Post on 05-Nov-2015
description
ANALOGUE
ELECTRONICS
& CIRCUITS Short Course
Dr. Sohiful Anuar
1
OBJECTIVES
To become proficient in analog circuits To understand and analyze the Bipolar Junction
Transistor To analyze the single stage amplifier circuits in
term of their frequency response To understand the AC & DC analysis
2
COURSE CONTENTS
TOPIC 1 Basic Bipolar Junction Transistor (BJT)
TOPIC 2 BJT Operation Mode
TOPIC 3 BJT Single Stage Amplifier
TOPIC 4 Bipolar Transistor Biasing
TOPIC 5 Bipolar Transistor Configurations
TOPIC 6 DC Analysis
TOPIC 7 AC Analysis
TOPIC 8 Frequency Response
TOPIC 9 BJT Design Example
3
BASIC BIPOLAR JUNCTION TRANSISTOR (BJT)
TOPIC 1
4
Has 3 separately doped regions and 2 p-n junctions
Single p-n junctions has 2 modes of operation
Forward bias
Reverse bias
Both electrons & holes participate in the conduction process
Modern bipolar transistors replaced the germanium with Si & replaced the point contacts with two closely coupled p-n
junctions in the form of p-n-p & n-p-n structures
Bipolar junction transistor (BJT) used extensively in high-speed circuits, analog circuits and power applications
Overview of BJT
5
Ideal BJT Structure
6
Perspective view of a silicon p-n-p bipolar transistor.
3-D BJT Stucture
7
Actual BJT Cross Section
8
BJT Layout
9
BJT Schematic Symbol
10
BJT Schematic Symbol
11
BJT Collector Characteristic
12
Collector Characteristic
13
Base-Emitter Voltage Control
14
Transistor Action
15
Diffusion Currents
16
Transistor Breakdown Voltage (VCBO) and Effective Common-BaseCurrent Gain (F)
17
Cont
18
BJT Current
19
TBE Vve/
TBE Vv
SFEFC eIii/
BJT : Avalanche
20
Origin of F
21
Collector Current
Majority of E current is due to injection of electrons into B
(No. of electrons reaching the C per unit time no. of electrons injected into B) function of B-E voltage
IC
IC Independent of the reverse-biased B-C voltage
F 1 (but less than 1)
F : Common-base current gain
TBE Vv
SFEFC eIii/
TBE Vve/
22
Base Current
Holes from B flow across B-E junction into E
Electrons recombine with holes in the base
Total IB:
TBE Vv
B ei/
1
TBE Vv
B ei/
2
TBE Vv
B ei/
23
Base-emitter junction: forward biased
Most cases: vBE>>VT (thermal voltage), (-1) term is valid
IS : multplying constant (contains electrical parameters of the junction)
IS active B-E cross-sectional area
Typical values of IS 10-12 to 10-15
TBETBE VvSVvSE eIeIi // 1
Emitter Current
24
Electron and hole currents in an npn transistor biased in the forward-
active mode
iB
iB2 iB1
iC iE
Electron & Hole Currents
25
Ebers-Moll Equations
The emitter & collector currents in terms of
internal currents at two junction
26
Ebers-Moll Equivalent Circuit
27
Forward Active Region
28
Simplified Ebers-Moll
29
Cont
30
Transconductace, gm
31
Cont
32
BJT Current
33
Comparison with MOSFET
34
BJT Base Currents
35
Small Signal Current Gain
36
Input Resistance r
37
Output Resistance ro
38
Graphical Interpretation of ro
39
The Early Voltage
40
Cont
41
BJT Small-Signal Model
42
BJT Capacitances
43
Complete Small-Signal Model
44
Parasitic Elements in BJT
45
BJT Operation Modes
TOPIC 2
46
Depends on voltage polarity BASE-EMITTER JUNCTION
COLLECTOR-BASE JUNCTION
VBE FB
VCB RB
VCE
n
p
n
c
b
e
npn
VBE +ve FB
VCB +ve RB
VCE +ve
FORWARD ACTIVE MODE
+ VCE
0
+ IC
saturation
cut-off
E F BE T BC T
C F F F B
I I V V V V
FB RB
I I I
RB: Reverse-biased
FB: Forward-biased
BJT Forward Active Mode
47
BJT Saturation Mode
CEsatCEBEonBEsat
TBECBF
VVVV
FB
VVII
VBE FB
VCB FB
VCE(sat)
n
p
n
c
b
e
n-p-n
VBE +ve FB
VCB -ve FB
VCE +ve VCE(sat)
+ VCE 0
+ IC
saturation mode
cut-off
depends on voltage polarity BASE-EMITTER JUNCTION
COLLECTOR-BASE JUNCTION
FB: Forward-
biased
48
BJT Cut-off Mode
VBE RB
VCB RB
VCE
n
p
n
c
b
e
depends on voltage polarity BASE-EMITTER JUNCTION
COLLECTOR-BASE JUNCTION
ESFCSC
CSRESE
III
III
npn
VBE -ve RB
VCB +ve RB
VCE +ve
+ VCE 0
+ IC
cut-off mode
cut-off
basically leakage currents
49
Mode of Operation (npn Transistor)
-VBE
SWITCH ON
FORWARD ACTIVE REGION IB > 0 IC = F IB
VBE > VBEon
VCE > VCEsat
VBEon ~ 0.7V
b
e
c F IB
VBEon
VBE FB VCB RB
AMPLIFIER
CUT OFF REGION
IC = IB = IE ~ 0 VBE < VBEon (RB)
VCB < VCBon (RB)
b
e
c
VCE = ? V
NOT used very often
SWITCH OFF
SATURATION REGION
IB > 0 IC > 0 IC < F IB VBE > VBEon VCEsat ~ 0.8V
b
e
C
VCEsat
VBEsat
VBE FB VCB FB
INVERSE ACTIVE REGION
IB > 0 IE = R IB VBC > VBEon
VEC > VCEsat
VBEon ~ 0.7V
B
E
C
R IB VBEon
VBE RB VCB FB
+VBC
+VBE
-VBC
-VBE
50
BJT Single Stage Amplifiers
TOPIC 3
51
VCC DC voltage
powers the amplifier
sets the DC operating point
provides the energy for the output ac signal
DC bias potential divider sets the Q point
emitter resistor stabilises Qpoint
VCC
RC
RE RB2
RB1
LOAD ?
Amplifier Basic BJT Amplifier
52
RC
R
E
VCC
RB2
RB1 CC2
ensures generator does not affect the bias (Q point of transistor) transistor DC voltage does not affect the source
ensures the load does not affect transistor bias to provide only ac output to the load
RL vout(ac)
vin(ac)
RS
CC1
Signal & Load Coupling
53
VCC
RC
RE RB2
RB1
RL
VCEQ
RS
DC analysis : replace capacitors with open circuit
DC analysis : replace ac source with internal impedance
CC2 CC1
Vin(ac)
Basic DC Analysis
54
(a) Common-emitter circuit with an npn transistor
and (b) dc equivalent circuit, with piecewise linear
parameters
Assume B-E junction: forward biased V drop is the cut-in /
turn-on V [VBE (on)]
IC represented as a dependent I
source (function of IB)
Neglect reverse-biased junction leakage current & Early effect
B
BEBBB
R
onVVI
)(
BC II
CCCCCE RIVV
CECCCC VRIV
VBB>VBE(on) IB>0
VBB
Fig. 3.22: (a) base-emitter junction characteristics and the input load line and (b)
common- emitter transistor characteristics and the collector-emitter load line
-help us visualize the characteristic
of a transistor
Load Line
56
Fig. 3.19: Common-emitter circuit
Cont
57
Based on fig. 3.19 above,
Kirchoffs voltage law equation (around B-E loop):
B
BE
B
BBB
R
V
R
VI Both load line & quiescent IB change as either
or both VBB & RB change
Kirchoffs voltage law equation (around C-E loop):
CCCCCE RIVV
)(2
5 mAV
R
V
R
VI CE
C
CE
C
CC
C IC & VCE relationship represents DC load line
Cont
58
59
Bipolar Transistor Biasing
TOPIC 4
60
i. Single Base Resistor Biasing
ii. Emitter Biasing
iii.Voltage-divider Biasing
iv.Collector-feedback Biasing
BJT Bias Circuits
61
RC
RB
+VCC
VBE
+
-
B
BECC
BR
VVI
B
BECC
DCCR
VVI
CCCCCE RIVV
Single Base Resistor Biasing
62
CC (Coupling capacitor): acts as open circuit to DC- isolating signal source from DC IB
If input signal freq & CC : signal can be coupled thru CC to B with little attenuation
Fig. 3.50: (a) Common emitter circuit with a single bias resistor in the base, (b)
dc equivalent circuit
*See example
3.13 page 138
Cont
63
RC
RB
RE
+VCC
-VEE
ECCEECCCE RRIVVV
CCCCC RIVV
DCBE
BEEEC
RR
VVI
Emitter Biasing
64
+VCC
RE
RC R1
R2
CCB VRR
RV
21
2
E
BEBC
R
VVI
ECCCCCE RRIVV
Voltage-Divider Biasing & Bias Stability
65
(a) A common-emitter circuit with an emitter resistor and
voltage divider bias circuit in the base; (b) the dc circuit
with a Thevenin equivalent base circuit
RB
is replaced
added
CCTH VRRRV )]/([ 212
21 || RRRTH
EEQBETHBQTH RIonVRIV )(
BQEQ II )1(
ETH
BETHBQ
RR
onVVI
)1(
)(
ETH
BETHBQCQ
RR
onVVII
)1(
)((
Around B-E loop:
Parallel resistors
Forward active-mode:
*See example 3.15 page 142
Current mirror
Cont
66
RC RB
+VCC
B
BEC
BR
VVI
DCBC
BECC
CRR
VVI
CCCCCE RIVV
Collector-feedback Biasing
67
Bipolar Transistor Configurations
TOPIC 5
68
69
3 basic single-transistor amplifier configurations can be formed:
COMMON EMITTER (C-E configuration)
COMMON COLLECTOR / EMITTER FOLOWER (C-C configuration)
COMMON BASE (C-B configuration)
Each configuration has its own advantage in the form of
INPUT IMPEDANCE
OUTPUT IMPEDANCE
CURRENT / VOLTAGE AMPLIFICATION
BJT Amplifiers Configuration
70
COMMON EMITTER AMPLIFIER
RC
RE RB2
RB1
RL
CC1 CC2
vin
RS vout
CC2
RE RB2 RB1
RL
CC1
vin
RS vout RC
e
b
c
input base-emitter
output collector-emitter
emitter common (to input & output)
COMMON EMITTER MODE
Prof. R T Kennedy
Common-Emitter Amp. (CE)
Basic CE Amplifier
71
Cont
72
73
RS
R1
R2 RE
RC
vs
vO
CC
VCC
(a)
CE amplifier with emitter resistor
(b)
Small-signal equivalent circuit
RC
RS
RE
R1 || R2
Vo
Vs
r Ib
Ri Ro
+
V_
Rib
+
Vin
_
Ib
C-E Amplifier with Emitter Resistor
74
Assume Early voltage is infinite, ro is neglected
Cbo RIV
Ebbbin RIIrIV
Eb
inib Rr
I
VR 1 ibi RRRR 21
s
Si
iin V
RR
RV
Si
i
E
Cv
sib
inC
s
Cb
s
ov
RR
R
Rr
RA
VR
VR
V
RI
V
VA
1
1
Si RR
rRE 1
EC
E
Cv
R
R
R
RA
1
1. ac output voltage
2. To find the small-signal voltage gain
3. Combining equations in (1) and (2)
If
and if
Cont
75
RS
R1
R2 RE
RC
vs
vO
CC
VCC
CE
B C
E
Vo
Vs RC
RS
r ro R1|| R2 gmV
CE provides a short circuit to
ground for the ac signals
C-E Amplifier with Emitter Bypass Capacitor
76
COMMON COLLECTOR AMPLIFIER
CC2
RC RB2 RB1
RL
CC1
vin
RS vout RE
collector common (to input & output)
COMMON COLLECTOR MODE
c
b
e
input base-collector
output emitter - collector
Prof. R T Kennedy
Common-Collector Amp. (CC)
RC
RE RB2
RB1
RL
CC1 CC2
vin
RS
vout
Basic CC Amplifier
77
vO
VCC
vS
CC
RE
RS
R1
R2
B C
E
RS
RE
R1||R2
ro r Ib
Vo
Vs Vin
V
+ +
+ -
-
-
Emitter-follower circuit Small-signal equivalent circuit
CC Amplifier Anlysis
78
bo II 1 Eobo RrIV 1
Eobin RrrIV 1
Eob
inib Rrr
I
VR 1
s
Si
iin V
RR
RV
Si
i
Eo
Eo
s
ov
RR
R
Rrr
Rr
V
VA
1
1
oE
S
o rRRRRr
R
1
21
C-C Amplifier
Another small-signal equivalent circuit
B
C
ERS
RE R1||R2 ro
r
Ib
Vo
Vs Vin
V + +
-
-
Ri Rib Ro
Ii
Ib
Io Ie
ibi RRRR 21
Cont
79
iei
I
IA
iib
bo IRRR
RRII
21
2111
o
Eo
oe I
Rr
rI
Eo
o
ibi
ei
Rr
r
RRR
RR
I
IA
21
211
If R1R2 Rib and ro RE then Ai (1+)
Current gain where
Cont
80
81
COMMON BASE AMPLIFIER
base common (to input & output)
COMMON BASE MODE
RC
RE RB2
RB1
RL CC1
CC2
RS vout
vin
CC2
RE
RB2 RB1 RL CC1
vin
vout RC RS
RS
RB2 RB1
CC2
RL RC
vout vin
CC1
Prof. R T Kennedy
Common-Base Amp. (CB)
vout
e
b
c
input emitter-base
output collector-base
Basic CB Amplifier
82
BCE
Vs
Vo
RS
RE RC RL r gmV
V
Ii Io
Ib
-
+
RE
RS
RB
RC RL
VCC VEE
CC2 CC1
vO
vS
CB
Common-base
circuit
Small-signal
equivalent
circuit
Ri = re Ro = RC Input resistance Output resistance
CB Amplifier Analysis
83
11
rgA mio
SE
S
LC
m
s
ov RR
r
R
RRg
V
VA
1
If RS approaches zero, then Av = gm(RC||RL)
Voltage gain
Current gain
If RE approaches infinity and RL approaches zero, then
E
LC
Cm
i
oi R
r
RR
Rg
I
IA
1
short-circuit
current gain
Cont
84
Summary of Two-Port Parameters
85
DC Analysis
TOPIC 6
86
Amplifier DC Equations
87
VCC
RC
RE RB2
RB1
VCC
RC
RE RB2
RB1
VCC
VCC
RC
RE
RBB
VBB
CCVBRBR
BRBBV
21
2
21
21
BRBR
BRBRBBR
Prof. R T Kennedy
88
GUSTAV ROBERT KIRCHOFF
1824-1887
VCC
RC
RE
RBB
VBB input loop
output loop
IB
IE
IE
VRE
VRC
IC
IB VBE
VRBB
VCE
IC
Prof. R T Kennedy
Cont
89
VCE
EBQCEQCCQCC
EECECCCC
RIVRIV
RIVRIV
)1(
CBE III
CCCEQCEsat VVV
VCC
RC
RE
RBB
VBB input loop
output loop
IB
IE
IE
VRE
VRC
IC
IB VBE
VRBB
IC
EBQBEonBBBQBB
EEBEBBBBB
RIVRIV
RIVRIV
)1(
Prof. R T Kennedy
Cont
90
Q POINT
FORWARD ACTIVE MODE
+ VCE 0
+ IC saturation
cut-off
ICQ
VCEQ
Prof. R T Kennedy
Q-Point
91
Q POINT LOCUS
FORWARD ACTIVE MODE
+ VCE 0
+ IC saturation
cut-off
ICQ
VCEQ
Q
CCV
LOCUS:
STRAIGHT LINE
DC LOAD LINE EC
CC
RR
V
EC RR
slope
1
Cmxy
VRR
VRR
I
RIVRIV
RIVRIV
CCEC
CEQEC
CQ
ECQCEQCCQCC
EECECCCC
11
assume ICQ=IE
Prof. R T Kennedy
Q-Point Locus
92
FORWARD ACTIVE MODE
+ VCE 0
+ IC saturation
cut-off
VCC
VCC
VCC
EC RRslopetcons
1tan
Prof. R T Kennedy
DC Load Line: Vcc Change
93
FORWARD ACTIVE MODE
+ VCE 0
+ IC saturation
cut-off
VCC
RC
RC
SLOPE CHANGES
Prof. R T Kennedy
DC Load Line: Rc Change
AC Analysis
TOPIC 7
94
4.1 Analog Signals & Linear Amplifiers
Signal- contains information -eg:sound waves Analog signal electrical signals are in the form of timevarying current & voltage such as o/p signal from compact disc, signal from microphone & ect. Analog circuits electronic circuits that process analog signal - example: linear amplifier magnifies an i/p signal to produce large o/p signal
Dc voltage
source
Signal
source Amp LOAD
Figure 4.1 Block diagram of a compact disc player system
* transistor is heart
of an amplifier
Analog Signal
95
DC biased transistor @ Q-pt ==> transistor biased in forward active region.
A time-varying signal (eg. Sinusoidal) is added / superimposed on dc input voltage (bottom ac)
Output = ac on left.
Linear amplifier - output follows input shape but with much larger amplitude; if output shape is different = distortion (measured as Total Harmonic Distortion, THD)
Circuit above functions as inverter - output is amplified but inverted by 1800
Traditionally-BJT is used as linear amplifier
Bipolar Linear Amplifier
96
Variable Meaning
iB, vBE Total instantaneous
values
IB, VBE DV values
ib, vbe Instantaneous ac
value
Ib, Vbe Phasor values
Summary of notation
Cont
97
98
Definition
Small signal : ac input signal voltages and
currents are in the order of 10 percent of Q-point voltages and currents.
e.g. If dc current is 10 mA, the ac current (peak-to-
peak) < 0.1 mA.
99
Rules for ac analysis
Replacing all capacitors by short circuits
Replacing all inductors by open circuits
Replacing dc voltage sources by ground connections
Replacing dc current sources by open circuits
RC
RE RB2
RB1
RL
CC1
CC2
vin(ac)
RS vout(ac)
VCC
ac analysis : replace DC source with internal impedance
Basic AC Analysis
100
101
RC
RB
vs
vO
vce
vbe
ic
ib +
+
-
-
AC equivalent circuit of C-E with npn transistor
AC Equivalent Circuit
102
beBbs vRiv
0 ceCc vRi
Input loop:
Output loop:
be
T
BQ
b vV
Ii
bc ii
0.026 V
Cont
103
Transconductance parameter
gm=ICQ/VT
r=VT/ICQ
Small-signal hybrid- equivalent circuit
104
ib(Ib )
Current gain parameter
Cont
105
RS
R1
R2 RE
RC
RL vs
vO
CC1
CC2
VCC
vO
vs R1 R2
RS
RE
RC RL
(a)
CE amplifier with emitter resistor
(b)
AC equivalent circuit
AC Operation
106
+ VCE 0
+ IC
ICQ
VCEQ
Q
CCV
EC
CC
RR
V
i
v
LC
CEQ
RR
Vi
)( LCCQ RRIv )( LCCQCEQoffcut RRIVv
LC
CEQCQcsat
RR
VIi
AC Load Line
4.2.1 Graphical Analysis & AC Equivalent Circuit
Fig 4.4 C-E transistor characteristics, dc load line, & Q-point
Graphical Analysis & AC Equavalent Circuit
107
Cont
108
Cont
IBQ IS
1 F
exp
VBEQ
VT
VBEQ VBEon
vBE VBEQ vbe
iB IS
1 Fexp
vBE
VT
This base current cannot written as an ac current superimposed on dc
quiescent value, unless.if then the exponential term can be expanded via Taylor series and keeping only LINEAR TERM which leads to
the SMALL SIGNAL approximation
vbe VT
iB IBQ 1vbe
VT
quiescent base current
109
Using the appropriate substitutions for the various voltages and currents,
and making the assumption that the ac signal source, vs=0 then we get a
term for the base-emitter loop when all dc terms are set to zero.
Similar re-arrangements will lead to an equation for the collector-emitter
loop, with all dc terms set to zero.
BOTH EQUATION RELATE THE AC PARAMETERS OF THE CIRCUIT
AND
HAVE BEEN OBTAINED BY SETTING ALL DC CURRENTS AND VOLTAGES
TO ZERO OR IN OTHER WORDS
DC VOLTAGE SOURCES = SHORT CIRCUITS
DC CURRENT SOURCES = OPEN CIRCUITS
THIS IS A DIRECT CONSEQUENCE OF SUPERPOSITION
Cont
110
Below is the ac equivalent circuit, due to the equations derived
previously.
All currents & voltages shown are time-varying signals.
Although this is an ac equivalent circuit = = > the implicit
assumption is that the transistor is appropriately forward-biased
vs
ib
ic
+
vbe
-
+
vce
-
RC
RB
+
-
Cont
111
Frequency Response
TOPIC 8
112
Midband
Gain falls of due to the
effects of CC and CE
Gain falls of due to the
effects of C and C
Amplifier gain vs frequency
113
Frequency response of an amplifier is the graph of its gain versus the frequency.
Cutoff frequencies : the frequencies at which the voltage gain equals 0.707 of its maximum value.
Midband : the band of frequencies between 10f1 and 0.1f2. The voltage gain is maximum.
Bandwidth : the band between upper and lower cutoff frequencies
Outside the midband, the voltage gain can be determined by these equations:
21 /1 ff
AA mid
22/1 ff
AA mid
Below midband Above midband
Definition
114
Gain-bandwidth product : constant value of the product of the voltage gain and the bandwidth.
Unity-gain frequency : the frequency at which the amplifiers gain is 1
BWAf midT
Cont
115
At low frequency range, the gain falloff due to coupling capacitors and bypass capacitors.
As signal frequency , the XC - no longer behave as short circuits.
Low Frequency
116
The gain falls off at high frequency end due to the internal capacitances of the transistor.
Transistors exhibit charge-storage phenomena that limit the speed and frequency of their operation.
Small capacitances exist between the
base and collector and between the
base and emitter. These effect the
frequency characteristics of the circuit.
C = Cbe ------ 2 pF ~ 50 pF
C = Cbc ------ 0.1 pF ~ 5 pF
High Frequency
117
Cob = Cbc Cib = Cbe
Output capacitance Input capacitance
Basic data sheet for the 2N2222 bipolar transistor
118
This theorem simplifies the analysis of feedback amplifiers.
The theorem states that if an impedance is connected between the input side and the output side of a voltage amplifier, this impedance can be replaced by two equivalent impedances, i.e. one connected across the input and the other connected across the output terminals.
Millers Theorem
119
Miller equivalent circuit Z
- A
I2 I1
V1 V2
A
Z
V
Z
AVI
VAV
Z
VVI
1
)1( 111
12
211
A
Z
VI
Z
AV
I
VAV
Z
VVI
11
11
22
2
2
12
122
Millers Theorem
120
- A
ZM2
ZM1V1 V2
A
ZZ
A
Z
I
V
A
Z
VI
M 11
11
11
2
2
2
22
A
ZZ
A
Z
I
V
A
Z
VI
M1
1
1
1
1
1
11
Cont
121
)1(
)1(
11
1
1
1
1
1
1
ACC
ACC
A
XX
A
ZZ
M
M
CCM
M
)1
1(
)1
1(
11
11
11
2
2
2
2
ACC
AC
C
A
XX
A
ZZ
M
M
CCM
M
- A
I2 I1
V1 V2
C
- A
CM2
CM1V1 V2
Miller Capacitance Effect
122
B C
E
r ro
C
V gmV C
-
+
C = Cbe C = Cbc
High-frequency hybrid- model
123
ACACC bcMi 11
AC
ACC bcMo
11
11
Miin CCC Moout CC
B C
E
r ro CMi gmV
C CMo
A : midband gain
High-frequency hybrid- model with Miller effect
124
BJT Design Example
TOPIC 9
125
C-E Amplifier - Design Example
126
Cont
127
128
Cont
129
Cont
130
Cont
131
Cont
132
Cont
REFERENCES
Donald A. Neamen, Electronic Circuit Analysis & Design, 2nd Ed., McGraw Hill International Edition, 2001 (ISBN 0-07-118176-8)
Adel S. Sedra, Kenneth C. Smith, Microelectronic Circuits, 5th Ed., Oxford University Press (ISBN 0-19-514252-7)
Thomas L. Floyd, Electronic devices: Conventional Current Version, 7th Ed., Prentice Hall (ISBN 0-13-127827-4)
133
ACKNOWLEDGEMENT
Prof. R.T Kaneddy, UniMAP
Assoc. Prof. Basir Saibon, UniKL
134