Osilator Elektronika (TKE 4012) Eka Maulana maulana.lecture.ub.ac.id
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Osilator
Elektronika(TKE 4012)
Eka Maulana
maulana.lecture.ub.ac.id
Osilator
• Dasar dan fungsi Osilator
• Prinsip kerja Osilator
• Jenis-jenis Osilator
• Osilator 555
• Aplikasi
Dasar Osilator
Vout
R
C
+Vcon
+ Vcoff
voutA
B
Sinusoidal oscillation requires
both the correct phase and loop gain.
AB < 1
AB = 1
AB > 1
= 0 = positive feedback
Sinusoidal oscillators
• The starting signal is thermal noise.
• AB > 1 at startup (AB is the loop gain).
• The feedback network determines B and
the phase of the feedback.
• Only one frequency arrives at the input
as an in-phase signal (positive feedback).
• Either A or B is eventually decreased so
that AB = 1.
R
vout
C
Wien-Bridge oscillator
RL2R’
Tungsten
lamp
C R
R’
2pRC
1fr =
vout t
Resistance of lamp
increases until
equilibrium is reached
R’
+VCCColpitts oscillator
2p LC
1fr =
R2
R1
RFC
RE
C2
C1
CE
L
C3
vout
C1 C2
C1 +C2
C =
C1
C2
B =
C2
C1
Amin =
+VCCColpitts CB oscillator
2p LC
1fr =
R2
R1
RFC
RE
C2
C1
LC3
C1 C2
C1 +C2
C =C1
C1 +C2
B =
C1
Amin =C1 +C2
RL
C4
+VCCHartley oscillator
2p LC
1fr =
R2
R1
RFC
R3
C L1
vout
L = L1 + L2
L2
L1
B =
L1
L2
Amin =
L2
Quartz crystal Slab cut from
crystal
Electrodes
and leads
Schematic
symbol
Crystal-controlled oscillators are used
when frequency stability is important.
+VCCCrystal oscillator
R2
R1
RFC
R3
C2
C1
CE
vout
Xtal
Crystals
• The fundamental frequency (series
resonance) is controlled by the slab
thickness.
• Higher multiples of the fundamental are
called overtones.
• The electrode capacitance creates a
parallel resonant frequency which is
slightly higher.
• Typical frequency accuracy is measured
in parts per million (ppm).
Monostable operation of the 555 timer IC
555 vout
+VCC
T
8
3
1
2
Wvout
T T = trigger
Astable operation of the 555 timer IC
555 vout
+VCC
8
3
1
5 kW
R
S Q
Q5 kW
5 kW
Gnd1
Out
3
+VCC8Discharge
Threshold
Control
Trigger
7
6
5
2
555
Reset4
UTPVCC
LTPVCC
RC RC
RB RB
RS RR
+VCC
S R
A discrete RS flip-flop
S
R
Q
Q
1
3
+VCC
7
6
2
8
555 IC configured for monostable operation
R
C
VCC
W
W = 1.1RC
1
3
+VCC
7
6
2
8
555 IC configured for astable operation
R2
CW
W = 0.693(R1 + R2)CR1
TT = 0.693(R1 + 2R2)C
R1 + 2R2
R1 + R2D =
1
3
+VCC
7
6
2
8
555 voltage-controlled oscillator
R2
C
R1
W = -(R1 + R2)C lnVCC - Vcon
VCC - 0.5Vcon
W + 0.693R2C
1f =
5
Vcon applied to pin 5
+Vcon
+ Vcon
+VCC
8
R
6 5
4
3
2 1
7
C
555
Pulse-width modulation with the 555 timer IC
Clock in
Modulating
signal in
A
B
PWM
out
UTP = VCC + vmod
W = -RC ln 1 -UTP
VCC( )
W
T
T
The output frequency is
established by the input clock.
Pulse width is variable
+VCC
8
R1
6 5
4
3
2 1
7
C
555
Pulse-position modulation with the 555 timer IC
Modulating
signal in
A
B
PPM
outR2Space is constant
The leading edge of each pulse
is a function of the modulation.
Space = 0.693R2C
Phase-locked loops
• It is possible to phase-lock an oscillator to
a signal by using a phase detector and
negative feedback.
• PLLs can be used to remove noise from a
signal.
• PLLs can be used to demodulate an FM
signal.
• PLLs are available as monolithic ICs.
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