The Signal Generator - Page 1 of 13 ELCT 301 Lab Report #5...

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Page 1 of 13 ELCT 301 Lab Report #5 Signal Generator ___________________ Jared Tucker Department of Electrical Engineering University of South Carolina Columbia, SC 29208
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Page 2 of 13 Laboratory Grade: Pre-lab computation ____ of 10 Technical Content ____ of 60 Format/Presentation Clarity ____ of 20 Other ____ of 10 Late Deductions ____ ____ of 100 Student Comments: Grader Comments:
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Page 3 of 13 Signal Generator I. Introduction The primary focus of this lab was to observe how the multiple stages of a linear system functioned together to generate a desired response. By understanding how each portion of the system reacts to an input, one is able to see how the multistage system reacts. The complete result of this linear system will include three different transient responses. The Schmitt trigger will produce a square wave; the integrator will produce a triangle while the diode network will generate a sin response. II. Theory The complete schematic for the signal generator is depicted in Figure (1). Figure 1. Signal Generator This circuit looks like some kind of bad hair day. So, let’s focus on just one portion of the system at a time. Let’s stick this mess into block form Figure (2)
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Page 4 of 13 Figure 2. Block Form Signal Generator I will now proceed to take each block separately and look at how the configuration causes it to create the desired output. Figure (3) depicts the Schmitt trigger stage alone. Figure 3. Schmitt trigger We know from circuit theory that square wave outputs are generated when the op-amp is forced to operate in the saturated region. That is, the output of the op-amp is forced to swing repetitively between positive saturation and negative saturation, resulting in the square- wave output. Because the op-amp is forced to operate in saturation mode there will most definitely be slew rate side effects, Figure (4). However, it is the slew and overdriving characteristics that enable a square wave to be generated. So the resistors are chosen in such a way to ensure the op-amp will operate in the saturation region. The Zener diodes are used to make sure the voltage swing remains constant regardless of supply variation Figure (4). (a) Before Zeners (b) After Zeners Figure 4. Transient Before and After Zeners Notice how the Zeners have a tendency to limit the voltage. Your first thought may be, “well, this is necessary so the next stage is not overdriven.” This is partially true, however they also perform another important task. What if the input voltage contained amplitude inconsistencies? The output would then also contain amplified inconsistencies (the problem gets bigger at the output). So, the Zener diodes clamp the output voltage down to such a degree that variations at the input are no longer an issue. Instead of worrying about amplitude change, the Zeners just cut off the problem regions and create
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Page 5 of 13 their own voltage amplitude. This is identical to the hysteresis properties a Schmitt trigger discussed in lab 1. 2
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This note was uploaded on 04/28/2008 for the course EE ELCT 301 taught by Professor Santi during the Spring '08 term at University of South Carolina Beaufort.

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The Signal Generator - Page 1 of 13 ELCT 301 Lab Report #5...

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