Analogue micropower FET techniques review

A detailed introduction to published analogue circuit design techniques using Si and Si/SiGe FET devices for very low-power applications is presented in this review. The topics discussed include sub-threshold operation in FET devices, micro-current mirrors and cascode techniques, voltage level-shifting and class-AB operation, the bulk-drive approach, the floating-gate method, micropower transconductance-capacitance and log-domain filters and strained-channel FET technologies

CMOS Hyperbolic Sine ELIN filters for low/audio frequency biomedical applications

Hyperbolic-Sine (Sinh) filters form a subclass of Externally-Linear-Internally-Non- Linear (ELIN) systems. They can handle large-signals in a low power environment under half the capacitor area required by the more popular ELIN Log-domain filters. Their inherent class-AB nature stems from the odd property of the sinh function at the heart of their companding operation. Despite this early realisation, the Sinh filtering paradigm has not attracted the interest it deserves to date probably due to its mathematical and circuit-level complexity. This Thesis presents an overview of the CMOS weak inversion Sinh filtering paradigm and explains how biomedical systems of low- to audio-frequency range could benefit from it. Its dual scope is to: consolidate the theory behind the synthesis and design of high order Sinh continuous–time filters and more importantly to confirm their micro-power consumption and 100+ dB of DR through measured results presented for the first time. Novel high order Sinh topologies are designed by means of a systematic mathematical framework introduced. They employ a recently proposed CMOS Sinh integrator comprising only p-type devices in its translinear loops. The performance of the high order topologies is evaluated both solely and in comparison with their Log domain counterparts. A 5th order Sinh Chebyshev low pass filter is compared head-to-head with a corresponding and also novel Log domain class-AB topology, confirming that Sinh filters constitute a solution of equally high DR (100+ dB) with half the capacitor area at the expense of higher complexity and power consumption. The theoretical findings are validated by means of measured results from an 8th order notch filter for 50/60Hz noise fabricated in a 0.35μm CMOS technology. Measured results confirm a DR of 102dB, a moderate SNR of ~60dB and 74μW power consumption from 2V power supply

Analogue micropower FET techniques review

Accepted versio

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

Study of fault tolerant software technology for dynamic systems

The major aim of this study is to investigate the feasibility of using systems-based failure detection isolation and compensation (FDIC) techniques in building fault-tolerant software and extending them, whenever possible, to the domain of software fault tolerance. First, it is shown that systems-based FDIC methods can be extended to develop software error detection techniques by using system models for software modules. In particular, it is demonstrated that systems-based FDIC techniques can yield consistency checks that are easier to implement than acceptance tests based on software specifications. Next, it is shown that systems-based failure compensation techniques can be generalized to the domain of software fault tolerance in developing software error recovery procedures. Finally, the feasibility of using fault-tolerant software in flight software is investigated. In particular, possible system and version instabilities, and functional performance degradation that may occur in N-Version programming applications to flight software are illustrated. Finally, a comparative analysis of N-Version and recovery block techniques in the context of generic blocks in flight software is presented

Near-surface magnetic resonance imaging

Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) are well established techniques. Both require samples to be placed inside spatially-homogeneous static magnetic and radio frequency magnetic fields. This research focuses on applying the principles of NMR spectroscopy and imaging to design a system that can produce images of the NMR signal from a sample placed adjacent to it. The long term goal is to image at distances of meters from the device. The specific application of interest is locating buried utilities in fully-hydrated soils by identifying non-signal bearing features in an NMR signal rich background. This thesis asserts that a minimum of three questions need to be answered to determine if near surface MRI is feasible. 1.) Can the Earth\u27s magnetic field (BEarth) be used as the applied static magnetic field? 2.) Is the NMR signal from the water found in fully-hydrated soils sufficient for imaging? 3.) Can a near-surface imaging technique be developed? This thesis research attempts to answer each of these questions in three stand alone investigations: 1.) In situ measurements of BEarth, 2.) laboratory-based relaxation studies of synthetic sands, and 3.) the development of a proof-of-concept near-surface magnetic resonance imaging device. It is the assertion of this thesis that the results of these three studies are needed to begin to properly understand the signal space that a viable surface instrument would have to operate within for practical use. The BEarth results showed that better selection performance would be achieved using a larger B0 field. The synthetic sands study gave results suggest that relaxation behavior of water was highly deterministic based on particle diameter. The imaging performance of the unilateral MRI device was measured and the results demonstrate that imaging at depths on the order of one centimeter is possible. Overall, the results from these three studies have advanced the understanding of near-surface inhomogeneous magnetic resonance, while giving strong indications that near-field MRI in fully-hydrated soil is promising

Multifrequency Aperture-Synthesizing Microwave Radiometer System (MFASMR). Volume 1

Background material and a systems analysis of a multifrequency aperture - synthesizing microwave radiometer system is presented. It was found that the system does not exhibit high performance because much of the available thermal power is not used in the construction of the image and because the image that can be formed has a resolution of only ten lines. An analysis of image reconstruction is given. The system is compared with conventional aperture synthesis systems