ELECTRONICS II Module 3 Lab: Op Amp Applications - Adding and Subtracting Voltages

ELEC 161 – Module 3 Laboratory - Page 1

ELEC 161 Electronics II

Module 3 Lab: Op Amp Applications – Adding and Subtracting Voltages

Introduction.- This lab explores two applications of Operational Amplifiers that are characterized by having multiple inputs and a single output. These are the Summing Amplifier (or Adder) and the Difference Amplifier.

Procedure

1. Summing Amplifier for DC Signals

1.1 Build the circuit shown in Figure 3-1 that is a basic summing amplifier with two inputs.

Figure 3- 1: Two-input summing amplifier

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1.2 Calculate the expected voltage at the output of the circuit.

1.3 Using the Digital Multimeter, measure the voltage at the output of the circuit.

1.4 Compare the results between 2.1 and 2.2. Are they similar? Why are they a little bit different? (If the calculated and measured values for Vout are very different, you should review your work in 2.1 and 2.2)

2. Summing Amplifier for AC signals.

2.1 We will now explore how the Summing Amplifier responds to AC signals. We will modify the input signals to the original circuit as shown in Figure 3-2.

Figure 3- 2: Summing amplifier with AC Signals

2.2 Calculate the expected Peak Value of the output signal.

2.3 Connect Channel A of the Oscilloscope to the output node. Run the simulation. Measure with the cursor the Peak value of the Output signal. Don’t forget to include a screenshot.

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2.4 Compare the calculated and measured values for the output voltage. Comment on your results.

3.- Summing Amplifier for AC signals at different frequencies.

The input signals in Section 2 had the same frequency, so they could be algebraically added. An interesting situation occurs when the two signals have different frequencies.

3.1 Using the same circuit from the previous section (Figure 2-2), modify the input AC Signals V3 and V4 as:

V3: 3 kHz and 1 Vp V4: 400 Hz and 1.2 Vp

3.2 Run the simulation. Include a screenshot. Feel free to experiment with other combinations of amplitude and frequency for the input signals.

3.3 Explain the resulting signal. Could you describe an application for this type of signals?

4.- Design of a Summing Amplifier

4.1 Design a circuit that given three input signals Va, Vb and Vc (we will assume they are DC signals for simplicity), will produce the following output:

Vout = - (3 Va + 2 Vb + 4 Vc)

4.2 Build the circuit and use Multsim to verify your results. Include screenshots of the circuit and results.

5.- Difference amplifiers

The circuits studied in the previous section add the input signals to produce the output signal . Sometimes it is convenient to use circuits that will produce an output signal that is the difference between two input signals. The circuit that does this function is called the Difference Amplifier. Figure 2-3 shows its basic structure.

5.1 Build the Difference Amplifier circuit shown in Figure 3-3

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Figure 3- 3: Difference Amplifier

5.2 Analyze the circuit shown in Figure 2-3 and calculate the expected output voltage.

5.3 Run the simulation and measure with the DMM the output voltage.

5.4 Compare the expected and measured values for Vout. Are they the same? Close? Explain any possible differences.

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6.- Design of a Difference Amplifier

6.1 Design a Difference Amplifier that given 2 input voltages V3 and V4 will produce the following output Voltage:

Vout = 2 (V4 – V3)

6.2 Build the circuit and run the simulations in Multisim. Attach the appropriate screenshots.

Laboratory Report Create a laboratory report using Word or another word processing software that contains at least these elements:

- Introduction: what is the purpose of this laboratory experiment?

- Results for each section : Measured and calculated values, calculations, etc. following the outline. Include screenshots for the circuits and waveforms as necessary -- You can press Alt + Print_Screen inside Multisim or if using Windows 7, you can use the “Snipping tool”. Either way, you can paste these figures into your Word processor. Also include here the charts and graphs that you have created with the data you have collected.

- Conclusion : What area(s) you had difficulties with in the lab; what did you lean in this experiment; how it applies to your coursework and any other comments.