Lab 5 - EE 420L 

Author: Dane Gentry

Email: gentryd2@unlv.nevada.edu

March 9, 2016

Op-Amps III: The Op-Amp Integrator

Click on any picture for its full size!

Pre-lab work

• Watch the video op_amps_III, review op_amps_III.pdf (associated notes), and simulate the circuits in op_amps_III.zip.
• Read the write-up seen below before coming to lab.

Lab Description

• Learn and experience how to design, build, and utilize an integrator to produce a triangle wave output from a square wave input.

Lab Requirements

• Calculate the frequency response of the following circuit. Ensure you show your clear hand calculations.
• What can you neglect to simplify the calculation?
• Does the circuit work if you remove the 100k? Why or why not?
• Does the 100k have much of an effect on the frequency response?  

                      Hand Calculations and Explanation

                      LTspice Schematic                                                                    LTspice Simulation (Ft = 157 Hz)

Part 2:

• Show, at the unity-gain frequency of the integrator, that the input and the output have the same peak values.
• Is the phase shift between the input and the output what you expect? Why or why not?

Experimental Results

                    Sinusoidal Signal (Ft = 159 Hz)                                                                 Square Wave Signal (Ft = 159  Hz)

The calculated unity-gain frequency is Ft = 159 Hz. The sinusoidal signal shown above displays input and output signals with peak values that

are approximately equal. The square wave signal shown above, however, displays an output (triangle wave) that has a peak value greater than

the input (notice the different voltage scales). The two peak values for the square wave signal are nonetheless the same order of magnitude.

In addition, both of the images above display an approximate 90 degree phase shift as expected from the hand calculations.

Part 3:

• Next, design, simulate, and build a square-wave to triangle wave generation circuit. 
• Assume the input/output frequency is 10 kHz and the output ramp must swing from 1 to 4 V centered around 2.5 V.
• Show all calculations and discuss the trade-offs (capacitor and resistor values, input peak, min, and average, etc.)

                   Hand Calculations

                    LTspice Schematic                                                                                      LTspice Simulation

                               Experimental Results

Conclusion

The triangle-wave output did not get as close to the power supply rails as expected, most likely due to manufacture defects/inconsistencies

or other flaws in the op amp. It is noted that in order to avoid an excessive DC offset, the 2.5 Vm voltage must be very close to the 2.5 Vin voltage.

By using a smaller capacitor value and thus calculating a higher value for the resistor, the swing of the output could theoretically increase.

Lab Conclusion

This lab demonstrated the operation and use of op-amp integrators, specifically in integrating a square wave input signal in order to produce a triangle-wave

output. The experiments in this lab provided excellent experience in how to design, build, and utilize an integrator to produce a triangle wave output from a

square wave input, and all experiments in this lab were performed with little difficulty and few encountered problems.

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