Lab Report:
EXPERIMENT #1:
OPERATIONAL
AMPLIFIERS
Fabian Cuba
ECE 340L Experiment #1
Fabian Cuba
ECE 340 L
Prof: Chattopadmyhay
2/28/21
Lab Report Write Up:
Experiment #1
Experiment: Operational Amplifiers
1.- Abstract:
In electronics, a signal amplifier behaves as a voltage-controlled voltage source whose
output voltage is always equal to its input voltage multiplied by a constant voltage gain. Ideally
the voltage gain should remain constant over all possible input voltage values and the resulting
amplifier is a linear circuit (a circuit that observes both the homogeneity and the additivity
properties). A practical amplifier, in general, operates properly only over a limited range of
input-signal-level fluctuations (known as the input dynamic range of the amplifier). Operation
outside this range results in a “distorted” output signal, as the output becomes a nonlinear
function of the input. A case in point is that of an amplifier circuit that consists entirely of one
component (an integrated circuit) known as the operational amplifier (Op-Amp). While the OpAmp offers a tremendous amount of signal amplification (order of °±²), the dynamic range it
provides is extremely tiny (order of μV). To be useful in building any practical amplifier circuit,
negative feedback must be applied around the Op-Amp. Among many benefits of negative
feedback, negative feedback empowers the amplifier circuit to trade amplification for dynamic
range: the larger the amount of negative feedback is applied, the wider the dynamic range
becomes, at the expense of a lesser amount of amplification. This experiment examines the
behavior of a general purpose Op Amp (LF411) as a circuit-building component. In addition, it
investigates the mechanism of negative-feedback application around the Op-Amp. The
characteristics of the two basic Op-Amp circuit configurations (Inverting & non-inverting) are
also investigated. This investigation looks at the conduct of a universally useful Op Amp
(LF411) as a circuit-building segment. Moreover, it researches the component of negativecriticism application around the Op-Amp. The attributes of the two fundamental Op-Amp circuit
arrangements (Inverting and non-transforming) are additionally explored.
2.- Tools:
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Digital Oscilloscope
MyDaq system
Breadboard
Wires
Resistors
MyDaq power supply
PSPICE
Computer
Multimeter
Digital function generator
3.- Theory:
In this lab, we will be simulating four basic configurations using the LF411 op amp. You
can get the LF411 part from the library called EVAL. Note that the amplifier has two terminals
labeled os1 and os2 besides the regular pins, and you can leave these two pins unconnected.
First, I was able to measure the offset voltage of the circuit, then I was able to invert the gain
amplifier. Finally, the last step of the experiment was to work with the operational amplifier as a
non-inverting gain amplifier, probably the most difficult part of the experiment. In order to
execute the experiment, I built the circuit on PSPICE software first, then I analyzed how
everything worked in the software. After that I got out my MyDaq digital power supply and
oscilloscope and built it using the LF411. I used my knowledge of IC chips as well as the
preliminary calculations to figure out the resistor values that I had to use for the circuit and all of
it different scenarios. I was able to test the current and power with the multimeter I had, then I
was able to connect the MyDaq and use both the function generator as well as the oscilloscope to
get the most accurate readings of the graph and make sure that the circuit was built correctly and
that there were no erroneous mistakes along the building process. I used ohm’s law as well as my
study of resistor color combinations to know what resistor to place.
Operational amplifiers can be used to perform mathematical operations on voltage signals such
as inversion, addition, subtraction, integration, differentiation, and multiplication by a constant
and comparison. Operational amplifiers are meant to amplify the readings throughout the circuit
which in our case it did work and was able to portray and show the way in which we got all the
calculations through the digital oscilloscope built into the MyDaq software.
Formulas:
V0 = V1 +V2 +V3
V0 = (V2-V1)
"
"
𝑉! = −("! 𝑉# + "! 𝑉$ )
%
"
#
"
Gain = %$ = 1 + "#
"
"
Vo = -1/RC òVin dt
Theorems:
• Superposition theorem
• Kirchhoff’s Laws
• Ohm’s Law
• Thevenin’s Theorem
• Miller Theorem
4.- Results and Discussion:
Presented are the following results, specifically going in sequential order following CSUN's
order lab report format.
1. Preliminary calculations
1A.
Measurement of V0, as giving with predefined values following (fig 1.4)
Thus, proving output voltage is applicable to (fig 1.4)
1B. Calculate values for the resistor (R1) and (R2), defined within their corresponding
voltage gain formulas.
These values are calculated as follows replace V0 and Vi by their corresponding values R1 and
R2 precede to solve. Following results show
R2 = 2kOhms
R1 = 100KOhms
1C. Calculate values for resistors R2 and R1. Utilizing the following
equations is quite simple and results in the values
R2 = 99Ohms
R1 = 101Ohms
2. Experimental Results
2A. Measuring Offset Voltage:
Following the listed procedures outlined in
(part 1: measuring off set voltage). I begin by constructing the following circuit (Fig 1.6).
Upon completion (Step 1), we must measure the following output
voltage V0 (Step 2). This following measurement yielded the results
V0 = 0.4 mV. Further instructions (Step 3) instructed building of (Fig
1.5) using the following resistor values R1 = 33kOhms, R2 = 3.3 M
ohms. (Step 4) asked for the re-measurement of V0, using above
derived equation in (1AB). Resulting in V0 =0.4 mV.
2B. Inverting Gain Amplifier:
As instructed by the lab manual, I was entrusted with making (Fig
1.7). Utilizing values in pre-lab directions (R1 = 2kOhms, R2 = 100 K ohms). When built,
following estimations were recorded utilizing steps laid out in page 8 of the manual. Utility the
estimations of Vi and V0 brought about Vi = 1.133 V, V0 = 87.89 mV. These estimations were
taken utilizing an oscilloscope (Fig 1.0). Following said estimations brought about the addition
count Av = 0.07757. Further estimations should be taken for the stage move. Coming about stage
move 36.87 0. When gain and Vi and V0, and stage move counts are finished. Produce to (Step
3), estimating the - 3dB move of recurrence. Methodology a – d, shows the legitimate strides to
finish this estimation. Step (d) requires the computation of gain at every recurrence using the
condition [Av(dB) = 20log(V0/Vi)]. Table and chart of results as follows:
The inverting amplifier contains one inverting operational amplifier, a function generator, no
resistors, and a short circuit replacing the feedback resistor.
Measured Vo
Simulated Vo
Re-simulated Vo Percent Error
w/ -100 gain
Values
0.5mV
10mV
-0.3mV
66.69%
myDAQ Bode Plot -100 Gain
PSPCIE: Bode Plot -100 Gain
After analyzing the bode plot, the -3 dB is measured at 2000 Hz at 37 dB.
Amplitude mV
Gain dB
93.75
38.35
101.6
39.05
70.31
35.85
68.36
35.61
83.98
37.33
82.03
37.19
76.17
36.55
52.73
33.35
52.73
33.36
37.71
30.44
48.93
32.70
44.92
31.96
35.16
39.83
23.44
36.31
29.30
28.25
42.97
31.57
29.30
28.25
17.58
23.81
19.53
24.72
19.21
24.58
Step 4 of the operating amplifier instructed that we observe the following effects that an increase
of the power supply will have on the output voltage. Unfortunately the MyDaq has a fixed
voltage of 15 + and 15 – Volts, therefore I am not able to complete this part.
Step 5 asked for a repeat of steps 1 – 4 with a gain of -100. Table and graph of results as follows:
Step 6 instructed that we compare results of both amplifiers, the following is the results.
Results as follows:
Graph:
Fb (Open loop gain cut off frequency): 0.707
Oscilloscope diagram with a set trigger fig. 1.10
Ft (Gain bandwidth product):
Oscilloscope Diagram with a set phase shift and a gain of -100
2C. Non-Inverting Gain Amplifier:
As instructed, I built the non-inverting amplifier as shown in (Fig 1.10). Utilizing previous
values of (R1 = 2kOhms, R2 = 100 K ohms). Once built, I recorded the following measurements
for V0 =--3.033 and gain of the amplifier equating to -32.55mW. Further steps must be taken to
calculate phase shift, resulting in a phase shift of -1.9 (DIV). Further instructions asked to repeat
previous steps 1 – 3 with a gain of 100.
Lab Manual Fig 1.10.
PSPICE Figure 1.10 1 Gain
Results as follows (Fig 1.10):
Graph:
Standard oscilloscope reading of the circuits (resistor values may vary due to
erroneous resistors given in Lab Kits
PSPICE: OSCILLOSCOPE 1 GAIN
After collecting the data for the 1 gain non-inverting amplifier in the table below, the PSpice
green wave represents Vo while the red wave represents Vi. Now for the myDAQ, the blue wave
represents Vo while the green wave represents Vi. The calculations match the data measured
physically and from PSpice with Vi calculated as 100mV, myDAQ measured as 100.64mV, and
PSpice measured as 100mVwith a 0.64% error. For Vo, the values also matched both the
calculated and measured values of Vo calculated as 100mV, myDAQ measured as 100.85mV,
and PSpice measured as 100V with a 0.85% error.
1 Gain
Vo myDAQBlue wave
V1 myDAQGreen wave
myDAQ
100.85mV
PSPICE
100mV
Calculated
100mV
%ERROR
0.85%
100.64mV
100mV
100mV
0.64%
Non-inverting Amplifier w/ 100 gain
Lab Manual Fig 1.10.
PSPICE Fig. 1.10, 100 Gain
Fb (Open loop gain cut off frequency): 15,000
Oscilloscope Diagram reading with a set trigger Ft (Gain bandwidth product): 15,000
Oscilloscope Diagram with a set phase shift and gain +100
PSPCICE OSCILLOSCOPE 100 GAIN
After collecting the data for the 1 gain non-inverting amplifier in the table below, the PSpice
green wave represents Vo while the red wave represents Vi. Now for the myDAQ, the blue wave
represents Vo while the green wave represents Vi. The calculations match the data measured
physically and from PSpice with Vi calculated as 100mV, myDAQ measured as 100.64mV, and
PSpice measured as 100mVwith a 0.64% error. For Vo, the values also matched both the
calculated and measured values of Vo calculated as 100mV, myDAQ measured as 100.85mV,
and PSpice measured as 100V with a 0.85% error.
100 Gain
Vo myDAQBlue wave
V1 myDAQGreen Wave
MyDaq
9.935V
PSPICE
10V
Calculated
9.9V
% ERROR
0.35%
100.69mV
100mV
100mV
0.69%
3. Pspice results
Results as follows (Fig 1.7) gain:
Schematic:
Graph:
* Note Pink graph = inverting
Purple graph = non-inverting
Fb (Open loop gain cut off frequency): 0.707
Ft (Gain bandwidth product): 15,000
Results as follows (Fig 1.7) gain -100:
Schematic:
Fb (Open loop gain cut off frequency): 0.707
Ft (Gain bandwidth product): 15,000
5.- Conclusion:
• It was very interesting to see and play with the operational amplifier as well as the
oscilloscope. I learned a lot about how to properly use the oscilloscope as well as
the function generator built into the MyDaq. The results were astonishing to see
the voltage fluctuating constantly even though the MyDaq had its limit of 15
volts. I found it very interesting how changing the setup of the circuit was able to
alter so many factors.
• I feel that this experiment set a foundation for future labs and gave a great review
of how to use the oscilloscope and function generator which I needed a refresher
on how to use it. I learned a lot about op-amps and feel confident that I can now
implement these into the actual field of engineering. I know that this can help me
learn all of the necessary and set the foundation for all future classes as well as
the upcoming labs. I also learned about managing gain and being able to change
the output of each circuit. I mastered my skills with the multimeter as well as
building the circuits from a blueprint.
• There was a lot of room for error in this experiment. One of the biggest problems
was when building the circuit students could build it incorrectly and potentially
cause a fluctuation in the way the voltage and current is portrayed in the
oscilloscope. It is simple to identify mistakes, because one of two scenarios will
happen. The IC chip (LF411) will overheat, or the oscilloscope readings will be
off the charts in which case you will know that something is not right. Obviously,
there will be variations in certain calculations as it is an experiment. In order to
get the % error, the formula is actual value-expected value/ expected value *
100%. In order for you to get the expected value, is through the PSPICE software.
This will give you the most accurate result since it is a simulated value, then the
actual value is what you calculate to be while performing the experiment. It was I
found that in my results there was little to no error maximum was about 1% error
throughout all three parts of the experiment. Remedies to fix your percent error
would be to alter the settings of the function generator to get it to match what
PSPICE would show. Also potentially changing the resistor values one had
chosen to get a different result when applying the oscilloscope readings. The most
obvious remedy is making sure one is using the correct components and chips
necessary for the experiment.