Transcript Oscillators

SHANTILAL SHAH
ENGINEERING COLLEGE
ELECTRICAL DEPARTMENT
BE ELECTRICAL SEM-3
ANALOG ELECTRONICS
OSCILLATOR
Guided by : A.M.Upadhyay sir
Submitted
Gohil
by:
Uma V.
Solanki Krupali K.
Damor Divyangini L.
Tuvar Beena B.
Zala Disha B.
(130430109019)
(130430109050)
(130430109012)
(130430109057)
(130430109062)
What we will going to learn?
•
•
•
•
Define the basic oscillator circuit
Identify the conditions for
oscillation to occur
Identify input and output
characteristics
Identify common uses of the
oscillator
Introduction


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
Oscillator is an electronic circuit that generates a
periodic waveform on its output without an
external signal source. It is used to convert dc to
ac.
Oscillators are circuits that produce a continuous
signal of some type without the need of an input.
These signals serve a variety of purposes.
Communications systems, digital systems
(including computers), and test equipment make
use of oscillators

An oscillator is a circuit that produces a
repetitive signal from a dc voltage.

The feedback oscillator relies on a positive
feedback of the output to maintain the
oscillations.

The relaxation oscillator makes use of an RC
timing circuit to generate a nonsinusoidal signal
such as square wave
Sine wave
Square wave
Sawtooth wave
Integrant of Linear Oscillators
Vs
+
V

Vo
Amplifier (A)
+
Positive
Feedback
Vf
Frequency-Selective
Feedback Network ()
For sinusoidal input is connected
“Linear” because the output is approximately sinusoidal
A linear oscillator contains:
- a frequency selection feedback network
- an amplifier to maintain the loop gain at unity
Ref:06103104HKN
EE3110 Oscillator
6
Basic Linear Oscillator
Vs
+

V
Vo
A(f)
+
Vf
Vo  AV  A(Vs  V f )

SelectiveNetwork
(f)
and
V f  Vo
Vo
A

Vs 1  A
If Vs = 0, the only way that Vo can be nonzero
is that loop gain A=1 which implies that
| A | 1 (Barkhausen Criterion)
A  0
Ref:06103104HKN
EE3110 Oscillator
7
Overview of the Oscillator
 One
of the basic building blocks of
electronics
 Input is a direct current (DC) power
source
 Output is alternating current (AC)
 Can generate sub-audible frequencies or
very high frequencies
 Most oscillators are amplifiers with
feedback
 Oscillation:
an effect that repeatedly and
regularly fluctuates about a mean value
 Oscillator: circuit that produces oscillation
 Characteristics: frequency, amplitude,
distortion, wave-shape, stability
Amplifiers as Oscillators?

Most amplifiers will oscillate when
conditions are correct
◦ Example: Too high of a volume on public
address system = loud noise and squeals that
are the result of acoustic waves traveling from
the speakers to the microphone

The result is oscillation
Electrical Feedback
Practical oscillators use electrical feedback
to produce oscillation
 Feedback circuits use resistors,
capacitors, coils, or transformers to
connect a portion of the output signal
back to the input of the amplifier

Basic principles for oscillation
In phase
Vf
Av
Noninverting
amplifier
Feedback
circuit
Vo
Types of oscillators
RC oscillators
1.
◦
◦
LC oscillators
2.
◦
◦
◦
3.
Wien Bridge
Phase-Shift
Hartley
Colpitts
Crystal
Unijunction / relaxation oscillators
RC Oscillators

RC feedback oscillators are generally
limited to frequencies of 1 MHz or less.

The types of RC oscillators that we will
discuss are the Wien-bridge and the
phase-shift
LC Oscillators
Use transistors and LC tuned circuits or
crystals in their feedback network.
 For hundreds of kHz to hundreds of MHz
frequency range.
 Examine Colpitts, Hartley and crystal
oscillator.

Feedback and Amplifier Gain
Conditions for Oscillation
Feedback alone does not promise
oscillation
 There is always some loss in the
feedback circuit
 Amplifier gain must be greater than
this loss
 Feedback must be in-phase

In-phase Feedback
In-phase feedback is also called
regenerative feedback or positive
feedback
 When the original amplifier input and
output signals are not in-phase, the
feedback circuit is used to reverse the
phase

Input Characteristics
Steady source of direct current (DC)
 In many applications, the DC source
requires a filter

Output Characteristics
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Amplitude
Frequency
Waveform type
Stability
On some oscillators, the capability to
change frequency
Oscillator Amplitude
Usually determined by the gain available
from the amplifier
 Supply voltage and circuit losses affect
amplitude

Oscillator Frequency
Frequency of operation is normally
determined by the feedback circuit
 Common feedback circuits used to
determine oscillator frequency include:

◦ crystals
◦ resistor and capacitor networks (RC)
◦ coil and capacitor networks (LC) {tank circuit}
Waveform Type

Generally, determined by:
◦
◦
◦
◦

Feedback circuitry
Output filter circuitry
Amplifier gain, or
Changes to input voltage
May be sinusoidal (sine wave), square
wave, or triangular wave
Oscillator Stability
Sometimes referred to as a stable
oscillator
 Source of a signal with consistent
amplitude
 Source of a signal with consistent
frequency

Ability to Change Frequency
Oscillators sometimes have the ability to
change frequencies
 Crystal oscillator frequency is controlled
by changing the crystal

◦ Crystals are usually cut from quartz to
generate a specified frequency when operating
Radio and television
stations require
oscillators to develop
the basic signal to
transmit their
information
Typical Uses of the Oscillator
Cell phones,
electronic keyboards,
and remote controls
use oscillators to
produce the required
frequencies for
operation
Digital devices such
as computers,
watches, calculators,
and iPods all require
oscillators to generate
the rectangular
waveform required for
operation
Variable oscillators,
known as signal
generators, are used
to generate
frequencies and
waveforms needed for
troubleshooting and
the testing of
electronic equipment
Typical Uses of the Oscillator
Thank you all…….
THANK YOU….