CHAPTER 8CHAPTER 8. Bioinstrumentation

BioinstrumentationBioinstrumentation

Electronics

Basic Parameters

AmplifierParameters

Passive Elements

ActiveElements Filter

Linear Circuit OP AmpLinear CircuitNetwork Analysis

OP Amp

8 12 TIME VARYING SIGNALS8.12 TIME-VARYING SIGNALS

V, I = Acos(ωt+φ)f = s(t) = Acos(ωt+φ)where t : time

A

tφ/ ω

where t : time,A : amplitude, ω : frequency, φ : phase angle

-A

T = 1/f = 2π/ω

- φ/ ωφ : phase angle

f = Re {Aejωt+φ}

Euler’s FormulaEuler s FormulaEuler’s formula :Euler s formula :

Relationship to trigonometry :

Proofs : using Talyor series,Proofs : using Talyor series,

PhasorPhasor• In physics and engineering, a phasor is a representationIn physics and engineering, a phasor is a representation

of a sine wave whose amplitude(A), phase(θ), and frequency(ω) are time-invariantPh d th d d i th f• Phasors reduce the dependencies on the frequency factor, which also includes the time-dependence of the sine wave, thereby simplifying certain kinds ofsine wave, thereby simplifying certain kinds of calculations.

• Using phasors, it can be factored out, leaving just the t ti lit d d h i f ti t b bi dstatic amplitude and phase information to be combined

algebraically (rather than trigonometrically). • Similarly linear differential equations can be reduced to• Similarly, linear differential equations can be reduced to

algebraic ones. phasor

Phasor AnalysisPhasor Analysis• Resistor Impedance :p• Capacitor Reactance :• Inductor Reactance :• Inductor Reactance :

Transform Analysis• In mathematics a transform is an operator applied to a

function so that under the transform certain operations• In mathematics a transform is an operator applied to a

function so that under the transform certain operationsfunction so that under the transform certain operations are simplified.function so that under the transform certain operations are simplified.

Laplace Frequency (Fourier)Time Domain Laplace domain

Frequency (Fourier) domain

V v(t) V(s) V(jω)

i i(t) I(s) I(jω)

R v(t)=R•i(t) V(s)=R•I(s) V(jω)=R•I(jω)

L v(t)=L • di(t)/dt V(s)=Ls•I(s) V(jω)=jωL•I(jω)

C i(t)=C • dv(t)/dt I(s)=Cs•V(s) I(jω)= jωC•V(jω)

Differential equation Algebraic equationsOut/In

Differential equation(impulse response)

Algebraic equations(transfer function)

Transfer Function

ViVoutVin

( )V ( )V j

• Transfer function :• Transfer function :

( )( )( )

out

in

V sT sV s

=( )( )( )

out

in

V jT jV j

ωωω

=

• Transfer function : – relationship between the input and output

of an instrument or system (in transform domain)

• Transfer function : – relationship between the input and output

of an instrument or system (in transform domain)of an instrument or system (in transform domain),

– transform of the impulse responseof an instrument or system (in transform domain),

– transform of the impulse response

Signal RepresentationTime Time vsvs FrequencyFrequency

시간축주파수축

시간축

Fourier SeriesHarmonic Analysis

Fourier Series : 주기적인신호는기본주기와이의정수배주기를갖는 sine파(고조파:harmonics)형의합으로나타낼수 있다.

Fundamental

Harmonics

Effect of Higher Harmonics

Original waveformN=1 N=3

Reconstructed waveform

N=7 N=19

N=79

abruptly changing points in time

Effect of Higher Harmonics

Effect of Higher Harmonics

시간과 주파수 도메인

8 11 OPERATIONAL8.11 OPERATIONAL AMPLIFIERAMPLIFIER

OP Amp HistoryOP Amp HistoryO i l A lifi i d i• Operational Amplifier : mentioned in the paper “Analysis of Problems in Dynamics” by John R. Ragazzinni 1943

• OP Amp concepts advanced around 1947

• K2 W tubes general purpose computing• K2-W tubes general purpose computing OP Amp from G.A. Philbrick Researches Inc. in 1952

• Solid-state OP Amp : by Burr-Brown & G.A. Philbrick Researches Inc. in 1962

• µA702 : first IC type OP Amp by• µA702 : first IC type OP Amp by Fairchild Semiconductor in 1963, $300, military & aerospace onlyA741 fi t i t ll t d OP• µA741 : first internally compensated OP

Amp by National Semiconductor in 1968

OP-Amp

Originally, the term, “Operational Amplifier,” was used in Originally, the term, “Operational Amplifier,” was used in g y, , p p ,the computing field to describe amplifiers that performed various mathematical operations.

g y, , p p ,the computing field to describe amplifiers that performed various mathematical operations.

It was found that the application of negative feedback around a high gain DC amplifier would produce a circuit

It was found that the application of negative feedback around a high gain DC amplifier would produce a circuit with a precise gain characteristic that depended only on the feedback used. with a precise gain characteristic that depended only on the feedback used.

By the proper selection of feedback components, operational amplifier circuits could be used to add,

bt t i t t d diff ti t

By the proper selection of feedback components, operational amplifier circuits could be used to add,

bt t i t t d diff ti tsubtract, average, integrate, and differentiate.

What the operational amplifier can do is limited only by

subtract, average, integrate, and differentiate.

What the operational amplifier can do is limited only by the imagination and ingenuity of the user.the imagination and ingenuity of the user.

OP-Amp

Circuit Model of the Single Ended Operational AmplifierCircuit Model of the Single Ended Operational AmplifierOp Amp Package Options

Pin description for general and forEquivalent Circuit of the Ideal Operational Amplifier

Pin description for general and for the 741 op-amp.

OP-Amp Circuit Analysis

Open Loop Operation

T I t t F db k Ci it Voltage Follo erTwo Important Feedback Circuits Voltage Follower

OP-Amp Circuit Analysis

The Differential Output Operational Amplifier

Biopotential Measurement- principle

Active cell → bathing medium → body surfaceActive cell → bathing medium → body surface(Constant Current Source) (Volume Conductor) (Potential Difference)

Ve eV

seaNa+ Cl-

BAT

sea

Biopotential Measurement - meaning

Source identification problem from projections

v source lead= •uuuuuuur uuuur

ECG lead EEG lead

Bioelectric Signal Amplifier3-electrode(active(+), active(-), reference/common/GND)

g p

Differential amplifier

Requirements of Amplifier1 Differential amplifier : subtraction1. Differential amplifier : subtraction 2. High input impedance3 Total gain and bandwidth3. Total gain and bandwidth

Noise

Unwanted signal componentUnwanted signal componentSignal-to-Noise Ratio(SNR)Internal vs External SourceSignal-to-Noise Ratio(SNR)Internal vs External Source• internal noise : in audio amplifier

– electronic components• internal noise : in audio amplifier

– electronic componentsp• external noise : in biopotential amplifier

– power line hum (capacitive coupling)

p• external noise : in biopotential amplifier

– power line hum (capacitive coupling)power line hum (capacitive coupling)– EM waves(radio, ESU,..etc)

supply voltage fluctuation

power line hum (capacitive coupling)– EM waves(radio, ESU,..etc)

supply voltage fluctuation– supply voltage fluctuation– maternal signal in fetal monitoring

Diff ti l A lifi

– supply voltage fluctuation– maternal signal in fetal monitoring

Diff ti l A lifiDifferential AmplifierDifferential Amplifier

Single-sided Amplifier

-A

C1

Z+

AsC2 EbEp

Zs

60Hz, 220V Eo

C1

C2

Equivalent Circuit

-A

Shield Room C

+As

-Ep

+As

p60Hz, 220V

Reduce C1 or ZsReduce C1 or Zs

Missions of Bio-Amplifier

• Amplifying the differential signal hil li th i l

• Amplifying the differential signal hil li th i lwhile canceling the common signal

to both electrodes : differential while canceling the common signal to both electrodes : differential amplifier/instrumentation amplifieramplifier/instrumentation amplifier

• Keeping the common signal as small as possible : ground

• Keeping the common signal as small as possible : groundas possible : ground electrode/negative feedback as possible : ground electrode/negative feedback

Differential Amplifier

by Matthews 1934by Matthews 1934At input terminals;

– Ep is in pahse through

At input terminals;– Ep is in pahse through

C1

Ep is in pahse through C1 and C2

– Eb is out of phase

Ep is in pahse through C1 and C2

– Eb is out of phaseC2

C1

+

-Ad

C2Eb

EpZs

60Hz, 220V

Ad

+

-

Eo

Try to make C1 and C2 same!Try to make C1 and C2 same!

Equivalent Circuit

Differential Amplifier

CMRR(common mode rejection ratio) : CMRR(common mode rejection ratio) : ( j )figure of merit for differential amplifierThe higher, the better : 106(=120dB) @ 60Hz

( j )figure of merit for differential amplifierThe higher, the better : 106(=120dB) @ 60Hzg , ( ) @g , ( ) @

EdAd

-

EcAd

-

Eo+ Eo

+

Differential gain:Gd = Eo/Ed Common gain:Gc = Eo/Ec

CMRR = Gd/GcCMRR = Gd/Gc

Differential Amplifier

R2Low Input Impedance!Low Input Impedance!

-Ein

E1

R1

+

Eout

in

E2 R3

RR4

⎛ ⎞

By superposition rule;

2 4 2 21 2 2 1

1 3 4 1 1

1 ( )out d inR R R RE E E E E G ER R R R R

⎛ ⎞= − + + = − =⎜ ⎟+ ⎝ ⎠

1 3 2 4,R R R R= =Need perfect match!Need perfect match!

Instrumentation Amplifier

+E

R4

R5-

E1

+

-R1

R2

R3Ein

EoutR6

R7

-

E2 +2

522 1dRRG

R R⎛ ⎞⎛ ⎞

= +⎜ ⎟⎜ ⎟⎝ ⎠⎝ ⎠

2 3 4 6 5 7, ,R R R R R R= = =if1 4R R⎝ ⎠⎝ ⎠

Need perfect match!Need perfect match!

8 13 ACTIVE ANALOG8.13 ACTIVE ANALOG FILTERSFILTERS

Frequency Response of Filter

de max( )T jω

de max( )T jω

Am

plit

ud

max( )

2T jω

Am

plit

ud max

max( )

2T jω

FrequencyclωFrequency

A 2

chω

High-pass Low-pass

mpl

itu

de max( )T jω

max( )T jω pl

itu

de max( )T jω

Frequency

Am

2

clωchω

Am

pmax

( )2

T jω

clω chωFrequencyFrequencycl ch

Band-pass Band-stop(notch)

Filter & Frequency Response

R’

V VoutR

C ( ) 1sT s

sRC

=+

R’C R

-Vin

VoutR

'( ) 1R sT sR s

=+

Vin Vout+

sRC

+

1st order high-pass

R 1

( ) 1RCT s

s=

+

CR’

-

R

Vin VoutCs

RC+

1'( ) R C

Vin Vout+

( ) 1R CT s

sRC

=+

1st order low-pass

Filter & Frequency Response

R2

C1+

C2

R+

R

C2

Vin Vout-R1

R2

C1Vin Vout-

R1

1ω

2nd order low-pass 2nd order high-pass

1 1 2 2c R C R C

ω =

2nd order low-pass 2nd order high-pass

8 14 BIOINSTRUMENTATION8.14 BIOINSTRUMENTATION DESIGNDESIGN

Instrumentation DesignVoltage and frequency ranges for some important

parameters that are measured in human bodyVoltage and frequency ranges for some important

parameters that are measured in human body

Parameter sensor location Voltage range Frequency range (Hz)

p yp y

ECG skin electrode 0.5 – 4 mV 0.01 – 250

EEG scalp electrode 5 – 200 μV DC – 150EEG scalp electrode 5 200 μV DC 150

EGG skin-surface electrodeEGG stomach-surface

electrode

10 - 1000μV0.5 – 80 mV

DC – 1DC – 1electrode

EMG needle electrode 0.1 – 5 mV DC – 10,000

EOG contact electrode 50 – 3500 μV DC – 50EOG contact electrode 50 3500 μV DC 50

ERG contact electrode 0 – 900 μV DC – 50

Nerve potentialsSurface or needle electrode

0.01 – 3 mV DC – 10,000

Instrumentation Design

• Signal AmplificationC d f lifi h i f 10 10 000

• Signal AmplificationC d f lifi h i f 10 10 000– Cascade of amplifier, each gain of 10-10,000

– Small DC offset must be removed5 V DC ff t 107 i 50(V) t t

– Cascade of amplifier, each gain of 10-10,000– Small DC offset must be removed

5 V DC ff t 107 i 50(V) t t• 5μV DC offset x 107 gain = 50(V) output• High-pass filter with 1.0(Hz) cutoff freq. used at

various points in the cascade of amplifier

• 5μV DC offset x 107 gain = 50(V) output• High-pass filter with 1.0(Hz) cutoff freq. used at

various points in the cascade of amplifierp pp p

G 1 G 1 G 1 000 G 100 G 10 iG=1 G=1 G=1,000 G=-100 G=-10

HPFbuff

Instrumentation Amplifier with

Integrator Feedback :V2

LPF HPFI.A.

HPFbuff VRef

Feedback :

2 1

( )1( ) ( )

outV s sGV s V s s

=− +

Vout

V1

Gain StagingIntegrator Feedback*

sRC

+

Instrumentation Design

• Noise reductionL f i

• Noise reductionL f i

( )T jω

– Low-frequency noise (amplifier DC offset, sensor drift temperature

– Low-frequency noise (amplifier DC offset, sensor drift temperature

G

sensor drift, temperature fluctuations, etc) : by a high-pass filter

sensor drift, temperature fluctuations, etc) : by a high-pass filter

Frequency1f 2f 3f 4f 5f 6fg p

– High-frequency noise (nerve conduction, radio

g p– High-frequency noise

(nerve conduction, radio

Frequency

- f1 : HPF cut-off

broadcasts, computers, cellular phones, etc.) : by a low pass filter

broadcasts, computers, cellular phones, etc.) : by a low pass filter

- f2 : lower limit of biosignal freq.- f3 : power-line freq.- f4 : upper limit of biosignal freq.

a low-pass filter– Power-line noise (50-

60Hz): by a band-stop

a low-pass filter– Power-line noise (50-

60Hz): by a band-stop

- f5 : LPF cut-off & anti-aliasing- f6 : A/D sampling freq

60Hz): by a band-stop (notch) filter60Hz): by a band-stop (notch) filter