Open-Source Synthesizable Analog Blocks for High-Speed Link Designs: 20-GS/s 5b ENOB Analog-to-Digital Converter and 5-GHz Phase Interpolator

Using digital standard cells and digital place-and-route (PnR) tools, we created a 20 GS/s, 8-bit analog-to-digital converter (ADC) for use in high-speed serial link applications with an ENOB of 5.6, a DNL of 0.96 LSB, and an INL of 2.39 LSB, which dissipated 175 mW in 0.102 mm2 in a 16nm technology. The design is entirely described by HDL so that it can be ported to other processes with minimal effort and shared as open source.Comment: 2020 IEEE Symposium on VLSI Circuit

Techniques for Wideband All Digital Polar Transmission

abstract: Modern Communication systems are progressively moving towards all-digital transmitters (ADTs) due to their high efficiency and potentially large frequency range. While significant work has been done on individual blocks within the ADT, there are few to no full systems designs at this point in time. The goal of this work is to provide a set of multiple novel block architectures which will allow for greater cohesion between the various ADT blocks. Furthermore, the design of these architectures are expected to focus on the practicalities of system design, such as regulatory compliance, which here to date has largely been neglected by the academic community. Amongst these techniques are a novel upconverted phase modulation, polyphase harmonic cancellation, and process voltage and temperature (PVT) invariant Delta Sigma phase interpolation. It will be shown in this work that the implementation of the aforementioned architectures allows ADTs to be designed with state of the art size, power, and accuracy levels, all while maintaining PVT insensitivity. Due to the significant performance enhancement over previously published works, this work presents the first feasible ADT architecture suitable for widespread commercial deployment.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Coupling techniques between dielectric waveguides and planar photonic crystals

El objetivo de esta tesis es la investigación de estructuras y técnicas de acoplo para minimizar las pérdidas de acoplo entre guías dieléctricas y cristales fotónicos planares. En primer lugar se ha estudiado el modelado del acoplo entre guías dieléctricas y guías en cristal fotónico así como la influencia de los principales parámetros del cristal en la eficiencia de acoplo. Se han obtenido expresiones cerradas para las matrices de reflexión y transmisión que caracterizan totalmente el scattering que ocurre en el interfaz formado entre una guía dieléctrica y una guía en cristal fotónico. A continuación y con el fin de mejorar la eficiencia de acoplo desde guías dieléctrica de anchura arbitraria, se ha propuesto como contribución original una técnica de acoplo basada en la introducción de defectos puntuales en el interior de una estructura de acoplo tipo cuña realizada en el cristal fotónico. Diferentes soluciones, incluida los algoritmos genéticos, han sido propuestas con el objetivo de conseguir el diseño óptimo de la configuración de defectos. Una vez conseguido un acoplo eficiente desde guías dieléctricas a guías en cristal fotónico, se ha investigado el acoplo en guías de cavidades acopladas. Como contribución original se ha propuesto una técnica de acoplo basada en la variación gradual del radio de los defectos situados entre cavidades adyacentes. Además, se ha realizado un riguroso análisis en el dominio del tiempo y la frecuencia de la propagación de pulsos en guías acopladas de longitud finita. Dicho estudio ha tenido como objetivo la caracterización de la influencia de la eficiencia del acoplo en los parámetros del pulso. Finalmente, se han presentado los procesos de fabricación y resultados experimentales de las estructuras de acoplo propuestas.Sanchis Kilders, P. (2005). Coupling techniques between dielectric waveguides and planar photonic crystals [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1854Palanci

Digital Centric Multi-Gigabit SerDes Design and Verification

Advances in semiconductor manufacturing still lead to ever decreasing feature sizes and constantly allow higher degrees of integration in application specific integrated circuits (ASICs). Therefore the bandwidth requirements on the external interfaces of such systems on chips (SoC) are steadily growing. Yet, as the number of pins on these ASICs is not increasing in the same pace - known as pin limitation - the bandwidth per pin has to be increased. SerDes (Serializer/Deserializer) technology, which allows to transfer data serially at very high data rates of 25Gbps and more is a key technology to overcome pin limitation and exploit the computing power that can be achieved in todays SoCs. As such SerDes blocks together with the digital logic interfacing them form complex mixed signal systems, verification of performance and functional correctness is very challenging. In this thesis a novel mixed-signal design methodology is proposed, which tightly couples model and implementation in order to ensure consistency throughout the design cycles and hereby accelerate the overall implementation flow. A tool flow that has been developed is presented, which integrates well into state of the art electronic design automation (EDA) environments and enables the usage of this methodology in practice. Further, the design space of todays high-speed serial links is analyzed and an architecture is proposed, which pushes complexity into the digital domain in order to achieve robustness, portability between manufacturing processes and scaling with advanced node technologies. The all digital phase locked loop (PLL) and clock data recovery (CDR), which have been developed are described in detail. The developed design flow was used for the implementation of the SerDes architecture in a 28nm silicon process and proved to be indispensable for future projects

Low Power Continuous-time Bandpass Delta-Sigma Modulators.

Low power techniques for continuous-time bandpass delta-sigma modulators (CTBPDSMs) are introduced. First, a 800MS/s low power 4th-order CTBPDSM with 24MHz bandwidth at 200MHz IF is presented. A novel power-efficient resonator with a single amplifier is used in the loopfilter. A single op-amp resonator makes use of positive feedback to increase the quality factor. Also, a new 4th-order architecture is introduced for system simplicity and low power. Low power consumption and a simple modulator structure are achieved by reducing the number of feedback DACs. This modulator achieves 58dB SNDR, and the total power consumption is 12mW. Second, a 6th-order CTBPDSM with duty cycle controlled DACs is presented. This prototype introduces new architecture for low power consumption and other important features. Duty cycle control enables the use of a single DAC per resonator without degrading the signal transfer function (STF), and helps to lower power consumption, low area, and thermal noise. This ADC provides input signal filtering, and increases the dynamic range by reducing the peaking in the STF. Furthermore, the center frequency is tunable so that the CTBPDSM is more useful in the receiver. The prototype second modulator achieves 69dB SNDR, and consumes 35mW, demonstrating the best FoM of 320fJ/conv.-step for CTBPDSMs using active resonators. The techniques introduced in this research help CTBPDSMs have good power efficiency compared with the other kinds of ADCs, and make the implement of a software-defined radio architecture easier which is appropriate for the future multiple standard radio receivers without a power penalty.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/98001/1/hichae_1.pd

Linear and nonlinear optical pulse characterisation

Developmental work on the generation and measurement of ultrashort pulses has been performed. A colliding pulse, passively mode-locked (CPM) ring dye laser has been investigated by spectral analysis and the nonlinear technique of second harmonic generation autocorrelation. Two systems for the intracavity compensation of group velocity dispersion (GVD) have been experimentally compared in the CPM laser. Initially one scheme, utilising Gires-Toumois interferometers, has achieved pulse durations of 64 fs. A second technique employing a four-prism sequence within the cavity gave typical pulse durations of -40 fs and focussing adjustments within the jets achieved durations as short as 19 fs for the first time. A realtime interferometric autocorrelator was constructed and detailed theoretical work has been performed to model the resultant fringe resolved autocorrelations as a function of pulseshape and frequency chirp. Spectral and autocorrelation analysis of the CPM laser led to the inference that the laser pulse intensity profiles were distinctly asymmetric. The main sources of frequency chirp within the laser cavity were assessed in order to find possible explanations for this type of laser behaviour. The linear pulse measurement technique employing synchroscan streak cameras was also critically assessed in terms of the available temporal resolutions as a function of phase noise in the RF deflection signal. Two streak tube designs, the Photochron II and the Photochron IV, have been experimentally compared employing the CPM laser as a test pulse source. Optimisation of the synchronisation circuitry has allowed the notable achievement of a temporal resolution of 0.93ps for the Photochron IV streak camera. A computer-interfaced readout system incorporating a charge coupled device (CCD) sensor has been developed which allows the recording of synchroscan streak events with a digitisation accuracy up to 12 bits. Preliminary experimentation was also performed to investigate the feasibility of incorporating a electron sensitive CCD structure within the envelope of the streak camera. It is intended that such a streak camera will be incorporated in a spaceborne laser ranging system and a theoretical assessment of the expected instrument performance has been performed. The above investigations have direct relevance to other types of ultrashort pulse sources and their application in optical communications, time-resolved spectroscopy and ultrafast electrooptic sampling

Time-resolved spectroscopy of two-dimensional systems: from the conventional method to a novel cavity-enhanced solution

The work presented in this dissertation is dedicated to the characterization of the excited state dynamics of thin films through time-resolved spectroscopy, with emphasis on developing a methodology that is able to resolve weak transient absorption signals from optically thin films. With this aim, the conventional transient absorption spectroscopy method is first utilized to characterize semiconducting monolayers and organic nanosheet semiconductors. Although these are physically thin, they present relatively strong transient absorption signals of a few mOD (units of optical density), which allows to characterize their excited state dynamics with the conventional machinery, not needing further signal enhancements or complex noise-minimizing techniques. Nonetheless, the former does not represent the reality of detecting the transient photoexcited dynamics of few-layered systems. For this reason, the last chapter of this thesis introduces a new approach for the sensitive detection of two-dimensional samples with marginal molecular extinction coefficients: A novel methodology that multiplies the interaction length of the light with the sample, designated cavity ring-down transient absorption spectroscopy (CRD-TAS). Being at the present time in the midst of its development, the prospect efficiency and working capabilities of the novel CRD-TAS technique are hereby evaluated, and the strategies for further improvements are discussed

Ultrafast electron-optical visible / X-ray-sensitivity streak and framing cameras

In this thesis the development of ultrafast electron-optical streak and framing cameras having radiation sensitivities ranging from the visible to soft X-ray are discussed. A framing camera incorporating a vacuum demountable image tube with ultraviolet / soft X-ray sensitivity has been demonstrated to be capable of providing multiple, temporally separated, two-dimensional images with picosecond image exposure times under various operating conditions. Experimental evidence has been presented to show that this camera system can provide up to four high quality temporally separated images with an exposure time of 230 ps (FWHM) and inter-frame times of ~1ns under UV illumination. In the two-frame operation with soft X-ray illumination (generated using a laser produced plasma) image exposure times of as short as 100 ps (FWHM) and inter-frame times of 400 ps have been achieved. The dynamic spatial resolution of the camera has been shown to be ~8 lp/mm and ~5 lp/mm for the UV and soft X-ray sensitive devices respectively. A visible-sensitivity electron-optical single-shot streak camera possessing a novel travelling-wave deflection structure has been experimentally evaluated using a mode-locked cw ring dye laser. The limiting temporal resolution for this has been measured to be 300 fs and the merits of the travelling-wave deflection structure have been discussed. The implementation of this type of deflector geometry has also been demonstrated in conjunction with the vacuum demountable framing camera system. Computer aided design techniques have been utilised to further optimise the electron-optical framing tube configuration, and modifications have been proposed to enable shorter frame periods to be obtained while maintaining the dynamic spatial resolution. Results from preliminary evaluations of this design using a vacuum demountable UV-sensitive system are included. A novel streak camera design has also been proposed in which very high electrostatic photocathode extraction fields (up to 12 kV/mm) may be employed without danger of structural damage arising from electrostatic breakdown. This has been achieved by the removal of the usual mesh electrode placed in close proximity to the photocathode. Preliminary evaluations of a vacuum demountable UV-sensitive version of this camera geometry have been achieved which demonstrate a static spatial resolution of 80 lp/mm (when referred to the photocathode)

Optical and electrical pumping of colour-centre media

Within this thesis the exploitation of the large homogeneously broadened bandwidth of the LiF:F+2 colour-centre laser by production of frequency tunable ultrashort optical pulses over the 0.8-1.0mum spectral region has been presented. A synchronously pumped LiF:F+2 colour-centre laser produced pulses of 700fs duration with average powers of 30mW when a colliding-pulse-modelocked travelling-wave cavity was implemented. Passive modelocking of the LiF:F+2 colour-centre laser was achieved over two spectral operating regions centred around 860nm and 930nm when the saturable absorber dyes IR140 and DaQTeC were employed. Pulse durations as short as 180fs and 130fs were obtained at 860nm and 930nm respectively using colliding-pulse-modelocked group-velocity-dispersion compensated resonators. The laser was pumped at a 10% duty cycle throughout. The use of coupled-cavity- modelocking techniques combined with passive modelocking was found to extend both the tuning range of the laser and useful operating lifetime of the saturable dye. A home built NaCl:OH- colour-centre laser which encorporates the stabilised F+2 colour- centre is presented. Output powers of up to 450mW were obtained for input pump powers of 4W and the laser tuned from 1.4-1.8?m. Electroluminescence studies of NaCl, CsI, CsI:Na, CsI:Tl, and KI crystals are also presented in a study to assess the feasibility of obtaining laser action from such materials by electrical excitation. KI is shown to be the favoured laser candidate by this excitation method and evidence of temporal narrowing and signal enhancement of the electroluminescence output is presented

Optimisation of a colliding-pulse modelocked dye laser

The work presented in this thesis describes the operation, characterisation and optimisation of a colliding-pulse modelocked (CPM) dye laser. A method of pulse analysis has been developed which is capable of determining the shape and chirp of the output pulses to a first approximation. It involves an iterative pulse-fitting to intensity autocorrelation, interferometric autocorrelation and spectral measurements. The use of a four-prism sequence for intracavity dispersion compensation in a CPM dye laser resulted in pulse durations of 40-50fs. However, operating the laser close to the instability regime so as to obtain strong focusing in the absorber dye jet enabled pulse durations as short as 19fs to be obtained. A detailed empirical study of the dispersion- compensated laser, together with a theoretical and experimental chirp analysis, indicated the presence of strong phase shaping arising from a net positive self-phase modulation, which was attributed to the optical Kerr effect occurring in the absorber dye solvent. Various modes of operation were observed, including unidirectional lasing and a higher- order solitonlike regime. The results of pulse-fitting were found to yield strong evidence for pulse asymmetry, the pulse profiles corresponding closely to an asymmetric sech2 pulse function with a longer leading edge. A computer simulation of the CPM dye laser provided a comprehensive understanding of the underlying pulse shaping dynamics of this system, elucidating fully the experimental behaviours observed, as well as providing a clear strategy for further optimisation of the laser. In particular, optimal performance was found to depend on strong amplitude and strong phase shaping, minimal spectral filtering, the control of higher-order dispersion and the provision of extracavity dispersion compensation. An experimental study of Gires-Tournois interferometers (GTI's) for intracavity cubic phase compensation identified the key requirements for cubic phase control in the CPM dye laser, while highlighting the limitations of utilising conventional GTI structures. A subsequent theoretical analysis enabled a more suitable strategy to be devised. It involved optimising the cavity optics and using a prism system with variable prism spacing, alone or in tandem with specially tailored GTI structures. Implementation of these findings resulted in pulse durations of around 30-40fs and the elimination of pulse asymmetry, which was attributed to a residual positive cubic phase. However, the appearance of a distinctive modulation in the wings of the pulse provided strong evidence that the pulse durations from the CPM dye laser had become limited by the next higher-order dispersion term; quartic phase. To demonstrate the direct relevance of this work to the more recently developed solid- state laser systems, an alternative all-solid-state femtosecond laser has been described. Based around a Ti:sapphire gain medium, the design of this laser incorporates the essential optimising principles and techniques developed for the CPM dye laser. The proposed system utilises a low-loss, broadband semiconductor saturable absorber mirror to initiate self-modelocking and a hybrid prism-chirped-mirror scheme for broadband intracavity and extracavity quintic-phase-limited dispersion compensation. When fully optimised, it is predicted that this laser should yield pulse durations as short as 5fs