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ISU EE C.Y. Lee
Chapter 17Transistors and
Applications
2ISU EE C.Y. Lee
Objectives
Describe the basic structure and operation of bipolar junction transistors (BJT)Explain the operation of a BJT class A amplifierAnalyze class B amplifiersAnalyze a transistor switching circuitDescribe the basic structure and operation of JFETsand MOSFETsAnalyze two types of FET amplifier configurations
3ISU EE C.Y. Lee
Bipolar Junction Transistors (BJTs)
The bipolar junction transistor (BJT) is constructed with three doped semiconductor regions separated by two pn junctionsRegions are called emitter, base and collector
4ISU EE C.Y. Lee
Bipolar Junction Transistors (BJTs)
The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structureIn order for the transistor to operateproperly, the two junctions must have the correct dc bias voltages the base-emitter (BE) junction is
forward biased the base-collector (BC) junction is
reverse biased
5ISU EE C.Y. Lee
DC Operation of Bipolar Junction Transistors (BJTs)
Transistor Currents:IE = IC + IB
alpha (DC):DC = IC/IE
beta (DC):DC = IC/IB
DC typically has a value between 20 and 200
6ISU EE C.Y. Lee
DC Operation of Bipolar Junction Transistors (BJTs)
DC voltages for the biased transistor:Collector voltage:
VC = VCC ICRC
Base voltage:VB = VE + VBE
for silicon transistors, VBE = 0.7 V
7ISU EE C.Y. Lee
DC Operation of Bipolar Junction Transistors (BJTs)
Example: Determine IB, IC, and VC in below circuit
IB = (10.7)/(22103) = 13.6 A
IC = DCIB = (50)(13.6106) = 680 A
VC = 10(680106)(1.0103)= 9.32 V
8ISU EE C.Y. Lee
DC Operation of Bipolar Junction Transistors (BJTs)
VBVC
VERIN
The two dc bias sources can be replaced by a single dc sourceInput resistance at the base:
Base voltage:
Emitter voltage:
EDCIN RR
CCB VRRRV
+
21
2
V.VV BE 70=
9ISU EE C.Y. Lee
DC Operation of Bipolar Junction Transistors (BJTs)
Example: Determine VB, VE, VC, VCE, IB, IE, and IC
VB (10k/32k)(30V) = 9.38 VVE = 9.38V0.7V = 8.68 VIE = VE/RE = 8.68V/1k = 8.68 mAIC = IEIB IE = 8.68 mAIB = IC/DC = 8.68mA/100 = 86.8 AVC = VCCICRC = 30V(8.68mA)(1k)
= 21.3 VVCE = VCVE = 21.3V8.68V = 12.6 V
10ISU EE C.Y. Lee
BJT Class A AmplifiersGenerally, class A amplifiers are used in low-power applicationsCollector characteristic curves:
11ISU EE C.Y. Lee
BJT Class A Amplifiers
The transistor is operated in the active (or linear)region, between saturation and cutoff saturation is when both
junctions are forward biased the transistor is in cutoff
when IB = 0The load line is drawn on the collector curves between saturation and cutoff
In a class A amplifier, the transistor conducts for the full cycle of the input signal (360)
12ISU EE C.Y. Lee
BJT Class A Amplifiers
The base current, IB, is established by the base biasThe point at which the base current curve intersects the dc load line is the quiescent or Q-point for the circuit
(CE)
13ISU EE C.Y. Lee
BJT Class A Amplifiers
A common-emitter (CE) amplifier voltage gain , current gain, and power gain are all
greater than 1
14ISU EE C.Y. Lee
BJT Class A Amplifiers
A common-collector (CC) amplifier voltage gain is approximately 1, but current gain is
greater than 1
15ISU EE C.Y. Lee
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
16ISU EE C.Y. Lee
BJT Class B AmplifiersWhen 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 Class B amplifier is more efficient than a class A, you can
get more output power for a given amount of input power
(CC)
17ISU EE C.Y. Lee
BJT Class B AmplifiersIn order to get a linear reproduction of the input waveform, the class B amplifier is configured in a push-pull arrangement
18ISU EE C.Y. Lee
BJT Class B AmplifiersIllustration of crossover distortion in a class B push-pull amplifier:
19ISU EE C.Y. Lee
BJT Class B AmplifiersThe transistors in a class B amplifier must be biased above cutoff to eliminate crossover distortion
20ISU EE C.Y. Lee
The BJT as a SwitchWhen 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
21ISU EE C.Y. Lee
Field-Effect Transistors (FETs)The junction field-effect transistor (JFET) is operated with a reverse biased junction to control current in a channel the device is identified by the material in the channel,
either n-channel or p-channel
22ISU EE C.Y. Lee
Field-Effect Transistors (FETs)The channel of JFET is formed between the gate regions controlling the reverse biasing voltage on the gate-to-
source junction controls the channel size and the drain current, ID
I I
ID ID
23ISU EE C.Y. Lee
Field-Effect Transistors (FETs)The metal-oxide semiconductor field-effect transistor (MOSFET) differs from the JFET in that it has no pn junction; instead, the gate is insulated from the channel by a silicon dioxide (SiO2) layer
24ISU EE C.Y. Lee
Field-Effect Transistors (FETs)MOSFETs may be depletion mode (D-MOSFET) or enhancement mode (E-MOSFET)
I I
(Normally ON)(D-mode)
p
ID ID
25ISU EE C.Y. Lee
Field-Effect Transistors (FETs)MOSFETs may be depletion mode (D-MOSFET) or enhancement mode (E-MOSFET)
I
(Normally OFF)(E-mode)
26ISU EE C.Y. Lee
Field-Effect Transistors (FETs)
D-MOSFET Channel may be
enhanced or restricted by gate voltage
E-MOSFET Channel is created by
gate voltage
27ISU EE C.Y. Lee
FET AmplifiersVoltage gain of a FET is determined by the transconductance (gm) with units of Siemens (S)
gm = Id / VgAll FETs provide extremely high input resistance
(CD Amplifier)(CS Amplifier)
28ISU EE C.Y. Lee
Cross-sectional View of IC
TRANSISTORS
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IC Fabrication Process1
2
3 /
5 IC
4
30ISU EE C.Y. Lee
Summary
A bipolar junction transistor (BJT) consists of three regions: emitter, base, and collectorThe two types of bipolar transistor are the npn and the pnpThe term bipolar refers to two types of current: electron current and hole currentA field-effect transistor (FET) has three regions: source, drain, and gate
31ISU EE C.Y. Lee
Summary
A junction field-effect transistor (JFET) is operated with a reverse-biased gate-to-source pn junctionJFET current between the drain and source is through a channel whose width is controlled by the amount of reverse bias on the gate-source junctionThe two types of JFETs are n-channel and p-channelMetal-oxide semiconductor field-effect transistors (MOSFETs) differ from JFETs in that the gate of a MOSFET is insulated from the channel
32ISU EE C.Y. Lee
Summary
The D-MOSFET has a physical channel between the drain and the sourceThe E-MOSFET has no physical channelTwo main types of BJT amplifier configurations are the common-emitter (CE) and common collector (CC). A third type is the common base (CB)Two main types of FET amplifier configurations are common-source (CS) and common-drain (CD)
33ISU EE C.Y. Lee
SummaryThe class A amplifier conducts for the entire 360of the input cycle and is normally used for low-power applicationsThe class B amplifier conducts for 180 of the input cycle and is normally used for high-power applications
Chapter 17ObjectivesBipolar Junction Transistors (BJTs)Bipolar Junction Transistors (BJTs)DC Operation of Bipolar Junction Transistors (BJTs)DC Operation of Bipolar Junction Transistors (BJTs)DC Operation of Bipolar Junction Transistors (BJTs)DC Operation of Bipolar Junction Transistors (BJTs)DC Operation of Bipolar Junction Transistors (BJTs)BJT Class A AmplifiersBJT Class A AmplifiersBJT Class A AmplifiersBJT Class A AmplifiersBJT Class A AmplifiersBJT Class A AmplifiersBJT Class B AmplifiersBJT Class B AmplifiersBJT Class B AmplifiersBJT Class B AmplifiersThe BJT as a SwitchField-Effect Transistors (FETs)Field-Effect Transistors (FETs)Field-Effect Transistors (FETs)Field-Effect Transistors (FETs)Field-Effect Transistors (FETs)Field-Effect Transistors (FETs)FET AmplifiersCross-sectional View of ICIC Fabrication ProcessSummarySummarySummarySummary