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Chapter 16
Analog Integrated Circuits
Microelectronic Circuit Design
Richard C. Jaeger
Travis N. Blalock
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Chapter Goals
Understand bipolar and MOS current mirror operation and mirror ratio errors.
Explore high output resistance current sources including cascode and Wilson
current sources.
Design current sources for both discrete and integrated applications.
Study reference current circuits such as VBE-based reference, bandgapreference and Widlar current source.
Use current mirrors as active loads in differential amplifiers to increase
voltage gain of single-stage amplifiers.
Study effects of device mismatch on amplifier performance.
Analyze design of classic mA741 op amp.
Study realization of four-quadrant analog multipliers with large input signal
range.
Increase understanding of SPICE simulation techniques.
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MOS Current Mirrors: DC Analysis
MOSFETsM1 andM2 are
assumed to have identical VTN,
Kn, l, and W/L ratios.
IREFprovides operating bias to
mirror.
VDS1 = VGS1= VGS2 =VGS
)1(1 DS1
Vn
KREF
2I
TNV
GS1V
l
DS2V
TNV
GS2Vn
K
D2I
OI l1
2
2
REFI
DS1VDS2
V
REFIOI
l
l
1
1
However, due to mismatches, VDS1 is
not equal to VDS2 and there is slightmismatch between output and
reference currents. Mirror ratio is:
DS1V
DS2V
REFI
OI
l
l
1
1MR
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MOS Current Mirror (Example)
Problem:Calculate output current for given current mirror.
Given data:IREF= 150 mA, VSS = 10 V, VTN= 1 V, Kn = 250 mA/V2, l=
0.0133 V-1
Analysis: (1+ lVDS1) term is neglected to simplify dc bias calculation.
V10.2
2V
A250
)A150(2V1211
nK
REFITN
VGS
VDS
V
A165
V)10.2(V
0133.01
V)10(V
0133.01
)A150(
OI
Actual currents are found to be mismatched by approximately 10%.
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MOS Current Mirrors: Changing Mirror
Ratio
Mirror ratio can be changed bymodifying W/L ratios of the two
transistors forming the mirror.
11
LW'nKn
K22
LW'nKn
K
DS1V
L
W
DS2V
LW
REFI
DS1V
n1K
DS2V
n2K
REFI
OI
l
l
l
l
11
12
1
1
DS1V
L
W
DS2V
L
W
l
l
11
1
2MR
In given current mirror,Io =5IREF. Again
mismatch in VDScauses error in MR.
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Bipolar Current Mirrors: DC Analysis
BJTs Q1 and Q2 are assumed to
have identicalIS, VA,bFO, and
W/L ratios.
Io =IC2, IREF=IC1 +IB1 +
IB2
VBE1= VBE2 =VBE
FOAV
CE2V
AV
CE2V
REFI
OI
b
21
)/(1
Finite current gain of BJT causes slight
mismatch betweenIo andIREF.
)/2(11MRFOREF
IOI
b
AVCE
V
TVBE
V
SI
CI 11exp1
AV
CEV
TVBE
V
SI
CI 21exp2
AVCE
V
FOF11
1bb
AVCE
V
FOF21
2bb
TVBEV
FO
SI
BI exp1 b
T
VBEV
FO
SIBI exp1 b
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Current Mirror (Example)
Problem:Calculate and compare mirror ratios for BJT and MOS current
mirror.
Given data:IREF= 150 mA, VGS = 2 V, VDS2 = VCE2 = 10 V, l= 0.02 V-1
VA = 50 V,bFO = 100, VSS = 10 V,M1 =M2, Q1 = Q2.
Analysis:
15.1
1
1
MOSMR
DS1V
DS2V
l
l
16.1
21
)/(1
BJT
MR
FOAVCE2V
AV
CE2V
b
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Bipolar Current Mirrors: Changing Mirror
Ratio
Mirror ratio can be changed by
modifying the emitter area of the
transistor.
A
EA
SOI
SI
Emitter area scaling changes thetransport equations using which,
Ideally, MR= n, but for finite gain,
FO
n
AV
CE2V
AV
CE2V
REFnI
OI
b
11
)/(1
E1A
E2A
n
FO
n1
n
b
MR
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Multiple Current Sources
Reference current enters diode-
connected transistorM1 establishing
gate-source voltage to biasM2 through
M5, each with different W/L ratio.
Absence of current gain defect permitslarge number of MOSFETs to be
driven by one reference transistor.
Similar multiple bipolar sources can
be built from one reference BJT.
As base current error term worsenswhen more BJTs are added, umber of
outputs of basic bipolar mirror are
limited.
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Buffered Bipolar Current Mirror
When large mirror ratio is used or
if many source currents are
generated from one reference BJT,
current gain defect worsens.
Current gain ofQ3 is used to
reduce base current that is
subtracted from reference current.
Assuming infinite Early voltage for simplicity,
FO3FO1
CI
n
REFI
B3I
REFI
C1I
b
b
1
1)1(
)1(
)1(1
1
FO3FO1
nREFnI
C1In
OI
bb
Thus error term in denominator is
reduced.
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Output Resistance of Current Mirrors
For diode connected BJT, from
small-signal model,
mgR
gogmg
1
i
v
v)(i
...Ifboand mF>>1
This simplifies the ac model of
the current mirror. Similar
analysis applies to MOSFET
current mirror except that the
current gain is infinite. Thus
orA2V
CSV
or
outR
2
2CS
Vl
1
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Two-port Model for Current Mirror
Since current mirror has acurrent input and current
output, we use h-parameters.
2
v
221
i
212
i2
v121
i111
v
hh
hh
n
mgm
g
rm
g
rm
gh
mgg
mg
h
1
2
211
22
02v1
i2i
21
1
1
21
1
02
v1i1v
11
For MOS current mirrors,
00
1i2
v1v
12
h
2
1
01i2
v2i
22
or
h
1
111
m
gh 0
12h
n
mgm
gh
1
221
2
122
or
h
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Bipolar Widlar Current Source
R in Widlar source allows
adjustment of mirror ratio.
1
ln
1
1ln
1 SI
REFI
T
V
SI
REFI
T
V
BE
V
2
ln
2
1ln2
SIO
I
TV
SIO
I
TV
BEV
Current throughR is given by:
If transistors are matched,
Typically 1
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PTAT Voltage
Voltage developed acrossR in Widlar current source is directly
proportional to absolute temperature.
Example: T= 300 K,IC1
=IC2
andAE2
= 10AE1
. Then =59.6 mV with
temperature coefficient of slightly< +0.2 mV/K
PTAT voltage combined with A-D converter is the core of electronic
thermometers.
T
V
EAE
A
CIC
I
qk
T
V
EAE
A
CIC
I
qkT
EAE
A
CIC
I
TV
BEV
BEVV
PTAT
1
2
2
1lnPTAT
1
2
2
1ln
1
2
2
1ln21PTAT
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MOS Widlar Current Source
IfIO is known,IREFcan be directly
calculated. IfIREF,R and W/L ratios are
known, we can write a quadratic
equation in terms of
Small-signal model for MOS Widlar
source represents a C-S stage with
resistorR in its source.
Current throughR is given by:
2)/(1)/(
1
1
21
2
2
1
2
21
LW
LW
REFI
OI
nKREF
I
R
R
nK
OI
nKREF
I
R
GSV
GSV
O
I
2)/(1)/(
11
21LW
LW
REFI
OI
nK
REFIR
REFI
OI
Rm
gor
outR
21
2
REFI
OI /
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MOS Wilson Current Source
During operation, all
transistors are in active
region.ID2 =IREF, ID3 =ID1
= IO, VGS3 = VGS1=VGS
GS
V
GSV
DI
D2I
l
l
1
21
1 GS
V
GSV
REFI
OI
l
l
1
21
1
2
nKREFI
TNV
GSV
where
1v3gsv3xi
1v
3vxv
ormg
From small-signal model,
322
1223xi
xv
orffforoutR mmm
)1v
2(
1
xi
1v
2vgsv f
mg
m
3
2
l
mf
CSV
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Bipolar Wilson Current Source
During operation, all transistors are
in active region. But some current is
lost at base ofQ3 and current gain
error is formed by Q1 and Q2.
IREF= IC2 +IB3
VCE1 = VBE VCE2 = 2VBE2
33 or
oout
Rb
2A
VoCS
Vb
AVBE
2V
FOFO
AV
BEV
REFI
OI
)2(
21
)/(1
bb
Addition of extra BJT can balance thecircuit and reduce errors due to mismatch.
VCE2 = VBE+VBE3 -VBE4
= VBE
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MOS Cascode Current Source
ID1 =ID3 =IREF AlsoIO =ID4 =ID2. So currentmirror forces output current to be approximately
equal to the reference current. If all transistors are
matched with equal W/L ratios,
VDS2 = VGS1+ VGS3 -VGS4 = VGS= VDS1
From the small-signal model,
24241
4 or
for
mg
or
outR m
4
4
2
4l
m
l
mff
CSV
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Bipolar Cascode Current Source
IC1 =IC3 =IREF AlsoIO =IC4 =IC2. So current
mirror forces output current to be approximately
equal to the reference current. If all transistors are
matched,
VCE2 = VBE1+ VBE3 -VBE4 = VGS= VCE1
From the small-signal model,
244 oro
outRb
2
44 AVoCS
Vb
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Electronic Current Source Design
ExampleProblem: Design IC current source to meet given specifications.
Given data:IREF= 25 mA, VSS = 20 V, l= 0.02 V-1,VTN = 0.75 V,Kn= 50
mA/V2,VA = 50 V,bFO = 100,ISO = 0.5 fA
Analysis: MR
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Reference Current Generation
Reference current is required by all current mirrors. When resistor is used, sources output current is directly
proportional to VEE.
Gate-source voltages of MOSFETs can be large andseveral MOS devices can be connected in series between
supplies to eliminate large resistors.
VDD + VSS= VSG4+ VGS3 + VGS1 and ID3 =ID1= I4
Change in supply directly alters gate-source voltage of
MOSFETs and the reference current. BJTs cant similarly be connected in series due to small
fixed voltage developed across each diode and
exponential relation between voltage and current.
RBE
VEE
V
REFI
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Supply-Independent Biasing: JFET
Constant Reference Current Source P-channel JFETs can be used to set a
fixed reference current.
JFET is operating with VSG=0 and thus
ID=IDSS, assuming that VSD is large
enough to pinch-off the JFET.
Depletion-mode MOSFETs can be used
in similar manner.
Since both these methods require special
IC processes, other methods are
preferred.
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Supply-Independent Biasing: VBE-based
Reference and Widlar Current Source
Output current is determined by
base-emitter voltage ofQ1 . For
high current gain,
1
V4.1
1
211 R
EEV
RBE
VBE
VEE
V
CI
11
V4.1ln
2
2
V7.0
2
11
2
1222
RS
IEEV
RT
V
OI
RRBEV
BI
RBEV
FEI
FOI
Output current is now logarithmically
dependent on supply voltage. However, it is
temperature dependent due to temperature
coefficients of both VBEandR.
Widlar source also achieves similar supplyindependence of output current.
1
2ln2
EAE
A
OIREF
I
RT
V
EI
FOI
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Variation of Reference Cell Current with
Power Supply Fluctuations
R is absorbed into transistor model in
simplified small-signal circuit model.
EEVCCVxv or SSVDDVxv
2v'
21v)'
21(xi o
gm
gm
g
)2
vxv(4i
mgUsing
Determinant of these nodal equations is:
2
v
4xv)
31
(xv)
34
(
m
ng
o
g
m
g
o
g
m
ng
2
v
4xv)
31
(xv)
34
(
m
ng
o
g
m
g
o
g
m
ng
2)v'
24(
1v'
2xv4 o
gm
gm
gm
g
32
1
'
2141
Fm
g
Om
gm
g
n-mgmg m
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Variation of Reference Cell Current with
Power Supply Fluctuations (contd.)
xv)'23
(41
v
f
ogmgOo
ngm
gm
gm
xv2
1
'21
412v
f
mgO
mgm
gn
mg
mg
m
1
'211
'2
1
'21
3
xixv
mgmgn
nor
mgm
gor
outR 1
1
'2
m
gm
g
nfor .This is important
for stability. Because of positive
feedback, overall output resistance
is reduced.
Output resistances of the Widlar source and current mirror, ro2and ro3determine sensitivity to power supply variations. To improve output resistance
of Widlar portion , cascode sources can be used and Wilson sources can be
used to improve output resistance of current mirror.
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Reference Current Design Example
Problem: Design supply-independent current source to meet givenspecifications.
Given data: output current= 45 mA,T=300 K, total current
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Bandgap Reference
To make the voltage reference
temperature independent,
negative temperature coefficient
of base-emitter junction can be
canceled by positive
temperature coefficient of
scaled PTAT voltage.
PTATGV
BEV
BGV
To have zero temperature coefficient,
VGO is silicon bandgap voltage at 0K (1.12
V)
BEV
TV
GOV
PTATGV
TPTAT
VG
T
TV
GOV
BEV
TPTATVG
TBEV
TBGV
3
03
TV
GOV
BGV 3
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Bandgap Reference Circuit Realization
1
2ln
1
221E
AE
A
TVR
R
BEVBGV
PTATV
BEV
TV
GOV
TPTATV
TBEV
R
R
2
31
2
1
1
2
Circuit gain G =2R2 /R1.
Voltages other than1.2 V can be obtained
by a adding resistive
voltage divider.
BG
V
R
R
O
V
3
41
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Bandgap Reference Example
Problem: Design bandgap reference to meet given specifications.Given data: VO = 5 V,T=320 K, collector current= 25 mA,IS= 0.5 fA.
Assumptions:VA is infinite,bFO is infinite,AE2 =10AE1, drop across R =2 V.
Analysis:
W
k539.2A25mV47.63PTAT
1
mV47.63mV)ln(10)57.27(1
2
2
1lnPTAT
mEI
VR
EA
EA
CI
CI
q
kTV
V6792.0
1
1lnTBE1
SIC
I
VV
124.42
3
1
2
PTATV
BEV
TV
GOV
R
R
W k47.101
124.42
RR
V203.1
1
221
PTAT
VR
RBE
VBG
V
157.31
3
4
BGV
OV
R
R
k24
33 I
BGVR k9.75
34
IBG
VO
VR
W k80A25
V2m
R
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CMOS Differential Amplifier with
Active Load: DC Analysis
ID3 =ID1= ID2 =ID4 =IDSS/2.
Mirror ratio is set byM3 andM4 and is exactlyunity when VSD4 = VSD3 and thus VSD1 = VSD2.
Differential amplifier is completely balanced at
dc when:
TP
V
pKSS
I
DDV
SDV
DDV
OV
4
TPV
pKSS
I
SGV
SDV
DDVpKSS
I
nKSS
I
TPVTNVDDVDSV
33
1
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CMOS Differential Amplifier with Active
Load: Differential-Mode Signal Analysis
The differential amplifier can be
represented by its Norton equivalent.
Total short circuit output current:
idv
22id
v22oi m
gmg
Thevenin equivalent output resistance:
Differential-mode voltage gain:
42 or
or
thR
2
242
for
or
m2g
thRscidm
Am
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CMOS Differential Amplifier with
Active Load: Output Resistance
AssumeRSS>>1/gm1.
Resistance looking into drain ofM2 (C-G transistor) is:
22
1
1
21
221
2 or
mgm
gor
SR
mg
or
o2R
Drain current ofM2 (vx/2ro2)is replicated by
current mirror as drain current ofM4. Total
current from source is 2(vx/2ro2)= vx/ro2.
Total current is:
Output resistance is:
4
xv
2
xv
iTx
or
or
42 or
or
odR
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CMOS Differential Amplifier with Active
Load: Common-Mode Signal Analysis
From small-signal equivalent:
where it is assumed thatgm4 =gm3 and Goc
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CMOS Differential Amplifier with Active
Load: CMRR and Mismatch Contribution
SSR
mg
for
or
SSRmgf
cmAdmA
232
/3
1
232CMRR mm
forro3 = ro2.
With mismatched transistors, assuming
vd1=0 and gate-sourcevoltages are equal,
With vgs= vic- vs, vd1=0 and vd2=0,
svoggsvmgdi
disci 21
icv
icv
SSRmgSS
Rmg
sv
21
2
ic
v
fSSRmgic
v
SSRmg
SSRog
gs
v
m
1
2
1
21
21
fog
og
fSSRmgmg
mg
or
ormg
cmA
dmAcmA
mm
11
2
1
42
1-CMRR
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Bipolar Differential Amplifier with
Active Load: DC Analysis
IC3 =IC1= IC2 =IC4 =IEE/2.
IfbFO is very large, currentmirror ratio is set by Q3 and
Q4 and is exactly 1 when VEC4
= VEC3=VEB.
EBV
CCV
OV
CCV
BEV
EBV
CCV
EV
CV
CEV
CEV )()(
21
Differential amplifier is completely balanced at dc when:
Current gain defect in current mirror upsets dc balance.
As longs as BJTs are in forward-active region, VEC4
adjusts to make up for current-gain defect.
AsIC2 =IC4 andIC2=IC1, MR must be
1.
FO4AVCE
V
AV
CE4V
C1I
C4I
b
21
)/(1
FO4A
V
EBVEC4V b
2
This causes an equivalentinput offset voltage of
ddA
EBV
EC4V
ddA
EC3V
EC4V
OSV
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Bipolar Differential Amplifier with Active
Load: Differential-Mode Signal Analysis
To eliminate offset error, buffered
current mirror active load is used.
Total short circuit output current:
idv
22id
v22sci m
gmg
Thevenin equivalentoutput resistance:
Differential-mode voltage gain:42 o
ror
thR
LRm2gLRororm2gdm
vth
RL
Rsci
dmA
42
With added stages,
output resistance of
differential input
stage is:
5542 rrororeqR
5/
25
2
CI
CI
o
eqRmg
dmA
b
Chap 16 - 37
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Bipolar Differential Amplifier with Active
Load: Common-Mode Signal Analysis
oroEERicv
CR ic
vccA
oci b12 1
EE
Rorof2
icv
or
mgEE
Roroicvsci 2
11
)2
2(3
12112
bmb
From small-signal equivalent:
1
22
1
2
1
3
2
/
2CMRR
EER
mg
fooicv
thRsci
thR
mg
mbb
EE
Rorooicvsci 2
112bb
Current forced in differential output resistance
is doubled due to current mirror action.
Due to mismatches,
fog
og
fSSR
mgg
g
mg
mg
mm
11
2
11-CMRR
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Jaeger/Blalock7/1/03 Microelectronic Circuit DesignMcGraw-Hill
Active Loads in Op Amps: Voltage Gain
2
5)52
(2
))10
(5
(52
2
2)
42
(
21f
or
or
mg
or
GGR
or
mg
vtA
f
o
r
o
r
m
g
vt
A
m
m
4
52
21)1(
21bvov
avbv
idvav
ff
vtA
vtA
vtA
vtA
dmA
mm
Gain of output stage is approximately 1.
If Wilson stage is used in first-stage activeload,Avt1 = mf2. If current sourceM10 is
replaced by a Wilson or cascode source,
Avt2 = mf5.Overall gain can be raised to:
52 ffdm
A mm
Chap 16 - 39
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Active Loads in Op Amps: DC Design
Considerations
When op amp with active load is
operated in closed-loop configuration,
ID5 =I2, the output current of source
M10.
For minimum offset voltage, (W/L)5
must be such that VSG5 = VSD4 = VSG3
precisely setsID5 =I2 and accounts for
VDSand ldifferences betweenM5 and
M10.
RGG, (W/L)6 and (W/L)7 determine
quiescent current in class-AB output
stage.
VGS11 can be used to bias output stage
in place ofRGG.
Chap 16 - 40
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CMOS Op Amp Analysis
Problem: Find small-signal characteristics of given CMOS op amp.
Given data:IREF= 100 mA, VDD = VSS = 5 V, VTN= 1 V, VTP= -0.75 V,
Kn= 25 mA/V2,Kp= 10 mA/V
2, l= 0.0125 V-1
Analysis:A100
12
REF
I/2I
D
I
A200225
REFII
DI
000,16
5
52
5
1
2
22
2
141
4
52
DI
pK
DI
nK
ffdm
A
ll
mm
ic
Rid
R
V54.2
11
112
1111
n
KD
I
TNV
GSV
AsID6=ID7, VGS6= VSG7 = VGS11/2
A7.33
2)V75.0V27.1(2V
A
2
25067
DI
DI
S4103.167
mgmg
W k85.3
7
1
6
1
mg
mgout
R
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Bipolar Op Amps
Q1 to Q4 form differential input
stage with active load.
First stage is followed by high-
gain C-E amplifier, Q5 and its
current source load, Q8.
Load resistance is driven by class-AB output stage formed by Q6 and
Q7 , biased byI2 and diodes Q11
and Q12.
2
55
5
225
5555
2
)1()16
(85252
321
fo
CIC
Ior
mgr
mg
mgm
g
LR
oor
or
mgr
mg
vt
A
vt
A
vt
A
dm
A
mb
b
Chap 16 - 42
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Bipolar Op Amps with Improved
Voltage Gain
To improve gain, 2-transistor Darlington circuit
with current gain ofbo1bo2, amplification factormf2 /4, output resistance ro2 /2 and input
resistance 2bo1 r2,is used to replace Q5. It
requires emitter-base bias of 2VEB.
Buffered current mirror maintains dcbalance at collectors ofQ3 and Q4.
2
7)
1437
2(
27
2
2
23.0)
76
2
2
2(
21f
oro
rm
g
vtA
f
r
o
or
m
g
vt
A
m
m
b
UsingI2 =2I1,bo=50, VA=60 V,
VCE= 15 V,
51015.422
72
321
ff
vtA
vtA
vtA
dmA
mm
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Jaeger/Blalock
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Microelectronic Circuit Design
McGraw-Hill
Input Stage Breakdown in Bipolar Op
Amps
Input stage of bipolar op amp has no
overvoltage protection and can easily be
destroyed by large input voltage
differences due to fault conditions or
unavoidable transients, such as slew-rate
limited recovery.
In worst-case fault condition, B-E junction
ofQ1 is forward-biased and that ofQ2 is
reverse-biased by(VCC+ VEE- VBE1). IfVCC
= VEE=22 V, reverse voltage > 41 V.
Early IC op amps used external
diode protection across input
terminals to limit differential input
voltage to about 1.4 V at the cost of
extra components.
Chap 16 - 44
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Microelectronic Circuit Design
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mA741 Op Amp
High gain, input resistance andCMRR, low output resistance
and good frequency response.
Fully protected input and output
stages and offset adjustment port.
Input stage is a differentialamplifier with buffered current
mirror active load.
Two stages of voltage gain
(emitter-follower driving C-E
amplifier) followed by short-circuit protected class-AB output
stage buffered from second gain
stage by emitter follower.
Chap 16 - 45
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Microelectronic Circuit Design
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mA741 Op Amp: Bias Circuitry
mA733.0
5
2
R
BEV
EEV
CCV
REF
I
1
ln50001 I
REFI
TV
ISolving iteratively,
I1 =18.4 mA.
Assuming VO =0, VCC=15 V and neglecting dropacrossR7 andR8 ,
VEC23 = 15+1.4=16.4 V and VEC24 = 15-0.7 =14.3 V
Given VA=60 V,bFO =50,
A666)50/2()60/7.0(1
)60/4.16(1mA)733.0(75.02 m I
A216)50/2()60/7.0(1
)60/4.14(1mA)733.0(25.0
3m
I
W
k115
mA666.0
16.4VV60
2
23232
I
ECV
AV
R
W
k344mA216.0
14.3VV60
3
24243 I
ECV
AV
R
Chap 16 - 46
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Jaeger/Blalock
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Microelectronic Circuit Design
McGraw-Hill
mA741 Op Amp:DC Analysis of Input
Stage
/2IC
I161
42
)8
/8
()8
/2(1
)8
/8
(1
22
1 BI
AV
EBV
FO
AV
ECV
CII
b
41
412
2222 B
IFO
FO
FOEI
FCI
bbb
4
1
8
2
8
881
121
2
FOFOAV
EBV
ECV
I
CI
bb
214
4
2
12
444 CI
FO
FO
FO
FOEI
FCI
b
b
b
b
CCV
BEV
EBV
CCV
CEV
CEV
2921
V1.2
V)4.1(--V7.0333
EEV
EEV
CV
EV
ECV
V7.07
V4.18
EEV
CEV
CCV
ECV
Chap 16 - 47
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Jaeger/Blalock
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Microelectronic Circuit Design
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mA741 Op Amp: Input Stage Bias
Currents Example
Problem: Calculate bias currents in the 741 input stage with given parameters.
Given data:I1 = 18 mA,VCC= VEE= 15 V,VAnpn = 75 V,bFOnpn = 150, VApnp = 60
V,bFOpnp = 60
Analysis:
A32.7
)160)(151/150(
1
)60/7.0()50/2(1
)60/4.16(11
2A18
21
V4.16318
mm
CI
CI
EBV
BEV
CCV
ECV
A25.735
A25.72151
150
61
60
214
4
2
12
2
2444436
m
m
b
b
b
b
CI
CI
CI
CI
FO
FO
FO
FO
F
CI
FEI
FCI
CI
CI
Chap 16 - 48
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Jaeger/Blalock
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Microelectronic Circuit Design
McGraw-Hill
mA741 Op Amp: Voltage Gain (Input
Stage)
idS)v41046.1(
idv
220
2id
v2-i2oi
C
Img
W
M54.6
4
79.0
4
2
6
3.1
42
261
646
o
r
o
r
o
r
orR
mg
or
outR
outR
thR
Based on values in Norton equivalent, open-
circuit voltage gain of first stage is -955.
Chap 16 - 50
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Jaeger/Blalock
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Microelectronic Circuit Design
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mA741 Op Amp: Voltage Gain (Second
Stage)
k189
10
1010
A8.19k5011
11
111010
CI
or
BV
F
CI
EICI
b
mb
k63.511
r
To findy11 andy21:
WW
W
.4M211
k501101011
k7.201001111111
1
inR
ory
or
inR
b
b
1v921.0
11k501
1010
11k501
101vev
W
W
inR
or
inR
o
b
b
1v006701.0100)11
/1( e
v
2i Wm
g
mS70.621
y
Chap 16 - 51
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Jaeger/Blalock
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Microelectronic Circuit Design
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mA741 Op Amp: Voltage Gain (Second
Stage contd.)
To findy12 andy22:
Open-circuit voltage gain for the first two
stages is:
W
W
k1.8911222
k40710011
11111
1
outRRy
ER
mg
or
outR
idv000,153)
idv256(597
2v
idv256
idv2.4M6.54M41046.1
1v
1v597
1v)k1.89(00670.0
2v
WW
W
Combined model for first and
second stages is:
Chap 16 - 52
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Microelectronic Circuit Design
McGraw-Hill
mA741 Op Amp: Voltage Gain (Output
Stage)
From simplified output stage without
short-circuit protection:
W
W
W
M27.81
1121212
k1622313141
k3041
15152
eqR
or
inR
eqRR
dr
dr
eqR
L
R
o
r
eq
R
b
b
W
W
2.261
15
315
k08.2
112
12212
131433
o
eqRroR
o
yr
dr
drR
eqR
b
b
Actual op amp output resistance is:
W 537
RoRoutR
Chap 16 - 53
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Jaeger/Blalock
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Microelectronic Circuit Design
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Gilbert Analog Multiplier
Q1 and Q2 have significant emitterdegeneration, transconductance of
the pair is 1/R1.Forv1
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Jaeger/Blalock Microelectronic Circ it Design
Four-Quadrant Gilbert Analog Multiplier
with Predistortion Circuit
Forv3