2009 - Flipped Voltage Follower SLIDES
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Transcript of 2009 - Flipped Voltage Follower SLIDES
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1The 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. Ramrez-Angulo2, R.G.Carvajal1, A. Lpez-Martn3,
ELEN 607 (ESS)
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2OUTLINE
1. Introduction.2. The Basic FVF.3. FVF Structures.4. Applications.5. Conclusions.
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3The Basic Flipped Voltage Follower (FVF)
gm1 gm2 ro1
gm1
gout
= 1IbHIGHb) FVF< 1HIGHIba) ConventionalAvSinkingSourcing
a) Conventional
Voltage Follower
[Ramirez-Angulo92] J.Ramrez-Angulo, R.G.Carvajal, A.Torralba, J.Galn, A.P.VegaLeal, and J.Tombs. The Flipped Voltage Follower: a useful cell for low-voltage low power circuit design, Proc. ISCAS02, vol. 3, pp. 615-618, 2002.
b) (FVF)Ib
M1
M2vo
vi
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4FVF transistors voltage limits to keep them in saturation
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5The 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)
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6Stability 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