Design document for Audio Amplifier email: {jb12, lb1, lb3, trw10}@ece.msstate.edu submitted to: Professor Joseph Picone ECE 4512: Senior Design I Department of Electrical and Computer Engineering 413 Hardy Road, Box 9571 Mississippi State University Mississippi State, Mississippi 39762 Prepared by: Jerome Buckingham, Lennon Brown III, LaCurtis Banks, and Terrance West April 29, 2004 Faculty Advisor: Professor Roger King; Raymond Winton Industrial Advisor: Tim Schlichter, Adtran Corporation Department of Electrical and Computer Engineering 413 Hardy Road, Box 9571 Mississippi State University Mississippi State, Mississippi 39762EXECUTIVE SUMMARY People are interested in increasing the sound quality of either their home entertainment system or car audio systems. These customers are searching for a good product, which can produce a high quality of sound but at an inexpensive price. Amplifiers that use digital signal processing are becoming more prevalent over analog systems, because they reduce the amount of distortion and overall noise found in the incoming source signal. Signal-to-noise (SNR) is also a common problem in audio systems. Producing a sufficient amount of power with a reasonable SNR rating can be a very cumbersome task. In addition, these systems lack sophisticated operating features that allow the customer to monitor the overall efficiency of the system, and apply other effects in order to increase the overall quality of sound. Therefore, amplifiers that use digital signal processing are becoming more in demand by customers than analog counterparts are. Our goal of our project is to design and construct an amplifier that will meet the needs of the average customer. The constraints that govern the design of our amplifier system are: the signal to noise ratio, efficiency, size, and cost of the overall system. The biggest constraint that controls the performance of our audio amplifier is the signal to noise ratio. The signal to noise ration of our device will be approximately 80 decibels. This means that the noise in the signal is 80 decibels above the noise that is being produced. In addition, the efficiency is also major constraint governing our device. We would like our device to operate at least at 50% of the maximum power sent to the load. By using operational amplifiers instead of power transistor, the size and cost of our system is reduced dramatically. By achieving the same amount power with a smaller device, our power per unit cost analysis is greatly improved. Our devices is designed to accept an incoming audio signal ranging in frequencies from 20 to 20 kHz, amplify the signal, and displayed the gain to the LCD. This particular range of frequencies was chosen, because this is range of frequencies in which most audio signals are produced. The incoming signal is sent to our filter system, where it will be converted to a digital signal by using an analog to digital converter. After the signal has been converted, the signal will then be sent to the digital system processor, where it will be filtered to cancel out the undesired frequencies. The digital signal will then be converted back to an analog signal by the use of a digital to analog converter. The analog signal will then be amplified by using class AB operational amplifier design. After the analog signal is amplified, the signal is then sent to the speakers and sent to the LCD to be displayed. In testing our amplifier system, the signal to noise ratio posed to most problems. During our first analysis we produced a signal to noise ratio of approximately 40 decibels with a large resonating frequency around 60 Hz. After successfully integrating our all of our hardware components onto our prototyping breadboard, we were able to raise our signal to noise ratio above 70 decibels, but not completely eliminate the 60 Hz noise completely from our circuit. In addition, we were also successfully able to maintain an efficiency level of 73%, which 22% higher than what we expected as stated in our design constraints. Currently our system’s SNR is approximately 72 decibels. Signal to noise ratio has been a constant problem throughout the designing process. Furthermore, heating within our p The audio amplifier that we are designing will be a device that supplies the quality and quantity of sound that customer’s desire, but a price in which every consumer can appreciate. The user level control options and display features make our amplifier system unique and very competitive to existing amplifiers on the market today. In the future, we would like to add an impedance matching option that would allow the consumer to attach various loads to the system and produce the same output at the load while maintaining the same level of efficiency.TABLE OF CONTENTS 1. PROBLEM ...................................................................................................................................1 2. DESIGN REQUIREMENTS ...................................................................................................... 3 2.1 TECHNICAL DESIGN CONSTRAINTS................................................................................. 3 2.1.1 Operating Frequency............................................................................................................... 3 2.1.2 Signal to Noise Ration and Distortion .................................................................................... 4 2.1.3 Efficiency................................................................................................................................ 4 2.2 PRACTICAL DESIGN CONSTRAINTS ................................................................................. 4 2.2.1 Output ..................................................................................................................................... 5 2.2.2 Weight, Packaged Size, and Connectors................................................................................. 5 2.2.3 Protection ................................................................................................................................ 5 2.2.4 Cost
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