Low-power and small size analog to digital converters (ADCs) are the strategic building blocks in state of the art mobile wireless communication systems. Various techniques have been developed to reduce both power consumption and die area of the ADC. Among these, the opamp-sharing technique shows the most promise. In opamp-sharing, power and die area are saved by sharing one opamp between two successive pipeline stages. However, this technique suffers from the well-known memory effect drawback due to the absence of the reset phase that discharges the opamp's input parasitics. In this dissertation, this drawback is solved by introducing a discharge phase before the opamp is used for the pipeline stages without compromising speed and resolution of the ADC. Further power and area reduction is achieved by using a capacitor-sharing technique. This technique reduces the effective load capacitance of the opamp by reusing the charge on the feedback capacitor for the MDAC operation of the following stage, resulting in faster settling without increasing opamp power. The proposed low input-capacitance variable-gm opamp also helps to reduce the memory effect and improves the settling behavior of the stage output by increasing the bandwidth of the opamp while input parasitics of the opamp are kept small. The prototype designs of a 10-bit 50MSample/s pipelined ADC and a 14-bit 100MSample/s pipelined ADC implemented in 0.18¹m CMOS technology demonstrate the effectiveness of the proposed techniques. The first ADC achieves 56.2dB SNDR and 72.7dB SFDR for a Nyquist input at full sampling rate while consuming 12 mW from a 1.8-V supply. The FOM, defined as, [power/2[superscript ENOB].Fs], is 0.46 pJ/step with Fin = 24.5MHz at 50MS/s. The second ADC achieves 72.4dB SNR and 88.5dB SFDR at 100MS/s with a 46MHz input and consumes 230mW from a 3V supply. The FOM of the second ADC is 0.69 pJ/step with Fin = 46MHz at 100MS/s.

Hand-held devices are among the most successful consumer electronics in modern society. Behind these successful devices, lies a key analog design technique that involves high-performance analog-to-digital conversion combined with very low power consumption. This dissertation presents two different approaches to achieving high power efficiency from a two-step pipelined architecture, which is generally known as one of the most power-consuming analog-to-digital converters. In the first approach, an analog feedback loop of a residue amplifier in a two-step pipelined analog-to-digital converter is reconfigured digitally using a single comparator and an R-2R digital-to-analog converter. This comparator-based structure can reduce power consumption of a conventional two-step pipelined analog-to-digital converter which consists of an opamp-based residue amplifier followed by a second- stage analog-to-digital converter. In addition, this dissertation includes circuit design techniques that provide a digital offset correction for the comparator-based two-step structure, binary-weighted switching for an R-2R digital-to-analog converter, and reference trimming for a flash analog-to-digital converter. A 10-b prototype analog-to-digital converter achieves an FOM of 121 fJ/conversion-step under 0.7-V supply. The second approach provides a way to achieve low power consumption for a high-resolution two-step pipelined analog-to-digital converter. An opamp is designed to consume optimized static power using a quarter-scaled residue gain together with minimized loading capacitance from the proposed second stage. A 14-b prototype analog-to-digital converter achieves an FOM of 31.3 fJ/conversion-step with an ENOB of 11.4 b, which is the lowest FOM in high-resolution analog-to-digital converters having greater than an ENOB of 10 b. Finally, the potential for further power reduction in a two-step pipelined analog-to-digital converter is discussed as a topic for future research. / Graduation date: 2012

Advances in electronic systems have lead to the demand for high resolution, high bandwidth Analog-to-Digital Converters (ADCs). Oversampled ADCs are well- known for high accuracy applications since they benefit from noise shaping and they usually do not need highly accurate components. However, as a consequence of oversampling, they have limited signal bandwidth. The signal bandwidth (BW) of oversampled ADCs can be increased either by increasing the sampling rate or reducing the oversampling ratio (OSR). Reducing OSR is a more promising method for increasing the BW, since the sampling speed is usually limited by the technology. The advantageous properties (e.g. low in-band quantization, relaxed accuracy requirements of components) of oversampled ADCs are usually diminished at lower OSRs and preserving these properties requires complicated and power hungry architectures. In this thesis, different combinations of delta-sigma and pipelined ADCs are explored and new techniques for designing oversampled ADCs are proposed. A Hybrid Delta-Sigma/Pipelined (HDSP) ADC is presented. This ADC uses a pipelined ADC as the quantizer of a single-loop delta-sigma modulator and benefits from the aggressive quantization of the pipelined quantizer at low OSRs. A Noise-Shaped Pipelined ADC is proposed which exploits a delta-sigma modulator as the sub-ADC of a pipeline stage to reduce the sensitivity to the analog imperfection. Three prototype ADCs were fabricated in 0.18μm CMOS technology to verify the effectiveness of the proposed techniques. The performance of these architectures is among the best reported for high bandwidth oversampled ADCs. / Graduation date: 2011

Real world is analog but the processing of signals can best be done in digital domain. So the need for Analog to Digital Converters(ADCs) is ever rising as more and more applications set in. With the advent of mobile technology, power in electronic equipment is being driven down to get more battery life. Because of their ubiquitous nature, ADCs are prime blocks in the signal chain in which power is intended to be reduced. In this thesis, four techniques to reduce power in high speed pipelined ADCs have been proposed. The first is a capacitor and opamp sharing technique that reduces the load on the first stage opamp by three fold. The second is a capacitor reset technique that aids removing the sample and hold block to reduce power. The third is a modified MDAC which can take rail-to-rail input swing to get an extra bit thus getting rid of a power hungry opamp. The fourth is a hybrid architecture which makes use of an asynchronous SAR ADC as the backend of a pipelined ADC to save power. Measurement and simulation results that prove the efficiency of the proposed techniques are presented. / Graduation date: 2009

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

A comprehensive and scalable solution for high-performance switched capacitor amplification is presented. Central to this discussion is the concept of ring amplification. A ring amplifier is a small modular amplifier derived from a ring oscillator that naturally embodies all the essential elements of scalability. It can amplify with accurate rail-to-rail output swing, drive large capacitive loads with extreme efficiency using slew-based charging, naturally scale in performance according to process trends, and is simple enough to be quickly constructed from only a handful of inverters, capacitors, and switches. In addition, the gain-enhancement technique of Split-CLS is introduced, and used to extend the efficacy of ring amplifiers in specific and other amplifiers in general. Four different pipelined ADC designs are presented which explore the practical implementation options and design considerations relevant to ring amplification and Split-CLS, and are used to establish ring amplification as a new paradigm for scalable amplification. / Graduation date: 2012 / Access restricted to the OSU Community, at author's request, from July 19, 2012 - July 19, 2013