Op-Amp Basics

57 Pages·2003·0.55 MB·English

Op-Amp Basics
Peggy Alavi
Application Engineer
September 3, 2003
Op-Amp Basics – Part 1
• Op-Amp Basics
– Why op-amps
– Op-amp block diagram
– Input modes of Op-Amps
– Loop Configurations
V
– Negative Feedback cc
– Gain Bandwidth Product
• Op-Amp Parameters -
IN PU TS
• Op-Amp Internal Circuit O U TPU T
+
-V
EE
© 2003 National Semiconductor Corporation
Op-Amp Basics – Part 2
• Op-Amp Basics – Common Mode
• Op-Amp Parameters Rejection
– Input Offset Voltage – CMRR
– Input Bias Current – CMVR
– Input Offset Current – PSRR
– Output Impedance – Gain and Phase Margin
– Slew Rate – Abs Max Rating
– Noise – Operating Ratings
• Op-Amp Internal Circuit
V
OS
3.1mV/ V
(50dB)
V
CM
© 2003 National Semiconductor Corporation
Op-Amp Basics – Part 3
• Op-Amp Basics V
CC
• Op-Amp Parameters
• Op-Amp Internal Circuit
Q Q
8 9
– Biasing circuit
– Differential Input Stage
IN + Q IN -
Q 2
1
– Voltage Gain Stage
– Output Stage Q3 Q4
Q
7
Q5 Q6 Q10
R1 R3 R2 R
4
-V
EE
© 2003 National Semiconductor Corporation
What is an Op-Amp?
• Inexpensive, efficient, versatile, and readily available
building blocks for many applications
• Amplifier which has
– Very large open loop gain
– Differential input stage
– Uses feedback to control the relationship
between the input and output
© 2003 National Semiconductor Corporation
What does an Op-Amp do?
• Performs many different “operations”
– Addition/Subtraction
– Integration/Differentiation
– Buffering
– Amplification
• DC and AC signals
+
dx
⌠
∑
dt
−
⌡ ×
© 2003 National Semiconductor Corporation
Where is an Op-Amp used?
• Many applications including
– Comparators
– Oscillators
– Filters
– Sensors
– Sample and Hold
– Instrumentation Amplifier
© 2003 National Semiconductor Corporation
Operational Amplifier
• Op-Amps must have:
– Very high input impedance
– Very high open loop gain
– Very low output impedance
V
cc
-
INPUTS
OUTPUT
+
-V
EE
© 2003 National Semiconductor Corporation
Op-Amp Block Diagram
V
CC
-
OUTPUT
INPUTS Differential Voltage Output
Amplifier Amplifier Amplifier
+
-V
EE
© 2003 National Semiconductor Corporation
Differential Amplifier Stage
• Provides differential input for the op-amp
• Provides dc gain
• Has very high input impedance
– Draws negligible input current
• Enables user to utilize ideal Op-Amp equations
for circuit analysis
V
CC
-
OUTPUT
INPUTS Differential Voltage Output
Amplifier Amplifier Amplifier
+
-V
EE © 2003 National Semiconductor Corporation