Transistorlar
Bipolar Transistorlar
◦ BJT
Alan Etkili Transistorlar
Yrd. Doç. Dr. Fatih KELEŞ ◦ FET
jFET
MOSFET
BIPOLAR JUNCTION TRANSISTORS (BJTs) Transistor Operation
Transistor Construction With the external sources, VEE and VCC, connected as shown:
There are two types of transistors: • The emitter-base junction is forward biased
• pnp • The base-collector junction is reverse biased
• npn pnp
The terminals are labeled:
• E - Emitter
• B - Base
• C - Collector
npn
3 4
Currents in a Transistor Common-Base Configuration
Emitter current is the sum of the collector and
base currents:
IE IC IB
The collector current is comprised of two
currents:
IC IC I CO
majority minority
The base is common to both input (emitter–base) and
output (collector–base) of the transistor.
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1
Common-Base Amplifier Common-Base Amplifier
Input Characteristics Output Characteristics
This curve shows the relationship This graph demonstrates
between of input current (IE) to input the output current (IC) to
voltage (VBE) for three output voltage an output voltage (VCB) for
(VCB) levels. various levels of input
current (IE).
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Operating Regions Approximations
Emitter and collector currents:
• Active – Operating range of the
amplifier. I I
C E
• Cutoff – The amplifier is basically
off. There is voltage, but little Base-emitter voltage:
current.
VBE 0.7 V (for Silicon)
• Saturation – The amplifier is full on.
There is current, but little voltage.
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Common–Emitter Configuration Common-Emitter Characteristics
The emitter is common to both input
(base-emitter) and output (collector-
emitter).
The input is on the base and the
output is on the collector.
Collector Characteristics Base Characteristics
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2
Beta ( ) Common–Collector Configuration
represents the amplification factor of a transistor. ( is
sometimes referred to as hfe, a term used in transistor modeling
calculations)
The input is on the
base and the output is
In DC mode: on the emitter.
IC
βdc
IB
In AC mode:
IC
ac VCE constant
IB
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Common–Collector Configuration Operating Limits for Each Configuration
VCE is at maximum and IC is at
minimum (ICmax= ICEO) in the cutoff
region.
The characteristics are
similar to those of the IC is at maximum and VCE is at
common-emitter minimum (VCE max = VCEsat = VCEO) in
configuration, except the the saturation region.
vertical axis is IE.
The transistor operates in the active
region between saturation and cutoff.
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Power Dissipation Transistor Specification Sheet
Common-base:
PCmax VCB I C
Common-emitter:
PCmax VCE I C
Common-collector:
PCmax VCE I E
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3
Transistor Specification Sheet Transistor Testing
• Curve Tracer
Provides a graph of the characteristic curves.
• DMM
Some DMMs measure DC or hFE.
• Ohmmeter
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Transistor Terminal Identification FETs vs. BJTs
The BJT transistor is a bipolar device—the prefix bi- revealing that the conduction level is
a function of two charge carriers, electrons and holes. The FET (Field Effect Transistor) is
a unipolar device depending solely on either electron (n-channel) or hole (p-channel)
conduction.
Similarities:
• Amplifiers
• Switching devices
• Impedance matching circuits
Differences:
• FETs are voltage controlled devices. BJTs are current controlled
devices.
• FETs have a higher input impedance. BJTs have higher gains.
• FETs are less sensitive to temperature variations and are more easily
integrated on ICs.
• FETs are generally more static sensitive than BJTs.
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FET Types JFET Construction
There are two types of JFETs
•n-channel
•p-channel
•JFET: Junction FET
The n-channel is more widely used.
•MOSFET: Metal–Oxide–Semiconductor FET
D-MOSFET: Depletion MOSFET
E-MOSFET: Enhancement MOSFET
There are three terminals:
•Drain (D) and Source (S) are connected to the n-channel
•Gate (G) is connected to the p-type material
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4
JFET Operation: The Basic Idea JFET Operating Characteristics
JFET operation can be compared to a water spigot.
There are three basic operating conditions for a JFET:
The source of water pressure is the
accumulation of electrons at the
• VGS = 0, VDS increasing to some positive value
negative pole of the drain-source
voltage. • VGS < 0, VDS at some positive value
• Voltage-controlled resistor
The drain of water is the electron
deficiency (or holes) at the positive
pole of the applied voltage.
The control of flow of water is the
gate voltage that controls the width
of the n-channel and, therefore, the
flow of charges from source to
drain.
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JFET Operating Characteristics: Saturation JFET Operating Characteristics
As VGS becomes more negative:
At the pinch-off point: • The JFET experiences
pinch-off at a lower voltage
• Any further increase in VGS does not (VP).
produce any increase in ID. VGS at
pinch-off is denoted as Vp. • ID decreases (ID < IDSS) even
though VDS is increased.
• ID is at saturation or maximum. It is
referred to as IDSS. • Eventually ID reaches 0 A.
VGS at this point is called Vp
• The ohmic value of the channel is or VGS(off)..
maximum.
Also note that at high levels of VDS the JFET reaches a breakdown situation. ID
increases uncontrollably if VDS > VDSmax.
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JFET Operating Characteristics: p-Channel JFETS
Voltage-Controlled Resistor
The region to the left of the
pinch-off point is called the
ohmic region. The p-channel JFET behaves the
same as the n-channel JFET,
The JFET can be used as a except the voltage polarities and
variable resistor, where VGS current directions are reversed.
controls the drain-source
resistance (rd). As VGS becomes
more negative, the resistance
(rd) increases.
ro
rd
2
V
1 GS
VP
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5
N-Channel JFET Symbol JFET Transfer Characteristics
The transfer characteristic of input-to-output is not as straightforward in
a JFET as it is in a BJT.
In a BJT, indicates the relationship between IB (input) and IC (output).
In a JFET, the relationship of VGS (input) and ID (output) is a little more
complicated:
2
VGS
I D I DSS 1
V P
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JFET Transfer Curve JFET Specifications Sheet
Electrical Characteristics
This graph shows the
value of ID for a
given value of VGS.
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JFET Specifications Sheet Case and Terminal Identification
Maximum Ratings
more…
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Testing JFETs MOSFETs
MOSFETs have characteristics similar to JFETs and additional
characteristics that make then very useful.
• Curve Tracer
A curve tracer displays the ID versus VDS graph for There are two types of MOSFETs:
various levels of VGS.
• Depletion-Type
• Specialized FET Testers • Enhancement-Type
These testers show IDSS for the JFET under test.
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Depletion-Type MOSFET Construction Basic MOSFET Operation
A depletion-type MOSFET can operate in two modes:
The Drain (D) and Source (S) connect • Depletion mode
to the to n-doped regions. These n- • Enhancement mode
doped regions are connected via an n-
channel. This n-channel is connected to
the Gate (G) via a thin insulating layer
of SiO2.
The n-doped material lies on a p-doped
substrate that may have an additional
terminal connection called Substrate
(SS).
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D-Type MOSFET in Depletion Mode D-Type MOSFET in Enhancement Mode
Enhancement Mode
Depletion Mode • VGS > 0 V
• ID increases above IDSS
The characteristics are similar • The formula used to plot
to a JFET. the transfer curve still
applies:
2
• When VGS = 0 V, ID = IDSS V
I D I DSS 1 GS
• When VGS < 0 V, ID < IDSS VP
• The formula used to plot the transfer
curve still applies: Note that VGS is now a positive polarity
2
V
I D I DSS 1 GS
VP
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p-Channel D-Type MOSFET D-Type MOSFET Symbols
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Specification Sheet Specification Sheet
Electrical Characteristics
Maximum Ratings
more…
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E-Type MOSFET Construction Basic Operation of the E-Type MOSFET
• The Drain (D) and Source (S) connect
to the to n-doped regions. These n- The enhancement-type MOSFET operates only in the enhancement mode.
doped regions would be connected via
an n-channel • VGS is always positive
• The Gate (G) connects to the p-doped • As VGS increases, ID
substrate via a thin insulating layer of increases
SiO2
• As VGS is kept constant
• There is no channel and VDS is increased,
then ID saturates (IDSS)
• The n-doped material lies on a p-doped and the saturation level,
substrate that may have an additional VDSsat is reached
terminal connection called the
Substrate (SS)
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E-Type MOSFET Transfer Curve p-Channel E-Type MOSFETs
To determine ID given VGS:
I D k ( VGS VT ) 2
Where:
VT = threshold voltage
or voltage at which the
MOSFET turns on
k, a constant, can be determined by using VDSsat can be calculated by:
values at a specific point and the formula: The p-channel enhancement-type MOSFET is similar to the n-
VDsat VGS VT channel, except that the voltage polarities and current directions
I D(ON)
k are reversed.
(VGS(ON) VT) 2
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MOSFET Symbols Specification Sheet
Maximum Ratings
more…
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Specification Sheet CMOS Devices
Electrical Characteristics
CMOS (complementary
MOSFET) uses a p-channel
and n-channel MOSFET;
often on the same substrate as
shown here.
Advantages
• Useful in logic circuit designs
• Higher input impedance
• Faster switching speeds
• Lower operating power levels
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Summary Table
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