1.
COLPITTS OSCILLATOR
by
Rasikh Tariq
ME-113006
&
Mehroze Ali Najmi
ME-113077
A Project Report submitted to the
DEPARTMENT OF ELECTRONIC ENGINEERING
in partial fulfillment of the requirements for the degree of
BACHELORS OF SCIENCE IN MECHANICAL ENGINEERING
Faculty of Engineering
Mohammad Ali Jinnah University
Islamabad
June, 203
2.
ii
Copyright 2012 by MAJU Student
All rights reserved. Reproduction in whole or in part in any form requires the prior
written permission of Rasikh Tariq & Mehroze Ali Najmi.
3.
iii
Colpitts Oscillator is designed for generation of high frequency waves
ranging from 10 kHz to 1000 MHz. They are widely used in commercial
purposes. They had got a lot of application in “Signals & Systems”.
4.
iv
DECLARATION
It is declared that this is an original piece of my own work, except where
otherwise acknowledged in text and references. This work has not been submitted in
any form for another degree or diploma at any university or other institution for
tertiary education and shall not be submitted by me in future for obtaining any degree
from this or any other University or Institution.
Rasikh Tariq
ME-113006
Mehroze Ali Najmi
ME-113077
June, 2013
5.
1
ABSTRACT
We have formulated a Colpitts Oscillator starting from a crude/reformable
circuit. Then we had formulated a better form of Colpitts Oscillator using computer
softwares like Personal Computer Simulation Program (PSPICE) and Printed Circuit
Board Wizard (PCB). Then we had implemented our project on Printed Circuit Board
by soldering circuit components.
As a result of completing the above procedure, we had got some results from
our circuit. We had achieved 1MHz (approx.) frequency of our circuit. We had
achieved almost the same results both theoretically and experimentally.
After this project we realized that certain engineering things are not so much
complicated then we really assume them. Now, we believe that Colpitts Oscillator
circuit is as simple as like rest of the circuits.
6.
Chapter 1
Project Charter Purpose
The purpose of the Project is:
Disseminate a brief summary about Colpitts Oscillator.
Provide an introduction to some of basic electronic components like Inductors,
Capacitors, Resistors and Transistors.
Provide an introduction about working of Colpitts Oscillator.
Chapter 2
Project Executive Summary
The project is devoted towards “Colpitts Oscillator”. Starting from the circuit
components used in our project then we had moved towards the advanced/complex
working of Colpitts Oscillator. Working of Tank Circuit is also introduced in our
project. The contributions of Personal Computer Simulation Program (PCB) and
Printed Circuit Board Wizard (PCB) in our project have also been introduced.
Chapter 3
Introduction
3.1 Oscillator
An oscillator is a mechanical or electronic device that works on the principles
of oscillation: a periodic fluctuation between two things based on changes in energy.
Computers, clocks, watches, radios, and metal detectors are among the many devices
that use oscillators.
7.
3
3.2 Hartley Oscillator
The Hartley oscillator is an electronic oscillator circuit that relies on two
inductors and a capacitor for its operation. The circuit was invented in 1915 by
American engineer Ralph Hartley. The Hartley oscillator is distinguished by its use of
two inductors (or one tapped inductor) and only one capacitor in its resonant tank.
Chapter 4
Colpitts Oscillator Electronic Components
Electronic Circuit Elements used in Colpitts Oscillator were:
4.1 Resistor
A resistor is a passive two-terminal electrical component that implements
electrical resistance as a circuit element.
The current through a resistor is in direct proportion to the voltage across the resistor's
terminals. This relationship is represented by Ohm's law:
=
Where:
V= Voltage across resistor
I= Current flowing through resistor
R= Resistance of resistor.
We had used 4 different resistors of rating 2k, 22k, 10k and 1k ohm.
4.2 Capacitor
A capacitor is a passive electronic component that stores energy in the form of
an electrostatic field. In its simplest form, a capacitor consists of two conducting
plates separated by an insulating material called the dielectric.
8.
4
In the case of capacitor, current passing through it is equal to time derivative of
voltage across it. Represented as follows:
( ) =
( )
Where:
dt= Change in time
C= Capacitance of Capacitor
Generally, Capacitors don’t permit Direct Current (DC) across it but they permit
Alternating Current (AC).
4.2.1 Solving Capacitors Combinations
To find equivalent capacitance Ceq in parallel configuration of capacitors we use:
= + + +∙∙∙∙∙∙∙∙∙ +
To find equivalent capacitors Ceq in series configuration of capacitors we use:
1
=
1
+
1
+
1
+∙∙∙∙∙∙∙∙∙ +
1
We had used 3 different capacitors in our circuit having market codes of: .102, 103,
and 104.
4.3 Inductor
An inductor, also called a coil or reactor, is a passive two-terminal electrical
component which resists changes in electric current passing through it. It consists of a
conductor such as a wire, usually wound into a coil. When a current flows through it,
energy is stored in a magnetic field in the coil. When the current flowing through an
inductor changes, the time-varying magnetic field induces a voltage in the conductor,
according to Faraday’s law of electromagnetic induction, which by Lenz's law
opposes the change in current that created it.
Voltage across inductor is given by the formulae:
=
Where:
L=Inductance of inductor.
9.
4.3.1 Solving Inductors Combination
To find equivalent inductance I
To find equivalent inductance I
1
=
1
+
1
+
We had used 1 inductor in our circuit of rating
27uH.
4.4 Tank or LC Circuit
An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit,
consists of an inductor, represented by the letter L, and a capacitor, represented by the
letter C. When connected together, they can act as an
analogue of a tuning fork, storing energy oscillating at the circuit's resonant
frequency.
LC circuits are used either for generating signals at a particular frequency, or
picking out a signal at a particular frequency f
key components in many electronic devices, particularly radio equipment, used in
circuits such as oscillators, filters, tuners and frequency mixers.
The frequency “f”
4.5 Transistor
A transistor is a semiconductor device used to amplify and switch electronic
signals and electrical power. It is composed of semiconductor material with at least
three terminals for connection to an external circuit.
Basically a transis
transistor has 3 legs:
Emitter
Base
Collector
We had used an npn (C945)
Solving Inductors Combinations
To find equivalent inductance Ieq in series configuration of inductors we use:
= + + +∙∙∙∙∙∙∙∙∙ +
To find equivalent inductance Ieq in parallel configuration of inductors we use:
+
1
+∙∙∙∙∙∙∙∙∙ +
1
We had used 1 inductor in our circuit of rating
Circuit
n LC circuit, also called a resonant circuit, tank circuit, or tuned circuit,
consists of an inductor, represented by the letter L, and a capacitor, represented by the
letter C. When connected together, they can act as an electrical resonator, an electrical
analogue of a tuning fork, storing energy oscillating at the circuit's resonant
LC circuits are used either for generating signals at a particular frequency, or
picking out a signal at a particular frequency from a more complex signal. They are
key components in many electronic devices, particularly radio equipment, used in
circuits such as oscillators, filters, tuners and frequency mixers.
“f” of LC circuit can find by using relation:
=
1
2 √
A transistor is a semiconductor device used to amplify and switch electronic
signals and electrical power. It is composed of semiconductor material with at least
three terminals for connection to an external circuit.
Basically a transistor has 2 types, npn transistor and pnp transistor. One
(C945) transistor in our circuit.
in series configuration of inductors we use:
configuration of inductors we use:
n LC circuit, also called a resonant circuit, tank circuit, or tuned circuit,
consists of an inductor, represented by the letter L, and a capacitor, represented by the
electrical resonator, an electrical
analogue of a tuning fork, storing energy oscillating at the circuit's resonant
LC circuits are used either for generating signals at a particular frequency, or
rom a more complex signal. They are
key components in many electronic devices, particularly radio equipment, used in
A transistor is a semiconductor device used to amplify and switch electronic
signals and electrical power. It is composed of semiconductor material with at least
tor has 2 types, npn transistor and pnp transistor. One
10.
Chapter 5
Colpitts Oscillator
A Colpitts oscillator, invented in 1918 and patented 1927 by American
engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators,
electronic oscillators that use a combination of inductors (L) and capacitors (C) to
determine the frequency
oscillator is that the feedback for the active device is taken from a voltage divider
made of two capacitors in series across the inductor.
The Colpitts oscillator is very similar to the
except that two capacitors are used in the tank circuit instead of a tapped coil (the
figure below). The Hartley oscillator has a tap between two coils, while the Colpitts
has a tap between two capacitors. You can change the f
by varying the inductance of the coil or by varying the capacitance of the two
capacitors in the tank circuit.
Basically, a Colpitts Oscillator can produce waves of frequency ranging from
10 kHz to 100 MHz.
Chapter 5
Formulating
Figure
Colpitts Oscillator: An Overview
A Colpitts oscillator, invented in 1918 and patented 1927 by American
engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators,
electronic oscillators that use a combination of inductors (L) and capacitors (C) to
determine the frequency of oscillation. The distinguishing feature of the Colpitts
oscillator is that the feedback for the active device is taken from a voltage divider
made of two capacitors in series across the inductor.
The Colpitts oscillator is very similar to the shunt-fed Hartley oscillator,
except that two capacitors are used in the tank circuit instead of a tapped coil (the
figure below). The Hartley oscillator has a tap between two coils, while the Colpitts
has a tap between two capacitors. You can change the frequency of the Colpitts either
by varying the inductance of the coil or by varying the capacitance of the two
capacitors in the tank circuit.
, a Colpitts Oscillator can produce waves of frequency ranging from
Formulating Colpitts Oscillator using PSPICE
Figure 1: Schematic Diagram (Collpits Oscillator)
A Colpitts oscillator, invented in 1918 and patented 1927 by American
engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators,
electronic oscillators that use a combination of inductors (L) and capacitors (C) to
of oscillation. The distinguishing feature of the Colpitts
oscillator is that the feedback for the active device is taken from a voltage divider
fed Hartley oscillator,
except that two capacitors are used in the tank circuit instead of a tapped coil (the
figure below). The Hartley oscillator has a tap between two coils, while the Colpitts
requency of the Colpitts either
by varying the inductance of the coil or by varying the capacitance of the two
, a Colpitts Oscillator can produce waves of frequency ranging from
using PSPICE
11.
5.1 Cicuit Diagram of Colpitts Oscillator
Figure 1 shows the circuit diagram that we had formulated using PSPICE for our
Colpitts Oscillator Project.
After adding all the components in the
PSPICE workspace we had switched on “Transient
Analysis” option from PSPICE. Figure 2 shows the
values that we had set for our analysis.
Then we had observed voltage-time and voltage-
frequency graphs of our circuit. By these two graphs
we had calculated frequency of our Oscillator. Figure
3. and figure 4. shows voltage-time and voltage-
frequency graphs respectively.
Now, at this stage we had calculated the
frequency from our Voltage-Time Graph i.e. Figure
3. At 1.0ns our one wave is completed so frequency
can be calculated using:
= = = 1 Figure 2
Figure 3: Voltage – Time Graph
12.
Thus, we had got a frequency of 1MHz from our circuit made by using PSPICE. The
same thing can also be verified using Fourier Transform of voltage-time graph i.e.
Figure 4.
Chapter 6
Working of Colpitts Oscillator
The transistor amplifiers emitter is connected to the junction of capacitors, C3
and C4 which are connected in series and act as a simple voltage divider. When the
power supply is firstly applied, capacitors C3 and C4 charge up and then discharge
through the coil L1. The oscillations across the capacitors are applied to the base-
emitter junction and appear in the amplified at the collector output.
The amount of feedback depends on the values of C3 and C4 with the smaller
the values of C the greater will be the feedback.
The amount of feedback is determined by the ratio of C3 and C4 which are
generally "ganged" together to provide a constant amount of feedback so as one is
adjusted the other automatically follows. The frequency of oscillations for a Colpitts
Figure 4: Voltage - Frequency Graph (Fourier Transform)
13.
9
oscillator is determined by the resonant frequency of the LC tank circuit and is given
as:
Colpitts Oscillation Frequency Equation
=
1
2 +
The configuration of the transistor amplifier is of a Common Emitter
Amplifier with the output signal 180o
out of phase with regards to the input signal.
The additional 180o
phase shift require for oscillation is achieved by the fact that the
two capacitors are connected together in series but in parallel with the inductive coil
resulting in overall phase shift of the circuit being zero or 360o
.
Resistors R1, R2, R3, and R4 provide the usual stabilizing DC bias for the
transistor in the normal manner while the capacitor acts as DC-blocking capacitors.
6.1 Calculating Frequency using Formulae
The formulae to calculate the frequency of Colpitts Oscillator is:
Thus, plugging values in the above mentioned formula of frequency using our
Capacitor values:
=
1
2 +
=
1
2 ∗ 3.14 (27 ∗ 10 )
(. 013 ∗ 10 ) ∗ (.001 ∗ 10 )
(.013 ∗ 10 ) + (.001 ∗ 10 )
≈ 1
Approximately the same result was interpreted using PSPICE i.e. Figure 3, 4.
Chapter 7
Formulating Colpitts Oscillator using PCB
We had designed our Colpitts Oscillator on Printed Circuit Board (PCB). Figure 5.
shows our circuit that we had designed using PCB and figure 6. shows the artwork
format of our project.
14.
7.1 Calculating Frequency of hardware
Now, we had calculated the frequency of our colpitts oscillator that we’ve formulated on
PCB sheet.
Number of horizontal boxes=2.2
Time per division= 0.5µs/boxes
Time period =T= (Number of horizontal boxes)*(Time per
division)
T=2.2* 0.5µs=1.1 µs
= =
1
=
1
1.1μs
= .9090 ≈ 1
Chapter 8
Conclusions
We had found the frequency of our Colpitts Oscillator using following methods:
1. Using theoretical formula of Tank circuit i.e. using values of capacitors and
resistors.
2. Using voltage-time graph i.e. dividing the time period with 1.
3. Using voltage-frequency graph i.e. Fourier Transform of voltage-time graph
15.
4. By formulating the circuit on a bread board.
5. By formulating the circuit on PCB Sheet.
And hence still getting almost the same results.
Figure 2: Artwork
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