EGRE 206 – Electrical Circuits
Project 9 – Op–Amp Circuits
Objective
At the end of this lab, the student will be able to:
• Use an operational amplifier in an inverting amplifier circuit
• Use an operational amplifier in an inverting summing amplifier circuit
• Explain how the power supplies affect the amplifier circuit
• Design an amplifier circuit that sums two different signals
Equipment Needed
Multism Simulation Software
Preparation
Review chapter 4 of the textbook for an understanding of op–amp circuits.
Procedure
Part A: Inverting Amplifier
Circuit 9.1 shows the layout of an inverting amplifier, using two resistors.
1. Using a feedback resistor (Rf) of 33k, determine the proper resistor Rs so that the overall gain of the circuit is –7V/V. That is: vo = –7 vs
2. In Multisim, place a 5–Terminal Op–amp. Build Circuit 9.1, using VCC = 10V. Apply an input signal of: vs = 0.8 cos (628t).
3. Take a screenshot, verifying that your circuit behaves as designed. Place both cursors at a time when the input signal is at its maximum of 0.8V. One cursor should measure the voltage of the input signal and the other should measure the voltage of the output signal. Be sure to include the names of all partners on the schematic diagram.
4. Change the input signal to: vs = 2 cos (628t), and run the simulation again.
5. Take a screenshot, explaining the behavior of the circuit. Is the output signal what you expected? Explain.
Part B: Inverting Summing Amplifier
1. Design an amplifier circuit that performs the following operation on two input signals:
vo = –0.5v1 – 4v2
2. In Multisim, build the circuit (using a 5–Terminal Op–amp) with VCC = 10V. Apply the following input signals:
v1 = 2V dc v2 = 0.2 cos (628t)
3. Take a screenshot of the schematic diagram, clearly showing the resistors and sources connected to the op–amp.
4. Take a screenshot (or screenshots) of the Grapher window, verifying that your circuit behaves as designed. Explain how you know that the circuit is performing properly, by using the cursors to measure values of the input signal(s) and output signal. Modify the “Name” of the simulation to include your last name.
5. Determine how you would modify your circuit so that it performs the operation:
vo = +0.5v1 + 4v2
Hint #1: Compare this output with the output from step B1
Hint #2: You can use more than one op–amp in your circuit
6. Build the circuit, using VCC = 10V. Apply the same input signals as step B2.
7. Take a screenshot of the schematic diagram, clearly showing the resistors and sources connected to the op–amp(s).
8. Take a screenshot (or screenshots) of the Grapher window, verifying that your circuit behaves as designed. Explain how you know that the circuit is performing properly, by using the cursors to measure values of the input signal(s) and output signal.
