Transcript Teaching DSP using PSpice - DIT: School of Electronic and

The role of PSpice in the
engineering teaching environment
Simulation software tools have been shown
to be effective in communicating abstract
ideas to students.
Several studies have shown that the
performance of students who used
simulation software scored higher marks
on written exams, when compared to those
who used laboratory methods only”
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Capacitive reactance
• Basic principles can be explored by simple
circuits. The following example looks at
reactance and the phase delays between I
and V.
•
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Capacitive reactance plot
PSpice allows the student to measure reactance at any
frequency.
Open circuit
Short circuit
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Time delay and Phase difference
Students find time delay a much easier concept
to understand than phase delay.
The student may convert the measured time delay to a phase delay as:
T
t
360xt 360x25 ms
  

 900
360 
T
100 ms
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Terminating a Transmission line
This example shows a transmission terminated
with different resistances, i.e. an open circuit to
a short circuit.
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Standing waves and VSWR
Standing waves occur when lines are incorrectly
terminated and are quantified by voltage standing wave
ratio (VSWR).
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The use of Macros in PSpice
Macros extend the horizons of PSpice greatly.
Here we examine signal errors in received
digital signals corrupted by noise. A macro
contains a series of steps, or equations
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Noise corrupts digital signal such that a ‘1’ may be
misinterpreted as a ‘0’, and vice versa. However, we
need to apply probabilities since we cannot say where
and when these errors occur.
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Gaussian distribution and errors
A binary data signal corrupting by noise has a probability
distribution described by the equation:
1
 ( vn  vd )2 / 2 vn
Pe (vd , vn ) 
e
vn 2
Pe (vd , vn ) 
1
 ( v  v )2 / 2 vn
e n d
vn 2
To quantify these errors we need to look at the probability of
these errors existing over a certain time period. A text editor,
such as Notepad, can be used to create the following macro:
• Gaussian1(vd,vn)=(1/(sqrt(rms(vn)*rms(vn)*2*pi)))*exp(-((vd-2)*(vd2)/(2*rms(vn)*rms(vn))))
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Gaussian distribution
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Implementing a Hilbert transform
A Hilbert transform introduces a constant 90-degree across the
passband region, and here it is implemented using a Finite Impulse
Response (FIR) digital filter
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Digital filter impulse response
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Magnitude and phase responses
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Sixth-order active filter
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Histogram and frequency response
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16-Quad Amplitude Modulator
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16-QAM scatter diagram
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Conclusions
A worrying trend in engineering education is a
reduction in teaching fundamental principles.
The paper attempted to demonstrate how PSpice
can help with this, and do so with a minimum of
mathematical rigor.
The student can examine complex sub systems
and consider the problems associated with
matching sub-systems connected together, a task
not easily done in practice
Thank you
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