Analysis and Application of Analog Electronic Circuits to Biomedical Instrumentation

Citation

Northrop, R. B. (2012). Analysis and Application of Analog Electronic Circuits to Biomedical Instrumentation (2nd ed.). CRC Press.

Chapter Summary

The book has fifteen chapters, an appendix, a glossary and a bibliography with recommended reading. The publisher states that every chapter includes an introduction and a chapter summary. The second edition adds three chapters (power amplifiers, wireless patient monitoring, and RFID, GPS and ultrasonic tags), a glossary and new end-of-chapter problems and examples. Chapter titles below follow the publisher's table of contents; the numbering follows the order in which the chapters are listed.

Chapter 1: Sources and Properties of Biomedical Signals

The opening chapter describes sources of endogenous bioelectric signals (nerve and muscle action potentials, the electrocardiogram and other biopotentials), the electrical properties of bioelectrodes, and exogenous bioelectric signals. It sets out the signals that the later circuits must condition.

Chapter 2: Properties and Models of Semiconductor Devices Used in Analog Electronic Systems

This chapter covers pn junction diodes, midfrequency models for bipolar and field-effect transistors, high-frequency transistor models and simple transistor amplifiers, and photons, photodiodes, photoconductors, LEDs and laser diodes.

Chapters 3–5: The Differential Amplifier; General Properties of Electronic, Single-Loop Feedback Systems; Feedback, Frequency Response, and Amplifier Stability

Chapter 3 treats differential amplifier architecture, common-mode rejection ratio, high-frequency gains, input resistance, the effect of source impedance on low-frequency CMRR, and the use of op amps to make differential amplifiers for medical applications. Chapter 4 classifies electronic feedback systems and describes the effects of negative voltage feedback, negative current feedback and positive voltage feedback. Chapter 5 reviews amplifier frequency response, defines feedback stability, and uses root locus in feedback amplifier design and in the design of linear oscillators.

Chapters 6–7: Operational Amplifiers and Comparators; Introduction to Analog Active Filters

Chapter 6 covers the ideal and practical op amp, gain-bandwidth relations for voltage-feedback and current-feedback op amps, analog voltage comparators and some applications in biomedicine. Chapter 7 introduces active filter applications and types, including electronically tunable filters.

Chapters 8–9: Instrumentation and Medical Isolation Amplifiers; Noise and the Design of Low-Noise Signal Conditioning Systems for Biomedical Applications

Chapter 8 covers instrumentation amplifiers, medical isolation amplifiers, safety standards for medical electronic amplifiers and medical-grade power supplies. Chapter 9 is a long treatment of noise: descriptors of random noise, propagation of noise through linear time-invariant filters, noise factor and figure, cascaded noisy amplifiers, noise in differential amplifiers, the effect of feedback on noise, examples of noise-limited resolution, some low-noise amplifiers, and "the art of low-noise signal conditioning system design".

Chapters 10–12: Digital Interfaces; Modulation and Demodulation of Biomedical Signals; Power Amplifiers and Their Applications in Biomedicine

Chapter 10 covers aliasing and the sampling theorem, digital-to-analog converters, sample-and-hold circuits, analog-to-digital converters and quantization noise. Chapter 11 treats amplitude, phase and frequency modulation and demodulation, and modulation of digital carriers. Chapter 12 covers power output devices, power amplifier classes and efficiency, class D amplifiers, nonlinearity and distortion, IC voltage regulators and heatsinking.

Chapters 13–14: Wireless Patient Monitoring; RFID Tags, GPS Tags, and Ultrasonic Tags Used in Ecological Research

Chapter 13 covers sensors and signals in wireless patient monitoring, modulation, RF communication protocols, UHF transmitters and antennas, complete systems, how wireless monitoring reduces the probability of patient microshock, and privacy. Chapter 14 covers RFID tag applications, tag design and readers, GPS tags and ultrasonic tags in fisheries biology.

Chapter 15: Examples of Special Analog Circuits and Systems Used in Biomedical Instrumentation

The last chapter treats the phase-sensitive rectifier, phase detectors, voltage- and current-controlled oscillators, phase-lock loops, true RMS converters and IC temperature sensors, and ends with three examples of medical instrumentation systems.

Key Concepts

Chapters 1–5: signals, devices and feedback

• Bioelectric signals and bioelectrodes: the properties of signals such as the ECG, and of the electrodes that pick them up, set the requirements the circuits must meet.
• Common-mode rejection ratio: a differential amplifier's ability to reject interference that appears on both inputs.
• Negative feedback and stability: how feedback alters gain, input and output resistance and frequency response, and when it becomes unstable; root locus as a design tool.

Chapters 6–9: amplifiers, filters, isolation and noise

• Operational amplifier: the ideal and practical op amp as the basic building block, with its gain-bandwidth limits.
• Active filters: filter types and their application to biomedical signals.
• Isolation and safety: isolation amplifiers, safety standards and medical-grade power supplies.
• Noise factor and noise figure: measures of how much noise an amplifier adds, and how noise accumulates in cascaded stages.

Chapters 10–15: interfaces, transmission and special circuits

• Sampling, aliasing and quantization noise: the limits on converting signals to digital form.
• Modulation: carrying biomedical signals on sinusoidal or digital carriers.
• Class D amplification: switched power amplifiers and their efficiency.
• Wireless patient monitoring: protocols, antennas, microshock and privacy.
• Phase-lock loops and phase-sensitive detection: special circuits for recovering signals.

Critical Analysis

Strengths

• A single signal chain. The book follows the path from the signal source (Chapter 1) and devices (Chapter 2) through amplifiers, feedback, filters, isolation, noise, conversion and transmission, so each circuit block is explained as part of a recording system.
• Noise treated at length. Chapter 9 has nine sections on noise, from random-noise descriptors to low-noise design, and the publisher highlights the mathematical tools for describing noise and its propagation through linear systems.
• Medical safety is built in. Isolation amplifiers, safety standards, medical-grade power supplies and the microshock risk in wireless monitoring appear as topics in their own right.
• Support for study. The second edition includes a glossary of terms from electronics, physiology and biochemistry, new end-of-chapter problems and examples, and an introduction and summary in every chapter.

Limitations

• Analog-focused. Digital conversion is covered in a single chapter. Digital signal processing and instrument software do not appear in the contents.
• Few sensors. Apart from bioelectrodes, photonic devices and IC temperature sensors, the contents list no chapters on transducers for pressure, flow or chemical measurement; a general instrumentation text is needed for those.
• Some chapters serve a narrower readership. Chapter 14 is on tags for ecological research, such as fisheries biology, and may be of limited use to readers focused on clinical instrumentation.
• Strong prerequisites. Topics such as root locus, noise analysis and op amp design call for undergraduate circuit analysis and electronics, Laplace transforms and basic signals and systems.
• Dated protocols. Published in 2012, the book's wireless chapter covers Wi-Fi and Bluetooth as they stood then.

Where It Fits in the Course

Northrop's book is a specialist treatment of the amplifier and signal-conditioning stage of biomedical instruments. Christe's Introduction to Biomedical Instrumentation is an accessible introduction to hospital equipment, and Webb's Principles of Biomedical Instrumentation follows the design of an instrument step by step from sensor to safety testing. Webster and Nimunkar's Medical Instrumentation: Application and Design is the standard engineering textbook covering sensors, amplifiers and signal conditioning and then clinical measurements, and Togawa, Tamura and Öberg's Biomedical Sensors and Instruments is organised by the quantity measured.

Read one of the broader texts first. Northrop then supplies the depth in electronics, noise and feedback that those books summarise in a chapter or two, and it is the book to return to when a design problem is about amplifier choice, noise budget or isolation.

How to Use This Book

The book is for graduate students and practising engineers in biomedical engineering who design or analyse recording electronics. Undergraduate circuit analysis and electronics, Laplace transforms and basic signals and systems are the practical prerequisites.

A practical plan:

• Core: Chapters 1, 3, 4–6, 8 and 9 for signals, differential and feedback amplifiers, op amps, isolation and noise.
• Filters and conversion: Chapters 7 and 10 as needed for the application at hand.
• Optional by interest: Chapter 2 as a device refresher; Chapters 11–15 for modulation, power amplifiers, wireless monitoring and special circuits.
• Use the problems and glossary. Work the end-of-chapter problems, and use the glossary for unfamiliar terms.