Op Amp Circuits

135 Pages·2016·8.51 MB·English

by  Gordon Roberts

304-330 Introduction To Electronic Circuits
Operational Amplifiers

Chapter 2
© 2009 G. W. Roberts Op Amp Circuits, slide 1
304-330 Introduction To Electronic Circuits
Outline
•  The Ideal Op Amp
•  The Inverting Configuration
•  The Noninverting Configuration
•  Difference Amplifiers
•  Integrators and Differentiators
•  DC Imperfections
•  Effects of Finite Open-Loop Gain and Bandwidth
on Circuit Performance
•  Large-Signal Operation of Op Amps
•  Simulating Op Amp Circuits With SPICE
•  Summary
© 2009 G. W. Roberts Op Amp Circuits, slide 2
304-330 Introduction To Electronic Circuits
The Universal Analog Building
Block: Main Terminals
Three terminals shown plus power
supply connections. Op amps have
other terminals that is used to tuned
its non-ideal behavior.
The Op Amp Symbol
C
€
C
€
(C)
The op amp shown connected to dc power supplies (with noise decoupling capacitors).
© 2009 G. W. Roberts Op Amp Circuits, slide 3
304-330 Introduction To Electronic Circuits
Electrical Equivalent Op Amp Circuit
v
out
= f(v ,v )
1 2
=
•  Input/Output Impedance:
v v v
Z− = 1 = ∞ Z+ = 2 = ∞ Z = o = 0
in i in i out i
v −v =K
1 2 o 1 2
i =i
o x
Output impedance is derived by setting the input sources to some constant
value, and a current into the output port and deriving the corresponding output
voltage.
€
© 2009 G. W. Roberts Op Amp Circuits, slide 4
304-330 Introduction To Electronic Circuits
Electrical Equivalent Op Amp Circuit
Av + A v
1 1 2 2
=
€
•  One output, two inputs:
( )
v = f v ,v
out 1 2
–  If circuit is linear, then
v = A v + A v
€
out 2 2 1 1
© 2009 G. W. Roberts Op Amp Circuits, slide 5
€
304-330 Introduction To Electronic Circuits
Equivalent Signal Representation:

CM and DM Signals
v Node voltages:
1
v
v = v − I,d
1 I,cm 2
v
v = v + I,d
2 I,cm 2
Solving For CM & DM signals:
v
2
v + v
€ v = 1 2
I,cm 2
v = v − v
I,d 2 1
•  Any two node voltages (relative to analog ground)
can be expressed as a linear combination of their
€
corresponding DM & CM signal components.
© 2009 G. W. Roberts Op Amp Circuits, slide 6
304-330 Introduction To Electronic Circuits
Creating The Differential Source
Arrangement
Av + A v
1 1 2 2
€
•  Op Amp circuits must be driven with the source
arrangement shown here.
© 2009 G. W. Roberts Op Amp Circuits, slide 7
304-330 Introduction To Electronic Circuits
Creating The Differential Source
Arrangement
Av + A v
1 1 2 2
€
1
v =A v +A v =(A +A )v + (A −A )v
out 2 2 1 1 v1=vI,cm−vI,d 2 1 2 I,cm 2 1 2 I,d
v =v +v 2
2 I,cm I,d
•  By design, A = -A = A: Amplification depends
1 2
only on the DM signal
( )
v = 0⋅v + A ⋅v = A v − v and not the CM signal
out I,cm 1 I,d 2 1
© 2009 G. W. Roberts Op Amp Circuits, slide 8
€
304-330 Introduction To Electronic Circuits
Creating The Differential Source
Arrangement
v = Av + A v
out 1 1 2 2
( ) ( )
= A v − v 2 + A v + v 2
1 I,cm I,d 2 I,cm I,d
1
( ) ( )
= A + A v + A − A v
Av + A v
1 1 2 2 1 2 I,cm 2 2 1 I,d
By design, A = -A :
€ 1 2
€
( )
v = 0⋅v + A ⋅v = A v − v
out I,cm 2 I,d 2 2 1
Amplification depends only on the DM and not the CM signal:
€
A 2-input system becomes a 1-input system.
© 2009 G. W. Roberts Op Amp Circuits, slide 9
304-330 Introduction To Electronic Circuits
Op Amp Internal Architecture
•  Example: Calculate the output
voltage as a function of the
input v and v using the
1 2
following parameters:
mA
G =10 , R =10 kΩ, µ=100
m V
•  Solution:
€
v V
A = o = −µG R = −104
1 v m V
1 v =0
2
v V
A = o = µG R =104
2 v m V
2 v =0
1
V
∴v =104(v − v )
O 2 1 V
€
© 2009 G. W. Roberts Op Amp Circuits, slide 10
€