Lab 7 - EE 420L 

Author:    Nicholas Mingura

Email:       mingura@unlv.nevada.edu

4/3/2019

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.

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Lab Report

For the first step of this lab the given circuit, seen below, was simulated to show what was happening with the audio with no amplifier built.
   

Image 1: Given circuit
 
From the circuit it can be seen that Vout1 is the voltage with no amplifier just the load of the resistor in seriers with RS1, where Vout2 uses a push pull amplifier to increase the signal at vout2.
 

Image 2: Circuit Simulation results.
 
As seen above without the amplifier Vout1 is almost none existant as almost all of the voltage is dropped by the 10k resistor, where as with the push pull amplifier it amplifies the signal to such a significant degree that it can be seen. The gain in the push pull amplifier can be calculated with the equations below.
 

Image 3: Push-pull amplifier gain calculations.

While the lab description specifies to build the circuit with a 8 ohm speaker the lab only had a 25 ohm resistor so all of the designs will be assuming that the speaker has a resistance of 25 ohms. The first step for designing the audio amplifier will be to get the push pull to have an output resistance lower than 1 ohm, one way to do this is by creating a common drain amplifier with the equations below. 

Image 4: Common drain amplifier output resistance 

Image 5: Common drain amplifier circuit. 

Then the circuit was put into LTSpice with a varying Resistance to see the output resistance for varying resitor values. 

Image 6: LTSpice output resistnace simulation with varying resistor values.

For the experimental values with the 25 ohm speaker the second amplifier was not needed because the push pull resistance is already below 20 ohms. The resistor value that was picked for the push pull was a 20k, and the group tested the amplifier at varying frequencies. 

Image 7: Experimental values measurerd from oscilliscope with 20kohm resistor at 100Hz , 1kHz.

Image 8: Experimental values measurerd from oscilliscope with 20kohm resistor at 10kHz, and 20kHz. 

Following measuring the circuit with the frequency generator the group input music to see how well the circuit worked and measure the output while the music was playing. 

Image 9: Experimental values measure while music was playing.

After playing the music the group measured the amount of power the circuit used.

Image 10: Voltage and current drawn from power supply.

From the above measurements we can tell that the power consumption is .08*10.1 = 808mW.

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