e e 2415
DESCRIPTION
E E 2415. Lecture 05 - Introduction to Operational Amplifiers. Operational Amplifiers. Ideal operational amplifiers are easily analyzed Assumptions for ideal operation are realistic Inexpensive commercial Op-Amps available as integrated circuits - PowerPoint PPT PresentationTRANSCRIPT
E E 2415
Lecture 05 - Introduction to Operational Amplifiers
Operational Amplifiers
• Ideal operational amplifiers are easily analyzed
• Assumptions for ideal operation are realistic
• Inexpensive commercial Op-Amps available as integrated circuits
• Practical applications for instrumentation, signal processing and control circuits
mA741 Pinout
1234
8765
mA741Offset Null
Inverting Input
Non-inverting Input
Vcc-
Vcc+
Output
Offset Null
NC
Op Amp Terminals
+Vcc
-Vcc
Positive supplyvoltage
OutputInverting
Input
NoninvertingInput
Negative supplyvoltage
Op Amp Terminal Currents
+Vcc
-Vcc
Vcc Vcc
ioin
ip
ic+
ic-
Common Node
Op Amp Terminal Voltages
+Vcc
-Vcc
Vcc Vcc
+vp
-
+
vo
-
+
vn
-
Common Node
Equivalent Circuit
A(Vp-Vn)Ro
Ri +vo-
ip
in
io
Assumptions for Ideal Op Amp
• Open loop Gain, A vp - vn 0 • Then vp - vn 0 Ri • Ri ip 0 and in 0• Gain is linear up to the saturation
voltage• Saturation voltage equals power supply
voltage
Open-Loop Characteristics
+Vcc
-Vcc
vp-vn
vo
A(vp-vn)
+Sat
-Sat
Linear
Inverting Amplifier
and
Vn = 0 and in = 0. Then KCL at node n yields:
+Vcc
-Vcc
RfRg
vg
+vn-
in
0
+vo-
0 00 0g o
g f
v vR R
f
o gg
Rv v
R
Saturated Mode
• Inverting Amplifier with +Vcc = 5 V and Vcc = -5V.
• Rf = 10 k and Rg = 1 k
t
1 V
-1 V
vgvo
t5 V
-5 V
Non-Inverting Amplifier
KCL at node n:
vn = vp = vg
+Vcc
-Vcc
vg
RgRs
Rf0
0n
p+
vo
-
+vp-
+vn
-
0g g o
s f
v v vR R
f so g
s
R Rv v
R
Summing Amplifier (1/2)
+Vcc
-Vcc
va
Ra
vb
Rb
vc
Rc
Rf
+
vo
-
Summing Amplifier (2/2)
0a b c o
a b c f
v v v vR R R R
f f fo a b c
a b c
R R Rv v v v
R R R
Difference Amplifier (1/3)
KCL @ n:
+Vcc
-Vcc
RbRa
Rc
Rdvb
va +vo-
+vp-
n
p
0n pi i
0n a n o
a b
v v v vR R
Difference Amplifier (2/3)
Voltage Divider @ p:
+Vcc
-Vcc
RbRa
Rc
Rdvb
va +vo-
+vp-
n
p
dn p b
c d
Rv v v
R R
Difference Amplifier (3/3)
Substitute:
into:
and simplify:
If: Then:
dn p b
c d
Rv v v
R R
0n a n o
a b
v v v vR R
d a b bo b a
a c d a
R R R Rv v v
R R R R
a c
b d
R RR R
bo b a
a
Rv v v
R
Analyzing an OpAmp Circuit
+Vcc
-VccRf
RyRL
Rx
Rg
vg
Analyzing an OpAmp Circuit
Analyzing an OpAmp Circuit
xp g
x g
Rv vR R
1 1op
f y f
v vR R R
1f x
o gy x g
R Rv vR R R
f y xo g
y x g
R R Rv vR R R
f
op
y
p
Rvv
Rv
0