Lab

Lab 5 - EE 421L

Authored by Marco Muniz,

Email: munizm1@unlv.nevada.edu

03/08/19

Lab description

Again, this lab will utilize the LM324 op-amp (LM324.pdf).

For the following questions and experiments assume VCC+ = +5V and VCC- = 0V.

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?

Verify your calculations with experimental results.
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?

file:///C:/Users/mmuni/Pictures/Lab5/cirucit.JPG

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.)

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Part 1:

Calculate the Freq. Response of the circuit:

file:///C:/Users/mmuni/Pictures/Lab5/Transfer_funct.JPG

What can you neglect to the simplify the calculation?

For these calculations, we can neglect R1/R2. This is possible because R2 is so much bigger than R1 that the value would be very small and could be considered negligible.

file:///C:/Users/mmuni/Pictures/Lab5/negligeble.JPG

file:///C:/Users/mmuni/Pictures/Lab5/negligeble.JPG

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

When we removed the 100k resistor in the feedback look, the circuit no longer worked as expected. We began to see issues with our DC offset point and we began to clip our signal. We assumed the 100k was helping in keeping our DC Offset value stable so we wouldn't shift into the rails and clip our signal.

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

Based on what we can see in the transfer function calculations, we see that the 100k (Or R2) has very little to almost no effect on the frequency response of this circuit.

Show, at the unity-gain frequency of the integrator, that the input and the output have the same peak values.

In the oscilloscope image below, we can see how the above integrator circuit behaves at its unity-gain frequency. We expect our gain to be 1 so our input and output will be equal. Additionally, from the calculated frequency response, we know we our signals should be out of phase by 90 degrees. We can see both of these things occur below.

Input is Yellow (CH 1) and output is Blue (CH 2)

file:///C:/Users/mmuni/Pictures/Lab5/tek00000.PNG

file:///C:/Users/mmuni/Pictures/Lab5/tek00000.PNG

(Input and Output signals at unity-gain frequency)

Anything below the unity-gain frequency gave us a larger gain. However, if the frequency would go too low, we would begin to see some clipping on the output due to the signal hitting the rails of this OP-Amp Circuit.

file:///C:/Users/mmuni/Pictures/Lab5/tek00001.png

file:///C:/Users/mmuni/Pictures/Lab5/tek00001.png

(Input and output relation at lower frequencies)

Is the phase shift between the input and the output what you expect? Why or why not?

Based on our frequency response calculations, we expected our output signal to Lead our input signal by 90 degrees. Our first oscilloscope plot matches our expected calculated results with the output leading by 89.3 degrees.

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Part 2:

Next, design, simulate, and build a square-wave to triangle wave generation circuit.

file:///C:/Users/mmuni/Pictures/Lab5/square_triangle.JPG

(calculations for Square to Triangle Wave circuit)

Simulation Schematic and Results:

file:///C:/Users/mmuni/Pictures/Lab5/square_triangle_schem.JPG

file:///C:/Users/mmuni/Pictures/Lab5/output.JPG

(Square to Triangle wave Schematic) (Schematic Output Plot)

Oscilloscope measurement of built circuit:

file:///C:/Users/mmuni/Pictures/Lab5/TEK00002.PNG

file:///C:/Users/mmuni/Pictures/Lab5/TEK00002.PNG

(Square to triangle wave Oscilloscope Plot)

Show all calculations and discuss the trade-offs (capacitor and resistor values, input peak, min, and average, etc.)

Overall, the experimental results were not very close to our simulation results. Additionally, they did not have any resistors with an exact value of 27.7k so we used the closest value available, 28.2k Ohms. This would attribute to the shift of the triangle. We also did not take into account the probe or oscilloscope capacitance or resistance when doing these calculations, thus this could have been a factor which effected our final calculated capacitance and resistance.

For overall trade-offs, we saw that if we decreased the value of the resistor or capacitor, we would see more output ramp swing and the output would dip below 1V or above 4V. Because of this, if we decreased the value of one, we must adjust the value of the other to compensate for this change. If we were to change the pulse voltage Amplitude, this would cause the offset voltage to move to either up or down. This would cause our output swing point to shift up or down and also effect the size of the amplitude.

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Back Up:

file:///C:/Users/mmuni/Pictures/Lab5/backup.JPG

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