Lab 4 - EE 420L
Authored
by Hongzhong Li ,
Today's
date: 02/27/2015
Email: lih12@unlv.nevada.edu
NSHE ID: 2000202827
Lab
description
Op-amps II, gain-bandwidth product and slewing
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 know that the unity gain frequency (Fun) is 1.3 MHz
For Non-Inverting op-amp the bandwidths: BW= Fun/AOL . Therefore:
| Gains | Bandwidth(BW) |
| 1 | 1.3MHz |
| 5 | 260KHz |
| 10 | 130KHz |
- 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.
When designing the circuit for different gains, we ultilize the formula Av=1+R2/R1 to achieve the desirable gain.
| Non-Inverting OP-AMP with gain of 1 |
| Schematic and Simulation |  |
| Experimental Result |  |
| Non-Inverting OP-AMP with gain of 5 |
| Schematic and Simulation |  |
| Experimental Result |  |
| Non-Inverting OP-AMP with gain of 10 |
| Schematic and Simulation |  |
| Experimental Result |  |
- Associated comments should include reasons for any differences between your estimates and experimental results.
The reason that the simulation bandwidths are higher than the
experimental results is because we are only supplying 5V to the op-amp
comparing to the 30V specified in the datasheet. If we use a 30V supply
voltage we can expect to see better matching result.
- Repeat these steps using the inverting op-amp topology having gains of -1, -5, and -10.
For Inverting op-amp the bandwidths: BW= R2/(R1+R2)/abs(-R2/R1) . Therefore:
| Gains | Bandwidth(BW) |
| -1 | 650KHz |
| -5 | 217KHz |
| -10 | 118KHz |
| Inverting OP-AMP with gain of 1 |
| Schematic and Simulation |  |
| Experimental Result |  |
| Inverting OP-AMP with gain of 5 |
| Schematic and Simulation |  |
| Experimental Result |  |
| Inverting OP-AMP with gain of 10 |
| Schematic and Simulation |  |
| Experimental Result |  |
- 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.
From the datasheet, we can get the following entry shown the slew rate of LM324.
Using
a pulse input signal to measure LM324 slew rate. The circuit and
simulation result are shown as below. The output from 10% to 90% is equal to 0.086V and the rise time is approximately 0.448us.The
slew rate being defined as the maximum change in voltage per unit time
can be calculated by dividing the ouput voltage by the rise time
(0.086V/0.448us = 0.192 V/us)
Similiary, we can measure the slew rate using a sinewave input signal. The circuit and simlation result is shown as below. The slew rate of a sine wave input to the LM324 op-amp is approximately equal to (0.6V/2.904us = 0.2 V/us)
- Provide comments to support your design decisions.
For this experiment, we increased our rail to 30 V to prevent our circuit from saturation. The
design is implemented using the non-inverting topology. By measuring
the rise time and output voltage from 10%-90% we estimate the slew
rate. Since the
slew rate of a circuit depends on both the amplitude and frequency of
the circuit becuase the slew rate can be achieved by increasing one or
the other (or both), therefore by increasing both, we can generate the
maximumin slew rate with a reasonable input signal.
- Comment on any differences between your measurements and the datasheet’s specifications.
Our
measurements are about half of the typical value (0.4V/us) of the
datasheet's specifications. This is due to our design not generating
enough output swing since the circuit's gain is relatively low.
Therefore our slewrate is not as high as the typical value of (0.4
V/us) from the datasheet.
Concluson:
From
above experiments, I learned the relationship between frequency,
close-loop gain, unity-gain frequency and gain-bandwidth product. By
studying gain-bandwidth product, we can deisgn circuit using the
two methods to measure the slew rate of an op-amp.
Ensure
that your html lab report includes your name, the date, and your email
address at the beginning of the report (the top of the webpage).
When finished backup your work.
Back up Work
After everything is completed, the lab is saved into a zip file and sent to my email.
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