Performance-Based Assessments for Analog Integrated Circuit Competencies

Students are free to connect the LED to the comparator in any way they choose (current-sourcing or current-sinking).

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.

You may wish to use either an operational amplifier or a true comparator for this exercise. Whether or not the specific device has rail-to-rail output swing capability is your choice as well.

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.

Use a dual-voltage, regulated power supply to supply power to the opamp.

I have had good success using the following values:

V = 12 volts

-V = -12 volts

V_TP1 = Any voltage well between V and -V

R_pot = 10 kΩ linear potentiometer

U₁ = TL081 BiFET operational amplifier (or one-half of a TL082)

In order to demonstrate latch-up, you must have an op-amp capable of latching up. Thus, you should avoid op-amps such as the LM741 and LM1458. I recommend using an op-amp such as the TL082 for this exercise because it not only latches up, but also does not swing its output voltage rail-to-rail. Students need to see both these common limitations when they first learn how to use op-amps.

In case your students ask, test point TP1 is for measuring the output of the potentiometer rather than as a place to inject external signals into. All you need to connect to TP1 is a voltmeter!

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.