642 research outputs found
Design and debugging of multi-step analog to digital converters
With the fast advancement of CMOS fabrication technology, more and more signal-processing functions are implemented in the digital domain for a lower cost, lower power consumption, higher yield, and higher re-configurability. The trend of increasing integration level for integrated circuits has forced the A/D converter interface to reside on the same silicon in complex mixed-signal ICs containing mostly digital blocks for DSP and control. However, specifications of the converters in various applications emphasize high dynamic range and low spurious spectral performance. It is nontrivial to achieve this level of linearity in a monolithic environment where post-fabrication component trimming or calibration is cumbersome to implement for certain applications or/and for cost and manufacturability reasons. Additionally, as CMOS integrated circuits are accomplishing unprecedented integration levels, potential problems associated with device scaling – the short-channel effects – are also looming large as technology strides into the deep-submicron regime. The A/D conversion process involves sampling the applied analog input signal and quantizing it to its digital representation by comparing it to reference voltages before further signal processing in subsequent digital systems. Depending on how these functions are combined, different A/D converter architectures can be implemented with different requirements on each function. Practical realizations show the trend that to a first order, converter power is directly proportional to sampling rate. However, power dissipation required becomes nonlinear as the speed capabilities of a process technology are pushed to the limit. Pipeline and two-step/multi-step converters tend to be the most efficient at achieving a given resolution and sampling rate specification. This thesis is in a sense unique work as it covers the whole spectrum of design, test, debugging and calibration of multi-step A/D converters; it incorporates development of circuit techniques and algorithms to enhance the resolution and attainable sample rate of an A/D converter and to enhance testing and debugging potential to detect errors dynamically, to isolate and confine faults, and to recover and compensate for the errors continuously. The power proficiency for high resolution of multi-step converter by combining parallelism and calibration and exploiting low-voltage circuit techniques is demonstrated with a 1.8 V, 12-bit, 80 MS/s, 100 mW analog to-digital converter fabricated in five-metal layers 0.18-µm CMOS process. Lower power supply voltages significantly reduce noise margins and increase variations in process, device and design parameters. Consequently, it is steadily more difficult to control the fabrication process precisely enough to maintain uniformity. Microscopic particles present in the manufacturing environment and slight variations in the parameters of manufacturing steps can all lead to the geometrical and electrical properties of an IC to deviate from those generated at the end of the design process. Those defects can cause various types of malfunctioning, depending on the IC topology and the nature of the defect. To relive the burden placed on IC design and manufacturing originated with ever-increasing costs associated with testing and debugging of complex mixed-signal electronic systems, several circuit techniques and algorithms are developed and incorporated in proposed ATPG, DfT and BIST methodologies. Process variation cannot be solved by improving manufacturing tolerances; variability must be reduced by new device technology or managed by design in order for scaling to continue. Similarly, within-die performance variation also imposes new challenges for test methods. With the use of dedicated sensors, which exploit knowledge of the circuit structure and the specific defect mechanisms, the method described in this thesis facilitates early and fast identification of excessive process parameter variation effects. The expectation-maximization algorithm makes the estimation problem more tractable and also yields good estimates of the parameters for small sample sizes. To allow the test guidance with the information obtained through monitoring process variations implemented adjusted support vector machine classifier simultaneously minimize the empirical classification error and maximize the geometric margin. On a positive note, the use of digital enhancing calibration techniques reduces the need for expensive technologies with special fabrication steps. Indeed, the extra cost of digital processing is normally affordable as the use of submicron mixed signal technologies allows for efficient usage of silicon area even for relatively complex algorithms. Employed adaptive filtering algorithm for error estimation offers the small number of operations per iteration and does not require correlation function calculation nor matrix inversions. The presented foreground calibration algorithm does not need any dedicated test signal and does not require a part of the conversion time. It works continuously and with every signal applied to the A/D converter. The feasibility of the method for on-line and off-line debugging and calibration has been verified by experimental measurements from the silicon prototype fabricated in standard single poly, six metal 0.09-µm CMOS process
Baseband analog front-end and digital back-end for reconfigurable multi-standard terminals
Multimedia applications are driving wireless network operators to add high-speed data services such as Edge (E-GPRS), WCDMA (UMTS) and WLAN (IEEE 802.11a,b,g) to the existing GSM network. This creates the need for multi-mode cellular handsets that support a wide range of communication standards, each with a different RF frequency, signal bandwidth, modulation scheme etc. This in turn generates several design challenges for the analog and digital building blocks of the physical layer. In addition to the above-mentioned protocols, mobile devices often include Bluetooth, GPS, FM-radio and TV services that can work concurrently with data and voice communication. Multi-mode, multi-band, and multi-standard mobile terminals must satisfy all these different requirements. Sharing and/or switching transceiver building blocks in these handsets is mandatory in order to extend battery life and/or reduce cost. Only adaptive circuits that are able to reconfigure themselves within the handover time can meet the design requirements of a single receiver or transmitter covering all the different standards while ensuring seamless inter-interoperability. This paper presents analog and digital base-band circuits that are able to support GSM (with Edge), WCDMA (UMTS), WLAN and Bluetooth using reconfigurable building blocks. The blocks can trade off power consumption for performance on the fly, depending on the standard to be supported and the required QoS (Quality of Service) leve
A Low-Power, Reconfigurable, Pipelined ADC with Automatic Adaptation for Implantable Bioimpedance Applications
Biomedical monitoring systems that observe various physiological parameters or electrochemical reactions typically cannot expect signals with fixed amplitude or frequency as signal properties can vary greatly even among similar biosignals. Furthermore, advancements in biomedical research have resulted in more elaborate biosignal monitoring schemes which allow the continuous acquisition of important patient information. Conventional ADCs with a fixed resolution and sampling rate are not able to adapt to signals with a wide range of variation. As a result, reconfigurable analog-to-digital converters (ADC) have become increasingly more attractive for implantable biosensor systems. These converters are able to change their operable resolution, sampling rate, or both in order convert changing signals with increased power efficiency.
Traditionally, biomedical sensing applications were limited to low frequencies. Therefore, much of the research on ADCs for biomedical applications focused on minimizing power consumption with smaller bias currents resulting in low sampling rates. However, recently bioimpedance monitoring has become more popular because of its healthcare possibilities. Bioimpedance monitoring involves injecting an AC current into a biosample and measuring the corresponding voltage drop. The frequency of the injected current greatly affects the amplitude and phase of the voltage drop as biological tissue is comprised of resistive and capacitive elements. For this reason, a full spectrum of measurements from 100 Hz to 10-100 MHz is required to gain a full understanding of the impedance. For this type of implantable biomedical application, the typical low power, low sampling rate analog-to-digital converter is insufficient. A different optimization of power and performance must be achieved.
Since SAR ADC power consumption scales heavily with sampling rate, the converters that sample fast enough to be attractive for bioimpedance monitoring do not have a figure-of-merit that is comparable to the slower converters. Therefore, an auto-adapting, reconfigurable pipelined analog-to-digital converter is proposed. The converter can operate with either 8 or 10 bits of resolution and with a sampling rate of 0.1 or 20 MS/s. Additionally, the resolution and sampling rate are automatically determined by the converter itself based on the input signal. This way, power efficiency is increased for input signals of varying frequency and amplitude
A built-in self-test technique for high speed analog-to-digital converters
Fundação para a Ciência e a Tecnologia (FCT) - PhD grant (SFRH/BD/62568/2009
Front-ends para LiDAR baseados em ADC e TDC
Autonomous vehicles are a promising technology to save over a million lives each
year that are lost in road accidents. However, bringing safe autonomous vehicles
to market requires massive development, starting with vision sensors. LiDAR is a
fundamental vision sensor for autonomous vehicles, as it enables high resolution
3D vision. However, automotive LiDAR is not yet a mature technology, and, also
requires massive development in many aspects.
This thesis aims to contribute to the maturity of LiDAR, focusing on sampling
architectures for LiDAR front-ends. Two architectures were developed.
The first is based on a pipelined ADC, available from an AD-FMCDAQ2-EBZ
board. The ADC is synchronized with the emitted pulse and able to sample
at 1 Gsample/s. The second architecture is based on a TDC that is directly
implemented in an FPGA. It relies on a tapped delay line topology comprising 45
delay elements and on a mux-based decoder, resulting in a resolution of 50 ps.
Preliminary test results show that both implementations operate correctly,
and are both suitable for sampling short pulses typically used by LiDARs. When
comparing both architectures, we conclude that an ADC consumes a significant
amount of power, and uses many FPGA resources. However, it samples the LiDAR
waveform without any loss of information, therefore enabling maximum range and
precision. The TDC is just the opposite: it consumes little power, and uses less
FPGA resources. However, it only captures one sample per pulse.Os veÃculos autónomos são uma tecnologia promissora para salvar mais de um
milhão de vidas por ano, colhidas por acidentes rodoviários. Contudo, colocar
veÃculos autónomos seguros no mercado requer inúmeros desenvolvimentos, a
começar por sensores de visão. O LiDAR é um sensor de visão fundamental para
veÃculos autónomos, pois permite uma visão 3D de alta resolução. Contudo, o
LiDAR automotivo não é uma tecnologia madura, e portanto requer também
desenvolvimento em vários aspectos.
Esta dissertação visa contribuir para a maturidade do LiDAR, com foco em
arquiteturas de amostragem para front-ends de LiDAR. Foram desenvolvidas duas
arquiteturas. A primeira assenta numa ADC pipelined, por sua vez implementada
numa placa de teste AD-FMCDAQ2-EBZ. A ADC opera em sincronismo com
o pulso emitido, e permite capturar amostras a 1 Gsample/s. A segunda
arquitetura assenta num TDC implementado diretamente numa FPGA. O
TDC baseia-se numa topologia tapped delay line com 45 linhas de atraso, e num
descodificador à base de multiplexers, permitindo uma resolução temporal de 50 ps.
Resultados preliminares mostram que ambas as implementações operam
corretamente, e são adequadas para amostrar pulsos curtos tipicamente associados
a LiDAR. Em termos comparativos, a arquitectura com base numa ADC tem
um consumo de potência considerável e requer uma quantidade significativa
de recursos da FPGA. Contudo, esta permite amostrar a forma de onda de
LiDAR sem nenhuma perda de informação, permitindo assim alcance e precisão
máximos. A arquitectura com base num TDC é exatamente o oposto: tem um
baixo consumo de potência e requer poucos recursos da FPGA. Contudo, permite
capturar apenas uma amostra por pulso.Mestrado em Engenharia Eletrónica e Telecomunicaçõe
High fidelity, radiation tolerant analog-to-digital converters
Techniques for an analog-to-digital converter (ADC) using pipeline architecture includes a linearization technique for a spurious-free dynamic range (SFDR) over 80 deciBels. In some embodiments, sampling rates exceed a megahertz. According to a second approach, a switched-capacitor circuit is configured for correct operation in a high radiation environment. In one embodiment, the combination yields high fidelity ADC (>88 deciBel SFDR) while sampling at 5 megahertz sampling rates and consuming <60 milliWatts. Furthermore, even though it is manufactured in a commercial 0.25-.mu.m CMOS technology (1 .mu.m=12.sup.-6 meters), it maintains this performance in harsh radiation environments. Specifically, the stated performance is sustained through a highest tested 2 megarad(Si) total dose, and the ADC displays no latchup up to a highest tested linear energy transfer of 63 million electron Volts square centimeters per milligram at elevated temperature (131 degrees C.) and supply (2.7 Volts, versus 2.5 Volts nominal)
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