Lab

Lab 7 - EE 420L Engineering Electronics II

Author: Matthew Meza

Email: mezam11@unlv.nevada.edu

March 20th, 2015

Design of an audio amplifier

Click on any picture for its full size!

Pre-lab work

This lab will again utilize the ZVN3306A and ZVP3306A MOSFETs so review lab 6.

Lab Description

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.

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.

Lab Data

For the following questions and experiments assume VCC+ = +10 Volts

Experiment 1

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.

Our Audio Amplifier design consisted of the push pull amplifier seen in the previous lab and output stage

which was used to increase the gain in the circuit. At first, when just using the push pull amplifier, we observed

that there was not enough gain as desired. Since we could not use any more capacitors, we were limited in ideas

to enhance the gain without modifiying the push pull resistor. By feeding the output to a seperate NMOS transistor

we were able to use the source of the NMOS as our output. We added an 8 ohm resistor in parallel with the capcaitor

and speaker such that the NMOS could operate at DC. Increasing the parallel resistor (Rp) can slightly

increase the gain. Any resistance value larger than 16 Ohms would not offer any significant gains.

The design we used is simulated below!

The output simulated and shown below and the input resistance can be easily obtained by the
simulation circuit to be around 10KOhms

Next we implemented the design on a breadboard. The amplifer output is shown below when

we only used the push pull amplifier without the output stage!

The amplifer output is shown below when we included the output stage!

The power supply was able to show the current used by the
circuit which is handy in calculating the power usage.

Experimentally we using 0.32*10.7 = 3.4 Watts of energy.

Our simulation showed approximately 3.6Watts of energy being used. This variation can be

due to the incorrect reading based off the power supply and or the irregularities from the

experimental MOSFETS used compared to the simulation values.

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