ELEC 320, Fall 2006

Profs. Wismer & Kozick

Profs. Wismer & Kozick

This lab will give you an opportunity to review ELEC 120 and ELEC 225-226
as you design electric circuits that behave as frequency-selective filters.
You will analyze and design your filters using basic
circuit analysis concepts.
The computer software package MATLAB will be used to
verify your designs.
Then you will build the filters and make measurements to
determine how closely your circuits come to achieving the
design specifications.
*Each student* will
submit a written lab report that
includes an explanation of your filter design procedures,
an analysis of your filters, and your experimental
measurements.

**Review Materials:**
Please review the items listed on the
Homework 1 assignment sheet,
as well as any other materials that will help you
design the filters specified below.

**Important Note:**
Your objective in this lab should be to understand the basic
concepts used to analyze and design the filters.
You will also become familiar with some MATLAB commands.
What you should *not* do is look up a circuit in a
textbook or handbook, plug numbers into a formula to get the
circuit R, L, and C values, and then build
the circuit, with little or no understanding about how or why it works!

The filter design specifications and lab activities are as follows.

- Design a first-order, low-pass filter with a passband gain of -5 volt/volt at low frequencies and a cutoff frequency of 500 Hz.
- Design a first-order, high-pass filter with a passband gain of -5 volt/volt at high frequencies and a cutoff frequency of 5000 Hz.
- Design a band-pass filter with a passband gain of -20 volt/volt, a low cutoff frequency of 1000 Hz, and a high cutoff frequency of 2000 Hz.
- Derive the analytical expression for the
magnitude and phase of the frequency response for each filter.
Explain how this formula is used to choose the circuit component
values to achieve the design specification.
Produce a Bode plot of each frequency response magnitude using
MATLAB.
An example MATLAB program
is available at

`http://www.eg.bucknell.edu/~kozick/elec32006/lab1_freq.m`

to help you produce this plot. Compare the Bode plot with the design specifications.

Tutorials on using MATLAB are available at

`http://www.eg.bucknell.edu/~kozick/tutorials.html` - Construct your filters and measure each frequency response.
Measure the frequency response at enough different frequencies
to clearly indicate the gain in the pass-band and the roll-off in the
stop-band.
Compare the measured results with the analytical Bode plot.
This can be done conveniently
in MATLAB, as shown in the example program
`lab1_freq.m` - If you have time, measure the unit step response of each circuit, and try to interpret the results. Are they consistent with your concepts of low-pass, high-pass, and band-pass filters?

** Lab reports:**
Each student will *individually* prepare and
submit a written lab report that
includes the following:

- An explanation of the reasoning behind the filter design procedures that you used
- The analysis of your filters and the formulas that you used in the design
- A presentation of your experimental measurements of the frequency response of each filter, and a comparison of your measured results with the design specifications

Thank you, and have fun!