Lab 5: Op-amps III, the Op-amp integrator - EE 420L 

 

Author: Mario Verduzco

Email: Verdum1@unlv.nevada.edu

Date: 03/08/17

 

 

 

  

 

Pre-lab:

· Watch the video op_amps_III, review op_amps_III.pdf (associated notes), and simulate the circuits in op_amps_II.zip.

· Read the write-up seen below before coming to lab.

Lab description:

           The objective for this lab is to understand the characteristics of the Op-amp Integrator. Such as the frequency response and changes in the feedback path. Also, we will use the Integrator topology to design, simulate, and build a square-wave to triangle generator.

Experimental Results:

Experiment #1: The op-amp integrator

Experiment #2: Design of a triangle wave generator

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1) Calculate the frequency response of the following circuit. Ensure you show your clear hand calculations.

2) What can you neglect to simplify the calculation?

3) Does the circuit work if you remove the 100k resistor? Why or why not?

         The circuit will work if the resistor is removed when doing a simulation or hand calculations, but since the Op-amp is not ideal in real life there is some offset voltage that will be amplified without the big resistor with an infinite gain causing the output to go to either the positive or negative rail.

5) Verify your calculations with experimental results

6) 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 expected? Why or why not?

1) Hand calculations   

2) Simulation

 

We are using the LM324 op-amp with a VCC+ = +5v and VCC- = 0v

           To simplify the calculation you can neglect to add the Rbig resistor. This is possible because since Rbig is much larger than R3 it will have little affect on the frequency response.

Fig 1.1 – Vout (Purple) without Rbig in the feedback

 

4) Does the 100k have much of an effect on the frequency response?

           The 100k resistor does not have much effect on the frequency response for frequencies above 100Hz.

 

Fig 1.2 – Vout (Purple) with Vin (Blue) at 50Hz Gain = 1.68

 

Fig 1.3 – Vout (Purple) with Vin (Blue) at 500Hz Gain = 0.31

 

Fig 1.4 – Vout (Purple) with Vin (Blue) at 1kHz Gain = 0.22

 

Fig 1.5 – Vout (Purple) with Vin (Blue) at Unity gain frequency

 

           The phase shift is what was calculated by hand. A –90 degree phase shift.

           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.

Fig 1.6 – Triangle wave generator simulation

 

3) Experimental results

 

Fig 1.7– Triangle wave (purple) Vin(blue)

 

           The resistor value was chosen based off of the capacitor value due to the fact that there is a larger variety of resistors than capacitors to choose from in our inventory.

           The output peak is a little squared off because it is going up to the input peak. I chose this Input peak value in order to not have such a voltage difference between the input and output.