TRANSISTORS BJT NPN PNP

1. Point-Contact Transistor –
first transistor ever made

2. The Wonder child of electronics By
AJAL.A.J ( ASSISTANT PROFESSOR)
ECE DEPARTMENT
MAIL: ec2reach@gmail.com
MOB: 8907305642

3. What is a transistor?
A transistor is a 3 terminal electronic device made of
semiconductor material.
Transistors have many uses, including amplification,
switching, voltage regulation, and the modulation of
signals

4. This session will help you to
understand the,
1.Evolution of transistor
2.Importance of transistor
3.Definition & transistor types
4.Transistor symbol & operation
5.Advantages of transistor
6.Latest in transistor technology

5. History of transistors
In 1906, an American inventor and physicist,
Lee De Forest, made the vacuum tube
triode or audion as he called it.
 Used in radios
 Used in early computers

6. Interesting story…
Picture shows the workbench of John
Bardeen (Stocker Professor at OU) and
Walter Brattain at Bell Laboratories. They
were supposed to be doing fundamental
research about crystal surfaces.
The experimental results hadn't been
very good, though, and there's a rumor that
their boss, William Shockley, came near to
canceling the project. But in 1947, working
alone, they switched to using tremendously
pure materials.
It dawned on them that they could
build the circuit in the picture. It was a
working amplifier! John and Walter
submitted a patent for the first working point
contact transistor.

7. Interesting story…
Shockley was furious and took their
work and invented the junction transistor
and submitted a patent for it 9 days later.
The three shared a Nobel Prize in 1955.
Bardeen and Brattain continued in
research (and Bardeen later won another
Nobel).
Shockley quit to start a
semiconductor company in Palo Alto. It
folded, but its staff went on to invent the
integrated circuit (the "chip") and to
found Intel Corporation.
By 1960, all important computers used
transistors for logic, and ferrite cores for
memory.

9. Qualitative basic operation of point-contact
transistor
Problems with first transistor…

10. First Bipolar Junction Transistors
W. Shockley invented the p-n junction transistor
The physically relevant region is moved to the bulk of the material

11. Moore’s Law
It’s an observation made by Gordon E. Moore, in
which he predicted that the number of transistors,
inside an Integrated Circuit, could
be doubled every 24 months.
At the density that also
minimized the cost of a transistor.

12. Transistor Definition
Transistor is an electronic device
made of three layers of semiconductor
material that can act as an insulator
and a conductor.
The three layered transistor is also
known as the bipolar junction
transistor.

13. Basic models of BJT

14. BJTs – Basic Configurations
pnp BJT npn BJT

15. Bipolar Junction Transistors (BJT’s)
The term bipolar refers to the use of both
holes and electrons as charge carriers in the
transistor structure
 There are two types of BJTs, the NPN and
PNP

16. Origin of the names
the Emitter 'emits' the electrons which pass through
the device
the Collector 'collects' them again once they've
passed through the Base
...and the Base?...

17. Transistor operation
force – voltage/current
water flow – current
- amplification

18. Architecture of BJTs
The bipolar junction transistor (BJT) is
constructed with three doped semiconductor
regions separated by two pn junctions
Regions are called emitter, base and collector

19. Basic construction

20. Architecture of BJTs
There are two types of BJTs, the npn and pnp
The two junctions are termed the base-emitter junction
and the base-collector junction
The term bipolar refers to the use of both holes and
electrons as charge carriers in the transistor structure
In order for the transistor to operate properly, the two
junctions must have the correct dc bias voltages
the base-emitter (BE) junction is forward
biased(>=0.7V for Si, >=0.3V for Ge)
the base-collector (BC) junction is reverse biased

21. Regions of a transistor
A transistor has three regions namely,
Emitter- heavily doped
Base- lightly doped
Collector- moderately doped

22. Transistor symbols Transistor symbols

25. How does IC vary with VCE for various IB?
Note that both dc sources are variable
Set VBB to establish a certain IB

26. Transistor biasing
 The base-emitter (BE) junction is forward biased
The base-collector (BC) junction is reverse biased.
IE=IB+IC

27. • Output current can toggle between large and small
(Switching  Digital logic; create 0s and 1s)

28. Operating regions of BJT
Cut off region
Linear region
Saturation region

29. Types of transistor
BJT - Bipolar Junction Transistor
UJT- Unipolar Junction Transistor
FET - Field Effect Transistor
MOS - Metal Oxide Semiconductor

30. Basic circuits of BJT

31. Operation of BJTs
BJT will operates in one of following four region
Cutoff region (for digital circuit)
Saturation region (for digital circuit)
Linear (active) region (to be an amplifier)
Breakdown region (always be a disaster)

33. DC Analysis of BJTs
Transistor Currents: IE = IC + IB
alpha (aDC) IC = aDCIE
beta (bDC) IC = bDCIB
bDC typically has a value between 20 and 200

34. DC Analysis of BJTs
DC voltages for the biased
transistor:
Collector voltage
VC = VCC - ICRC
Base voltage
VB = VE + VBE
for silicon transistors, VBE = 0.7 V
for germanium transistors, VBE = 0.3 V

35. Q-point
The base current, IB, is established by the base
bias
The point at which the base current curve
intersects the dc load line is the quiescent or Q-point
for the circuit

36. Q-point

37. DC Analysis of BJTs
The voltage divider
biasing is widely used
Input resistance is:
RIN @ bDCRE
The base voltage is
approximately:
VB @ VCCR2/(R1+R2)

38. BJT as an amplifier
Class A Amplifiers
Class B Amplifiers

39. Class A Amplifiers

40. BJT Class A Amplifiers
In a class A amplifier, the transistor conducts for the
full cycle of the input signal (360°)
used in low-power applications
The transistor is operated in the active region,
between saturation and cutoff
saturation is when both junctions are forward biased
the transistor is in cutoff when IB = 0
The load line is drawn on the collector curves between
saturation and cutoff

41. BJT Class A Amplifiers

42. BJT Class A Amplifiers
Three biasing mode for class A amplifiers
common-emitter (CE) amplifier
common-collector (CC) amplifier
common-base (CB) amplifier

43. BJT Class A Amplifiers
A common-emitter (CE) amplifier
capacitors are used for coupling ac without disturbing dc
levels

44. BJT Class A Amplifiers
A common-collector (CC) amplifier
voltage gain is approximately 1, but current gain is
greater than 1

45. BJT Class A Amplifiers
BJT Class A Amplifiers
The third configuration is the common-base (CB)
the base is the grounded (common) terminal
the input signal is applied to the emitter
output signal is taken off the collector
output is in-phase with the input
voltage gain is greater than 1
current gain is always less than 1

46. BJT Class B Amplifiers

47. BJT Class B Amplifiers
When an amplifier is biased such that it operates in the
linear region for 180° of the input cycle and is in cutoff for
180°, it is a class B amplifier
A class B amplifier is more efficient than a class A
In order to get a linear reproduction of the input
waveform, the class B amplifier is configured in a push-pull
arrangement
The transistors in a class B amplifier must be biased
above cutoff to eliminate crossover distortion

49. The BJT as a Switch
When used as an electronic switch, a transistor
normally is operated alternately in cutoff and
saturation
A transistor is in cutoff when the base-emitter junction
is not forward-biased. VCE is approximately equal to VCC
When the base-emitter junction is forward-biased and
there is enough base current to produce a maximum
collector current, the transistor is saturated

50. The BJT as a Switch

51. An example -- NOR

52. Transistor applications
Transistor as a switch
When used as an electronic switch, the transistor is
normally operated alternately in cut-off and
saturation regions.

53. Transistor as amplifier
Due to the small changes in
base current the collector
current will mimic the input
with greater amplitude

54. Future of Transistors
Molecular electronics
Carbon nanotube transistors
Nano inspiration wire transistors
Quantum computing
CMOS devices will add functionality to CMOS non-volatile
memory, opto-electronics, sensing….
CMOS technology will address new markets
macroelectronics, bio-medical devices, …
Biology may provide for new technologies bottom-up
assembly, human intelligence

55. What’s new in transistor technology?
3D Transistor made using
Tri-Gate transistors on its 22nm logic
technology.
Advantage of Tri-Gate Transistors
·More than 50% power reduction at
constant performance.
·37% performance increase at low voltage
·Improved performance and efficiency.

56. BJTs – Practical Aspects

57. BJTs – Practical Aspects
Heat sink

58. BJTs – Testing

59. BJTs – Testing