module 3 bipolar junction transistor prepared by h v balachandra achar senior lecturer, dept. of...
DESCRIPTION
BASIC ELECTRONICS. MODULE 3 Bipolar Junction Transistor Prepared by H V Balachandra Achar Senior Lecturer, Dept. of E&C Engg., M I T, Manipal. Introduction to Bipolar Junction Transistor BJT Operation BJT Configurations Tutorials BJT Biasing Tutorials BJT Amplifier Tutorials. - PowerPoint PPT PresentationTRANSCRIPT
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
MODULE 3
Bipolar Junction Transistor
Prepared by
H V Balachandra AcharSenior Lecturer,
Dept. of E&C Engg.,M I T, Manipal
BASIC ELECTRONICS
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Syllabus• Introduction to Bipolar Junction Transistor• BJT Operation• BJT Configurations• Tutorials• BJT Biasing• Tutorials• BJT Amplifier• Tutorials
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Reference Books1. “Electronic Devices and Circuit Theory” by Boylestad & Nashelsky, 2. “Integrated Electronics” by Millman & Halkias,
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction• Solid state transistor was invented by a team of scientists at Bell laboratories during 1947-48• It brought an end to vacuum tube era• Advantages of solid state transistor over vacuum devices:
– Smaller size, light weight– No heating elements required– Lower power consumption and operating voltages– Low price
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction
Figure showing relative sizes of transistor, IC and LED
Figure showing different transistor packages
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction• Bipolar Junction Transistor (BJT) is a sandwich consisting of three layers of two different types of semiconductor • Two kinds of BJT sandwiches are: NPN and PNP
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction• The three layers of BJT are called Emitter, Base and Collector• Base is very thin compared to the other two layers• Base is lightly doped. Emitter is heavily doped. Collector is moderately doped• NPN – Emitter and Collector are made of N-type semiconductors; Base is P-type• PNP – Emitter and Collector are P-type, Base is N-type• Both types (NPN and PNP) are extensively used, either separately or in the same circuit
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction• Transistor symbols:
Note: Arrow direction from P to N (like diode)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Introduction• BJT has two junctions – Emitter-Base (EB) Junction and Collector-Base (CB) Junction• Analogous to two diodes connected back-to-back:
– EB diode and CB diode• The device is called “bipolar junction transistor” because current is due to motion of two types of charge carriers – free electrons & holes
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• Operation of NPN transistor is discussed here; operation of PNP is similar with roles of free electrons and holes interchanged• For normal operation (amplifier application)
– EB junction should be forward biased – CB junction should be reverse biased
• Depletion width at EB junction is narrow (forward biased)• Depletion width at CB junction is wide (reverse biased)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
Un-biased transistor showing barriers at the junctions
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
C-B junction is reverse biased – increased barrier height
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
E-B junction is forward biased – aids charge flow
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
Electron-hole combination – leads to small base current
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• When EB junction is forward biased, free electrons from emitter region drift towards base region• Some free electrons combine with holes in the base to form small base current • Inside the base region (p-type), free electrons are minority carriers. So most of the free electrons are swept away into the collector region due to reverse biased CB junction
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• Three currents can be identified in BJT1. Emitter current
• This is due to flow of free electrons from emitter to base • Results in current from base to emitter
2. Base current• This is due to recombination of free electrons and holes in the base
region• Small in magnitude (usually in micro amperes)
3. Collector current• Has two current components:• One is due to injected free electrons flowing from base to collector• Another is due to thermally generated minority carriers
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
• Note the current directions in NPN and PNP transistors• For both varieties: ---(1)
C
E
B
IC
IE
IB
NPN
C
E
B
IC
IE
IB
PNP
BCE III
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• As noted earlier, collector current has two components:
– One due to injected charge carriers from emitter– Another due to thermally generated minority carriers
• Both results in current in the same direction. Hence--- (2)
αdc is the fraction of charge carriers emitted from emitter, that enter into the collector regionICBO is the reverse saturation current in CB diode
--- (3)
CBOEdcC III
E
CBOCdc I
II
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• As approximation, we can neglect ICBO compared to IE and IC
• Hence approximate equations are:
• Like the reverse saturation current of ordinary diode, ICBO also doubles for every 10o rise in temperature.• So ICBO cannot be neglected at higher temperatures• The parameter αdc is called common-base dc current gain• Value of αdc is around 0.99
EdcC II
E
Cdc I
I
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation
• We have• Substituting for IE, we get
CBOEdcC III
CBOBCdcC IIII
CBOBdcCdc III )1(
)1()1( dc
CBOB
dc
dcC
III
CEOBdcC III
• Where and
)1( dc
dcdc
CBOdcdc
CBOCEO III 1
)1(
--- (4)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Operation• Equations (2) and (4) are two alternate forms of BJT current equation• Since value of αdc is around 0.99, ICEO >> ICBO
• However, ICEO is still very small compared to IC
• Hence approximation of (4) gives: or
• Parameter βdc is called common emitter dc current gain• Values of αdc and βdc vary from transistor to transistor. Both αdc and βdc are sensitive to temperature changes
BdcC II B
Cdc I
I
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Problems1. A BJT has alpha (dc) 0.998 and collector-to-base reverse sat current 1μA. If emitter current is 5mA, calculate the collector and base currents. (Ans: 4.99 mA, 10 μA)
2. An npn transistor has collector current 4mA and base current 10 μA. Calculate the alpha and beta values of the transistor, neglecting the reverse sat current ICBO (Ans: 0.9975, 400)
3. In a transistor, 99% of the carriers injected into the base cross over to the collector region. If collector current is 4mA and collector leakage current is 6 μA, Calculate emitter and base currents (Ans: 4.034 mA, 34 μA)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• BJT has three terminals• For two-port applications, one of the BJT terminals needs to
be made common between input and output
• Accordingly three configurations exist:– Common Base (CB) configuration– Common Emitter (CE) configuration– Common Collector (CC) configuration
• (The last one is not discussed in this course)
Input Output2-port device
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• Common Base configuration
(Resistors are not shown here for simplicity)
• Base is common between input and output– Input voltage: VEB Input current: IE
– Output voltage: VCB Output current: IC
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
• CB Input characteristics– A plot of IE versus VEB
for various values of VCB
– It is similar to forward biased diode characteristics
– As VCB is increased, IE increases only slightly
– Note that second letter in the suffix is B (for base)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
constVwithI
Vr CBE
EBi
constIwithVVA E
EB
CBV
• Input resistance ri
• Voltage amplification factor AV
• Both can be determined from the CB input characteristics
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
21
21
EE
EBEBi II
VVr
21
21
EBEB
CBCBV VV
VVA
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• CB Output characteristics
– A plot of IC versus VCB for various values of IE– Three regions are identified: Active, Cutoff, Saturation– Active region:
• E-B junction forward biased• C-B junction reverse biased• IC is positive, VCB is positive• IC increases with IE
• For given IE, IC is almost constant; increases only slightly with increase in VCB. This is due to base-width modulation (Early effect)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
CB Output characteristics
1.Active Region2.Saturation Region3.Cut off Region
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• Base Width modulation
– As the reverse bias voltage VCB is increased, the depletion region width at the C-B junction increases. Part of this depletion region lies in the base layer. So, effective base width decreases. Hence number of electron-hole combination at the base decreases. So base current reduces and collector current increases.– Note that IE = IC + IB
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• When IE = 0, IC = ICBO
– ICBO is collector to base current with emitter open– Below this line we have cut-off region– Here both junctions are reverse biased
• Region to the left of y-axis (VCB negative) is saturation region– Here both junctions are forward biased– IC decreases exponentially, and eventually changes direction
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
• Both can be measured from output characteristics
constIwithI
Vr EC
CBO
• Output resistance ro
• Current amplification factor AI or αac
constVwithII
CBE
Cac
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• Common Emitter configuration
(Resistors are omitted for simplicity)
• Emitter is common between input and output– Input voltage: VBE Input current: IB
– Output voltage: VCE Output current: IC
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
CE input characteristics
• Plot of IB versus VBE for various values of VCE
• Similar to diode characteristics• As VCE is increased, IB
decreases only slightly• This is due to base-width modulation• Note that second suffix is E (for emitter)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• CE output characteristics
– A plot of IC versus VCE for various values of IB
– Three regions identified: Active, Cut-off, Saturation– Active region:
• Linear region in the output characteristics• E-B junction forward biased• C-B junction reverse biased• IC increases with IB
• For given IB, IC increases slightly with increase in VCE; this is due to base-width modulation (Early effect)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
CE output characteristics
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations• Note that VCE = VCB + VBE
• So if VCE is increased, effectively VCB also increases• For saturation to take place, C-B junction should be forward biased.• This happens when VCE is approximately 0.3 V (or less) for Si• Note that when VCE= 0.3V, and VBE= 0.6 V, VCB= – 0.3V (a forward bias of 0.3 V)• So region to the left of the vertical line VCE=VCE(sat)=0.3V (for silicon) is considered as saturation region• Region below IB=0 line (or IC=ICEO) is cut-off region
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
• ICEO is much larger than ICBO because of the relation:
dc
CBOCEO
II
1 • Note that value of αdc is around 0.99
• The values of αdc & αac, and βdc & βac are almost the same. Hence the subscripts can be omitted for simplicity
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
• Input resistance ri
• Voltage gain AV
• Output resistance ro
• Current gain AI or βac
constVwithI
Vr CEB
BEi
constIwithVVA B
BE
CEV
constIwithI
Vr BC
CEo
constVwithII
CEB
Cac
• All these parameters can be determined from CE characteristics
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Configurations
• Experimental setup for determining CE characteristics:
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Tutorials1. A Ge transistor with β = 100 has collector-to-base leakage
current of 5 µA. If the transistor is connected in common-emitter operation, find the collector current for base current (a) 0 (b) 40 µA.
Sol: Given that ICBO = 5µA, and β = 100 We know that
When IB = 0, IC = ICEO = (β+1)ICBO = 505 µAWhen IB = 40 µA, IC = βIB + ICEO
= (100 × 40 × 10–6) + (505 × 10–6)
= 4.505 mA
CEOBdcC III
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Tutorials2. A Ge Transistor has collector current of 51 mA when the base current is 0.4 mA. If β = 125, then what is its collector cutoff current ICEO? (Ans: 1 mA)
3. In a transistor circuit, when the base current is increased from 0.32 mA to 0.48 mA, the emitter current increases from 15 mA to 20 mA. Find αac and βac values. (Ans: 0.968, 30.25)
4. A transistor with α = 0.98 and ICBO = 5 µA has IB = 100 µA. Find IC and IE. (Ans: 5.15 mA, 5.25 mA)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing• What is meant by biasing the transistor?
– Applying external dc voltages to ensure that transistor operates in the desired region • Which is the desired region?
– For amplifier application, transistor should operate in active region– For switch application, it should operate in cut-off and sat.
• What is meant by quiescent point (Q-point)?– The point we get by plotting the dc values of IC , IB and VCE (when ac input is zero) on the transistor characteristics
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Transistor characteristics showing Q-point– Q-point is in the middle
of active region.– This is called “Class-A”
operation. (Other classes are discussed later)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Types of biasing: – Fixed bias and Self bias
• Fixed bias:– The value of IB is “fixed” by choosing
proper value for RB– Equations to consider are:
B
BECCB R
VVI
CCCCCE RIVV
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing• Pros and Cons of Fixed bias:
– Pros: 1) Simple circuit2) Uses very few resistors
– Cons: Q-point is unstable1) If temperature increases, then β increases, and hence ICQ and VCEQ vary (effectively Q-point shifts)2) If the transistor is replaced with another transistor having different β value, then also Q-point shifts
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Load Line– We have:
CCCCCE RIVV
– This is an equation of straight line with points VCC/RC and VCC lying on y-axis and x-axis respectively
– This line is called “Load line” because it depends on resistor RC considered as “Load” and VCC
– Intersection of load line and transistor characteristic curve is the Q-point or operating point
– This point is the common solution for characteristics and load line equation
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
Variation in load line with circuit parameters VCC, RC and RB
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Voltage divider bias or Self bias– Resistor RE connected between
emitter and ground– Voltage-divider resistors R1 & R2
replace RB
– Circuit can be analyzed in two methods:• Exact method (using
Thevenin’s theorem)• Approximation method
(neglecting base current)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Exact method:– Input side of self-bias
(Fig. a) transformed into Thevenin’s equivalent circuit (Fig. b) where, RTH is the resistance looking into the terminals A & B (Fig. c) and VTH is given by:
21
2
RRRV
V CCTH
21
2121 ||
RRRR
RRRTH
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
ETH
BETHB RR
VVI
)1(
E
BETHB R
VVI
E
BETHBC R
VVII
• Equations to consider:
• Since β >> 1 and (β+1)RE >> RTH
• Since IC is almost independent of β, Q-point is stable
• Self-bias circuit redrawn with input side replaced by Thevenin’s equivalent :
EECCCCCE RIRIVV
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Biasing
• Approximate analysis:– Carried out only if βRE ≥ 10R2
• IB is negligible compared to I1 and I2
• So,
EECCCCCE RIRIVV
21
2
RRRV
V CCB
E
BEBE R
VVI
EC II
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Tutorials1. For a fixed bias circuit using Si transistor, RB = 500 kΩ, RC = 2 kΩ, VCC =
15 V, ICBO = 20 µA and β = 70. Find the collector current ICQ and VCEQ at Q-point. Take VBE as 0.7 V. (Ans: 3.422mA, 8.156V)
2. A Si transistor is biased for a constant base current. If β = 80, VCEQ = 8 V, RC = 3 kΩ and VCC = 15 V, find ICQ and the value of RB required. (Ans: 2.33 mA, 493 K)
3. Repeat problem 2 if the transistor is a germanium device. (VBE=0.3V) (Ans: 2.33 mA, 507 K)
4. For a fixed bias circuit, VCC = 12 V and RC = 4 kΩ. The Ge transistor used is characterized by β = 50, ICEO = 0 and VCE sat = 0.2 V. Find the value of RB that just results in saturation. (Ans: 198.3K)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Tutorials5. For a self bias circuit using silicon transistor, RE = 300 Ω, RC = 500 Ω,
VCC = 15 V, β = 100 and . If 10R2= βRE, then determine the value of R1 to get VCEQ = VCC / 2. (Ans: 9.85K)
6. For a self bias circuit, the transistor is a Si device, RE = 200 Ω, R1 = 10R2 = 10 kΩ, RC = 2 kΩ, β = 100 and VCC = 15 V. Determine the values of ICQ and VCEQ.
7. Suppose if the transistor used in problem 6 failed, and was replaced with a new transistor with β = 75. Is the new transistor still biased for active region operation?
8. A self bias circuit uses Si transistor, RC = 330 Ω, RE = 100 Ω and VCC = 12 V. Estimate the values of R1 and R2 required to provide a base current of 0.3 mA, so as to locate the operating point at ICQ = 18 mA and VCEQ = 4.25 V.
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier• Amplifier
– Device which gives larger swing in output voltage proportional to the input voltage swing– BJT basically amplifies current: Collector current equals beta times Base current– With proper circuit designs, we can get voltage amplification and power (both voltage and current) amplification– For faithful amplification (no distortion), BJT should operate in Active region throughout the input cycle (Class A)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
– Without any bias, transistor is in cut-off (IC=0, VCE=0)
– Biasing circuit fixes the operating point in the middle of active region required for faithful amplification
– Figure shows common-emitter amplifier circuit employing fixed bias
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier• With reference to the fig in previous slide, as input voltage vin varies, iin varies, thus base current iB varies• This variation in base current is amplified beta times to get variation in collector current iC
• Output voltage vout is VCC – iC RC
• Note that if vin increases, there is proportional decrease in vout, but of greater magnitude• Similarly if vin decreases, vout increases proportionally• Thus output voltage of CE amplifier is 180o out of phase with input voltage• (Note that small letters are used to represent ac quantities)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
• Voltage gain or voltage amplification factor is vout /vin which is dependent on β, RC and other physical parameters of the transistor
• Figure shows input and output waveforms for the amplifier circuit shown previously
• Note the dc shift in the output voltage waveform. i.e., when vin = 0, vout = VCEQ
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
• This animation shows the working of Common Emitter transistor circuit
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
• Gain of the amplifier is usually expressed in decibels• (AV)dB = 20 log10 | AV |• Usually a gain of 100 (i.e., 40 dB) can be obtained using single
transistor. For higher gain requirement, two or more amplifier stages are to be cascaded
• Overall gain is product of individual gains; But when expressed in dB, overall gain is sum of individual gains (in dB)
VNVVV AAAA ........ 21
dBVNdBVdBVdBV AAAA )(.......)()()( 21
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
• RC coupling– Fig shows CE amplifier
employing self bias– Additional components
are CC and CE
– CC is called coupling capacitor – used to prevent dc component from entering or leaving amplifier stage
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier– CE is called emitter bypass capacitor – used to bypass the ac emitter current – preventing it from flowing through RE
– If ac emitter current is allowed to pass through RE, then vBE reduces and hence output voltage reduces
• Frequency response of amplifier– It’s important to know the behavior of amplifier at different frequencies – Gain is NOT constant at all frequencies – depends on various factors– Frequency response is a plot of gain versus frequency
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier
• Figure shows frequency response plot
• At lower and higher frequencies, gain is less
• Gain attains const value at mid frequencies
• Bandwidth of amplifier is range of frequencies over which gain is not less than 3 dB of maximum gain
20 log | 0.707 AVO | = 20 log | AVO | – 3
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier• Analysis of frequency response curve
– At very low frequencies, reactance of coupling capacitors is high, hence there is loss of signal voltage across capacitors, resulting in reduced gain– Also at low frequencies, emitter bypass capacitor does not fully bypass the ac emitter current, hence ac voltage drop develops across RE, resulting in reduced gain– At very high frequencies, shunt capacitances due to wiring and inter-layer junction capacitances will be prominent, hence resulting in signal loss– At mid frequencies, gain is maximum and constant
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Transistor Amplifier• Classification of amplifiers:
– Based on mode of operation: • Class A: collector current flows throughout the complete input cycle (360o); Q-point is in the centre of active region (no distortion)• Class B: collector current flows during (positive or negative) half cycle of input; Q-point is at “just cut-off” or “just saturation”• Class AB: collector current flows for more than half cycle, but less than full cycle of input waveform; Q-point is “near cut-off” or “near saturation”• Class C: collector current flows for less than half cycle of input waveform; Q-point is in “deep cutoff” or “deep saturation”• (For classes B, AB and C, output is distorted or clipped)
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
Tutorials1. A three-stage amplifier circuit has first stage gain of 45 dB, second stage gain of 50 dB and third stage gain of –5 dB. What is the overall gain? If input to the first stage is 0.1mV, what is the output of final stage?2. An amplifier has maximum gain of 200 and bandwidth of 500 kHz. If lower cutoff freq is 50 Hz, what is the upper cutoff freq and gain at this frequency?3. Design a self bias circuit, given the following parameters:
IC=1mA, VCC=12V, VCE=VCC/2, VB=VCC/10, beta=100, VBE=0.6V, R2=2K
Department of Electronics and Communication Engineering,Manipal Institute of Technology, Manipal, INDIA
End of Module 3