2. DESIGN REQUIREMENTS2. DESIGN REQUIREMENTSOur main goal is to design an audio amplifier that is ideal for customers looking for high quality sound ata reasonable price. The amplifier will have features that include: gain display and user level controlsoptions to suit the customer’s needs. This product will use digital filtering to improve the overall depth,quality and tone of the signal produced by the amplifier. By using this method, the amplifier will producea higher quality signal at the user’s desired listening volume at an affordable price. In order to design suchan amplifier, there are certain design constraints that should be met. Listed below are descriptions ofthese design constraints. 2.1 Technical Design ConstraintsOur product will have constraints that are among some of the top selling audio amplifiers on the market.These constraints will be accomplished with hardware and software design, which will control and limitthe signals that are sent and received. These controls and limitations will allow the audio amplifier toperform at its highest capabilities. Listed below are the technical constraints and a description of eachone. Name DescriptionOperating FrequencyThe incoming signal will be filtered to only allow frequencies in therage of 20Hz to 20kHz to pass through the amplifier.Signal to Noise RatioThe signal-to-noise ratio for our amplifier will be approximately80dB.Efficiency The amplifier will have a 50% efficiency of the maximum outputpower produced.Operating TemperatureThe operational temperature of the amplifier is in between the rangeof 45o C to 150oC, with safety margin of 30oC.Distortion The amplifier will have a total harmonic distortion of .01%Table 1. Technical design constraints2.1.1 Operating FrequencyThe incoming analog audio signal will be sampled at a rate of 44.1 kHz. We know from the nyquisttheorem, that the signal must be sampled at twice the maximum range of frequencies (fs) foundthroughout the audio signal range of 20Hz to 20 kHz. If the signal is not sampled between the nyquistintervals of 22,fsfs, replication caused by digitizing the signal will begin to overlap causing aliasingand distortion. After the signal has been sampled, it is received by the Digital Signal Processor (DSP),which will filter the signal to pass frequencies only in the range of 20Hz to 20 kHz. This selected rangeof frequencies covers the entire audio band of frequencies that is capable of being detected by the humanear with reasonable clarity and distinction. 2.1.2 Signal to Noise Ratio and DistortionThe incoming analog signal will be quantized at a rate of 16 bits per sample. This converts the signalfrom analog to a digital version allowing us to add features such as reverb, echo, and equalizing effects tothe digitized signal. We would like for our signal to noise ratio (SNR) to be 80 decibels below the rangeof the digitized audio signal. This will minimize the amount of excess noise, distortion, and aliasing,which appears in the signal after it has been filtered. Also, the amplifier will be designed to have totalharmonic distortion of .01%. The total harmonic distortion value will be obtained by designing thepackaging of the amplifier so that the frequencies above the fundamental frequencies are not introduced. 2.1.3 Efficiency Ensuring the best efficiency will depend on the type of power operational amplifier or transistor, whichwill be used. The audio amplifier will use a class-AB amplifier and transistor design to produce a desiredpower rating of 60 watts peak to peak across the load. By using this method, class – AB amplifiers willgive an efficiency of 78.5%, which is over 28.5% of the desired efficiency for our design. The higher theefficiency means that the transistors in the circuit dissipate less power. Using a class- AB design, crossover distortion will be reduced, thus allowing more power to be delivered to the load. 2.1.4 Operational TemperatureThe operational temperature range of any audio amplifier is based on the components used to make upthat amplifier. Components such as transistors and operational amplifiers have certain temperature rangesin which they operate. In order to perform at there highest optimum levels, these components mustoperate in their temperature ranges. Temperatures and thermal resistances are essential in designingpower amplifiers. These components are essential because they allow maximum power to be delivered tothe load. There are five major components that affect the performance of an amplifier. The first beingjunction temperature, which is the maximum operating temperature the power operational amplifier orpower transistor can handle. Our maximum junction temperature is Tj (max) = 150oC for both the poweroperational amplifier and power transistor. The next two components are case and ambient temperatures.Ambient temperatures are typical surrounding temperatures that are usually on the order of 25oC. Thecase temperatures on the other hand, are temperatures that can range between -55oC – +125oC dependingon the device. Thermal resistances exist between the junction, case, and ambient temperatures. Junctionto case (Θjc) is a thermal resistance that is usually on the order of .2oC/W to .5oC/W (heat sink grease).Case to ambient (Θca) is the thermal resistance or heat sink that is needed. Our amplifier will have a heatsink less than 5.4oC/W to ensure that power is not lost within the circuitry in the form of heat.2.2 Practical Design ConstraintsProducts of today have many constraints, which set them apart from the rest of the market. Cost, size,and weight are some of the practical constraints that are found on the majority of audio amplifiers on themarket today. We plan on designing our amplifier to met and in some areas exceed some of the practicalconstraints that govern audio amplifiers on shelves in stores. Name DescriptionPowerOur amplifier will have an output power of 125W (max) perchannel. Packaged Size Our amplifier will have the dimensions of 3” x 6” x 9” (H x W xD). The amplifier is packaged this way for easy storageConnections Our amplifier will receive the input signal through a set of normalRCA Audio/Video jacks. The speakers will connect to theamplifier by using wire insert clamps.Protection Our amplifier will be provided with a protection mode feature.This mode will prevent the
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