Lab 7 - EE 420L
April 3, 2019
Design an
audio amplifier (frequency range from roughly 100 Hz to 20 kHz) assuming that you can use as many resistors, ZVN3306A
transistors, and ZVP3306A transistors as you need along with only one 10 uF capacitor and one 100 uF
capacitor. Assume that the supply voltage is 10 V, the input is an audio signal
from an MP3 player (and so your amplifier should have at least a few kiloohms
input resistance), and the output of your design is connected to an 8-ohm
speaker (so, ideally, the output resistance of your amplifier is less than 1
ohm).
·
Your lab report should detail your thoughts on the design of the
amplifier including hand-calculations.
o A good place
to start is with the push-pull amplifier characterized in lab 6.
·
Simulate your design. Document the results in your lab report.
·
Build and test your design.
·
Document the performance of the design including power
dissipation, output swing, input resistance, output resistance.
Ensure that
your html lab report includes your name, the date, and your email
address at the beginning of the report (the top of the webpage).
When finished backup your work.
Below is a
comparison between driving a speaker without (red, Vout1) and with (black,
Vout2) an audio amplifier. The source resistance is 10k meaning that the source
can supply 1 V (blue, Vs) at 100 uA maximum. The
simulation files used to generate this figure are found in lab7_sims.zip.
We started
with the basic push pull amplifier that was taken from lab 6 and then we
modified it a bit.
Below are the hand calculations for the gain
and the output resistance. We are looking for an output resistance of one ohm.
From the hand
calculations you can see that the output resistance is at 8 Ohms which is not
what we want for an 8 Ohm speaker and could be greatly reduced with a source
follower. We were only provided a 25ohm speaker so we decided that the push pull amplifier alone
would work better for the bigger speaker.
Finding our
value for R1 to adjust our gain
This is a
simulation of the gain and power in the amplifier and how it behaves at various
resistances for R1. The nicest looking wave was 20k so, that’s what we used.
20k had the greatest gain and the least distortion.
We then
simulated the amplifier the same way, but changed the R2 to see how our output
would change
This is the
power and gain of the amplifier with the different values for R2. The best gain
with the lowest power consumption came from the 25 Ohm resistor
With the new
resistor values for R1(20k) and R2(25ohm) we looked at the input and output
resistance.
We got 23k for
the input and 25ohm for the output resistance from the simulations.
We then built
the circuit and measured the input vs the output with 100Hz and 20kHz respectively.
My output
signal for 100Hz is 664mV and for 20kHz is 944mV while the simulations for
100Hz showed 350mV for a 1V input. The sound from the signal generator was loud
and clear.
The wave form
we got form an Auxiliary connection was not what we were looking for. It had distortion and we also had low volume,
but we were still able to hear Hit'Em Up by 2PAC
clearly through the speaker.
Conclusion:
This lab
showed me how to approach a design problem and the full operation of the push
pull amplifier.