Noise Efficient Integrated Amplifier Designs for Biomedical Applications

The recording of neural signals with small monolithically integrated amplifiers is of high interest in research as well as in commercial applications, where it is common to acquire 100 or more channels in parallel. This paper reviews the recent developments in low-noise biomedical amplifier design based on CMOS technology, including lateral bipolar devices. Seven major circuit topology categories are identified and analyzed on a per-channel basis in terms of their noise-efficiency factor (NEF), input-referred absolute noise, current consumption, and area. A historical trend towards lower NEF is observed whilst absolute noise power and current consumption exhibit a widespread over more than five orders of magnitude. The performance of lateral bipolar transistors as amplifier input devices is examined by transistor-level simulations and measurements from five different prototype designs fabricated in 180 nm and 350 nm CMOS technology. The lowest measured noise floor is 9.9 nV/√Hz with a 10 µA bias current, which results in a NEF of 1.2

Amplificador de ganho variável controlado por razão cíclica

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2012Um amplificador de ganho variável (VGA) ajustado digitalmente pela razão cíclica do sinal de controle é apresentado neste trabalho. O circuito baseia-se no principio superregenerativo criado por Armstrong na década de 1920. Através desta técnica, consegue-se obter um ajuste fino do ganho sem necessidade de utilizar um DAC como interface entre o controle digital e o amplificador, como visto nos VGAs convencionais. O projeto foi contextualizado dentro de um sistema de aquisição de sinais biopotenciais e foi realizado em um processo de fabricação de 0,18 µ m CMOS padrão. Os resultados, a partir de simulações, mostraram que o projeto cumpre com as especificações, atingindo, entre outras características, uma faixa de ganho de 45 dB com uma banda de 1,25 kHz, um consumo de 6,4 µ W e uma faixa linear de 900 mV para uma THD de 0,5 %. Algumas medições preliminares foram feitas as quais comprovaram o funcionamento do circuito. Em complemento ao VGA integrado, uma versão com componentes discretos foi implementada com o intuito de verificar a sua funcionalidade numa aplicação real. O circuito final precisou de um AFE completo, o qual foi voltado para a medição de sinais cardíacos utilizando apenas dois eletrodos. Os resultados do protótipo discreto validaram o principio de amplificação proposto no VGA para este tipo de aplicação.Abstract : In this work, a variable-gain amplifier (VGA) adjusted by the duty-cycle of a control signal is presented. This circuit is based on the superregenerative concept created by Armstrong back in the 1920's. The chosen technique allows to perform a fine control of the gain without any DAC at the interface between the digital control and the amplifier, as usually seen in other VGAs. A 0.18mm standard CMOS process was used for the design. Specifications were satisfied by simulation results, in which, among other results, it was obtained a gain range of 45dB within a 1.25kHz bandwidth, a power consumption of 6.4mW and 900mV of linear range for a 0.5% THD. Some preliminary measurements of the chip proved also the correct functioning of the circuit. As a complement of the integrated VGA, a discrete-component version was also implemented in order to verify its functionality in a real application. The final circuit included a complete analog front-end which was optimize for cardiac signals measurement using only two electrodes. The results of the discrete-component prototype validated the amplification principle proposed in the VGA for this type of aplication

Instrumentación para neuroprótesis vestibles

La tesis pretende contribuir al conocimiento en adquisición de biopotenciales mediante técnicas no invasivas con aplicación a neuroprótesis (NPs). Las NPs son dispositivos que, interactuando con el cuerpo humano, permiten recuperar o reemplazar capacidades perdidas o disminuidas incrementando drásticamente la comodidad e independencia de las personas. Por lo tanto es de interés que las NPs se utilicen de forma muy sencilla y sin asistencia profesional, en correspondencia con el paradigma de los sistemas ``vestibles''. El objetivo general de la tesis es desarrollar etapas de instrumentación que permitan adquirir biopotenciales útiles a las NPs en forma robusta en las condiciones de medida impuestas por los sistemas vestibles. Por lo tanto, se desarrollan sistemas de adquisición de señal mixta en el estado del arte como plataformas para validar los modelos y circuitos de acondicionamiento propuestos, y se diseñan, implementan y verifican experimentalmente circuitos de acondicionamiento analógico que permiten enfrentar este desafío. En primer lugar, se desarrolla un circuito de realimentación de modo común con ganancia aumentada como estrategia general para la robustez frente a interferencia electromagnética. En segundo lugar se proponen electrodos activos para la medición de señales de electromiograma, desarrollando herramientas de análisis e implementando amplificadores para electrodos de múltiples contactos. Finalmente, los electrodos secos son el factor clave del registro de biopotenciales en sistemas vestibles. Por lo tanto, se desarrolla un electrodo activo con impedancia de entrada aumentada utilizando bootstrap de fuente y conservando una topología de baja complejidad.This thesis contributes to the topic of non-invasive biopotential acquisition techniques applied to Neuroprostheses (NPs). NPs are technological devices that, through interaction with the body, allow to recover or replace lost or diminished capabilities, thus dramatically increasing the comfort and independence of a person. It is desirable for NPs to be able to be used in a simple manner without professional assistance, in correspondence with the paradigm of wearable devices. The general objective of the thesis is to develop instrumentation circuits which allow to acquire the biopotential signals that NPs need robustly, even under the measurement conditions imposed by wearable systems. Therefore, state of the art mixed-signal acquisition systems are developed as a platform upon which models and conditioning circuits can be validated, and a set of analog conditioning circuits are designed, implemented, and experimentally tested. First, a common mode feedback circuit with increased gain is developed as a general strategy for increased robustness against electromagnetic interference. Next, active electrodes for electromyography signal measurement are proposed. An analysis tool as well as an implementation alternative for multiple-input electrodes are proposed. Finally, dry-contact electrodes are a key factor in wearable biopotential measurements. Hence, an active electrode with increased input impedance is developed using power supply bootstrapping and a low complexity topology.Facultad de Ingenierí