Post on 15-Oct-2015
description
Willy Sansen 10-05 111
Rail-to-rail input and output amplifiers
Willy Sansen
KULeuven, ESAT-MICASLeuven, Belgium
willy.sansen@esat.kuleuven.be
Willy Sansen 10-05 112
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiers Zener diode rtr amplifiers Current regulator rtr amplifier on 1.5 V Supply regulating rtr amplifier on 1.3 V Other rtr amplifiers and comparison
Willy Sansen 10-05 113
For low supply voltages : use full range for maximum dynamic range
Fully differential signal processing Rail-to-rail output is always required But not necessarily rail-to-rail-input !
Why rail-to-rail amplifiers ?
Willy Sansen 10-05 114
Symmetrical CMOS OTA
12
345
VDD
VSS
vOUT
CLM1 M2
M3 M4
M8
M6
M7
+-
M5
M9
1 : BB : 1Rail-to-rail output swing !
Symmetrical OTA1 : : 1
Willy Sansen 10-05 115
When rail-to-rail input ?
+- vOUT
R2
R1vIN
+-
vOUT
R2
R1
vIN
+-
vOUTvIN
No !No !
Yes !
+
-
+
-
+
-
Willy Sansen 10-05 116
Rail-to-rail input for CMFB
Avind+
- +- +
-+
CL
voutd
CL
Ad Acvinc
CMFB
For a rail-to-rail output swing in fully-differential amplifiersA CMFB amplifier is requiredWith rail-to-rail input capability !
Willy Sansen 10-05 117
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiersZener diode rtr amplifiersCurrent regulator rtr amplifier on 1.5 VSupply regulating rtr amplifier on 1.3 VOther rail-to-rail amplifiers
Willy Sansen 10-05 118
Problem ?
VDD
VSS = 0
VGSn
VDSsatn
VGSp
VDSsatp
VINCM > 1.1 V VINCM < VDD - 1.1 V
VGS 0.9 V & VDSsat 0.2 V >>> VGSDS = 1.1 V
+
= VGSDS +
= VGSDS
Willy Sansen 10-05 119
Problem : limited input CM range
VDD
VSS = 0
IB
IB
+ -
iout+iout-
iout+iout-
To be operational :
VINCM > 1.1 V
VINCM < VDD - 1.1 V
gmn gmp
VDDmin = 2.2 V
Willy Sansen 10-05 1110
Problem: unequal gmtot
nMOST on :VINCM > 1.1 V
VINCMVSS = 0 VDD /2 VDD
gm
pMOST on : VINCM < VDD - 1.1 V
nMOSTpMOST
gmtot
1.1 V VDD-1.1 V
gmn gmp
Willy Sansen 10-05 1111
Solution : gm equalization
nMOST on :VINCM > 1.1 V
VINCMVSS = 0 VDD /2 VDD
gm
pMOST on : VINCM < VDD - 1.1 V
nMOSTpMOST
gmtot
1.1 V VDD-1.1 V
Increase gm:gmn+ gmp= ct
gmn gmp
Willy Sansen 10-05 1112
Equalize gmtot in strong inversion
gmn + gmp = ct1
2 Kn IBn + 2 Kp IBp = ct1
Kn IBn + Kp IBp = ct2
WnLn
WpLp
IBn + IBp = ct3
3 x Current mirror : 1 + 1 = 0 + 4 > 4 - 1 = 3
Willy Sansen 10-05 1113
3x Current mirror for nMOSTs
VDD
VSS = 0
IB
IB
+ -
iout+iout-
iout+iout-
gmn gmp
1 : 3
Vrn
IB x 4
Mrn
Willy Sansen 10-05 1114
VDD
VSS = 0
IB
IB
+ -
gmn gmp
1 : 3
Vrn
IB x 43 : 1
Vrp
IB x 4
3x Current mirror for all MOSTs
Mrn
Mrp
Willy Sansen 10-05 1115
3x Current mirror : performance
VINCMVSS = 0 VDD /2 VDD
gm
nMOSTpMOST
gmtot
1.1 V VDD-1.1 V
gmn gmp
gm/gm = 15%
gmtot ~ (4 - 3x) IB + x IB gm/gm = 15% (x=1/3)
Willy Sansen 10-05 1116
Ref.Hogervorst, JSSC Dec.1994, 1505-1512
6.4 MHz/ 10 pF
6.4 V/s
31 nV/ Hz
3.3 V0.18 mA3 mApk
1: 3
1: 3
Rail-to-rail opamp
Willy Sansen 10-05 1117
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiersZener diode rtr amplifiersCurrent regulator rtr amplifier on 1.5 VSupply regulating rtr amplifier on 1.3 VOther rail-to-rail amplifiers
Willy Sansen 10-05 1118
Zener diodes
VZ
IDS
VGSVT0 VZ
ID
VDVBEon
0.7 V
0
VZ
Electronic Zener
Willy Sansen 10-05 1119
VDD
VSS = 0
8IB
8IB
+ -gmn gmp
Rail-to-rail amplifier with Zener diode
1 : 6
1 : 6
6 : 1
6 : 1
VZ
VZ = VGSn +VGSp
IBIB
Willy Sansen 10-05 1120
VDD
VSS = 08IB
+ -gmn
Rail-to-rail amplifier with Zener diode
1 : 6
1 : 6
6 : 1
6 : 1
V
Willy Sansen 10-05 1121
VDD
VSS = 0
8IB
8IB
+ -gmn gmp
Rtr amp. with electronic Zener
IB
IB
VZ
Willy Sansen 10-05 1122
Rail-to-rail amp. with Zener : performance
VINCMVSS = 0 VDD /2 VDD
gm
nMOSTpMOST
gmtot
1.1 V VDD-1.1 V
gmn gmp
Zener: gm/gm = 25% Electronic Zener: gm/gm = 6%
High currentHigh SR !
Ref.Hogervorst, JSSC July 1996, 1035-1040
Willy Sansen 10-05 1123
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiersZener diode rtr amplifiersCurrent regulator rtr amplifier on 1.5 VSupply regulating rtr amplifier on 1.3 VOther rail-to-rail amplifiers
Willy Sansen 10-05 1124
Equalize gmtot in weak inversion
gmn + gmp = ct
+ = ctIBn
2 nn kT/qIBp
2 np kT/q
IBn + IBp = ctnpnn
n = 1 + Cox
CD (VBS)
Willy Sansen 10-05 1125
VDD
VSS = 04IB
+ -
gmngmp1 :
Vref
Rail-to-rail amplifier with current switch
npnn
I-switch IBIB IB IB2IB
Mr
Willy Sansen 10-05 1126
Rtr amp. with I-switch : performance
VINCMVSS = 0 VDD /2 VDD
gm
nMOSTpMOST
gmtot
1.1 V VDD-1.1 V
gmn gmp
Current switch : Vref very critical !
Vref = 0.5 V
Vref = 0.3 V
Vref = 0.4 V
Willy Sansen 10-05 1127
Ref. : Wu etal, JSSC Jan.1994, pp.63-66
14 MHz/ 11pF
5.6 MHz/ 100pF
4 V/s36 nV/ Hz
5 V0.4 mA
gm1vin
gm3vin
Willy Sansen 10-05 1128
IDS x 2
gm x 2
Biasing :
Ref. : Wu etal, JSSC Jan.1994, pp.63-66
Willy Sansen 10-05 1129
Input rail-to-rail stage
VDD2
VDD = 5V
0V
VDD
20
20
5
5
5
5
1010
10
10
20
20
20
0
0
20
5V
1.5V1.5VpMOSTs off !
V+- high :
nMOSTs :IDS1 x 2gm1 x 2
Willy Sansen 10-05 1130
VDD
VSS = 0
2IBp
2IBn
+ -
gmn gmp
Current regulator FB loop
180oCc
IBpIBn
4IB
np
nn
S
Willy Sansen 10-05 1131
2IBp
2IBn
gmn gmp
Current regulator FB loop : replica biasing
2IBp
2IBn
gmn gmpin+ in- in+ in-
Willy Sansen 10-05 1132
Replica biasing with one transistor
+-
RLRL
RS
vIN vOUT
VREF
Willy Sansen 10-05 1133
Replica biasing with differential pair
gmnin+ in-
2IBn
gmnin+ in-
180o
2IBnIREF
Willy Sansen 10-05 1134
4IB
Cc
+ -
VDD
Current regulator rail-to-rail amplifier
+ -
VSS
2IBp
2IBn
np
nn1 :
Replica biasing block Input stage
S
Willy Sansen 10-05 1135
I-regulator rtr amplifier
E.Peeters etal,CICC 1997
Willy Sansen 10-05 1136
Total amplifier schematic
E.Peeters etal, CICC 1997
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Output stage
Willy Sansen 10-05 1138
VINCMVSS = 0 VDD /2 VDD 3 V
gm
nMOSTpMOST
gmtot
VDD- 1.1 V 1.1 V
gmn gmp
n - mismatch : gm/gm 4%
Current-regulator rtr amp. : performance
Willy Sansen 10-05 1139
VINCMVSS = 0 VDD 1.5 V
gm
nMOSTpMOSTgmtot
VDD- 1.1 V 1.1 V
gmn gmp
n - mismatch : gm/gm 4%
Current-regulator rtr amp. : towards 1.5 V
0
Willy Sansen 10-05 1140
GBW error
4 %
Willy Sansen 10-05 1141
Input offset voltage
Willy Sansen 10-05 1142
Rail-to-rail Opamp with Current regulator
VDD = 1.5 V
ITOT = 0.2 mA
gm/gm = 4 %GBW = 4.3 MHz
CL = 15 pF
E.Peeters etal, CICC 1997
Willy Sansen 10-05 1143
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiersZener diode rtr amplifiers Current regulator rtr amplifier on 1.5 V Supply regulating rtr amplifier on 1.3 V Other rail-to-rail amplifiers
Willy Sansen 10-05 1144
VINCM
VSS = 0 VDD 1.3 V
gmnMOSTpMOST
gmtot
gmn gmp
n - mismatch and gmtot dip : gm/gm 15 %
Internal VDD Regulator
IBn + IBp = ctnpnn
Weak inversion :
VDD /2
gmtot/2 Minimum VDD ?Minimum VGS+VDSsat ?
Independent of VTs !0
Willy Sansen 10-05 1145
VDD 1.3 V
VSS = 0
IBp ?
IBn ?
+ -
iout+iout-
iout+iout-
gmn gmp
Regulating VDD : total schematic
VDDext
CcVOUT
Willy Sansen 10-05 1146
IB
VDD
Replica biasing block
VSS
IBp
IBn
VDDVDD
VSS
VDDext
VSS
S
Ferri, .. JSSC Oct.97, 1563-1567
Willy Sansen 10-05 1147
VDD
Internal VDD regulator
VSS
IBp
IBn
VDDext2 : 1
2 : 1
VGSn
VGSp
VDSsatn
VDSsatp MR
MP
MA
Willy Sansen 10-05 1148
Total amplifier schematicVext
Ferri, .. JSSC Oct.97, 1563-1567
Willy Sansen 10-05 1149
Internal supply voltage
V
V
Willy Sansen 10-05 1150
GBW error
VIN,CM (V)
GBW(MHz)
Willy Sansen 10-05 1151
Rail-to-rail amp. with VDD regulator : Specs
VDDmin = 1.3 VGBW = 1.3 MHz in CL = 15 pFgm1 = 200 SIDSn1 = 10 AW/Lin = 830ITOT = 354 AVin,eq = 25 nVRMS/HzVin,offset = 0.8 mV (3 = 0.2 mV)
Ferri, .. JSSC Oct.97, 1563-1567
Willy Sansen 10-05 1152
Rtr Opamp with VDD-regulator
Willy Sansen 10-05 1153
Rail-to-rail with VDD regulator : min VDD
VDDmin = 2 (VGS + VDSsat)= 2 (VGS - VT + VT + VGS - VT)= 2 [VT + 2(VGS - VT)]= 2 [0.6 + 2(0.15)] = 1.8 V
= 2 [0.3 + 2(0.10)] = 1.0 V !!!!
Willy Sansen 10-05 1154
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiersZener diode rtr amplifiersCurrent regulator rtr amplifier on 1.5 VSupply regulating rtr amplifier on 1.3 VOther rail-to-rail amplifiers
Willy Sansen 10-05 1155
Rail-to-rail opamp with current summation
Redman-White, JSSC May 97, 701-712
3.3 V2.3 mW(2.2 V min.)
Gm 10%THD :-55 dB
40 MHz9 mW0.5 m CMOS
Willy Sansen 10-05 1156
Duisters, .., JSSC July 98,pp.947-955
Opamp with voltage multiplier
Vddx - Vdd 1 V
= Vdd/2
1.8 - 3.3 V0.75 mA6.5 MHz
On 3 V :
2.8 VptptTHD :-90 dB /10k-81 dB/32
0.5 m CMOS
Willy Sansen 10-05 1157
Rail-to-rail opamp with differential signal proc.
Ref.Lin, AICSP 1999, 153-162
Idsn
Idsp
Willy Sansen 10-05 1158
Maximum-current selecting circuits
Ref.Lin, AICSP 1999, 153-162
Idsn
Idsp
Willy Sansen 10-05 1159
Maximum-current selecting circuit
VDD
+ -
VSS Input stage
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Transconductance equalizer circuit
Ref.Lin, AICSP 1999, 153-162
VGS3 + VGS2 = VGS1 + VGS4KpIpbias = KnInbias
gmp = gmn
Willy Sansen 10-05 1161
Rail-to-rail opamp with max.-current selector
Ref.Lin, AICSP 1999, 153-162
1.9 MHz 20 pF 3 V/ 0.26 mA
max.curr.selector max.curr.selectorgm equalizer
Willy Sansen 10-05 1162
Rail-to-rail opamp with max.-current selector
max.curr.selectorgm equalizer
Ref.Lin, AICSP 1999, 153-162
1.9 MHz 20 pF 3 V/ 0.26 mA
Willy Sansen 10-05 1163
Rail-to-rail opamp on 1 Volt Supply
Ref.Duque-Carrillo, JSSC Jan.2000, 33-43
VIN
VDD = 1 V
0 V
VIN
IDS
0 0.5 1 V
IDSp IDSn
Willy Sansen 10-05 1164
Rail-to-rail opamp on 1 Volt
Ref.Duque-Carrillo, JSSC Jan.2000, 33-43
R
R
IB
IB
VINVIN
VDD = 1 V VDD = 1 V
0 V 0 V
Willy Sansen 10-05 1165
Rail-to-Rail opamp on 1 Volt
Ref.Duque-Carrillo, JSSC Jan.2000, 33-43
R
R
IB
IB
VIN
VDD = 1 V
0 V
IB
0 0.5 1 V
VINn
VINp
VIN
0 0.5 1 VVIN
VINn
VINp
IBmax
VINp RIBmax
VINn1 V
0
0.5
Willy Sansen 10-05 1166
Ref.Duque-Carrillo, JSSC Jan.2000, 33-43
2 MHz15 pF
1 V0.4 mA
Ioffset< 1 A
R Ioffset noise
RtR opamp : full opamp schematic
Willy Sansen 10-05 1167
Ref.Duque-Carrillo, JSSC Jan.2000, 33-43
RtR opamp : current generator
IB
current summer
Willy Sansen 10-05 1168
Comparison rail-to-rail input amplifiers
Type Ref. gm/gm GBW ITOT VDDmin% MHzpF/mW A V
3x Curr.mirr. JSSC-12-94 15 110 150 3Electr. Zener JSSC-7-96 6 70 215 2.7Curr.switch AICSP-5-94 8 1.1 500 3.3Curr.regulat. CICC 97 4 210 200 1.5Regulat. VDD JSSC-10-97 6 43 350 1.3MOST translin. AICSP-6-94 8 4.2 800 2.5Improv.CMRR JSSC-2-95 9 3 1400 5Max. current AICSP-1-99 10 77 260 3Resistive input JSSC-1-00 x 75 400 1
Willy Sansen 10-05 1169
Table of contents
Why rail-to-rail ? 3 x Current mirror rtr amplifiers Zener diode rtr amplifiers Current regulator rtr amplifier on 1.5 V Supply regulating rtr amplifier on 1.3 V Other rail-to-rail amplifiers
Willy Sansen 10-05 1170
References
T. Duisters, etal, A -90 dB THD rail-to-rail input opamp using a new local charge pump in CMOS", IEEE Journal Solid-State Circuits, Vol. SC-33, pp. 947-955, July 1998.
R. Duque-Carillo, etal, "A 1 V rail-to-rail operational amplifier in standard CMOS technology", IEEE Journal Solid-State Circuits, Vol. SC-35, pp. 33-43, Jan. 2000.
G.Ferri, W.Sansen, A rail-to-rail constant-gm low-voltage CMOS operational transconductance amplifier", IEEE Journal Solid-State Circuits, Vol. SC-32, pp. 1563-1567, Oct.1997.
R. Hogervorst, etal, "A compact power-efficient 3V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries", IEEE Journal Solid-State Circuits, Vol. SC-29, pp. 1504-1512, Dec.1994.
R. Hogervorst, etal, Compact CMOS constant-gm rail-to-rail input stage with gm-control by an electronic Zener diode", IEEE Journal Solid-State Circuits, Vol. SC-31, pp. 1035-1040, July 1996.
R. Lin, etal, "A compact power-efficient 3V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries", Analog Integrated Circuits and Signal Processing, Kluwer Ac., pp. 153-162, Jan.1999.
Willy Sansen 10-05 1171
References
E. Peeters, etal, "A compact power-efficient 3V CMOS rail-to-rail input/output operational amplifier for VLSI cell libraries", CICC 1997.
W. Wu, etal, Digital-compatible high-performance operational amplifier with rail-to-rail input and output stages", IEEE Journal Solid-State Circuits, Vol. SC-29, pp. 63-66, Jan 1994.