PSpice AC Analysis
Name:
Objectives: Each student will be able to use: (a) PSpice/OrCAD to determine voltage and current
amplitudes and phase angles in an AC circuit, and (b) the AC sweep capability of PSpice to compute
and plot the frequency response of a circuit.
1. Single-Frequency Analysis:
The circuit has L = 100 mH, R = 1 kΩ, C = 0.05 µF, and the
sinusoidal source shown in the figure which is described by the
equation:
vg = 10 cos(2πf t + 90°) V
where f = 3 kHz.
In this single-frequency step, you will use PSpice to find the
magnitude and phase of VL, VR, VC, and the current in the series circuit. Then you are to check your
PSpice results against an analytical solution.
A PSpice schematic representation of this circuit is shown below. It uses printer devices (parts).
(a) PSpice current and voltage “printers” cause the
result of the analysis to be printed in the output
file. In order to get the desired output data, we
must edit the property spreadsheets for each of
these parts. You must specify the output to be from
AC analysis by placing a “Y” (for “yes”) in the
column labeled AC. Also place a Y in the columns
labeled MAG and PHASE to have output values in
polar form.
Question: How can you get the output values in
rectangular form, i.e., placing a Y in what columns?
(b) Select AC Sweep as the type of analysis. Since we only need a single frequency, set the Start and
End “sweep” frequencies to the same value and the Number of Total Points to 1. Note that we
must specify the source file frequency in hertz. Try doing this by omitting the End frequency;
what happens?
(c) Run the analysis and examine the output file (PSpice → View → Output File in the PSpice
window, or find it another way). Describe what happens, and what you do to find it. Find the
results for the two voltage amplitudes and phase angles and for the one current amplitude and
phase angle; list the results in your report and mark them in your printed .Out file. The results will
be listed under the heading AC Analysis toward the end of the file. You could save the .OUT file
as a text (*.txt) file for future reference.
2. Swept Frequency Analysis
Usually AC Sweep is used to vary the frequency of the source, plotting the effect using Probe. (Did
you see “Probe” in (1c) above? Explain.) This type of analysis is called a "frequency response." To
run a frequency response, enable AC Sweep using the decade sweep type with 60 points per decade, a
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start frequency of 150 Hz, and an end frequency of 50 kHz. Note that PSpice uses Hz and not
radians/sec!
Run the analysis and plot ‘IM(R)’. Run it again and plot ‘IP(R)’. Describe briefly on each plot what
you have plotted. See if you can create one plot with two separate vertical axes to show both of these
values together.
Using the cursor on the IM(R) plot, determine the resonant-frequency and both of the two frequencies
at which the current is reduced to 70.7% of its peak value.
Figure out how to do another plot which gives the “voltage gain” of this circuit. That is, plot
M(V(C)/V(Vg)).
3. Parametric Analysis
Now change the schematic by replacing the value of R with a "global parameter" named “r_value”
contained in curly brackets: {r_value}. The curly brackets are used to indicate a global parameter.
The default value of such a parameter is specified using the part named PARAM. Double click the
PARAM part to specify a default value of r_value; do not use the curly brackets here. Set the default
value of r_value to 1 kΩ, the original value of R.
During a swept-frequency analysis, a global parameter can also be swept using a "parametric sweep."
Examine the Parametric option under Options and notice the type of information required to specify
the Sweep Variable Type and Sweep Type. List the possible Sweep Variable Types and the possible
Sweep Types.
Use what you have just learned about AC Sweep analysis and about parametric sweeps to examine the
effect of the resistor value on the magnitude response of I(R). Use the following list of values: 500 Ω,
1 kΩ, and 5 kΩ. Print and label the Probe results in your report.
Report: Include all data, results, observations, and answers to questions, written neatly and legibly in
ink on the front of standard engineering paper. Use this lab sheet attached as a cover. Normally with
PSpice work like this, at least one example schematic, one printed .OUT file, and several Probe outputs
must be included. Include NOTES on your PSpice printouts.
EXECUTIVE SUMMARY: Write an executive summary describing the experiment you
ran in Step 2 (Only Step 2) above. See the example EXECUTIVE SUMMARY.doc in the
Narnia/web shared folder.
The lab report and the Executive Summary are due as indicated on the syllabus.
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