Lab Assignment1.5 Report Zachary Trotter

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Electrical Engineering

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EET380 1.5: Baseband Pulse Modulations Instructor: Dr. Setoodehnia Campus: Lab 1.5 Baseband Plus Modulations Student Name(s): Zachary Trotter Click or tap here to enter text.

2 Contents Honor Pledge: .............................................................................................................................................. 2 Abstract ....................................................................................................................................................... 3 Introduction ................................................................................................................................................. 3 Procedures .................................................................................................................................................. 3 Data Presentation & Analysis ...................................................................................................................... 3 Table: Current Reading for different voltage values ................................................................................ 3 Conclusion ................................................................................................................................................... 4 References ................................................................................................................................................... 4 Honor Pledge: I pledge to support the Honor System of ECPI. I will refrain from any form of academic dishonesty or deception, such as cheating or plagiarism. I am aware that as a member of the academic community, it is my responsibility to turn in all suspected violators of the honor code. I understand that any failure on my part to support the Honor System will be turned over to a Judicial Review Board for determination. I will report to the Judicial Review Board hearing if summoned. Date: 12/11/2023 12/29/2023 Zach Trotter

3 Abstract In this lab we were asked to analyze three different circuits and look at the different sine waves they produced. Along with the analyzing of the circuits we were also asked after further explanation of how they worked who we could reproduce the original signal. Introduction Baseband pulse modulations are mainly used over guided transmission media such as pair wires and optical fiber communications. In most of the times, these modulations are used for industrial control applications where one analog signal is controlling a device through a digital interface, or to read a specific data such as a tag, which is printed on an object. In pulse amplitude modulation (PAM), the amplitude of the generated pulse follows the amplitude of the analog signal at the sampling instance. The following figure shows how a PAM signal is generated: In pulse width modulations (PWM), the width of the pulse varies proportional to the amplitude of the intelligence signal at the sampling instance. PWM has applications in DC motor control, servo motor control, dimmer’s light control, very high efficient class D power amplifier (is used in car radio amplifiers), etc. There are several ways to create PWM signal. One of these ways is using a single operational amplifier, which works as a comparator. Please see the following figure. 12/29/2023 Zach Trotter

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4 The magnitude of the signal B is compared with the instantaneous magnitude of a Sawtooth which has a much higher frequency and the output of the OpAmp is switching between V Max to V Min and vice versa, which accordingly makes the PWM signal. When the signal’s magnitude is big, output of the OpAmp also stays at V Max for longer duration of time, and the same when the signal’s magnitude is small, the OpAmp’s output stays at V Min longer. As result PWM is created. In pulse position modulation (PPM), the position of the appearance of the pulse varies proportional to the amplitude of the signal at the sampling instance. PPM can be created from PWM as it is explained in page 216 of the textbook and is illustrated in Figure 7-6. In this lab you will use two 555 chip to create PPM. 12/29/2023 Zach Trotter

5 Procedures Assemble the following circuit using MultiSIM. If you have difficulties to assemble the circuit, please download the MultiSIM file of PAM_1.ms11. The 4066 chip is a quad of analog switches. As shown above, a square signal with peak of 5 V and valley of 0 V is applied into pin 13, which closes or opens the first analog switch. The input to this switch is pin 1 and its output is pin 2. The capacitor and the unity gain OpAmp amplifier works as holder and keeps a constant voltage till next pulse. Experiment A.1 : Run the simulation and look at the oscilloscope screen. Describe your observation briefly. Both the triangle wave and the square wave follow the same path so they both peak at the same voltage, but they are slightly off on the rise and fall 12/29/2023 Zach Trotter

6 Experiment A.2 : Increase the duty cycle of the pulse source, which is connected to the pin 13 of the 4066 chip, from 10% to 50%. Describe your observation. The paths follow each other more closely although they still peak at the same voltage at the same time. Experiment A.3 : Return the duty cycle of the square wave to 10% and look at the spectrum of the PAM. You need to adjust the spectrum analyzer for this reason. To do so, after connecting the PAM signal to the IN input of the spectrum analyzer follow these steps: 1. Double click on spectrum analyzer to bring it up 2. Click on stop button 3. Select 0 Hz as the Start frequency 4. Select 3 kHz as the End frequency (roughly 3 times of the pulse frequency) 5. Click on Enter button of the spectrum analyzer 6. Then change the frequency resolution option of the spectrum analyzer to Hz and then select a small value (for instance 10 Hz). 7. Click on Start button on and then start the simulation. Wait for about 1 or 2 minutes to let the spectrum analyzer’s algorithm converges and shows you an accurate result. Task: Place the snapshot of the spectrum analyzer’s screen in here and describe your observation briefly. You may use the spectrum analyzer’s probe. 12/29/2023 Zach Trotter

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7 12/29/2023 Zach Trotter

8 As the frequency climbs the voltage drops inversely in comparison this continues until the voltage is near zero. Experiment A.4 : Based on your observation in previous task, briefly write how you can reconstruct the original signal. By following the peak voltages in the spectrum analyzer you can compare the frequency and back calculate the timing to better reconstruct the original signal Part B. Pulse Width Modulation Procedure: Assemble the following circuit using MultiSIM. If you have difficulties to assemble the circuit, please download the MultiSIM file of PWM_1.ms11. Experiment B.1 : Run the simulation and look at the oscilloscope screen. Describe your observation briefly. While the sinewave is constant the square wave varies in length of time in the positive along with but the peak is constant 12/29/2023 Zach Trotter

9 Experiment B.2 : Place the snapshot of the spectrum analyzer’s screen in here and describe your observation briefly. You may use the spectrum analyzer’s probe. 12/29/2023 Zach Trotter

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10 Experiment B.3 : Based on your observation in previous task, briefly write how you can reconstruct the original signal. You can reconstruct the original signal by reversing the modulation process to recover the original signal. 12/29/2023 Zach Trotter

11 Part C. Pulse Position Modulation Procedure: Assemble the following circuit using MultiSIM. If you have difficulties to assemble the circuit, please download the MultiSIM file of PPM_1.ms11. Experiment C.1 : Run the simulation and look at the oscilloscope screen. Describe your observation briefly. As the sinewave moves to the positive the square wave drops dramatically until the sinewave is on the decline Experiment C.2 : Place the snapshot of the spectrum analyzer’s screen in here and describe your observation briefly. You may use the spectrum analyzer’s probe. The analyzer shows massive peaks followed by steep drops then a gradual build up back to the original peak. Please place the snap of the spectrum analyzer on the next page. 12/29/2023 Zach Trotter

12 Experiment C.3 : Based on your observation in previous task, briefly write how you can reconstruct the original signal. You could reconstruct the signal using inverse Fourier transforms that are designed to reconstruct signals from their frequency domain representation Data Presentation & Analysis This section is the most important section of the report. Data representations and analysis is crucial in the Engineering field. This section should include all raw data collected, e.g., voltage and current readings. All results are to be presented in both tabular and graphical form. All tables must have titles and all figures must have brief captions. 12/29/2023 Zach Trotter

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13 Conclusion  Describe PAM, PWM and PPM in three lines. PAM (Pulse Amplitude Modulation) encodes data by varying pulse amplitudes; PWM (Pulse Width Modulation) alters pulse widths; PPM (Pulse Position Modulation) changes pulse positions in time, all techniques used in signal modulation for data transmission and control systems.  Based on your observations in frequency domain, please shortly explain how to demodulate PAM, PWM and PPM. PAM (Pulse Amplitude Modulation): Demodulation in PAM typically involves using a simple envelope detector or amplitude demodulator to extract the original analog signal by capturing the amplitude variations of the modulated signal in the time domain. PWM (Pulse Width Modulation): PWM demodulation often requires converting the PWM signal back into an analog signal. This process might involve integrating the pulse train to recover an average voltage level or using a low-pass filter to extract the original signal by smoothing out the pulse-width variations. PPM (Pulse Position Modulation): Demodulating PPM involves detecting the timing differences between pulses in the time domain. By comparing the time positions of successive pulses to a reference time, the encoded information can be decoded, typically using a time interval decoder or a system that measures time intervals between pulses. References Cite any material used in the preparation of your lab report. 12/29/2023 Zach Trotter