Biopotential Amplifiers CKT Design Biom5100 Slides12 Amplifier Circuits 20091031
Biopotential Amplifier
-
Upload
nahin-amin -
Category
Documents
-
view
234 -
download
0
Transcript of Biopotential Amplifier
-
8/13/2019 Biopotential Amplifier
1/17
Biopotential Amplifier
-
8/13/2019 Biopotential Amplifier
2/17
Other
Biopotentials
ECG
EMG
ERG
-
8/13/2019 Biopotential Amplifier
3/17
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
-
8/13/2019 Biopotential Amplifier
4/17
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
.
-
8/13/2019 Biopotential Amplifier
5/17
SAFETY
Amplifiers are powered, should not shock or electrocute the subject
Subject Electronics
No large current
Ground
.Also no potentials
>>0 or
-
8/13/2019 Biopotential Amplifier
6/17
SAFETY:
PROTECTION
CIRCUITS
If potential >>0, high current grounded through D1
If potential
-
8/13/2019 Biopotential Amplifier
7/17
Potential transferred through optoelectronics (shown), transformers etc.
Circuits are electrically isolated, no current leakage
Power
Power
ElectronicsSubject
Ground
Electricity
>
Light
>
Electricity
Provides
electrical
isolation
-
8/13/2019 Biopotential Amplifier
8/17
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
-
8/13/2019 Biopotential Amplifier
9/17
ECG:EinthovensTriangle
Threevectors
LeadsI,II,III
usedto
fully
identifythe
Vectorshownin
frontalplane
of
thebody
Kirchhoffslawis
leads
I+II+III=0
-
8/13/2019 Biopotential Amplifier
10/17
ECG:ElectrodePlacement
Augmentedleads:
aVR aVL aVF
Right,left,
foot
Withrespecttocentral
term na
-
8/13/2019 Biopotential Amplifier
11/17
ECG:TransversePlane
Chestleads:
V1,V6
ChestleadsusedtoobtaintheECGinthetransverse
lane ObtainsECGfromthe osteriorsideoftheheart
All
together:
12
leads
(I,II,III;
aVR,
aVL,
aVF,
V1V6)
-
8/13/2019 Biopotential Amplifier
12/17
APPLI ATI N: F l EProblem:RecordedECG=mothersECG+
fetusECG
F+M
Solution:cancel
meaningsubtract
mothersECGfromfetal
ECG?
M
M
.
DN:fetusECGampl.
fetusECGfilters
OUT= o
fetusECG
-
8/13/2019 Biopotential Amplifier
13/17
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
-
8/13/2019 Biopotential Amplifier
14/17
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
-
8/13/2019 Biopotential Amplifier
15/17
INSTRUMENTATIONAMPLIFIER:
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
-
8/13/2019 Biopotential Amplifier
16/17
INSTRUMENTATIONAMPLIFIER:
COMPLETE
VOUT = (V1 V2)(1 + 2R2/R1)(R4/R3)
Gainfrom
Stage
I and
Stage
II
-
8/13/2019 Biopotential Amplifier
17/17
INSTRUMENTATIONAMPLIFIER:
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)