Department of Computer Engineering
Circuit Analysis
Faculty Member: Dated:
Lab Engineer: Semester:
Session:
Group:
LAB-8 Study of Operational Amplifier – Part 1
Reg. No. Report Assessment Total / 50
Name Marks / 15 Rubrics
Marks / 35
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8.1 Objective
This experiment extends the concept of closed-loop (feedback) in op-amps and how op-amp can
be made to operate in linear operating region over larger range of input voltage by some of its important
closed loop configurations that include resistors only. The operation of inverting, non-inverting, summing,
and difference amplifier is observed and input-output relation of each is verified.
8.2 Equipment
1. Operational amplifier IC LM741
2. Resistors (1k x 4, 3.3k x 2, 10k) Ω
3. 2 potentiometers (1k or 10k)
4. Connecting wires
5. 2 batteries (9V DC)
6. Breadboard
7. Digital Multimeter
8.3 Theory
The operational amplifier is an active circuit element that amplifies a differential voltage input with
a high gain. Its symbol and connections are shown in Figure 8-1.
Figure 8-1 Op-amp symbol
The open-loop gain A of an ideal op-amp is infinite. The output VO can be defined by the following
conditional equation:
8.3.1 LM741 Operational Amplifier
741 is a popular op-amp design, first introduced in 1968. This design is nowadays available in a DIP
(Dual In-line Package) 8-pin IC called LM741. Figure 8-2 shows its pin configuration and internal
connections.
Figure 8-2 LM741 pin configuration
Labels of pins 2, 3, 4, 6 and 7 can be recognized from the op-amp symbol (Figure 8-2). Pins 1 and 5
are for Offset Null. These pins are used rarely to compensate for the degradation of the op-amp. Pin
8 has no connection with the amplifier circuit.
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Before introducing the four closed loop configurations, let us first summarize the operational
amplifier’s idealized characteristics:
Figure 8-3 An equivalent circuit of op-amp, modeling its internal resistances
1. Infinite open-loop gain A
2. Infinite input resistance Rin, so zero I+ and I-
3. Zero output resistance Rout
4. Zero input offset voltage i.e. Vout=VDIFF=0 simultaneously
8.3.2 Op-amp closed-loop configurations
The four closed-loop configurations of op-amps that are the topic of this lab are explained
compactly in Figure 8-4 and 8-5. You may consult your textbook for details of these configurations.
Figure 8-4 (a) Non-inverting amplifier and (b) Inverting amplifier
8.4 Procedure
1. Build the non-inverting amplifier circuit of Figure 8-6 on breadboard. The op-amp is biased with
9V and -9V as shown. A potentiometer is used between 9V and -9V. The center terminal of the
potentiometer provides the input voltage to this non-inverting amplifier. The non-inverting input
of op-amp is connected to ground (node between the 9V batteries is being referred to as ground).
Select the values of Rf and Rin according to Table 8-1 and measure all labeled voltages and
currents. Enter your readings in Table 8-1.
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Figure 8-5 Non-inverting amplifier circuit
2. Build the inverting amplifier of Figure 8-7 on breadboard. In this circuit, you will again be using
the potentiometer to supply input voltage to the amplifier. Vary the input voltage by turning the
knob of the potentiometer and measure all labeled voltages and currents. Use the values of R f and
Rin from Table 8-2 and fill the Table with your measurements.
Figure 8-6 Inverting amplifier circuit
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8.5 Observation
Table 8-1 non-inverting amplifier readings
Vout
Rf Rs Vout (practical) Vp Vn
Vin Vout (theoretical) (Multisim) Ip In
3.3k 1k
3.3k 3.3k
3.3k 10k
Table 8-2 Inverting amplifier readings
Vout
Rf Vout (practical)
Rin Vin Vout (theoretical) (Multisim) Vp Vn Ip In
3.3k 1k
3.3k 3.3k
3.3k 10k
8.6
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8.7 Student Learning Outcomes
What you have learnt in the lab? describe.
`
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Assessment Rubrics for: Circuit Analysis
Method:
Lab report evaluation and instructor observation during lab sessions. Outcomes Assessed:
a. Ability to conduct experiments as well as to analyze and interpret data.
b. Ability to function in a team and adhere to rules and guidelines.
c. Ability to use the techniques, skills and modern engineering tools necessary for engineering practice.
Performance Exceeds expectation (5-4) Meets expectation (3-2) Does not meet expectation (1) Marks
Selects relevant equipment / Needs guidance to select Incapable of selecting relevant
Realization of parts to the experiment, relevant equipment / parts to equipment / parts to the
experiment (a) develops circuit diagrams of the experiment and to experiment and unable to
part connections or wiring develop setup diagrams develop setup diagrams
Actively engages and
Cooperates with other group Distracts or discourages other
cooperates with other group
Teamwork (b) members in a reasonable group members from conducting
members in an effective
manner the experiments
manner
Connects circuit components Connects circuit parts, sets
Conducting properly, sets input signals input states according to the Unable to connect circuits parts,
experiment (a, according to the requirement of requirement of experiment and perform the procedure of
c) experiment and examines the and examines the output experiment
output meticulously with minor error
Observes lab safety rules;
Laboratory
handles the equipment and Observes safety rules and
safety and Disregards lab safety and
components with care and disciplinary guidelines with
disciplinary disciplinary rules
adheres to the lab disciplinary minor deviations
rules (b)
guidelines aptly
Completes data collection from
the experiment setup by giving Completes data collection Fails at collecting data by giving
proper input signals and with minor error and enters proper inputs and observing
Data
observing the outputs, ensures data in lab manual with output states of experiment
collection (c) that the data is entered in the slight deviation from setup, unable to fill the lab
lab manual according to the guidelines manual properly
specified instructions
Analyzes the data obtained
Analyzes data with minor
from experiment thoroughly Unable to establish the
error and correlates it with
and accurately verifies it with relationship between practical
Data analysis theoretical values
theoretical understanding, and theoretical values and lacks
(a, c) reasonably. Attempts to
accounts for any discrepancy in the theoretical understanding to
account for any discrepancy
data from theory with sound explain any discrepancy in data
in data from theory
explanation
Operate the NI ELVIS II VI
Uses NI ELVIS II VI
interfaces of oscilloscope, Unable to launch and operate the
Computer use interfaces of digital
digital multimeter, power on-PC NI ELVIS II Vis with or
(c) instruments with guidance
supplies, VI analyzer, etc. with without assistance
from instructor
little to no help
Total
Lab Engineer:
Name: ___________________________
Signature: ________________________
Date: ____________________________
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