Analog dithering techniques for highly linear and efficient transmitters

The current thesis is about investigation of new methods and techniques to be able to utilize the switched mode amplifiers, for linear and efficient applications. Switched mode amplifiers benefit from low overlap between the current and voltage wave forms in their output terminals, but they seriously suffer from nonlinearity. This makes it impossible to use them to amplify non-constant envelope message signals, where very high linearity is expected. In order to do that, dithering techniques are studied and a full linearity analysis approach is developed, by which the linearity performance of the dithered amplifier can be analyzed, based on the dithering level and frequency. The approach was based on orthogonalization of the equivalent nonlinearity and is capable of prediction of both co-channel and adjacent channel nonlinearity metrics, for a Gaussian complex or real input random signal. Behavioral switched mode amplifier models are studied and new models are developed, which can be utilized to predict the nonlinear performance of the dithered power amplifier, including the nonlinear capacitors effects. For HFD application, self-oscillating and asynchronous sigma delta techniques are currently used, as pulse with modulators (PWM), to encode a generic RF message signal, on the duty cycle of an output pulse train. The proposed models and analysis techniques were applied to this architecture in the first phase, and the method was validated with measurement on a prototype sample, realized in 65 nm TSMC CMOS technology. Afterwards, based on the same dithering phenomenon, a new linearization technique was proposed, which linearizes the switched mode class D amplifier, and at the same time can reduce the reactive power loss of the amplifier. This method is based on the dithering of the switched mode amplifier with frequencies lower than the band-pass message signal and is called low frequency dithering (LFD). To test this new technique, two test circuits were realized and the idea was applied to them. Both of the circuits were of the hard nonlinear type (class D) and are integrated CMOS and discrete LDMOS technologies respectively. The idea was successfully tested on both test circuits and all of the linearity metric predictions for a digitally modulated RF signal and a random signal were compared to the measurements. Moreover a search method to find the optimum dither frequency was proposed and validated. Finally, inspired by averaging interpretation of the dithering phenomenon, three new topologies were proposed, which are namely DLM, RF-ADC and area modulation power combining, which are all nonlinear systems linearized with dithering techniques. A new averaging method was developed and used for analysis of a Gilbert cell mixer topology, which resulted in a closed form relationship for the conversion gain, for long channel devices

Optical sampling and metrology using a soliton-effect compression pulse source

A low jitter optical pulse source for applications including optical sampling and optical metrology was modelled and then experimentally implemented using photonic components. Dispersion and non-linear fibre effects were utilised to compress a periodic optical waveform to generate pulses of the order of 10 picoseconds duration, via soliton-effect compression. Attractive features of this pulse source include electronically tuneable repetition rates greater than 1.5 GHz, ultra-short pulse duration (10-15 ps), and low timing jitter as measured by both harmonic analysis and single-sideband (SSB) phase noise measurements. The experimental implementation of the modelled compression scheme is discussed, including the successful removal of stimulated Brillouin scattering (SBS) through linewidth broadening by injection dithering or phase modulation. Timing jitter analysis identifies many unwanted artefacts generated by the SBS suppression methods, hence an experimental arrangement is devised (and was subsequently patented) which ensures that there are no phase modulation spikes present on the SSB phase noise spectrum over the offset range of interest for optical sampling applications, 10Hz-Nyquist. It is believed that this is the first detailed timing jitter study of a soliton-effect compression scheme. The soliton-effect compression pulses are then used to perform what is believed to be the first demonstration of optical sampling using this type of pulse source. The pulse source was also optimised for use in a novel optical metrology (range finding) system, which is being developed and patented under European Space Agency funding as an enabling technology for formation flying satellite missions. This new approach to optical metrology, known as Scanning Interferometric Pulse Overlap Detection (SIPOD), is based on scanning the optical pulse repetition rate to find the specific frequencies which allow the return pulses from the outlying satellite, i.e. the measurement arm, to overlap exactly with a reference pulse set on the hub satellite. By superimposing a low frequency phase modulation onto the optical pulse train, it is possible to detect the pulse overlap condition using conventional heterodyne detection. By rapidly scanning the pulse repetition rate to find two frequencies which provide the overlapping pulse condition, high precision optical pulses can be used to provide high resolution unambiguous range information, using only relatively simple electronic detection circuitry. SIPOD’s maximum longitudinal range measurement is limited only by the coherence length of the laser, which can be many tens of kilometres. Range measurements have been made to better than 10 microns resolution over extended duration trial periods, at measurement update rates of up to 470 Hz. This system is currently scheduled to fly on ESA’s PROBA-3 mission in 2012 to measure the intersatellite spacing for a two satellite coronagraph instrument. In summary, this thesis is believed to present three novel areas of research: the first detailed jitter characterisation of a soliton-effect compression source, the first optical sampling using such a compression source, and a novel optical metrology range finding system, known as SIPOD, which utilises the tuneable repetition rate and highly stable nature of the compression source pulses

3Dscanner

This project entails designing, prototyping, and testing a 3D scanner. The device that we are building uses LIDAR to take position data of a 3D object, then analyze and encode the sensor data as an STL file that can later be 3D printed out at the same resolution. We aim to build an affordable, high-performance 3D scanner that takes advantage of the falling cost of LIDAR in order to bring 3D scanning capabilities to individuals, the maker community, and even small businesses. We begin this process by choosing a sensor, the YDLIDAR X4, as our primary method of taking position data of the object. We take calibration data with this sensor to ensure that it is suitable to our needs. In doing so, we find that we may need to incorporate certain statistical methods, like dithering, in order to increase the accuracy of the system. We determine an effective layout for scanning all sides of an object, overcoming obstacles like scanning objects with concave surfaces. The physical system is mocked up in Solidworks, enabling us to 3D print, laser cut, and buy all the necessary components of the system. The system is constructed while an interactive user interface is created. We develop an algorithm for turning individual data points from the raw data of the X4 sensor into 3D printable STL files, and interface it with a program that controls the motors to take consistent, comprehensive scans of any object on the platform. In the end, we find two limitations of LIDAR in 3D scanning systems - high-gloss black surfaces and certain steep angles cannot be scanned adequately by LIDAR. However, once our system is constructed, we are able to take 3D scans of common objects, and even 3D print one of our scanned objects. The scan is compared to the original object, and the dimensional accuracy of our scanner is verified

Integrated CMOS Energy Harvesting Converter with Digital Maximum Power Point Tracking for a Portable Thermophotovoltaic Power Generator

This paper presents an integrated maximum power point tracking system for use with a thermophotovoltaic (TPV) portable power generator. The design, implemented in 0.35 μm CMOS technology, consists of a low-power control stage and a dc-dc boost power stage with soft-switching capability. With a nominal input voltage of 1 V, and an output voltage of 4 V, we demonstrate a peak conversion efficiency under nominal conditions of over 94% (overall peak efficiency over 95%), at a power level of 300 mW. The control stage uses lossless current sensing together with a custom low-power time-based ADC to minimize control losses. The converter employs a fully integrated digital implementation of a peak power tracking algorithm, and achieves a measured tracking efficiency above 98%. A detailed study of achievable efficiency versus inductor size is also presented, with calculated and measured results.Interconnect Focus Center (United States. Defense Advanced Research Projects Agency and Semiconductor Research Corporation