EE 420L
Engineering Electronics II Lab- Lab 7
Design of an Audio Amplifier
Authored by Shadden Abdalla
Email: abdals1@unlv.nevada.edu
April 3, 2019
Prelab work:
Real
lab work:
Instructions:
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.
PMOS
Kpp = 0.145A/V^2 from datasheet
Vthp = 2.875V from datasheet
Gmp = 0.262A/V from LTSpice
NMOS
Kpn = 0.1233A/V^2 from datasheet
Vthn = 1.824V from datasheet
Gmn = 0.24 A/V from LTSpice
With 100k Resistor
Resistance
- Simulate your design. Document the results in your lab
report. Document the test performance of the design including power
dissipation, output swing, input resistance, output resistance.
My
design and Trade-offs:
Below
is the LTSpice simulation of the circuit I decided to build. The input signal
from the frequency generator is a 1Vpp input voltage at a 10kHz frequency. I
decided to use the classic push pull amplifier after trying to build a
two-stage amplifier and failing because we were only allowed to use two
capacitors. The only way to successfully implement a multistage amplifier is by
using a capacitor, as I will discuss more below. I initially wanted to use the
NMOS source follower as a preamplifier before the push- pull amplifier. After
testing different methods, this one worked best. The 100k resistor, R1, allowed
the sound to be very loud but it also made the circuit’s current very high and
the NMOS began to burn up. Reducing the resistor value to 10k or 15k still made
the circuit work, however, the sound was less loud and less amplified. When
increasing the resistor value, more power was sent through the circuit. The
tradeoff here is that even though a large resistor added creates better sound,
it actually sends too much power and causes the
circuit to burn up faster. Testing the circuit with 5V instead of 10V gives a
similar effect. The sound is not as loud with a 5V input,
however, the circuit does not eat up as much power and burn the transistors.
Below
is the design I choose:
In
the LTSpice simulation, you can see that Vout is
slightly larger than Vin.
Power
simulations with a 100k resistor: Shown below is the power dissipation through
the resistor and at the drain of the MOSFET. The power dissipated is not too
high, however, if the circuit is on for too long it could burn a transistor.
Different
Attempts of the Same Circuit:
SAME
DESIGN WITH 15K RESISTOR: the power dissipated is slightly less than it was
with a higher resistance.
We
also tried the same circuit with an input of 5V instead of 10V. We noticed that
the gain was not as high and the power dissipated is less, however, it did not
burn the circuit as quickly. This is the result of the 15k circuit.
We
also tried the same circuit with a 5V input and 100k resistor. The power
dissipated is less than it was with a 10V input.
- Build and test your design.
Below is a photo of the
breadboard circuit with a 100k resistor. We changed the frequencies from 100Hz
to 20kHz to test the circuit.
200Hz – At a lower frequency
such as 200Hz, the input amplitude is 1V and the output amplitude is 60mV.
At 10kHz – You can see
that the amplitude of the input is 1.12V and the input of the output is 960mV.
20kHz – At 20kHz the input is
at amplitude of 1.96V and the output has an amplitude of 1.48V.
This is the link to a video
of our audio amplifier working and playing different tones with different
frequencies ranging from 100Hz to 20kHz. All frequencies in that range are
accounted for in the following video:
Click on the image!
Click
on the image below to watch a video of our audio amplifier playing “Sicko Mode”
by Travis Scott very clearly.
Click
on the image below to watch a video of our audio amplifier playing “Highway
Tune” by Greta Van Fleet.
Attempted Circuits (Not Push-Pull) Before
Reaching Final Design:
Pre
amplifier and push pull circuit with capacitor:
This is the ideal design that we attempted,
however, we were not able to actually use this for the
lab because there is a 10u capacitor, C1, and we were only able to use two
capacitors. With the capacitor, we would’ve been able to implement a two-stage
amplifier. In this lab, that is not permitted but this is the ideal situation.
In the simulation, the amplification is shown.
Pre
amplifier and push pull circuit with capacitor:
Since we are not allowed to use more than
two capacitors in this lab, this is the design that would be implemented if we
were to use two stages. It does not work since we need the capacitor in between
the two circuits. Since we were not able to use a third capacitor, this design
did not work in this case and we resorted to a push pull amplifier instead, without
a second stage. In an ideal situation, a two-stage amplifier would be best,
however, a push pull is the best at the time.
Overall, the push pull
circuit worked best for us with a 100k resistor, even though the power dissipated
was slightly higher than the 10k or 15k resistors. The videos above show how
clear the sound was with our design.