4t1~
09
om
o po
12-2
Electronic Feedback Systems
Blackboard 12.1
Blackboard 12.2
Feedback Compensation of an OperationalAmplifier
Viewgraph 12.1
t
Open-loop transfer
function for one-pole
compensation.
o
Viewgraph 12.2
Cc
Vi
VO 01
Noninverting amplifier.
12-3
12-4
Electronic FeedbackSystems
Viewgraph 12.3
This side to
input of highgain stage
This side from
output of highgain stage
Vn
Network for two-pole
compensation
Viewgraph 12.4
\,-Approximation
t
M
-90
t
-180
-2700|
Open-loop transfer function
for two-pole compensation.
Feedback Compensation of an OperationalAmplifier
Viewgraph 12.5
2.2 k92
301+
7
0
A
3OpF 30pF
*-~-
Open this connection
for one-pole compensation.
Unity-gain inverter with
two-pole compensation.
IiViewgraph
Dominant pole pair
A
beyond here for
high ao f0
High-frequency
amplifier poles
-1.1 X 10
Dominant pole
pair in this region
for low ao f
0
s -p
s plane
Root-locus diagram for inverter
with two-pole compensation.
12.6
12-5
12-6
ElectronicFeedback Systems
Demonstration Photograph
12.1 Operational-amplifier
compensation demonstration
Demonstration Photograph
12.2 Close-up of operationalamplifier for compensation circuit
Feedback Compensation of an OperationalAmplifier
In this session we show how minor-loop compensation is used to
control the dynamics of an available integrated-circuit operational
amplifier. We find that in certain applications, dramatic performance improvements are possible compared with a similar amplifier that uses fixed compensation that is selected for unity-gain
stability.
Comments
While specific values for the compensating components are
selected based on parameters of the amplifier type used, the general
methods are applicable to any amplifier that allows the choice of
the components used for minor-loop compensation.
In about the middle of the first blackboard I give the expression
for the closed-loop gain as:
Correction
1
f 2Ces
f+
1
2Ces
1 + 2Cs
The final expression should read:
1
1
f 2Ces
g,nf + 1
(There is a g,, missing in the equation on the blackboard.)
Textbook: Sections 13.3.2 and 13.3.3.
Reading
12-7
12-8
Problems
Problem 12.1 (P13.5)
Problem 12.2 (P13.6)
Problem 12.3 (P13.7)
Problem 12.4 (P13.8)
MIT OpenCourseWare
http://ocw.mit.edu
RES.6-010 Electronic Feedback Systems
Spring 2013
For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.