NCSU Senior Design Program Uses NI AWR Software to Achieve Success in LNA and X-band PA Design Projects
The North Carolina State University (NCSU) Department of Electrical and Computer Engineering (ECE) has as its mission the accumulation, generation, and dissemination of knowledge in electrical and computer engineering. NCSU’s ECE Department is nationally and internationally recognized as one of the premier engineering programs in the world and serves as a statewide focal point for innovation, entrepreneurship, and economic development. The NCSU ECE Senior Design Program (SDP) cooperates with local industries and campus research units to provide real-world design projects for students to address.
The Design Challenge
Dr. Alan Victor, principal engineer at Nitronex and NCSU graduate, mentors students in the SDP. In particular, he hosted two projects in the 2013 spring semester: one designing a low noise amplifier (LNA) and a second designing a microwave power amplifier (PA). Thanks to sponsorship by Nitronex, a leading provider of gallium nitride (GaN)-on-silicon RF power devices, Dr. Victor’s project was offered to undergraduate SDP students, making it the only RF/microwave research and design study available.
The program required the students to learn RF circuit design, microwave techniques, electromagnetic (EM) properties, and a software design tool all within a semester—not an easy task. There were a myriad of RF topics from which to choose, including RF switches, LNAs, and PAs. Dr. Victor mentored two groups of three students each and the two design topics chosen were a low noise GPS amplifier and an X-band power amplifier targeting the 8-10 GHz frequency span.
The students used AWR’s Microwave Office® circuit design software and AXIEM® EM simulation software for both projects. Active device models were provided by Nitronex. Because of the ease-of-use and integration of the software, the students were able to quickly learn to use Microwave Office layout tools, import the artwork of the printed circuit (PC) cards from the Nitronex CAD PC card library, and reuse available designs.
Low Noise Amplifier (LNA) Project
In the case of the LNA project, the task was to investigate and redesign a new matching interface, enabling the card to be applied to the GPS frequency band. The seamless interface between the Microwave Office layout and EM simulation tools significantly reduced the design effort. More importantly, this interface increased the students’ understanding of the effect of parasitic components on RF performance. They developed a deeper respect for PC card employment and the fact that the traces were not just copper lines on an epoxy laminate. Figure 1 shows that the GPS LNA provided excellent agreement with simulation and an unconditionally stable amplifier at 1.57 GHz with NF under 2.5 dB and gain over 15 dB.
Figure 1: The AWR Microwave Office tiled view of schematic, layout, and results for the LNA design project.
X-band Power Amplifier (PA) Project
For the X-band amplifier, the students fabricated the PC card by utilizing the copper traces as impedance matching components. The parasitics and self-resonant frequency associated with the design and use of real LC component models resulted in the students gaining a new appreciation that every R, L, and C may also come along with its own LC, RC and RL coupling respectively. Again, the ability to easily integrate real elements and their footpads into a circuit simulation environment was crucial to the students’ understanding of microwave design and their ultimate success in the project. As shown in Figure 2, the X-band PA operated at 8.2-8.5 GHz with output power of nearly 0.5 W and operational over a 10 percent bandwidth.
Figure 2: The AWR Microwave Office tiled view of schematic, layout, and results for the X-band PA design project.
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