Lab 7 - EE 420L 

Authored by Tyler Ferreira,

ferret1@unlv.nevada.edu

March 29, 2017

Pre-lab work

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

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.
• I decided to use a push-pull amplifier topology for my audio amplifier. I initially chose to add a source follower amplifer to the output of my push-pull to lower my output resistance but it ended up messing with my gate voltage and my source current.

• My initial design

  My gate voltage and source current

• Since the added source follower circuit was messing with my gate voltage and source current I decided to just add an additional resistor to my push-pull amplifier output.
• I decided to just use the push-pull amplifier with an added resistor on the output to decrease the output resistance.

• Hand calculations for DC

  Hand calculations for AC

  Hand calculations for Resistance

• Gain	-8.837
  Power	4.68
  Rin	1829.7
  Rout	6.53

• 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.

• To start my simulations I initially started by adding an additional 25 ohm resistor to my output to match the impedance of my speaker.
• Since I choose my output resistor I will change my gate-drain resistor to see how my power and gain of my amplifier change.
  

• Schematic	Simulation
  10k - Green 15k - Blue 20k - Orange 25k - Teal 30k - Pink

• As I can see in my simulations, as the resistor got larger my output voltage would be larger but there would be more distortion to my signal. Also my power supplied by my source and dissipated by my load is much larger with a larger resistor.
• After examining my simulations for a while I chose to go with a resistor in between 15k and 20k in order to reduce distortion while still maintaining a high gain.
• Now that I have my gate-drain resistor I will run a simulation varying my output resistor to observe the affects it has on my amplifier.

• Schematic	Simulation
  1 - Green 21 - Blue 41 - Orange 61 - Teal 81 - Pink 101 - Gray

• From the simulations a 1 ohm speaker is obviously not a good choice. As the resistor increases the gain barely increases but the power dissipated by the speaker increases a lot.
• I decided to go with a resistor around 21 ohms as it gives me a reasonable gain with almost no distortion on my output signal.
• Below is the schematic that I decided to build on my breadboard.

• Schematic	Simulation

• Input Resistance	Output Resistance

• Gain	-3.478
  Power	2.35
  Rin	14k
  Rout	12.5

• Looking at my final schematic I can see that my output signal has a good amount of gain with almost no distortion. This will allow the output audio to sound close to the original input signal.

• Circuit on my breadboard	Circuit with the speaker and AUX cable input

• Scope at 100Hz	Scope at 20kHz

• Looking at my experimental results I can see that my gain is a little bit lower than my simulations. This may be due to the difference between gmn, gmp, input resistance, and output resistance.
• My output signal amplitude at 100Hz is 232mV and 336mV at 20kHz. When I used a frequency generator on my input I was able to hear my speaker from around 500Hz to 17kHz. 
• When I used a 3.5mm cable to play music on my speaker I could hear the songs clearly but it was a little bit quieter than the signal generator.
  

I will backup my work on to my OneDrive and my desktop:

 
 
 

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