Low-Noise Energy-Efficient Sensor Interface Circuits

Today, the Internet of Things (IoT) refers to a concept of connecting any devices on network where environmental data around us is collected by sensors and shared across platforms. The IoT devices often have small form factors and limited battery capacity; they call for low-power, low-noise sensor interface circuits to achieve high resolution and long battery life. This dissertation focuses on CMOS sensor interface circuit techniques for a MEMS capacitive pressure sensor, thermopile array, and capacitive microphone. Ambient pressure is measured in the form of capacitance. This work propose two capacitance-to-digital converters (CDC): a dual-slope CDC employs an energy efficient charge subtraction and dual comparator scheme; an incremental zoom-in CDC largely reduces oversampling ratio by using 9b zoom-in SAR, significantly improving conversion energy. An infrared gesture recognition system-on-chip is then proposed. A hand emits infrared radiation, and it forms an image on a thermopile array. The signal is amplified by a low-noise instrumentation chopper amplifier, filtered by a low-power 30Hz LPF to remove out-band noise including the chopper frequency and its harmonics, and digitized by an ADC. Finally, a motion history image based DSP analyzes the waveform to detect specific hand gestures. Lastly, a microphone preamplifier represents one key challenge in enabling voice interfaces, which are expected to play a dominant role in future IoT devices. A newly proposed switched-bias preamplifier uses switched-MOSFET to reduce 1/f noise inherently.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137061/1/chaseoh_1.pd

NASA Hybrid Wing Aircraft Aeroacoustic Test Documentation Report

This report summarizes results of the Hybrid Wing Body (HWB) N2A-EXTE model aeroacoustic test. The N2A-EXTE model was tested in the NASA Langley 14- by 22-Foot Subsonic Tunnel (14x22 Tunnel) from September 12, 2012 until January 28, 2013 and was designated as test T598. This document contains the following main sections: Section 1 - Introduction, Section 2 - Main Personnel, Section 3 - Test Equipment, Section 4 - Data Acquisition Systems, Section 5 - Instrumentation and Calibration, Section 6 - Test Matrix, Section 7 - Data Processing, and Section 8 - Summary. Due to the amount of material to be documented, this HWB test documentation report does not cover analysis of acquired data, which is to be presented separately by the principal investigators. Also, no attempt was made to include preliminary risk reduction tests (such as Broadband Engine Noise Simulator and Compact Jet Engine Simulator characterization tests, shielding measurement technique studies, and speaker calibration method studies), which were performed in support of this HWB test. Separate reports containing these preliminary tests are referenced where applicable

Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

Ultra-Low-Power IoT Solutions for Sound Source Localization: Combining Mixed-Signal Processing and Machine Learning

With the prevalence of smartphones, pedestrians and joggers today often walk or run while listening to music. Since they are deprived of auditory stimuli that could provide important cues to dangers, they are at a much greater risk of being hit by cars or other vehicles. We start this research into building a wearable system that uses multichannel audio sensors embedded in a headset to help detect and locate cars from their honks and engine and tire noises. Based on this detection, the system can warn pedestrians of the imminent danger of approaching cars. We demonstrate that using a segmented architecture and implementation consisting of headset-mounted audio sensors, front-end hardware that performs signal processing and feature extraction, and machine-learning-based classification on a smartphone, we are able to provide early danger detection in real time, from up to 80m distance, with greater than 80% precision and 90% recall, and alert the user on time (about 6s in advance for a car traveling at 30mph). The time delay between audio signals in a microphone array is the most important feature for sound-source localization. This work also presents a polarity-coincidence, adaptive time-delay estimation (PCC-ATDE) mixed-signal technique that uses 1-bit quantized signals and a negative-feedback architecture to directly determine the time delay between signals in the analog inputs and convert it to a digital number. This direct conversion, without a multibit ADC and further digital-signal processing, allows for ultra low power consumption. A prototype chip in 0:18μm CMOS with 4 analog inputs consumes 78nW with a 3-channel 8-bit digital time-delay output while sampling at 50kHz with a 20μs resolution and 6.06 ENOB. We present a theoretical analysis for the nonlinear, signal-dependent feedback loop of the PCC-ATDE. A delay-domain model of the system is developed to estimate the power bandwidth of the converter and predict its dynamic response. Results are validated with experiments using real-life stimuli, captured with a microphone array, that demonstrate the technique’s ability to localize a sound source. The chip is further integrated in an embedded platform and deployed as an audio-based vehicle-bearing IoT system. Finally, we investigate the signal’s envelope, an important feature for a host of applications enabled by machine-learning algorithms. Conventionally, the raw analog signal is digitized first, followed by feature extraction in the digital domain. This work presents an ultra-low-power envelope-to-digital converter (EDC) consisting of a passive switched-capacitor envelope detector and an inseparable successive approximation-register analog-to-digital converter (ADC). The two blocks integrate directly at different sampling rates without a buffer between them thanks to the ping-pong operation of their sampling capacitors. An EDC prototype was fabricated in 180nm CMOS. It provides 7.1 effective bits of ADC resolution and supports input signal bandwidth up to 5kHz and an envelope bandwidth up to 50Hz while consuming 9.6nW

Plasmonic color filter array, high performance analog to digital converter architectures and novel circuit techniques

Part I: Plasmonic color filters can be manufactured at lower cost since they can be fabricated in single lithographic process step as compared to Fabry-Perot based filters. In addition, they have narrow passband making resolving sharp features in sample spectrum possible. Due to these benefits, in this thesis, Plasmonic color filters are investigated as alternative to conventional color filters and their feasibility for spectroscopy demonstrated through reconstruction of 6 sample spectra by using a set of 20 color filters. The error in reconstructed sample spectra is less than 0.137 root mean squared error across all samples. Part II: A novel 12-bit pipelined successive approximation analog to digital converter is investigated for high speed data conversion. The design was implemented in TSMC 65nm process to demonstrate the feasibility of the architecture. Furthermore, a high dynamic range audio delta sigma modulator using pseudo-pseudo differential topology was investigated and feasibility simulated using TSMC 65nm process. In addition, various novel systems and circuit techniques including efficient calibration of feedback digital to analog converters, new boosted switch and push-pull source follower circuits were investigated to improve upon existing circuit topologies

Analog front end circuits for highly integrated MUT based ultrasound imaging systems

Over the last 20 years, MEMS technology (which stands for Micro-Electro-Mechanical Systems) has revolutionized the world of consumer electronics in many ways, enabling the so-called second silicon revolution. Its production process leverages the same batch fabrication techniques used in the integrated circuit industry, which translates into low per-device production costs; in addition, the fabrication of highly integrated systems often is able to outperform their competitors made using the most precise macroscale level machining technique. Today, the most notable example of MEMS are microsensors and microactuators since they are a primary players in many market segments such as automotive, industrial, and, more recently, smart medical care systems. In this regard, the so-called MUTs (Micromachine Ultrasound Transducers) are fundamental for the development of next generation ultrasound imaging systems since they enable the cost effective production of highly complex 2D imaging arrays capable of capturing 3D volumes. This, combined with efficient edge AI to guide data acquisition and interpretation, will enable the development of medical diagnostic appliances that can be operated by users with limited medical knowledge. It is important to note that the real potential of MUTs starts to become fulfilled only when these miniaturized transducers are able to be merged onto a common silicon substrate along with integrated circuits: while the electronics are fabricated using integrated circuit process sequences (e.g., CMOS), the micromechanical components are integrated using compatible processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. For this reason, research nowadays is heavily focused into the design and optimization of highly integrated front end electronic interfaces for both CMUT based (capacitive MUTs) and PMUT based (piezoelectric MUTs) ultrasound imaging systems. In this framework, compact size, low power and high dynamic range are fundamental design targets for the circuital front end since they are key enablers for a widespread deployment of next generation ultrasound smart probes. The objective of this dissertation is to analyze different ultrasound systems and, for each of them, to identify and design the best integrated solution in order to optimize the front end performances. The proposed circuital interfaces are then fabricated and electrically characterized. This thesis is organized as follows: • Chapter 1 introduces the MUTs operative principle, their fabrication process and circuital modelling, as well as describing a modern imaging system for medical ultrasound diagnostic. • Chapter 2 presents the design and fabrication of a transceiver front end for a 1D PMUT array to be used in low frequency sonography, which was measured and proved to achieve significant optimization features. • Chapter 3 shows a design solution of a bipolar 3-level high-voltage pulser for PMUT probes which is able to minimize the number of mosfets and, thus, limits its overall area. • Chapter 4 describes a novel Low Noise Amplifier (LNA) solution to be employed in a 2D PMUT matrix; the LNA was designed to achieve optimal performances in terms of noise-power tradeoff as well as a minimal area occupation able to be integrated successfully into the pitch of the matrix. The circuit was fabricated and electrically characterized, demonstrating outstanding performances with respect to what is reported in open literature. • Chapter 5 verifies via a feasibility study that the same LNA previously described can be employed successfully in the fabrication of the analog front end of a 2D CMUT matrix, proving that it is a versatile solution as well. • Chapter 6, lastly, draws the conclusions of this work. This work is part of the Moore4Medical project funded by the ECSEL Joint Undertaking under grant number H2020-ECSEL-2019-IA-876190.Over the last 20 years, MEMS technology (which stands for Micro-Electro-Mechanical Systems) has revolutionized the world of consumer electronics in many ways, enabling the so-called second silicon revolution. Its production process leverages the same batch fabrication techniques used in the integrated circuit industry, which translates into low per-device production costs; in addition, the fabrication of highly integrated systems often is able to outperform their competitors made using the most precise macroscale level machining technique. Today, the most notable example of MEMS are microsensors and microactuators since they are a primary players in many market segments such as automotive, industrial, and, more recently, smart medical care systems. In this regard, the so-called MUTs (Micromachine Ultrasound Transducers) are fundamental for the development of next generation ultrasound imaging systems since they enable the cost effective production of highly complex 2D imaging arrays capable of capturing 3D volumes. This, combined with efficient edge AI to guide data acquisition and interpretation, will enable the development of medical diagnostic appliances that can be operated by users with limited medical knowledge. It is important to note that the real potential of MUTs starts to become fulfilled only when these miniaturized transducers are able to be merged onto a common silicon substrate along with integrated circuits: while the electronics are fabricated using integrated circuit process sequences (e.g., CMOS), the micromechanical components are integrated using compatible processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices. For this reason, research nowadays is heavily focused into the design and optimization of highly integrated front end electronic interfaces for both CMUT based (capacitive MUTs) and PMUT based (piezoelectric MUTs) ultrasound imaging systems. In this framework, compact size, low power and high dynamic range are fundamental design targets for the circuital front end since they are key enablers for a widespread deployment of next generation ultrasound smart probes. The objective of this dissertation is to analyze different ultrasound systems and, for each of them, to identify and design the best integrated solution in order to optimize the front end performances. The proposed circuital interfaces are then fabricated and electrically characterized. This thesis is organized as follows: • Chapter 1 introduces the MUTs operative principle, their fabrication process and circuital modelling, as well as describing a modern imaging system for medical ultrasound diagnostic. • Chapter 2 presents the design and fabrication of a transceiver front end for a 1D PMUT array to be used in low frequency sonography, which was measured and proved to achieve significant optimization features. • Chapter 3 shows a design solution of a bipolar 3-level high-voltage pulser for PMUT probes which is able to minimize the number of mosfets and, thus, limits its overall area. • Chapter 4 describes a novel Low Noise Amplifier (LNA) solution to be employed in a 2D PMUT matrix; the LNA was designed to achieve optimal performances in terms of noise-power tradeoff as well as a minimal area occupation able to be integrated successfully into the pitch of the matrix. The circuit was fabricated and electrically characterized, demonstrating outstanding performances with respect to what is reported in open literature. • Chapter 5 verifies via a feasibility study that the same LNA previously described can be employed successfully in the fabrication of the analog front end of a 2D CMUT matrix, proving that it is a versatile solution as well. • Chapter 6, lastly, draws the conclusions of this work. This work is part of the Moore4Medical project funded by the ECSEL Joint Undertaking under grant number H2020-ECSEL-2019-IA-876190

Analog and Mixed Signal Design towards a Miniaturized Sleep Apnea Monitoring Device

Sleep apnea is a sleep-induced breathing disorder with symptoms of momentary and often repetitive cessations in breathing rhythm or sustained reductions in breathing amplitude. The phenomenon is known to occur with varying degrees of severity in literally millions of people around the world and cause a range of chronicle health issues. In spite of its high prevalence and serious consequences, nearly 80% of people with sleep apnea condition remain undiagnosed. The current standard diagnosis technique, termed polysomnography or PSG, requires the patient to schedule and undergo a complex full-night sleep study in a specially-equipped sleep lab. Due to both high cost and substantial inconvenience, millions of apnea patients are still undiagnosed and thus untreated. This research work aims at a simple, reliable, and miniaturized solution for in-home sleep apnea diagnosis purposes. The proposed solution bears high-level integration and minimal interference with sleeping patients, allowing them to monitor their apnea conditions at the comfort of their homes. Based on a MEMS sensor and an effective apnea detection algorithm, a low-cost single-channel apnea screening solution is proposed. A custom designed IC chip implements the apnea detection algorithm using time-domain signal processing techniques. The chip performs autonomous apnea detection and scoring based on the patient’s airflow signals detected by the MEMS sensor. Variable sensitivity is enabled to accommodate different breathing signal amplitudes. The IC chip was fabricated in standard 0.5-μm CMOS technology. A prototype device was designed and assembled including a MEMS sensor, the apnea detection IC chip, a PSoC platform, and wireless transceiver for data transmission. The prototype device demonstrates a valuable screening solution with great potential to reach the broader public with undiagnosed apnea conditions. In a battery-operated miniaturized medical device, an energy-efficient analog-to-digital converter is an integral part linking the analog world of biomedical signals and the digital domain with powerful signal processing capabilities. This dissertation includes the detailed design of a successive approximation register (SAR) ADC for ultra-low power applications. The ADC adopts an asynchronous 2b/step scheme that halves both conversion time and DAC/digital circuit’s switching activities to reduce static and dynamic energy consumption. A low-power sleep mode is engaged at the end of all conversion steps during each clock period. The technical contributions of this ADC design include an innovative 2b/step reference scheme based on a hybrid R-2R/C-3C DAC, an interpolation-assisted time-domain 2b comparison scheme, and a TDC with dual-edge-comparison mechanism. The prototype ADC was fabricated in 0.18μm CMOS process with an active area of 0.103 mm^(2), and achieves an ENoB of 9.2 bits and an FoM of 6.7 fJ/conversion-step at 100-kS/s

Design of a hermetically sealed MEMS resonator with electrostatic actuation and capacitive third harmonic sensing

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Page 146 blank. Cataloged from PDF version of thesis.Includes bibliographical references (p. 138-140).A microscale beam resonator has been designed and fabricated for use as a modular pressure sensor for vacuum applications. The device dimensions have been optimized to provide measurable signals with low noise. Electrostatic actuation and sensing are both performed using only one pair of electrodes. The motion of the cantilever changes the capacitance of the actuation electrodes at a frequency three times that of the actuation signal. This method allows the desired motion to be picked out using a lock-in amplifier with minimal interference from other unwanted signals such as parasitic leakage and noise. Unlike previous work, packaging and electrical contacts have been integrated into the fabrication to create a hermetically sealed device that can easily be incorporated into other MEMS designs. Most resonators operate in vacuum because air damping at higher pressures greatly decreases both resonant frequency and quality factor. This loss is directly related to the pressure of the surrounding air, and therefore has been used in this design to measure the pressure. While the relationship is not linear, it is one-to-one. This means that once the device has been characterized, pressure can be determined uniquely over a range from atmospheric pressure down to ~10- Torr. The device was fabricated from two SOI wafers using standard wafer processing techniques. This means that unlike previous work, it can be readily integrated into other designs via wafer bonding. A single access port on the base provides a connection between the otherwise hermetically sealed sensor and other devices. To prevent squeeze film damping from limiting the motion of the beam, the cantilever tip has been perforated with an array of holes and a cavity was etched above where the cantilever will oscillate. Electrical contact can easily be made with the device as fabricated, so no additional packaging is necessary. While the fabricated devices are hermetically sealed, resonance was never detected due to a combination of factors including: poor wafer bonding, parasitic leakage, a Schottky barrier at one terminal and a design error that led to an unexpectedly high frequency and quality factor. Modifications to the current design are proposed that should eliminate these problems in the next iteration.by Eric B. Newton.S.M