Lab 4 - EE 420L: Engineering Electronics II
Again, this lab will utilize the LM324 op-amp (LM324.pdf).
For the following questions and experiments assume VCC+ = +5V
and VCC- = 0V.
Experiment 1:
Estimate, using the datasheet, the bandwidths for
non-inverting op-amp topologies having gains of 1, 5, and 10.
The datasheet indicates the unity gain frequency seen below
in figure 1, 
, is 1.3MHz at
30V.
Figure 1
Below in figure 2 is
the open loop frequency response graph which can be used to esitmate the
bandwidths of each gain.
Figure 2
From figure 2 I can esitimate the unity gain frequency around
700kHz and a gain of 5 is around 120kHz and a gain of 10 is roughly 80kHz. These estimates are based on a V+ voltage
of 10 to 15 Vdc. After the experimental
resluts will be a table consolidating the extracted information.
Below in figure 3 is the schematic used to obtain the
experimental unity gain bandwidth and the 3 db frequency followed by the
experimental results. A 200mv pk-pk sine
wave signal was used for the input. As
you can see there is a delay on the output signal, I believe this is due to the
slew rate which will be discussed at the end of this report.
Figure 3
Below in figure 4 is the schematic used to obtain the
experimental results of an opamp with a gain of 5 and it’s correlating
bandwidth and the 3 db frequency followed by the experimental results. A 50mV RMS sine wave signal was used for the
input.
Figure 4
Below in figure 5 is the schematic used to obtain the experimental
results of an opamp with a gain of 10 and it’s correlating bandwidth and the 3
db frequency followed by the experimental results. A 50mV RMS sine wave signal was used for the
input.
Figure 5
Below in table 1 is the consolidated information gathered
above. *The 3db frequency was obtained by taking the Vout without roll off and
multiplying by .707*. Bandwidth is the
corresponding 3db frequency.
|
Gain |
Input Voltage (mV RMS) |
3db Output (mV RMS) |
Experimental Bandwidth (kHz) |
Estimated Bandwidth (kHz) |
Theoretical Bandwidth from GBP @30V V+ |
|
1 |
70 |
53 |
728 |
700 |
1.3MHz |
|
5 |
50 |
175 |
170 |
120 |
260kHz |
|
10 |
50 |
350 |
85 |
80 |
130kHz |
Table 1
My esitmated Bandwidths were fairly close to the experimental
results, the difference can be explained in the V+ Voltage I used in
my experiments vs the V+ voltage used to obtain the results on the
data sheet. I used 5V V+ the
data sheet uses 10-15V V+. The
theortical bandwidth was obtained with the following equation: 
Repeat these steps using the inverting op-amp topology having
gains of -1, -5, and -10.
Below in figure 6 is the schematic used to obtain the
experimental negative unity gain bandwidth and the 3 db frequency followed by
the experimental results. A 50mv RMS
signal was used to show the -1 gain while A 70mv RMS sine wave signal was used
for the input to show the 3db frequency.
This is because the pictures were taken on separate days.
Figure 6
Below in figure 7 is the schematic used to obtain the
experimental results of an opamp with a gain of -5 and it’s correlating
bandwidth and the 3 db frequency followed by the experimental results. A 15mV RMS sine wave signal was used for the
input.
Figure 7
Below in figure 8 is the schematic used to obtain the experimental
results of an opamp with a gain of -10 and it’s correlating bandwidth and the 3
db frequency followed by the experimental results. A 15mV RMS sine wave signal was used for the
input.
Figure 8
Below in table 2 is the consolidated information gathered
above. *The 3db frequency was obtained by taking the Vout without roll off and
multiplying by .707*. Bandwidth is the
corresponding 3db frequency.
|
Gain |
Input Voltage (mV RMS) |
3db Output (mV RMS) |
Experimental Bandwidth (kHz) |
Estimated Bandwidth (kHz) |
Theoretical Bandwidth from GBP @30V V+ |
|
-1 |
70 |
49 |
546 |
600 |
650kHz |
|
-5 |
15 |
53 |
141 |
200 |
217kHz |
|
-10 |
15 |
106 |
80 |
85 |
118kHz |
Table 2
At lower gains the bandwidth is much lower than the positive
gain counterparts. This needs to be
taken into consideration when estimating the bandwitdh of the inverting
topology vs the non-inverting topology.
The theoretical values were obtained with the following equation: 
.
Experiment 2
Design 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.
The LM324 datasheet lists the slew rate at 
as seen from figure 9 below.
Figure 9
Below in figure 10 is the schematic used to determine the
slew rate of the LM324 followed by the square wavie input signal and the sine
wave input signal results.
Figure 10
The slew rate was calculated using the following equation: 
. My experimental slew rate is roughly
half of that shown on the data sheet. My
experiment was not driving a load, and the data sheet’s result was determined
using an RC load. A resitor value of 2k
and a capcitance of 100pf which introduces a time delay of 0.14us. I believe this would bring my experimental
slew rate value up to roughly .25V/us which is still far off from the data
sheet value. A different reason could be
the V+ of my setup vs the V+ of the data sheet, I used 5V
and the data sheet value was obtained with a V+ of 15V. *NOTE* The frequency needed to be much higher
for the sine wave input vs the square wave input to obtain the slew rate. Which makes sense as the square wave’s demand
for change in voltage over time is much greater then that of the sine wave.
After the slew rate experiment I have concluded that the slew
rate introduced the phase shift found in experiment 1.
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