- •Analysis and Application of Analog Electronic Circuits to Biomedical Instrumentation
- •Dedication
- •Preface
- •Reader Background
- •Rationale
- •Description of the Chapters
- •Features
- •The Author
- •Table of Contents
- •1.1 Introduction
- •1.2 Sources of Endogenous Bioelectric Signals
- •1.3 Nerve Action Potentials
- •1.4 Muscle Action Potentials
- •1.4.1 Introduction
- •1.4.2 The Origin of EMGs
- •1.5 The Electrocardiogram
- •1.5.1 Introduction
- •1.6 Other Biopotentials
- •1.6.1 Introduction
- •1.6.2 EEGs
- •1.6.3 Other Body Surface Potentials
- •1.7 Discussion
- •1.8 Electrical Properties of Bioelectrodes
- •1.9 Exogenous Bioelectric Signals
- •1.10 Chapter Summary
- •2.1 Introduction
- •2.2.1 Introduction
- •2.2.4 Schottky Diodes
- •2.3.1 Introduction
- •2.4.1 Introduction
- •2.5.1 Introduction
- •2.5.5 Broadbanding Strategies
- •2.6 Photons, Photodiodes, Photoconductors, LEDs, and Laser Diodes
- •2.6.1 Introduction
- •2.6.2 PIN Photodiodes
- •2.6.3 Avalanche Photodiodes
- •2.6.4 Signal Conditioning Circuits for Photodiodes
- •2.6.5 Photoconductors
- •2.6.6 LEDs
- •2.6.7 Laser Diodes
- •2.7 Chapter Summary
- •Home Problems
- •3.1 Introduction
- •3.2 DA Circuit Architecture
- •3.4 CM and DM Gain of Simple DA Stages at High Frequencies
- •3.4.1 Introduction
- •3.5 Input Resistance of Simple Transistor DAs
- •3.7 How Op Amps Can Be Used To Make DAs for Medical Applications
- •3.7.1 Introduction
- •3.8 Chapter Summary
- •Home Problems
- •4.1 Introduction
- •4.3 Some Effects of Negative Voltage Feedback
- •4.3.1 Reduction of Output Resistance
- •4.3.2 Reduction of Total Harmonic Distortion
- •4.3.4 Decrease in Gain Sensitivity
- •4.4 Effects of Negative Current Feedback
- •4.5 Positive Voltage Feedback
- •4.5.1 Introduction
- •4.6 Chapter Summary
- •Home Problems
- •5.1 Introduction
- •5.2.1 Introduction
- •5.2.2 Bode Plots
- •5.5.1 Introduction
- •5.5.3 The Wien Bridge Oscillator
- •5.6 Chapter Summary
- •Home Problems
- •6.1 Ideal Op Amps
- •6.1.1 Introduction
- •6.1.2 Properties of Ideal OP Amps
- •6.1.3 Some Examples of OP Amp Circuits Analyzed Using IOAs
- •6.2 Practical Op Amps
- •6.2.1 Introduction
- •6.2.2 Functional Categories of Real Op Amps
- •6.3.1 The GBWP of an Inverting Summer
- •6.4.3 Limitations of CFOAs
- •6.5 Voltage Comparators
- •6.5.1 Introduction
- •6.5.2. Applications of Voltage Comparators
- •6.5.3 Discussion
- •6.6 Some Applications of Op Amps in Biomedicine
- •6.6.1 Introduction
- •6.6.2 Analog Integrators and Differentiators
- •6.7 Chapter Summary
- •Home Problems
- •7.1 Introduction
- •7.2 Types of Analog Active Filters
- •7.2.1 Introduction
- •7.2.3 Biquad Active Filters
- •7.2.4 Generalized Impedance Converter AFs
- •7.3 Electronically Tunable AFs
- •7.3.1 Introduction
- •7.3.3 Use of Digitally Controlled Potentiometers To Tune a Sallen and Key LPF
- •7.5 Chapter Summary
- •7.5.1 Active Filters
- •7.5.2 Choice of AF Components
- •Home Problems
- •8.1 Introduction
- •8.2 Instrumentation Amps
- •8.3 Medical Isolation Amps
- •8.3.1 Introduction
- •8.3.3 A Prototype Magnetic IsoA
- •8.4.1 Introduction
- •8.6 Chapter Summary
- •9.1 Introduction
- •9.2 Descriptors of Random Noise in Biomedical Measurement Systems
- •9.2.1 Introduction
- •9.2.2 The Probability Density Function
- •9.2.3 The Power Density Spectrum
- •9.2.4 Sources of Random Noise in Signal Conditioning Systems
- •9.2.4.1 Noise from Resistors
- •9.2.4.3 Noise in JFETs
- •9.2.4.4 Noise in BJTs
- •9.3 Propagation of Noise through LTI Filters
- •9.4.2 Spot Noise Factor and Figure
- •9.5.1 Introduction
- •9.6.1 Introduction
- •9.7 Effect of Feedback on Noise
- •9.7.1 Introduction
- •9.8.1 Introduction
- •9.8.2 Calculation of the Minimum Resolvable AC Input Voltage to a Noisy Op Amp
- •9.8.5.1 Introduction
- •9.8.5.2 Bridge Sensitivity Calculations
- •9.8.7.1 Introduction
- •9.8.7.2 Analysis of SNR Improvement by Averaging
- •9.8.7.3 Discussion
- •9.10.1 Introduction
- •9.11 Chapter Summary
- •Home Problems
- •10.1 Introduction
- •10.2 Aliasing and the Sampling Theorem
- •10.2.1 Introduction
- •10.2.2 The Sampling Theorem
- •10.3 Digital-to-Analog Converters (DACs)
- •10.3.1 Introduction
- •10.3.2 DAC Designs
- •10.3.3 Static and Dynamic Characteristics of DACs
- •10.4 Hold Circuits
- •10.5 Analog-to-Digital Converters (ADCs)
- •10.5.1 Introduction
- •10.5.2 The Tracking (Servo) ADC
- •10.5.3 The Successive Approximation ADC
- •10.5.4 Integrating Converters
- •10.5.5 Flash Converters
- •10.6 Quantization Noise
- •10.7 Chapter Summary
- •Home Problems
- •11.1 Introduction
- •11.2 Modulation of a Sinusoidal Carrier Viewed in the Frequency Domain
- •11.3 Implementation of AM
- •11.3.1 Introduction
- •11.3.2 Some Amplitude Modulation Circuits
- •11.4 Generation of Phase and Frequency Modulation
- •11.4.1 Introduction
- •11.4.3 Integral Pulse Frequency Modulation as a Means of Frequency Modulation
- •11.5 Demodulation of Modulated Sinusoidal Carriers
- •11.5.1 Introduction
- •11.5.2 Detection of AM
- •11.5.3 Detection of FM Signals
- •11.5.4 Demodulation of DSBSCM Signals
- •11.6 Modulation and Demodulation of Digital Carriers
- •11.6.1 Introduction
- •11.6.2 Delta Modulation
- •11.7 Chapter Summary
- •Home Problems
- •12.1 Introduction
- •12.2.1 Introduction
- •12.2.2 The Analog Multiplier/LPF PSR
- •12.2.3 The Switched Op Amp PSR
- •12.2.4 The Chopper PSR
- •12.2.5 The Balanced Diode Bridge PSR
- •12.3 Phase Detectors
- •12.3.1 Introduction
- •12.3.2 The Analog Multiplier Phase Detector
- •12.3.3 Digital Phase Detectors
- •12.4 Voltage and Current-Controlled Oscillators
- •12.4.1 Introduction
- •12.4.2 An Analog VCO
- •12.4.3 Switched Integrating Capacitor VCOs
- •12.4.6 Summary
- •12.5 Phase-Locked Loops
- •12.5.1 Introduction
- •12.5.2 PLL Components
- •12.5.3 PLL Applications in Biomedicine
- •12.5.4 Discussion
- •12.6 True RMS Converters
- •12.6.1 Introduction
- •12.6.2 True RMS Circuits
- •12.7 IC Thermometers
- •12.7.1 Introduction
- •12.7.2 IC Temperature Transducers
- •12.8 Instrumentation Systems
- •12.8.1 Introduction
- •12.8.5 Respiratory Acoustic Impedance Measurement System
- •12.9 Chapter Summary
- •References
Examples of Special Analog Circuits and Systems |
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VB, Gto, and Vs do not change in time, so this steady-state analysis is valid. Using superposition, the system’s response to a time varying, δGt, can be examined. The transfer function, δV2 δGt, can be written:
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s(s2 |
ωn2 + s2ζ ωn + 1+ Vs βKAKP (10RC)) |
The damping of the cubic closed-loop system is adjusted with the attenuation β. The dc steady-state incremental gain is:
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A prototype of this system was run at 75 kHz and tested on the chests of
several volunteers after informed consent was obtained. Both δV2 δGt and
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V1 δGt were recorded. System outputs followed the subjects’ respiratory volumes, as expected.
A second type of IP makes use of a novel self-balancing, two-phase, lockin amplifier (LIA) developed by McDonald and Northrop (1993); the system is described in Northrop (2002). A lock-in amplifier is basically nothing more than a synchronous or phase-controlled full-wave rectifier followed by a low-pass filter. Its input is generally a noisy amplitude-modulated or double- sideband-suppressed carrier ac signal. The LIA output is a dc voltage proportional to the peak height of the input signal; the low-pass filter averages out the noise and any other zero-mean output component of the rectifier. Signal buried in as much as 60 dB of noise can be recovered by an appropriately set-up LIA.
Figure 12.51 illustrates how the LIA is connected to the voltage across the tissue, Vo, where Vo = Is (Rt + jBt), (Bt = −1/ωCt). Note that if the angle of Is is taken as zero (reference), then the angle of Vo is θs = tan−1(Bt Rt). The ac reference voltage, Vr, in phase with Is is used to control the LIA’s synchronous rectifier. Vr also allows one to monitor Is because Vr = Is RF. The self-nulling quadrature LIA outputs a dc voltage, Vϕ, proportional to the phase difference between Is and Vo and a dc voltage, Vp, proportional to the magnitude of the impedance, Zt , of the tissue under study. Vp and Vϕ follow the slow physiological variations in Zt caused by blood flow and/or breathing. The modulation of Rt and Bt by pulsatile blood flow or lung inflation can have diagnostic significance.
12.8.5Respiratory Acoustic Impedance Measurement System
Acoustic impedance in this section is defined as the vector (phasor) ratio of pressure (e.g., dynes/cm2) to the volume flow (e.g., cm3 sec) caused by that
© 2004 by CRC Press LLC
534 |
Analysis and Application of Analog Electronic Circuits |
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FIGURE 12.51
An impedance plethysmograph in which a constant ac current is passed through the body part being studied. A self-nulling, two phase lock-in amplifier is used to output voltages proportional to the impedance magnitude and angle. These voltages can be used to generate a polar plot of Zt.
pressure at a given sinusoidal frequency. Acoustic impedance has been used experimentally to try to diagnose obstructive lung diseases, as well as problems with the eardrum and middle ear (Northrop, 2002). This section describes the electronic circuitry associated with a simple prototype acoustic impedance measurement system. Figure 12.52 illustrates an electric circuit that is an analog of the acoustic system used to measure the complex acoustic impedance vector looking into the respiratory system through the mouth. Note that phasor sound pressure levels P1 and P2 are analogous to voltages; acoustic resistance, Rac, and complex acoustic impedance, Zac(jω), are analo-
gous to electrical resistance and impedance; and the complex volume flow · ω ω
rate, Q2(j ), is analogous to the phasor electrical current, I2(j ). Thus, by the “acoustical Ohm’s law”:
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© 2004 by CRC Press LLC
Examples of Special Analog Circuits and Systems |
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FIGURE 12.52
Electric circuit analog of the system used by the author to measure the acoustic impedance, Zac(f), of the respiratory system. In the circuit, voltage is analogous to pressure and current is analogous to volume flow.
Assume that a microphone output voltage is proportional to the incident acoustical sound pressure, i.e., V2 = Km P2, V1 = Km P1. Thus, the vector Zac(jω) can be found by substituting the conditioned microphone voltages into Equation 12.132.
Figure 12.53 illustrates the system devised by the author to measure Zac(jω) in polar form — i.e.,
Vθ – Zac (jω) = −–(V1 − V2 ), |
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where the angle of V2 is taken as 0 (reference).
Note that the angle between V1 and V2 (P1 and P2) is measured by passing these sinusoidal voltages into voltage comparators serving as zero-crossing detectors producing 50% duty cycle TTL waves with the same phase difference as the analog V1 and V2. The TTL phase difference is sensed by a digital phase detector of the MC4044 type (see Section 12.3.3), giving a dc output, Vθ. Simultaneously, the ac voltages (V1 − V2) and V2 are converted to their dc RMS values, VQ and VP, respectively. Vθ, VP, and VQ are sampled and converted to digital format and passed through a computer interface. The computer calculates and displays:
© 2004 by CRC Press LLC
536 |
Analysis and Application of Analog Electronic Circuits |
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FIGURE 12.53
Block diagram of the RAIMS system developed by the author. Infrasound pressure between 0.3 to 300 Hz was introduced into the trachea and lungs through the mouth. Output signal processing by computer allowed display of Zac(f ) in polar form over this frequency range.
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as a polar plot for the range of frequencies used.
An 8-in. loudspeaker drove the acoustic resistance chamber. The loudspeaker was driven by a power amplifier with sinusoidal input from a VFC. The VFC, in turn, got its dc input voltage, VC, from an 8-bit DAC with input from the computer.
© 2004 by CRC Press LLC