Transcript biomedical instrumentation

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Introduction
Goal: Understand the design of op-amp based ICs (comparators, oscillators, integrators, differentiators, instrumentation amplifiers) for
applications in biomedical instrumentation.
Short Description of the course
Operational Amplifier
Ideal characteristics
Inverting amplifiers
Summing amplifier
Non-inverting amplifier
Follower
Differential amplifier Comparator
Rectifiers
Inverting amplifier input resistance
Non-inverting configuration
Effect of negative feed back on output resistance
Non-inverting op-amp input resistance
Voltage follower
Band width limitation
Bode plot
Cascade amplifiers
OP- Amp with complex impedance
inverting with complex impedance
non inverting with complex impedance
Differentiator integrator
Practical differentiator
Differentiator of non sinusoidal inputs
Practical Integrator
Integrator for non sinusoidal inputs
Square wave integration
Non linear op-amp
Logarithmic amplifier
Anti-log amplifier
Analog multiplier
Application: pressure transmitter
Precision rectifiers (half and full wave)
OP-Amp Application
summing amplifier
practical summing amplifier
averager,
additional summing amplifier circuits
Differential and instrumentation amplifiers
Variable gain inst. Amplifier
Commercial instrumentation amplifier
Voltage to current and current to voltage conversion
Howland current source
Photodiode and phototransistor as current sources
Active filters
filter fundamentals
LP, HP, BP, Notch , all pass
LP response curve characteristic
Second order LP filter
Design of LP and HP filters
Sallen-key LP and HP filters
Higer order LP and HP filters
Band pass filters, MFBP filter
Band stop filters
States variable filters
All pass filters
Comparators , comparator with positive and
negative Feedback, application to
comparator.
Astable multivibrator (oscillators)
triangular wave generator
square wave generator
Digital Vs Linear Electronics
• Digital Electronics: All phases of electronics in which
signals are represented in terms of finite number of
digits (binary); all arithmetic computations on such
numbers, as well as associated logic operations.
• Linear (Non-digital) Electronics: All phases of
electronics in which signals are represented by
continuous or analog variables; all associated signal
processing functions (e.g., amplification).
– Nonlinear circuits also categorized in this category
Ideal Amplifier
• Output signal is directly
proportional to input signal,
but amplified
• All amplifiers require dc
power (bias) supplies to
provide amplification
+
Vi(t)
-
Linear Amplifier
(voltage gain
= A)
• Voltage gain
A= V0(t) / Vi(t)
V0(t) = A Vi(t)
+
Vo(t)
-
Source Models
• Ideal sources: independent
of any external loads
• Practical sources:
combination of ideal sources
and one or more passive
components (resistance)
–
–
–
–
is = Vs / Rs (short circuit)
Vs = isRs (open-circuit)
Thevenin model: Rs < Rload
Norton model: Rs > Rload
Ideal voltage and current source models
+
is
Vs
-
Thevenin and Norton models for
practical sources
+
Vs
-
Rs
is
Rs
Operational Amplifier (Op-Amp)
• Most important single linear
integrated circuit (building
block of analog circuit field)
• High-gain, integrated-circuit,
direct-coupled amplifier
• Linear and nonlinear signalprocessing function
A component level diagram of the common 741 op-amp
(Wikipedia.org(
Op-Amp: power supply connections
• Commonly used: dual
power supplies
• Common values:
– +15V (+V or V+)
– -15V (-V or V-)
• All output loads connected
between output terminal
and common ground point
• Usually power supply
connections are omitted
for ease
Positive power
supply terminal
+
15 v
+
15 v
-
Negative power
supply terminal
Common
ground
point
Op-Amp: symbol and circuit model
• Two signal input
terminals
– Inverting terminal (-)
– Noninverting terminal (+)
• One output signal
terminal
• Differential input voltage
(Vd)
• Output voltage Vo=AVd
Inverting input
terminal
V-
Output
terminal
Vd
Vo
V+
Noninverting
input terminal
V-
+
Vd = V+ - VAVd = A(V+ - V-)
-
V+
A∞
Vo
Ideal Op-Amp
• Input impedance of op-amp is ∞
– No current flow in or out of input terminals
• Output impedance of op-amp (with respect to ground) is
‘0’
– Voltage V0 does not change with load
• Open-loop gain A  ∞
– Vd = V+ - V- = V0 / A
– Since circuit is operated in linear stable mode, V0 must be finite
voltage (usually 13 V)
– As A  ∞, Lim Vd = Lim (V0/A) = 0
– Vd0; V+ - V- = 0; V+ = V-
Inverting Amplifier
• Under stable linear operation
–
–
–
–
Vd0 or V+ = VSince V+ = 0, V- = 0 (virtual ground)
ii = Vi / Ri
Since input current should be 0, ii
flows through Rf
– Vf =Rfii = Rf(Vi/Ri) = (Rf/Ri)Vi
– Vo= -Vf = -(Rf/Ri)Vi
– Closed loop voltage gain of
circuit ACL = Vo/Vi = -(Rf/Ri)
– Input impedance Rin = Vi/ii = Ri
V- = 0
Rf
ii
ii
+
Vi
-
+ Vf -
Ri
-
+
Vo