Transistors and Amplifiers

7/26/2019 Transistors and Amplifiers

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TRANSISTORS and AMPLIFIERS

I. TRANSISTOR FUNDAMENTALS

TRANSISTOR Developed in December 23,1947 in Bell laboratories

By John Bardeen, William Shockley and Walter Brattain

Basically a resistor that ampliies electrical imp!lses as they are transerred

rom its inp!t to its o!tp!t terminals"

Basic Types

1. BIPOLAR JUNCTION TRANSISTOR (BJT) #t is a three layer semicond!ctor device consistin$ o either t%o & and one '(

type layers o materials or t%o ' and one &(type layers o semicond!ctormaterials"

T!ee !e"i#ns #$ BJTa" Base

)e$ion to %hich carriers lo% rom emitter to collector

1*1+ dopantscm3

-i$htly doped

b" .mitter )e$ion rom %hich carriers lo%

1*19dopantscm3

/eavily doped c" 0ollector

)e$ion to %hich carriers lo%

1*17dopantscm3

oderately doped

-ar$est

BJT S%!&c%&!e and C#ns%!&c%i#n

Mac!# In%e"!a%ed T!ainin" and Re'ie Cen%e! E*c+!,ni-

Dry0ell


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/0 Transistors and Amplifiers

T!ansis%#! C&!!en%s and C#n$i"&!a%i#ns a" 0ommon Base 0oni$!ration

#n this circ!it, the inp!t si$nal is applied at the emitter, the o!tp!t is taken at the

collector and the base is the common terminal his has very lo% inp!t impedance

Apa ( ) #n the dc mode the levels o #0 and #. d!e to maority carriers are related by a !antity

called alpha and deined by the ollo%in$ e!ation5

e

c

I

I

b" 0ommon .mitter 0oni$!ration he inp!t is applied at the base, the ampliied o!tp!t is taken rom the

collector, and the emitter is the common terminal" his circ!it is the one $enerally !sed or transistors beca!se the 0. ampliier

has the best combination o c!rrent and volta$e $ains

E*c+!,ni- Mac!# In%e"!a%ed T!ainin" and Re'ie Cen%e!


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Transistors and Amplifiers - 2

Ie c3 II

Be%a () )atio o the collector c!rrent to the base c!rrent

=3

c

I

I

c" 0ommon 0ollector 0oni$!ration his circ!it has the inp!t applied at the base, the o!tp!t taken at the emitter

terminal and the collector is the common terminal #mpedance matchin$

4a55a (

) 6or%ard c!rrent $ain or common collector coni$!ration

3

e

I

I

C#5pa!is#n #$ A5pi$ie! C#n$i"&!a%i#ns

Ca!ac%e!is%ic C#55#n

Base

C#55#n

E5i%%e!

C#55#n

C#ec%#!P#e! 4ain moderate hi$hest moderate6#%a"e 4ain hi$hest moderate less than 1C&!!en% 4ain lo%est less

than1moderate hi$hest



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Inp&%I5pedance

lo%est moderate hi$hest

O&%p&%I5pedance

hi$hest moderate lo%est

PaseIn'e!si#n

none 1*8 !t o phase none

Appica%i#ns )6 amp !niversal isolation

T!ansis%#! Biasin" Bias

an electrical, mechanical, or ma$netic orce applied to a device to establish a

desired electrical or mechanical reerence level or its operation" is a D0 volta$e or c!rrent that sets the operatin$ point or ampliyin$ the :0

si$nal

a" 6i;ed Bias is taken rom a battery or po%er s!pply

b" Sel Bias he ampliier prod!ces its o%n D0 volta$e rom an #) drop across a resistor in

the ret!rn circ!it o the common terminal" Sel(bias is probably the type o bias !sed most oten beca!se it is economical

and has stabili


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c" =olta$e(Divider Bias he most stable type o circ!it biasin$

d" Si$nal Bias



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Re"i#ns #$ T!ansis%#! Ac%i#n

a" :ctive )e$ion Base(emitter !nction is or%ard biased and the collector(base !nction is

reverse biased" ransistor>s active operation as an ampliier

b" Sat!ration )e$ion both !nctions are or%ard biased

?s%itch on@ operation or the transistor

c" 0!t o )e$ion

both !nctions are reverse biased ?s%itch o@ operation or the transistor

L#adine and :/p#in%



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Transistors and Amplifiers - ;

L#adine is a strai$ht line dra%n on the collector c!rves bet%een the c!t(o

and sat!ration points o the transistor :/p#in%A!iescent 'ointC is the operatin$ point o the transistor %ith the time

varyin$ so!rces o!t o the circ!it

Re'ie :&es%i#n)

2" hr ( open circ!it reverse volta$e $ain Avolta$e eedback ratioC

! 6#

6i(Ii >)

3" h ( short circ!it or%ard c!rrent $ain

$ Ii

I#( 6# >)

4" ho ( open circ!it o!tp!t admittance

# 6#

I#(Ii >)

0. FIELD EFFECT TRANSISTOR (FET) Unipolar devicebeca!se they operate only %ith one type o char$e carrier

Voltage controlled device %here the volta$e bet%een t%o o the terminals

A$ate and so!rceC controls the c!rrent thro!$h the device" aor eat!re is very high input resistance

a. J&nc%i#n Fied E$$ec% T!ansis%#! (JFET) perates %ith a reverse(biased '& !nction to control c!rrent in the channel

S!are la% device beca!se o the relation o #Dand =S



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Transistors and Amplifiers - ?

IDE

0

)#$$(4S

4SDSS6

61I

J6.D(S6. transer characteristics 0an be n(channel or p(channel

JFET Sy53#s

Ope!a%i#n #$ JFET J6. is al%ays operated %ith the $ate(so!rce '& !nction reversed biased

)everse biasin$ o the $ate(so!rce !nction %ith ne$ative volta$e prod!ces a

depletion re$ion alon$ the '& !nction %hich e;tends into the n(channel andth!s increases its resistance by restrictin$ the channel %idth as sho%n in theprecedin$ i$!re"



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/1> Transistors and Amplifiers

3. Me%a O@ide Se5ic#nd&c%#! Fied E$$ec% T!ansis%#! (MOSFET) second cate$ory o the ield eect transistor

beca!se o the presence o an ins!lated $ate then it is sometimes called

#6.s S6.S diers rom J6. in that it has no '& !nction str!ct!re

#t has t%o basic types, D GS6. and . G S6.

Depe%i#n MOSFET (D/MOSFET) he drain and so!rce are di!sed into the s!bstrate material and connected by

a narro% channel adacent to the ins!lated $ate

#t can be operated in t%o modes(the depletion mode or the enhancement modeand sometimes called depletionenhancement mode S6.

#t can be operated %ith a


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Depe%i#n M#de &e$ative $ate to so!rce volta$e is applied

n Gchannel is depleted o some electrons hence decreasin$ channel

cond!ctivity

Enance5en% M#de

positive $ate volta$e is applied more cond!ction electrons are attracted to the channel th!s enhancin$ channel

cond!ctivity

Enance5en% MOSFET (E/MOSFET) operates only in the enhancement mode

has no depletion mode

it has no str!ct!ral channel

it has no #DSS parameter

or an n(channel type o this device, a positive $ate volta$e above threshold

ind!ces a channel by creatin$ a layer o ne$ative char$es Ainversion layerC inthe s!bstrate portion that is adacent to the Si2layer"

:n n(channel .(S6. has a positive =S%hile a p(channel .(S6. has

a ne$ative =S he cond!ctivity o its channel is enhanced by increasin$ the $ate to so!rce

volta$e 6or $ate volta$e belo% the threshold, there is no channel to be ormed

# coni$!red as a s%itch, this device is normally o

LD MOSEFT, VMOSFET and TMOSFET are .S6. technolo$ies

developed or hi$her po%er dissipation



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II. AMPLIFIERS



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.lectronic devices capable o ampliication or increasin$ the amplit!de o

po%er, c!rrent or volta$e at its o!tp!t 0irc!its desi$ned to increase the amplit!de or level o an electronic si$nal"

Hsed as boosters

Cassi$ica%i#ns #$ A5pi$ie!s< 1. Acc#!din" %# F&nc%i#n

a"=olta$e :mpliier

=olta$e controlled so!rce p(amps are volta$e ampliier

b"0!rrent :mpliier 0!rrent controlled so!rce

BJs are c!rrent ampliier

c"'o%er :mpliier Boost the po%er level o the si$nal

0. Acc#!din" %# C#n$i"&!a%i#n a" 0ommon Base :mpliier

ransistor ampliier %here inp!t is applied at the emitter and o!tp!t is takenrom the collector terminal

he base is common to both inp!t and o!tp!t

a;im!m c!rrent $ain is 1

&o phase inversion rom inp!t to o!tp!t

b" 0ommon 0ollector :mpliier Aemitter ollo%erC ransistor ampliier %here inp!t is applied at the base, o!tp!t is taken rom the

emitter terminal a;im!m volta$e $ain is 1

0apacitors m!st have a ne$li$ible reactance at the re!ency o operation

&o phase inversion rom inp!t to o!tp!t

c" 0ommon .mitter :mpliier ransistor ampliier %herein the inp!t is applied at the base and the o!tp!t is

taken rom the collector terminal here is a phase inversion rom inp!t to o!tp!t



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2. Acc#!din" %# Cass #$ Ope!a%i#na" 0lass : :mpliierb" 0lass B :mpliierc" 0lass 0 :mpliierd" 0lass :B :mpliier

Cass A Cass B Cass C Cass AB

E$$iciency +*I 7"+I 1**I Bet%een : B

C#nd&c%i#nAn"e

3K* 1* Belo%

1*

Sli$htly$reater

than 1*

Dis%#!%i#n -o% /i$h e;treme moderate

Bias(3ase e5i%%e!)

-inearportion

:bovec!t(o

Belo%c!t(o

c!t(o

inp!t o!tp!t

o!tp!t o!tp!to!tp!to!tp!t

C#5pa!is#n #$ A5pi$ie! Casses

7. Acc#!din" %# F!e&encya" D0 :mpliier

:mpliies D0 si$nalA


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8. Acc#!din" %# %e Si"na 3ein" a5pi$ieda" Small Si$nal :mpliiers:mpliier that !tili


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C#5p#&nd C#n$i"&!a%i#ns a" 0ascade 0onnection

a cascade connection is a series connection %ith the o!tp!t o one sta$e then

applied as inp!t to the second sta$e" he cascade connection provides a m!ltiplication o the $ain o each sta$e or

a lar$er overall $ain"A' A'1A'0A'2.. A'n

A'(dB) 0>#" (A')

b" 0ascode 0onnection a cascode connection has one transistor on top o Ain series %ithC another

his arran$ement is desi$n to provide hi$h inp!t impedance %ith lo% volta$e

$ain to ens!re that the inp!t iller capacitance is minim!m"

c" Darlin$ton 0onnection he main eat!re o the Darlin$ton connection is that the composite transistor

acts a sin$le !nit %ith a c!rrent $ain that is the prod!ct o the c!rrent $ains othe individ!al transistors"

#t is a circ!it meant to boost inp!t resistance

D 10

d" 6eedback 'air he eedback pair connection is a t%o(transistor circ!it that operates like the

Darlin$ton circ!it #t !ses a pnp transistor drivin$ an npn"

TEST OURSELF 8



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Transistors and Amplifiers - 1;

Re'ie :&es%i#ns

1" : '&' transistor is made oa" siliconb" $ermani!mc" carbond" either silicon or $ermani!m

Anse!d" either silicon or $ermani!m

2" he transistor is !s!ally encaps!lated ina" $raphite po%derb" enamel paintc" epo;y raisind" black plastic

Anse! c" epo;y raisin

3" 'o%er transistors are invariably provided %itha" solder connectionsb" heat sinkc" metallic casin$d" scre% bolt

Anse!b" heat sink

4" he transistor speciication n!mber 2& reers to aa" diodeb" !nction transistorc" 6. %ith one $ated" S0)

Anse!b" !nction transistor

+" Which i the ollo%in$ is necessary or a transistor actionMa" the base re$ion m!st be very %ideb" the base re$ion m!st be very narro%c"the base re$ion m!st be made rom ins!latin$ materialsd" the collector re$ion m!st be heavily doped

Anse!b" the base re$ion m!st be very narro%

K" :s compared to a 0B ampliier a 0. ampliier hasa" lo% c!rrent ampliicationb" hi$her c!rrent ampliication

c" lo%er inp!t resistanced" hi$her inp!t resistance

Anse! b" hi$her c!rrent ampliication

7" #t is the most stable type o circ!it biasin$



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a" sel(biasb" si$nal bias

c" volta$e(divider biasd" i;ed bias

Anse!c" volta$e(divider bias

" he !iescent state o a transistor impliesa"


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Transistors and Amplifiers - 1?

a" ind!ctively co!pled

b" capacitively co!pledc" direct co!pledd" transormer co!pled

Anse!c" direct co!pled

14" /i$hest operatin$ re!ency can be e;pected in case oa" bipolar transistorb" J6.c" S6.d" #6.

Anse! a" bipolar transistor

1+" Which o the ollo%in$ is e;pected to have the hi$hest inp!t impedanceM

a" S6.b" J6. ampliierc" 0. bipolar transistord" 00 bipolar transistor

Anse!a" S6.

1K" he OOOOOOis !ite pop!lar in di$ital circ!its especially in 0S %hich re!ire very lo% po%ercons!mption"

a" J6.b" BJc" D(type S6.d" .(type S6.

Anse!d" .(type S6.

17" What is the ampliication actor in 6. transistor ampliiersMa" Nib" $mc" #Dd" #

Anse!b" $m

1" he .(S6. is !ite pop!lar in %hat type o applications"a" di$ital circ!itryb" hi$h re!encyc"b!erin$d" a, b and c

Anse! d" a, b and c

19" : J6. !st operates %ith speciically



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/0> Transistors and Amplifiers

a" the drain connected to $ro!ndb" $ate to so!rce '& !nction or%ard biased

c" $ate connected to the so!rced" $ate to so!rce '& !nction reverse biased

Anse!d" $ate to so!rce '& !nction reverse biased

2*" he main dierence o a S6. rom a J6. is thata" J6. has '& !nctionb" o the po%er ratin$c" S6.S has t%o $atesd" S6.s do not have physical channel

Anse! a" J6. has '& !nction

21" : small si$nal ampliiera" !ses only a small portion o its loadlineb" al%ays has an o!tp!t si$nal in the m= ran$ec" $oes into sat!ration once on each inp!t cycled" is al%ays a common emitter ampliier

Anse! a" !ses only a small portion o its loadline

22" he parameter hecorresponds toa" PD0b" P:0c" r>ed" r>c

Anse!b" P:0

23" # the D0 emitter c!rrent in a certain transistor ampliier is 3 m:, the appro;imate val!e o r>e isa" 3LQb" 3Qc" "33 Qd" *"33 LQ

Anse!c" "33 QS#&%i#n

r>e E = KK"7m:3

m=2K

24" he inp!t resistance o a common base ampliier isa" very lo%b" very hi$h

c" the same as 0.d" the same as 00

Anse! a" very lo%

2+" .ach sta$e o a o!r sta$e ampliier has a volta$e $ain o 1+" he overall volta$e $ain is



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a" K*

b"1+c" +*K2+d" 3*7

Anse! c" +*K2+S#&%i#n

=over(allE A1+CA1+CA1+CA1+C E +* K2+

2K" he ma;im!m eiciency o a transormer co!pled 0lass : ampliier isOO"a" 2+b" +*c" 7"+d" 1**

Anse!b" +*

27" #n a S6., the process o creatin$ a channel by the addition o char$e carrier is called"a" ind!cementb" improvementc" balancin$d" enhancement

Anse! d" enhancement

2" What is the c!rrent $ain o a common base circ!it calledMa" $ammab" deltac" bravod" alpha

Anse! d" alpha

29" he name o the very irst transistora" diodeb" !nction transistorc" point contact transistord" triode

Anse!c" point contact transistor

3*" )e$ion in a transistor that is heavily doped"a" collectorb" emitterc" based" $ate

Anse! b" emitter

31" #n a common Gbase ampliier the volta$e $ain isOOOOO"A:pril, 2**3C



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a" medi!mb" lo%

c"

Transistors and Amplifiers

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