eee161 applied electromagnetics laboratory...

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Dr. Milica Markovic Applied Electromagnetics Laboratory page 1

EEE161 Applied Electromagnetics Laboratory 2

Instructor: Dr. Milica MarkovicOffice: Riverside Hall 5026

Email: [email protected]:http://gaia.ecs.csus.edu/˜milica

1 Learning Objectives

In this lab you will

1. Learn how to simulation a circuit in ADS using AC Simulation and display phasors on a polarplot.

2. Review using phasors to derive and calculate voltages and currents in simple series and parallelcircuits.

3. Define Kirchoff’s Voltage Law (KVL) and Kirchoff’s Current Law (KCL) in both frequencyand time domains.

4. Describe how are the equations in the time and frequency domain different? How are they thesame?

5. Proove that KVL and KCV are valid in both frequency in time domain.

6. Design a simple circuit to fit specifications.

(a) Gustav Robert Kirchoff (b) Keysight’s cartoon.

Figure 1: The first two steps to plot a signal as a function of angle.

California State University Sacramento EEE161 revised: January 16, 2018


2 Series RC Circuit - Hand Calculations

Q−→ Calculate on paper the magnitude and phase of the current and voltages in a seriesRC circuit if the source voltage is vs = cosωt, R=1 kΩ, C=0.159 pF, f=1 GHz. Answerthe following questions:

1. What are the magnitude, phase and time delay of the source voltage.

2. What are the magnitude, phase and time delay of the voltage across the resistor.

3. What are the magnitude, phase and time delay of the voltage across the capacitor.

4. Sketch the phasor diagram of the three voltages.

5. On the phasor diagram, what is the angle between the vector of voltage on the capacitor andresistor? Why?

6. Explain why the voltage magnitudes on capacitor and resistor do not add up. For example, inFigure 6, the voltage magnitude across the resistor is about 0.5V and the voltage magnitudeacross the capacitor is about 0.85V. 0.85V+0.5V6=1V. Why? Does that mean that the KVLdoesn’t work? Hint: Think about KVL in frequency domain. You are using phasors now. Writethe equation for KVL using phasors. Write an equation that describes this addition. Whatkind of equation is this? What kind of numbers do you have to use to describe this addition?Which domain is this equation in?

7. Sketch the voltage on the capacitor and resistor as a function of time. What is the totalvoltage equal to at any time instance? For example, look at the time instance t=0, t=0.5 ns,then calculate the voltages on resistor, capacitor and input voltage. What can you conclude?Hint: Look at the Figure 6 and marker m1. At that time, voltage on a capacitor is zero, andvotage on the resistor and source are 0.5V. Write an equation that describes this addition.What kind of equation is this? What kind of numbers do you have to use to describe thisaddition? Which domain is this equation in?

In the following section, we will simulate a series RC circuit in ADS.

3 Accessing ADS

First you will open ADS on Hydra. If you are loged in on Windows computer, you will login remotelyto hydra.ecs.csus.edu, by using Start, All programs, Remote Desktop. Make sure that you are loggingin to ECS domain with ECS\yourusername and ECS password. If you are in RVR 3009, you areloged in on Unix computers. Click on

The following instructions assume that you are already on Hydra.

1. Select Start, All programs, Advanced Design System 2015 (or the current installed version, forexample Advanced Design System 2016)



2. ADS windows opens, wait several minutes, especially if the entire lab is logging on at the sametime. You should see several windows open, the top one Getting Started with ADS. Close thatwindow.

3. From window: Advanced Design System 2015 (Main) click on the icon W+ to create the newworkspace. ( Later when you are returning to work again on ADS you would select W-¿ opena workspace).

4. New Workspace Wizard window opens. Click on Next.

5. Worskpace name: Name the workspace (for example Phasorlab_wrk). Create in: T:\ADS2015-HOMEdrive. Click Next then Finish.

6. Click on the schematic icon in Advanced Deisng System 2015 (Main) window. Schematic iconis the white icon with a resistor under a capacitor.

7. New Schematic window opens. Cell: Problem1B (or something like that). Schematic DesignTemplates: wizard_templates:GS_AC

In the next section, using the circuit diagram in Figure 2(a) as a guide, reproduce the voltageson capacitor and resistor as shown in Figure 2(b). Note that the figures you will get will not lookexactly like the figures below because the circuit in Figure 2 is similar but not exactly the same asyour circuit.

4 Simulation of Series RC Circuit in ADS

Once the circuit diagram is open:

1. You should see an AC source, a 1kOhm resistor and the gear icon on your schematic.

2. Make sure that at the top left corner Lumped-Components section is selected.

3. Select the top left choice for the capacitor C. Do not select C-Model, select just C. Click on itand drag it to the place where you want the series resistor. Click on the Arrow icon on the topof the window (or escape) to stop placing capacitors on your schematic. If you placed morethan one resistor click on the X icon on the top of the window, then on extra capacitors toremove them. Again click on the arrow (or escape) to continue. Note that the default valuefor the capacitor is 1 pF. Click on the C=1 pF, then change it to 0.159 pF.

4. To add the current probe, go to the Lumped-Components drop-down menu and change it toProbe Components. Select the top left choice I_Probe. Place it between the source and thecircuit.

5. Double click on AC gear icon on the schematic. AC Small Signal Simulation:1 opens. On thefrequency tab (default) Change the Sweep Type to Single point. Set the frequency to 1GHz.The default frequency is usually 1GHz, but check that this is so.



6. Click on the icon Name, WirePin Label window opens. Write vin, then click on the wire thatconnects the source and the circuit.

7. Click on the gear icon on top menu to simulate the circuit.

8. Data window shows two windows, one shows the magnitude of the output voltage as a functionof frequency, and the other phase as a function of frequency. In this case we simulated onlyone frequency point, so there is really no sweep.

9. Click on the icon that shows a 4by3 table from the Palette and place it on the Data window.This opens a rectangular x-y plot on data window. Plot Traces&Attributes Window appears.Click on Vout then Add. A window opens reminding you that you are accessing a variable thatis complex, e.g. it has a magnitude and the phase information. Select Time Domain Signal.

10. Repeat step 9 for vin.

11. To plot the voltage on the resistor R1 (from Figure 1, you will need to write an equation fromone or the other element, depending on how your circuit was connected), one needs to write anequation in Data Window. Click on Eqn con from the Palette. Enter Equation windows open.Write the equation as shown in Figure2:vr=1000*, then click on the variable I_Probe1.i fromthe right window and select Insert. This will place I_Probe1.i in your equation. Note thatyou have other variables such a freq in the same window.

12. To place Vr on the time-domain graph, double click on the graph, then select from Datasetsand Equations pull-down menu Equations instead of Problem 1, then select Vr, click Add, andselect Time Domain Signal. You should see a graph as shown in Figure 2(b).



(a) Series RC Circuit in ADS Schematic Diagram

(b) Voltages as a function of time

Figure 2: Create a circuit diagram and display voltages.



13. To plot phasors of voltages, select the icon from the Palette that looks like a target. A windowPlot Traces & Attributes opens. Select Vout and vin and add them to the plot. If you wantto increase the size of dots representing the voltages, double click on the dot, a Trace Optionswindows opens. Select larger thickness of the point, for example 3. You should see a graph asshown below in Figure 3(a). To make a plot as shown in Figure 3(b), click on the top dropdownmenu: Insert, then select Line.

(a) Polar plot display in Ads

(b) Polar plot with voltage vectors drawn in.

Figure 3: Displaying signals on a polar plot.



14. To plot time domain plots as a function of angle in radians or degrees, you have to defineangle as ωt. Since this is a frequency-domain simulation, we have to define time as t=ts(freq).ts() performs frequency to time transform. Select Equation from the pallete menu, place iton the Data Display. In a window that opens, write equation as defined in Figure 4(a). Nowwe will replace “time” with the equation for omega on x-axis of the rectangular plot. Placethe rectangular plot on the Data Display, select the voltage you want to plot as a functionof angle, and select Time-Domain signal Figure 4(b). Then, select the pull-down menu (anupside down triangle) as shown in figure 5(a) and select Equation, as shown in Figure 5(b),then select omega. When you select OK, new window opens as shown in Figure 5(c). SelectTime-Domain Signal and click OK. You should now see the window as shown in Figure 5(d).When you click OK, voltage as a function of angle in radians is displayed, as shown in Figure5(e). Now you can plot all voltages as shown in Figure 6.

15. You can now repeat the process for angle in degrees, or you can directly change the graph inradians. Click on omega, then multiply omega with the conversion factor 180/π.

(a) Define equation for angle. (b) Place the rectangular plot on theData Display.

Figure 4: The first two steps to plot a signal as a function of angle.



(a) Voltage as a function of angle in radians. (b) Voltage as a function of an-gle in degrees.

(c) Voltage as a function ofangle in radians.

(d) Voltage as a function of angle in de-grees.

(e) Voltage as a function of angle in degrees.

Figure 5: Displaying signals as a function of angle in radians.



(a) Voltage as a function of angle in radians.

(b) Voltage as a function of angle in degrees.

Figure 6: Displaying signals as a function of angle in radians and degrees.



5 Simulation Analysis

Q−→ Answer the following questions:

1. Read the magnitude, phase and time delay of the source voltage from the diagrams above. UseMarkers to read graphs precisely. Compare with your hand calculations in Section 2. How dothey compare? Name all the graphs that you can use to read magnitude, phase and time-delay?

2. Answer the questions above for the voltage on the resistor.

3. Answer the questions above for the voltage on the capacitor.

4. On the phasor diagram, what is the angle between the vector of voltage on the capacitor andresistor? Explain how can you confirm this by reading the graph voltage as a function of anglein degrees. Compare these values with yoru calculations. Do they match?

5. Explain why the voltage magnitudes on capacitor and resistor do not add up. Compare withyour calculations. Do they match?

6. Sketch the voltage on the capacitor and resistor as a function of time. What is the totalvoltage equal to at any time instance? For example, look at the time instance t=0, t=0.5 ns,then calculate the voltages on resistor, capacitor and input voltage. What can you conclude?Compare these values with your calculations. Do they match?

6 Series RL Circuit

In this section, you will check whether you are able to repeat the simulations above for a differentcircuit. Simulate in ADS the currents and voltages in a series RL circuit, R=1kΩ, L=200 nH.

Q−→ Using markers measure the magnitude of the voltage on the resistor and in-ductor. Add them up. Do they add up to the voltage of the source? Why or why not?When do the voltages add up?

7 Design a Parallel RL Circuit

Simulate the currents and voltages in a parallel RL circuit. Pick R and L values in such a way thatall currents have the magnitudes of about 0.5 of the source current.

Q−→ Simulate and record the magnitude of the current through the resistor andinductor. Add them up. Do they add up to the current of the source? Why or whynot. When do you see that the currents add up to the source current?

8 Hand Calculations

Solve the problems 6 and 7 on paper using phasors. Look at the KVL equation for the voltage.



Q−→ The voltage on the resistor and inductor (or capacitor) should add up to thevoltage of the source. What is the issue in addition of these two voltages/currents?Assuming you measured 1V for the voltage across the capacitor and 2V for the voltageacross the resistor, is the source voltage then 3V? Why or why not. Draw a vectordiagram for the voltage or current to prove your point. Discuss time and frequencydomains.

9 What is a linear circuit?

Assume that a sinusoidal source is driving the linear circuit.Q−→ Without knowing the topology of the circuit, what can you state about all

currents and voltages in this linear circuit? Explain what is a definition of a linearcircuit?


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