Electrical Engineering Department
BS in Electrical Engineering
Dr. Dennis Derickson
How to Read this Document:
This document combines two senior project reports. The first senior project documents designing a class AB RF amplifier. The second, discusses the design and implementation of a software Costas loop for audio frequencies. The first report begins on the next page, while the Costas loop report starts on page 24. The two reports are orthogonal from one another. It is not a prerequisite to read the RF amplifier report before reading the Costas loop report. This document is merely two reports combined into one document. The second report, about the Costas loop, was written as a replacement to the first. However, it was decided, to include the first senior project, in order to make available information and insights that were encountered during the RF amplifier design and construction process, that someone else might find helpful.
RF Amplifier Abstract:
In this senior project, a 4W 2.4 GHz power amplifier (PA) is designed as an entry for IEEE s high frequency amplifier design contest. The design uses Cree s CGH40010F Gallium Nitride (GaN) transistor, because it is capable of outputting 10W up to 6 GHz. Cree also provides simulation models for the Agilent Design System (ADS) the RF design software used to design this PA. In order to maximize both efficiency and linearity, the PA is class AB biased. Matching networks are implemented on FR4 substrate. Tuning the gate voltage on the final design minimizes intermodulation distortion (IMD) and improves linearity. The final design exhibits 40% power added efficiency (PAE) and greater than 20 dBc IMD within a 5 MHz bandwidth.
Software Costas Loop Abstract:
A Costas loop is implemented in software with Python. A small-signal linear model is derived in order to determine loop stability. An interactive program was developed to tune loop parameters in order to obtain critically damped step response. The effect of lowpass filter phase delay on stability is discussed.