Yousof Mortazavi (The University of Texas at Austin) "Analog-to-Digital Converter Circuit and System Design to Improve with CMOS Scaling" (2015)

Yousof Mortazavi (The University of Texas at Austin) "Analog-to-Digital Converter Circuit and System Design to Improve with CMOS Scaling", Advisor: Brian L. Evans

Nanometer-scale CMOS processes create a hostile environment for voltage-domain analog processing due to reduced supply voltage and smaller capacitance, which increase speed and power efficiency for digital circuits. This dissertation explores alternative analog processing in the time-domain to design oversampled analog-to-digital converters (ADC) for nanoscale CMOS processes. The ADC first converts the analog input voltage to a pulse shape whose length is proportional to the voltage, and performs delta-sigma modulation by adding and subtracting pulse shapes. Unlike traditional voltage-domain processing, the time-domain approach improves circuit performance with CMOS process scaling. Two time-domain oversampled delta-sigma ADCs were designed and fabricated in TSMC 180 nm CMOS and IBM 45 nm Silicon-On-Insulator processes. Both chips achieve bandwidths of 5-20 MHz and 50 dB SNR with very low ADC core area of 0.0275 mm2 and 0.0192 mm2, respectively. Based on the measured responses of the two ADC chips, I determine the source of the harmonic distortion and demonstrate a digital calibration algorithm that sufficiently mitigates the distortion.

For detailed information, please see the thesis page.