Digital Controlled Multi-phase Buck Converter with Accurate Voltage and Current Control

abstract: A 4-phase, quasi-current-mode hysteretic buck converter with digital frequency synchronization, online comparator offset-calibration and digital current sharing control is presented. The switching frequency of the hysteretic converter is digitally synchronized to the input clock reference with less than ±1.5% error in the switching frequency range of 3-9.5MHz. The online offset calibration cancels the input-referred offset of the hysteretic comparator and enables ±1.1% voltage regulation accuracy. Maximum current-sharing error of ±3.6% is achieved by a duty-cycle-calibrated delay line based PWM generator, without affecting the phase synchronization timing sequence. In light load conditions, individual converter phases can be disabled, and the final stage power converter output stage is segmented for high efficiency. The DC-DC converter achieves 93% peak efficiency for Vi = 2V and Vo = 1.6V.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Data Processing and Investigations for the GRACE Follow-On Laser Ranging Interferometer

This thesis presents first in-depth results of the Laser Ranging Interferometer (LRI) onboard the Gravity Recovery And Climate Experiment - Follow On (GRACE-Follow On) mission. The LRI is a novel instrument, which was developed in a U.S.-German collaboration including the Albert-Einstein Institute (AEI) in Hanover. It successfully demonstrated the feasibility of ranging measurements by means of laser interferometry between two distant spacecraft and will push space-borne gravimetry missions to the next sensitivity level. The author of this thesis contributed to this project by programming a comprehensive framework for ground-processing of LRI telemetry and analyzing various kinds of instrument data streams. Therefore, the title of this thesis covers both topics, data processing and investigations within the data. Within this thesis, an introduction to laser interferometry is given and the various payloads of the GRACE-Follow On satellites are presented. Furthermore, the design of the LRI itself is discussed, in order to understand the profound causal relations when getting into the details of investigations. The various kinds of telemetry data and their processing levels are presented, giving an insight about the variety of data sets, that are downlinked from the satellites. The investigations cover various major topics. These reach from different models to assess the absolute laser frequency, which sets the scale to convert the raw phase measurements into corresponding inter-satellite displacements, and comprise a detailed investigation of the carrier to noise ratio, which provides information about the signal quality. Furthermore, the laser’s beam properties in the far-field are investigated by means of the intensity and the phasefront. These investigations even lead to a proposal for a new scan pattern, which has actually been performed. Last but not least, a comprehensive assessment of the LRI spectrum was performed, which reveals correlation between the satellite’s attitude and orbit control system (AOCS), i.e. the star cameras for attitude determination and thruster activations for attitude control, and the ranging signal, measured by the LRI. In summary, this thesis is concerned with several aspects of the LRI characterization and data analysis. Since the overall data quality and sensitivity of the LRI exceeds the needs and expectations for the current gravimetric mission, many of the discussed effects are rather of academic interest, e.g. to deepen the instrument understanding of the LRI team and for the development of future missions in the field of geodesy or the space-based gravitational wave detection (LISA mission)

Laser Ranging Interferometry for Future Gravity Missions : Instrument Design, Link Acquisition and Data Calibration

The presented study aims to improve the design solution adopted for the Laser Ranging Instrument of the GRACE Follow-On mission in terms of instrument layout, algorithms for the laser link acquisition and techniques for mitigating the range measurement noise. The first part of this work describes viable layout solutions of a heterodyne interferometer employed for intra-satellite range metrology and the major noise contributions which degrade the overall accuracy of the instrument. Together with the optical layout of the instrument, novel design concepts of the instrumenta s subsystems are also analyzed and tested. Precisely, a phasemeter designed to autonomously acquire and track a heterodyne signal with low signal-to-noise ratio in a frequency band that spans from 1MHz to 25MHz is presented. Particular attention is also dedicated to the mathematical modeling of the steering mirror dynamics and to the enhancement of its pointing performance by means of feedforward control. In the second part of this work, solutions for autonomously acquiring a laser signal buried in noise are analyzed and put in relation with the boundary constraints of the acquisition problem. The acquisition algorithms presented and the robustness of their design is verified mainly using numerical simulations. Experimental tests have also been performed for validating the simulation hypothesis and verifying their compliancy to a realistic mission scenario. The last part of this work describes a calibration algorithm which has been developed for minimizing, during data post-processing, the noise due to the tilt-to-piston coupling which represents one of the highest contributors to the overall measurement noise

Design considerations for future geodesy missions and for space laser interferometry

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Arm length stabilisation for advanced gravitational wave detectors

Currently the Laser Interferometric Gravitational-wave Observatory (LIGO) is undergoing upgrades from Initial LIGO to become Advanced LIGO. Amongst these upgrades is the addition of a signal recycling mirror at the output port of the interferometer; upgrades of the mirror suspensions to quadruple pendulums; the implementation of less invasive and hence weaker test mass actuators; and the change of readout scheme from a heterodyne based RF readout to a homodyne based DC readout. The DC readout scheme requires the installation of an Output Mode Cleaner (OMC), to stop `junk light' generated in the interferometer from making its way to the DC photodetector where it can limit the sensitivity of the gravitational wave detector. The steering of the interferometer beam into the OMC will be handled by Tip Tilt mirrors designed at the Australian National University. The first core piece of work presented in this thesis was the characterisation of a prototype Tip Tilt mirror, which involved measuring the various eigenmodes of the mirror

Intersatellite clock synchronization and absolute ranging for gravitational wave detection in space

The Laser Interferometer Space Antenna (LISA) is a European Space Agency (ESA) large-scale space mission, aiming to detect gravitational waves (GWs) in the observation band of 0.1mHz to 1Hz. The constellation is formed by three spacecrafts (SCs), exchanging laser beams with each other. The detector adopts heterodyne interferometry with MHz frequency offsets. GW signals are then encoded in optical beatnote phases, and the phase information has to be extracted by a core device called phasemeter (PM). Unequal and time- varying orbital motions introduce an overwhelming laser noise coupling that impedes the LISA performance levels of 10 ucycle/sqrt(Hz). Thereby, the post-processing technique called time-delay interferometry (TDI) time-shifts phase signals to synthesize virtual equal-arm interferometers. TDI requires absolute-ranging information, as its input, to the accuracy of 1 m rms, which will be provided by monitors like pseudo-random noise ranging (PRNR) and time-delay interferometry ranging (TDIR). An additional challenge is independent clocks on each SC that time-stamp PM data. This, alongside TDI, requires the synchronization of the onboard clocks in post-processing. This thesis reports on the experimental demonstrations of such key components for LISA. This is done by extending the scope of the hexagonal optical testbed at the Albert Einstein Institute (AEI): the "Hexagon". The first part of the thesis focuses on clock synchronization, utilizing the TDIR-like algorithm. With representative technologies both in devices and data analysis, this shows a new benchmark performance of LISA clock synchronization, achieving a 1 ucycle/sqrt(Hz) mark above 60 mHz and a TDIR accuracy of 1.84 m in range. This part also includes the first-ever verification of three noise couplings stemming from TDI and clock synchronization in an optical experiment. The second part of the thesis evolves the Hexagon further with PRNR. It commences with a review of the latest development using a transmission/reception loopback on a single hardware platform. This is followed by the research on the impact of the pseudo-random noise (PRN) modulation on phase tracking. This reveals that the codes, used at best knowledge so far, hinder the carrier phase extraction from achieving the 1 ucycle/sqrt(Hz) mark with realistic data encoded for intersatellite data communication. Some adaptations of PRN codes are proposed, and it is shown that these offer enough suppression of the noise coupling into phase tracking. After phase tracking is confirmed to be compatible with PRN modulations, PRNR itself is inves- tigated. The key novelty of this thesis in terms of PRNR is the study of its absolute-ranging feature, while previous research on this technology focused on stochastic noise properties. This requires the resolution of PRNR ambiguity and the correction of ranging biases. There suggests that the PRNR estimate, alongside some calibrations, can constantly function as absolute ranging with sub-meter accuracy

Design techniques for high-performance digital PLLs and CDRs

Phase-Locked Loops (PLLs) are essential building blocks in many communication systems. Designing high performance analog PLLs in the presence of technology imposed constraints such as leakage, poor analog transistor behavior, process variability, and low supply voltage is a challenging task. To overcome these drawbacks, digital PLLs (DPLLs) have recently emerged as an alternative to analog PLLs. In this work, a digital PLL employing a linear proportional path and a double integral path is proposed to achieve low jitter, wide operating range and low power. Moreover, the approach of bandwidth and tuning range tracking is achieved. The prototype DPLL fabricated in a 90nm CMOS process operates from 0.7 to 3.5GHz. At 2.5GHz, the proposed DPLL consumes only 1.6mW power and achieves 1.6ps r.m.s jitter. Moreover, the design techniques for a novel digital clock and data recovery (CDR) with linear loop dynamics are presented. The PLL-based digital CDR avoid the use of TDC, achieves static phase offset free (SPO-free) and well-controlled jitter transfer bandwidth. The prototype digital CDR fabricated in a 0:13μm CMOS process achieves error-free operation (BER < 10⁻¹²) for PRBS data sequences ranging from 2⁷-1 to 2³¹-1 and a near-constant bandwidth of 4.5MHz

The Telecommunications and Data Acquisition

This quarterly publication provides archival reports on developments in programs managed by JPL's Office of Telecommunications and Data Acquisition (TDA). In space communications, radio navigation, radio science, and ground-based radio and radar astronomy, it reports on activities of the Deep Space Network (DSN) in planning, supporting research and technology, implementation, and operations. Also included are standards activity at JPL for space data and information systems and reimbursable DSN work performed for other space agencies through NASA. The preceding work is all performed for NASA's Office of Space Communications (OSC)