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:
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.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
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                                                                                                         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.

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

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:
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..