Analog Electronics
Mr.P.Sandeep
Asst Prof, Department of ECE
Vignan Institute of Technology and Science

Passive electronic components are those that
don’t have the ability to control electric
current.
 Active electronic components are those
that can control the flow of electricity.
MATERIALS
Classification based on Conduction

CONDUCTORS

INSULATORS

SEMICONDUCTORS
Conductors

Conductors have loosely bound electrons in
their outer shell

These electrons require a small amount of
energy to free them for conduction
 Conductors are said to have a low resistivity /
resistance
Insulators

Insulators have tightly bound electrons in their
outer shell

These electrons require a very
large amount of energy to free
them for conduction

Insulators are said to have a
high resistivity / resistance
Semiconductors
 Semiconductors have a resistivity/resistance between
that of conductors and insulators
 Their electrons are not free to move but a little energy
will free them for conduction
 The two most common semiconductors are silicon and
germanium
Energy Band
Insulator- SEMICONDUCTOR –
Conductor
Energy Band Diagrams
The Silicon - Si Atom
 Silicon has a 4 valence electrons and each Si atom shares its 4 outer electrons with 4
neighbouring atoms
Silicon – The Crystal Lattice
 At Room Temperature
 No free electrons
 No Conduction
 Therefore it behaves
like an insulator
Electron Movement in Silicon
At higher temperature
An electron gains enough
energy to break free of its
bond…
Free electron - conduction
Movement of electrons : CURRENT
Hole
Hole- Absence of electron
Hole Movement in Silicon
An electron – in a nearby bond –
may occupy this hole…
Effectively causing the hole to
move…
Movement of Holes :
CONVENTIONAL CURRENT
Silicon
electrons free from their
bonds…
This creates electron-hole
pairs which are then
available for conduction
Temperature Increases :
New electron –hole pair ,
Conduction increases
Classification :
Intrinsic Conduction
Take a piece of
silicon…
And apply a potential
difference across it…
This sets up an
electric field
throughout the
silicon – seen here as
dashed lines
When heat is applied an electron is
released and…
Slide 18
Intrinsic Conduction
The electron feels a
force and moves in
the electric field
It is attracted to the
positive electrode
and re-emitted by the
negative electrode
Slide 19
Intrinsic Conduction
Now, let’s apply
some more heat…
Another electron
breaks free…
And moves in the
electric field.
We now have a
greater current than
before…
And the silicon has
less resistance…
Intrinsic Conduction
If more heat is
applies the process
continues…
More heat…
More current…
Less resistance…
The silicon is acting
as a thermistor
Its resistance decreases
with temperature
Doping – Making n-type Silicon
Relying on heat or
light for conduction
does not make for
reliable electronics
Suppose we remove
a silicon atom from
the crystal lattice…
and replace it with a
phosphorus atom
We now have an electron that is not bonded – it is thus free for
conduction
Slide 22
The Phosphorus Atom
Phosphorus is
number 15 in the
periodic table
It has 15 protons and
15 electrons – 5 of
these electrons are in
its outer shell
Slide 23
Doping – Making n-type Silicon
Let’s remove another
silicon atom…
and replace it with a
phosphorus atom
As more electrons
are available for
conduction we have
increased the
conductivity of the
material
Phosphorus is called
the dopant
If we now apply a potential difference
across the silicon…
Slide 24
Extrinsic Conduction – n-type
Silicon
A current will
flow
Note:
The negative
electrons move
towards the
positive
terminal
Slide 25
N-type Silicon




From now
on n-type
will be
shown like
this.
This type of silicon is called n-type
This is because the majority charge carriers are
negative electrons
A small number of minority charge carriers – holes –
will exist due to electrons-hole pairs being created in
the silicon atoms due to heat
The silicon is still electrically neutral as the number of
protons is equal to the number of electrons
Slide 26
The Boron Atom
Boron is number 5
in the periodic table
It has 5 protons and
5 electrons – 3 of
these electrons are
in its outer shell
Slide 27
Doping – Making p-type Silicon
As before, we
remove a silicon
atom from the crystal
lattice…
This time we replace
it with a boron atom
Notice we have a
hole in a bond – this
hole is thus free for
conduction
Slide 28
Doping – Making p-type Silicon
Let’s remove another
silicon atom…
and replace it with
another boron atom
As more holes are
available for
conduction we have
increased the
conductivity of the
material
Boron is the dopant
in this case
If we now apply a potential difference
across the silicon…
Slide 29
Extrinsic Conduction – p-type
silicon
A current will
flow – this time
carried by
positive holes
Note:
The positive
holes move
towards the
negative terminal
Slide 30
P-type Silicon




From now
on p-type
will be
shown like
this.
This type of silicon is called p-type
This is because the majority charge carriers are positive
holes
A small number of minority charge carriers – electrons –
will exist due to electrons-hole pairs being created in the
silicon atoms due to heat
The silicon is still electrically neutral as the number of
protons is equal to the number of electrons
Slide 31