Date of Final Oral Examination (Defense)
Type of Culminating Activity
Doctor of Philosophy in Electrical and Computer Engineering
Electrical and Computer Engineering
Vishal Saxena, Ph.D.
In recent years, Continuous-time Delta-Sigma(CT-ΔΣ) analog-to-digital converters (ADCs) have been extensively investigated for their use in wireless receivers to achieve conversion bandwidths greater than 15 MHz and higher resolution of 10 to 14 bits. This dissertation investigates the current state-of-the-art high-speed single-bit and multi-bit Continuous-time Delta-Sigma modulator (CT-ΔΣM) designs and their limitations due to circuit non-idealities in achieving the performance required for next-generation wireless standards. Also, we presented complete architectural and circuit details of a high-speed single-bit and multi-bit CT-ΔΣM operating at a sampling rate of 1.25 GSps and 640 MSps respectively (the highest reported sampling rate in a 0.13 μm CMOS technology node) with measurement results. Further, we propose novel hybrid ΔΣ architecture with two-step quantizer to alleviate the bandwidth and resolution bottlenecks associated with the contemporary CT-ΔΣM topologies. To facilitate the design with the proposed architecture, a robust systematic design method is introduced to determine the loop-filter coefficients by taking into account the non-ideal integrator response, such as the finite opamp gain and the presence of multiple parasitic poles and zeros. Further, comprehensive system-level simulation is presented to analyze the effect of two-step quantizer non-idealities such as the offset and gain error in the sub-ADCs, and the current mismatch between the MSB and LSB elements in the feedback DAC. The proposed novel architecture is demonstrated by designing a high-speed wideband 4th order CT-ΔΣ modulator prototype, employing a two-step quantizer with 5-bits resolution. The proposed modulator takes advantage of the combination of a high-resolution two-step quantization technique and an excess-loop delay (ELD) compensation of more than one clock cycle to achieve lower-power consumption (28 mW), higher dynamic range (>69 dB) with a wide conversion bandwidth (20 MHz), even at a lower sampling rate of 400 MHz. The proposed modulator achieves a Figure of Merit (FoM) of 340 fJ/level.
Balagopal, Sakkarapani, "High-Speed Delta-Sigma Data Converters for Next-Generation Wireless Communication" (2014). Boise State University Theses and Dissertations. 822.