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ELECTRONIC DEVICES AND CIRCUITS
BRIEF NOTES
SEE WWW.UANDISTAR.BLOGSPOT.COM FOR MORE JNTU
MATERIALS UNIT – I :: ELECTRON DYNAMICS: CRO
¾ kg−
, ‘F’ force on electron in uniform electric field ‘E’ 19 311.602 10 , 9.1 10e C m
−= × = ×
¾ F=eE; accelerationeE
am
=
¾ If electron with velocity ' 'v moves in field ' ' E making an angle ' 'θ can be
resolved to , cossinv vθ θ .
¾ Effect of Magnetic Field ‘B’ on Electron.
¾ When B & Q are perpendicular path is circular2
; 'mv m
eriod t 'r Pπ
Be Be= =
¾ When slant with ' 'θ path is # Helical. ¾ EQUATIONS OF CRT
¾ ELECTROSTATIC DEFLECTION SENSITIVITY2
lL
dV = e
a
S
¾ MAGNETIC DEFLECTION SENSITIVITY2
e
m
a
S lLmV
=
2eV v
m= ¾ Velocity due to voltage V,
¾ When E and B are perpendicular and initial velocity of electron is zero, the path is
Cycloidal in plane perpendicular to B & E. Diameter of Cycloid=2Q, whereu
Qω
= ,
E u
B= ,
Be
mω = .
UNIT – II :: SEMICONDUCTOR JUNCTION
¾ ,i eS G have 4 electrons in covalent bands. Valency of 4. Doping with trivalent
elements makes ' ' p , Pentavalent elements makes ' 'n semiconductor.
¾ Conductivity p p( )ne nσ μ = μ + where ,n p are concentrations of Dopants.
&n pμ μ are mobility’s of electron and hole respectively.
Diode equation
1d
T
V nV
d s I I e⎛ ⎞
= −⎜ ⎟⎝ ⎠
;T V q
=kT
K= Boltzman Constant
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¾ 2
; lnd T Ad o
d i
V V N kT r V
I I q
P N ⎛ ⎞Δ= = = ⎜ ⎟
Δ ⎝ ⎠n
¾ 9C
−× 0 10 273; 1.602 10T C q= + =
¾ Diode drop changes0@ 2 2 /mv C , Leakage current. s I doubles on
010 C
¾ Diffusion capacitance isd
dqc
dv= of forward biased diode it is I ∝
¾ Transition capacitanceT
C is capacitance of reverse biased dioden
V −∝ 1 1
2 3to n =
¾ RECTIFIERS
¾ COMPARISION
HW FW CT FW BR
DC V mV
π
2 mV π
2 mV
π
rmsV 2
mV
2
mV
2mV
γ Ripple factor
1.21 0.482 0.482
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η
Rectification efficiency40.6% 81% 81%
PIV Peak Inverse Voltage m m mV 2V V
UNIT – III :: FILTERS
¾ Harmonic Components in FW Output, 0
2 4 1 1cos 2 cos 4
3 15mV
t wπ π
.....v w t ⎧ ⎫
+= − +⎨ ⎬ ⎩ ⎭
Capacitance Input Filter,1
4 3 L
f CRγ =
¾ ZENER DIODE
Inductor Input Filter,3 2
L R
Lγ
ω =
C L
ve+ ve−
Critical inductance is that value at which
diode conducts continuously, in or
half cycle.
LC FILTER,
22
12 LC γ
ω = or 1.2 , 50 , , . for Hz L in H C in F
LC μ
π FILTER, 1 22
. .3
C C
L L
X X
R X γ =
RC FILTER, 1 22. .C C
L
X X
R Rγ =
FWD Bias Normalis
Diode 0.7 V Drop
Reverse Bias
z z Zener drop V forV V = >
1 2
1 2
2. . .....
3n
n
cc c
L L L
X X X
X X X γ = LC LADDER,
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¾ ZENER REGULATOR
¾ ;i zs i z
s
V V I V V
R
−= >>
¾ z z
z
V r
I Δ
=Δ
¾ TUNNEL DIODE
¾ Conducts in , f r b b
, Quantum mechanical tunneling in region a-0-b-c.
¾ -ve resistance b-c, normal diode c-d.
p I = peak current, v I = valley current; =peak voltage≈
65 mV, =valley voltage0.35 V. Heavy Doping, Narrow Junction , Used for switching & HF oscillators.
pv vv
¾ VARACTOR DIODE
Used in reverse bias & as tuning variable capacitance.
¾ ( )
T
T R
C V V
=+
n
K ; n=0.3 for diffusion, n=0.5 for alloy junction,
1
oT n
R
T
C C
V V
=⎛ ⎞+⎜ ⎟⎝ ⎠
¾ 25
BC
C is figure of merit, Self resonance
1
2o
S T
f L C π
=
¾ PHOTO DIODES
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¾ Diode used in reverse bias for light detection.
¾ Different materials have individual peak response to a range of wave lengths.
UNIT - IV
¾ BJT, Bipolar Junction Transistor has 2 Junctions: BE, BC
¾ Components of current are ,nE pE I I at EB junction where nE nE
nE pE E
I I
I I I γ = =
+
¾ γ = Emitter efficiency,* nc
nE
I
I β = transportation factor.
¾ / B / ; E f b B= =C r b
¾ Leakage currents : , ,CBO CEO EBO I I I
¾ ( )1CEO CBO I I β = +
e b c I I I = +
;c c
e b
I I
I I α β = =
Doping Emitter Highest
Base Lowest
e c b I I I > >
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¾ 3 Configurations are used on BJT, CE, CB & CC
¾ ¾ Common Emitter, VI characteristics
¾ 0; ce BE i ie e ce
B c
V V R h r r r
I I β
ΔΔ= = = = =
Δ Δ
AC Equivalent Circuit
¾ COMMON BASE VI CHARACTERISTICS
¾ ;1
C
E
I
I
β α α
β = =
+
CE
C V
B
I
I β =
Input Characteristics Circuit Output Characteristics
AC Equivalent Circuit
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¾ ; ;V CB
C cb EBib e fb cb
E e c
I V V h r h r
Δ
I I I
Δ= = =
Δ Δ=
UNIT - V
¾ h- parameters originate from equations of amplifier
2 2 0 2,i i i r f i
v h i h v i h i h v= + = +
&iv ii
2
, ,ib
are input voltage and current
2&v i are output voltage and current
¾ ih → input impedance
ie ich h h ( )1 er +, ,e er r β β ⎡ ⎤⎣ ⎦
¾ f h → current gain , , fe fb fc
h h h ( )1, , β α β +⎡ ⎤⎣ ⎦
¾ r h → reverse voltage transfer , ,re rb rc h h h
¾ oh → output admittance , ,ob och h
oe h
¾ FIELD EFFECT TRANSISTOR, FET is Unipolar Device
Construction n-Channel p-Channel
¾ S=Source, G=Gate, D=Drain
¾ GS Junction in Reverse Bias Always ¾
gsV Controls Gate Width
COMPARISON
BE BC
SATURATION f/b f/b
ACTIVE f/b r/b
CUT OFF r/b r/b
AMPLIFIER COMPARISON
CB CE CF
i R LOW MED HIGH
I I A A 1 β β +
V A High High <1
o R High High low
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¾ VI CHARACTERSTICS
Tr ansfer Characteristics Circuit Forward Characteristics
¾ Shockley Equation
¾ 2
1 gs
d dss
p
V I I
V ⎛ ⎞= −⎜ ⎟⎜ ⎟⎝ ⎠
, 0 1 gs
m m
p
V g g
V ⎛ ⎞= −⎜ ⎟⎜ ⎟⎝ ⎠
¾ MOSFET: Metal Oxide Semiconductor FET, IGFET
De pletion Type Mosfet Symbols Enhancement Mosfet
¾ Depletion Type MOSFET can work width 0gsV > and 0gsV <
MOSFET JPET
High1010i R = 810−
Transfer Forward
Characteristics Characteristics
¾ Enhancement MOSFET operates with,gs t V V > ,
t V Threshold Voltage=
0 50 R k = Ω 1m≥ Ω
DepletionEnhancement Mode
DepletionMode
Delicate Rugged
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Forward Characteristics Transfer Characteristics
( ) , DS GS V sat V V = − T ( )2
( )ds GS T
I ON K V V = −
D JFET I Table
UNIT – VI :: BIASING in BJT & JFET
¾ Fixing Operating Point Q is biasing
Fixed Bias Emitter Stabilized Feedback Bias
CC B B BE V I R V = + Fixed Bias ( )1CC C B B B BE V R I I R β = + + +V
( )1 ReCC B B BE
V I R V β = + + +
gsV D I
0 DSS I
0.3PV
2 DSS I
0.5PV
4 DSS I
PV 0
COMPARISIONS
BJT FET
Current controlled Voltage controlled
High gain Med gain
Bipolar Unipolar
Temp sensitive Little effect of T
High GBWP Low GBWP
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; E E B BE C
E V V V V I R= − ≈
2
1 2
CC B
V RV
R R=
+,
( )( )1 Re
.
Vcc Rc Ib
Ib Rb Vbe
β = + +
+ +
VOLTAGE DIVIDER BIAS EMITTER STABILIZEDFIXED BIAS
STABILITY EQUATIONS
¾ 1 0 2 3c c BE I S I S V S β
Δ = Δ + Δ + Δ
( )¾ 1 2 3; ;C C C
CO BE
I I I S S S
I V β
Δ Δ= =
Δ Δ
Δ=
Δ, STABILITY FACTOR
1
1 B
C
dI
dI
β
β
+=
−S
¾ S must be as small as possible, Most ideal value =1
¾ How to do determine stability factor for bias arrangement? Derive B
C
dI
dI and
substitute in S
¾ Amplifier formulae: l I V
i
Z A A
Z
= ,i Z measured with output shorted
¾ 0Z measured with input shorted
¾ feh or CE amplifier IA β ≅ ;
¾ ;i Z re β = T e
V r ;
I = ; L
R
ve
Ar
= −
CB amplifier 1A ; Lv i
e
R A Z
r α = =
CC a ( )
; er = ¾
IA 1 ; 1V i
A ;ieh R
β = + = − ( )1i fe E ie
R h R h= + + ¾ mplifier
¾ H Parameter Model CE
¾ ; fe
h z+
1 I
oe l
h A = L
V fe
ie
Z A h
h=
¾ CB amplifier ; ; . Li ib I fb V fb
ib
R R h A h A h
h= = =
¾ FET
¾ CS amplifier 0 d ( )|| ;V m d d A g R r = − Z R=
¾ Common Gate Amplifier ,
1
s R
g R
V m d i
m s
A g R Z = =
+
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¾ Common Drain1
;1
m sV o
m s m
g R A Z
g R g= =
+
¾ RC Coupled Amplifiers
¾ If cut off frequency 1
1
2 f RC π = ,
1 1
1
1
tan ; 1
f
A f f j
f φ
− ⎛ ⎞
= =⎜ ⎟⎝ ⎠ ⎛ ⎞+ ⎜ ⎟⎝ ⎠
¾ ,6 / ,20 /Slope dB octave dB decade= f Octave= 22
or f
¾ f β is beta cut off frequency where 0.707
feh falls by→
¾ f α is α cut off frequency where 0.707α =
¾ t
f is 1 fe
h = gain bandwidth product.
UNIT – VII :: FEED BACK AMPLIFIERS
¾ Amplifier gain stands for any of Voltage amplifier, Current amplifier, Trans resistanceTrans admittance amplifier
0
0
; ;1
X
¾ +
−
Ve feed back amplifier depends on |1 1 e f | 1 ,b b A ve f v β + > − <
)
+
¾ Feed back reduces noise distortion, gain variation due to parameters, increases BW.
(1 A β + is called de-sensitivity factor.
¾ Feed back amplifiers
Voltage series, voltage shunt; Current series, current shunt
UNIT – VIII :: OSCILLATORS
¾ Barkausen Criterion for oscillation loop gain =1, θ =00, 3600.
f
f
i
X A A A
A X X β
β = = =
+
f
i s X X X = −
for voltage, current series
( )1 f i i z z A β = +
1 f
A A
A β =
+, for all
1 f
i
i
z z
A β =
+, for voltage or current shunt
( )1 f o o z z A β = + , for current series, shunt
0
1 f o
z z
A β =
+
, for voltage series and shunt.
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¾ HARTLEY OSCILLATOR
2
1
L
L β =
1
2 T
f L C π
= 1 2T L L L M = + ± , ;, ,
COLLPITS OSILLATOR,
1 2, L L replaced by C ,1 2,C
1
2 T
f LC π
=C replaced by L;
¾ CRYSTAL OSCILLATORS
¾ Tuned ckt replaced with Crystal
1s
LC ω = ,
1 p
T LC ω =
¾ Phase shift oscillator
FET MODEL
12 6
f RC π
= 29 A =, ,
Minimum RC sections 3
BJT MODEL1
42 6 C
f R
RC R
π
=⎛ ⎞
+ ⎜ ⎟⎝ ⎠
, 29 A = ,
Minimum RC sections 3
¾ Wein Bridge Oscillator
1 2 1 2
1
2 f
R R C C π = ,
if R1=R2=R, C1=C2=C ,1
2 f
RC π = ;
13 A
β = =