Lab 4 - EE 420L
Authored
by Tyler Ferreira,
ferret1@unlv.nevada.edu
February 21, 2017
Pre-lab work
Again, this lab will utilize the LM324 op-amp (LM324.pdf).For the following questions and experiments assume VCC+ = +5V and VCC- = 0V.
- Estimate, using the datasheet, the bandwidths for non-inverting op-amp topologies having gains of 1, 5, and 10.
From
the datasheet we can see that the gain bandwidth product of our
amplifier is typically 1.3MHz. We can easily solve for our bandwidths
at different gains by dividing the
gain bandwidth product by the gain.
Hand calculations for bandwidth of a non-inverting op-amp topology:
- Experimentally verify these estimates assuming a common-mode voltage of 2.5 V.
- Your
report should provide schematics of the topologies you are using for
experimental verification along with scope pictures/results.
- Associated comments should include reasons for any differences between your estimates and experimental results.
Schematics of the topologies that I implemented on to my breadboard for testing:
| Gain of 1 | Gain of 5 | Gain of 10 |
 |  |  |
I chose to use a 100k resistor for my R value in these schematics.
Scope Pictures:
| Gain of 1 | Gain of 5 | Gain of 10 |
Signal at low frequency to find the amplitude of the output signal with maximum gain. | 
Signal at low frequency to find the amplitude of the output signal with maximum gain. | 
Signal at low frequency to find the amplitude of the output signal with maximum gain. |
Signal at the 3dB frequency (Vout*0.707). | 
Signal at the 3dB frequency (Vout*0.707). | 
Signal at the 3dB frequency (Vout*0.707). |
| Comparison of Results | Gain of 1 | Gain of 5 | Gain of 10 |
| Calculated | 1.3MHz | 260kHz | 130kHz |
| Experimental | 1.2MHz | 123kHz | 46kHz |
By
comparing my calculated results with my experimental results I noticed
that as my gain increased my experimental bandwidth values were getting
worse. One reason for this can be because I used a VCC of +5V, but in
the datasheet VCC = +15V. I also used Vin = 100mV, but in the
datasheet they used Vin = 10mV.
- Repeat these steps using the inverting op-amp topology having gains of -1, -5, and -10.
Hand calculations for bandwidth of an inverting op-amp topology:
Schematics of the topologies that I implemented on to my breadboard for testing:
| Gain of -1 | Gain of -5 | Gain of -10 |
 |  |  |
Just like in my non-inverting topology I used a 100k resistor for R.
Scope Pictures:
| Gain of -1 | Gain of -5 | Gain of -10 |
Signal at low frequency to find the amplitude of the output signal with maximum gain. | 
Signal at low frequency to find the amplitude of the output signal with maximum gain. | 
Signal at low frequency to find the amplitude of the output signal with maximum gain. |
Signal at the 3dB frequency (Vout*0.707). | 
Signal at the 3dB frequency (Vout*0.707). | 
Signal at the 3dB frequency (Vout*0.707). |
| Comparison of Results | Gain of -1 | Gain of -5 | Gain of -10 |
| Calculated | 650kHz | 216kHz | 118kHz |
| Experimental | 690kHz | 80kHz | 39kHz |
By comparing my calculated results with my experimental results I
noticed that as the magnitude of my gain increased, my experimental bandwidth values were
getting worse. One reason for this can be because I used a VCC of +5V,
but in the datasheet VCC = +15V. I also used Vin = 100mV, but in the
datasheet they used Vin = 10mV.
- Design
two circuits for measuring the slew rate of the LM324. One circuit
should use a pulse input while the other should use a sinewave input.
- Provide comments to support your design decisions.
- Comment on any differences between your measurements and the datasheet’s specifications.
Schematics for measuring the slew rate of the LM324:
| Pulse Input | Sinewave Input |
 |  |
I
decided to use the non-inverting op-amp topology with a gain of 1. I
used this topology so that I could easily compare the input and output
signals on the scope without using different volts/div settings. I also
used this gain because unity gain is what the datasheet uses for the
typical slew rate of the op-amp.
To measure the slew rate of the
op-amp I will start the experiment with a low frequency (around 1kHz)
and then speed up the signal until the output signal can't keep up with
the input. This will cause the slew rate of the op-amp to show on the
scope.
Scope Pictures:
 |  |
Calculations from experiments:
For the step input I took the difference in voltage and time between the 10% and 90% point.
For the sinewave input I took the difference in voltage and time between the peaks.
Entry from the LM324 datasheet:
The typical value for slew rate according to the datasheet is 0.4 V/us.
My
experimental values for the slew rate with a step input and a sinewave
input are very close to the typical slew rate of this op-amp. One
reason my experimental value might be different from the datasheet
value is because I used a VCC = +5V, but in the datasheet they used VCC
= +15V. I used the same Vin and gain as the data sheet but without a
load.
I will backup my work on to my OneDrive and my Desktop:
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