1 The Flipped Voltage Follower (FVF) A useful cell for low-voltage, low-power circuit design part of this material was provided by Profs. A.Torralba 1 J. Ramírez-Angulo 2 , R.G.Carvajal 1 , A. López-Martín 3 , ELEN 607 (ESS)
1
The Flipped Voltage Follower (FVF)
A useful cell for low-voltage, low-power circuit design
part of this material was provided by Profs. A.Torralba1 J. Ramírez-Angulo2, R.G.Carvajal1, A. López-Martín3,
ELEN 607 (ESS)
2
OUTLINE
1. Introduction.2. The Basic FVF.3. FVF Structures.4. Applications.5. Conclusions.
3
The Basic Flipped Voltage Follower (FVF)
gm1 gm2 ro1
gm1
gout
= 1IbHIGHb) FVF< 1HIGHIba) ConventionalAvSinkingSourcing
a) Conventional
Voltage Follower
[Ramirez-Angulo’92] J.Ramírez-Angulo, R.G.Carvajal, A.Torralba, J.Galán, A.P.VegaLeal, and J.Tombs. “The Flipped Voltage Follower: a useful cell for low-voltage low power circuit design,” Proc. ISCAS’02, vol. 3, pp. 615-618, 2002.
b) (FVF)Ib
M1
M2
vo
vi
4
FVF transistors voltage limits to keep them in saturation
5
The Basic FVF Analysis
I b
M1
VoX
rb
M 2
Cc
Vi
Vr
Y Compensation
Dc gainAOL = Vr / Vi = - gm2 ROLYROLY = rb || gm1 ro1 ro2 ,ROLX ≈ (1+rb/ro1)/gm1 || ro2
Dominant PoleAt Y: wpY = 1 / CY ROLY
Non-Dominant PoleAt X: wpX = 1 / CX ROLX
Gain-Bandwidth ProductGB = gm2 / CY
Open Loop Analysis
CX parasitics at node X (incl. LOAD)CY parasitics at node Y (incl. Cc if any)
6
Stability Criterion: wpX > 2 GB
• For Ib a simple current mirror (rb≈ ro1)
• For Ib a cascode current mirror(rb ≈ gm1 ro1 ro2)
usually requires compensation
2. The Basic FVF
I b
M1
VoX
rb
M 2
Cc
Vi
Vr
Y
2
1
4gmgm
CC
Y
X <
Stability Analysis
CX parasitics at node X (incl. LOAD)CY parasitics at node Y (incl. Cc if any)
22
1rogmC
C
Y
X <
wpX = 1 / CX ROLX
7
Closed Loop Output Resistance
• For Ib a simple current mirror (rb ≈ ro1)
• For Ib a cascode current mirror (rb ≈ gm1ro1 ro2)
The Basic FVF
b
M1
M2
vovi
X
Y
( )2112
211
||
||11
1 rorogmrgm
roror
gmA
RRb
b
OL
OXCLX
⎟⎟⎠
⎞⎜⎜⎝
⎛+
≈+
=
121
1rogmgm
RCLX →
ACL ≈ 1 and RCLX is only a few Ohms (20 – 100) in all cases
121
2rogmgm
RCLX →
8
DC considerations
• VDDMIN = VGS
MIN + VDSsat ≈ 0.8 V for
0.6μm CMOS technology. It is a low-voltage cell.
The Basic FVF
[Chung-Chih’95] H.Chung-Chih, H.Changku, M. Ismail, “CMOS low-voltage rail-to-rail V-I converter,” Proc. 38th MWSCAS, vol.2, pp. 1337-1340, 1995.
M1
M2
X
Y
vo
vi
M3
Ib
Ib1
High-voltage version
• But, for large VDD, biasing M2 in saturation is difficult for low vi. A high-voltage version includes a voltage shifter in the feedback loop[Chung-Chih’95]
9
3-terminal cell (strong inv.)
• For M2 in saturation
• For M2 in ohmic
The Basic FVF
b
M1
M2
vX
vZ
X
Y
ZiZ
vY
iyvY
iX
( )
( ) ( ) ( )( )
0
2,;,,,
,
1
=
−+==
+=
Z
Mp
YbTpYbZYXbY
YbZX
i
LWkiIViIfviiIgv
iIfvv
( ) ( )( )
2
2,,,Mp
XYbTpDDZYXb LWk
iiIVVviiIg −−−−=
The most interesting case is for iY = 0
( ) ( ) XMp
XYbXTpDDZYXb vLWk
iiIvVVviiIg 12
,,,2
⋅−−
−−−=M1 in saturation
Const
Relation
= 0
10
FVF Structures for different applications
Current sensor (FVF-CS)
in
5
out
2
1
b
b
Y
X
M2 saturation
I out
(uA)
M2 ohmic
M5 saturation
11
FVF Structures
Non-Symmetrical Class-AB Differential Pair (FVF-NDP)
0
2.5
5.0
7.5
10.0 DM3
I b
(mV)V3V1-
12
3.FVF Structures
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
vinCM=(v3+v4)=V1
13
Flipped voltage follower applicationsFlipped voltage follower applications
Class A DifferentialPair
Class AB pseudoDifferntial pair
Comparison
I(D1) I(D2)
0
2.5
5.0
7.5
10.0
12.5
-400 -200 0 200 400VIN (mV)
DC
TRA
NS
FER
CU
RV
ES
(uA
)
M1 M2
iD1
Ib
V1 V2
iD2
X
M1 M2
iD1
V1 V2
iD2
X
Ma
M3
Ib
Va
I(D1P)
I(D2P)
I(D2P)
I(D1P)
satDSTPDD VVV ,min, 2+=
"A new Class AB differential Input stage for implementation of low voltage high slew rate op-amps and linear transconductors," J. Ramirez-Angulo, R. Gonzalez-Carvajal, A. Torralba and Carlos Nieva, IEEE International Symposium on Circuits an Systems, May 6-9, Sidney Australia
14
3.FVF Structures
Symmetrical Class-AB DifferentialPair (FVF-SDP)
0
2.5
5.0
7.5
10.0 DM3
I b
(mV)V3V1-
DM6
15
3.FVF Structures. SummaryCurrent sensor (FVF-CS)
Iin
M5
Iout
M2
M1
Ib
Vb
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
V1M1M3
I b
V3
M2
M4 V4
X
IDM3 IDM4
Symmetrical Class-AB Differential Pair (FVF-SDP)
16
3.FVF Structures. SummaryCurrent sensor (FVF-CS)
Iin
M5
Iout
M2
M1
Ib
Vb
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
V1M1M3
I b
V3
M2
M4 V4
X
IDM3 IDM4
Symmetrical Class-AB Differential Pair (FVF-SDP)
Current sensor (FVF-CS)
17
3.FVF Structures. SummaryCurrent sensor (FVF-CS)
Iin
M5
Iout
M2
M1
Ib
Vb
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
V1M1M3
I b
V3
M2
M4 V4
X
IDM3 IDM4
Symmetrical Class-AB Differential Pair (FVF-SDP)
X
Y
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
18
3.FVF Structures. SummaryCurrent sensor (FVF-CS)
Iin
M5
Iout
M2
M1
Ib
Vb
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
V1M1M3
I b
V3
M2
M4 V4
X
IDM3 IDM4
Symmetrical Class-AB Differential Pair (FVF-SDP)
X
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
19
4.FVF-CS ApplicationsCurrent sensor (FVF-CS)
Low voltage current mirrors
iIN
IB
V1
M2
M1
M5
IB
IOUT
[Rijns’93] J.J.F. Rijns, “54 MHz switched-capacitor video channel equalizer” Electr.Lett.,
vol. 29, no. 25, pp. 2181-2182, Dec. 1993[Ramirez-Angulo’04] J. Ramírez-Angulo, R.G.Carvajal,
A.Torralba, “Low-supply voltage high-performance CMOS current mirror with low input and output voltage requirements,”
IEEE TCAS-II, vol.51, no. 3, pp. 124-129, March 2004.• Vin
MIN = VDSsat• Very low input resistance(a few Ohms)
20
4.FVF-CS ApplicationsCurrent sensor (FVF-CS)
Low voltage current mirrors
[Torralba’02] A. Torralba, R.G.Carvajal, J.Ramírez-Angulo, “Output stage for low supply voltage CMOS current mirrors” Electr.Lett., vol. 38, no. 24, pp. 1528-1529, Nov. 2002
A few OhmsInput impedance
≈ 1 GOhmOutput impedance
-66dBTHD (10 μA pp, @10KHz)
20nsSettling time (1%, 4 μA step)
1.5 pA/√HzInput referred noise(@10MHz)
120 MHzBandwidth
10 KOhmLoad resistor
1 VMinimum supply voltage
0,35μm CMOS AMSTechnology
21
4.FVF-CS ApplicationsCurrent sensor (FVF-CS)
Other applications
[Docudray’03] G.O.Ducodray, R.G.Carvajal, J.Ramírez-Angulo, “A high-speed dynamic current sensor scheme for IDD test using a FVF” Proc. SSMSD, pp. 50-53, 2003
[Karthikeyan’01] S. Karthikeyan, A. Tamminneedi, E.K.F.Lee, “Design of low-voltage front-end interfaces for switched-opamp circuits,” IEEE TCAS-II, vol.48, no. 7, pp. 722-726, July 2001.
[Rout’00] S. Rout, E.K.F.Lee, “Design of 1 V switched-current cells in standard CMOS process,” Proc. ISCAS, vol.2, pp. 421-424, 2000
M 2
M1
Iin
M 5
Φ
ΦI out
IbIbΦ= HIGH)(
MB1 MB2
IDD TEST CURRENT SENSOR
LINEAR V-I CONVERTER
SI Circuits
22
4.FVF-NDP Applications
[Peluso’00] V.Peluso, P. Vancorenland, A.M.Marques, M.S.J.Steyaert, W.Sansen, “A 900mV low-power ΔΣ A/D converter with 77dB dynamic range,” IEEE J.Solid-State Circuits, vol. 35, no. 4, pp. 632-636, April 2000.
[Carvajal’02] R.G.Carvajal, A. Torralba, J.Ramírez-Angulo, J.Tombs, F. Muñoz, “Compact low-power high slew-rate CMOS buffer for large capacitive loads,” Electron. Lett., vol.38, no. 32, pp. 1348-1349, Oct. 2002.
NON-LINEAR CLASS_ABTRANSCONDUCTOR
Non-Symmetrical Class-AB Differential Pair (FVF-NDP)
I b
V1
I b
V1
V2
M2b
M1aM3a M1bM3b
Ioa I ob
M4a
Vo1Vo2
M2a M4b
M8b M9b
M7b
M8aM9a
M7a VbVb
CLASS-AB OUTPUT BUFFER
I b
I b
V i Vo
M1PM3P
M3NM1N
M2P
B
2N
A
M
23
4. FVF-NPD Applications
More than 100uA max. output current with 30uA total quiescent current !
2 V supply, 10pF capacitor load, 250 KHz input signal
time (s)
Out
put t
rans
isto
rcu
rren
t (A
)O
utpu
t vol
tage
(V)
CLASS-AB OUTPUT BUFFER
I b
I b
V i Vo
M1PM3P
M3NM1N
M2P
B
2N
A
M[Carrillo’04] J.M.Carrilo R.G.Carvajal,, A. Torralba, J.Duque-Carrillo, “Rail-to-rail, low-power high slew-rate CMOS analog buffer,” Electron. Lett., vol.40, no. 14, July 2004.
24
4.FVF-NPD Applications
CLASS-AB OUTPUT STAGE
Moutp
Vout
Moutn
Io
X
Io
+-
+-
Y
W
Z
M1p
M1n M2n
M2p
α:1
α:1
VABVAB
MoutnI
MoutpI
M3p
M3n
25/1 25/1
50/1
8/1 8/1
16.5/1 165/1
500/1
3,75 uA
3,75 uA
Biasing STAGE
2-STAGE AMPLIFIER
[Torralba’00] A. Torralba, R.G.Carvajal, J. Martínez-Heredia, J.Ramírez-Angulo, “Class-AB output stage for low voltage CMOS op-amps with accurate quiescent current control,” Electron. Lett., vol.36, no. 21, pp. 1753-1754, Oct. 2000.
Rc Cc
Min2Min1
I = 100 uAdp
+
Output Stage(figure 13a)
-
VVout
X
V
a)
500/1 500/1
25
4.FVF ApplicationsCLASS-AB OUTPUT STAGE in a 2-STAGE OP-AMP
500µAPeak output current * (@ 0.3 V peak)
10V/µsSlew Rate * (@ 0.3 V peak)
21nV2/HzInput referred noise (100kHz)
65dBTHD (1kHz)
45dBCMRR
38dBPSRR
218(µA)Supply current
38(µA)Minimum current through output transistors
76(µA)Quiescent output current
15MHzUnity Gain frequency
75ºdeg (o)Phase Margin
65dBDC Gain
VDD=1.5 V, CL=10pF, 0.8 μm CMOS (Vt ≈ 0.85 V)Op-amp comp. CC=10pF, RC=500Ω
Unitary feedback
Non-inverting Gain= 5 with 2 internalresistors
26
4.FVF-PDP Applications
Ib
M1 M2
M5
Ma1
V2Va
Ib
M3 M4
M6
MbV1Vb
Vb'Va'
ID4ID3ID2ID1
I D1 I D3 ID2 ID4+ +
[Ramirez-Angulo’00] J.Ramírez-Angulo, R.G.Carvajal, J.M.Martínez-Heredia, “1.4V supply, wide swing, high frequency CMOS analogue multiplier with high current efficiency,” Proc. ISCAS, vol. 5, pp. 533-536, 2000[Ramirez-Angulo’03] J.Ramírez-Angulo, S.Thoutam, A.López-Martín, R.G.Carvajal, “Low voltage CMOS analogue four quadrant multiplier based on Flipped-Voltage-Followers,” Electron. Lett., vol.39, no. 25, Dec. 2003.
CLASS-AB LINEAR MULTIPLIERS
Symmetrical Class-AB Pesudo-Differential Pair (FVF-PDP)
-50
-30
-10
10
30
50
-300 -100 100 300
(uA
)
a)
b)
Vd12=V1 -V2
-300 mV=Va- Vb
(uA
)I D
2+I D
4-
-I D
1I D
3I o
ut=
50
70
30
-10
10
-30
-50-500 -100 300 700
ID2+ID4- -ID1 I D3
ID2+ID4+ +ID1 I D3
+ID1 I D3
ID1+ ID3- -ID2 I D4
+ID2 I D4
Vd12=V1 -V2
300 mV=Va- Vb
27
4.FVF-PDP Applications
• [Carvajal’02] R.G.Carvajal, J.Galán, J.Ramírez-Angulo, A. Torralba, “Low-power, low voltage differential class-AB OTAs for SC circuits,” Electron. Lett., vol.38, no. 22, pp. 1304-1305, Oct. 2002.• [Galan’02] J.Galán, A.P. VegaLeal, F. Muñoz, R.G.Carvajal, A.Torralba, J.Tombs, J. Ramírez-Angulo, “A 1.1V very low-power SD modulator for 14-b 16 KHz A/D conversion using a novel class AB transconductance amplifier,” Proc. ISCAS, vol. 2, pp. 616-619, 2002.
NON-LINEAR CLASS_AB TRANSCONDUCTORS
V i+Vi -
I b
M4
Vcasn
Vcasp
M 3 M2M1 Vo+Vo -
Mon -
Mop -
M on+
M op+V CM
MCMc MCMcVCMc
M cas M cas
M casM cas
VCMc
Vb
MCM VCMMCM
VDD
V SS
451
451
451
301
101
101
10110
1
101
101
101
101
101
101
301
30130
1
301
301
451
=1u
301
301
101
301
301
101
VcaspVcaspVcasp
Vcasn Vcasn Vcasn
28
4. FVF-PDP Applications
10 V/usec SR with only 11 uA total quiescent current ! (0.35 μm CMOS)
time (s)
( V )
Diff
eren
tial V
olta
geO
utpu
t tra
nsis
tor
Cur
rent
( A
)
1.1 V, SC Integrator. 1pF capacitor load, 2MHz switching frequency
29
4.FVF-PDP Applications
gm-C Filter
+ +
_ _ +
+_
_
+ +
_ _ +
+_
_gm1 gm2 gm3 gm4
C1
C1
C2
C2
Vo+
Vo-
Vin+
Vin-
+ +
_ _gm5
(Va - Vb)fo
(Va - Vb)Q
CMFB1 CMFB2
0.7 MHz
30
4.FVF-PDP Applications
gm-C Filter
0.8 μm CMOSTechnology
42 dBCMRR (@ 10.7 MHz)
39 dBPSRR (@ 10.7 MHz)
8 dBmIIP3
46 dBIM3 (@10.7MHz)
45 dBSNR
−40dB@200 mVppTHD (@10.7MHz)
1.18−1.8 mWPower consumption range
14 mVVo,CM variation in the entire tuning range
4−501Q range (@10.7MHz)
300 kHz−32 MHzFrequency tuning range
1.44 mm2Chip area
2 VPower supply
31
4.FVF-PDP Applications
gm-C VCO
• [Galan’03] J.Galán, R.G.Carvajal, F. Muñoz, A.Torralba, J. Ramírez-Angulo, “A low-power low-voltage OTA-C sinusoidal oscillator with more than two decades of linear tuning range,” Proc. ISCAS, vol. 1, pp. 677-680, 2003.• [Galán’04] J. Galan, R. G. Carvajal, A. Torralba, F. Muñoz, and J. Ramirez-Angulo, A low-power, low-voltage OTA-C simusoidal oscillator with a large tuning range. IEEE Trans. On CAS-II. (to appear)
150
250
350
450
550
650
750
850
250 260 270 280 290 300 310
Vtuning (Gm3) (mV)Am
plitu
de (m
Vpp)
32
4.FVF Applications
1.12% / 0.66%THD (2 / 25 MHz) @200 mVpp
−67 dBc/HzPhase Noise at 10kHz offset
1.05−1.58 mWPower consumption range
1 MHz−25 MHzFrequency tuning range
25 mV−500 mVVtuning control
0.8 μmTechnology
0.63 mm2Chip area
2 VPower supply
gm-C VCO
Symmetrical Class-AB Pseudo-Differential Pair (FVF-PDP)
33
3.FVF Structures. SummaryCurrent sensor (FVF-CS)
Iin
M5
Iout
M2
M1
Ib
Vb
Non-SymmetricalClass-AB
Differential Pair(FVF-NDP)
Symmetrical Class-AB Pseudo Differential Pair (FVF-PDP)
V1M1M3
I b
V3
M2
M4 V4
X
IDM3 IDM4
Symmetrical Class-AB Differential Pair (FVF-SDP)
Y
Symmetrical Class-AB Differential Pair (FVF-SDP)
34
4.FVF-SDP Applications
[Baswa’04] S. Baswa, A. López-Martín, R.G.Carvajal, J.Ramírez-Angulo, “Low voltage micro-power super class-AB CMOS OTA,” Electron. Lett., vol.40, no. 4, Feb. 2004.
Symmetrical Class-AB Differential Pair (FVF-SDP)
V1
M2
M1M3
I b
V3
Y
M5
M4
Ib
M6
R R
Ibo Ibo
SUPER CLASS_AB TRANSCONDUCTORS
Quiescent power consumption = 120 uWSR = 78 V/us, 1% settling time = 110 nsTHD (@100 kHz) = 0.15 %
0.5 μCMOS, VDD = 2 V, CL = 80pF2 MHz square input signal
35
4.Other Applications
• A.J. López-Martín and A. Carlosena, “Current-mode multiplier/divider circuits based on the MOS translinear principle”, Analog Integrated Circuits and Signal Processing, vol. 28, no. 3, pp. 265-278, 2001.• A.J. López-Martín and A. Carlosena, “Systematic design of compandingsystems by component substitution”, Analog Integrated Circuits and Signal Processing, vol. 28, no. 1, pp. 91-106, 2001.• A.J. López-Martín and A. Carlosena, “A 3.3V CMOS RMS-DC converter based on the MOS Translinear principle”, VLSI Design, 2002
Translinear loops, Geometric Mean, Square-Root Domain Filters, etc.
36
4. FVF-NPD ApplicationsCLASS-AB OUTPUT BUFFER
[Carrillo’04] J.M.Carrilo R.G.Carvajal,, A. Torralba, J.Duque-Carrillo, “Rail-to-rail, low-power high slew-rate CMOS analog buffer,” Electron. Lett., vol.40, no. 14, July 2004.
37
Conclusions
1. A new cell, called Flipped Voltage Follower (FVF) has been identified.
2. For low-voltage, low power, class AB operation.
3. Different applications have been reviewed(current mirror, voltage buffer, mixer, OTA, transconductance multiplier and op-amp output stage, filters, VCO, SD modulators…).
4. Simulation and experimental results have been presented that show the potential of the so-called FVF structure.