05 Fakultät Informatik, Elektrotechnik und Informationstechnik
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/6
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Item Open Access Parallel-Analog/Digital-Umsetzer für Gigabaud-Applikationen(2021) Du, Xuan-Quang; Berroth, Manfred (Prof. Dr.-Ing.)Communication systems with digital signal processors (DSPs) rely on data converters as interface blocks between the analog and the digital domain. The channel data rates in these systems can be increased by choosing a higher symbol rate and/or a more complex modulation format. Both approaches motivate the design of data converters with high sample rates and/or high effective bit resolution. As the improvement of the converter linearity in terms of power efficiency is more difficult to realize, especially at high operation frequencies, current research on ultrahigh data-rate mm-wave communication systems (e.g., 100 Gbit/s wireless communication) focuses on increasing the symbol rate while keeping the modulation format simple (e.g., quadrature phase shift keying). These systems require data converters with nominal bit resolutions of around 4-8 bit and sample rates of more than 25 GS/s. In order to satisfy the future needs for high-speed data converters, new circuit topologies need to be investigated. This work presents the design of a 35.84-GS/s 4-bit analog-to-digital converter (ADC) from its idea to its first silicon implementation. The ADC is based on a single-core flash architecture that makes use of a special traveling-wave signal distribution. Contrary to classical approaches with a power-hungry and area-consuming front-end track-and-hold (T/H), no analog preprocessing is needed. The analog input and the clock signal are rather directly distributed over a pair of delay-matched transmission lines from one comparator to the next adjacent one. Due the spatial location of these components, both signals do not arrive at the same time at every comparator, but as they travel synchronously along the transmission lines, each comparator will always see the same input value at each sampling event. This work gives detailed insight into critical design aspects of this approach and new mathematical models to predict the impact of data-to-clock time skews onto the converter linearity. Furthermore, essential building components (e.g., linear amplifiers, encoder, etc.) and a real-time digital communication interface for multi-gigabit/s data transmission to external devices are presented. The ADC is implemented in a 130-nm SiGe BiCMOS technology from IHP (SG13G2) and exhibits a die area of 1.3 mm^2. For experimental tests, the ADC is wire-bonded on a specially designed radio frequency (RF) printed circuit board. At a sampling rate of 35.84 GS/s, the peak spurious-free dynamic range (SFDR) is 35.4 dBc and the peak signal-to-noise-and-distortion ratio (SNDR) is 24.6 dB (3.8 bit). The effective resolution bandwidth (ERBW) is 14.52 GHz and covers almost the complete first Nyquist frequency band. Up to input frequencies of 20 GHz, a SFDR of more than 26.7 dBc and a SNDR of more than 19.8 dB (3 bit) is achieved. Even at a sample rate of 40.32 GS/s, full Nyquist performance can be demonstrated (SNDR = 18.4 dB @20 GHz). The presented ADC improves the sample rate of current state-of-the-art single-core ADCs by 61% from 25 GS/s to 40 GS/s, making it not only the smallest, but also the fastest reported single-core implementation up to date.Item Open Access Design of active and passive photonic components for an optical transmitter in silicon-on-insulator technology(2022) Félix Rosa, María; Berroth, Manfred (Prof. Dr.-Ing.)This work presents research on active and passive nanooptical structures on silicon-on insulator technology for high speed data communication. The utilized technology is cost efficient and complementary metal-oxide-semiconductor (CMOS) compatible allowing the integration of optical and electrical circuits on the same die. The work consists of two parts presenting the two main structures that are investigated: the two-dimensional grating coupler and the optical modulator. The first chapter introduces the motivation and the goal of the work. The second chapter describes the design and simulation of two-dimensional grating couplers. This is a passive structure used to couple light from the optical fiber into the optical waveguides embedded on a die. Two-dimensional grating couplers with an orthogonal and a focusing grid are investigated. The geometrical parameters of the structure are optimized to achieve high coupling efficiencies and enable the splitting of the two orthogonal polarizations of the input light, i.e. the transversal electric (TE) from the transversal magnetic (TM) polarization, into the two outputs of the coupler. This allows the transmission of one information channel at each polarization increasing the data rate. For periodic orthogonal two-dimensional grating couplers a simulated coupling efficiency of −1.9 dB and −2.1 dB are achieved for TE and TM polarizations, respectively. The coupling efficiency is enhanced by the use of an aperiodic grating achieving a simulated coupling efficiency of −1.7 dB for TE and −1.9 dB for TM polarization at the telecommunication wavelength of 1550 nm. In addition, two-dimensional focusing grating couplers are designed in order to reduce the area of the coupling structure. The spatial dimension of the grating and the taper, used to guide the optical signal from the grating coupler to a single mode waveguide, are optimized maximizing the coupling efficiency. Customized tapers are developed for each focusing grating design. The design and simulation of different focusing grating couplers and tapers are presented achieving a total coupling efficiency of −3.1 dB and a 1 dB-bandwidth of 40 nm with a grating coupler with a side width of less than 13 µm and a customized taper of 26.2 µm. Using an adiabatic taper with a length of 100 µm, the coupling efficiency is −2.4 dB, which is a promising result for a comparably structure which includes the tapered waveguide. At the end of the chapter the measurement results of a fabricated two-dimensional focusing grating coupler with customized taper is presented. A prototypical structure is fabricated at Institut für Mikroelektronik Stuttgart (IMS CHIPS) for design validation, which can be optimized in future adding a backside metal mirror to avoid light losses into the substrate increasing the coupling efficiency. The third chapter concentrates on the modulation of light by applying an electrical signal by means of the designed active optical structure. Key parameters for the design of these structures as the geometrical dimensions, the doping profile and the electrical properties are described in detail as well as the impact on the performance of the modulator if these parameters are modified. Different designs of modulators together with various optical and electrical test structures are fabricated with the novel technology of IMS CHIPS. The first fabricated optical modulator using this technology is successfully measured. This is a Mach-Zehnder modulator which exhibits a measured modulation efficiency of 3.1 Vcm at 2 V reverse bias voltage. The total insertion loss on-chip is 4.2 dB for the operating point with the maximum absorption of light. Transmission lines with a 3 dB electrical bandwidth higher than 50 GHz are designed and measured to be used as traveling wave electrode of the modulator. The influence of the phase shifter of the modulator below the transmission lines is analyzed and an equivalent circuit model is developed. The electrical coplanar lines of the modulator are measured showing a 3 dB electrical bandwidth of 27 GHz and a 6 dB electrical bandwidth of 30 GHz at 2 V reverse bias voltage, which theoretically corresponds with the 3 dB electro-optical bandwidth of the modulator. Additionally, modulators and test structures are designed and fabricated in a different technology with a 220 nm silicon-on-insulator substrate at the Leibniz Institute for High Performance Microelectronics (IHP). Optical and electrical measurements of the most relevant designs are presented. A modulation efficiency of 0.25 Vcm at 2 V bias voltage is demonstrated for a push-pull modulator with a 6 dB electrical bandwidth of the traveling wave electrode of 10 GHz. Finally, the most important results are outlined as conclusion and an outlook for further investigations based on the research of this work is given at the end of the thesis.