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PhD Final Oral Examination – Sumit Talwalkar


Tuesday, May 21, 2013 9:30 AM - 11:30 AM

Modeling and Analysis of Spur Structure of Digital-to-time Conversion Based Frequency Synthesizers
Frequency synthesizers are critical components of all communication systems. This thesis considers the issue of undesirable frequency spurs of a relatively recent type of frequency synthesis architecture called digital-to-time conversion (DTC). The DTC-based frequency synthesis architecture has important performance benefits over older frequency synthesizers, such as fast frequency switching, large frequency range and fine frequency resolution. A DTC-based frequency synthesizer requires less power than a traditional direct synthesis based synthesizer with comparable frequency range, resolution and switching time. The DTC architecture also has ease of scalability to newer low-cost digital complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC) fabrication technologies. However, the DTC architecture suffers from an important undesirable characteristic: sub-harmonic spurious tones, or hereafter referred to as spurs. Spurs have undesirable effects in both the transmitter and the receiver. For a transmitter, spurs create an out-of-band emission of power that may breach the spectral emission mask set by regulatory agencies to enable co-existence of multiple transmitters in a crowded frequency spectrum. In a receiver, an inopportune-located spur in the local oscillator (LO) signal can mix an out-of-band strong interfering signal into the baseband on top of a mixed-down weak desirable signal. Unlike harmonic spurs that are known to be at multiples of the carrier frequency, sub-harmonic spurs are especially problematic as they have been difficult to predict as part of the design process. In fact, the spur patterns for most pairs of closely placed desired output frequencies for a DTC-based frequency synthesizer are seemingly unrelated. While one output frequency setting might have an output spectrum with only a few spurs, many other close-by output frequency settings have output spectra with many weaker spurs.

The primary contribution of this thesis is the development of spur creation models and analysis tools that can predict spur spectrum and spur power levels for frequency synthesizers of DTC-based architecture. This is an important contribution for assuring frequency synthesizer achievable performance during the design process. The modeling approach has been successful in accounting of more than 99% of spur spectral locations. Predicted power levels for more than 95% are within in 10 dB of actual fabricated DTC-based frequency synthesizer ICs. The results developed in this thesis allow for an understanding the relationship between spur patterns for different selected output frequencies.

Major Advisor: S. Lawrence Marple
Committee: Raviv Raich
Committee: Huaping Liu
Committee: Adel Faridani
GCR: Yevgeniy Kovchegov 


Kelley Engineering Center (campus map)
1007
Nicole Thompson
1 541 737 3617
Nicole.Thompson at oregonstate.edu
Sch Elect Engr/Comp Sci
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