chapter 2 ee 301
TRANSCRIPT
-
8/10/2019 chapter 2 ee 301
1/58
Topic 2
Oscillators
1
Sudahkah anda mengisi COURSE
ENTRANCE SURVEY? Hanya 4
orang sahaja yang mengisinyasehingga 16/1/2013
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
2/58
COURSE LEARNING OUTCOMES
(CLO)
CLO1. explain correctly the principles of electronic
circuits by using block diagram or circuit diagram (C4)CLO2. conduct the construction of electronic circuits
application during practical works based on the theory
and principle operation of the circuits. (P4)
CLO3. deliver an oral presentation to display good
communication skills. (A2)
2http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
3/58
LEARNING OUTCOMES
Upon completion of this topic students should be able to:
Draw block diagram of an oscillator2.1
Explain requirements of oscillator circuit2.2
2.3
2.4
2.5
Construct the oscillator circuit
Explain applications each oscillator
Compare the performance of the oscillator
3
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
4/58
Oscillator
Oscillators are devices that can
convert the DC voltage to AC voltage
without any external source at a
particular frequency.
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
5/58
Basic oscillator block diagram
5
http://modul2poli.blogspot.com/
http://localhost/var/www/apps/conversion/tmp/Oscilator.FLV -
8/10/2019 chapter 2 ee 301
6/58
Oscillator
Oscillator is divided into two classes
depending on the waveform produced as
follows:
i. Harmonic oscillator - the sine wave.ii. Non-harmonic oscillator - in terms of the
fourth wave, triangle wave, etc..
6
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
7/58
Oscillator
7
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
8/58
Oscillator circuit
All the basic oscillator circuit consists of
three parts:
i. Amplifier
ii. Feedback
iii. Frequency Generation Circuit
8
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
9/58
Block diagram of oscillator
circuit
9
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
10/58
Question
Draw the block diagram of an oscillator
and name each block
10
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
11/58
Answer
11
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
12/58
Amplifier
Generally, an amplifier or simply amp is a
device for increasing the power of a signal.
For electronic amplifier, the input "signal"
is usually a voltage or a current.
In this case oscillator requires DC power
supply to produce output. That means this
DC power supply is used as an input of
the amplifier
12
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
13/58
Feedback
Feedback is a condition where part of the
output signal supplied to the input.
Since the oscillator has no input signal, thefeedback signal is the input signal to the
amplifier in the oscillator circuit.
13
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
14/58
Feedback
There are two principles of feedback,
positive feedback and negative feedback.
Oscillators using the principle of positive
feedback.
14
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
15/58
Concept feedback
15
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
16/58
Feedback
16
Figure below shows the basic block diagram of a feedback
system that are commonly used:
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
17/58
Feedback
17
http://modul2poli.blogspot.com/
A di ill d f i i h
http://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Audio_oscillator -
8/10/2019 chapter 2 ee 301
18/58
Frequency generation circuit
Generally, the frequency of the oscillator
circuit generation in consumer goods is
divided into two categories:
i.Audio frequency oscillator whichgenerates: Oscillator Network RC
(resistance-capacitor). It is to produce low
and medium frequency signal.Example is the oscillator RC type oscillator
phase shift and Wein bridge Oscillator.
18
An audio oscillatorproduces frequencies in the
audiorange, about 16 Hz to 20 kHz
http://modul2poli.blogspot.com/
A l f ill t (LFO) i l t i ill t th t t f b l
http://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/Audio_frequencyhttp://en.wikipedia.org/wiki/Audio_oscillatorhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillation -
8/10/2019 chapter 2 ee 301
19/58
Frequency generation circuit
ii. Radio frequency generating oscillator:
Oscillator Networks LC(inductor-
capacitor). It is also known as tank circuits.
It is to produce a high frequency signal (>1MHz), and usually it produces a stable
frequency.
LC oscillator is an example ofArmstrongOscillator, Colpitts, Hartley and crystal.
19
An RF oscillator produces signals in the radio frequency(RF) range of about 100 kHz to
100 GHz
A low-frequency oscillator(LFO) is an electronic oscillator that generates a frequency below
20Hz. This term is typically used in the field of audio synthesizers, to distinguish it from an
audio frequency oscillator.
http://modul2poli.blogspot.com/
http://en.wikipedia.org/wiki/Radio_frequencyhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Synthesizershttp://en.wikipedia.org/wiki/Synthesizershttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Low_frequency_oscillationhttp://en.wikipedia.org/wiki/Radio_frequency -
8/10/2019 chapter 2 ee 301
20/58
RC Oscillator
Combination of resistors and capacitors.
Operate in low frequency. Two types of
RC oscillator:-
Phase shift oscillator
Wein bridge oscillator
20http://modul2poli.blogspot.com/
http://localhost/var/www/apps/conversion/tmp/scratch_2//upload.wikimedia.org/wikipedia/commons/c/c5/RC_phase_shift_oscillator.svg -
8/10/2019 chapter 2 ee 301
21/58
LC Oscillator
Armstrong Oscillator
Crystal Oscillator Hartley Oscillator
Colpitts Oscillator
21
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
22/58
LC Oscillator
Combination of inductor and
capacitor.
Operate in high frequency
22
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
23/58
Armstrong Oscillator
23
Using a combination of a transformer to step the phase of 180.
FREQUENCY-DETERMINING DEVICEFEEDBACK NETWORK
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
24/58
Operation
Resistors R1, R2 and R3 is usage
to provide bias voltage to the
transistor. Capacitors C1 and C2are used to block an alternating
signal. This configuration will
provide 180phase difference ofoutput signal.
24
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
25/58
Operation
The transformer Tr is selected to produce
a phase shift of 180 to get the feedback
voltage in phase with the input transistor.
Usually the ratio between the coil windings
L1 with L2 coil arranged.
So that the product of the gain, A, with the
feedback factor, , is a (| A| = 1).
25
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
26/58
The frequency of oscillation
26
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
27/58
Colpitts Oscillator
27
Using a separate capacitor for resonant circuit.
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
28/58
Operation
Transistors and resistors R1, R2, R3 and
R4 is a combination of amplifier circuit
(amplifier manufacturers Common Voltage
Divider bias technique). Capacitors C3and C4 are used to intercept an alternating
signalto the ground.
28
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
29/58
Operation
The amplifier will provide 180 phase
difference of the output signal. LC circuit in
the feedback loop will produce a phaseshift of 180. So the feedback voltage will
be in phase with the input voltage on the
transistor.
29
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
30/58
The frequency of oscillation
30
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
31/58
Example
A Colpitts Oscillatorcircuit having two capacitors of 10pF and
100pF respectively are connected in parallel with an inductor of10mH.
Determine the frequency of oscillations of the circuit.
The frequency of oscillations for a Colpitts Oscillator is given as:
The circuit consists of two capacitors in series, so the total capacitance is given as:
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
32/58
The inductor is of 10mH then the frequency of oscillation is:
Then the frequency of oscillations for the Oscillator is 527.8kHz
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
33/58
33
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
34/58
Hartley Oscillator
34
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
35/58
35
R1
R2
RE
RFC
C1
LP
VCC
vout
R1
R2
RE
RFC
C1
L1
VCC
vout
L2
Hartley oscillator.
1 2
1
1
2
T
r
T
L L L
f
L C
1
1
2r
P
fL C
Using a tappedinductor for the
resonant circuit
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
36/58
Operation
Transistors and resistors R1, R2, R3 and
R4 is a combination of amplifier circuit
(amplifier manufacturers Common Voltage
Divider bias technique). Inductance L1 andL2 are used to intercept an alternating
signal to the ground
36Intercept - memintas
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
37/58
Operation
The amplifier will provide 180 phase
differenceof the output signal. LC circuit in
the feedback loop will produce a phase
shift of 180. So the feedback voltage willbe in phase with the input voltage on the
transistor.
37
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
38/58
The frequency of oscillation
38
The Hartley oscillator was extensively used on allbroadcast bandsincluding the
FM 88-108 MHz band.
http://modul2poli.blogspot.com/
http://en.wikipedia.org/wiki/Broadcast_bandhttp://en.wikipedia.org/wiki/Broadcast_band -
8/10/2019 chapter 2 ee 301
39/58
Example
A Hartley Oscillator circuit having two individual inductors of 0.5mH each, are
designed to resonate in parallel with a variable capacitor that can be varied from 100pF to
500pF. Determine the upper and lower frequencies of oscillation and also the Hartleyoscillators bandwidth.
The frequency of oscillations for a Hartley Oscillator is given as:
The circuit consists of two inductive coils in series, so the total inductance is given as:
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
40/58
Upper Frequency
Lower Frequency
Oscillator Bandwidth
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
41/58
-
8/10/2019 chapter 2 ee 301
42/58
Answer
42http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
43/58
Crystal oscillator
43http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
44/58
Crystal oscillator
The most stable oscillator and precisely
using a piezoelectric crystal in the
feedback circuit. When an alternating
voltage applied to these crystals, themechanical vibrations and these vibrations
occur with the natural resonance
frequency depends on the thickness of thecrystal. To obtain a high frequency crystal
to be thinner.
44http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
45/58
Crystal oscillator
Electrical properties of crystals can be
expressed with resonant circuit in Figure
below. Inductance Lh represents the
electrical equivalent of the mass of thecrystal. Capacitance, Ch represents the
elasticity of crystals, Rh represents the
frictional resistance in the crystal structure.Cm represents the capacitance of the
capacitor crystal loaded containers.
45http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
46/58
Represents the capacitance of the capacitor
Cm crystal loaded containers.
46http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
47/58
The frequency of oscillation
47http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
48/58
Crystal oscillator
Wide frequency range (depending on the
size of the crystal) are often used in the
emitter circuit
48http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
49/58
Example
A series resonant crystal has the following values after
being cut, R = 1k,C = 0.05pF and L = 3H. Calculate the
fundamental frequency of oscillations of the crystal.
The frequency of oscillations for Crystal Oscillators is given
as:
Then the fundamental frequency of oscillations for the crystal is
given as
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
50/58
Phase shift oscillator
Phase shift oscillator comprising an
amplifier and feedback network with three
RC circuit.
50http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
51/58
Phase shift oscillator
51http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
52/58
Operation
The output signal from the amplifier
different phase 180o with the input signal.
To generate a positive feedback signal,
the output signal phase should be shiftedby 180o to be in phase with the input. RC
network to produce a phase shift of 180o
RC network where each one will transferphase by 90o.
52http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
53/58
If all the resistors, Rand the capacitors, Cin the phase shift
network are equal in value, then the frequency of
oscillations produced by the RC oscillator is given as:
Where:
is the Output Frequency in Hertz
R is the Resistance in Ohms
C is the Capacitance in Farads
N is the number of RCstages. (in our example N = 3)
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
54/58
Example
Determine the frequency of oscillations of a RCOscillator circuit having 3-stages each with a resistor
and capacitor of equal values. R = 10kand C = 500pF
The frequency of oscillations for a RC Oscillator is givenas:
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
55/58
The circuit is a 3-stage oscillator which consists of three
10k resistors and three 500pF capacitors thereforethe frequency of oscillation is given as:
http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
56/58
THE END
56http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
57/58
57http://modul2poli.blogspot.com/
-
8/10/2019 chapter 2 ee 301
58/58
58http://modul2poli.blogspot.com/