1,525 research outputs found

    A general theory of phase noise in electrical oscillators

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    A general model is introduced which is capable of making accurate, quantitative predictions about the phase noise of different types of electrical oscillators by acknowledging the true periodically time-varying nature of all oscillators. This new approach also elucidates several previously unknown design criteria for reducing close-in phase noise by identifying the mechanisms by which intrinsic device noise and external noise sources contribute to the total phase noise. In particular, it explains the details of how 1/f noise in a device upconverts into close-in phase noise and identifies methods to suppress this upconversion. The theory also naturally accommodates cyclostationary noise sources, leading to additional important design insights. The model reduces to previously available phase noise models as special cases. Excellent agreement among theory, simulations, and measurements is observed

    Low jitter phase-locked loop clock synthesis with wide locking range

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    The fast growing demand of wireless and high speed data communications has driven efforts to increase the levels of integration in many communications applications. Phase noise and timing jitter are important design considerations for these communications applications. The desire for highly complex levels of integration using low cost CMOS technologies works against the minimization of timing jitter and phase noise for communications systems which employ a phase-locked loop for frequency and clock synthesis with on-chip VCO. This dictates an integrated CMOS implementation of the VCO with very low phase noise performance. The ring oscillator VCOs based on differential delay cell chains have been used successfully in communications applications, but thermal noise induced phase noise have to be minimized in order not to limit their applicability to some applications which impose stringent timing jitter and phase noise requirements on the PLL clock synthesizer. Obtaining lower timing jitter and phase noise at the PLL output also requires the minimization of noise in critical circuit design blocks as well as the optimization of the loop bandwidth of the PLL. In this dissertation the fundamental performance limits of CMOS PLL clock synthesizers based on ring oscillator VCOs are investigated. The effect of flicker and thermal noise in MOS transistors on timing jitter and phase noise are explored, with particular emphasis on source coupled NMOS differential delay cells with symmetric load elements. Several new circuit architectures are employed for the charge pump circuit and phase-frequency detector (PFD) to minimize the timing jitter due to the finite dead zone in the PFD and the current mismatch in the charge pump circuit. The selection of the optimum PLL loop bandwidth is critical in determining the phase noise performance at the PLL output. The optimum loop bandwidth and the phase noise performance of the PLL is determined using behavioral simulations. These results are compared with transistor level simulated results and experimental results for the PLL clock synthesizer fabricated in a 0.35 µm CMOS technology with good agreement. To demonstrate the proposed concept, a fully integrated CMOS PLL clock synthesizer utilizing integer-N frequency multiplier technique to synthesize several clock signals in the range of 20-400 MHz with low phase noise was designed. Implemented in a standard 0.35-µm N-well CMOS process technology, the PLL achieves a period jitter of 6.5-ps (rms) and 38-ps (peak-to-peak) at 216 MHz with a phase noise of -120 dBc/Hz at frequency offsets above 10 KHz. The specific research contributions of this work include (1) proposing, designing, and implementing a new charge pump circuit architecture that matches current levels and therefore minimizes one source of phase noise due to fluctuations in the control voltage of the VCO, (2) an improved phase-frequency detector architecture which has improved characteristics in lock condition, (3) an improved ring oscillator VCO with excellent thermal noise induced phase noise characteristics, (4) the application of selfbiased techniques together with fixed bias to CMOS low phase noise PLL clock synthesizer for digital video communications ,and (5) an analytical model that describes the phase noise performance of the proposed VCO and PLL clock synthesizer

    Optical Microwave Signal Generation for Data Transmission in Optical Networks

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    The massive growth of telecommunication services and the increasing global data traffic boost the development, implementation, and integration of different networks for data transmission. An example of this development is the optical fiber networks, responsible today for the inter-continental connection through long-distance links and high transfer rates. The optical networks, as well as the networks supported by other transmission media, use electrical signals at specific frequencies for the synchronization of the network elements. The quality of these signals is usually determined in terms of phase noise. Due to the major impact of the phase noise over the system performance, its value should be minimized. The research work presented in this document describes the design and implementation of an optoelectronic system for the microwave signal generation using a vertical-cavity surface-emitting laser (VCSEL) and its integration into an optical data transmission system. Considering that the proposed system incorporates a directly modulated VCSEL, a theoretical and experimental characterization was developed based on the laser rate equations, dynamic and static measurements, and an equivalent electrical model of the active region. This procedure made possible the extraction of some VCSEL intrinsic parameters, as well as the validation and simulation of the VCSEL performance under specific modulation conditions. The VCSEL emits in C-band, this wavelength was selected because it is used in long-haul links. The proposed system is a self-initiated oscillation system caused by internal noise sources, which includes a VCSEL modulated in large signal to generate optical pulses (gain switching). The optical pulses, and the optical frequency comb associated, generate in electrical domain simultaneously a fundamental frequency (determined by a band-pass filter) and several harmonics. The phase noise measured at 10 kHz from the carrier at 1.25 GHz was -127.8 dBc/Hz, and it is the lowest value reported in the literature for this frequency and architecture. Both the jitter and optical pulse width were determined when different resonant cavities and polarization currents were employed. The lowest pulse duration was 85 ps and was achieved when the fundamental frequency was 2.5 GHz. As for the optical frequency comb, it was demonstrated that its flatness depends on the electrical modulation conditions. The flattest profiles are obtained when the fundamental frequency is higher than the VCSEL relaxation frequency. Both the electrical and the optical output of the system were integrated into an optical transmitter. The electrical signal provides the synchronization of the data generating equipment, whereas the optical pulses are employed as an optical carrier. Data transmissions at 155.52 Mb/s, 622.08 Mb/s and 1.25 Gb/s were experimentally validated. It was demonstrated that the fundamental frequency and harmonics could be extracted from the optical data signal transmitted by a band-pass filter. It was also experimentally proved that the pulsed return-to-zero (RZ) transmitter at 1.25 Gb/s, achieves bit error rates (BER) lower than 10910^{-9} when the optical power at the receiver is higher than -33 dBm.La masificación de los servicios de telecomunicaciones y el creciente tráfico global de datos han impulsado el desarrollo, despliegue e integración de diferentes redes para la transmisión de datos. Un ejemplo de este despliegue son las redes de fibra óptica, responsables en la actualidad de la interconexión de los continentes a través de enlaces de grandes longitudes y altas tasas de transferencia. Las redes ópticas, al igual que las redes soportadas por otros medios de transmisión, utilizan señales eléctricas a frecuencias específicas para la sincronización de los elementos de red. La calidad de estas señales es determinante en el desempeño general del sistema, razón por la que su ruido de fase debe ser lo más pequeño posible. El trabajo de investigación presentado en este documento describe el diseño e implementación de un sistema optoelectrónico para la generación de señales microondas utilizando diodos láser de cavidad vertical (VCSEL) y su integración en un sistema de transmisión de datos óptico. Teniendo en cuenta que el sistema propuesto incorpora un láser VCSEL modulado directamente, se desarrolló una caracterización teórico-experimental basada en las ecuaciones de evolución del láser, mediciones dinámicas y estáticas, y un modelo eléctrico equivalente de la región activa. Este procedimiento posibilitó la extracción de algunos parámetros intrínsecos del VCSEL, al igual que la validación y simulación de su desempeño bajo diferentes condiciones de modulación. El VCSEL utilizado emite en banda C y fue seleccionado considerando que esta banda es comúnmente utilizada en enlaces de largo alcance. El sistema propuesto consiste en un lazo cerrado que inicia la oscilación gracias a las fuentes de ruido de los componentes y modula el VCSEL en gran señal para generar pulsos ópticos (conmutación de ganancia). Estos pulsos ópticos, que en el dominio de la frecuencia corresponden a un peine de frecuencia óptico, son detectados para generar simultáneamente una frecuencia fundamental (determinada por un filtro pasa banda) y varios armónicos. El ruido de fase medido a 10 kHz de la portadora a 1.25 GHz fue -127.8 dBc/Hz, y es el valor más bajo reportado en la literatura para esta frecuencia y arquitectura. Tanto la fluctuación de fase (jitter) y el ancho de los pulsos ópticos fueron determinados cuando diferentes cavidades resonantes y corrientes de polarización fueron empleadas. La duración de pulso más baja fue 85 ps y se obtuvo cuando la frecuencia fundamental del sistema era 2.5 GHz. En cuanto al peine de frecuencia óptico, se demostró que su planitud (flatness) depende de las condiciones eléctricas de modulación y que los perfiles más planos se obtienen cuando la frecuencia fundamental es superior a la frecuencia de relajación del VCSEL. Tanto la salida eléctrica como la salida óptica del sistema fueron integradas en un transmisor óptico. La señal eléctrica permite la sincronización de los equipos encargados de generar los datos, mientras que los pulsos ópticos son utilizados como portadora óptica. La transmisión de datos a 155.52 Mb/s, 622.08 Mb/s y 1.25 Gb/s fue validada experimentalmente. Se demostró que la frecuencia fundamental y los armónicos pueden ser extraídos de la señal óptica de datos transmitida mediante un filtro pasa banda. También se comprobó experimentalmente que el transmisor de datos pulsados con retorno a cero (RZ) a 1.25 Gb/s, logra tasas de error de bit (BER) menores a 10-9 cuando la potencia óptica en el receptor es mayor a -33 dBm.Gobernación de NariñoBPIN 2013000100092Doctorad

    System-Level Design of All-Digital LTE / LTE-A Transmitter Hardware

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    This thesis presents a detailed system-level analysis of an all-digital transmitter hardware based on the Direct-Digital RF-Modulator (DDRM). The purpose of the presented analysis is to evaluate whether this particular transmitter architecture is suitable to be used in LTE / LTE-A mobile phones. The DDRM architecture is based on the Radio Frequency Digital-to-Analog Converter (RF-DAC), whose system-level characteristics are investigated in this work through mathematical analysis and MATLAB simulations. In particular, a new analytical model for the timing error in the distributed upconversion is developed and verified. Moreover, this thesis reviews the LTE and LTE-A standards, and describes how a baseband environment for signal generation/demodulation can be implemented in MATLAB. The presented system enables much more flexibility with respect to current commercial softwares like Agilent Signal Studio. Simulation results show that the most challenging specification to meet is the out-of-band noise floor, because of the stringent linearity and timing requirements posed on the RF-DAC. This suggests that new means of reducing the out-of-band noise in all-digital transmitters should be researched, in order not to make their design more complicated than for their analog counterpart

    Study of voltage controlled oscillator based analog-to-digital converter

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    A voltage controlled oscillator (VCO) based analog-to-digital converter (ADC) is a time based architecture with a first-order noise-shaping property, which can be implemented using a VCO and digital circuits. This thesis analyzes the performance of VCO-based ADCs in the presence of non idealities such as jitter, nonlinearity, mismatch, and the metastability of D flip-flops. Based on this analysis, design criteria for determining parameters for VCO-based ADCs are described. Further, the study involves the use of VCO based Dual-slope A/D converter and its behaviour under different input voltage level. Graph is plotted between output voltages of the integrator vs. time. Digital circuits like a bit-counter and logic circuits are used for operation mode. A normal VCO model is also done in MATLAB-simulink environment and studied under variable input frequency and corresponding output plots are view

    Generation and optimization of picosecond optical pulses for use in hybrid WDM/OTDM networks

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    The burgeoning demand for broadband services such as database queries, home shopping, video-on-demand, remote education, telemedicine and videoconferencing will push the existing networks to their limits. This demand was mainly fueled by the brisk proliferation of Personal Computers (PC) together with the exceptional increases in their storage capacity and processing capabilities and the widespread availability of the internet. Hence the necessity, to develop high-speed optical technologies in order to construct large capacity networks, arises. Two of the most popular multiplexing techniques available in the optical domain that are used in the building of such high capacity networks, are Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM). However merging these two techniques to form very high-speed hybrid WDM/OTDM networks brings about the merits of both multiplexing technologies. This thesis examines the development of one of the key components (picosecond optical pulses) associated to such high-speed systems. Recent analysis has shown that RZ format is superior to conventional NRZ systems as it is easier to compensate for dispersion and nonlinear effects in the fibre by employing soliton-like propagation. In addition to this development, the use of wavelength tunability for dynamic provisioning is another area that is actively researched on. Self-seeding of a gain switched Fabry Perot laser is shown to one of the simplest and cost effective methods of generating, transform limited optical pulses that are wavelength tunable over very wide ranges. One of the vital characteristics of the above mentioned pulse sources, is their Side Mode Suppression Ratio (SMSR). This thesis examines in detail how the pulse SMSR affects the performance of high-speed WDM/OTDM systems that employ self-seeded gain-switched pulse sources
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