es3_lab4 - Tufts University School of Engineering...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES3 - Introduction to Electrical Circuits Fall 2007 Lab Section: Friday 2:30-4:30pm Experiment 4 Amplification, Impedance, and Frequency Response Name: Teddy Portney Edward . Portney@ tufts . edu Submitted to: Bertan Hallacoglu Experiment Performed: November 9, 2007 Experiment Due: November 16, 2007
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I. PURPOSE The purpose of this lab was not only to use the breadboard to prototype a somewhat complex circuit, but also to examine the physical attributes of amplification, revisit the idea of electrical impedance, and explore the concept of frequency response, or the idea of a natural filter. The idea of Thevenin equivalency was also revisited from Lab #3. The concept of gain was introduced in describing what an amplifier does, and the process of construction for a Bode plot was explored using Microsoft Excel. Also the idea of using a logarithmic scale to represent gain was introduced, using a unit of decibels, or dB. II. INTRODUCTION In electrical systems, it is often necessary to amplify extremely weak signals. Most common in audio electronics, an amplifier is a device that does exactly that. Used frequently with electric musical instruments, an amplifier is a necessity for any non- acoustic musician. Specific to this lab, an extremely weak signal was produced by the function generator. This signal was so small that, if hooked up directly to either a speaker or an oscilloscope, the signal would most likely not produce any noticeable change. The signal would move the speaker, but not strongly enough for it to produce a sound wave loud enough to be heard by human ears. With the concept of amplification come several other important audio concepts, such as gain. Gain is defined as the ability of a circuit to increase the amplitude of a signal. Gain is defined physically as the ratio of the output voltage to the input voltage. This, mathematically, is shown as V out / V in . These voltages must be AC signals, as a DC voltage will not produce a sound wave in a speaker. In many audio-related systems, this gain is not rated linearly, as it becomes difficult to see what is happening in a system graphically once the value of the gain approaches 0. For this reason, the unit of decibels, or dB, is used. In order to find the gain in decibels, one simply needs to find the gain in volts/volts and taking the logarithm in base 10 of that number and multiply by 20. Written symbolically, this looks like A V,dB = 20 log 10 ( V out / V in ). Also included with the idea of amplification and important in everyday life is the concept of frequency response. Although there is no filter in this circuit, the output voltages may be different at different frequencies. This is because the amplifier can act as a natural filter, and amplify different frequency signals at slightly different rates. This lab marks the first time this class has dealt with integrated circuit (IC) chips.
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This note was uploaded on 03/27/2008 for the course ES 3 taught by Professor A during the Fall '08 term at Tufts.

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es3_lab4 - Tufts University School of Engineering...

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