A Paradigm Shift in the Design of Analog and Mixed-Signal Nanoelectronic Circuits and Systems.

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Publicações

Design of Analog-to-Digital Converters with Embedded Mixing for Ultra-Low-Power Radio Receivers

Publication . Pereira, Nuno Ruben Ferreira; Goes, João

In the field of radio receivers, down-conversion methods usually rely on one (or more) explicit mixing stage(s) before the analog-to-digital converter (ADC). These stages not only contribute to the overall power consumption but also have an impact on area and can compromise the receiver’s performance in terms of noise and linearity. On the other hand, most ADCs require some sort of reference signal in order to properly digitize an analog input signal. The implementation of this reference signal usually relies on bandgap circuits and reference buffers to generate a constant, stable, dc signal. Disregarding this conventional approach, the work developed in this thesis aims to explore the viability behind the usage of a variable reference signal. Moreover, it demonstrates that not only can an input signal be properly digitized, but also shifted up and down in frequency, effectively embedding the mixing operation in an ADC. As a result, ADCs in receiver chains can perform double-duty as both a quantizer and a mixing stage. The lesser known charge-sharing (CS) topology, within the successive approximation register (SAR) ADCs, is used for a practical implementation, due to its feature of “pre-charging” the reference signal prior to the conversion. Simulation results from an 8-bit CS-SAR ADC designed in a 0.13 μm CMOS technology validate the proposed technique.

2019Tese de doutoramento

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A Paradigm Shift in the Design of Analog Circuits Targeting Nanoscale CMOS and Large-scale TFT Technologies

Publication . Correia, Ana Paula Pinto; Goes, João; Barquinha, Pedro

Despite the strong developments in complementary metal-oxide-semiconductor (CMOS) or non-CMOS technologies such as, in oxide thin-film transistors (TFTs), their nonidealities and constraints impact on the circuits performance. This aspect is even more relevant in complex circuits, such as in analog-to-digital converters (ADCs), where the design is thorough. Then, using techniques capable to attenuate the impact of these limitations such as, negative feedback, or recurring to almost passive or digital (synthesizable and scalable) circuitry, it is possible to design outstanding ADCs in different technologies. Therefore, two ADCs were designed in this work, using two distinct technologies. A Digital-delta-modulator (DM) with noise-shaping (NS) was designed using a deep-nanoscale CMOS technology. Employing almost passive and digital-circuitry, this topology comprises a split-capacitor 10-bit digital-to-analog converter (DAC) with embedded sample-and-hold (S/H), a pseudo-differential inverter-based switched-capacitor (SC) integrator with a fully-passive SC common mode feedback (CMFB) circuit, a single-bit comparator, an accumulator and a clock and phase generators. Simulations revealed a signal-to-noise-and-distortion ratio (SNDR) close to 74 dB, a 12-bit effective number of bits (ENOB), with a Walden figure-of-merit (FoM), FoMWalden, of 12.5 fJ/conv.-step. Using oxide TFTs, a 2nd-order delta-sigma modulator (DSM) was designed. Given the technology limitations, an almost passive structure was considered, with a design that relied essentially on the comparator project. During schematic simulations, a SNDR close to 69 dB, corresponding to an ENOB of ≈ 11:3-bit, was achieved (FoMWalden of 40 nJ/conv.-step). After the fabrication, individual transistors were characterised but they provided completely different electrical properties from the devices used to create the simulation model. The circuits, where comparators are included, were also measured but fabrication problems were detected. Strategies to mitigate these effects are currently being implemented.

2022-12-19Tese de doutoramento

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Entidade financiadora

Fundação para a Ciência e a Tecnologia

Programa de financiamento

3599-PPCDT

Número da atribuição

EXCL/EEI-ELC/0261/2012