Lab7 - EE 420L
Authored
by Allan Pineda
pineda3@unlv.nevada.edu
March 29, 2017
Lab Description: Design of an Audio Amplifier
- This
lab was about designing an audio amplifier that has a frequency range
of 100Hz~20kHz using the ZVN3306A and ZVP3306A transistors, as well as
two capacitors one is a 10 uF and the other had to be a 100 uF.
- Using a 10 V VDD to power the transistor, and an output of 8 ohm speaker.
Lab report should include:
- Design process along with hand calculations.
- Simulations using LTspice of the circuit.
- results from testing design.
- comments on the performance of the design.
Experiment
This experiment is about designing an audio amplifier to implement the
topic that was covered in the previous laboratory experiment. Common
source, common drain, common gate as well as push-pull amplifier are
can be use to design an audio amplifier. The first step in the
experiment was to build a schematic and simulate it in the LTspice to
see how the circuit work. One must undestand the concept of each
amplifier to build a better design. The picture below is the schematic
along with the simulation result showing the gain with push-pull and
the gain without the amplifier.
Given Schematic
Waveform Result
Looking at the waveform result above one can see that the output
(Vout1) without push-pull ampilfier is not amplified as well as the
current, meaning that the 8 ohm speaker will not produce any
sounds. On the other hand, a push-pull amplifier connected to an 8
ohms load was implemented. Using a push-pull amplifier, one can have
high gain in circuit. However, in this experiment, having a 8 ohm
resistor as a load it was not enough to have a good amount of gain to
make sounds coming out from the speaker at a low frequency.
This design circuit will work only at a very limited frequency
range.
Due to this observation a push-pull amplifier as well as the other
method of amplification from the previous lab must use to achive the
goal of having good enough gain and current to make sounds coming out
from the speaker or to meet the required specification. See the circuit below for implementation.
Final Design
Schematic
Waveform Schematic
Input resistance:
Output Resistance:
So the circuit above is combination of common source amplifier and a
push-pull amplifier. As shown above the gain of the push-pull is in
thousand range but the output resistance is fix with approximately
9ohms a little far away from the specification required to this lab.
To fix the problem a common source amplifier was connected in the
output of the push-pull to get flexibility in controlling the output
resistance. The output resistance came out to be 3.79 ohms which is
really close to the required out resistance of 1 compare to a 9 ohms resistance.
Hand Calculation
The results from the simulations above show that adding the common-source
did effect the gain but it helped in reducing the output impedence to a
lower value so this circuit was tested again on the bread board to see
how well it will perform. See the figure below for different range of frequency.
1000Hz
5kHz
10kHz
100Hz
| Frequency | 100Hz | 5kHz | 10kHz | 1kHz | 20kHz |
| Peak to peak | 584mV | 672mV | 704mV | 648mV | 736mV |
The input impedence of my design can be easily seen from the schematic
to be 20k ohms as well as shown in the picture above. The 20k ohms
input impedence is a typical input for a audio amplifier. As
for the output impedence, it is just the parallel connection between
the 8ohms as well as the gm of the transistor and 8 ohms impedance of
the speaker which came out to be at almost 4ohm which is really close
to the calculated value.
Power Dissipation:
For
calculating the power dissipation of the circuit, one needs to measure
power supply voltage and the current through each stage of the
whole circuit. So to have the total currents of all the stages we
can use the current shown in the power supply as shown above. The
total current drawn to the circuit is about 320mA thus multiplying this
current to the voltage power supply which is 10V will result in
approximately 3.2 watts dissipation which proved from the simulation above.
Conclusion:
I therefore conclude that in designing a audio amplifier can be done in
different technique depend on the specification or required parameters.
A combination of common-source, common-gate, source follower or
push-pull amplifier can be use to design a good amplifier.
However, a impedance matching is very important to take into
consideration in designing amplifier. having a matched impedance can
increase the performance of the amplifier and it can reduce the risk of
burning the transistor during the design process.