Lab 9

ENEE 3517 – Electronics Lab 9

Precision Rectifiers

The objective of this lab is to build precision rectifiers using an LM 741 operational amplifier. Notice

that the feedback is negative in this case.

In Lab:

1. Build the following circuit for R = 1k. Use a sinusoidal input of frequency 1kHz and magnitude 5V peak.

Observe signals vA and vo at the oscilloscope. Try to get pictures of as accurate waveforms as

possible. You may have to “zoom in” the voltage signals, especially at the peaks and when they

are close to 0 volts. You may do so by choosing appropriate voltage and time scales.

LM 741 Diagram:

Brief introduction to the operation of the above circuit: The voltage at the output of the

operational amplifier, vA, is be equal to the difference between the input voltage and vo times

the amplifier gain, A. In other words, it will be vA = A(vi - vo). If the diode is “ON”, then vo = vA

– 0.7V, and if it is “OFF”, then vo = 0V, because there cannot be any current on R (the diode is

“OFF”, so there is no current coming from that branch, and there cannot be any current going

into the operational amplifier’s negative input).

2. Build the following circuit for R = 1k. Again, use a sinusoidal input of frequency 1kHz and magnitude 5V peak. Observe signal vo at the oscilloscope.

Observe signal vo at the oscilloscope. As in part 1, try to get pictures of as accurate waveforms

as possible. Again, you may have to “zoom in” the voltage signals by choosing appropriate

voltage and time scales.

For the report:

1. Simulate the circuits above.

2. Do the circuit analysis for both circuits and compare with the results in the lab. For the analysis, do

not assume that the gain of the operational amplifier is infinite, but a large number, A. In other

words, you have to use that the output of the amplifier is equal to A(V+ – V-), where V+ – V- are the

voltages at the positive and negative input terminals, respectively, of the operational amplifier.

3. As always, include all necessary parts for the report as stated in the syllabus.