2 class days
Lab 8: Op Amps
Lab Assignment
1. Open-Loop Test Circuit
HH 8.1. Answer all questions.
2. Inverting Amplifier
Source: Eyler, lab 7 (HH 8.2)
Construct an inverting amplifier with an LF411 op amp, as shown in the figure
below. Use R1= 10 kΩ.
Vs = supply, typically ± 12V or ± 15V.
Bal = balance, not needed here.
Basic Inverting Amplifier with an LF411 Op Amp
Choose R2 for a gain of about 100. Measure the gain, Vout/Vin, for several DC
input voltage levels. You may find it easiest to construct a voltage divider with a
miniature trimmer potentiometer to provide the input, since many power supplies
produce voltages that are inconveniently large for this purpose. Now change R2
to set the gain to about 1, then to about 10. Does the output behave as
expected? At what input and output voltages does the op amp “saturate” to a
level that does not increase further?
What determines the input impedance of this circuit? Confirm your prediction
either by adding 1K in series with the input, or by measuring the input current
directly, using a digital multimeter.
Apply a SMALL sine wave to the input and determine the frequency at which the
output amplitude drops by a factor of 2 relative to its predicted value. What is
the approximate phase shift at this 3-dB frequency? Be sure to measure both the
input and output voltages, since the signal generator may not produce a constant
amplitude as its frequency is adjusted. Is the phase shift similar to that expected
of a simple “single-pole” RC low-pass filter?
3. Non-inverting Amplifier
HH 8.3. Answer all questions. Don’t forget about the input impedance of your
scope! Do not try to measure the circuit’s input impedance. Compare your
measured gain to expected.
4. I to V converter
HH 8.6. Answer all questions.
5. Push-Pull Buffer
HH 8.8. Answer all questions. Ignore the parts that involve a breadboard
speaker. Do not answer the questions under “Listen to this improved ..”. What
happens to the shape of the output as the frequency increases from 100 Hz to
500 Hz?