ECE210 Spice/MATLAB Project 1 Fall 2011 Voltage Divider Analysis and Simulation

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1 ECE210 Spice/MATLAB Project 1 Fall 2011 Voltage Divider Analysis and Simulation This three-part project assignment will count for 30 homework points. Since the major portion of the project involves a MATLAB component, please plan ahead to assure you can complete it on time. It is very important that your review the Project Requirements document before you begin your work. Failure to follow those requirements will lead to deductions in this assignment. The grading total for the 3 parts will be: Part 1 5 homework points Part 2 5 homework points Part 3 20 homework points Create a document file [named using the format FirstnameLastnameProject1.(doc or docx)]. This document should begin with a 2-3-inch margin at the top followed by your name and Student ID. Note the additional document requirements for each part of the project. The problem: We have the following circuit shown in Figure 1 in which we will have a value for R1, a value for Vin, and 9 values for R2. Determine the value for Vout as a function of the component values. Figure 1 Voltage divider circuit. Part 1: Determine the single values for Vin, R1, and the nine values for R2 in the following way: Begin with the nine digits in your Student ID and consider each one to be an integer. Add the value of 1 to each of these integers. Then find the cumulative sum of these integers and assign these values to R2 in Ohms. For example, consider the arbitrary Student ID The 9 values for R2 would then be 2, 4, 8, 10, 15, 17, 23, 33, and 37. The value for V1 should be the fourth number in the R2 array, in volts (10 Volts in this case). The value for R1 should be the fifth number in the R2 array, in Ohms (15Ω in this case). Then calculate the 9 values you would expect for Vout according to the 9 values you have calculated for R2. Include these R2 and corresponding Vout values in a table in your document. For Part 1document content, following the procedures in the Project Requirements document, include your calculations, results, and observations. The results of your calculations should be neatly inserted in a table in the document. Your observations should include at least your comments about the relationship between the component values and the value for Vout as well as the range of Vout relative to Vin. What is the value of R2 that leads to Vout=.5Vin, and why?

2 Part 2: Open LTspice and create the circuit shown in Figure 1. Refer to the.step Parameter sweeps section in the LTspice help file to understand the syntax for the spice example.step param RLOAD LIST provided. This can be inserted into the schematic by pressing the s key or selecting the.op command on the right of the toolbar at the top of LTspice. You can shorten this SPICE directive slightly by using RL for the variable name, and assigning the variable {RL} to the value for R2 (being sure to use the curly brackets). You will want to make sure the list contains the values you calculated for R2 in Part 1. Also assign the appropriate values to R1 and Vin in your schematic. When you run this simulation in LTspice using the DC operating point (DC op pnt) simulation command, you should get the result similar to that shown in Figure 2 when you plot V(Vout): Show the schematic and the resulting plot in the document you submit for this assignment. Also be sure to include your FirstnameLastnameProject1.asc file in your submitted files. Points will be deducted for schematics and plots that are not formatted in a way that makes them easily readable. Figure 2 LTspice result. For Part 2 document content, following the procedures in the Project Requirements document, copy the schematic and plot from the LTspice application Your observations should include at least a comparison of these results with Part 1 and your comments about any problems you had with LTspice and the use of the parameterized values for the resistor..

3 Part 3: Use the MATLAB code shown in Table 1. Table 1 Uncommented MATLAB code. %% this is one way of writing code to solve the Voltage Divider problem clear all; close all; ID = [ ]; IDplus = zeros(1,length(id)); R2 = zeros(1, length(id)); for k=1:length(id) IDplus(k) = ID(k)+1; if k==1 R2(k) = IDplus(k); else R2(k) = R2(k-1)+IDplus(k); Vs = R2(4); R1 = R2(5); Vout = zeros(1,length(k)); for k=1:length(id) Vout(k) = Vs*R2(k)/(R2(k)+R1); figure plot(r2, Vout, 'linewidth', 2), grid titlestr = ['Voltage Divider for Vs = ' int2str(vs) ' V, R1 = ' int2str(r1)]; title([titlestr ' \Omega, for loop'], 'fontsize', 14); xlabel('r2, \Omega', 'fontsize', 14); ylabel('vout, Volts', 'fontsize', 14); set(gca, 'fontsize', 12); disp([titlestr ' Ohms']); disp(' R2 Vout using "for loop"'); disp([r2' Vout']); %% This is another way of writing code to solve the Voltage Divider problem % This approach takes advantages of some of the powerful features of MATLAB. % Notice that no loops are necessary in this code. clear all ID = [ ]; IDplus = ID+1; R2 = cumsum(idplus); Vs = R2(4); R1 = R2(5); Vout = Vs*R2./(R2+R1); figure plot(r2, Vout, 'linewidth', 2), grid titlestr = ['Voltage Divider for Vs = ' int2str(vs) ' V, R1 = ' int2str(r1)]; title([titlestr ' \Omega, Matrices'], 'fontsize', 14); xlabel('r2, \Omega', 'fontsize', 14); ylabel('vout, Volts', 'fontsize', 14); set(gca, 'fontsize', 12); disp([titlestr ' Ohms']); disp(' R2 Vout using Matrices'); disp([r2' Vout']); Copy this code into a MATLAB editor window and save the editor file in your project directory as a FirstnameLastnameProject1.m file (this is also known as a script file). Replace the student ID in the example code in the MATLAB editor with your own student ID. Then make sure the code is properly indented for good readability. The indenting can be done by selecting the entire code page in the editor (Ctrl-a) and the auto indent (Ctrl-i) commands.

4 For every line in this code, add a comment to the right of the line describing exactly what the line does. You should use both the help capabilities of MATLAB and the single-step capabilities combined with the Command Window to make sure you understand and describe what is happening with each line. Your comment should begin with a % and the MATLAB editor should automatically make the comment font green. Your grade for this portion of the project is based largely on the completeness and accuracy of your comments. Copy your commented code into your document as described in the Part 3 description of the document content. This code should produce two plots that look something like the plots in Figure 3 and Figure 4 and an output to the Command Window that should look something like Table 1. 8 Voltage Divider for Vs = 10 V, R1 = 15 Ω, for loop Voltage Divider for Vs = 10 V, R1 = 15 Ω, Matrices Vout, Volts 5 4 Vout, Volts R2, Ω Figure 3 Plot result for the code using the for loops R2, Ω Figure 4 Plot result for the code using the MATLAB matrix approach Table 2 MATLAB results. Voltage Divider for Vs = 10 V, R1 = 15 Ohms R2 Vout using "for loop" Voltage Divider for Vs = 10 V, R1 = 15 Ohms R2 Vout using Matrices A note that may be helpful: You may find the MATLAB Function Browser to be useful, but the information it provides is generally not as complete as the information in the MATLAB Help window. You can also access the Help capabilities by typing doc function_name) in the Command Window.

5 For Part 3 document content, following the procedures in the Project Requirements document, copy your well-commented MATLAB code, the two MATLAB plots, and the results table produced in the Command Window to the document. Place your wellcommented code on separate landscape pages of the document, using margins and sufficiently small font as necessary to minimize the occurrence of line wrap and maintaining the colors from the editor window. Compare the MATLAB results with of the results of Part 1 and explain any differences. Your observations should include at least your comments about the difference in the two approaches used in the MATLAB code, what is being done in the second approach that avoids the need for using for loops, and the advantages of each approach. Also explain separately how the code is producing the plots (including the details of the title) and how the code is producing the output to the Command Window. Finally, discuss the benefits and drawbacks of the approaches used in all three parts of this assignment, describing situations where each method would be the preferred approach. Please submit by to the instructor the following prior to 10 AM on the due date: A document file containing the items listed above. An LTspice.asc file from your simulation. A MATLAB.m file containing your well-commented code.