Edc Chapter Wise Formulas 6h193h
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- Pages: 12
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Page No. 1
ELECTRONIC DEVICES AND CIRCUITS BRIEF NOTES
SEE WWW.UANDISTAR.BLOGSPOT.COM FOR MORE JNTU MATERIALS UNIT – I :: ELECTRON DYNAMICS: CRO ¾ ¾ ¾
e = 1.602 ×10−19 C , m = 9.1×10−31 kg , ‘F’ force on electron in uniform electric field ‘E’ eE F=eE; acceleration a = m If electron with velocity ' v ' moves in field ' E ' making an angle 'θ ' can be resolved to v sin θ , v cos θ .
¾
Effect of Magnetic Field ‘B’ on Electron.
¾
When B & Q are perpendicular path is circular r =
¾ ¾
When slant with 'θ ' path is # Helical. EQUATIONS OF CRT
¾
ELECTROSTATIC DEFLECTION SENSITIVITY Se =
¾
MAGNETIC DEFLECTION SENSITIVITY S m = lL
¾
Velocity due to voltage V, v =
¾
When E and B are perpendicular and initial velocity of electron is zero, the path is
mv 2π m ; Period ' t ' = Be Be
lL 2dVa
e 2mVa
2eV m
Cycloidal in plane perpendicular to B & E. Diameter of Cycloid=2Q, where
u=
Q=
u
ω
,
E Be , ω= . m B UNIT – II :: SEMICONDUCTOR JUNCTION
¾
Si , Ge have 4 electrons in covalent bands. Valency of 4. Doping with trivalent Pentavalent elements makes ' n ' semiconductor. elements makes ' p ' ,
¾
Conductivity
σ = e ( n μn + p μ p )
μn & μ p
mobility’s of electron and hole respectively.
are
where
n, p are concentrations of Dopants.
Diode equation
⎛ Vd ⎞ I d = I s ⎜ e nVT − 1⎟ ⎝ ⎠
-1-
VT =
kT ; K= Boltzman Constant q
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Page No. 2
ΔVd VT kT ⎛ N A N P ⎞ = ; Vo = ln ⎜ ⎟ ΔI d I q ⎝ ni 2 ⎠
¾
rd =
¾
T = 00 C + 273; q = 1.602 × 10−19 C
¾
Diode drop changes @ 2.2mv / C ,
¾
Diffusion capacitance is cd =
¾
Transition capacitance CT is capacitance of reverse biased diode ∝ V
¾
RECTIFIERS
¾
COMPARISION
0
0
Leakage current I s doubles on 10 C
dq of forward biased diode it is ∝ I dv
HW
VDC
Vm
Vrms
Vm
γ Ripple factor
π
FW CT
FW BR
2Vm
2Vm
π
Vm
π
Vm
2
2
2
1.21
0.482
0.482
-2-
−n
n = 1 to 1 2 3
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Page No. 3
η Rectification efficiency
40.6%
81%
81%
Vm
2 Vm
Vm
PIV Peak Inverse Voltage
UNIT – III :: FILTERS
¾
Harmonic Components in FW Output,
v0 =
2Vm
π
−
4 ⎧1 1 ⎫ ⎨ cos 2wt + cos 4 wt + .....⎬ 15 π ⎩3 ⎭
Capacitance Input Filter,
Inductor Input Filter,
γ=
γ=
1 4 3 f CRL
RL 3 2 ωL
Critical inductance
LC is that value at which diode conducts continuously, in + ve or −ve half cycle. LC FILTER,
γ=
2 1.2 , for 50 Hz , L in H , C in μ F . or LC 12ω LC 2
γ=
LC LADDER,
π
FILTER,
γ=
RC FILTER,
¾
ZENER DIODE
FWD Bias Normal si Diode 0.7 V Drop Reverse Bias
Zener drop = Vz forV > Vz -3-
Xc 2 X c1 X c2 . . ..... n X Ln 3 X L1 X L2
2 X C1 X C2 . . 3 RL X L
γ = 2.
X C1 X C2 . RL R
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¾
ZENER REGULATOR
¾
Is =
¾
rz =
¾
TUNNEL DIODE
¾
Conducts in
¾
-ve resistance b-c, normal diode c-d.
Page No. 4
Vi − Vz ;Vi >> Vz Rs ΔVz
ΔI z
f b
, r , Quantum mechanical tunneling in region a-0-b-c. b
I p = peak current, I v = valley current; v p =peak voltage ≈ 65 mV, vv =valley voltage 0.35 V. Heavy Doping, Narrow Junction , Used for switching & HF oscillators.
¾
VARACTOR DIODE
Used in reverse bias & as tuning variable capacitance.
K
¾
CT =
¾
CB 1 is figure of merit, Self resonance f o = C25 2π LS CT
¾
PHOTO DIODES
(VT + VR )
n
; n=0.3 for diffusion, n=0.5 for alloy junction, CT =
-4-
Co ⎛1 + VR ⎞ ⎜ VT ⎟⎠ ⎝
n
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Page No. 5
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 I nE , I pE at
¾
γ = Emitter efficiency, β * =
¾
BE = f / b; BC = r / b
EB junction where γ =
I nc transportation factor. I nE
Ie = Ib + Ic
α=
Ic I ;β = c Ie Ib
Doping Emitter Highest Base Lowest
Ie > I c > Ib ¾ ¾
Leakage currents : I CBO , I CEO , I EBO
I CEO = (1 + β ) I CBO
-5-
I nE I = nE I nE + I pE I E
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Page No. 6
¾
3 Configurations are used on BJT, CE, CB & CC
¾ ¾
Common Emitter,
VI characteristics
β =
¾
Ri = hie =
IC IB
VCE
ΔV ΔVBE = β re ; rce = r0 = ce ΔI B ΔI c
Input Characteristics
Circuit
Output Characteristics
AC Equivalent Circuit
¾
COMMON BASE VI CHARACTERISTICS
¾
α=
IC β ;α = IE 1+ β -6AC Equivalent Circuit
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¾
hib =
I ΔVEB = re ; h fb = C Ie ΔI E
VCB
Page No. 7
; rcb =
ΔVcb ΔI c
AMPLIFIER COMPARISON COMPARISON BE SATURATION ACTIVE CUT OFF
¾
CB
CE
CF
Ri
LOW
MED
HIGH
AI
AI
β
β +1
AV
High
High
<1
Ro
High
High
low
BC
f/b
f/b
f/b
r/b
r/b
r/b
UNIT - V h- parameters originate from equations of amplifier
vi = hi ii + hr v2 , i2 = h f ii + h0v2 vi & ii are input voltage and current v2 & i2 are output voltage and current ¾
hi → input impedance hie , hib , hic ⎡⎣ β re , re , ( β + 1) re ⎤⎦
¾
h f → current gain h fe , h fb , h fc
¾
hr → reverse voltage transfer hre , hrb , hrc
¾
ho → output ittance hoe , hob , hoc
¾
FIELD EFFECT TRANSISTOR, FET is Unipolar Device
Construction
⎡⎣ β , α , (1 + β ) ⎤⎦
n-Channel
¾ ¾
S=Source, G=Gate, D=Drain GS Junction in Reverse Bias Always
¾
Vgs Controls Gate Width
p-Channel
-7-
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¾
Page No. 8
VI CHARACTERSTICS
Transfer Characteristics
Circuit
Forward Characteristics
¾
Shockley Equation
¾
⎛ Vgs I d = I dss ⎜ 1 − ⎜ V p ⎝
¾
MOSFET: Metal Oxide Semiconductor FET, IGFET
2
⎞ ⎟⎟ , ⎠
⎛ V g m = g m 0 ⎜1 − gs ⎜ V p ⎝
Depletion Type Mosfet
¾
⎞ ⎟⎟ ⎠
Symbols
Enhancement Mosfet
Depletion Type MOSFET can work width Vgs > 0 and Vgs < 0 MOSFET
JPET
High Ri = 10
10
Transfer Characteristics
¾
−108
R0 = 50 k Ω
≥ 1mΩ
Depletion Enhancement Mode
Depletion Mode
Delicate
Rugged
Forward Characteristics
Enhancement MOSFET operates with, Vgs > Vt , Vt = Threshold Voltage
-8-
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Page No. 9
Forward Characteristics
Transfer Characteristics
VDS ( sat ) = VGS − VT , I ds (ON ) = K (VGS − VT )
2
COMPARISIONS
JFET I D Table Vgs
ID
0
I DSS
0.3 VP
I DSS
0.5 VP
I DSS
VP
BJT
FET
Current controlled
Voltage controlled
High gain
Med gain
Bipolar
Unipolar
Temp sensitive
Little effect of T
High GBWP
Low GBWP
2 4
0
UNIT – VI :: BIASING in BJT & JFET ¾
Fixing Operating Point Q is biasing
Fixed Bias
VCC = I B RB + VBE
Emitter Stabilized Fixed Bias
VCC = I B RB + VBE + ( β + 1) Re
-9-
Bias
VCC = ( β + 1) RC I B + I B RB +VBE
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Page No. 10
VB =
VCC R2 , R1 + R2
VE = VB − VBE ; I C ≈
VE
RE Vcc = ( β + 1)( Rc + Re ) Ib + Ib.Rb + Vbe
VOLTAGE DIVIDER BIAS
EMITTER STABILIZED FIXED BIAS
STABILITY EQUATIONS ¾
ΔI c = S1ΔI c 0 + S2 ΔVBE + S3 Δβ
¾
S1 =
¾
S must be as small as possible, Most ideal value =1
¾
How to do determine stability factor for bias arrangement?
( β + 1) ΔI C ΔI C ΔI ; S2 = ; S3 = C , STABILITY FACTOR S = dI ΔI CO ΔVBE Δβ 1− β B dI C Derive
substitute in S
AV = AI
Zl , Z i measured with output shorted Zi
¾
Amplifier formulae:
¾
Z0 measured with input shorted
¾
CE amplifier A I ≅ h fe or β ;
¾ ¾
VT R ; Av = − L ; re I R CB amplifier A1 = α ; Av = L ; Z i = re re Z i = β re; re =
¾
CC amplifier A I = ( β + 1) ; AV = 1 −
¾
H Parameter Model CE
¾
AI =
¾
CB amplifier Ri = hib ; AI = h fb ; AV = h fb .
¾
FET
¾
CS amplifier AV = − g m ( Rd || rd ) ; Z 0 = Rd
¾
h fe 1 + hoe zl
; AV = h fe
Common Gate Amplifier
hie
Ri
; Ri = ( h fe + 1) RE + hie
ZL hie
AV = g m Rd , Z i =
RL hib
Rs 1 + g m Rs
- 10 -
dI B and dI C
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AV =
Page No. 11
g m Rs 1 ; Zo = 1 + g m Rs gm
¾
Common Drain
¾
RC Coupled Amplifiers
¾
If cut off frequency
¾
Slope = 6dB / octave, 20dB / decade ,
f1 =
1 , 2π RC
φ = tan −1 ⎛⎜ f1 f ⎞⎟ ; A = ⎝ ⎠ 1+
1 f j ⎛⎜ 1 ⎝
⎞ f ⎟⎠
Octave= f
¾
or 2 f 2 f β is beta cut off frequency where h fe → falls by 0.707
¾
fα is α cut off frequency where α = 0.707
¾
ft is h fe = 1 gain bandwidth product. UNIT – VII :: FEED BACK AMPLIFIERS
¾
Amplifier gain stands for any of Voltage amplifier, Current amplifier, Trans resistance Trans ittance amplifier
Af =
X X A ; A= 0 ; β = f Xi X0 1 + Aβ
Xi = Xs − X f ¾
+
¾
Feed back reduces noise distortion, gain variation due to parameters, increases BW.
−
Ve feed back amplifier depends on |1 + Aβ | > 1 − ve f b , < 1 + ve f b
(1 + Aβ ) ¾
is called de-sensitivity factor.
Feed back amplifiers Voltage series, voltage shunt; Current series, current shunt
for voltage, current series zi f = zi (1 + Aβ ) A , for all 1 + Aβ zi , for voltage or current shunt zi f = 1 + Aβ zo f = zo (1 + Aβ ) , for current series, shunt Af =
zo f =
z0 , for voltage series and shunt. 1 + Aβ
UNIT – VIII :: OSCILLATORS ¾
Barkausen Criterion for oscillation loop gain =1, - 11 -
θ =00, 3600.
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¾
Page No. 12
HARTLEY OSCILLATOR
f =
1 , 2π LT C
LT = L1 + L2 ± M , ; β =
L2 , L1
COLLPITS OSILLATOR,
L1 , L2 replaced by C1 ,C2 , C replaced by L; f =
¾
CRYSTAL OSCILLATORS
¾
Tuned ckt replaced with Crystal
1 2π LCT
1 , LC 1 ωp = LCT
ωs =
¾
Phase shift oscillator
FET MODEL f =
1 , A = 29 , 2π 6 RC
Minimum RC sections 3
f =
BJT MODEL 1 ⎛ 4R ⎞ 2π RC 6 + ⎜ C ⎟ ⎝ R ⎠
, A = 29 ,
Minimum RC sections 3
¾
Wein Bridge Oscillator
f =
1 , 2π R1 R2C1C2
if R1=R2=R, C1=C2=C , f =
- 12 -
1 1 ; A= =3 β 2π RC
Page No. 1
ELECTRONIC DEVICES AND CIRCUITS BRIEF NOTES
SEE WWW.UANDISTAR.BLOGSPOT.COM FOR MORE JNTU MATERIALS UNIT – I :: ELECTRON DYNAMICS: CRO ¾ ¾ ¾
e = 1.602 ×10−19 C , m = 9.1×10−31 kg , ‘F’ force on electron in uniform electric field ‘E’ eE F=eE; acceleration a = m If electron with velocity ' v ' moves in field ' E ' making an angle 'θ ' can be resolved to v sin θ , v cos θ .
¾
Effect of Magnetic Field ‘B’ on Electron.
¾
When B & Q are perpendicular path is circular r =
¾ ¾
When slant with 'θ ' path is # Helical. EQUATIONS OF CRT
¾
ELECTROSTATIC DEFLECTION SENSITIVITY Se =
¾
MAGNETIC DEFLECTION SENSITIVITY S m = lL
¾
Velocity due to voltage V, v =
¾
When E and B are perpendicular and initial velocity of electron is zero, the path is
mv 2π m ; Period ' t ' = Be Be
lL 2dVa
e 2mVa
2eV m
Cycloidal in plane perpendicular to B & E. Diameter of Cycloid=2Q, where
u=
Q=
u
ω
,
E Be , ω= . m B UNIT – II :: SEMICONDUCTOR JUNCTION
¾
Si , Ge have 4 electrons in covalent bands. Valency of 4. Doping with trivalent Pentavalent elements makes ' n ' semiconductor. elements makes ' p ' ,
¾
Conductivity
σ = e ( n μn + p μ p )
μn & μ p
mobility’s of electron and hole respectively.
are
where
n, p are concentrations of Dopants.
Diode equation
⎛ Vd ⎞ I d = I s ⎜ e nVT − 1⎟ ⎝ ⎠
-1-
VT =
kT ; K= Boltzman Constant q
www.Uandistar.blogspot.com
Page No. 2
ΔVd VT kT ⎛ N A N P ⎞ = ; Vo = ln ⎜ ⎟ ΔI d I q ⎝ ni 2 ⎠
¾
rd =
¾
T = 00 C + 273; q = 1.602 × 10−19 C
¾
Diode drop changes @ 2.2mv / C ,
¾
Diffusion capacitance is cd =
¾
Transition capacitance CT is capacitance of reverse biased diode ∝ V
¾
RECTIFIERS
¾
COMPARISION
0
0
Leakage current I s doubles on 10 C
dq of forward biased diode it is ∝ I dv
HW
VDC
Vm
Vrms
Vm
γ Ripple factor
π
FW CT
FW BR
2Vm
2Vm
π
Vm
π
Vm
2
2
2
1.21
0.482
0.482
-2-
−n
n = 1 to 1 2 3
www.Uandistar.blogspot.com
Page No. 3
η Rectification efficiency
40.6%
81%
81%
Vm
2 Vm
Vm
PIV Peak Inverse Voltage
UNIT – III :: FILTERS
¾
Harmonic Components in FW Output,
v0 =
2Vm
π
−
4 ⎧1 1 ⎫ ⎨ cos 2wt + cos 4 wt + .....⎬ 15 π ⎩3 ⎭
Capacitance Input Filter,
Inductor Input Filter,
γ=
γ=
1 4 3 f CRL
RL 3 2 ωL
Critical inductance
LC is that value at which diode conducts continuously, in + ve or −ve half cycle. LC FILTER,
γ=
2 1.2 , for 50 Hz , L in H , C in μ F . or LC 12ω LC 2
γ=
LC LADDER,
π
FILTER,
γ=
RC FILTER,
¾
ZENER DIODE
FWD Bias Normal si Diode 0.7 V Drop Reverse Bias
Zener drop = Vz forV > Vz -3-
Xc 2 X c1 X c2 . . ..... n X Ln 3 X L1 X L2
2 X C1 X C2 . . 3 RL X L
γ = 2.
X C1 X C2 . RL R
www.Uandistar.blogspot.com
¾
ZENER REGULATOR
¾
Is =
¾
rz =
¾
TUNNEL DIODE
¾
Conducts in
¾
-ve resistance b-c, normal diode c-d.
Page No. 4
Vi − Vz ;Vi >> Vz Rs ΔVz
ΔI z
f b
, r , Quantum mechanical tunneling in region a-0-b-c. b
I p = peak current, I v = valley current; v p =peak voltage ≈ 65 mV, vv =valley voltage 0.35 V. Heavy Doping, Narrow Junction , Used for switching & HF oscillators.
¾
VARACTOR DIODE
Used in reverse bias & as tuning variable capacitance.
K
¾
CT =
¾
CB 1 is figure of merit, Self resonance f o = C25 2π LS CT
¾
PHOTO DIODES
(VT + VR )
n
; n=0.3 for diffusion, n=0.5 for alloy junction, CT =
-4-
Co ⎛1 + VR ⎞ ⎜ VT ⎟⎠ ⎝
n
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Page No. 5
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 I nE , I pE at
¾
γ = Emitter efficiency, β * =
¾
BE = f / b; BC = r / b
EB junction where γ =
I nc transportation factor. I nE
Ie = Ib + Ic
α=
Ic I ;β = c Ie Ib
Doping Emitter Highest Base Lowest
Ie > I c > Ib ¾ ¾
Leakage currents : I CBO , I CEO , I EBO
I CEO = (1 + β ) I CBO
-5-
I nE I = nE I nE + I pE I E
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Page No. 6
¾
3 Configurations are used on BJT, CE, CB & CC
¾ ¾
Common Emitter,
VI characteristics
β =
¾
Ri = hie =
IC IB
VCE
ΔV ΔVBE = β re ; rce = r0 = ce ΔI B ΔI c
Input Characteristics
Circuit
Output Characteristics
AC Equivalent Circuit
¾
COMMON BASE VI CHARACTERISTICS
¾
α=
IC β ;α = IE 1+ β -6AC Equivalent Circuit
www.Uandistar.blogspot.com
¾
hib =
I ΔVEB = re ; h fb = C Ie ΔI E
VCB
Page No. 7
; rcb =
ΔVcb ΔI c
AMPLIFIER COMPARISON COMPARISON BE SATURATION ACTIVE CUT OFF
¾
CB
CE
CF
Ri
LOW
MED
HIGH
AI
AI
β
β +1
AV
High
High
<1
Ro
High
High
low
BC
f/b
f/b
f/b
r/b
r/b
r/b
UNIT - V h- parameters originate from equations of amplifier
vi = hi ii + hr v2 , i2 = h f ii + h0v2 vi & ii are input voltage and current v2 & i2 are output voltage and current ¾
hi → input impedance hie , hib , hic ⎡⎣ β re , re , ( β + 1) re ⎤⎦
¾
h f → current gain h fe , h fb , h fc
¾
hr → reverse voltage transfer hre , hrb , hrc
¾
ho → output ittance hoe , hob , hoc
¾
FIELD EFFECT TRANSISTOR, FET is Unipolar Device
Construction
⎡⎣ β , α , (1 + β ) ⎤⎦
n-Channel
¾ ¾
S=Source, G=Gate, D=Drain GS Junction in Reverse Bias Always
¾
Vgs Controls Gate Width
p-Channel
-7-
www.Uandistar.blogspot.com
¾
Page No. 8
VI CHARACTERSTICS
Transfer Characteristics
Circuit
Forward Characteristics
¾
Shockley Equation
¾
⎛ Vgs I d = I dss ⎜ 1 − ⎜ V p ⎝
¾
MOSFET: Metal Oxide Semiconductor FET, IGFET
2
⎞ ⎟⎟ , ⎠
⎛ V g m = g m 0 ⎜1 − gs ⎜ V p ⎝
Depletion Type Mosfet
¾
⎞ ⎟⎟ ⎠
Symbols
Enhancement Mosfet
Depletion Type MOSFET can work width Vgs > 0 and Vgs < 0 MOSFET
JPET
High Ri = 10
10
Transfer Characteristics
¾
−108
R0 = 50 k Ω
≥ 1mΩ
Depletion Enhancement Mode
Depletion Mode
Delicate
Rugged
Forward Characteristics
Enhancement MOSFET operates with, Vgs > Vt , Vt = Threshold Voltage
-8-
www.Uandistar.blogspot.com
Page No. 9
Forward Characteristics
Transfer Characteristics
VDS ( sat ) = VGS − VT , I ds (ON ) = K (VGS − VT )
2
COMPARISIONS
JFET I D Table Vgs
ID
0
I DSS
0.3 VP
I DSS
0.5 VP
I DSS
VP
BJT
FET
Current controlled
Voltage controlled
High gain
Med gain
Bipolar
Unipolar
Temp sensitive
Little effect of T
High GBWP
Low GBWP
2 4
0
UNIT – VI :: BIASING in BJT & JFET ¾
Fixing Operating Point Q is biasing
Fixed Bias
VCC = I B RB + VBE
Emitter Stabilized Fixed Bias
VCC = I B RB + VBE + ( β + 1) Re
-9-
Bias
VCC = ( β + 1) RC I B + I B RB +VBE
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Page No. 10
VB =
VCC R2 , R1 + R2
VE = VB − VBE ; I C ≈
VE
RE Vcc = ( β + 1)( Rc + Re ) Ib + Ib.Rb + Vbe
VOLTAGE DIVIDER BIAS
EMITTER STABILIZED FIXED BIAS
STABILITY EQUATIONS ¾
ΔI c = S1ΔI c 0 + S2 ΔVBE + S3 Δβ
¾
S1 =
¾
S must be as small as possible, Most ideal value =1
¾
How to do determine stability factor for bias arrangement?
( β + 1) ΔI C ΔI C ΔI ; S2 = ; S3 = C , STABILITY FACTOR S = dI ΔI CO ΔVBE Δβ 1− β B dI C Derive
substitute in S
AV = AI
Zl , Z i measured with output shorted Zi
¾
Amplifier formulae:
¾
Z0 measured with input shorted
¾
CE amplifier A I ≅ h fe or β ;
¾ ¾
VT R ; Av = − L ; re I R CB amplifier A1 = α ; Av = L ; Z i = re re Z i = β re; re =
¾
CC amplifier A I = ( β + 1) ; AV = 1 −
¾
H Parameter Model CE
¾
AI =
¾
CB amplifier Ri = hib ; AI = h fb ; AV = h fb .
¾
FET
¾
CS amplifier AV = − g m ( Rd || rd ) ; Z 0 = Rd
¾
h fe 1 + hoe zl
; AV = h fe
Common Gate Amplifier
hie
Ri
; Ri = ( h fe + 1) RE + hie
ZL hie
AV = g m Rd , Z i =
RL hib
Rs 1 + g m Rs
- 10 -
dI B and dI C
www.Uandistar.blogspot.com
AV =
Page No. 11
g m Rs 1 ; Zo = 1 + g m Rs gm
¾
Common Drain
¾
RC Coupled Amplifiers
¾
If cut off frequency
¾
Slope = 6dB / octave, 20dB / decade ,
f1 =
1 , 2π RC
φ = tan −1 ⎛⎜ f1 f ⎞⎟ ; A = ⎝ ⎠ 1+
1 f j ⎛⎜ 1 ⎝
⎞ f ⎟⎠
Octave= f
¾
or 2 f 2 f β is beta cut off frequency where h fe → falls by 0.707
¾
fα is α cut off frequency where α = 0.707
¾
ft is h fe = 1 gain bandwidth product. UNIT – VII :: FEED BACK AMPLIFIERS
¾
Amplifier gain stands for any of Voltage amplifier, Current amplifier, Trans resistance Trans ittance amplifier
Af =
X X A ; A= 0 ; β = f Xi X0 1 + Aβ
Xi = Xs − X f ¾
+
¾
Feed back reduces noise distortion, gain variation due to parameters, increases BW.
−
Ve feed back amplifier depends on |1 + Aβ | > 1 − ve f b , < 1 + ve f b
(1 + Aβ ) ¾
is called de-sensitivity factor.
Feed back amplifiers Voltage series, voltage shunt; Current series, current shunt
for voltage, current series zi f = zi (1 + Aβ ) A , for all 1 + Aβ zi , for voltage or current shunt zi f = 1 + Aβ zo f = zo (1 + Aβ ) , for current series, shunt Af =
zo f =
z0 , for voltage series and shunt. 1 + Aβ
UNIT – VIII :: OSCILLATORS ¾
Barkausen Criterion for oscillation loop gain =1, - 11 -
θ =00, 3600.
www.Uandistar.blogspot.com
¾
Page No. 12
HARTLEY OSCILLATOR
f =
1 , 2π LT C
LT = L1 + L2 ± M , ; β =
L2 , L1
COLLPITS OSILLATOR,
L1 , L2 replaced by C1 ,C2 , C replaced by L; f =
¾
CRYSTAL OSCILLATORS
¾
Tuned ckt replaced with Crystal
1 2π LCT
1 , LC 1 ωp = LCT
ωs =
¾
Phase shift oscillator
FET MODEL f =
1 , A = 29 , 2π 6 RC
Minimum RC sections 3
f =
BJT MODEL 1 ⎛ 4R ⎞ 2π RC 6 + ⎜ C ⎟ ⎝ R ⎠
, A = 29 ,
Minimum RC sections 3
¾
Wein Bridge Oscillator
f =
1 , 2π R1 R2C1C2
if R1=R2=R, C1=C2=C , f =
- 12 -
1 1 ; A= =3 β 2π RC
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