The thesis demonstrates a low-cost, low-bandwidth and low-resolution Analog-to- Digital Converter(ADC) in 0.35 um CMOS Process. A second-order Sigma-Delta modulator is used as the basis of the A/D Converter. A Semi-Uniform quantizer is used with the modulator to take advantage of input distributions that are dominated by smaller-amplitude signals e.g. Audio, Voice and Image-sensor signals. A Single-bit feedback topology is used with a multi-bit quantizer in the modulator. This topology avoids the use of a multi-bit DAC in the feedback loop – hence the system does not need to use digital correction techniques to compensate for a multi-bit DAC nonlinearity. High-Level Simulations of the second-order Sigma-Delta modulator single-bit feedback topology along with a Semi-Uniform quantizer are performed in Cadence. Results indicate that a 5-bit Semi-Uniform quantizer with a Over-Sampling Ratio of 32, can achieve a resolution of 10 bits, in addition, a semi-uniform quantizer exhibits a 5-6 dB gain in SNR over its uniform counterpart for input amplitudes smaller than –10 dB. Finally, this system is designed in 0.35um CMOS process.

There is a need to rethink the design of analog/mixed-signal circuits to be viable in state-of-the-art nanometer-scale CMOS processes due to the hostile environment they create for analog circuits. Reduced supply voltages and smaller capacitances are beneficial to circuit speed and digital circuit power efficiency; however, these changes along with smaller dimensions and close coupling of fast-switching digital circuits have made high-accuracy voltage domain analog processing increasingly difficult. In this work, techniques to improve analog-to-digital converters (ADC) for nanometer-scale processes are explored. First, I propose a mostly-digital time-based oversampling delta-sigma (∆Σ) ADC architecture. This system uses time, rather than voltage, as the analog variable for its quantizer, where the noise shaping process is realized by modulating the width of a variable-width digital "pulse." The merits of this architecture render it not only viable to scaling, but also enable improved circuit performance with ever-increasing time resolution of scaled CMOS processes. This is in contrast to traditional voltage-based analog circuit design, whose performance generally decreases with scaling due to increasingly higher voltage uncertainty due to supply voltage reduction and short-channel effects. In conjunction with Dr. Woo Young Jung while he was a Ph.D. student at The University of Texas at Austin, two prototype implementations of the proposed architecture were designed and fabricated in TSMC 180 nm CMOS and IBM 45 nm Silicon-On-Insulator (SOI) processes. The prototype ADCs demonstrate that the architecture can achieve bandwidths of 5-20 MHz and ∼50 dB SNR with very small area. The first generation ADC core occupies an area of only 0.0275 mm² , while the second generation ADC core occupies 0.0192 mm² . The two prototypes can be categorized as some of the smallestarea modulators in the literature. Second, I analyze the measured results of the prototype ADC chips, and determine the source for the harmonic distortion. I then demonstrate a digital calibration algorithm that sufficiently mitigates the distortion. This calibration approach falls in the general philosophy of digitally-assisted analog systems. In this philosophy, digital calibration and post-correction are favored over traditional analog solutions, in which there is a high cost to the analog solution either in complexity, power, or area. / text

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2006 Nov 28

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The ability of satellites to actively control their attitude has changed the way we live. Navigation systems, satellite television, and weather forecasting, for example, all rely on satellites which are able to determine and control their attitude accurately. This project was aimed at designing and analysing an attitude determination and control system (ADCS) for a 20 kg Earth observation satellite by means of simulation. A realistic simulation toolset, which includes the space environment, sensor, and actuator models, was created using MATLAB and Simulink. An ADCS hardware suite was selected for the satellite based on a given set of pointing and stability requirements, as well as current trends in the small satellite industry. The hardware suite consists of among others a star tracker and three reaction wheels. A variety of estimators and controllers were investigated, after which an application specific ADCS state machine was defined. The state machine included a Safe Mode for de-tumbling, a Nominal Mode for normal operation, a Forward Motion Compensation (FMC) Imaging Mode for Earth observation, and a Target Tracking Mode for ground station tracking. Simulation results indicated that de-tumbling, coarse and fine sun tracking, FMC factor 4 imaging, and target tracking were successfully implemented. Lastly, the satellite’s pointing error and stability were determined to be less than 70 arcseconds and 7 arcseconds per second respectively, both values well within the given requirements. / AFRIKAANSE OPSOMMING: Satelliete se vermoë om hul oriëntasie aktief te beheer, het die manier waarop ons lewe, verander. Navigasiestelsels, satelliettelevisie en weervoorspelling, byvoorbeeld, maak staat op satelliete wat hul oriëntasie akkuraat kan bepaal en beheer. Die mikpunt van hierdie projek was die ontwerp en analise van ’n oriëntasiebepaling- en -beheerstelsel (ADCS) vir ’n 20 kg aardwaarnemingsatelliet deur middel van simulasie. ’n Realistiese simulasieopstelling, wat modelle van die ruimteomgewing, sensore en aktueerders insluit, was ontwikkel deur gebruik te maak van MATLAB en Simulink. ’n ADCS hardewarestel was gekies vir die satelliet op grond van ’n stel rig- en stabiliteitsvereistes, sowel as die huidige tendense in die klein-satellietbedryf. Die hardewarestel bestaan onder andere uit ’n stervolger en drie reaksiewiele. Nadat verskeie afskatters en beheerders ondersoek was, was ’n toepassingspesifieke ADCS toestandmasjien gedefinieer. Die toestandmasjien het ’n Veilige Modus vir onttuimelling, ’n Nominale Modus vir normale operasie, ’n Vorentoe-bewegingskompensering (FMC) Beeldskandeermodus vir aardwaarneming en ’n Teikenvolgmodus vir grondstasie volging ingesluit. Simulasieresultate het aangedui dat onttuimeling, growwe- en fyn sonvolging, FMC faktor 4 beeldskandering en teikenvolging suksesvol geïmplementeer was. Laastens was die satelliet se rigfout en stabiliteit bepaal as minder as 70 boogsekondes en 7 boogsekondes per sekonde onderskeidelik, albei waardes gemaklik binne die vereistes.

No description available.

Beyond Atlas, a company based in Danderyd, Sweden is working on a Low Earth Orbit (LEO) 3U-CubeSat (Cube Satellite) exploration mission. As part of their maiden mission, they aim to validate the navigation, propulsion, and communication techniques of a CubeSat while it performs orbital maneuvers to collect photographs of space debris. This study briefly introduces the Beyond Atlas mission and its CubeSat design. The thesis work then mainly focuses on the details of the Attitude Determination and Control System (ADCS) peripherals and software onboard the CubeSat. It describes the Attitude Determination peripherals such as the sun sensor, star tracker, magnetometer, and gyroscope that will be onboard the CubeSat, followed by the description of the Attitude Control peripherals, namely, the magnetorquer and the reaction wheel. Subsequently, it discusses the hardware’s configuration and interface techniques with the flight computer that specifically caters to the satellite’s attitude determination and control aspect. Finally, it reports a Hardware-in-the-loop (HIL) testing methodology, and the corresponding results obtained from the unit testing of the peripherals and the operational testing (Detumbling and Pointing) of the ADCS of the Beyond Atlas CubeSat. Based on the testing results, the report concludes that the selected hardware for the Beyond Atlas mission, when integrated, can perform the principal functionalities. / Beyond Atlas baserat i Danderyd, Sverige är ett företag som arbetar med ett rymdutforsknings projekt. Som en del av deras jungfruuppdrag används en 3UCubeSat för att validera navigering, framdrivning och kommunikationsningar medan den utför banmanövrer för relativnavigation och tar bilder av rymdskräp. Denna studie introducerar kort Beyond Atlas uppdraget och dess CubeSat-design. Rapporten fokuserar sedan huvudsakligen på detaljerna i ADCS kringutrustning och programvara ombord på CubeSat. Den beskriver attitydkännande utrustning som solsensorer, startracker, magnetometer och rategyro som finns ombord, följt av beskrivningen av attitydst yrenheter, nämligen magnetorquer och reaktionshjul. Därefter diskuteras hårdvarans konfiguration och gränssnitt med navigationsdatorn som dedikerat utför satellitens attitydbestämning och attitydkontroll ADCS. Slutligen rapporterar studien testmetodik av inledande validerings-tester (Detumbling and Pointing) av ADCS i Beyond Atlas CubeSat. Baserat på testresultaten drar rapporten slutsatsen att den valda hårdvaran för satelliten kan utföra de primära navigationsfunktionerna.

The purpose of this paper was to implement Kalman filtering in the form of pre-existing Simulink blocks into a CubeSat attitude determination and control system simulation and to evaluate their performance. In recent versions of Simulink, the block library has been expanded, providing a new level of abstraction for simulation engineers. The capabilities of such library filter blocks have previously not been explored for space applications and could offer a faster and more simplified filter integration process. Three types of filter implementations have been realized, being classic Kalman filter, extended Kalman filter and unscented Kalman filter. These have been applied to the outputs of the coarse Sun sensor and Earth horizon sensor, as well as to the simulation attitude estimate. State propagation functions have been defined in the form of constant and linear approximations in addition to state propagation following the same structure as the simulation reference truth. Filter efficiency was evaluated using control error, pointing knowledge, pointing accuracy and variance as performance measures. Furthermore, interventions were introduced in the form of sensor data loss and solar panel deployment. The Kalman filter blocks were successfully integrated into the simulation. Performance measures revealed that constant state transition functions provided the best performance in most cases, exceptions being the extended Kalman filter and unscented Kalman filter of the attitude estimate application. Here, the true state propagation instead outperformed the other filters. Signal data loss showed that the true state propagation was the only one that could accurately predict the attitude state in a scenario when sensors fail to provide data. Solar panel deployment could not be utilized to evaluate the filter performance as the filter implementation did not support prediction of a dynamic attitude state. Results suggest that the pre-existing Simulink filter blocks can provide an easier alternative to defining filters from scratch. However, great care needs to be taken when tuning block parameters and constructing state transition functions to assure proper behavior. / Syftet med arbetet har varit att implementera Kalmanfilter i formen av fördefinierade Simulink-block i en simulering av ett system för attitydbestämning och styrning för en CubeSat, och utvärdera prestandan. I nyare versioner av Simulink har blockbiblioteken utökats, vilket har introducerat nya nivåer av abstraktion för simuleringsingenjörer. Möjligheterna hos filterblock i sådana bibliotek har ännu inte utforskats för rymdtekniska tillämpningar, och skulle kunna leda till snabbare och enklare integrering av filter. Tre typer av filterimplementationer har genomförts: klassiska Kalmanfilter, utökat Kalmanfilter och oparfymerat Kalmanfilter. Dessa har applicerats till utdata från solsensor och jordhorisontsensor, samt till simuleringens uppskattade attityd. Funktioner för tillståndspropagering har definierats i formen av konstanta och linjära approximationer tillsammans med den verkliga tillståndspropageringen, som har samma struktur som simuleringens sanna referensvärde. Effektiviteten hos filtren har utvärderats genom kontrollfel, riktningskunskap, riktningsnoggrannhet och varians som prestandamått. Vidare har interventioner introducerats i form av förlust av sensordata och utfällning av solpaneler. Kalmanfilterblocken integrerades med framgång i simuleringen. Prestandamåtten visade att de konstanta funktionerna för tillståndspropagering gav bäst prestanda i de flesta fallen, förutom i fallet av utökat Kalmanfilter och oparfymerat Kalmanfilter i appliceringen på den uppskattade attityden. I det sistnämnda fallet var det den verkliga tillståndspropageringen som presterade bättre än de andra filtren. Förlust av signaldata visade att den verkliga tillståndspropageringen är den enda som med säkerhet kan förutsäga utvecklingen av attityden i ett läge där sensorerna inte längre levererar data. Utfällningen av solpanelerna kunde inte utnyttjas för att utvärdera prestandan hos filtren, då implementeringen av filtren inte kan förutsäga utvecklingen av ett dynamiskt attitydtillstånd. Resultaten antyder att fördefinierade Simulink-filter kan erbjuda ett enklare alternativ till att definiera filter helt från början. Dock så krävs noga omsorg vid inställning av blockparametrar och vid konstruktion av funktioner för tillståndspropagering för att säkerställa korrekt beteende

No description available.

The MIST(MIniature Student saTellite) project is a 3U CubeSat developed by student teams at KTH Royal Institute of Technology in Stockholm. One of the fundamental systems of the satellite is the Attitude Determination and Control System (ADCS), re sponsible for estimating and correcting the satellite’s orientation using magnetic fields and sun sensors. This final degree work belongs to the MIST functional test team. It focuses on building a test environment that verifies that all ADCS components will be have as expected once the satellite is in orbit. This thesis focuses on creating a test framework that can be used to verify the operation of the ADCS. This test framework is composed of several hardware and software components developed to be reliable and flexible, so it can be adapted to verify the behavior of other systems on the satel lite by other teams in the future. The value of this test framework is demonstrated by setting up a HardwareIntheLoop (HIL) simulation of the ADCS in which real flight hardware is used along with other hardware and software components to create a test scenario as close as possible to the orbit. / MIST­projektet (MIniature Student saTellite) är en 3U CubeSat som utvecklats av studentgrupper vid Kungliga tekniska högskolan (KTH) i Stockholm. Ett av satellitens grundläggande system är Attitude Determination and Control System (ADCS), som ansvarar för att uppskatta och korrigera satellitens orientering med hjälp av magnetfält och solsensorer. Det här examensarbetet hör till MIST:s funktionstestgrupp. Det fokuserar på att bygga en testmiljö som verifierar att alla ADCS-­komponenter kommer att bete sig som förväntat när satelliten väl är i omloppsbana. Det här examensarbetet fokuserar på att skapa en testram som kan användas för att verifiera ADCS:s funktion. Testramen består av flera hardware och software komponenter som utvecklats för att vara tillförlitliga och flexibla, så att den kan anpassas för att verifiera beteendet hos andra system på satelliten av andra team i framtiden. Värdet av denna testram demonstreras genom att man sätter upp en HIL­simulering (Hardware­In­the­Loop) av ADCS där riktig flygmaskinvara används tillsammans med andra hardware och software komponenter för att skapa ett testscenario som ligger så nära omloppsbanan som möjligt.

Since the dawn of the space race, satellites have grown rapidly in complexity and shrunk equally rapidly in size. Most of them contain an Attitude Determination and Control System (ADCS) on board for pointing and detumbling manoeuvres. These intricate systems are designed for an outer space environment, hence, phenomenon otherwise abscent in space, such as gravity and aerodynamic drag present a challenge in validating these systems on Earth. The gimbal suspension testbed aims to provide a 3 Degree of Freedom (DoF) suspension where the mounted satellite under test can rotate about either axis. The suspension induces disturbance torques that must be modeled in order for the testbed to be characterized. This is accomplished by formulating the necessary gimbal dynamics, bearing friction, aerodynamic and Center of Mass (CoM) displacement torque model. This yields a relationship from which all torques present in the system can be expressed in terms of the angles, angular velocities and angular accelerations of the gimbal frames. By measuring the angles and obtaining the velocities and accelerations through numerical differentiation, the torques that correspond to a certain motion can be calculated. Furthermore, the thesis covers the iterative design of the gimbal suspension and all of its constituents, the angular measurement method and a Finite Element Method (FEM) simulation to estimate deformations. The result is presented in terms of a simulation that validates the models by predicting its behaviour for certain movement. The final result is a series of characterization plots that tells the user of the gimbal testbed how much torque must be produced by the CubeSat ADCS in order to operate it. / Sedan begynnelsen av rymdkapplöpningen har satelliter snabbt ökat i komplexitet och lika snabbt minskat i storlek. De flesta satelliter har ett attitydsbestänings- och kontrollsystem (ADCS) ombord för att kunna utföra vissa manövrar. Dessa system är designade för rymdmiljön, därför kan fenomen som annars är frånvarande i rymden, så som gravitation och luftmotstånd, innebära en utmaning då man önskar att validera systemet på jorden. Gimbalupphängningen förmedlar rotation med tre frihetsgrader där satelliten under test kan rotera kring alla tre axlar. Upphängningen inducerar störmoment som måste modelleras för att den ska bli ordentligt karaktäriserad. Detta åstadkoms genom att formulera gimbalens dynamiska förhållanden, kullagerfriktion, luftmotstånd och masscenterförflyttning. Dessa samband kopplar samman alla moment som är närvarande i systemet som funktion av gimbalramarnas vinklar, vinkelhastigheter och vinkelaccelerationer. Genom att mäta vinklarna och erhålla vinkelhastigheter och vinkelacceleration genom numerisk derivering kan momenten som motsvarar den uppmätta rörelsen beräknas. Dessutom presenteras den iterativa designen av gimbalupphängningen och alla dess beståndsdelar, vinkelmätningsmetoden och en finita elementmetodssimulering för att uppskaffa deformationer. Resultatet presenteras i form av simuleringar som validerar modellen genom att förutspå dess beteende för viss rörelse. Det slutgiltiga resultatet är en serie av karaktäriseringsgrafer som förmedlar till användaren just hur mycket moment dess CubeSats ADCS måste producera för att kunna använda gimbalupphängingen.