EE 210 Laboratory 05 Spring Semester
This is the second of two laboratory sessions that provide an introduction to the op-amp. In this session, you will study three amplifiers designs: (1) the voltage follower/buffer, (2) an inverting summing amplifier, and (3) a voltage level display using the op-amp in comparator mode.
⦁ Pre-Lab Activities
⦁ Read the remainder of this handout.
⦁ Read the laboratory supplement entitled “Light Emitting Diodes.”
⦁ In Figure 3, first determine the values of R1, R2, and R3 so that:
⦁ The gain Vout/Vleft = -2 (assuming that Vright is grounded)
⦁ The gain Vout/Vright = -6 (assuming that Vleft is grounded).
⦁ Are these resistor values unique? For these resistor values chosen, compute the amplitude of Vout with:
⦁ Vleft amplitude = 0 Vpp and Vright amplitude = 1 Vpp.
⦁ Vleft amplitude = 1 Vpp and Vright amplitude = 0 Vpp.
⦁ Both Vleft and Vright have amplitude = 1 Vpp simultaneously.
⦁ Complete the analysis in steps 1-2 of Experiment 3.
⦁ Upload your work to Canvas before the beginning of the lab.
⦁ In-Lab Activities
⦁ Required Items:
⦁ Parts Kit
⦁ Breadboard and wires
Experiment 1: Voltage Follower/Buffer – Loading Effect
The purpose of this experiment is to study how the buffer is used to overcome the loading effect for a practical source. In Lab 2, you studied the loading effect in the myDAQ +15V output. In this experiment, you will instead look at how a small load influences the output of a simulated practical source, and you will see how a buffer can be used to mitigate these effects.
All real signal sources (called “practical” as opposed to “ideal” sources) have internal resistances that cause the voltage at the terminal of the source to vary with respect to the current being drawn from the source. This phenomenon is known as the loading effect and is generally an undesirable effect that circuit designers need to deal with. In circuit analysis, a practical source is modeled as an ideal voltage source in series with a small resistance (called a source resistance, Rs). Depending on the source being modeled, this source resistance can be < 1 Ω or as high as hundreds of ohms. The higher the source resistance, the more pronounced the loading effect becomes for the practical source. In the myDAQ, the source resistance of the function generator is very small, so the loading effect is minimal and difficult to observe/measure. For the purposes of this lab, then, we will artificially increase the loading effect by placing a 330 Ω resistor in series with the function generator.
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