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PhD Final Oral Examination – Yue Hu


Friday, July 25, 2014 3:00 PM - 5:00 PM

Efficient Use of Time Information in Analog-to-Digital Converters
Time-domain data conversion has recently drawn increased research attention for its highly digital nature in favor of process technology scaling. Also, as the time information carried by binary voltage, time-domain operation is much less sensitive to voltage noise compared to conventional voltage domain operation. However, for analog-to-digital converter (ADC) application, the challenge lies in the methodology of benefiting from time-domain operation while maintaining/improving the overall data conversion accuracy and power efficiency. This dissertation has a focus on investigation of novel data conversion topologies based on classic voltage domain operation that is capable of generating time information, to improve ADC resolution, system stability and speed without power penalty.

In the first approach, a novel continuous-time (CT) delta-sigma modulator (DSM) using a time-interleaved quantizer is proposed and implemented. Along with the doubled sample rate, the proposed architecture utilizes time information to perform correlated coupling between the two quantizer channels. A 120MS/s CT ΔΣ ADC using proposed technique is implemented in 0.18µm CMOS process. The measurement results achieve second order noise coupling from the interleaved quantizer itself without extra phases. More importantly, excess loop delay of two full sample clocks is compensated by time-domain signal coupling; the resulted CT DSM is fully stabilized in 120MHz sampling rate and achieves 11 effective number of bits (ENOB).

In the second approach, a new category of pulse-width-modulation (PWM) scheme is proposed and described: time symmetric PWM (TSPWM). An ADC structure is further proposed utilizing this novel voltage-to-time converter, followed by a first order noise-shaped switched-ring-oscillator (SRO) TDC quantizer. This ADC topology takes advantage of the TDC speed scaling for its digitized operation to boost the overall ADC resolution and signal bandwidth, while the voltage to time front-end is able to remain at a much lower speed than the TDC thanks to the proposed technique. This is the first work that decouples the PWM modulation rate from TDC quantizing speed without distortion penalty.

Built in 0.18µm, the implemented ADC is able to sample at a range from 20MHz to 40MHz, the generated pulse train is quantized by the following SRO TDC at a rate of 400MHz. The prototype chip shows a SFDR improvement over 24dB on the ADC output when TSPWM is used.

Major Advisor: Un-Ku Moon
Committee: Arun Natarajan
Committee: Gabor Temes
Committee: Karti Mayaram
GCR: Maggie Niess


Kelley Engineering Center (campus map)
1005
Nicole Thompson
1 541 737 3617
Nicole.Thompson at oregonstate.edu
Sch Elect Engr/Comp Sci
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