Lab 7: Design of an audio amplifier - EE 420L 

 

Author: Mario Verduzco

Email: Verdum1@unlv.nevada.edu

Date: 03/28/17

 

 

 

  

 

Pre-lab:

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

Lab description:

         The objective of this lab is to design, simulate, and build an audio amplifier with specific design parameters. Once built it is necessary to document the performance of the amplifier.

Design parameters:

· Frequency range– 100Hz to 20KHz

· Power supply– 10v

· Output to an 8-ohm speaker

· Input from an MP3 player

· Use as many resistors as needed, one 10uF, and 100uF capacitors

· Use as many ZVN3306A and ZVP3306A MOSFETs as needed.

 

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Hand Calculations:

Simulations:

Design:

         Keeping in mind an input resistance of a few kilo-ohms and an output resistance of about an ohm and although there was no specific requirement on the gain I decided to design for a gain greater than 1. In order to do this I chose to use the push-pull amplifier with a feedback resistor as the output stage and a common source amplifier for the input stage. The push pull has a low output resistance so it will be able to drive the 8-ohm speaker. The input common source will have a relatively high input resistance due to the bias resistors. 

Frequency Response: 100Hz - 20KHz

Fig 1.1– AC analysis simulation

 

Transient Analysis: 100 Hz input

Fig 1.2– Transient analysis simulation

 

Transient Analysis: 1KHz Hz input

Fig 1.3– Transient analysis simulation

 

Experimental Results:

Vout (green) with Vin (purple) at 1KHz

Vout (green) with Vin (purple) at 100Hz

Vout (green) with Vin (purple) at 10KHz

Fig 1.5– Vout (green) on Oscilloscope

 

Fig 1.6– Vout (green) on Oscilloscope

 

Fig 1.7– Vout (green) on Oscilloscope

 

Vout (light blue) with Vin (dark blue) at 20KHz

Fig 1.8– Vout (green) on Oscilloscope

 

Vout (green) with 8-Ohm resistor (output resistance)

Vout (green) without load

Fig 1.9– Vout (green)

 

Fig 1.12– Vin (purple) to measure input resistance

 

Vout at different frequencies:

Input and Output resistances:

Vin (purple)

Vin (purple) with 75-Kohm resistor (input resistance)

Power consumption:

Fig 1.11– Vin (purple)

 

Fig 1.10– Vout (green) to measure output resistance

 

Vout (purple) through speaker, Iout (green) through speaker, and Power consumed (red)

Fig 1.13– Power consumed by the speaker

 

           In order to measure the power consumed by the speaker a 1-ohm resistor was added in series with the speaker and the voltage across that resistor was outputted onto the scope (green). This signal is also the current through the resister. The red wave is a multiplication of the voltage across the speaker and the current.

Power Consumption through 8-ohm speaker

 

Fig 1.4– Power consumption simulation

 

Summary of results:

Conclusion:

         The amplifier was designed and built with the given parameters. When tested the output was a little lower than the simulated value but close to the magnitude of the input signal. The amplifier did indeed work and was tested using the iphone music as an input. The sound was good quality. This lab introduced me to real life design using transistors to meet specific design criteria.