Lab5 - EE 420L
Authored
by Allan Pineda
pineda3@unlv.nevada.edu
March 08, 2017
Lab Description: Op-amps III, the op-amp integrator
Again this lab will utilize the LM324 op-amp (LM324.pdf).
For the following questions and experiments assume VCC+ = +5V and VCC- = 0V.
Experiment # 1:
- Calculate the frequency response of the following circuit. Ensure you show your clear hand calculations.
Answer:
The frequency response can be calculated using derive formula from the class.See hand calculation in
Figure_1. Upon completion of hand calculation, one need
to constructs the circuit in breadboard to verify the result of
experiment from the hand calculated data.
Here, we can calculate the frequency and phase by doing a KCL at
the node between R1 and the R2//C1. Since the gain is 1, we can
conlcude that the frequency is 159kHz. See Figure 1.
Figure 1:
Hand Calculation
Schematic
Oscilloscope
showing a unity gain and the frequency response of the system.- What can you neglect to simplify the calculation?
Answer:
We
can neglect the R2 in the hand calculation since R2 do not have a
significant effect because it is way bigger compare to R1. See Figure_2
Below.
Figure 2:
Schematic
without Resistor 2
Simulation
Result
- Does the circuit work if you remove the 100k? Why or why not?
Answer:
When
100k resistor is removed from the circuit, the oscillation in the scope
slightly change but overall one can conclude that the 100k
resistor do
not have much effect in the system. However, the system will not work
properly as it should be in a real world situation. In the
oscilloscope, the output waveform is slightly clip when the 100k
resistor is remmoved.See Figure_3 Below.
Figure_3
Schematic without
Resistor2
- Does the 100k have much of an effect on the frequency response?
Answer:
No.
The 100k ohms resistor does not have much effect in the frequency
response as shown in Figure_3 above. It slightly change from 159.003 to
about 159.001 kHz.
- Show, at the unity-gain frequency of the integrator, that the input and the output have the same peak values.
Answer:
As
shown in figure_4 below, the unity-gain frequency of the integrator
have the same output peak to peak values of 1.02V. When different
frequencies is used in the circuit, the gain of the op-amp is changing
depend on the value of the frequency.
Figure 4:
Unity Gain
Frequency
Low Frequency
High
Frequency
Schematic with R2
- Is the phase shift between the input and the output what you expect? Why or why not?
Answer:
The Figure 4 above shows the input and output signal of the unity gain frequency that is ~159kHz and the phase is ~90 degrees which is really close to the calculated phase above. Thus, the result is what one can expected.
Experiment # 2:
- 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.
In
this experiment, it is required to build an integrator circuit that can
transform a square-wave to triangle using the parameter given
in the instruction. To do this, one must calculate the values for
capacitor and resistor. See Figure 5. In figure 5, the given parameter
was used to solve the remaining values to eperform the experiment. One must
pick a specific values for capacitor to solve for resistance value. A
1.389n capacitance was picked to get the value of resistance which is
come out to be 30.081k ohms. These values must be accurate in order for the
experiment to work. Also, a VCM of 2.5V was used and maintained to get
a almost perfect square-wave.
Figure5:
Hand Calculation for Experiment 2
Schematic for Experiment#2
Waveform from LTspice For
Experiment #2
Oscilloscope
Waveform Result for Experiment# 2
Notice that the phase is still
approximately a 90 degrees in the wave form shown above. And the change
in the output signal is 3V just as shown in the hand calculation.
Conclusion:
The
laboratory experiment is about understanding the operation of
integrator op-amp. One can conclude that by choosing a
set capacitor or resistor, one can estimate a desired output
voltage. These values must accurately selected in order for the circuit
to work. The experiment provide us a ability to understand how to
transfer from square-wave to traingle wave..