Upload
others
View
3
Download
0
Embed Size (px)
Citation preview
전자회로전자회로Ch5 Bipolar Amplifiers
김 영 석
충북대학교 전자정보대학
2012.3.1
E il ki @ b kEmail: [email protected]
Ch5-1
Ch5 Bipolar Amplifiers
5.1 General Considerations
5.2 Operating Point Analysis and Design p g y g
5.3 Bipolar Amplifier Topologies
5.4 Summary and Additional Examples
Ch5-2
5.1 General Considerations: Voltage Amplifier
To be Vout=Av*Vm Rin= Rout=0 (Ideal Voltage Amplifier)To be Vout=Av*Vm, Rin=∞, Rout=0 (Ideal Voltage Amplifier)
Ch5-3
Input/Output Impedances
V=0(Short)I=0(Open)
V
x
xx i
VR =
The figure above shows the techniques of measuring input d t t i d
Ch5-4
and output impedances.
(소신호) 이득, 저항(Impedance) 개념
중요한 개념이니 꼭 기억할 것.
이득은 소신호 입력 전압에 대한 소신호 출력 전압의 비율임
입출력저항(Impdeances)은 소신호 전류에 대한 소신호 전압의 비율임입출력저항(Impdeances)은 소신호 전류에 대한 소신호 전압의 비율임
대신호 혹은 DC 전류, 전압이 아님
예:예
inININoutOUTOUTinININ
acDCiIivVvvVv
+=
+=+=+=
성분소신호성분신호 )( ,,
in
out
IN
OUTv v
vv
vA
acC
=∂∂
==이득소신호
성분소신호성분신호
)(
)(
in
in
IN
INin
inIN
iv
ivR =∂∂
==입력저항소신호)(
Ch5-5
Impedance at Base
vR πrivR
x
xbase ==
When calculating input/output impedance, small-signalanalysis is assumed.
Ch5-6
Impedance at Collector
rR = ocollector rR =
With Early effect, the impedance seen at the collector is equal to the intrinsic output impedance of the transistor
Ch5-7
(if emitter is grounded).
Impedance at Emitter
)(1 ,11
∞=≈= oemitterx rRv )(,1
+o
memitter
mx g
rgi
π
The impedance seen at the emitter of a transistor is approximately equal to one over its transconductance (if th b i d d)
Ch5-8
the base is grounded).
Three Master Rules of Transistor Impedances
Rule # 1: looking into the base, the impedance is rπ ifemitter is (ac) grounded.Rule # 2: looking into the collector the impedance is r ifRule # 2: looking into the collector, the impedance is ro if emitter is (ac) grounded.Rule # 3: looking into the emitter, the impedance is 1/gmif base is (ac) grounded and Early effect is neglected.
Ch5-9
s s ( ) g y s g
DC Analysis vs. Small-Signal Analysis
First, DC analysis is performed to determine operating point and obtain small-signal parametersand obtain small-signal parameters.
Second, sources are set to zero and small-signal model is used.
Ch5-10
5.2 Operating Point (DC) Analysis and Design: Biasing with Base Resistor
),(, CCB
BECCC
B
BECCB Vf
RVVI
RVVI ββ =
−=
−=
Assuming a constant value for VBE,=0.7V, one can solve for d d d fboth IB and IC and determine the terminal voltages of the
transistor.
However, bias point is sensitive to β variations.
Ch5-11
β
5.2.2 Resistive Divider Biasing (Improved)
21
2CCX
VR
VRR
RV+
=
)()exp(21
2CC
T
CCSC Vf
VV
RRRII =+
=
Using resistor divider to set VBE, it is possible to produce an IC that is relatively independent of β if base current is
Ch5-12
small.
Accounting for Base Current
⎞⎛⎟⎠
⎞⎜⎝
⎛ −=
T
ThevBThevSC V
RIVII exp
With proper ratio of R1 and R2, IC can be insensitive to β; however, its exponential dependence on resistor d i ti k it l f l
Ch5-13
deviations makes it less useful.
5.2.3 Emitter Degeneration Biasing (Good)
The presence of RE helps to absorb the error in VX so VBE stays relatively constantrelatively constant.
This bias technique is less sensitive to β (I1 >> IB) and VBE
variations.
Ch5-14
Emitter Degeneration: Design Procedure
Choose an IC to provide the necessary small signal parameters, g , r , etc.parameters, gm, rπ, etc.
Considering the variations of R1 R2 and VBE chooseConsidering the variations of R1, R2, and VBE, choose a value for VRE.
With VRE chosen, and VBE calculated, Vx can be determined.
Select R1 and R2 to provide Vx.
Ch5-15
5.2.4 Self-Biasing Technique
BECCBECCC
BEBBBCCCC
VVVVI
VIRIIRV−
≈−
=
+++= )(
BC
CBCC
RR
RRRI
>>
≈++
)1(
/)/11(
β
ββ
Thi bi t h i tili th ll t lt t id th
BECCBE VVV −<<Δ )2(β
This bias technique utilizes the collector voltage to provide the necessary Vx and IB.
VC > VB, thus guaranteeing active operation of the transistor.
(1) id i iti it t(1) provides insensitivity to β .
(2) provides insensitivity to variation in VBE
이 절에서 언급된 모든 바이어스 회로는 Discrete 회로 구성시에 사용함
IC에서는 저항은 사용(면적 증가)하지 않고 TR로만 구성된 바이어스 회로(Current Mirror) 사용함
Ch5-16
5.3 Bipolar Amplifier Topologies
C E itt : ( )(d)Common Emitter: (a)(d)
Common Base: (b)(d)
Common Collector: (a)(e)
Ch5-17
Common Collector: (a)(e)
5.3.1 Common-Emitter(CE) Amplifier
))(||( moCout vgrRv −= π
)||( oCmi
outv rRg
vvA −==
)||( , oCoutin
in
rRRrRv
== π
Ch5-18
Emitter Degenerated CE Stage
By inserting a resistor in series with the emitter, we “degenerate” the CE stage.
Degeneration=Negative Feedback: Vin↑=>IC↑=>RE*IC↑=VBE↓=> IC↓Degeneration=Negative Feedback: Vin↑=>IC↑=>RE IC↑=VBE↓=> IC↓
This topology will decrease the gain of the amplifier but improve other aspects, such as linearity, and input impedance.
Ch5-19
Emitter Degenerated CE Stage
),(: minminEininin rgirgiRirvR =++= πππ β
00)(
)1(Ein
inin
vRR
RrivR ++==∴
π
π β
0,0)(:
Cx
out
mEinout
RivR
vvgr
RvvR
==∴
=∴=++= πππ
ππ
)/1 ( 1)( EmE
C
E
CCm
in
out
inv
x
RgifRR
R
RRgRr
vv
vvA
i
<<≈+
−≈−== π
π
π
Emg
Av,CE=-(Collector Resistance)/(Emitter Resistance)=-RC/(1/gm+RE)
Ch5-20
Ex1: Emitter Degenerated CE Stage
Cv
R
rRA −= 2
1|| π
Em
Rg
+1
Ch5-21
Ex2: Degenerated CE Stage with RB
CmEB
out
inin
outv Rg
RrRr
vv
vv
vvA −
+++=== )(
)1(.
βπ
π
π
π
Ein
oA
RrRrV
++=∞=∞=
)1()(
1 βπ
EB
C
RRR
++
−≈ 1
βCout
EBin
Ein
RRRrRR
=+++= )1(22
1
βπ
π
Emgβ
Ch5-22
Output Impedance of Degenerated Stage with VA<∞
)||( xEp iRrvv ππ =−=
)||)(1( ))(1()(
xEOmxo
Omxomxox
iRrrgirvrgirvvgirv
π
πππ
++=−++=−−=
Emitter degeneration boosts the output impedance by a
)||)(1( EOmOout
xEOmxo
RrrgrR π
π
++=∴
Emitter degeneration boosts the output impedance by a factor of 1+gm(RE||rπ).
This improves the gain of the amplifier and makes the circuit a better current source
Ch5-23
circuit a better current source.
Complete CE Stage
π== outxoutv
vvvvA
)]||([)1()]1([||||
)]1([|||| 21
βββ ππ
π
−+++++
++= LCm
E
xininv
RRgRr
rRrRRR
RrRRvvvv
)])1([|| (1||
)1()]1([||||
21
21
β
ββ
π
ππ
++>>−
≈
+++++
ELC
EES
RrRRifRRR
RrRrRRR
1β
++ Em
s Rg
R
Ch5-24
5.3.2 Common Base (CB) Amplifier
oCoutin
oCmv
rRRR
rRgA
||,1)||(
==
+=
oCoutm
in g||
)||(),||( ,, oCmCBvoCmCEv rRgArRgAthatNote +=−=
Ch5-25
CB Stage with Source Resistance
outxoutv
vvvA ==
oCmmS
m
xininv
rRggR
gvvv
)]||([/1
/1 +
=
mS
C
gR
R1
+≈
)||)(1( πrRrgrR Somoout ++=
Ch5-26
CB Stage with RB
)0(1
1β
=+
+= oB
min rR
gR
)(π
π
π
π
++== Cm
BinE
inout
ein
e
in
out
R
RgRr
rRR
Rvv
vv
vv
vv
)1/(/1
β+++≈
BmE
C
RgRR
)](||[)( xBEmxox iRrRvgirv ++−= ππ
)](||[
)](||[)(
BxBE
xBEmxox
RrriRrRv
g
+−
+=π
πππ
ππ
)](||)[/1
1(1 BEB
omo
x
xout RrR
rRrgr
ivR +
+++== π
π
Ch5-27
Input Impedance Seen at Emitter and Base
Ch5-28
5.3.3 Emitter Follower (Common Collector Amplifier)
When the input is increased by ΔV, output is also increased by an amount that is less than ΔV due to the increase in collector current and hence the increase in potential drop across RE.
However the absolute values of input and output differ by a VBE.
Ch5-29
Emitter Follower
∞=AV
)(
||1),1( Em
outEin Rg
RRrR =++=
β
βπ
)/1( 1/1)1(
)1(Em
Em
E
E
E
in
out RgRg
RRr
Rvv
<<≈+
≈++
+=
ββ
π
Ch5-30
Emitter Follower with Source Resistance
∞=AV
Ein RrR ++= )1( βπ
Em
Sout
Ein
Rg
RR ++
= ||)11
(
)(
β
βπ
S
E
in
out
m
RRR
vv
g
++= 1
β
Em
Sin Rg
+++1β
Ch5-31
Emitter Follower with Early Effect
OES
OEv
rRg
RrRA
||11
||
+++
=
β( )( )OEin
m
R
rRrRg
1
||11
⎟⎞
⎜⎛
++=+
ββ
π
OEm
sout rR
gRR ||||1
1 ⎟⎟⎠
⎞⎜⎜⎝
⎛+
+=
β
Ch5-32
Amplifier Example I
)]1([|| β++ rRrRvvvv
)])1([(||
)]||([)1()]1([||
)]1([||
21
21
1
β
βββ
π
π
π
π
π
π −+++++
++==
C
CmEES
Eout
bin
b
in
out
fRRR
RRgRr
rRrRR
RrRvv
vv
vv
vv
)])1([(1|| 1
2
1
1 βπ ++<<+
⋅+
−≈ E
Em
C
S
RrRifR
g
RRRR
R
Ch5-33
Amplifier Example II
)()1()]1([||
)]1([|| 21
βββ πππ −
++== Rg
Rr
RRRRrRvvvv
Cmoutbout
)])1([ (1
)()1()]1([||
211
221
β
ββ
π
πππ
++<<⋅+
−≈
+++++
RrRifRRR
R
gRrRrRRvvvv
C
CmSbinin
12
1 ++ Rg
RRm
S
Ch5-34
Amplifier Example III
1 R
211
1
2 11
i
meq
rRrR
Rg
R
++=+
+=β
1
211
11C
v
in
RRA
rRrR
++
−=
++ ππ
Ch5-3521 1 mm gg
++
+β
Amplifier Example IV
Cv
R
RRA 1|| 1=
mS g
R +
Ch5-36
Amplifier Example V
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛+
++
+=+
+=βββ 1
1||1
111
1
211
SE
eqin
Rg
Rg
Rg
R⎦⎣ ⎠⎝ +++ βββ 111 211 mmm ggg
Ch5-37
Amplifier Example VI
OEOEoutbout rRRrRRrRvvv )1)(||||()]1)(||||([|| 2211 +++==
ββπ
OE
OEOESbinin
RR
rRRRR
RrRRrrRRrRRvvv
||||1||||
)1)(||||()]1)(||||([||
21
21211
+≈
+++++ ββ ππ
RR ||1 ⎞⎛
OEm
S rRRg
RR ||||12
1
1 ++
OES
mout rRRRR
gR ||||||
1||1
21⎟⎟⎠
⎞⎜⎜⎝
⎛+
+=β
Ch5-38
Amplifier Example VII
( )( )1 11 +++= βπ eqEin RRrR
( )1
11 1
21 ⎟⎟
⎠
⎞⎜⎜⎝
⎛+
++++=β
βπB
mE
Rg
Rr
1 2
2
++=
+=
B
eqCout
RR
RRR
11
2
1
++
+++=β
B
mC
RR
gR
111
11
1
+++
+++
−=
β
βB
E
mC
v RR
gR
A
123 +βmE
m gg
Ch5-39
Summary
ImpedancesImpedances
Ch5-40
Summary
BJT AmplifiersBJT Amplifiers
)||( rRgA )||(RA + ERA =
)||(
)||(
in
oCmv
rRRrR
rRgA
==−=
π 1)||(
in
oCmv
gR
rRgA
=
+≈
)1(/1
Ein
Emv
RrRRg
A
++=+
=
βπ)||( oCout rRR =)||( oCout
m
rRRg
= )||1( Em
out Rg
R =
Ch5-41