5,433 research outputs found
Available Techniques for Magnetic Hard Disk Drive Read Channel Equalization
This paper presents an extensive, non-exhaustive, study of available hard disk drive read channel equalization techniques used in the storage and readback of magnetically stored information. The physical elements and basic principles of the storage processes are introduced together with the basic theoretical definitions and models. Both read and write processes in magnetic storage are explained along with the definition of simple key concepts such as user bit density, intersymbol interference, linear and areal density, read head pulse response models, and coding algorithm
On Coding and Detection Techniques for Two-Dimensional Magnetic Recording
Edited version embargoed until 15.04.2020
Full version: Access restricted permanently due to 3rd party copyright restrictions. Restriction set on 15/04/2019 by AS, Doctoral CollegeThe areal density growth of magnetic recording systems is fast approaching the superparamagnetic limit for conventional magnetic disks. This is due to the increasing demand for high data storage capacity. Two-dimensional Magnetic Recording (TDMR) is a new technology aimed at increasing the areal density of magnetic recording systems beyond the limit of current disk technology using conventional disk media. However, it relies on advanced coding and signal processing techniques to achieve areal density gains. Current state of the art signal processing for TDMR channel employed iterative decoding with Low Density Parity Check (LDPC) codes, coupled with 2D equalisers and full 2D Maximum Likelihood (ML) detectors. The shortcoming of these algorithms is their computation complexity especially with regards to the ML detectors which is exponential with respect to the number of bits involved. Therefore, robust low-complexity coding, equalisation and detection algorithms are crucial for successful future deployment of the TDMR scheme.
This present work is aimed at finding efficient and low-complexity coding, equalisation, detection and decoding techniques for improving the performance of TDMR channel and magnetic recording channel in general. A forward error correction (FEC) scheme of two concatenated single parity bit systems along track separated by an interleaver has been presented for channel with perpendicular magnetic recording (PMR) media. Joint detection decoding algorithm using constrained MAP detector for simultaneous detection and decoding of data with single parity bit system has been proposed. It is shown that using the proposed FEC scheme with the constrained MAP detector/decoder can achieve a gain of up to 3dB over un-coded MAP decoder for 1D interference channel. A further gain of 1.5 dB was achieved by concatenating two interleavers with extra parity bit when data density along track is high. The use of single bit parity code as a run length limited code as well as an error correction code is demonstrated to simplify detection complexity and improve system performance.
A low-complexity 2D detection technique for TDMR system with Shingled Magnetic Recording Media (SMR) was also proposed. The technique used the concatenation of 2D MAP detector along track with regular MAP detector across tracks to reduce the complexity order of using full 2D detection from exponential to linear. It is shown that using this technique can improve track density with limited complexity. Two methods of FEC for TDMR channel using two single parity bit systems have been discussed. One using two concatenated single parity bits along track only, separated by a Dithered Relative Prime (DRP) interleaver and the other use the single parity bits in both directions without the DRP interleaver. Consequent to the FEC coding on the channel, a 2D multi-track MAP joint detector decoder has been proposed for simultaneous detection and decoding of the coded single parity bit data. A gain of up to 5dB was achieved using the FEC scheme with the 2D multi-track MAP joint detector decoder over un-coded 2D multi-track MAP detector in TDMR channel. In a situation with high density in both directions, it is shown that FEC coding using two concatenated single parity bits along track separated by DRP interleaver performed better than when the single parity bits are used in both directions without the DRP interleaver.9mobile Nigeri
ON REDUCING THE DECODING COMPLEXITY OF SHINGLED MAGNETIC RECORDING SYSTEM
Shingled Magnetic Recording (SMR) has been recognised as one of the alternative technologies
to achieve an areal density beyond the limit of the perpendicular recording technique,
1 Tb/in2, which has an advantage of extending the use of the conventional method
media and read/write head.
This work presents SMR system subject to both Inter Symbol Interference (ISI) and Inter
Track Interference (ITI) and investigates different equalisation/detection techniques in order
to reduce the complexity of this system.
To investigate the ITI in shingled systems, one-track one-head system model has been extended
into two-track one-head system model to have two interfering tracks. Consequently,
six novel decoding techniques have been applied to the new system in order to find the Maximum
Likelihood (ML) sequence. The decoding complexity of the six techniques has been
investigated and then measured. The results show that the complexity is reduced by more
than three times with 0.5 dB loss in performance.
To measure this complexity practically, perpendicular recording system has been implemented
in hardware. Hardware architectures are designed for that system with successful
Quartus II fitter which are: Perpendicular Magnetic Recording (PMR) channel, digital
filter equaliser with and without Additive White Gaussian Noise (AWGN) and ideal
channel architectures. Two different hardware designs are implemented for Viterbi Algorithm
(VA), however, Quartus II fitter for both of them was unsuccessful. It is found that,
Simulink/Digital Signal Processing (DSP) Builder based designs are not efficient for complex
algorithms and the eligible solution for such designs is writing Hardware Description
Language (HDL) codes for those algorithms.The Iraqi Governmen
Feasibility of self-structured current accessed bubble devices in spacecraft recording systems
The self-structured, current aperture approach to magnetic bubble memory is described. Key results include: (1) demonstration that self-structured bubbles (a lattice of strongly interacting bubbles) will slip by one another in a storage loop at spacings of 2.5 bubble diameters, (2) the ability of self-structured bubbles to move past international fabrication defects (missing apertures) in the propagation conductors (defeat tolerance), and (3) moving bubbles at mobility limited speeds. Milled barriers in the epitaxial garnet are discussed for containment of the bubble lattice. Experimental work on input/output tracks, storage loops, gates, generators, and magneto-resistive detectors for a prototype device are discussed. Potential final device architectures are described with modeling of power consumption, data rates, and access times. Appendices compare the self-structured bubble memory from the device and system perspectives with other non-volatile memory technologies
Design of adaptive analog filters for magnetic front-end read channels
Esta tese estuda o projecto e o comportamento de filtros em tempo contínuo de
muito-alta-frequência. A motivação deste trabalho foi a investigação de soluções de filtragem
para canais de leitura em sistemas de gravação e reprodução de dados em suporte
magnético, com custos e consumo (tamanho total inferior a 1 mm2 e consumo inferior a
1mW/polo), inferiores aos circuitos existentes. Nesse sentido, tal como foi feito neste
trabalho, o rápido desenvolvimento das tecnologias de microelectrónica suscitou esforços
muito significativos a nível mundial com o objectivo de se investigarem novas técnicas
de realização de filtros em circuito integrado monolítico, especialmente em tecnologia
CMOS (Complementary Metal Oxide Semiconductor). Apresenta-se um estudo comparativo
a diversos níveis hierárquicos do projecto, que conduziu à realização e caracterização
de soluções com as características desejadas.
Num primeiro nível, este estudo aborda a questão conceptual da gravação e transmissão
de sinal bem como a escolha de bons modelos matemáticos para o tratamento da
informação e a minimização de erro inerente às aproximações na conformidade aos princípios
físicos dos dispositivos caracterizados.
O trabalho principal da tese é focado nos níveis hierárquicos da arquitectura do
canal de leitura e da realização em circuito integrado do seu bloco principal – o bloco de
filtragem. Ao nível da arquitectura do canal de leitura, apresenta-se um estudo alargado
sobre as metodologias existentes de adaptação de sinal e recuperação de dados em suporte
magnético. Este desígnio aparece no âmbito da proposta de uma solução de baixo custo,
baixo consumo, baixa tensão de alimentação e baixa complexidade, alicerçada em tecnologia
digital CMOS, para a realização de um sistema DFE (Decision Feedback Equalization)
com base na igualização de sinal utilizando filtros integrados analógicos em tempo
contínuo.
Ao nível do projecto de realização do bloco de filtragem e das técnicas de implementação
de filtros e dos seus blocos constituintes em circuito integrado, concluiu-se que
a técnica baseada em circuitos de transcondutância e condensadores, também conhecida como filtros gm-C (ou transcondutância-C), é a mais adequada para a realização de filtros
adaptativos em muito-alta-frequência. Definiram-se neste nível hierárquico mais baixo,
dois subníveis de aprofundamento do estudo no âmbito desta tese, nomeadamente: a pesquisa
e análise de estruturas ideais no projecto de filtros recorrendo a representações no
espaço de estados; e, o estudo de técnicas de realização em tecnologia digital CMOS de
circuitos de transcondutância para a implementação de filtros integrados analógicos em
tempo contínuo.
Na sequência deste estudo, apresentam-se e comparam-se duas estruturas de filtros
no espaço de estados, correspondentes a duas soluções alternativas para a realização de
um igualador adaptativo realizado por um filtro contínuo passa-tudo de terceira ordem,
para utilização num canal de leitura de dados em suporte magnético.
Como parte constituinte destes filtros, apresenta-se uma técnica de realização de
circuitos de transcondutância, e de realização de condensadores lineares usando matrizes
de transístores MOSFET para processamento de sinal em muito-alta-frequência realizada
em circuito integrado usando tecnologia digital CMOS submicrométrica. Apresentam-se
métodos de adaptação automática capazes de compensar os erros face aos valores nominais
dos componentes, devidos às tolerâncias inerentes ao processo de fabrico, para os
quais apresentamos os resultados de simulação e de medição experimental obtidos.
Na sequência deste estudo, resultou igualmente a apresentação de um circuito passível
de constituir uma solução para o controlo de posicionamento da cabeça de leitura
em sistemas de gravação/reprodução de dados em suporte magnético. O bloco proposto
é um filtro adaptativo de primeira ordem, com base nos mesmos circuitos de transcondutância
e técnicas de igualação propostos e utilizados na implementação do filtro adaptativo
de igualação do canal de leitura.
Este bloco de filtragem foi projectado e incluído num circuito integrado (Jaguar) de
controlo de posicionamento da cabeça de leitura realizado para a empresa ATMEL em
Colorado Springs, e incluído num produto comercial em parceria com uma empresa escocesa
utilizado em discos rígidos amovíveis.This thesis studies the design and behavior of continuous-time very-high-frequency
filters. The motivation of this work was the search for filtering solutions for the readchannel
in recording and reproduction of data on magnetic media systems, with costs and
consumption (total size less than 1 mm2 and consumption under 1mW/pole), lower than
the available circuits. Accordingly, as was done in this work, the rapid development of
microelectronics technology raised very significant efforts worldwide in order to investigate
new techniques for implementing such filters in monolithic integrated circuit, especially
in CMOS technology (Complementary Metal Oxide Semiconductor). We present
a comparative study on different hierarchical levels of the project, which led to the realization
and characterization of solutions with the desired characteristics.
In the first level, this study addresses the conceptual question of recording and
transmission of signal and the choice of good mathematical models for the processing of
information and minimization of error inherent in the approaches and in accordance with
the principles of the characterized physical devices.
The main work of this thesis is focused on the hierarchical levels of the architecture
of the read channel and the integrated circuit implementation of its main block - the filtering
block. At the architecture level of the read channel this work presents a comprehensive
study on existing methodologies of adaptation and signal recovery of data on
magnetic media. This project appears in the sequence of the proposed solution for a lowcost,
low consumption, low voltage, low complexity, using CMOS digital technology for
the performance of a DFE (Decision Feedback Equalization) based on the equalization of
the signal using integrated analog filters in continuous time.
At the project level of implementation of the filtering block and techniques for implementing
filters and its building components, it was concluded that the technique based
on transconductance circuits and capacitors, also known as gm-C filters is the most appropriate
for the implementation of very-high-frequency adaptive filters. We defined in
this lower level, two sub-levels of depth study for this thesis, namely: research and analysis
of optimal structures for the design of state-space filters, and the study of techniques for the design of transconductance cells in digital CMOS circuits for the implementation
of continuous time integrated analog filters.
Following this study, we present and compare two filtering structures operating in
the space of states, corresponding to two alternatives for achieving a realization of an
adaptive equalizer by the use of a continuous-time third order allpass filter, as part of a
read-channel for magnetic media devices.
As a constituent part of these filters, we present a technique for the realization of
transconductance circuits and for the implementation of linear capacitors using arrays of
MOSFET transistors for signal processing in very-high-frequency integrated circuits using
sub-micrometric CMOS technology. We present methods capable of automatic adjustment
and compensation for deviation errors in respect to the nominal values of the
components inherent to the tolerances of the fabrication process, for which we present
the simulation and experimental measurement results obtained.
Also as a result of this study, is the presentation of a circuit that provides a solution
for the control of the head positioning on recording/playback systems of data on magnetic
media. The proposed block is an adaptive first-order filter, based on the same transconductance
circuits and equalization techniques proposed and used in the implementation
of the adaptive filter for the equalization of the read channel.
This filter was designed and included in an integrated circuit (Jaguar) used to control
the positioning of the read-head done for ATMEL company in Colorado Springs, and
part of a commercial product used in removable hard drives fabricated in partnership with a Scottish company
CROSSTALK-RESILIANT CODING FOR HIGH DENSITY DIGITAL RECORDING
Increasing the track density in magnetic systems is very difficult due to inter-track interference
(ITI) caused by the magnetic field of adjacent tracks. This work presents a
two-track partial response class 4 magnetic channel with linear and symmetrical ITI; and
explores modulation codes, signal processing methods and error correction codes in order
to mitigate the effects of ITI.
Recording codes were investigated, and a new class of two-dimensional run-length
limited recording codes is described. The new class of codes controls the type of ITI
and has been found to be about 10% more resilient to ITI compared to conventional
run-length limited codes. A new adaptive trellis has also been described that adaptively
solves for the effect of ITI. This has been found to give gains up to 5dB in signal to noise
ratio (SNR) at 40% ITI. It was also found that the new class of codes were about 10%
more resilient to ITI compared to conventional recording codes when decoded with the
new trellis.
Error correction coding methods were applied, and the use of Low Density Parity
Check (LDPC) codes was investigated. It was found that at high SNR, conventional
codes could perform as well as the new modulation codes in a combined modulation and
error correction coding scheme. Results suggest that high rate LDPC codes can mitigate
the effect of ITI, however the decoders have convergence problems beyond 30% ITI
MODELOWANIE URZĄDZEŃ SPINTRONICZNYCH DO ZASTOSOWANIA W PAMIĘCI O DOSTĘPIE SWOBODNYM RAM
The article analyzes the physical processes that occur in spin-valve structures during recording process which occurs in high-speed magnetic memory devices. Considered are devices using magnetization of the ferromagnetic layer through transmitting magnetic moment by polarized spin (STT-MRAM). Basic equations are derived to model the information recording process in the model of symmetric binary channel. Because the error probability arises from the magnetization process, a model of the magnetization process is formed, which is derived from the Landau-Lifshitz-Gilbert equations under the assumption of a single-domain magnet. The choice of a single-domain model is due to the nanometer size of the flat magnetic layer. The developed method of modeling the recording process determines the dependence of such characteristics as the bit error probability and the rate of recording on two important technological characteristics of the recording process: the value of the current and its duration. The end result and the aim of the simulation is to determine the optimal values of the current and its duration at which the speed of the recording process is the highest for a given level of error probability. The numerical values of the transmission rate and error probability were obtained for a wide range of current values (10–1500 μA) and recording time of one bit (1–70 ns), and generally correctly describe the process of information transmission. The calculated data were compared with the technical characteristics of existing industrial devices and devices which are the object of the scientific research. The resulting model can be used to simulate devices using different values of recording currents: STT-MRAM series chips using low current values (500-100 μA), devices in the stage of technological design and using medium current values (100–500 μA) and devices that are the object of experimental scientific research and use high currents (500–1000 μA). The model can also be applied to simulate devices with different data rates, which have different requirements for both transmission speed and bit error probability. In this way, the model can be applied to both high-speed memory devices in computer systems and signal sensors, which are connected to sensor networks or connected to the IoT.W tym artykule analizowane są procesy fizyczne zachodzące w strukturach zaworów spinowych podczas procesu rejestrowania informacji, który występuje w urządzeniach z szybką pamięcią magnetyczną. Obiektem badań są urządzenia wykorzystujące magnetyzację warstwy ferromagnetycznej poprzez przenoszenie momentu magnetycznego za pomocą spolaryzowanego spinu (STT-MRAM). Wyprowadzono podstawowe równania potrzebne do modelowania procesu rejestrowania informacji w modelu symetrycznego kanału binarnego. W związku z tym, że prawdopodobieństwo błędu wynika z procesu magnesowania, stworzony jest model procesu magnesowania, który został wyprowadzony z równań Landaua-Lifshitza-Hilberta przy założeniu magnesu jednodomenowego. Wybór modelu jednodomenowego wynika z nanometrycznej wielkości płaskiej warstwy magnetycznej. Opracowana metoda modelowania procesu rejestrowania informacji określa zależność wskaźników, takich jak prawdopodobieństwo błędnego bitu i szybkość transmisji informacji, od dwóch ważnych właściwości procesu rejestrowania: natężenia prądu i czasu jego trwania. Końcowym rezultatem i zarazem celem symulacji jest określenie optymalnych wartości natężenia prądu i czasu trwania rejestracji informacji, przy których prędkość procesu zapisu będzie najwyższa dla danego stopnia prawdopodobieństwa błędu. Uzyskano wartości liczbowe dla szybkości transmisji i prawdopodobieństwa błędu dla szerokiego zakresu natężenia prądu (10–1500 μA) i czasu rejestracji jednego bitu (1–70 ns), które ogólnie poprawnie opisują proces transmisji informacji. Wyniki obliczeń zostały porównane ze specyfikacją techniczną istniejących urządzeń przemysłowych i urządzeń będących obiektami badań naukowych. Powstały model można wykorzystać do symulacji urządzeń wykorzystujących różne wartości natężenia prądu: układy szeregowe STT-MRAM wykorzystujące niskie natężenie prądu (500–100 μA), urządzenia na etapie projektowania technologicznego, które wykorzystują średnie natężenie prądu (100–500 μA) oraz urządzenia będące obiektami eksperymentalnych badań naukowych, które wykorzystują wysokie natężenie prądu (500–1000 μA). Model można również zastosować w symulacjach urządzeń o różnych szybkościach transmisji danych, które mają różne wymagania dotyczące zarówno szybkości transmisji, jak i prawdopodobieństwa błędu w jednym bicie informacji. W ten sposób model ten można wykorzystać zarówno w urządzeniach z szybką pamięcią w systemach komputerowych, jak i w czujnikach sygnałów, które są podłączone do sieci czujników lub podłączone do Internetu rzeczy
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