diodes and amplifiers

7/27/2019 Diodes and Amplifiers

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DiodesDiodes1. Understand diode operation and select diodes for variousapplications.

2. Analyze nonlinear circuits using the graphical load-linetechnique.

3. Analyze and design simple voltage-regulator circuits.

4.

Solve circuits using the ideal-diode model andpiecewise-linear models.

5. Understand various rectifier and wave-shaping circuits.

6. Understand small-signal equivalent circuits.


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10.1 Basic Diode Concepts

10.1.1 Intrinsic Semiconductors

* Energy Diagrams Insulator, Semiconductor, and Conductor

the energy diagram for the three types of solids

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* Intrinsic (pure) Si Semiconductor:

Thermal Excitation, Electron-Hole Pair, Recombination,

andEquilibrium

3

)cm105~is

densityatomcrystalSi:Note(

K300atcrystalSiintrinsicfor

cm101.5pn

densityholedensityelectron

:reachedis

ionrecombinatandexcitation

betweenmequilibriuWhen

3-22

3-10

ii

==

=


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*Apply a voltage across

a piece ofSi:

electron currentand hole current

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10.1.2 N- and P- Type Semiconductors

* Doping: adding of impurities (i.e., dopants) to theintrinsic semi-conductor material.

* N-type: adding Group V dopant (or donor) such as As, P,Sb,

5

( )

carriercahageminorthehole

carrierchargemajortheelectron

callWe

pp,nNn

nconceratiodonortheNn

materialtype-nIn

101.5pnpn

300KatSiFor

ctorsemiconduaforconstantpn

iid

d

2102i

2i

=

===

=


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10.1.2 N- and P- Type Semiconductors

* Doping: adding of impurities (i.e., dopants) to the intrinsic

semi-conductor material.* P-type: adding Group III dopant (or acceptor) such as Al,

B, Ga,

( )

carriercahageminortheelectron

carrierchargemajorthehole

callWenn,pNp

nconceratioacceptortheNp

materialtype-pIn

101.5pnpn

300KatSiFor

ctorsemiconduaforconstantpn

iia

a

2102

i

2

i

=

===

=

6


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10.1.3 The PN-Junction

* The interface in-between p-type and n-type material iscalled a

pn-junction.

7

.V,Tas:300Kat

Gefor0.3VandSifor0.7V6.0VpotentialbarrierThe

B

B


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10.1.4 Biasing the PN-Junction

* There is no movement of

charge through a pn-junction at equilibrium.

* The pn-junction form adiode which allowscurrent in only onedirection and prevent thecurrent in the otherdirection as determinedby the bias.

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*Forward Bias: dc voltage positive terminal connected tothe p region and negative to the n region. It is the

condition that permits current through the pn-junctionof a diode.

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*Forward Bias: dc voltage positive terminal connected tothe p region and negative to the n region. It is thecondition that permits current through the pn-junction

of a diode.

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*Forward Bias:

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*Reverse Bias: dc voltage negative terminal connectedto the p region and positive to the n region. Depletionregion widens until its potential difference equals thebias voltage, majority-carrier current ceases.

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*Reverse Bias:

majority-carrier currentceases.

* However, there is still avery small currentproduced by minoritycarriers.

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* Reverse Breakdown: As reverse voltage reachcertain value, avalanche occurs and generates

large current.

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10.1.5 The Diode Characteristic I-V Curve

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10.1.6 Shockley Equation

* The Shockley equation is atheoretical result under certain

simplification:

16

0vwhenapplicablenotisequationThis

VnvexpIi0.1V,vwhen

C101.60qconstant,sBoltzman'theisk

voltagethermaltheis300Kat0.026Vq

TkV

t,coefficienemissiontheis2to1ncurrent,

nsaturatio(reverse)theis300KatA10Iwhere

1Vn

vexpIi

D

T

DsDD

19-

T

14-

s

T

DsD

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