Some Harmonic oscillators ppt for those who need it...........

1. Presentation On
Harmonic Oscillators
By:-
Vishal Thakur
Page 1

2. What is an oscillator…???
An oscillator is an electronic circuit that
produces a repetitive electronic
signal, often a sine wave or a square
wave. They are widely used in electronic
devices .
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3. Harmonic Oscillators
• The harmonic, or linear, oscillators are
those oscillators that produces
a sinusoidal output.
• The basic form of a harmonic oscillator is
an electronic amplifier connected in a
positive feedback loop with its output fed
back into its input through a filter.
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4. Essential Parts of any Oscillator
• Tank Circuit (R-C , L-C , etc.)
• Transistor Amplifier (180 phase shift)
• Feedback Circuit
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5. Barkhausen Stability Criteria
• The loop gain should be unity.
i.e Aβ = 1
• Phase shift around loop is zero or an
integral multiple of 2π (Positive
Feedback).
Page 5

6. Some Harmonic Oscillators…
Tuned Collector Oscillator
• It is called the tuned-collector oscilla-tor
because the tuned circuit (L-C circuit) is
connected to the collector of the transistor.
• The tuned circuit constitutes of the
capacitor C and inductor L.
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7. • When the supply is switched on, a transient
current is produced in the tuned L-C circuit.
• It induces voltage in L1 by mutual induction
which causes corresponding vari-ations in
base current.
• These variations in base current are
amplified β times and appear in the
collector circuit.
• A part of this amplified energy is used to
meet the losses that occur in the tank circuit
and the rest is radiated out.
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8. Frequency of oscillation , f = 1/2π √(L.C)
Page 8

9. Colpitt’s Oscillator
• In this type of oscillator , the transistor
amplifier’s emitter is connected to the
junction of capacitors, C1 and C2 which are
connected in series and act as a simple
voltage divider.
• When the power supply is firstly
applied, capacitors C1 and C2 charge up
and then discharge through the coil L.
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10. • The amount of feedback depends on the
values of C1 and C2
• Feedback Coefficient , β = C1/C2
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11. Hartley’s Oscillator
• Widely used as local oscillator in radio
receivers.
• Hartley oscillator circuit is similar to
Colpitt’s oscillator circuit, except that
phase-shift network consists of two
inductors L1 and L2 and a capacitor C
instead of two capacitors and one
inductor.
• Feedback Fraction , β = L1/L2
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12. F = 1 / 2π√[C (L1 + L2 + 2M)]
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13. Phase Shift Oscillator
• The phase shift oscillator
produces positive feedback by using an
inverting amplifier and adding another
180 of phase shift with the three high-
pass filter circuits.
• The most common way of achieving this
kind of oscillation is using three identical
cascaded resistor-capacitor filters.
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14. Page 14

15. Wein-Bridge Oscillator
• It is one of the most popular type of
oscillators used in audio frequency ranges.
• It is a two-stage amplifier with an R-C
bridge circuit.
• This type of oscillator is simple in
design, compact in size, and remarkably
stable in its frequency output.
• Furthermore, its output is relatively free
from distortion and its fre-quency can be
varied easily.
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16. • The overall gain is high because of use of
two transistors.
• When C1 = C2 = C
and R1 = R2 = R
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17. Crystal Oscillator
• This is a type of oscillator that is controlled
by a crystal.
• The big advantage of a crystal oscillator is
high frequency stablility. Common crystals
used are Rochelle salts and quartz.
• The natural frequency of a crystal's
vibrations is found to be more constant
than the oscillations in a LC circuit.
Natural Ferquency = K/T
where K = cut angle constant
and T = thickness of crystal
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18. • The LC circuit is the electricial equilavent of
the crystal.
• It has limited power output.
• Crystals will overheat or crack when fed
with too much voltage. The current flowing
through a crystal generally should not be
more than 100mA (.1A)
• Frequencies :-
• Series resonant Frequency , fs =1/2π √(L.C)
• Parallel Resonant Frequency
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19. • Quality factor = √L/(R √C)
• Crystal Circuit
• Equivalent Circuit
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