{{projectinfo|Tutorial| Designing Low and High Frequency a Wien Bridge Oscillator Circuits |TUT12-85.png|In this project, the basic concepts of RF.Spice A/D are demonstrated, you will design and realize a simple voltage divider is modeled Wien bridge oscillator and examinedanalyze its operation.|
*[[CubeCAD]]Operational Amplifier*VisualizationWien Bridge*[[EM.Tempo#Lumped Sources | Lumped Sources]]Oscillation Frequency*[[EM.Tempo#Scattering Parameters and Port Characteristics | S-Parameters]] Barkhausen Criterion*[[EM.Tempo#Far Field Calculations in FDTD | Far Fields]] *[[Advanced Meshing in EM.Tempo]] Positive Feedback|All versions|{{download|http://www.emagtech.com/contentdownloads/project-file-download-repository|EMProjectRepo/AnalogLesson9.Tempo zip Analog Lesson 1|[[EM.Cube]] 14.89}} }}
=== What You Will Learn ===
[[File:TUT12-1.png|thumb|400px| The Wien Bridge Oscillator.]] In the first part of this tutorial lesson, you will build a Wien Bridge Oscillator using an LM741 Op-Amp and will analyze its oscillatory behavior. In the second part, you will build and test a high frequency Colpitts oscillator using a parallel resonant LC circuit. The primary objective of this tutorial lesson is to underline the challenges of analyzing oscillator circuits.
== Designing a Wien Bridge Oscillator ==
The following is a list of parts needed for this part of the tutorial lesson:
{| border="0"|-| valign="top"||-{| class="wikitable"|-! scope="col"| Part Name! scope="col"| Part Type! scope="col"| Part Value|-! scope="row"| VCC| DC Voltage Source VCC: | 15V|-! scope="row"| VEE| DC Voltage Source VEE: | -15V LM741 Op|-Amp: Accessible form ! scope="Parts > Integrated Circuitsrow" menu Four Resistors: | R1, R2, - R3 and | Resistor| 10k|-! scope="row"| R4| ResistorTwo Capacitors: | 20k|-! scope="row"| C1 and - C2| Capacitor| 1n|-! scope="row"| X1| LM741 Op---Amp| Defaults|}
The Wien Bridge Oscillator comprises an Op-Amp, four resistors and two capacitors. The oscillator can also be viewed as a positive gain amplifier combined with a bandpass filter that provides positive feedback. At the resonant frequency, the reactance of the series R2–C2 arm will be an exact multiple of the shunt R1–C1 arm. If the two R3 and R4 arms are adjusted to the same ratio, then the bridge is balanced. These conditions can be written as:
<math>f_o = \frac {1}{2 \pi RC}</math>
For this project, you will initially choose R1 = R2 = 10k, R3 = 10k, R3 = 2 R3 = 20k, and C1 = C3 = 100pF. Place and connect all the parts as shown in the above figure. Place a voltage probe marker at the output of the Op-Amp. The oscillation frequency of this circuit must be f<sub>o</sub> = 1 / (2π . 1e+4 . 1e-9) = 15.9kHz. <table><tr><td>[[File:TUT12-1.png|thumb|550px| The Wien Bridge Oscillator.]] </td></tr></table>
== Testing the Wien Bridge Oscillator ==
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[[File:TUT12-2.png|thumb|800px720px|The output voltage of the Wien Bridge Oscillator when R4 = 20k.]]
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[[File:TUT12-3.png|thumb|800px720px|The output voltage of the Wien Bridge Oscillator when R4 = 21k.]]
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In order to calculate the oscillation frequency, first zoom in the graph window by clicking the "Zoom In" button of the [[Graph toolbar|Graph Toolbar]]. Then use the "Delta Tool" of the [[Graph toolbar|Graph Toolbar]] to measure the distance between two successive peaks of the sinusoidal signal. The period is about 78.5μs, which gives an oscillation frequency of 12.75kHz.
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[[File:TUT12-4.png|thumb|800px720px|Measuring the signal period on a close-up of the output voltage of the Wien Bridge Oscillator when R4 = 21k.]]
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