CMOS Transmitter using Pulse-Width Modulation Pre-Emphasis achieving 33dB Loss Compensation at 5-Gb/s

A digital transmitter pre-emphasis technique is presented that is based on pulse-width modulation, instead of finite impulse response (FIR) filtering. The technique fits well to future high-speed low-voltage CMOS processes. A 0.13 /spl mu/m CMOS transmitter achieves more than 5 Gb/s (2-PAM) over 25 m of standard RG-58U low-end coaxial copper cable. The test chip compensates for up to 33 dB of channel loss at the fundamental signaling frequency (2.5 GHz), which is the highest figure compared to literature

40 Gb/s PAM-4 transmitter IC for long-wavelength VCSEL links

Conventional 850 nm multimode fiber links deployed in warehouse-scale data centers will be limited by modal dispersion beyond 10 Gb/s when covering distances up to 1 km. This can be resolved by opting for a single-mode fiber (SMF), but typically requires the use of power-hungry edge-emitting lasers. We investigate the feasibility of a high-efficiency SMF link by reporting a 0.13 mu m SiGe BiCMOS laser diode driver optimized for long-wavelength vertical-cavity surface-emitting lasers (VCSELs). Bit-error rate experiments at 28 and 40 Gb/s up to 1 km of SMF reveal that four-level pulse amplitude modulation can compete with non-return-to-zero in terms of energy efficiency and scalability. With 9.4 pJ/b, the presented transmitter paves the way for VCSEL-based SMF links in data centers

High-speed equalization and transmission in electrical interconnections

The relentless growth of data traffic and increasing digital signal processing capabilities of integrated circuits (IC) are demanding ever faster chip-to-chip / chip-to-module serial electrical interconnects. As data rates increase, the signal quality after transmission over printed circuit board (PCB) interconnections is severely impaired. Frequency-dependent loss and crosstalk noise lead to a reduced eye opening, a reduced signal-to-noise ratio and an increased inter-symbol interference (ISI). This, in turn, requires the use of improved signal processing or PCB materials, in order to overcome the bandwidth (BW) limitations and to improve signal integrity. By applying an optimal combination of equalizer and receiver electronics together with BW-efficient modulation schemes, the transmission rate over serial electrical interconnections can be pushed further. At the start of this research, most industrial backplane connectors, meeting the IEEE and OIF specifications such as manufactured by e.g. FCI or TE connectivity, had operational capabilities of up to 25 Gb/s. This research was mainly performed under the IWT ShortTrack project. The goal of this research was to increase the transmission speed over electrical backplanes up to 100 Gb/s per channel for next-generation telecom systems and data centers. This requirement greatly surpassed the state-ofthe-art reported in previous publications, considering e.g. 25 Gb/s duobinary and 42.8 Gb/s PAM-4 transmission over a low-loss Megtron 6 electrical backplane using off-line processing. The successful implementation of the integrated transmitter (TX) and receiver (RX) (1) , clearly shows the feasibility of single lane interconnections beyond 80 Gb/s and opens the potential of realizing industrial 100 Gb/s links using a recent IC technology process. Besides the advancement of the state-of-the-art in the field of high-speed transceivers and backplane transmission systems, which led to several academic publications, the output of this work also attracts a lot of attention from the industry, showing the potential to commercialize the developed chipset and technologies used in this research for various applications: not only in high-speed electrical transmission links, but also in high-speed opto-electronic communications such as access, active optical cables and optical backplanes. In this dissertation, the background of this research, an overview of this work and the thesis organization are illustrated in Chapter 1. In Chapter 2, a system level analysis is presented, showing that the channel losses are limiting the transmission speed over backplanes. In order to enhance the serial data rate over backplanes and to eliminate the signal degradation, several technologies are discussed, such as signal equalization and modulation techniques. First, a prototype backplane channel, from project partner FCI, implemented with improved backplane connectors is characterized. Second, an integrated transversal filter as a feed-forward equalizer (FFE) is selected to perform the signal equalization, based on a comprehensive consideration of the backplane channel performance, equalization capabilities, implementation complexity and overall power consumption. NRZ, duobinary and PAM-4 are the three most common modulation schemes for ultra-high speed electrical backplane communication. After a system-level simulation and comparison, the duobinary format is selected due to its high BW efficiency and reasonable circuit complexity. Last, different IC technology processes are compared and the ST microelectronics BiCMOS9MW process (featuring a fT value of over 200 GHz) is selected, based on a trade-off between speed and chip cost. Meanwhile it also has a benefit for providing an integrated microstrip model, which is utilized for the delay elements of the FFE. Chapter 3 illustrates the chip design of the high-speed backplane TX, consisting of a multiplexer (MUX) and a 5-tap FFE. The 4:1 MUX combines four lower rate streams into a high-speed differential NRZ signal up to 100 Gb/s as the FFE input. The 5-tap FFE is implemented with a novel topology for improved testability, such that the FFE performance can be individually characterized, in both frequency- and time-domain, which also helps to perform the coefficient optimization of the FFE. Different configurations for the gain cell in the FFE are compared. The gilbert configuration shows most advantages, in both a good high-frequency performance and an easy way to implement positive / negative amplification. The total chip, including the MUX and the FFE, consumes 750mW from a 2.5V supply and occupies an area of 4.4mm × 1.4 mm. In Chapter 4, the TX chip is demonstrated up to 84 Gb/s. First, the FFE performance is characterized in the frequency domain, showing that the FFE is able to work up to 84 Gb/s using duobinary formats. Second, the combination of the MUX and the FFE is tested. The equalized TX outputs are captured after different channels, for both NRZ and duobinary signaling at speeds from 64 Gb/s to 84 Gb/s. Then, by applying the duobinary RX 2, a serial electrical transmission link is demonstrated across a pair of 10 cm coax cables and across a 5 cm FX-2 differential stripline. The 5-tap FFE compensates a total loss between the TX and the RX chips of about 13.5 dB at the Nyquist frequency, while the RX receives the equalized signal and decodes the duobinary signal to 4 quarter rate NRZ streams. This shows a chip-to-chip data link with a bit error rate (BER) lower than 10−11. Last, the electrical data transmission between the TX and the RX over two commercial backplanes is demonstrated. An error-free, serial duobinary transmission across a commercial Megtron 6, 11.5 inch backplane is demonstrated at 48 Gb/s, which indicates that duobinary outperforms NRZ for attaining higher speed or longer reach backplane applications. Later on, using an ExaMAX® backplane demonstrator, duobinary transmission performance is verified and the maximum allowed channel loss at 40 Gb/s transmission is explored. The eye diagram and BER measurements over a backplane channel up to 26.25 inch are performed. The results show that at 40 Gb/s, a total channel loss up to 37 dB at the Nyquist frequency allows for error-free duobinary transmission, while a total channel loss of 42 dB was overcome with a BER below 10−8. An overview of the conclusions is summarized in Chapter 5, along with some suggestions for further research in this field. (1) The duobinary receiver was developed by my colleague Timothy De Keulenaer, as described in his PhD dissertation. (2) Described in the PhD dissertation of Timothy De Keulenaer

Design of communication systems based on broadband sources for fiber and free space optical links

[ES] Las comunicaciones ópticas inalámbricas (OWC) constituyen una tecnología muy prometedora para el desarrollo de futuras comunicaciones inalámbricas. De hecho, ha despertado un interés creciente entre los investigadores y varias empresas de todo el mundo trabajan actualmente en el desarrollo de redes inalámbricas de muy alta velocidad. Las comunidades científica e industrial consideran la OWC como una tecnología complementaria en sus diversas formas: comunicaciones ópticas en el espacio libre (FSO), comunicaciones de luz visible (VLC) o fidelidad de la luz (Li-Fi). El espectro óptico ha sido considerado durante muchos años como una gran oportunidad para las comunicaciones inalámbricas, especialmente debido a la saturación del espectro de radiofrecuencia (RF). Esta disertación trata del uso de fuentes de banda ancha en sistemas de transmisión de luz visible (VLC), así como en sistemas de transmisión en el espectro infrarrojo por fibra óptica. En el trabajo de investigación realizado se pueden distinguir tres partes: En la primera parte, se considera el estudio y la simulación de componentes de Diodos Emisores de Luz (LED) con el software WIEN2k centrándose en las propiedades ópticas y eléctricas de los elementos II-VI. La segunda parte trata del diseño, la implementación y las pruebas de diferentes prototipos de comunicación VLC para la transmisión analógica y digital en modo simplex y semidúplex. Hemos demostrado un sistema OWC empleando una fuente de banda ancha (LED) para la transmisión no sólo de datos, sino también para la transmisión inalámbrica de energía. Además, se aborda el problema de la sincronización y la detección del nivel "1" o "0" de un bit en los sistemas de comunicación inalámbrica óptica implementados que surge como consecuencia de la atenuación de la luz a lo largo de la distancia y al problema de la pérdida de línea de visión (NLOS) entre el emisor y el receptor. Para hacer frente a este problema, se ha proporcionado un protocolo de comunicación que garantiza la transmisión fiable de datos digitales con un algoritmo de detección de nivel de bits adaptativo y se ha demostrado su eficacia mediante la transmisión de textos e imágenes. Además, esta tesis aporta una solución para la implementación de transmisores multiplexados en redes con división de longitud de onda (WDM) para formatos de modulación con multiplexación por división de frecuencia ortogonal (OFDM) basados en el uso de fuentes de banda ancha en el espectro infrarrojo para redes de fibra bidireccionales centralizadas. A pesar de las limitaciones impuestas por la dispersión cromática en el uso de este tipo de fuentes ópticas, la inclusión de ciertas estructuras antes de la detección permite la transmisión de señales OFDM en enlaces ópticos. En este trabajo se ha demostrado experimentalmente la reutilización de portadoras, la asignación dinámica de ancho de banda y la transmisión de señales OFDM multibanda mediante el uso de fuentes ópticas de banda ancha en redes WDM. Los principales resultados obtenidos en cada parte de esta tesis doctoral muestran los procedimientos de estudio, la eficacia de las soluciones propuestas y las limitaciones encontradas.[CA] Les comunicacions òptiques sense fils (OWC) constitueixen una tecnologia molt prometedora per al desenvolupament de futures comunicacions sense fils. De fet, ha despertat un interés creixent entre els investigadors i diverses empreses de tot el món treballen actualment en el desenvolupament de xarxes sense fils de molt alta velocitat. Les comunitats científica i industrial consideren la OWC com una tecnologia complementària en les seues diverses formes: comunicacions òptiques en l'espai lliure (FSO), comunicacions de llum visible (VLC) o fidelitat de la llum (Li-Fi). L'espectre òptic ha sigut considerat durant molts anys com una gran oportunitat per a les comunicacions sense fils, especialment a causa de la saturació de l'espectre de radiofreqüència (RF). Aquesta dissertació tracta de l'ús de fonts de banda ampla en sistemes de transmissió de llum visible (VLC), així com en sistemes de transmissió en l'espectre infraroig per fibra òptica. En el treball de recerca realitzat es poden distingir tres parts: ¿ En la primera part, es considera l'estudi i la simulació de components de Díodes Emissors de Llum (LED) amb el software WIEN2k centrant-se en les propietats òptiques i elèctriques dels elements II-VI. ¿ La segona part tracta del disseny, la implementació i les proves de diferents prototips de comunicació VLC per a la transmissió analògica i digital de manera simplex i semidúplex. Hem demostrat un sistema OWC emprant una font de banda ampla (LED) per a la transmissió no sols de dades, sinó també per a la transmissió sense fil d'energia. A més, s'aborda el problema de la sincronització i la detecció del nivell "1" o "0" d'un bit en els sistemes de comunicació sense fil òptica implementats, que sorgeix a conseqüència de l'atenuació de la llum al llarg de la distància i al problema de la pèrdua de línia de visió (NLOS) entre l'emissor i el receptor. Per a fer front a aquest problema, s'ha proporcionat un protocol de comunicació que garanteix la transmissió fiable de dades digitals amb un algorisme de detecció de nivell de bits adaptatiu i s'ha demostrat la seua eficàcia mitjançant la transmissió de textos i imatges. ¿ A més, aquesta tesi aporta una solució per a la implementació de transmissors multiplexats en xarxes amb divisió de longitud d'ona (WDM) per a formats de modulació amb multiplexació per divisió de freqüència ortogonal (OFDM) basats en l'ús de fonts de banda ampla en l'espectre infraroig per a xarxes de fibra bidireccionals centralitzades. Malgrat les limitacions imposades per la dispersió cromàtica en l'ús d'aquest tipus de fonts òptiques, la inclusió d'unes certes estructures abans de la detecció permet la transmissió de senyals OFDM en enllaços òptics. En aquest treball s'ha demostrat experimentalment la reutilització de portadores, l'assignació dinàmica d'amplada de banda i la transmissió de senyals OFDM multibanda mitjançant l'ús de fonts òptiques de banda ampla en xarxes WDM. Els principals resultats obtinguts en cada part d'aquesta tesi doctoral mostren els procediments d'estudi, l'eficàcia de les solucions proposades i les limitacions trobades.[EN] Optical wireless communication (OWC) is a very promising technology for future wireless communications developments. It has attracted increasing interest from researchers and several companies around the world are currently working on the development of very high-speed wireless networks. The scientific and industrial communities believe that OWC will be a complementary technology in its various forms: Free Space Optical communications (FSO), Visible Light Communications (VLC), Light Fidelity (Li-Fi). In fact, the optical spectrum has been considered for many years as a great opportunity for wireless communications especially due to the saturation of the radio frequency (RF) spectrum. This dissertation deals with the use of broadband sources in visible light transmission systems (VLC) as well as fiber optic systems. To carry out the research, three parts can be distinguished: In the first part, we consider the study and simulation of Light Emitting Diode (LED) components with the WIEN2k software by focusing on the optical and electrical properties of elements II-VI. The second part deals with the design, implementation and testing of different VLC communication prototypes for analog and digital transmission in simplex and half-duplex mode. We have demonstrated that an OWC system using a broadband source (i.e. an LED) can be used not only for data transmission, but also for wireless power transmission. Moreover, the synchronization problem and the detection of level "1" or "0" of a bit often arise in the optical wireless communication systems. This is a result of the attenuation nature of the light over the distance and the problem of Non Line-Of-Sight (NLOS) between the emitter and the receiver. To deal with this problem, a communication protocol ensuring reliable digital data transmission with an adaptive bit level detection algorithm has been provided and its effectiveness has been demonstrated by the transmission of texts and images. In addition, this thesis provides a solution for the implementation of wavelength division multiplexed - orthogonal frequency division multiplexed (WDM-OFDM) transmitters based on the use of broadband sources in the infrared spectrum for centralized bidirectional fiber networks. Despite the chromatic dispersion that avoids the use of this type of optical sources, the inclusion of certain structures before detection allows the transmission of OFDM signals in optical links. Carrier reuse, dynamic bandwidth allocation and multiband OFDM signals transmission will be experimentally demonstrated by using optical broadband sources in WDM networks. The main results obtained during this thesis work demonstrate the study procedures, for each part, the effectiveness of the proposed solutions as well as the constraints encountered.Sekkiou, I. (2021). Design of communication systems based on broadband sources for fiber and free space optical links [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172542TESI

High Performance Optical Transmitter Ffr Next Generation Supercomputing and Data Communication

High speed optical interconnects consuming low power at affordable prices are always a major area of research focus. For the backbone network infrastructure, the need for more bandwidth driven by streaming video and other data intensive applications such as cloud computing has been steadily pushing the link speed to the 40Gb/s and 100Gb/s domain. However, high power consumption, low link density and high cost seriously prevent traditional optical transceiver from being the next generation of optical link technology. For short reach communications, such as interconnects in supercomputers, the issues related to the existing electrical links become a major bottleneck for the next generation of High Performance Computing (HPC). Both applications are seeking for an innovative solution of optical links to tackle those current issues. In order to target the next generation of supercomputers and data communication, we propose to develop a high performance optical transmitter by utilizing CISCO Systems®\u27s proprietary CMOS photonic technology. The research seeks to achieve the following outcomes: 1. Reduction of power consumption due to optical interconnects to less than 5pJ/bit without the need for Ring Resonators or DWDM and less than 300fJ/bit for short distance data bus applications. 2. Enable the increase in performance (computing speed) from Peta-Flop to Exa-Flops without the proportional increase in cost or power consumption that would be prohibitive to next generation system architectures by means of increasing the maximum data transmission rate over a single fiber. 3. Explore advanced modulation schemes such as PAM-16 (Pulse-Amplitude-Modulation with 16 levels) to increase the spectrum efficiency while keeping the same or less power figure. This research will focus on the improvement of both the electrical IC and optical IC for the optical transmitter. An accurate circuit model of the optical device is created to speed up the performance optimization and enable co-simulation of electrical driver. Circuit architectures are chosen to minimize the power consumption without sacrificing the speed and noise immunity. As a result, a silicon photonic based optical transmitter employing 1V supply, featuring 20Gb/s data rate is fabricated. The system consists of an electrical driver in 40nm CMOS and an optical MZI modulator with an RF length of less than 0.5mm in 0.13&mu m SOI CMOS. Two modulation schemes are successfully demonstrated: On-Off Keying (OOK) and Pulse-Amplitude-Modulation-N (PAM-N N=4, 16). Both versions demonstrate signal integrity, interface density, and scalability that fit into the next generation data communication and exa-scale computing. Modulation power at 20Gb/s data rate for OOK and PAM-16 of 4pJ/bit and 0.25pJ/bit are achieved for the first time of an MZI type optical modulator, respectively

Pulse-Width Modulation Pre Emphasis applied in a Wireline Transmitter, achieving 33dB Loss Compensation at 5-Gb/s in 0.13-μm CMOS

Abstract—A transmitter pre-emphasis technique for copper cable equalization is presented that is based on pulse-width modulation (PWM). This technique is an alternative to the usual 2-tap symbol-spaced FIR (SSF) pre-emphasis. The technique uses timing resolution instead of amplitude resolution to adjust the filter transfer function, and therefore fits well with future high-speed low-voltage CMOS processes. Spectral analysis and time domain simulations illustrate that PWM pre-emphasis offers more relative high frequency boost than 2-tap SSF. Only one coefficient needs to be set to fit the equalizer transfer function to the channel, which makes convergence of an algorithm for automatic adaptation straightforward. A proof-of-concept 0.13- m CMOS transmitter achieves in excess of 5 Gb/s (2-PAM) over 25 m of standard RG-58U low-end coaxial copper cable with 33 dB of channel loss at the Nyquist frequency (2.5 GHz). Measured BER at this speed and channel loss is 10 12

Parametric Macromodels of Differential Drivers with Pre-Emphasis

This paper discusses the extraction of behavioral models of differential drivers with pre-emphasis for the assessment of signal integrity and electromagnetic compatibility effects in multigigabit data transmission systems. A suitable model structure is derived and the procedure for its estimation from port transient waveforms is illustrated. The proposed methodology is an extension of the macromodeling based on parametric relations applied to plain differential drivers. The obtained models preserve the accuracy and efficiency strengths of behavioral parametric macromodels for conventional devices. A realistic application example involving a high-speed communication path and a 3.125 Gb/s commercial driver model with pre-emphasis is presente

Research of M-PAM and Duobinary Modulation Formats for Use in High-Speed WDM-PON Systems

The exponential growth of Internet data traffic and progress of Information and Communication Technology (ICT) sector pushes hard the telecommunication infrastructure for upgrading the transmission data rate. Wavelength division multiplexed passive optical networks (WDM-PONs) can be the next generation solution for nowadays problems which are related to transmission capacity. Next-generation WDM-PON systems based on mixed wavelength transmitters are expected to become more cost-efficient at high per user data rates, e.g., over 10 Gbit/s per channel. Important advantage of this technology is to set various channel spacing and use different modulation formats to increase spectral efficiency in the same time and provide different transmission speeds for end user, based on pay-as-you-grow approach. Therefore, several modulation formats like non-return to zero (NRZ) also called 2-level pulse-amplitude modulation (PAM-2), four level PAM or PAM-4 and Duobinary (DB) are investigated to understand their limitations, advantages and disadvantages to be further used in next generation PON systems to increase its capacity and spectral efficiency

Dynamic Optical Networks for Data Centres and Media Production

This thesis explores all-optical networks for data centres, with a particular focus on network designs for live media production. A design for an all-optical data centre network is presented, with experimental verification of the feasibility of the network data plane. The design uses fast tunable (< 200 ns) lasers and coherent receivers across a passive optical star coupler core, forming a network capable of reaching over 1000 nodes. Experimental transmission of 25 Gb/s data across the network core, with combined wavelength switching and time division multiplexing (WS-TDM), is demonstrated. Enhancements to laser tuning time via current pre-emphasis are discussed, including experimental demonstration of fast wavelength switching (< 35 ns) of a single laser between all combinations of 96 wavelengths spaced at 50 GHz over a range wider than the optical C-band. Methods of increasing the overall network throughput by using a higher complexity modulation format are also described, along with designs for line codes to enable pulse amplitude modulation across the WS-TDM network core. The construction of an optical star coupler network core is investigated, by evaluating methods of constructing large star couplers from smaller optical coupler components. By using optical circuit switches to rearrange star coupler connectivity, the network can be partitioned, creating independent reserves of bandwidth and resulting in increased overall network throughput. Several topologies for constructing a star from optical couplers are compared, and algorithms for optimum construction methods are presented. All of the designs target strict criteria for the flexible and dynamic creation of multicast groups, which will enable future live media production workflows in data centres. The data throughput performance of the network designs is simulated under synthetic and practical media production traffic scenarios, showing improved throughput when reconfigurable star couplers are used compared to a single large star. An energy consumption evaluation shows reduced network power consumption compared to incumbent and other proposed data centre network technologies