Popovic has received numerous prestigious awards, has written hundreds of technical papers, and is the co-author of the junior-level textbook “Introductory Electromagnetics.”
The Design Challenge
Students in Dr. Popovic’s class were tasked with choosing a MMIC that supported their respective thesis research projects. These projects are funded by an impressive list of government agencies and private industries ranging from the National Science Foundation (NSF), the National Institute of Standards and Technology (NIST), and the Defense Advanced Research Projects Agency (DARPA), to the Office of Naval Research (ONR), Nuvotronics, BAE Systems, Sandia Laboratories, National Semiconductor, and the Coleman Institute.
All of the MMICs were designed using Microwave Office circuit design software, and their manufacturability was verified using ICED, a no-cost plug-in feature in Microwave Office. The students then used an NI AWR Design Environment process design kit (PDK) for Qorvo’s TQPED 0.5-μm E/D pseudomorphic high electron mobility transistor (pHEMT) process, which helped them quickly and easily transfer their designs to fabrication. Qorvo provided the University of Colorado with a quarter of their gallium arsenide (GaAs) wafer, and the devices were fabricated in roughly a one month turn-around timeframe. The students then characterized their fabricated devices using a probe station, and in some cases packaged them for full testing.
An additional challenge, similar to the tight product development schedules in the business world, was that the entire project had to be accomplished within the time constraints of one semester. For many of the students, the first step was to learn how to use Microwave Office, which turned out to be a pleasant surprise. “Frankly, I found the ease with which the students learned the software rather remarkable,” said Dr. Popovic. “They attended a single training class and got great help from the NI AWR software applications engineer along the way, but otherwise they were on their own. And they did it.”
Dr. Popovic, thinly disguising her pride in their efforts, describes some of the circuits designed by her students as truly unconventional, and frequently uses the word “novel” when referring to them. She further states that the engineers at Qorvo were impressed with the device complexity, which in some cases they thought would push the limits of the process, perhaps revealing some of its undiscovered capabilities. An example of a project is a four-stage distributed amplifier that included a set of RTL standard and had a flat frequency response to 20GHz (shown on right). Other devices included a lumped-element broadband Wilkinson divider published in the IEEE MTT Transactions, a low-noise amplifier, a switched delay line, a switched-capacitor tuning circuit, a high-efficiency harmonically-tuned switchedmode power amplifier with lumped-element harmonic terminations, a broadband lumped-element power amplifier, a Class-D 1.5-GHz, balanced amplifier, and a nonlinear transmission line that uses pHEMT devices as varactor diodes.
Why NI AWR Design Environment
A course as comprehensive as Dr. Popovic’s obviously requires a considerably greater amount of effort for both the instructor and the students than most engineering courses, but the professor strongly feels the end result was worth the extra work. “I’m very proud of the work they’ve done,” she says. “The ability to actually fabricate and test the MMIC devices they create is incredibly helpful to my students. Some of these circuits are truly unusual and to get results that agree so well with the simulation is both a credit to the students, Microwave Office software, and the quality of the Qorvo pHEMT process.”
With course requirements complete and final measurements being slowly conducted using the university’s test equipment, Dr. Popovic looks to the next course, and a new increased crop of 23 graduate students. “We’re definitely going to continue this course,” she says. “If there ever was a ‘win-win’ situation, this is it.”
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