Performance-Based Assessments for Analog Integrated Circuit Competencies

I recommend setting the function generator output for 1 volt, to make it easier for students to measure the point of “cutoff”. You may set it at some other value, though, if you so choose (or let students set the value themselves when they test the circuit!).

I also recommend having students use an oscilloscope to measure AC voltage in a circuit such as this, because some digital multimeters have difficulty accurately measuring AC voltage much beyond line frequency range. I find it particularly helpful to set the oscilloscope to the “X-Y” mode so that it draws a thin line on the screen rather than sweeps across the screen to show an actual waveform. This makes it easier to measure peak-to-peak voltage.

Be sure to choose component values that will yield a frequency well within the range that the specified opamp can handle! It would be foolish, for example, to specify a cutoff frequency in the megahertz range if the particular opamp being used was an LM741.

I recommend setting the function generator output for 1 volt, to make it easier for students to measure the point of “cutoff”. You may set it at some other value, though, if you so choose (or let students set the value themselves when they test the circuit!).

I also recommend having students use an oscilloscope to measure AC voltage in a circuit such as this, because some digital multimeters have difficulty accurately measuring AC voltage much beyond line frequency range. I find it particularly helpful to set the oscilloscope to the “X-Y” mode so that it draws a thin line on the screen rather than sweeps across the screen to show an actual waveform. This makes it easier to measure peak-to-peak voltage.

Be sure to choose component values that will yield a frequency well within the range that the specified opamp can handle! It would be foolish, for example, to specify a cutoff frequency in the megahertz range if the particular opamp being used was an LM741.

I also recommend having students use an oscilloscope to measure AC voltage in a circuit such as this, because some digital multimeters have difficulty accurately measuring AC voltage much beyond line frequency range. I find it particularly helpful to set the oscilloscope to the “X-Y” mode so that it draws a thin line on the screen rather than sweeps across the screen to show an actual waveform. This makes it easier to measure peak-to-peak voltage.

Values that have proven to work well for this exercise are given here, although of course many other values are possible:

V = 12 volts

-V = -12 volts

R₁ = 10 kΩ

R₂ = 10 kΩ

R₃ = 5 kΩ (actually, two 10 kΩ resistors in parallel)

R₄ = 20 kΩ (actually, two 10 kΩ resistors in series)

C₁ = 0.001 μF

C₂ = 0.001 μF

C₃ = 0.002 μF (actually, two 0.001 μF capacitors in parallel)

U₁ = one-half of LM1458 dual operational amplifier

This combination of components gave a predicted notch frequency of 15.92 kHz, with an actual cutoff frequency (not factoring in component tolerances) of 15.87 kHz.