ENGR337 Lab 2018
Lab 4 Operational Amplifiers.
Due Feb 5, Monday 10 pm.
of this lab:
Be familiar with the parameters of an OpAmp.
2. Be able to use an OpAmp to amplify a small signal.
We'll use LM833-N Dual Audio Operational Amplifier
for this lab.
1. We all know that an OpAmp has a very large 'open-loop' gain (~1
million probably). Open the datasheet of the OpAmp and try to find out
the DC open-loop gain on one of its plottings. I have a screen shot for
you below, can you find the DC open-loop gain in one of the plottings? Show it in your report.
When you use an OpAmp, for example, it is powered up by 0-5V. The input
signal is usally small (in the mV range, for example -100 mV - 100 mV).
Since the lowest voltage in your power supply is 0 V, if you don't add
an offset voltage to your input signal, the output cannot be correct.
In the following circuit, it is in an ideal condition since your ideal
OpAmp doesn't have a power supply limit. Do the simulation below, and show the results in your report. (The resistor-capacitor circuit will be used later, but useless here, the capacitor can be 4.7 nF, doesn't have to be 0.01 uF).
the circuit on a breadboard, show the input and the output at the same
time. Explain what you see on the oscilloscope in your report.
However, in real-life, the small signal has to 'ride' on an DC offset.
you cannot see both input and output at the same screen on the
oscilloscope, Press the channel menu button, on the left side, swop it
to AC, then you will remove all the DC signal).
Now, let's Bring the signal to normal. I'll use the DC voltage divider
to make a 2.5 V DC offset voltage, and at the same time, add a DC
offset to the sine wave.
Show the simulation results and compare to the results on your oscilloscope, report these results.
4. Let's add some gain to it.
1) Change R3 to 100k, show the simulation and the measurement on your report.
2) Change R3 to 200k, show the simulation and the measurement on your report, and explain why the signal looks bad.
Discuss in your report that ideally, if you have your OpAmp powered up
at 0-5V, DC offset is 2.5 V, close-loop gain is 20, what is the maximum
input signal is allowed for this configuration? Use Simulation and
Oscilloscope to demonstrate your prediction.
4) What if you change the offset to 1V, answer the same question in item '3)'.
Design the circuit that uses a non-inverting OpAmp to amplify a 100 mV
signal to 200 mV, DC offset 2.5V DC, 0-5V power supply. Show both
simulation and oscilloscope data in your report.
Follow the lab
to avoid losing points.