5 research outputs found
Doctor of Philosophy
dissertationDeep Neural Networks (DNNs) are the state-of-art solution in a growing number of tasks including computer vision, speech recognition, and genomics. However, DNNs are computationally expensive as they are carefully trained to extract and abstract features from raw data using multiple layers of neurons with millions of parameters. In this dissertation, we primarily focus on inference, e.g., using a DNN to classify an input image. This is an operation that will be repeatedly performed on billions of devices in the datacenter, in self-driving cars, in drones, etc. We observe that DNNs spend a vast majority of their runtime to runtime performing matrix-by-vector multiplications (MVM). MVMs have two major bottlenecks: fetching the matrix and performing sum-of-product operations. To address these bottlenecks, we use in-situ computing, where the matrix is stored in programmable resistor arrays, called crossbars, and sum-of-product operations are performed using analog computing. In this dissertation, we propose two hardware units, ISAAC and Newton.In ISAAC, we show that in-situ computing designs can outperform DNN digital accelerators, if they leverage pipelining, smart encodings, and can distribute a computation in time and space, within crossbars, and across crossbars. In the ISAAC design, roughly half the chip area/power can be attributed to the analog-to-digital conversion (ADC), i.e., it remains the key design challenge in mixed-signal accelerators for deep networks. In spite of the ADC bottleneck, ISAAC is able to out-perform the computational efficiency of the state-of-the-art design (DaDianNao) by 8x. In Newton, we take advantage of a number of techniques to address ADC inefficiency. These techniques exploit matrix transformations, heterogeneity, and smart mapping of computation to the analog substrate. We show that Newton can increase the efficiency of in-situ computing by an additional 2x. Finally, we show that in-situ computing, unfortunately, cannot be easily adapted to handle training of deep networks, i.e., it is only suitable for inference of already-trained networks. By improving the efficiency of DNN inference with ISAAC and Newton, we move closer to low-cost deep learning that in turn will have societal impact through self-driving cars, assistive systems for the disabled, and precision medicine
High Temperature Silicon Carbide Mixed-signal Circuits for Integrated Control and Data Acquisition
Wide bandgap semiconductor materials such as gallium nitride (GaN) and silicon carbide have grown in popularity as a substrate for power devices for high temperature and high voltage applications over the last two decades. Recent research has been focused on the design of integrated circuits for protection and control in these wide bandgap materials. The ICs developed in SiC and GaN can not only complement the power devices in high voltage and high frequency applications, but can also be used for standalone high temperature control and data acquisition circuitry.
This dissertation work aims to explore the possibilities in high temperature and wide bandgap circuit design by developing a host of mixed-signal circuits that can be used for control and data acquisition. These include a family of current-mode signal processing circuits, general purpose amplifiers and comparators, and 8-bit data converters. The signal processing circuits along with amplifiers and comparators are then used to develop an integrated mixed-signal controller for a DC-DC flyback converter in a microinverter application. The 8-bit SAR ADC and the 8-bit R-2R ladder DAC open up the possibility of a remote data acquisition and control system in high temperature environments. The circuits and systems presented here offer a gateway to great opportunities in high temperature and power electronics ICs in SiC
The simulation and optimization of steady state process circuits by means of artificial neural networks
Dissertation (Ph.D.) -- University of Stellenbosch, 1993.ENGLISH ABASTRACT: Since the advent of modern process industries engineers engaged in the
modelling and simulation of chemical and metallurgical processes have had to
contend with two important dilemmas. The first concerns the ill-defined nature
of the processes they have to describe, while the second relates to the
limitations of prevailing computational resources.
Current process simulation procedures are based on explicit process models in
one form or another. Many chemical and metallurgical processes are not
amenable to this kind of modelling however, and can not be incorporated
effectively into current commercial process simulators. As a result many
process operations do not benefit from the use of predictive models and
simulation routines and plants are often poorly designed and run, ultimately
leading to considerable losses in revenue.
In addition to this dilemma, process simulation is in a very real way constrained
by available computing resources. The construction of adequate process models
is essentially meaningless if these models can not be solved efficiently - a
situation occurring all too often.
In the light of these problems, it is thus not surprising that connectionist
systems or neural network methods are singularly attractive to process
engineers, since they provide a powerful means of addressing both these
dilemmas. These nets can form implicit process models through learning by
example, and also serve as a vehicle for parallel supercomputing devices. In this
dissertation the use of artificial neural networks for the steady state modelling
and optimization of chemical and metallurgical process circuits is consequently
investigated.
The first chapter is devoted to a brief overview of the simulation of chemical
and metallurgical plants by conventional methods, as well as the evolution and
impact of computer technology and artificial intelligence on the process
industries.
Knowledge of the variance covariance matrices of process data is of paramount
importance to data reconciliation and gross error detection problems, and
although various methods can be employed to estimate these often unknown variances, it is shown in the second chapter that the use of feedforward neural
nets can be more efficient than conventional strategies.
In the following chapter the important problem of gross error detection in
process data is addressed. Existing procedures are statistical and work well for
systems subject to linear constraints. Non-linear constraints are not handled
well by these methods and it is shown that back propagation neural nets can be
trained to detect errors in process systems, regardless of the nature of the
constraints.
In the fourth chapter the exploitation of the massively parallel information
processing structures of feedback neural nets in the optimization of process
data reconciliation problems is investigated. Although effective and
sophisticated algorithms are available for these procedures, there is an ever
present demand for computational devices or routines that can accommodate
progressively larger or more complex problems. Simulations indicate that neural
nets can be efficient instruments for the implementation of parallel strategies
for the optimization of such problems.
In the penultimate chapter a gold reduction plant and a leach plant are modelled
with neural nets and the models shown to be considerably better than the linear
regression models used in practice. The same technique is also demonstrated
with the modelling of an apatite flotation plant. Neural nets can also be used in
conjunction with other methods and in the same chapter the steady state
simulation and optimization of a gravity separation circuit with the use of two
linear programming models and a neural net are described.AFRIKAANSE OPSOMMING: Sedert die ontstaan van prosesingenieurswese, het ingenieurs gemoeid met die
modellering en simulasie van chemiese en metallurgiese prosesse met twee
belangrike dilemmas te kampe gehad. Die eerste het te make met die swakgedefinieerde aard van chemiese prosesse, wat die beskrywing en dus ook die
beheer daarvan kompliseer, terwyl die tweede verband hou met die beperkinge
van huidige berekeningsmiddele.
Die prosesse wat tans gebruik word om chemiese prosesse te simuleer is
gebaseer op eksplisiete prosesmodelle van een of ander aard. Baie chemiese en
metallurgiese prosesse kan egter nie op 'n eksplisiete wyse gemodelleer word
nie, en kan gevolglik ook nie doeltreffendheid deur kommersiële
prosessimulators beskryf word nie. Die bedryf van baie prosesse vind derhalwe
nie baat by die gebruik van voorspellende modelle en simulasie-algoritmes nie
en aanlegte word dikwels suboptimaal ontwerp en bedryf, wat uiteindelik tot
aansienlike geldelike verliese kan lei.
Prosessimulasie word op die koop toe ook beperk deur die beskikbaarheid van
berekeningsfasiliteite. Die konstruksie van geskikte prosesmodelle hou geen
voordeel in as hierdie modelle nie doeltreffendheid opgelos kan word nie.
Teen die agtergrond van hierdie probleme is dit nie verrassend dat neurale
netwerke 'n besondere bekoring vir prosesingenieurs inhou nie, aangesien hulle
beide hierdie dilemmas aanspreek. Hierdie nette kan implisiete prosesmodelle
konstrueer deur te leer van voorbeelde en dien ook as 'n raamwerk vir parallelle
superrekenaars. In hierdie proefskrif word die gebruik van kunsmatige neurale
netwerke vir gestadigde toestandsmodellering en optimering van chemiese en
metallurgiese prosesse gevolglik ondersoek.
Die eerste hoofstuk word gewy aan 'n kort oorsig oor die simulasie van
chemiese en metallurgiese aanlegte met konvensionele tegnieke, asook die
ontwikkeling en impak van rekenaartegnologie en skynintelligensie in die
prosesnywerhede.
Kennis van die variansie-kovariansie-matrikse van prosesdata is van kardinale
belang vir datarekonsiliasie en die identifikasie en eliminasie van sistematiese
foute en alhoewel verskeie metodes aangewend kan word om hierdie onbekende variansies te beraam, word daar in die tweede hoofstuk getoon dat
die gebruik van neurale netwerke meer doeltreffend is as konvensionele
strategieë.
In die volgende hoofstuk word die belangrike probleem van sistematiese foutopsporing
in prosesdata ondersoek. Bestaande prosedures is statisties van aard
en werk goed vir stelsels onderworpe aan lineêre beperkinge. Nie-lineêre
beperkinge kan nie doeltreffend deur hierdie prosedures hanteer word nie en
daar word gewys dat terugwaarts-propagerende nette geleer kan word om
sulke foute in prosessisteme op te spoor, ongeag die aard van die beperkinge.
In die vierde hoofstuk word die rekonsiliasie van prosesdata met behulp van
massiewe parallelle dataverwerkingstrukture soos verteenwoordig deur
terugvoerende neurale nette, ondersoek. Alhoewel doeltreffende en
gesofistikeerde algoritmes beskikbaar is vir die optimering van die tipe
probleme, is daar 'n onversadigbare aanvraag na rekenaars wat groter en meer
komplekse stelsels kan akkommodeer. Simulasie dui aan dat neurale nette
effektief aangewend kan word vir die implementering van parallelle strategieë
vir dié tipe optimeringsprobleme.
In die voorlaaste hoof stuk word die konneksionistiese modellering van 'n
goudreduksie- en 'n logingsaanleg beskryf en daar word aangetoon dat die
neurale netwerk-modelle aansienlik beter resultate lewer as die linneêre regressie modelle
wat in die praktyk gebruik word. Dieselfde tegnieke vir die modellering
van 'n flottasie-aanleg vir apatiet word ook bespreek. Neural nette kan ook
saam met ander metodes aangewend word en in dieselfde hoofstuk word die
gebruik van twee lineêre programmeringsmodelle en 'n neural net om 'n
gravitasieskeidingsbaan onder gestadigde toestande te simuleer en te optimeer,
beskryf