re-lanjut-feedback and oscillator circuit
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RANGKAIAN ELEKTRONIKA LANJUT(ADVANCED ELECTRONIC CIRCUITS)
Taufiq Alif Kurniawan, ST, MSc.Eng.
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1. Robert L. Boylestad and Louis Nashelsky, Electronic Devices and CircuitTheory, Pearson Education, Inc., Uppersaddle River, New Jersey 07458,USA, 2006.
2. Jacob Millman & Arvin Grabel, Microelectronics, McGRAW-HILLINTERNATIONAL EDITIONS, 1988.
3. Behzad Razavi, RF Microelectronis, Prentice Hall, 1998.
Lecture notes and supplementary materials will be provided on thecourse website (http://scele.ui.ac.id/)
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ADVANCED ELECTRONIC CIRCUIT
INTRODUCTION
CHAPTER 1. Low Noise Amplifier CHAPTER 2. Power Amplifier
CHAPTER 3. Linier-Digital Ics
CHAPTER 4. Feedback and Oscillator Circuits
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CHAPTER 5. Power Supplies (Voltage Regulators) CHAPTER 6. Two-Terminal & pnpn Devices
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ADVANCED ELECTRONIC CIRCUIT
INTRODUCTION
CHAPTER 1. Low Noise Amplifier CHAPTER 2. Power Amplifier
CHAPTER 3. Linier-Digital Ics
CHAPTER 4. Feedback and Oscillator Circuits
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CHAPTER 5. Power Supplies (Voltage Regulators) CHAPTER 6. Two-Terminal & pnpn Devices
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FEEDBACK AND OSCILLATOR CIRCUITS
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Barkhausens Criteria for Oscillation.
For sinusoidal oscillations,
Barkhausens criteria state-
( ) +1=o
jT
0=o
jT Or even multiples of 3600
( )( )
( ) ( )
( )
( )sT
sA
ssA
sAsvA
=
=
11
Phase shift around feedback loop
should be zero degrees and
magnitude of loop gain must beunity.
Loop gain greater than unity causes
distorted oscillations.
( ) 1=ojT
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Oscillators with Frequency-Selective
RC Networks: Phase-Shift Oscillator
142223
1233
)('oV
)(oV)(
1)(
2
V
)(oV
++
==
=
sRCCRs
RRCs
s
ssT
sCRs
s
ase s w e zero = ,
At 0
o
RCo
3
1=
R
R
4
RRCo)
oT(j 1
12
1122
==
Use node equations at v1 and v2
To find the relation between V2 and Vo
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Oscillators with Frequency-Selective RC
Networks: Wien-Bridge Oscillator (HP 200A)
)(2)(1
)(2)(
1V)(oV
sZsZ
sZss
+=
13)222
1()(IV
)(oV
++
==
sRCCR
sRCG
s
sT(s)
Phase shift will be zero if = 02221 CR
At 0 =1/RC
This oscillator is used for frequencies upto few
MHz, limited primarily by characteristics of
amplifier. (variable freq.?)
3
G)oT(j +=
3
G)oT(j =
= 0)oT(j
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Amplitude Stabilization
Loop gain of oscillator changes due to power supply voltage, component
value or temperature changes.
If loop gain is too small, desired oscillation decays and if it is too large,
waveform is distorted.
loop gain and place poles exactly onjw axis.
At power on, loop gain is larger than that required for oscillation.As
oscillation builds up, gain is reduced to minimum required to sustain
oscillations.
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Amplitude Stabilization in RC
Oscillators: Method 1
R1 is replaced by a lamp. Small-signal resistance of lamp depends on
temperature of bulb filament.
If amplitude is large, current is large, resistance of lamp increases, gain isreduced. If amplitude is small, lamp cools, resistance decreases, loop gain
increases. Thermal time constant of bulb averages signal current and amplitude
is stabilized.
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Amplitude Stabilization in RC
Oscillators: Method 22
1
32 >+
R
RR2
1
432 3 ensuring oscillation, but, when
one diode is on, gain is reduced to
For positive signal at vo,D1 turns on as
voltage acrossR3 exceeds diode turn-on voltage.R4 is in parallel withR3,
loop gain is reduced.D2 functions
similarly at negative signal peak.
.
Same method can also be used in phase
shift oscillators.
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LC Oscillators: Colpitts
Oscillator
CCGmg
GCGCGD
CsCCGD
CCCs
s
s
GmgCCs
sC
mgCs
sLGD
CCs
)31
(3
)3
()31
(31
2
)(sV
)(gV
)
31
(3
)
3
(
/1)3
(
0
0
+
++
+
+++++=
+++
+
++=
)/(1 orSRG=
GSCCC +=
23
s
=0, collect real and imaginary parts and setthem to zero.
TCLC
o1
=
31
31CC
CC
GDC
TCC
++=
At 0
13
CCRmg =
Generally more gain is used to ensure
oscillation with amplitude stabilization.
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LC Oscillators: Hartley Oscillator
+++++=
+++
+
+
=
2
1
1
1
2
1
2
)(sV
)(gV
)2
/1()1
/1(2
/1
)2
/1(
2/1
0
0
LLC
LLssL
mg
og
mgsC
s
s
og
mgsLsL
sL
mgsL
sLsC
=0, collect real and imaginary parts and setthem to zero.
)21
(
1
LLCo
+=
G-S and G-D capacitancesare neglected, assume no
mutual coupling between
inductors.
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Crystal Oscillators
Crystal: A piezoelectric device that vibrates
is response to electrical stimulus, can be SC
PC
TLCL
Rss
S
LCL
Rss
PsC
SZ
PZ S
Z
P
Z
CZ++
++
=+=
12
12
1
modeled electrically by a very high Q(>10,000) resonant circuit.
L, CS,R represent intrinsic series resonance
path through crystal. CP is package
capacitance. Equivalent impedance has seriesresonance where CS resonates withL and
parallel resonance whereL resonates with
series combination ofCS and CP.
SCPCT +
Below S and above P,crystal appears capacitive,
between S and P it exhibitsinductive reactance.
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Crystal Oscillators: Example Problem: Find equivalent circuit elements for crystal with given parameters.
Given data: fS=5 MHz, Q=20,000R =50 W, CP =5 pF
Analysis:
mH8.31)6105(2
)000,20(50=
==
RQL
5.02MHz
fF)6.31mH)(8.31(2
1
2
1
fF8.31
)0318.0(2
710
12
1
=
=
+
=
===
SC
PC
SCPCLP
f
LS
SC
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Crystal Oscillators: TopologiesColpitts Crystal Oscillator Crystal Oscillator using BJT
Crystal Oscillator using JFET
Crystal Oscillator using CMOS
inverter as gain element.
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Amplitude Stabilization
Loop gain of oscillator changes due to power supply voltage, component
value or temperature changes.
If loop gain is too small, desired oscillation decays and if it is too large,
waveform is distorted.
loop gain and place poles exactly onjw axis. At power on, loop gain is larger than that required for oscillation.As
oscillation builds up, gain is reduced to minimum required to sustain
oscillations.
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Amplitude Stabilization in RC
Oscillators: Method 1
R1 is replaced by a lamp. Small-signal resistance of lamp depends on
temperature of bulb filament.
If amplitude is large, current is large, resistance of lamp increases,gain is reduced. If amplitude is small, lamp cools, resistance
decreases, loop gain increases. Thermal time constant of bulb
averages signal current and amplitude is stabilized.
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Active LC oscillator
Higher range
Higher Q factor (=> ??)
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Hartely (b) and Colpitt (a) oscillators
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LC Oscillators: Colpitts Oscillator
CCGmg
GCGCGD
CsCCGD
CCCs
s
s
GmgCCs
sC
mgCs
sLGD
CCs
)31
(3
)3
()31
(31
2
)(sV
)(gV
)31
(
3)
3(
/1)3
(
0
0
+
++
+
+++++=
+++
+
++=
)/(1 orSRG=
GSCCC +=
23
=0, collect real and imaginary parts andset them to zero.
TCLC
o1
=
31
31CC
CC
GDC
TCC
++=
At 0
13
C
CRmg =
Generally more gain is used to ensure
oscillation with amplitude
stabilization.
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LC Oscillators: Hartley Oscillator
+++++=
+++
+
+
=
2
1
1
12
1
2
)(s
V
)(gV
)2
/1()1
/1(2
/1
)2
/1(
2/1
0
0
LLC
LLssL
mg
og
mgsC
s
s
og
mgsLsL
sL
mgsL
sLsC
=0, collect real and imaginary parts andset them to zero.
)21
(
1
LLCo
+=
At 021L
L
f=
Generally more gain is used to ensure
oscillation with amplitude
stabilization.
G-S and G-Dcapacitances are
neglected, assume no
mutual coupling
between inductors.
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Another practical Colpitt Osc.
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Crystal oscillator In its heart is a piezoelectric crystal
Pizo crystal have opposite faces platedwith electrodes.
ma or a van ages: Very high Q (10s to 100s of thousands)
Stable with temp. and time
Can give freq. upto several MHz
Q and res. Freq. depends on the size,orientation of faces, and mount
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Crystal Oscillators
Crystal: A piezoelectric device that
vibrates is response to electrical SC
PC
TLCL
Rss
SLCL
Rss
PsC
SZ
PZ
SZ
PZ
CZ++
++
=+
=
12
12
1
stimulus, can be modeled electrically
by a very high Q(>100,000) resonant
circuit.
L, CS, R represent intrinsic series
resonance path through crystal. CP
is
package capacitance. Equivalent
impedance has series resonance where
CS resonates with L and parallel
resonance where L resonates with series
combination ofCS and CP.
SCPCT
+
Below S and above P,crystal appears
capacitive, between Sand P it exhibitsinductive reactance.
Used to replace L in
Colpitt
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Crystal
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Crystal Oscillators: Example Problem: Find equivalent circuit elements for crystal with given parameters.
Given data: fS=5 MHz, Q=20,000R =50 W, CP =5 pF
Analysis:
mH8.31)
6105(2
)000,20(50=
==
RQL
5.02MHz
fF)6.31mH)(8.31(2
1
2
1
fF8.31
)0318.0(2
710
12
1
=
=
+
=
===
SC
PC
SCPCL
Pf
LS
SC
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Pierce crystal oscillator
configuration
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Crystal Oscillators: TopologiesColpitts Crystal Oscillator Crystal Oscillator using BJT
Crystal Oscillator using JFET
Crystal Oscillator usingCMOS inverter as gain
element.
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The classic 555 timer circuit Since 1972 (by Signetics Co.) called IC
Time Machine! Numerous clones available
ow-cos , accura e an easy o es gnwith (>1B units per year)
~23 Transistors; 2 diodes; ~16 resistors
(DIP-8) Can work in monostable, astable and
bistable configurations29/93ADVANCED ELECTRONIC CIRCUITS DEPARTMENT ELECTRICAL ENG. UI 2011/2012
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From the SE555 datasheet
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Schemtics
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Block diagram S=R=0; Q=Q
S=1;R=0; Q=1 S=0; R=1; Q=0
Vcc ~ 5V
Vth = 2/3Vcc Vtl = 1/3Vcc
Why 555?
Transistor ~ switch
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Monostable configuration
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Astable configuration
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