1
ELEC 321
Laboratory Report of Applied Electronics III
E
XPERIMENT
#1
FEEDBACK PRINCIPLE & STABILITY ANALYSIS IN MULTIPLE-POLE AMPLIFIER
Lo Wang Fu, DA828447
Faculty of Science and Technology, University of Macau
davis62600991@msn.com
Major: EEE
Section No. : Section A
Lab Date: 14/09/2010, Hand-in Date: 06/10/2010, Instructor: Prof. Tam, Pedro Cheong
Abstract
— By using negative feedback network, it could stabilize
the system, and create a oscillating sinusoidal wave.
Keywords
—
Stability, s-plane, voltage mixing voltage sampling,
feedback, close-loop gain
I.
OBJECTIVE
It’s to study the basic negative feedback principle and
stability analysis with multi-stage amplifiers.
II.
APPARATUS
Components
：
Four Op-Amp chips (UA741), three 0.1uF
capacitors, one 1nF capacitor, two 100
Ω
resistors, one 1k
Ω
resistor, five 10k
Ω
resistors, two 100k
Ω
resistors, one
potentiometer, several pieces of connecting wires.
Instrumentation
：
Digital multi-meter, function generator,
oscilloscope, prototype board, DC power supply.
III.
PROCEDURE WITH DATA ANALYSIS
A.
Set-up and Analyze circuit
The building block, consisted of four operational amplifiers
connected in cascade and several components, should be
constructed on the prototype board firstly, the op-amps could
be power up by DC supply with +15V and -15V on the
prototype board. Set R
a
as 10k
Ω
and R
b
as 1k
Ω
.
By Thévenin's theorem and Norton’s theorem, to gradually
simplify the circuit first, then the input part of experiment
circuit would be changed as shown in Fig. 1.
By analyzing the circuit, for the feedback path with a 100k
Ω
resistor of such large resistance relatively to R
b
of 1k
Ω
or
even up to 10k
Ω
, so there should be just little amount of
current being able to go through 100k
Ω
resistor, instead
mainly flow through the 1k
Ω
resistor, then the 100k
Ω
resistor could be eliminated so that R
a
and R
b
would act as a
voltage divider, thereof, the experimental circuit should be
Voltage mixing Voltage sampling, and for the feedback circuit,
it could be taken as in series-shunt mode shown in Fig. 2, so
the calculation would be processed with y parameter.
Fig. 1 The input part of circuit after transformation with
Thévenin's
(T)
theorem and Norton’s
(N)
theorem
Fig. 2 Shunt-shunt mode for feedback circuit
2
22
1
21
2
2
12
1
11
1
v
y
v
y
i
v
y
v
y
i
5
21
1
5
11
10
1
10
1
y
y
1
5
22
5
12
10
1
10
1
y
y
Thereof, the feedback gain β would be attained as y
12
, being
-10
-5
V/A. And the experimental circuit would be expressed as
shown in Fig. 3, and the circuit A in Fig. 3 would be
constructed as Fig. 4,
(T)
(N)