Appendix G: Operational Amplifiers.
This appendix will instruct you on how to use the Operational Amplifier circuit.
There are some important things you need to know before you start using the Operational Amplifier circuit.
Those are,
• Identify the terminals.
• How to connect the power supplies.
• Troubleshooter.
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Identify the terminals.
The terminals of the operational Amplifier can be grouped into three groups,
• Input-Output terminals: These terminals are,
– Positive Input I+ .
– Negative Input I− .
– Output Out.
most of the time, when doing analysis, those are the only teminals shown on the diagrams.
• Power terminals: These terminals are,
– Positive Supply Voltage V+ .
– Negative Supply Voltage V− .
Those terminals must be connected to a propper power supply.
• Compensation terminals: These terminals can be several things, most common are,
– Offset Balance: These terminals are used to compensate for imbalances that drive the Operational
Amplifier to a nonzero output for a zero input.
– Frequency compensation: These terminals are used to place an external element in order to modify
the frequency response of the amplifier.
The best way to know what is each terminal is consulting the Data sheet for the circuit you are about to
use. Another reliable source is the PsPice schematics for that circuit.
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How to connect the power supplies.
The major problem for the students is to understand how to supply the voltages, V+ and V− , and how to
get the ground node.
Figure 1 show a way to connect two power supplies in order to get the three terminals needed, V+ , V− and
GN D.
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Troubleshooter.
Another important thing to know is how to ”debug” your circuit in case it is not working as you expected
or not working at all.
The best thing to do is build your circuit by stages. Starting from the power supplies then the elements and
the last thing conect the signals. Check your circuit between stages.
If you like to build circuits all at once and something is not working properly, follow these steps to find what
is wrong.
1. Check you have the proper power supply voltage attached to your Operational Amplifier/s by measuring
directly to the Operational Amplifier V+ and V− terminals.
2. Check your gounds, all the grouns should be connected together.
3. Check you have connected the external elements where they should be.
4. Check you have connected the signal to the appropriate place.
5. Check you have connected the measuring instrument, Oscilloscope or Multimeter to the appropriate
place.
6. If everithing looks fine but your ciruit still does not work, there are still two things you can check.
• The breadboard: Check continuity between the external components and the Operational Amplifier. You could try placing the circuit on a different breadboard’s area.
• The Operational Amplifier circuit: The last thing we can do is to blame the ciruit. You can check
if the circuit is working by using a voltage follower configuration, which is the simplest one.
7. If all of the above fail call for help. Your TA or your Instructor will be happy to help you.
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Figure 1: How to conect the power supplies.
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