3. HISTORY
• At the Bell Laboratories in 1947, J.Barden & Walter Braltain were the
first to invent the transistor by adding another junction to a p-n
junction diode. Which could control the flow of majority charge
carriers.
• William Shocleley in 1951 made the modern version of the transistor.
4. CONTI…
• The first working silicon transistor was developed at Bell Labs on
January 26, 1954 by Morris Tanenbaum.
• The first MOSFET (metal–oxide–semiconductor field-effect
transistor) actually built was by Kahng and Atalla at Bell Labs in 1960.
5. DEFINITION
1. A transistor consist of two back to back pn-junctions made in a single
piece of semi conductor crystal.
2. A semiconductor device with three connections, capable of
amplification in addition to rectification.
3. A transistor is a semiconductor device used
to amplify or switch electronic signals and electrical power. It is
composed of semiconductor material usually with at least
three terminals for connection to an external circuit.
6.
7. STRUCTURE
Today’s transistors are made using sophisticated processes and the
transistor structure enables them to have very high levels of
performance.
The original transistor made by Bardeen, Brattain and Shockley
consisted of two very closely spaced contacts on a germanium base. The
structure of this transistor consisted of two point contacts on a
germanium base area.
Today the transistors are made in a variety of ways and have a variety of
different structures. They may be diffused, epitaxially grown or they may
use a mesa construction.
8. CONTI…
Whatever the construction method, the base layer is kept very thin. It is
typically less than 1µm for high current gain.
In terms of doping levels within the transistor structure, the emitter
doping is generally the highest. This provides the highest injection
efficiency. Next is the base doping. Finally the collector is given the lowest
doping level so that the neutral base function is a weak function of the
collector base voltage.
10. CONTI…
P-N-P
when n-type substance ( Si or Ge ) is sandwiched between two p-type
substances, then device formed is called p-n-p transistor.
Symbol
11.
12. CONTI..
N-P-N
When a p-type substance is sandwiched between two n-type substances, the device formed
is called n-p-n transistor.
Symbol
16. CONTI…
Emitter
• The emitter has greater concentration of impurity atoms as compared
to collector, so it has more charge carriers than collector.
• The arrow on emitter terminal shows the direction of conventional
current.
• The width of emitter is slightly smaller in size as compared to collector.
17. CONTI…
Base
• The central region is know as base, usually the base is very thin of the
order of 10^-6 m.
• It has least concentration of impurity as compared t emitter and
collector.
• It has the key role in transistor. It controls the flow of electron from
emitter to collector.
18. CONTI…
Collector
• The collector’s function is to collect majority charge carriers through
the base.
• The collector has less concentration of impurity as compared to
emitter.
• The collector is comparatively large in size than the emitter because it
has dissipate mush greater power.
19. WORKING
A transistor is a miniature electronic component that can do two different jobs. It can work
either as an amplifier or a switch.
As an Amplifier
A transistor is used as an amplifier to amplify the current and a small change in base current
makes a large change in CC (collector current). For example, microphone.
20. CONTI…
As a Switch
In a transistor, the current flow is zero in the collector circuit except for a
current flow in the base circuit. By changing the base terminal, it can be
used as a switch to turn ON/OFF. There are different types of switching
circuits which are operated by transistors such as
• Light operated switch.
• Heat operated the switch.
22. CONTI…
Bipolar Junction Transistor (BJT)
Bipolar Junction Transistors are transistors which are built up of 3 regions, the
base, the collector, and the emitter. Bipolar Junction transistors, different FET
transistors, are current-controlled devices. A small current entering in the base
region of the transistor causes a much larger current flow from the emitter to
the collector region. Bipolar junction transistors come in two major types, NPN
and PNP. A NPN transistor is one in which the majority current carrier are
electrons. Electron flowing from the emitter to the collector forms the base of
the majority of current flow through the transistor. The further types of charge,
holes, are a minority. PNP transistors are the opposite. In PNP transistors, the
majority current carrier is holes.
23. CONTI…
Field Effect Transistor
Field Effect Transistors are made up of 3 regions, a gate, a source, and a
drain. Different bipolar transistors, FETs are voltage-controlled devices. A
voltage placed at the gate controls current flow from the source to the drain of
the transistor. Field Effect transistors have a very high input impedance, from
several mega ohms (MΩ) of resistance to much, much larger values. This
high input impedance causes them to have very little current run through
them. (According to ohm’s law, current is inversely affected by the value of
the impedance of the circuit. If the impedance is high, the current is very
low.) So FETs both draw very little current from a circuit’s power source.
24. CONTI…
Heterojunction Bipolar Transistor (HBT)
Heterojunction bipolar transistors (HBTs) are used for digital and analog
microwave applications with frequencies as high as Ku band. HBTs can
supply faster switching speeds than silicon bipolar transistors mostly because
of reduced base resistance and collector-to-substrate capacitance. HBT
processing requires less demanding lithography than GaAs FETs, therefore,
HBTs can priceless to fabricate and can provide better lithographic yield.
25. CONTI…
Multiple-Emitter Transistor
A multiple-emitter transistor is specialize bipolar transistor frequently used as
the inputs of transistor transistor logic(TTL) NAND logic gates. Input signals
are applied to the emitters. Collector current stops flowing simply, if all
emitters are driven by the logical high voltage, thus performing a NAND
logical process using a single transistor. Multiple-emitter transistors replace
diodes of DTL and agree to reduction of switching time and power
dissipation.
27. CONTI…
• If both input & output sides are reverse bias the current will not flow
and it is called cutoff.
• If both are forward bias a lot of current will flow & it is called
saturation.
• If input side is forward bias & output side is reverse bias, current will
flow. It will amplify & it is called active.
• If current will be more than its limit then it will break down.
28. LOAD LINE REGULATION
Transistor Load Line Analysis
The load line analysis of transistor means for the given value of collector-
emitter voltage we find the value of collector current. This can be done
by plotting the output characteristic and then determine the collector
current IC with respect to collector-emitter voltage VCE. The load line
analysis can easily be obtained by determining the output characteristics
of the load line analysis methods.
29. CONTI…
DC Load Line
The DC load represents the desirable combinations of the collector
current and the collector-emitter voltage. It is drawn when no signal is
given to the input, and the transistor becomes bias.
Consider a CE NPN transistor circuit shown in the figure where no signal
is applied to the input side. For this circuit, DC condition will obtain, and
the output characteristic of such a circuit is shown in the figure .
30. The DC load line curve of the above circuit is shown in the figure
31. CONTI…
By applying Kirchhoff’s voltage law to the collector circuit, we get,
1. The collector-emitter voltage VCE is maximum when the collector current IC= 0 then from the
equation (1) we get,
2. The collector current IC becomes maximum when the collector-emitter voltage VCE = 0 then from
the equation (1) we get.
