19 research outputs found
An Improved Wideband CMOS Current Driver for Bioimpedance Applications
A wideband, CMOS current driver for bioimpedance measurement applications has been designed employing nonlinear feedback. With the introduction of phase compensation, the circuit is able to operate at frequencies higher than the pole frequency of the output transconductor with minimum phase delay. Moreover, it isolates the poles required for stability from the high frequency characteristics of the output transconductor. The circuit has been simulated in a 0.35-μm CMOS technology and operates from ±2.5 V power supplies. Simulations show that for a 1 mAp-p output current, the phase delay is less than 1° for frequencies up to 3 MHz, rising to 1.5° at 5 MHz. Dual frequency currents to the load are demonstrated
Advances in Integrated Circuits and Systems for Wearable Biomedical Electrical Impedance Tomography
Electrical impedance tomography (EIT) is an impedance mapping technique that can be used to image the inner impedance distribution of the subject under test. It is non-invasive, inexpensive and radiation-free, while at the same time it can facilitate long-term and real-time dynamic monitoring. Thus, EIT lends itself particularly well to the development of a bio-signal monitoring/imaging system in the form of wearable technology. This work focuses on EIT system hardware advancement using complementary metal oxide semiconductor (CMOS) technology. It presents the design and testing of application specific integrated circuit (ASIC) and their successful use in two bio-medical applications, namely, neonatal lung function monitoring and human-machine interface (HMI) for prosthetic hand control. Each year fifteen million babies are born prematurely, and up to 30% suffer from lung disease. Although respiratory support, especially mechanical ventilation, can improve their survival, it also can cause injury to their vulnerable lungs resulting in severe and chronic pulmonary morbidity lasting into adulthood, thus an integrated wearable EIT system for neonatal lung function monitoring is urgently needed. In this work, two wearable belt systems are presented. The first belt features a miniaturized active electrode module built around an analog front-end ASIC which is fabricated with 0.35-µm high-voltage process technology with ±9 V power supplies and occupies a total die area of 3.9 mm². The ASIC offers a high power active current driver capable of up to 6 mAp-p output, and wideband active buffer for EIT recording as well as contact impedance monitoring. The belt has a bandwidth of 500 kHz, and an image frame rate of 107 frame/s. To further improve the system, the active electrode module is integrated into one ASIC. It contains a fully differential current driver, a current feedback instrumentation amplifier (IA), a digital controller and multiplexors with a total die area of 9.6 mm². Compared to the conventional active electrode architecture employed in the first EIT belt, the second belt features a new architecture. It allows programmable flexible electrode current drive and voltage sense patterns under simple digital control. It has intimate connections to the electrodes for the current drive and to the IA for direct differential voltage measurement providing superior common-mode rejection ratio (CMRR) up to 74 dB, and with active gain, the noise level can be reduced by a factor of √3 using the adjacent scan. The second belt has a wider operating bandwidth of 1 MHz and multi-frequency operation. The image frame rate is 122 frame/s, the fastest wearable EIT reported to date. It measures impedance with 98% accuracy and has less than 0.5 Ω and 1° variation across all channels. In addition the ASIC facilitates several other functionalities to provide supplementary clinical information at the bedside. With the advancement of technology and the ever-increasing fusion of computer and machine into daily life, a seamless HMI system that can recognize hand gestures and motions and allow the control of robotic machines or prostheses to perform dexterous tasks, is a target of research. Originally developed as an imaging technique, EIT can be used with a machine learning technique to track bones and muscles movement towards understanding the human user’s intentions and ultimately controlling prosthetic hand applications. For this application, an analog front-end ASIC is designed using 0.35-µm standard process technology with ±1.65 V power supplies. It comprises a current driver capable of differential drive and a low noise (9μVrms) IA with a CMRR of 80 dB. The function modules occupy an area of 0.07 mm². Using the ASIC, a complete HMI system based on the EIT principle for hand prosthesis control has been presented, and the user’s forearm inner bio-impedance redistribution is assessed. Using artificial neural networks, bio-impedance redistribution can be learned so as to recognise the user’s intention in real-time for prosthesis operation. In this work, eleven hand motions are designed for prosthesis operation. Experiments with five subjects show that the system can achieve an overall recognition accuracy of 95.8%
Firmware design of a portable medical device to measure the quadriceps muscle group after a total knee arthroplasty by EMG, LBIA and clinical score methods
El objetivo de este proyecto es el diseño del firmware de un dispositivo médico portátil para
mediciones de EMG y LBIA, que se utilizará para la evaluación de pacientes de artroplastia total de
rodilla, para estudiar la progresión de diferentes prótesis de rodilla (Medial-Pivot y Ultra-Congruente).
En la tesis, se expone el conocimiento actual de los estudios y aplicaciones de EMG y LBIA, junto con
los dispositivos comerciales utilizados actualmente. Además, se han estudiado e implementado las
diferentes técnicas de filtrado y procesamiento digital para señales de EMG y LBIAs. Adicionalmente,
se ha realizado un estudio estadÃstico preliminar con datos LBIA de 12 pacientes de artroplastia total
de rodilla.
El diseño del firmware de esta tesis incluye: los procesos de adquisición de datos con el uso de
diferentes ADCs (Conversor Analógico a Digital) (de la propia placa y externos, utilizando la interfaz SPI)
y un DAC (Conversor Digital a Analógico), el correspondiente procesamiento de la señal y la extracción
de sus caracterÃsticas, la comunicación con un dispositivo externo utilizando un módulo BLE externo
con interfaz UART, el proceso de encriptación de los datos médicos, la funcionalidad de manejo de
errores y la aproximación del nivel de baterÃa.
En esta tesis, todos los flujos de trabajo de los procesos se exponen y explican mediante diagramas de
flujo, mientras que se justifica cada cálculo y configuración. Además, todo el código correspondiente
se ha programado en lenguaje C y se expone en los anexos. También se ha revisado la normativa
aplicable y se ha analizado tanto el impacto ambiental como el coste económico del producto. Por
último, se proponen mejoras para futuros trabajos.The aim of this project is the firmware design for a portable medical device for EMG and LBIA
measurements which will be used for the assessment of total knee arthroplasty patients to study the
progression of different knee prostheses (Medial-Pivot and Ultra-Congruent). For its realization, the
state of the art of the EMG and LBIA studies and applications are exposed, along with the currently
used medical devices. In addition, the different digital filtering and processing techniques for these
studies have been studied and implemented. Furthermore, a preliminary statistical study has been
performed with LBIA data from 12 patients with total knee arthroplasty.
The firmware design of this thesis includes: the acquiring data processes with the use of different ADCs
(from the actual board and external, using the SPI interface) and a DAC, the corresponding signal
processing and feature abstraction, the communication with an external device using an external BLE
module with UART interface, the medical data encrypting process, the error handling functionality, and
the battery level approximation.
In this work, all the process workflows are exposed and explained using flowcharts, while every
calculation and configuration is justified. In addition, all the corresponding code has been programmed
using C language and exposed in the Annexes. Moreover, the applicable regulation has been reviewed,
and both the environmental impact and economic cost of the product have been analyzed. Finally,
improvements are proposed for future work.L'objectiu d'aquest projecte és el disseny del microprogramari d'un dispositiu mèdic portà til per a
mesures d'EMG i LBIA. L’aparell mèdic s'utilitzarà per a l'avaluació de pacients d'artroplà stia total de
genoll per estudiar la progressió de dues pròtesis de genoll (Medial-Pivot i Ultra- Congruent). En el
treball, s'exposa el coneixement actual dels estudis i aplicacions d'EMG i LBIA, juntament amb els
dispositius comercials utilitzats actualment. A més, s'han estudiat i implementat les diferents tècniques
de filtrat i processament digital dels senyals de EMG i LBIA. Addicionalment, s'ha fet un estudi estadÃstic
preliminar amb dades de LBIA de 12 pacients amb artroplà stia total de genoll.
El disseny del microprogramari d'aquesta tesi inclou: els processos d'adquisició de dades fent ús de
diferents ADCs (de la pròpia placa i externs, utilitzant la interfÃcie SPI) i un DAC, el processament dels
senyals i l'abstracció de les seves caracterÃstiques, la comunicació amb un dispositiu extern utilitzant
un mòdul BLE extern amb interfÃcie UART, el procés d'encriptació de les dades mèdiques, la
funcionalitat de l’avaluació d'errors i l'aproximació del nivell de bateria.
En aquest treball, totes les funcionalitats del dispositiu s'exposen i s'expliquen mitjançant diagrames
de flux i es justifiquen els cà lculs i configuracions corresponents. Tot el codi desenvolupat s'ha
programat en llenguatge C i s'exposa als annexos. A més, s'ha revisat la normativa aplicable i s'ha
analitzat tant l'impacte ambiental com el cost econòmic de l’aparell. Finalment, es proposen millores
per a futurs desenvolupaments
The Investigation and Implementation of electrical Impedance Tomography Hardware System
Electrical impedance tomography (EIT) is a medical imaging technology that
provides a tomographic representation of the distribution of electrical impedance within
the body. As the electrical impedance varies for different body tissues, it is possible to
characterize tissues from the images and to detect physiological events.
EIT systems have been developed from applying a single signal frequency to a
range of frequencies. Imaging at multiple frequencies significantly improves the ability to
characterize and differentiate heterogeneity within the region of interest. Applications of
EIT are limited by its poor resolution as a consequence of limited number of electrodes
and lack of independently published measurements.
In a practical EIT system design the parallel structure is normally adopted as it
provides a real time monitoring structure. However, there is a difficulty in expanding to a
2-dimensitional or 3-dimensitional high resolution imaging system, as the number of
electrodes increase.
In this thesis, a serial structure spectrum EIT system has been investigated and
developed. Modelling of the electrical circuit has shown that the system bandwidth is
degraded primarily by the signal transmission in the coaxial cable and multiplexer. To
remove the capacitive effect of these components, a distribute system concept has been
developed. The concept uses active electrodes in which a current source and a front end
amplifier are embedded in the electrode which makes direct contact with the tissue being
measured.
The active electrode is based on the Howland current source. The required high
output impedance of Howland current source can be realised by matching the two resistor
arms. However, from the electrical equivalent circuit analysis the actual output impedance
of this circuit was found to be degraded by the op-amp' s limited open loop gain,
especially at higher frequencies. To solve the problem, the author describes in detail a
novel method of compensating for the above effects. Subsequent circuit tests showed
significant improvement after the compensation. Further, to improve the small signal
noise ratio a programmable gain amplifier to adapt the frame data measurement was
developed. These developments have led to the feasibility of active electrodes. The thesis
describes in detail the development, of the MK2 EIT system which is presented as the
output of this research