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ME 4447: Mechatronics
Transistors
Paxton Billingsley
Faiza Hassan
Hanif Hunter
David Stone
Definition
• A transistor is an C
electronic three
terminal device, B
consisting of a
collector, base and
emitter. E E
Transistor Properties
• One-way property
• signal gain
• coupling of circuits with differing impedance
levels
• switch (as in ME 4447)
• non-linear effects used in communication
circuits
Transistor Types
• Bipolar junction • FETS
transistors
-JFETS
-npn
-MOSFETS
-pnp
Transistors
BJTS FETS
p-channel or
n-channel
npn pnp JFETS MOSFETS other
Bipolar Junction Transistors (BJT)
• Invented in 1948 by Bill Shockley at Bell
Laboratories to amplify telephone signals
• First practical design to replace vacuum tubes
• Constructed as a “sandwich” of
semiconductors doped with N-type and P-type
impurities
Two Types of BJT’s
• NPN BJT C • PNP BJT E
C E
N-type P-type
B B
B P-type N-type B
E N-type C P-type
E
C
How They Work
• Holes flow from (1) to (2)
• Forward bias voltage controls the collector
current
• IC is independent of VBE
Summary of BJT Operation
• N-type: electrons are majority carriers
• P-type: holes are majority carriers
• Majority carriers always flow from emitter
to collector
• Increasing base-emitter voltage increases
current flow from emitter to collector
Common Emitter
• Emitter is common to input and output
• Most commonly used configuration
• Medium input and output impedance
• High voltage gain
• High current gain
Common Base
• Base is common to • Low input impedance
input and output • High output impedance
• Used in high • Unity current gain
frequency applications • High voltage gain
Common Collector
• More commonly known as “emitter follower”
• Used as a buffer for circuits with different
impedences
• High input impedence, low output impedence
• Unity current gain, high voltage gain
Summary of BJT Configurations
COMMON
CONFIGURATION COMMON BASE COMMON EMITTER COLLECTOR
(Emitter Follower)
INPUT/OUTPUT
PHASE 0° 180° 0°
RELATIONSHIP
VOLTAGE GAIN HIGH MEDIUM LOW
CURRENT GAIN LOW MEDIUM HIGH
POWER GAIN LOW HIGH MEDIUM
INPUT RESISTANCE LOW MEDIUM HIGH
OUTPUT HIGH MEDIUM LOW
RESISTANCE
Field Effect Transistors
(Paxton Billingsley)
History
• Invented in late 1940’s by Shockley.
• Late 1960’s manufacturing enabled
effective use of field-effect transistors.
• Shockley never prospered in Silicon Valley.
Field Effect Operations
• Control one electrical signal with another.
• 3 - connections, gate, source and drain.
• Transfer patterns of signal fluctuation from
a small input signal to larger output.
Why is it called Field Effect?
• Because of the Field Effect!
• Strong electrical field created .
• This field controls a second signal.
• The second signal mimics the gate signal
but larger.
Polarity
• 2 types
• n-channel corresponds to npn
• p-channel corresponds to pnp
• Behave similarly except in p-type hole not
electrons cause the current.
Variety
• 2 varieties of FET
• junction FET (JFET)
• metal-oxide semiconductor (MOSFET)
• similar properties
Junction FET (JFET)
Basic JFET
Drain
iG
+
iD
Gate VDS
+
VGS -
- Source
JFET Terminals
• 3 Terminals
• Gate (G) this is the input signal with
information
• Source (S) this is the source voltage
• Drain (D) this is the output
JFET Characteristics
JFET Regions of Operation
• Ohmic Region: Behaves as a resistor. Gate
Voltage controls level of resistance,
starting linear then moving non-linear as VD
increases.
• Saturation Region: Device behaves as a
current source controlled by gate source
voltage.
FET Applications
• Preferred for weak-signal work, for example
in wireless communications and broadcast
receivers.
• Not used for high-power amplification.
• Single chip may contain many thousands of
FETs along with other components.
Mosfet
Power Transistors
• Used for power amplification.
• They can be BJTs and MOSFETs or any
other type of transistor.
• Power transistor is just an application of any
transistor
Uses
• Audio Amplification
• Amplification in a RF (radio frequency)
systems
• Many more uses
Some points
• Common-means that that part is grounded and is not the
input nor the output signal.
• AV is the voltage gain.
• AI is the current gain.
• AP is the power gain and the product of AV and AI.
• Whenever there is a thevinin voltage that part of the circuit
was “thevinised”. To change back we multiply by vth/vo.
• Transconductance of BJT’s is gm. This number is constant for
given BJT’s.
3 Types Bipolar Power Transistor
Setups or 3 ways a BJT is hooked
up in a circuit
• Common Emitter (CE)
• Common Base (CB)
• Common Collector (CC)
Bipolar Power Transistor CE
• AVth=-gmRL=vth/vo
For R5 = 0, otherwise:
• AVth=-RL/R5=vth/vo
• AI=-o
• AP= Avth*vin/vth* AI
Bipolar Power Transistor CC
• AVth=1=vth/vo
• AI=o+1
• AP= Avth*vin/vth* AI
=o+1
Bipolar Power Transistor CB
• AVth=gmRL=vth/vo
• AI=1
• AP= Avth*vin/vth* AI
=gmRL=vth/vo
3 Types FET Power Transistor
Setups or 3 ways a FET is hooked
up in a circuit
• Common Source (CS)
• Common Drain (CD)
• Common Gate (CG)
FET Power Transistor CS
• AVth=gmRL=vth/vo
For R5 = 0, otherwise:
AVth=-RL/R5=vth/vo
• AI=
• AP =
FET Power Transistor CD
• AVth=1=vth/vo
• AI=
• AP =
FET Power Transistor CG
• AVth=gmRL=vth/vo
• AI= 1
• AP= gm *vin/vth* RL
Power Transistors
• Used for power amplification.
• They can be BJTs and MOSFETs or any
other type of transistor.
• Power transistor is just an application of any
transistor
Uses
• Audio Amplification
• Amplification in a RF (radio frequency)
systems
• Many more uses
Some points
• Common-means that that part is grounded and is not the
input nor the output signal.
• AV is the voltage gain.
• AI is the current gain.
• AP is the power gain and the product of AV and AI.
• Whenever there is a thevinin voltage that part of the circuit
was “thevinised”. To change back we multiply by vth/vo.
• Transconductance of BJT’s is gm. This number is constant for
given BJT’s.
3 Types Bipolar Power Transistor
Setups or 3 ways a BJT is hooked
up in a circuit
• Common Emitter (CE)
• Common Base (CB)
• Common Collector (CC)
Bipolar Power Transistor CE
• AVth=-gmRL=vth/vo
For R5 = 0, otherwise:
• AVth=-RL/R5=vth/vo
• AI=-o
• AP= Avth*vin/vth* AI
Bipolar Power Transistor CC
• AVth=1=vth/vo
• AI=o+1
• AP= Avth*vin/vth* AI
=o+1
Bipolar Power Transistor CB
• AVth=gmRL=vth/vo
• AI=1
• AP= Avth*vin/vth* AI
=gmRL=vth/vo
3 Types FET Power Transistor
Setups or 3 ways a FET is hooked
up in a circuit
• Common Source (CS)
• Common Drain (CD)
• Common Gate (CG)
FET Power Transistor CS
• AVth=gmRL=vth/vo
For R5 = 0, otherwise:
AVth=-RL/R5=vth/vo
• AI=
• AP =
FET Power Transistor CD
• AVth=1=vth/vo
• AI=
• AP =
FET Power Transistor CG
• AVth=gmRL=vth/vo
• AI= 1
• AP= gm *vin/vth* RL
Conclusion
Most common applications of transistors:
•switch
•amplifier
QUESTIONS
