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Lab 2: Op Amp Lab

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Lab 2 Op Amp Lab
VE215 Intro to Circuits
VE215
Lab 2: Op Amp Lab
I. Goals
Learn how to build and test a variety of circuits based on LM 741 Op Amp
chip: non-inverting and inverting amplifiers with fixed gain.
Measure the gain of the amplifier and compare it with theoretical calculations.
Determine the saturated output voltage of the amplifier.

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Lab 2 Op Amp Lab
VE215 Intro to Circuits
VE215
Lab 2: Op Amp Lab
I. Goals
Learn how to build and test a variety of circuits based on LM 741 Op Amp
chip: non-inverting and inverting amplifiers with fixed gain.
Measure the gain of the amplifier and compare it with theoretical calculations.
Determine the saturated output voltage of the amplifier.
II. Introduction
Operational amplifiers (Op Amps) are integrated circuits (ICs) used in many
applications. In this lab, you will build and study LM741.
Op Amp terminals
In Fig1, there are:
 Two terminals for input signals: inverting (labeled -) and non-inverting
(labeled +)
 A terminal for the output signal
 Two terminals for the power supply voltages: positive +Vcc and negative
–Vcc. (e.g. In this lab, set +Vcc = 5V; -Vcc = -5V. )
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2016
Accordingly, for LM741 op amp chip you see in reality, the pin numbers are
shown in Fig2:
Fig2. Pin numbers for LM 741 op amp
Note:
 Pin #8 is not connected; pins #1 and #5 are not used in this lab.
 Do not mistake the connections of input signals (# 2 labeled – and #3
labeled +) for the connections to the power supply (#4 for -Vcc and #7 for
+Vcc).
 Make sure you connect the grounds of oscilloscope, function generator
and DC source together.
The gain of amplifier circuits
The amplifier circuits are characterized by their gain values. The voltage gain
is the ratio of output voltage to the input voltage in the circuit:
Output Voltage Voltage
Input Vol
Gain
tage

In the lab, you can use oscilloscope to measure the input and output
peak-to-peak (ppk) amplitudes of the signals through two channels at the same
time.
Inverting amplifier
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2016
Fig3. Inverting amplifier
For inverting amplifier, the theoretical gain should be:
output F
s A
V R
V
Ga n
R
i   
Non-inverting amplifier
Fig3. Non-inverting amplifier
For non-inverting amplifier, the theoretical gain should be:
1
output F
S A
Ga
V
R
in R
V
  
III.Apparatus
Apart from the DC source you are already familiar with in Lab 1, we are going
to use function generator and oscilloscope this time.
Function generator
Check the next page about the main buttons we would use
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2016
 “Parameter”: to change the amplitude, frequency of wave to generate
*Note: The amplitude here equals to half of the pp value. (i.e. If you set a wave
whose amplitude is 100mV, the measured pp value would be 200 Vpp.)
pp means peak to peak value.
 “1”/ “2”: to switch on the channel.
Oscilloscope
 “Auto scale”: to automatically achieve an output on the screen with proper scale
 “Meas”: to turn on the measurement of the wave
 “1”/”2”: to show or hide the wave you detecting through channel 1 or 2
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2015
IV.Pre-lab Assignment (Finish it before lab or you lose your score for
this part)
1. What would be the gain of a non-inverting amplifier if RF= 100  and RA =
50? What about an inverting amplifier? (Predict your theoretical result.)
2. What should be connected to pins #4 and #7 of LM741? What about #1 and
#5?
3. Should the ground and “–Vcc” be connected together?
4. Connect the components to form a non-inverting amplifier following the steps
in procedure part. This question may save you a lot of troubles during the lab.
V. Procedure
Part I Non-inverting amplifier
You are going to build a non-inverting amplifier in this part.
1. Build the circuit according to the figure below. (You may want to refer to
Fig.2). RF =100, RA=50.
Note:
a. Use the power supply to provide +Vcc=+5V and -Vcc=-5V to the op amp.
b. Use the COM port on the power supply as the ground in the schematic.
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2016
2. Use the function generator to generate a sine wave, and use it as the input
voltage (vi in the figure above). Set the initial amplitude of the sine wave to
0.1Vpp. Use the oscilloscope to measure the output voltage (vo in the figure
above).
3. Increase the input voltage by 0.1Vpp each time and record the corresponding
output until the output voltage is saturate, which means the output voltage is
not increasing any more as the input voltage increases.
Part II Inverting amplifier
You are going to build an inverting amplifier in this part.
1. Build the circuit according to the figure below. (You may want to refer to
Fig.2). RF =100, RA=50.
Note:
a. Use the power supply to provide +Vcc=+5V and -Vcc=-5V to the op amp.
b. Use the COM port on the power supply as the ground in the schematic.
Lab 2 Op Amp Lab
VE215 Intro to Circuits Fall 2016
2. Use the function generator to generate a sine wave, and use it as the input
voltage (vi in the figure above). Set the initial amplitude of the sine wave to
0.1Vpp. Use the oscilloscope to measure the output voltage (vo in the figure
above).
3. Increase the input voltage by 0.1Vpp each time and record the corresponding
output until the output voltage is saturate, which means the output voltage is
not increasing any more as the input voltage increases.
VI.Post-lab
In your post-lab report, you are required to do the following things:
1. You have to give a plot which illustrates the relation between the input
voltage and the output voltage (vpp(out) versus vpp(in)).
2. Calculate the gain of your amplifier based on the data you gather during the
lab and give a plot which illustrates the relation between the gain and the
input. (gain versus vpp(in))
3. You may compare the difference between the expected gain and the measured
gain and perform some error analysis.
4. Using Pspice to simulate the lab circuit is encouraged; bonus is available if
you do it correctly.
Reference:
1. Circuits Make Sense, Alexander Ganago, Department of Electrical Engineering
and Computer Science, University of Michigan,Ann Arbor.