Download How to make Frequency plots with Pspice

ECEN 3021 Experimental Methods-II
Frequency Response using PsPice
1. Vac
Is it possible to have a source in PSpice where the frequency is changing with time? This can
be useful when we are trying to determine the frequency response of a given circuit. The Vac
source is perfect for this goal. Vac has the main parameters of Vac (AC amplitude) and Vdc
(DC offset voltage).
a) To demonstrate this source, we’ll use the following circuit.
b) In order to obtain a source whose frequency is swept through a range of frequencies, go
back to the Simulation Settings and switch to AC Sweep/Noise analysis. With the
selections shown below, the frequency will sweep in linear steps from 1KHz to 1MHz.
There will be a total of 100 points.
c) The graph below shows the magnitude of the output sine wave (voltage across the
resistor) as a function of the frequency of the input sine wave. As you see, the output
magnitude starts out very low, and then at higher frequencies the output magnitude
almost equals the input magnitude (5 volts).
Electrical & Computer Engineering
Oklahoma State University
ECEN 3021 Experimental Methods-II
Frequency Response using PsPice
2. Bode Plots (Frequency Reponse)
When a sine wave source is applied to a linear circuit, all currents and voltages in the circuit will
be sine waves of the same frequency. The only differences between the source sine wave and a
response sine wave will be the magnitude difference and the phase shift. Bode plots are graphs
that show the variation in gain (magnitude difference) and phase shift produced by a circuit, as
the frequency is varied.
a) Let’s go back to the example of the RC circuit. Using this example, we will now run our AC
Sweep.
b) Now we’ll go to Functions or Macros and we’ll select Plot Window Templates. As you can
see, there are many options depending on what information you are seeking about the circuit.
Select Bode Plot – separate(1). Then you’ll place V(OUT) into the parenthesis, so Trace
Expression should look like:
c) The output should look as it does in the figure below:
.Then click “OK.”
In this particular figure, the top plot is the ratio of the amplitude of the output voltage to the
amplitude of the source voltage (gain), while the bottom plot is the phase difference between the
input voltage and the output voltage.
Electrical & Computer Engineering
Oklahoma State University