Lab 7 - EE 420L - Design of an Audio Amplifier

Jonathan K DeBoy
deboyj@unlv.nevada.edu
20 March 2015


Pre-lab work

 

Introduction

This lab required us to design an audio amplifier with the knowledge that we have gained from our previous labs. We are allowed to use as many resistors and transistors as we desire along with only one 10uF and one 100uF capacitor. Audio amplifiers must operate with large voltage swings, low output impedance, and in the frequency range from 10-20kHz.


The Push Pull

schematic.JPG     waveform.JPG


IMG_20150320_113625_604.jpg

At first using, using a resistor of 100k had too much gain for our 10mV input voltage so we decresed the resistance to allow for a lower gain.

Output Swing

Our output swing ranged from +10V to -15V

 

Power Dissipation

With VDD is 10V and our current near 250mA => power = 2.5 Watts.

 

Input Resistance

The input resistance depends entirely on our resistor value in series with 1/gmn || 1/gmp. With 1/gmn~=1/gmp~=56, Rin = 510+23~= 510 (the value of the resistor used).

 

Output Resistance

The output resistance depends on R || 1/gmn || 1/gmp ~= 1/gmn||1/gmp ~= 23 ohms. This needs to be near 8 ohms to properly drive our 8 ohm speaker. With this load, we see a large voltage drop across the output resistance leaving only 25.8% of the voltage left for the speaker. For louder sound, we need either more gain or much lower output resistance.




Conclusion


We designed an audio amplifier capable of accepting input from an aux cord and driving an 8 ohm small speaker using a basic push pull amplifier configuration.
 
 
 
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