Lab 4 - ECE 420L
Authored
by Silvestre Solano,
Email: Solanos3@unlv.nevada.edu
2-27-2015
For
the following questions and experiments assume VCC+ = +5V and VCC- = 0V. The LM324 Op-amp is used.
Estimate, using the
datasheet, the bandwidths for non-inverting op-amp topologies having
gains of 1, 5, and 10.
According to the data sheet, the bandwidth product for this op-amp is 1.3 MHz at unity gain as shown below.
For
a gain of 1, the bandwidth is obviously 1.3 MHz. For a gain of 5, the
bandwidth is 1.3 MHz/5 = 260 KHz and for a gain of 10, the bandwidth is
1.3 MHz/10 = 130 KHz.
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.
Gain of 1
For
the gain of 1, the op-amp shown above was built in the lab and tested.
The circuit was tested at frequencies above the 3 dB frequency and the
bandwidth gain product was estimated from these readings. The results
are shown below.
| 500 KHz | 800 KHz |
 |  |
| Bandwidth Gain Product= (500 KHz)*(136/216) = 314KHz | Bandwidth Gain Product = (800 KHz)*(80/216) = 296 KHz |
| At unity gain frquency, bandwidth = 300 KHz |
In
the above table, it can be seen from both experiments that the
bandwidth gain product is about 300 KHz, which would also be the same
bandwidth for the unity gain frquency.
Gain of 5
| 200 KHz | 500 KHz |
 |  |
| Bandwidth Gain Product = (200 KHz)*(640/210) = 592 KHz | Bandwidth Gain Product = (500 KHz)*(320/210) = 740 KHz |
| The Bandwidth Gain Product is about 700 KHz. At a gain of 5, the Bandwidth is about (700 KHz)/5 = 140 KHz |
In
the above experiment, the bandwidth gain product is estimated to be
about 700 KHz. At a gain of 5, This would correspond to a bandwidth of
about 140 KHz.
Gain of 10
| 100 KHz | 500 KHz |
 |  |
| Bandwidth Gain Product = (100 KHz)*(1.12/0.192) = 583 KHz | Bandwidth Gain Product = (500 KHz)*(320/192) = 833 KHz |
| The Bandwidth Gain Product is about 700 KHz. At a gain of 10, the Bandwidth is about (700 KHz)/10 = 70 KHz |
In
the above experiment, the bandwidth gain product is estimated to be
about 700 KHz. At a gain of 10, This would correspond to a bandwidth of
about 70 KHz.
In
the experiments performed, none of the measured values matched the
theoretical values. This is probably because the gain bandwidth product
obtained from the datasheet was measured under specific conditions that
were not present in my experiments. Hence, the measured results will be
different from the theoretical. And also, the measured bandwidths are
rough estimates given that the bandwidth gain product was never really
constant to begin with.
| Gain | Theoretical BW | Measured BW |
| 1 | 1.3 MHz | 300 KHz |
| 5 | 260 KHz | 140 KHz |
| 10 | 130 KHz | 70 KHz |
Repeat these steps
using the inverting op-amp topology having gains of -1, -5, and
-10.
Gain of -1
The result from the implementation of the above circuit is shown below.
Apparently, the 311 lab has better oscilloscopes than the 350 lab. The bandwidth is measured directly to be about 800 KHz.
Gain of -5
Experiment Results
The measured bandwidth is about 110 KHz
Gain of -10
Experimental Results
The measured bandwidth is about 65 KHz.
Total Results.
| Gain | Bandwidth |
| -1 | 800 KHz |
| -5 | 110 KHz |
| -10 | 65 KHz |
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.
| Square Wave | Sine Wave |
| Schematic |  |  |
| Result |  |  |
| Slew Rate | 86 mV / 348 nS = 0.24 Volts/uS | 600 mV / 2.904 uS = 0.21 Volts/uS |
In
the above experiments, the design of both op-amp circuits was choosen
because this would theoretically measure the slew rate of the op-amp
itself without any unecesary components like resistors or capacitors.
It is essentially a unity gain follower. The slew rate according to the
data sheet is shown below and it is 0.4 Volts/uS.
The
experimental results are about half of the theoretical value. Again
this is a result of the different conditions in which the slew rates
were obtained. As shown above, the datasheet specifications used a Vcc
of 15. In this lab, we had to use 5 volts for our Vcc. Clearly, the
results will be different since the op-amp will have different power in
the different setups.
As always, I will backup my stuff as shown below.
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