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This report is submitted in partial fulfilment of the requirements of the degree of Master of Science
in Medical Electronics and Physics
in the University of London
By
Zhiwei (Jerry) Bao
Medical Electronics and Physics, Department of Engineering, Queen Mary, University of London, Mile End, LONDON E1 4NS
September 2003
Electrocardiography (ECG) has been used in clinical for the diagnosis and monitoring of heart abnormalities nearly a century. It remains the best and least invasive method for the task it performs. ECG recording normally uses three-electrode – two for the differential inputs of the ECG amplifiers and the third for ground. But what will be analyzed in this thesis were two-electrode ECG amplifiers.
Since 1980, Thakor and Webster suggested a two-electrode biopotential amplifier with bootstrapped buffer input amplifier, no others new two-electrode amplifiers have been developed except some improvement (Thakor and Webster, 1980). Two new two-electrode biopotential amplifiers without bootstrapped buffer have been developed in 2002 by Dobrev and Daskalov (Dobrev and Daskalov, 2002) (Dobrev, 2002).
In the project, these two new two-electrode amplifiers will be constructed to compare with the conventional one. The main relevant principles of ECG amplifier will be discussed to provide a basic understanding. Lots of practical techniques were also involved for producing a real ECG device to achieve measurement on human body.
The help and the support of many people was the main factor for accomplishing this project.
Firstly, the author would like to show his gratitude to the Department of Medical Electronics with Physics of the University of Queen Mary for giving him the opportunity to use the laboratory facilities and the equipment. This assistance was imperative for fulfilling all project aims.
The deepest appreciation goes for Dr. D. P. Jones, for his invaluable help and guidance. Without his support, the author would have faced many difficulties.
The author would also like to sincerely thank Dr. P. A. Kyriacou for his unlimited help and advices he provides for this project.
Acknowledgements also devote to author’s father Guoguang Bao, mother Huina Xu and friends for being very patient and supportive all the way through.
Investigation of New ECG Amplifier Circuits and Heart Rate Detector
Acknowledgements
Table of Contents
Index of the Figures
Chapter One INTRODUCTION
1.1 Introduction
1.2 Overview of Remaining Chapters
Chapter Two Electrocardiograph
2.1 Cardiovascular System
2.1.1 The Working Liquid: Blood
2.1.2 The Piping Network: Blood Vessels
2.1.3 The heart
2.2 The Electrocardiograph (ECG)
2.2.1 The Cardiac Conduction System
2.2.2 The ECG Waveform
Chapter Three Electrocardiograph Measurement
3.1 12-Lead Systems
3.1.1 Bipolar Leads (Einthoven Triangle)
3.1.2 Unipolar Leads
3.2 Electrodes
Chapter Four ECG Instrumentation
4.1 ECG requirement
4.2 ECG Instrument Design
4.2.1 Biopotential Electrode
4.2.2 Instrumentation Amplifier
4.2.3 Filter
4.2.4 Isolation
4.3 Driven-Right-Leg Circuit
Chapter Five HEART RATE DETECTOR
5.1 Heart Rate Detector
5.2 R-wave Detector
5.2.1 Full Wave Rectifier
5.2.2 Peak Detector
5.2.3 Comparator
5.2.4 Monostable Multivibrator
5.2.5 LED Indicator
Chapter Six TWO-ELECTORDE ELECTROCARDIOGRAPH
6.1 Power-line Interference
6.1.1 Magnetic Field Component
6.1.2 Electric Field Component
6.2 Conventional Two-electrode Amplifier
6.2.1 Model for ECG System
6.2.2 Conventional Two-electrode ECG Amplifier
6.3 Two-electrode Biopotential Amplifier with Current-Driven Inputs
6.3.1 Subscribe Line Interface Circuit (SLIC)
6.3.2 Current Source
6.3.3 Practical Amplifier Circuit
6.4 Two-electrode Non-differential Biopotential Amplifier
6.4.1 Potential Equaliser Amplifier
6.4.2 Practical Amplifier Circuit
Chapter Seven CIRCUIT DESIGN AND CONSTRUCTION
7.1 Methods Introduction
7.2 Practical Circuit Design
7.2.1 First Channel Circuit
7.2.2 Second Channel Circuit
7.2.3 Third Channel Circuit
7.2.4 Isolation Amplifier
7.2.5 Filter and Amplifier
7.2.6 Heart Rate Detector
7.2.7 Power Supply
7.2.8 Strip Board Circuit (Practical)
7.3 Evaluation and Performance
7.3.1 Performance on the ECG Simulator
7.3.2 Performance on the Human Body
7.3.3 Frequency Response
7.3.4 Evaluation
Chapter Eight CONCLUSIONS AND FURTHER DEVELOPMENT
8.1 Conclusion
8.2 Further Development
REFERENCES
GLOSSARY
Figure 2. 1: Internal Anatomy of the Heart (Kenneth, 1998)
Figure 2. 2: Systemic Circulation and Pulmonary Circulation (Kenneth, 1998)
Figure 2. 3: Cardiac Conduction System (Kenneth, 1998)
Figure 2. 4: A typical ECG waveform (Kenneth, 1998)
Figure 3. 1 The standard 12-lead ECG (Joseph, 2000)
Figure 3. 2 Einthoven limb leads and Einthoven triangle (Jaakko and Robert, 1995)
Figure 3. 3 Wilson Central Terminal (WCT) (Jaakko and Robert, 1995)
Figure 3. 4 Location of the chest electrodes (Jaakko and Robert, 1995)
Figure 3. 5 Goldberger augmented leads (Jaakko and Robert, 1995)
Figure 4. 1 Schematic block diagram of an electrocardiograph instrument (Richard, 2000)
Figure 4. 2 A typical instrumentation amplifier
Figure 4. 3 Characterizes of Band-pass and Band-stop Filters (Jerry, 2001)
Figure 4. 4 The effects of filter order on roll-off (Butterworth filter) (Jerry, 2001)
Figure 4. 5 Driven-right-leg Circuit (Joseph, 2000)
Figure 5. 1 R-Wave Detector Block Diagram
Figure 5. 2 Full-wave Rectifier
Figure 5. 3 Waveform on D and A
Figure 5. 4 Peak Detector
Figure 5. 5 Adjustable Comparator
Figure 5. 6 Monostable Multivibrator
Figure 5. 7 LED Indicator
Figure 6. 1 Equivalent Circuit of the Patient-amplifier Interface (Dobrev and Daskalov, 2002)
Figure 6. 2 Bootstrapped Input Amplifier
Figure 6. 3 Conventional Two-electrode ECG Amplifier
Figure 6. 4 Amplifier with Current Sources (Dobrev and Daskalov, 2002)
Figure 6. 5 (a) Voltage-driven Current Source (b) Norton Equivalent Circuit (Dobrev and Daskalov, 2002)
Figure 6. 6 Original Amplifier Circuit One (Dobrev and Daskalov, 2002)
Figure 6. 7 Equivalent Circuit of the Patient-amplifier Interface (Dobrev, 2002)
Figure 6. 8 Potential Equaliser Amplifier Equivalent Circuit (Dobrev, 2002)
Figure 6. 9 Original Amplifier Circuit Two (Dobrev, 2002)
Figure 7. 1 Circuit Blocks Diagram
Figure 7. 2 Two-electrode Non-differential Biopotential Amplifier
Figure 7. 3 Two-electrode Biopotential Amplifier with Current-driven Inputs
Figure 7. 4 Conventional Two-electrode Amplifier
Figure 7. 5 Filter and Amplifier
Figure 7. 6 Characterize of Filter
Figure 7. 7 Heart Rate Detector
Figure 7. 8 Power Supplies
Figure 7. 9 Strip Board Circuit
Figure 7. 10 Strip Copper Stuck Side
Figure 7. 11 Standard ECG signal
Figure 7. 12 Distorted ECG signal
Figure 7. 13 ECG from Author
Figure 7. 14 Distorted ECG from Author
Figure 7. 15 Frequency Response
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