Simulation of optoelectronic oscillator injection locking, pulling and spiking phenomena

Complex envelope and reduced phase simulation models describing the dynamical behavior of an optoelectronic oscillator (OEO) under injection by an external source are described. The models are built on the foundations of a previously reported delay integral differential equation (DDE) theory of injection locking of time delay oscillators (TDO) such as the OEO. The DDE formulation is particularly amenable to high precision simulation using the Simulink block diagram environment. The correspondence between the blocks and the oscillator components offers intuition and considerable freedom to explore different circuit architectures and design variations with minimal coding effort. The simulations facilitate the study of the profound effect the multimode nature of a TDO has on its dynamical behavior. The reduced phase models that make use of the Leeson approximation are generally successful in reproducing the results of complex envelope models for established oscillations except for spiking phenomena for which the Leeson approximation fails. Simulation results demonstrating phenomena not captured by classical injection theory are presented, including multimode oscillation, the appearance of sidemodes in the RF and phase noise spectrum, and persistent spike trains redolent of recent experimental observations of 2pi phase pulse trains in a broadband OEO under injection

Adaptive optical feedforward linearization of optical transceiver for radio over fiber communication link

With the tremendous growth in numbers of mobile data subscribers and explosive demand for mobile data, the current wireless access network need to be augmented in order to keep up with the data speed promised by the future generation mobile network standards. Radio over fiber technology (RoF) is a cost effective solution because of its ability to support numerous numbers of simple structured base stations by consolidating the signal processing functions at the central station. RoF systems are analog systems where noise figure and spurious free dynamic range (SFDR) are important parameters in an RoF link. The nonlinearity of a laser transmitter is a major limiting factor to the performance of an RoF link, as it generates spurious spectral components, leading to intermodulation distortions (IMD), which limit the achievable SFDR of the analog RF wave transmissions. The device nonlinearity can be mitigated through various linearization schemes. The feedforward linearization technique offers a number of advantages compared to other techniques, as it offers good suppression of distortion products over a large bandwidth and supports high operating frequencies. On the other hand, feedforward linearization is a relatively sensitive scheme, where its performance is highly influenced by changing operating conditions such as laser aging, temperature effect, and input signal variations. Therefore, for practical implementations the feedforward system has to be real-time adaptive. This thesis aims to develop an adaptive optical feedforward linearization system for radio over fiber links. Mathematical analyses and computer simulations are performed to determine the most efficient algorithm for the adaptive controller for laser transmitter feedforward linearization system. Experimental setup and practical measurement are performed for an adaptive feedforward linearized laser transmitter and its performance is optimized. The adaptive optical feedforward linearization system has been modeled and simulated in MATLAB Simulink. The performances of two adaptive algorithms, which are related to the gradient signal method, such as least mean square (LMS) and recursive least square (RLS) have been compared. The LMS algorithm has been selected because of its robustness and simplicity. Finally, the adaptive optical feedforward linearization system has been set up with digital signal processor (DSP) as the control device, and practical measurement has been performed. The system has achieved a suppression of 14 dB in the third order IMD products over a bandwidth of 30 MHz, in a two-tone measurement at 1.7 GHz

Recent Trends in Communication Networks

In recent years there has been many developments in communication technology. This has greatly enhanced the computing power of small handheld resource-constrained mobile devices. Different generations of communication technology have evolved. This had led to new research for communication of large volumes of data in different transmission media and the design of different communication protocols. Another direction of research concerns the secure and error-free communication between the sender and receiver despite the risk of the presence of an eavesdropper. For the communication requirement of a huge amount of multimedia streaming data, a lot of research has been carried out in the design of proper overlay networks. The book addresses new research techniques that have evolved to handle these challenges

A 2.4 GHz Phase Modulator for a WLAN OFDM Polar Transmitter in 0.18 um CMOS

This research focuses on the design and implementation of a digital active phase modulator path of a polar transmitter in the case of orthogonal frequency division multiplex WLAN application. The phase modulation path of the polar transmitter provides a constant envelope phase modulated signal to the Power amplifier(PA) , operating in nonlinear high efficient switching mode. The core design of the phase modulator is based on linear vector-sum phase shifting topology to differential quadrature input signals. The active phase shifter consists of a DAC that generates binary weighted currents for I and Q branches and differential signed adder that vector-sums the generated quadrature currents to generate the phase at the output.6 bits control the phase shifter, creating 64 states with the resolution of 5:625° for the whole 360°. The linear (binary weighted) vector-sum technique generates a reduction in the resultant amplitude that should be taken into consideration in case of nonlinear PA in polar transmission. On the other hand, the digital phase information is applied as the control bits to the phase shifter that determine the weightings and the signs of the I and Q vectors. The key point is the operation of the phase modulator in terms of phase accuracy, with the wideband modulation standard such as OFDM WLAN. A technique has been proposed to enable the polar phase modulator to operate with a real-time wideband data and to compensate for the phase shifter output reduction. Since the reduction in gain is due to vector sum resultant of I and Q currents, it is compensated by modifying the I and Q currents for each 64 phase states. The design is implemented using 0.18 um CMOS technology and measured with maximum data rate of 64 QAM,OFDM modulation of WLAN standard. The output amplitude of the phase shifter with the correction technique is approximately constant over the 64 states with maximum variation of 3.5mv from the constant peak to peak value. The maximum achieved phase error is about 2° with a maximum DNL of 0.257

Successive-approximation-register based quantizer design for high-speed delta-sigma modulators

High-speed delta-sigma modulators are in high demand for applications such as wire-line and wireless communications, medical imaging, RF receivers and high-definition video processing. A high-speed delta-sigma modulator requires that all components of the delta-sigma loop operate at the desired high frequency. For this reason, it is essential that the quantizer used in the delta-sigma loop operate at a high sampling frequency. This thesis focuses on the design of high-speed time-interleaved multi-bit successive-approximation-register (SAR) quantizers. Design techniques for high-speed medium-resolution SAR analog-to-digital converters (ADCs) using synchronous SAR logic are proposed. Four-bit and 8-bit 5 GS/s SAR ADCs have been implemented in 65 nm CMOS using 8-channel and 16-channel time-interleaving respectively. The 4-bit SAR ADC achieves SNR of 24.3 dB, figure-of-merit (FoM) of 638 fJ/conversion-step and 42.6 mW power consumption, while the 8-bit SAR ADC achieves SNR of 41.5 dB, FoM of 191 fJ/conversion-step and 92.8 mW power consumption. High-speed operation is achieved by optimizing the critical path in the SAR ADC loop. A sampling network with a split-array with unit bridge capacitor topology is used to reduce the area of the sampling network and switch drivers

CMOS systems and circuits for sub-degree per hour MEMS gyroscopes

The objective of our research is to develop system architectures and CMOS circuits that interface with high-Q silicon microgyroscopes to implement navigation-grade angular rate sensors. The MEMS sensor used in this work is an in-plane bulk-micromachined mode-matched tuning fork gyroscope (M² – TFG ), fabricated on silicon-on-insulator substrate. The use of CMOS transimpedance amplifiers (TIA) as front-ends in high-Q MEMS resonant sensors is explored. A T-network TIA is proposed as the front-end for resonant capacitive detection. The T-TIA provides on-chip transimpedance gains of 25MΩ, has a measured capacitive resolution of 0.02aF /√Hz at 15kHz, a dynamic range of 104dB in a bandwidth of 10Hz and consumes 400μW of power. A second contribution is the development of an automated scheme to adaptively bias the mechanical structure, such that the sensor is operated in the mode-matched condition. Mode-matching leverages the inherently high quality factors of the microgyroscope, resulting in significant improvement in the Brownian noise floor, electronic noise, sensitivity and bias drift of the microsensor. We developed a novel architecture that utilizes the often ignored residual quadrature error in a gyroscope to achieve and maintain perfect mode-matching (i.e.0Hz split between the drive and sense mode frequencies), as well as electronically control the sensor bandwidth. A CMOS implementation is developed that allows mode-matching of the drive and sense frequencies of a gyroscope at a fraction of the time taken by current state of-the-art techniques. Further, this mode-matching technique allows for maintaining a controlled separation between the drive and sense resonant frequencies, providing a means of increasing sensor bandwidth and dynamic range. The mode-matching CMOS IC, implemented in a 0.5μm 2P3M process, and control algorithm have been interfaced with a 60μm thick M2−TFG to implement an angular rate sensor with bias drift as low as 0.1°/hr ℃ the lowest recorded to date for a silicon MEMS gyro.Ph.D.Committee Chair: Farrokh Ayazi; Committee Member: Jennifer Michaels; Committee Member: Levent Degertekin; Committee Member: Paul Hasler; Committee Member: W. Marshall Leac

Inertia emulation control of VSC-HVDC transmission system

The increasing penetration of power electronics interfaced renewable generation (e.g. offshore wind) has been leading to a reduction in conventional synchronous-machine based generation. Most converter-interfaced energy sources do not contribute to the overall power system inertia; and therefore cannot support the system during system transients and disturbances. It is therefore desirable that voltage-source-converter (VSC) based high voltage direct current (HVDC) interfaces, which play an important role in delivery of renewable power to AC systems, could contribute a virtual inertia and provide AC grid frequency support. In this paper, an inertia emulation control (IEC) system is proposed that allows VSC-HVDC system to perform an inertial response in a similar fashion to synchronous machines (SM), by exercising the electro-static energy stored in DC shunt capacitors of the HVDC system. The proposed IEC scheme has been implemented in simulations and its performance is evaluated using Matlab/Simulink

GaN LIGHT EMISSION FOR CONTROL SYSTEM FEEDBACK

This work explores previous research showing the correlation of light emission to current and temperature in a gallium nitride (GaN) vertical diode to predict current within a power converter circuit. Use of light emissions to measure current would offer an improvement over present sensors, since light would not be affected by the EMI found in most switched power converters. Matrices of the light emissions at 370, 380, 390, 400, 440, and 550 nm wavelengths over a range of 0.2 A to 4 A and 20 °C to 110 °C were used to develop best-fit polynomials for each matrix. Two of these polynomials can then be utilized to derive a unique solution of current and temperature based on the light output at the distinct wavelengths. Lock-in amplifiers allowed the amplification of weak light signals without gain bandwidth product limitations. Future efforts will be to duplicate the lock-in amplifier as well as the current and temperature prediction with use of a microcontroller.Lieutenant, United States NavyApproved for public release; distribution is unlimited