re-lanjut-feedback and oscillator circuit

7/31/2019 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/)

ADVANCED ELECTRONIC CIRCUITS DEPARTMENT ELECTRICAL ENG. UI 2011/2012


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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

4/93ADVANCED ELECTRONIC CIRCUITS DEPARTMENT ELECTRICAL ENG. UI 2011/2012


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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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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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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 =


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=


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



28/34

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

32ADVANCED ELECTRONIC CIRCUITSDEPARTMENT ELECTRICAL ENG. UI

2011/2012


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Monostable configuration



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Astable configuration


re-lanjut-feedback and oscillator circuit

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