ECE 323 Design Project Due: Nov. 29, 2005
Note: This design project is equivalent to a take-home exam. You are to do your own
work and you may not consult with others. If you need help you may consult your
instructor or the TA.
The activist group SUCCR$ (Students for Undergraduate Curriculum Cost
Reductions) is seeking a circuit for an inexpensive megaphone to help them
shout their slogans around the administration building.
You are to design an audio amplifier to amplify the signal from a high
impedance (15 kΩ) microphone and directly drive an 8-ohm speaker.
The amplifier will have the following specifications:
a) Midband gain (vo/vs) of 100 ± 15%. (Note: This includes the effect of source and load
resistance. To achieve this gain, your input resistance must be quite large and output
resistance must be low. Assume 8-ohm load. )
b) Operate with a source resistance (of microphone) of 15 kΩ.
c) Output resistance should be less than 10 Ω (for good power transfer).
d) Bandpass frequency response from 20 Hz to 20 kHz. Frequencies indicated are –3dB
cutoff points.
e) Use only capacitors, 1% resistors (see appendix G), and 2N3904 transistors.
f) Operate on a single 12 V battery.
g) AC couple the input and output.
h) Above specifications must be met for the full range (min to max) of transistor
parameters indicated on the data sheets.
i) -3dB cutoff points of the frequency response should not depend on capacitances of the
transistor.
j) Output voltage swing must be at least 2 V p-p.
Submit a report, which includes:
a) Schematic diagram of your final design with all component values indicated.
b) Analysis clearly demonstrating that your design meets the above requirements for the full
range of transistor parameters.
c) SPICE simulation results showing mid-band gain and –3dB cutoff frequencies.
Note: You will be graded not only on correct design but also on the clarity with which you
present it. I should be able to easily follow your analysis. Your report should not be a play-by-
play of how you arrived at your design; rather, it should be a concise analysis of your final design
demonstrating that it meets the specifications.
Resist the temptation to “design by SPICE”, i.e. blindly adjusting your circuit until SPICE gives
you the desired results. SPICE simulation is for verification only. A design that meets spec. in
SPICE but has no supporting analysis will get no credit! However, if SPICE gives you results
much different from your analysis it usually indicates that either your analysis is wrong or that
your SPICE netlist/diagram is mis-wired.
Although not required for the report, you may find it useful to use SPICE to verify that your DC
bias conditions are correct.
For designs that meet the specifications, extra credit will be given for clever design to reduce
component count or cost.
