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PhD Final Exam – Hamidreza Maghami

Digital friendly Continuous-Time Delta-Sigma Analog-to-Digital Converters

Conventional delta-sigma ADCs utilize operational transconductance amplifiers (OTAs) in their loop filter implementation followed by multi-bit voltage domain quantizers. As the technology scales to the lower nodes, the minimum transistor length and the intrinsic gain of the transistors decrease. Moreover, by process scaling the voltage headroom decreases as well. Therefore, designing the OTAs in advanced CMOS processes is becoming increasingly difficult. Also, due to the decrease of the voltage headroom, multibit quantizers are becoming more difficult to design due to their offset and noise requirements. In this thesis, alternative digital solutions are introduced to replace traditional analog blocks. In the proposed solutions, compressed voltage-domain processing is shifted to the time-domain which benefits from process scaling as the transistors become faster. First, a novel highly linear VCO-based 1-1 multi stage noise shaping (MASH) delta-sigma ADC structure is presented. The proposed architecture does not require any OTA-based analog integrators or integrating capacitors. Second order noise shaping is achieved by using a VCO as an integrator in the feedback loop of the first stage and an open loop VCO quantizer in the second stage. A prototype was fabricated in 65nm CMOS and achieves 79.7 dB SNDR in 2MHz signal bandwidth. Second, a novel time-domain phase quantization noise extraction for a VCO-based quantizer is introduced. This technique is independent of the OSR and the input signal amplitude of the VCO-based quantizer making it attractive for higher bandwidth applications. Using this technique, a novel 0-1-1 MASH ADC is presented. The first stage is implemented using a 4-bit SAR ADC. The second and the third stages use a VCO-based quantizer (VCOQ). Behavioral simulation results confirm the second-order noise shaping with 75dB SNDR for an OSR of 20.

Co Advisor: Kartikeya Mayaram
Co Advisor: Terri Fiez
Committee: Gabor Temes
Committee: Un-Ku Moon
GCR: Sharmodeep Bhattacharyya

Monday, May 20 at 11:00am to 1:00pm

Kelley Engineering Center, 1007
110 SW Park Terrace, Corvallis, OR 97331

Event Type

Lecture or Presentation

Event Topic


Electrical Engineering and Computer Science
Contact Name

Calvin Hughes

Contact Email

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