Lab 7 - EE 420L 

Authored by Marco Muniz ,

04/02/2019

Email: munizm1@unlv.nevada.edu

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:
 
                                       

                                                                                   (Audio Amp Circuit)  

For this lab, we will be designing an audio amplifier. These amplifiers works by taking in small amplitude audio signals, from mp3 players or phones, 

and amplifies this signal to a level where it is audible to the human ear. The circuit above is an example of the differences between an amplified audio signal and one that is simply output.

In the above simulation plot, we can see the differences between outputting a flat signal and outputting an amplified signal. We can see in (vout1) that most of the amplitude is lost through the 10k Source resistor. Furthermore, we note the amplification occuring in (vout2). 

From the previous lab, we can look at the gain of a push-pull amplifier so we can see how the signal will be increased. 

                                                                           
 
For this instance, we are using a Feedback resistor of 10k instead of 100k. Thus, the gain of the audio amplifying circuit would be 280 in this instance.  
 
                                             
 
This amplifier was set for its low output resistance so that we could get as much voltage through the speaker as possible. We chose our R2 by running a step paramater to see how the output resistance would change with different values..
 

We can see that if we were to use a 8 Ohm speaker, we would want to choose a R2 Value to be as small as possible. The smallest size available to us in the lab was a 2 Ohm resistor which would have us at an output resistance of roughly 1.4 Ohm.

However, since we did not receive an 8 Ohm speaker but instead a 25 Ohm speaker, we found it better to just amplify the signal with a push-pull amplifyer instead of a push-pull in series with a common source. We found the output resistance restrictions satisfied enough to be able to amplify with that alone.
 
The resulting circuit:
 
                                       
 
We chose a feedback resistance of 20k(R1) to give us a slightly higher gain through the Amp so we could get some substantial volume through the speaker.
 
                                     
                                                                                     (Audio Amp Output displaying Gain)
   
       
                                                                                            (Power Consumption)

 
                   
                                                                                                 (Output Resistance)
 
_____________________________________________________________________________________________________________
 
Built Circuit
 

                         
                                                      
                                                                                  (Output with no speaker)
 
                                                              
                                                                         (Output with Music input from phone)
 
 
                         
                                                                  (Power Consumption Volts(Left) and Amps(Right))
 
The power consumption of our circuit overall was roughly 808 mW. Although, for a few instances, the current would jump up to about 1.1 mA so we would say the Max Power Consumption would be around 1.11 Watts which would be acceptable for a Speaker of this size.
 
 
     
 
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