Amplificador de Biopotencial
Prof. Sérgio F. Pichorim
Baseado no cap 6 do Webster e
cap 17 do Kutz & Towe
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Right leg
electrode
Sensing
electrodes
Amplifier
protection
circuit
Driven
right leg
circuit
Lead-fail
detect
Lead
selector
Amplifier
Isolation
circuit
Auto
Baseline
calibration restoration
ADC
Driver
amplifier
Memory
Recorder
printer
Isolated
power
supply
Parallel circuits for simultaneous recordings from different leads
Micro
computer
Control
program
Figure 6.7 Block diagram of an electrocardiograph
Operator
display
Keyboard
© From J. G. Webster (ed.), Medical instrumentation: application
and design. 3rd ed. New York: John Wiley & Sons, 1998.
ECG analysis
program
Figure 6.27 Block diagram of a system used with cardiac monitors
to detect increased electrode impedance, lead wire failure, or
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
electrode fall-off.
rd
Composição espectral dos sinais captados pelos eletrodos de ECG e
composições
espectrais de artefatos de movimento e ruído muscular
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
(EMG), sinais que interferem no registro do ECG.
rd
Efeito de filtragem inadequada do sinal de ECG
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Faixa dos Filtros:
• 0,5 a 40 Hz para Monitor de ECG
• 0,01 a 150 Hz para Eletrocardiógrafo
• Outros:
– Detector de onda R
– Rejeita 60 Hz (filtro notch)
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 6.8 Effect of a voltage transient on an ECG recorded on an
electrocardiograph in which the transient causes the amplifier to
saturate, and a finite period of time is required for the charge to bleed
off
enough to bring the ECG back into the amplifier’s active region
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
of operation. This is followed by a first-order recovery of the system.
rd
RESTAURAÇÃO RÁPIDA DA LINHA DE BASE
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Figure 6.9 (a) 60 Hz power-line interference.
Neste exemplo:
ECG com 1mVpp e ruído com 200 µVpp
(b) Electromyographic interference on the ECG.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
BIOELECTRICITY by TOWE in STANDARD HANDBOOK of
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
BIOMEDICAL
ENG. and DESIGN by KUTZ (2002) Cap 17
rd
BIOELECTRICITY by TOWE in STANDARD HANDBOOK of
BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
BIOELECTRICITY by TOWE in STANDARD HANDBOOK of
BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
BIOELECTRICITY by TOWE in STANDARD HANDBOOK of
BIOMEDICAL ENG. and DESIGN by KUTZ (2002) Cap 17
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
Power line
C2
Z1
Z2
120 V
C1
Id1
C3
A
Id2
B
Electrocardiograph
G
ZG
Id1+ Id2
Figure 6.10 A mechanism of electric-field pickup of an electrocardiograph resulting from the power line. Coupling capacitance
between
the (ed.),
hotMedical
sideinstrumentation:
of the power
and
lead
wires
causes
current
© From J. G. Webster
application line
and design.
3 ed.
New York:
John Wiley
& Sons, 1998.
to flow through skin-electrode impedances on its way to ground.
rd
Power line 120 V
Cb
idb
Z1
υcm
Electrocardiograph
A
υcm
Zin
B
Z2
Zin
υcm
ZG
G
idb
Figure 6.11 Current flows from the power line through the body and
ground impedance, thus creating a common-mode voltage everywhere
onWebster
the(ed.),
body.
only resistive
as John
a result
of1998.
RF
© From J. G.
Medical Z
instrumentation:
and design. 3 ed.but,
New York:
Wiley & Sons,
in is notapplication
bypass capacitors at the amplifier input.
rd
Figure 6.12 Magnetic-field pickup by the elctrocardiograph (a)
Lead wires for lead I make a closed loop (shaded area) when patient
and electrocardiograph are considered in the circuit. The change in
magnetic
field
passing
through
thisand
area
a current
in the
© From J. G. Webster
(ed.),
Medical instrumentation:
application
design.induces
3 ed. New York:
John Wiley & Sons,
1998. loop.
(b) This effect can be minimized by twisting the lead wires...
rd
Figure 6.13 A voltage-protection scheme at the input of an
electrocardiograph to protect the machine from high-voltage
transients. Circuit elements connected across limb leads on left© From J.side
G. Webster
(ed.),
Medical instrumentation: application
and design. 3 ed. New York: John Wiley & Sons, 1998.
hand
are
voltage-limiting
devices.
rd
Figure 6.14 Voltage-limiting devices (a) Current-voltage
characteristics of a voltage-limiting device. (b) 0,7V Parallel silicondiode voltage-limiting circuit. (c) 2 to 20 V Back-to-back silicon
Zener-diode
voltage-limiting circuit. (d) 50 to 90 V Gas-discharge
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
tube (neon light) voltage-limiting circuit element.
rd
id
−
+
Ra
−
Ra
+
υcm
RL
RRL
υ3
Rf
υ4
Auxiliary
op amp
−
Ro
+
Figure 6.15 Driven-right-leg circuit for minimizing commonmode interference The circuit derives common-mode voltage from a
pair
ofJ. G.averaging
resistors
connected
to v3 and
right
leg
© From
Webster (ed.), Medical
instrumentation:
application and design.
ed. NewvYork:
John Wiley
& Sons,
1998.is not
4. The
grounded but is connected to output of the auxiliary op amp.
rd
Ra/2
Rf
id
υo/Rf
2υcm/Ra
υcm
+
−
υcm
Ro
+
RRL
id
Figure E6.1 Equivalent circuit of driven-right-leg system.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
υo
Figure 6.16 Voltage and frequency ranges of some common
biopotential signals; dc potentials include intracellular voltages as
well as voltages measured from several points on the body (EOG,
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3 ed. New York: John Wiley & Sons, 1998.
EEG, ECG, EMG, and AAP is the axon action potential).
rd
Figure 6.18 This ECG amplifier has a gain of 25 in the dc-coupled stages. The highpass filter feeds a noninverting-amplifier stage that has a gain of 32. The total gain is
25 × 32 = 800. When µA 776 op amps were used, the circuit was found to have a
CMRR
dB(ed.),
at Medical
100 Hz
and a noise
level
403 mV
peak
peak
atSons,
the1998.
output.
© From J.of
G. 86
Webster
instrumentation:
application
and of
design.
ed. New
York:to
John
Wiley &
The frequency response was 0.04-150 Hz for ±3 dB and was flat over 4-40 Hz.
rd
byMedical
TOWE
in STANDARD
HANDBOOK
BIOMEDICAL
and
©BIOELECTRICITY
From J. G. Webster (ed.),
instrumentation:
application
and design. of
3rd ed.
New York: JohnENGINEERING
Wiley & Sons, 1998.
DESIGN by KUTZ (2002) Cap 17
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.
© From J. G. Webster (ed.), Medical instrumentation: application and design. 3rd ed. New York: John Wiley & Sons, 1998.