Lab 4 - EE 420L
For the following
questions and experiments assume VCC+ = +5V and VCC- = 0V.
·
Experimentally verify these estimates assuming a common-mode
voltage of 2.5 V.
o Your report
should provide schematics of the topologies you are using for experimental
verification along with scope pictures/results.
o Associated
comments should include reasons for any differences between your estimates and
experimental results.
·
Repeat these steps using the inverting op-amp topology having
gains of -1, -5, and -10.
·
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.
o Provide
comments to support your design decisions.
o Comment on any
differences between your measurements and the datasheet’s specifications.
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.
Estimate,
using the datasheet, the bandwidths for non-inverting op-amp topologies having
gains of 1, 5, and 10.
The
Gain Bandwidth Product (GPB) is the closed loop gain multiplied by the
bandwidth at that gain and is constant (1xBW=GBP). So at a gain of 1 we
can see from the data sheet that the Band width is at 1.3MHz. To find the BW of
the 5 gain and the 10 gain you just divide 1.3MHz by the gain.
1gain
has a BW of 1.3MHz; 5gain has a BW of 260kHz;10gain has a BW of 130kHz
This
is the simulation of the 1gain.
This is the
simulation of the 5gain.
This is the
simulation of the 10gain.
As you can see
from the simulations the BW gets smaller as the gain gets larger. This is also shown in the hand calculations.
Experimentally
verify these estimates assuming a common-mode voltage of 2.5 V.
oYour report
should provide schematics of the topologies you are using for experimental
verification along with scope pictures/results.
oAssociated
comments should include reasons for any differences between your estimates and
experimental results.
When determining
the BW of the op-amp you sweep the frequency until the output has droped by
-3db or 70.7% of the output
The 1 gain we
used was a signal of 200mV so the -3db of this voltage is 70.7% of this which
is 141.4mV and the frequency that this was achieved was 700KHz
The 5 gain we used was a signal of 200mV and the -3db of this is 707mV at
a frequency of 140kHz
The 10 gain we
used was a signal of 100mv and the -3db was 707mV at a frequency of 80kHz. The
reason that the voltage at 3db for the 10 gain and the 5 gain 0are the same is
because I picked half the amplitude as the 5 gain and doubled the gain to 10.
This caused the output voltages to match, but as you can see the BW is still
effected by the gain.
The data is
summerized below.
|
|
Estimated |
Simulated |
Expeimental |
|
1
gain |
1.3MHz |
1MHz |
700kHz |
|
5 gain |
260kHz |
200kHz |
140kHz |
|
10
gain |
130kHz |
100kHz |
80kHz |
Repeat these
steps using the inverting op-amp topology having gains of -1, -5, and
-10.
Using the same
method of estimation above we will find the BW of -1 to b 1.3MHz, -5 gain to be
260Hz, and the -10 gain to be 130kHz. Our simulation shows that the frequencies
are lower than the estimated values.
The -1 gain we
used was a signal of 200mV so the -3db of this voltage is 141.4mV and the
frequency that this was achieved was 425KHz
The -5 gain we
used was a signal of 200mV and the -3db of this is 707mV at a frequency of
125kHz
The -10 gain we
used was a signal of 100mv and the -3db was 1.414V at a frequency of 65kHz
The Data is
summerized below
|
|
Estimated |
Simulated |
Expeimental |
|
1 gain |
1.3MHz |
500kHz |
425kHz |
|
5 gain |
260kHz |
164kHz |
125kHz |
|
10 gain |
130kHz |
89kHz |
65kHz |
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.
Slew is the rate
at which the op amp output changes fot a LM 324 the slew rate is about 0.4V/us
For our first
experiment we used a voltage follower and pulsed it to see that the output cant
follow as fast as the in put and we see some delay.
With this pulse
we can take the input of 500mV and divide it by the rise time 1.418us and we
get 0.352V/us which is very close to the data sheet.
For our second experiment
we used a sinusoid input to a voltage follower.
If we sweep the amplitude you will notice that as the amplitude gets
larger the slope on the output gets steeper, and if this slope gets steeper
than the slew rate of the op amp the output will be distorted. This is because
it cannot change fast enough to keep up with the sine wave.
With these
results we can look at the rise time and see that if we take the output of 1.5V
and divide it by the rise time we will get the slew rate. This is calculated to
be 0.38V/us
Conclution: I learned about slew rate and Band Width in
this lab. Reading the data sheet is very
important when deciding whether you are looking for speed or gain.