Laboratory No. 2- Characterization of Some Basic Op-Amp Circuits

ECSE 331
Laboratory No. 2
Characterization of Some Basic
Op-Amp Circuits
Objective:
Investigate the dynamic behavior of some typical op-amp circuits constructed using the 741 op-amp.
Compare your results with that predicted by SPICE. Models of the electronic components can be
found on the course web site.
Equipment Required:
1. NI Elvis-II+ test instrument
2. PC with ELVIS-II+ software installed
3. Components:
a. 741 op-amp (LM741 from TI, UA741 from STMicroelectronics)
b. resistors: 1kΩ, 2 kΩ, 4 kΩ, 8 kΩ, 10 kΩ, 16 kΩ, 100 kΩ
c. capacitors: 0.22 µF
Description of the NI Elvis-II+ Test Instrument:
The National Instruments Educational Laboratory Virtual Instrumentation Suite (NI ELVIS-II+
) is a
hands-on design and prototyping platform that integrates the 12 most commonly used instruments –
including oscilloscope, digital multi-meter, function generator, bode analyzer, and more. It connects to
a PC through a USB connection, providing quick and easy acquisition and display of measurements.
The National Instruments Educational Laboratory Virtual Instrumentation Suite consists of two main
components:
1. The bench-top workstation (NI ELVIS-II+
), which provides instrumentation hardware and
associated connectors, knobs, and LEDs as shown in Fig. 1(a). A prototyping
board (breadboard) sits on top of the workstation, plugged into the NI ELVIS-II+ platform,
and offers hardware workspace for building circuits and interfacing experiments.
2. NI ELVIS-II+ software, which includes soft front panel (SFP) instruments. Fig. 1(b) illustrates
the PC screen view of the oscilloscope interface.
The Elvis-II+ prototype board consists of 5 separate areas: four small prototype areas on the
peripheral of the board, and a much larger central prototype area. The boards on the peripheral are
used to interface to the internal data acquisition board of the Elvis-II+ system. There are marking
along the perimeter of the board indicating the connection. The student was introduced to this test
bench back in Laboratory 1. The student should refer back to this lab for a detailed description of the
NI ELVIS-II+ test system. 
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Practical Information for the Student:
In performing this experiment, you will construct several building blocks of modern transistor circuits.
On doing so, keep the following points in mind:
1. In the figures, more positive voltages are always shown closer to the top of the page, so that
current flows in the circuit from top to bottom.
2. Keep all connecting leads as short as possible and pushed down to the surface of the circuit
board. You want to avoid a “rat’s nest” of wiring whereby unwanted coupling capacitances and
series inductances are created. These parasitics can prevent your circuit from working
correctly.
3. Use different color wires in your circuit. The standard convention is red for positive supply
voltages, blue for negative supply voltages and black for ground. Use colors that are different
than these for signals. If you use a single color for everything, your circuit should still work.
However, the debug process will be much more difficult if something goes wrong. It is
important for the student to understand that when asked to design a circuit it is not limited to
just the arrangement and component selection for the circuit but also to the fact that the
design may not work the first time it is assembled. In general, all design will require at least
two iterations before one can declare success!
4. In understanding circuits, as well as designing them, keep in mind that that there are two
interleaved problems: the dc design, which establishes the operating points, and the ac
design, which is responsible for how the circuit responds to signals. The student must design
(a)
(b)
Figure 1: (a) Elvis-II+ instrumentation hardware with prototyping board, and (b) menu
for various virtual instrument.
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both problems at the same time; if you make a change to one, be sure that you haven’t
changed the other.
Write-Up Requirements:
A good laboratory report should contain a brief description of what the experiment was about,
including circuit diagrams, and what you did, your data, your results, and anything else called for in
the assignment, such as questions inserted in the laboratory. Answers to these questions require
observations that need to be made at the time you do the experiment.
The laboratory report should be written using the IEEE paper style consisting of a double-column
single-space format, and must adhere to the following:
1. Title page - Title of the assignment/project, authors' name, and course name.
2. Abstract - Abstract of the assignment/project report.
3. Introduction
4. Main body of the assignment/project report including figures.
6. Conclusions
7. References
8. Appendices
Procedure:
Connect the following circuits using the 741 op-amp with pin-outs shown in Fig. 2.
1) Comparator (Fig. 3). Apply a 1 kHz sine-wave of about 1 Vpp to the noninverting (+) input with the
inverting (-) input grounded. Observe this signal on the oscilloscope through channel A, set the trigger
to external and capture the output on channel B. Does it change if you reduce the input amplitude to
0.1 V? What is the effect of grounding the + input terminal, and connecting the signal to the – input
terminal?
(2) Voltage Follower (Fig. 4): Apply the same signal to the input as in part 1. Note that with negative
feedback (output to the – input terminal) the op-amp will adjust its output so that the inverting input is
at the same voltage as the noninverting input. What is the signal at the output? What is the input
impedance of the circuit? Justify your answer with actual measured data. What happens with a
square-wave input?
(3) Noninverting Amplifier (Fig. 5): Apply the same signal as in part 1 to the input of the noninverting
amplifier shown in Fig. 5. What is the signal at its output? What is the signal at the inverting input
terminal to the op-amp? What is the gain of the amplifier? Be precise. If the input signal amplitude is
increased what happens at the output of the amplifier? What happens with a square-wave input with a
1 Vpp amplitude? Change the circuit so that it realizes a gain of 10 V/V and show that it operates
correctly.
(4) Inverting Amplifier (Fig. 6): With the input to this amplifier grounded, measure the voltage at the
inverting input terminal to the op-amp. This terminal is said to be at a “virtual ground.” Apply the same
signal as in part 1, observe the output signal with respect to the input signal in a manner like that
performed in part 1. What is the gain of the circuit? What do you observe at the output of this
amplifier if the inverting input terminal to the op-amp is connected to “real” ground? How would you
change this circuit to make the magnitude of the gain equal to 10 V/V? The input impedance of a
circuit is the ratio of the input voltage to the input current. With a 5 Vpp input, compute the current 
G. Roberts/Y. Li, Feb. 28, 2017 4
flowing through the 1-kΩ resistor. What is the input impedance to this circuit?
(5) Differentiator (Fig. 7): This circuit differentiates the input voltage signal. Since the inverting input
is at a virtual ground, the current that flows through the 0.2-μF capacitor is proportional to the
derivative of the input voltage signal, i.e.,
i
C = C dvIN (t)
dt = 0.2 ×10−6 dvIN (t)
dt
As this current passes directly through the 1-kΩ feedback resistor, the output voltage will be
proportional to the derivative of the input voltage, i.e.,
vO (t) = −R × i
C = −R ×C dvIN (t)
dt = −0.2 ×10−3 dvIN (t)
dt
Apply the same signal as in part 1 to the input of the differentiator and observe the output signal. Set
the trigger on the oscilloscope carefully. Superimpose the input and output signals on the same plot
and observe any differences. Repeat with a triangular wave input.
(6) Integrator (Fig. 8): In this circuit the capacitor and the resistor are interchanged from those in the
differentiator circuit of Fig. 7, resulting in a circuit that produces an output, which is proportional to the
integral of the input signal, i.e.,
vO (t) = − 1
R ×C
vIN (τ )
0
t
∫ dτ = − 1
0.2 ×10−3 vIN (τ )
0
t
∫ dτ
In order to stabilize the circuit at DC, an additional 100-kΩ resistor has been placed across the
feedback capacitor. Apply the same signal as in part 1 to the input of the integrator and observe the
output signal. Set the trigger on the oscilloscope carefully. Superimpose the input and output signals
on the same plot and observe any differences. Repeat with a square-wave wave input.
(7) D/A Converter (Fig. 9): The circuit shown in Fig. 9 is a 4-bit digital-to-analog (D/A) converter
circuit. In essence, it consists of an inverting amplifier with four separate inputs. As the inverting input
is held at virtual ground, currents from the four inputs are added and flow together into the output
feedback resistor. The value of four input resistors have been chosen so that each contributes
approximately twice as much current as the previous one, beginning with input 1. With a +5 V input
signal, close the switch to each feed-in resistor in accordance to the Table 1, and observe the
corresponding output voltage. A 0 indicates a switch is opened and a 1 indicates that the switch is
closed.
Plot the output voltage of the D/A converter (y-axis) as a function of the integer value of the digital
control signal. Join the two end points with a straight-line, and observe the maximum distance the
measured points deviates from the straight-line.
This concludes this lab.
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Table 1: D/A Converter Switch Arrangement
Integer
Switch
Arrangement
b3b2b1b0
0 0000
1 0001
2 0010
3 0011
4 0100
5 0101
6 0110
7 0111
8 1000
9 1001
10 1010
11 1011
12 1100
13 1101
14 1110
15 1111
Fig. 2: 741 Pin-Out
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Fig. 4: Voltage Follower
Fig. 3: Comparator
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Fig. 5: Noninverting Amplifier
Fig. 6: Inverting Amplifier
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Fig. 7: Differentiator
Fig. 8: Integrator
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Fig. 9: D/A Converter