Experiment 1
OperationalAmplifiers
Introduction​:
This lab studies some of the basic uses of op amps. Because the main use of the op amp is
as an amplifier, the three most common configurations will be studied. These include the
inverting, non-inverting, and differential amplifier circuits. The lab will also investigate
powering an op-amp from a single supply.
Equipment Used:
Type
Oscilloscope
Function Generator
DC Power Supply
Digital Multi Meter
​Model
HP123
Serial No.
Calibration Date
123456
07-11-10
Parts Used:
QTY Component
1
1
1
1
1
1
1
Value
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Op-amp
Type
10K
100K
33K
1K
3.3M
1.5M
Carbon, +/-5%
Carbon, +/-5%
Carbon, +/-5%
Carbon, +/-5%
Carbon, +/-5%
Carbon, +/-5%
LF411
Software Used:
Pspice
MS Office 2010
Released Version: 16.0.0.s001
Theory:
The LM741 Op amps have eight terminals, but we will only examine five of them: the
VS+ , VS-, inverting input (V- ), non-inverting input (V+), and output (Vout ). The VS+ and VSare the positive and negative power supplies. The output voltage cannot be greater than the
positive power supply nor can it be less than the negative power supply. In an ideal op amp, no
current flows into the inverting and non-inverting inputs, although current can flow out of the
input-controlled output. There is also no voltage difference between the inputs. One of these
inputs cannot have its voltage change without the other input either increasing or decreasing in
voltage to match. This ensures linear operation and keeps the output at the same voltage. This
equilibrium is maintained by negative feedback through a feedback loop. Feedback loops direct
the output voltage back to the inverting input. This negative feedback drives the circuit back to
equilibrium in a manner specific to the circuit configuration.
Procedure:
Part 1​: Measuring Offset Voltage
Constructed the following circuit and our Vo was measured to be ​0.78mV
Graph from Pspice Simulation
We then constructed the following circuit and measured Vo again. R1 was set to 33kΩ
ohm and R2 was set to 3.3MΩ. Our measured result was Vo=0.259V
Graph from Pspice Simulation
Part 2: ​Inverting Gain Amplifier
Constructed the following circuit. Using the Pre-Lab to obtain a -​10 Gain​. We let
R2=100kΩ and R1=1KΩ
Graph from Pspice Simulation
Oscilloscope reading of -10 gain w/ phase shift.
Frequency(khZ)
Vi
Vo
20dB Gain
1
0.098
0.98
20.00
10
0.098
0.96
19.82
30
0.098
0.92
19.45
35
0.098
0.88
19.07
40
0.098
0.88
19.07
45
0.098
0.86
18.87
50
0.098
0.84
18.66
60
0.098
0.8
18.24
70
0.098
0.72
17.32
80
0.1
0.7
16.9
90
0.102
0.66
16.22
100
0.102
0.6
15.39
120
0.102
0.56
14.79
Oscilloscope reading of -100 gain w/ phase shift.
Frequency(khZ)
Vi
Vo
20dB Gain
1
0.098
9.6
39.82
5
0.098
8.4
38.66
10
0.098
6.4
36.30
15
0.098
4.8
33.80
20
0.098
4.0
32.22
25
0.098
3.2
30.28
30
0.102
2.8
28.77
50
0.102
1.6
23.91
60
0.102
1.36
22.50
75
0.102
1.04
20.17
90
0.102
0.88
18.72
100
0.102
0.8
17.89
120
0.102
0.68
16.48
Part 3​: Non-inverting Gain Amplifier
Constructed the following circuit. Using pre-lab equations obtain a gain of 1. Let R1= 1.53 M
ohm and R2=1K ohm.
Graph from Pspice Simulation
Oscilloscope reading of 1 gain.
Oscilloscope reading of 100 gain.
Conclusion:
In this lab we learned based on the experiment’s results,using a specific circuit, collecting and
measuring data, a summing amplifier with two inputs was built, and the group has established a
better understanding on how an amplifier operates. We were able to see our Vout remains pretty
consistent at low frequencies and then dives at around 35kHz. The similarities between the
inverting op-amp and non inverting op amp were pretty striking. We expected them to be
completely different but they were very similar. This laboratory gave us opportunity to see
working amplifiers and prove the theoretical formulas for their gains and output voltages. In this
lab, we also experienced building circuits for inverting, non-inverting and summing amplifiers
and got basic understanding by analyzing their output signals with the help of oscilloscope and
multimeter