Kelly SedlickHilary RickyTyler Moradi

Background

An oscillator is a circuit that outputs a repetitive electronic signal i.e. a sine wave.

The Colpitts oscillator was invented by Edwin H. Colpitts

The Colpitts oscillator is known for using a capacitor voltage divider as its feedback source

Advantages include: Frequency stability A simple and robust design

Background

For oscillation to occur the Barkhausen criteria must be met.

Loop Gain Phase Shift must equal zero Magnitude equal to unity

Realistically the magnitude will be greater than 1

Determine if criteria is satisfied by checking the loop gain at the frequency of oscillation

Goals

Design a Colpitts oscillator using Barkhausen Criteria

Build and test design Obtain frequency of oscillation Output a non-distorted sine wave from self-

oscillation

Design

Components

2N2222 Transistor Resistors (.5 Watt):

680 Ω 12 k Ω (2) 1.2 k Ω

Capacitors: .1uF (3) 1 nF .01uF

Inductor 8.2 uH 27 mH

Procedure and Results

Determine whether the transistor was biased close to the theoretical values

Apply a 20 mVpp sine wave with an initial frequency of 1.8 Mhz

Fine tune frequency to obtain a maximum amplitude at Vc

Procedure and Results (cont’)

Measure the amplitude and phase angle at the test frequency of V1, Vc, and Vf.

Procedure and Results (cont’) Check to make sure the final Barkhausen

criteria was met Av*β >1 = Vf/V1

Connect jumper between TP1 and TP2 Disconnect function generator Check for distortion in waveform

Results

•We were able to output a non-distorted waveform without having to make adjustments to our design

References

Beasley, Jeffery S., and Gary M. Miller. Laboratory Manual to Accompany Modern Electronic

Communication. Columbus: Prentice Hall, 2008.

Beasley, Jeffery S., and Gary M. Miller. Modern Electronic Communication. Ninth ed. Columbus:

Prentice Hall, 2008.

Sedra, Adel S., and Kenneth C. Smith. Microelectronic Circuits. Fifth ed. New York: Oxford, 2004.

QUESTIONS??