Biopotential Amplifier

8/13/2019 Biopotential Amplifier

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Biopotential Amplifier


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Other

Biopotentials

ECG

EMG

ERG


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Si nal

(Hz)

range(mV)

ECG 0.01 100 0.05 3

EEG 0.1 80 0.001 1

EOG 0.01 10 0.001 0.3

EMG 50 3000 0.01 100


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WHYFREQUENCY?

When measuring biopotentials (say ECG), EVERYTHING else

even other biopotentials (like EEG, EMG, EOG)

are noise sources. These have characteristic frequencies. So use Band Pass

ers.

fL to fHattenuate

fL fH

.


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SAFETY

Amplifiers are powered, should not shock or electrocute the subject

Subject Electronics

No large current

Ground

.Also no potentials

>>0 or


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SAFETY:

PROTECTION

CIRCUITS

If potential >>0, high current grounded through D1

If potential


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Potential transferred through optoelectronics (shown), transformers etc.

Circuits are electrically isolated, no current leakage

Power

Power

ElectronicsSubject

Ground

Electricity

>

Light

>

Electricity

Provides

electrical

isolation


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TELEMETRY Means wireless transmission of data from and to the device

HOME

No limits: can be done across the

world. Internet will play a huge role.

HOSPITAL


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ECG:EinthovensTriangle

Threevectors

LeadsI,II,III

usedto

fully

identifythe

Vectorshownin

frontalplane

of

thebody

Kirchhoffslawis

leads

I+II+III=0


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ECG:ElectrodePlacement

Augmentedleads:

aVR aVL aVF

Right,left,

foot

Withrespecttocentral

term na


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ECG:TransversePlane

Chestleads:

V1,V6

ChestleadsusedtoobtaintheECGinthetransverse

lane ObtainsECGfromthe osteriorsideoftheheart

All

together:

12

leads

(I,II,III;

aVR,

aVL,

aVF,

V1V6)


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APPLI ATI N: F l EProblem:RecordedECG=mothersECG+

fetusECG

F+M

Solution:cancel

meaningsubtract

mothersECGfromfetal

ECG?

M

M

.

DN:fetusECGampl.

fetusECGfilters

OUT= o

fetusECG


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Inverting

amplifier

Gaininthemultiplestages:i.e.

HighGain so,youcanamplify

smallsignals

Asa

onus,

put

some

lowpass

Differential

am lifierbut

and

high

pass

withvery

high

input

impedance

Noninverting

amplifierSo,youcan

connect

to

sensors

rejectscommonmode

interference

>so

you

canrejectnoise


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INSTRUMENTATIONAMPLIFIER:

STAGE1

Recall virtual ground of opamps

I1 = (V1 V2)/R1

eca no curren can en er opamps an

Kirchoffs current law

I2 = I3 = I1I2

Recall Kirchoffs voltage law

VOUT = (R1 + 2R2)(V1 V2)/R1

I3

1

2 2 1


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STAGE2

Recall virtual ground of opamps and voltage

divider

V = V = V R / R + R-

Recall no current can enter opamps

(V1 V-)/R3 = (V- VOUT)/R4I2

Solving,

VOUT = (V1 V2)R4/R3

I3


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COMPLETE

VOUT = (V1 V2)(1 + 2R2/R1)(R4/R3)

Gainfrom

Stage

I and

Stage

II


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COMPLETE

Features:

Differentialamp

Veryhighgain

VOUT = (V1 V2)(1 + 2R2/R1)(R4/R3)

Very

ig

inputR

Commonmode

rejection

Gainfrom

Stage

I and

Stage

II

(wealsoneed

filters)

Biopotential Amplifier

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