T.Sakurai

2004 Digital -- Advanced Solid State Circuits Forum:“Managing Variability in sub-100nm Designs”

Adaptive Circuit Techniques for Managing Variations

Takayasu SakuraiCenter for Collaborative Research,

University of TokyoE-mail: tsakurai@iis.u-tokyo.ac.jphttp://lowpower.iis.u-tokyo.ac.jp/

2004/2/19 San Francisco

T.Sakurai

Active leakage may ruin the Moore’s law Po

wer

per

chi

p [W

]

1980 1985 1990 1995 20000.01

0.1

1

10

100

1000

Year

MPU

x4 / 3

years

DSP

x1.4 / 3 years

Processors published in ISSCC

2005 2010 2015

x1.1 / 3 years

ITRS requirement

10000

Dynamic

Leakage1/100

T.Sakurai

Active leakage makes things more challenging

Year2002 ’04 ’06 ’08 ’10 ’12 ’14 ’160

0.2

0.4

0.6

0.8

1

1.2

0

20

40

60

80

100

120

Tech

nolo

gy n

ode[

nm]

Volta

ge [V

]

VTH

VDD

Technology node

2002 ’04 ’06 ’08 ’10 ’12 ’14 ’160

1

2

Year

PDYNAMIC

PLEAK

Pow

er [µ

W /

gate

]

Subthreshold leak(Active leakage)

T.Sakurai

Workload0 0.2 0.4 0.6 0.8 1

Norm

aliz

ed p

ower

P

ƒV2

0

0.2

0.4

0.6

0.8

1

Dynamic power reduction by compensating workload variability

Controller

Clock & VDD

Requiredspeed

Processor

Software

S. Lee et al, DAC, June 2000

HardwareSuper-linear

T.SakuraiCourtesy Hitachi Central Research Lab.

Power reduced to 1/3 by software ƒ-V control

1.5[V] 1.25[V]

Voltage

CurrentSleep Mode

0mA

250mA100mA

50mA

Multi-tasking:MPEG4 & MP3decoding

Application to cellular phones

T.Sakurai

Changing supply voltage is effective

0 0.5 10

0.5

1

Norm

aliz

ed p

ower

VDD [V]

PDYNAMIC

PSUBTHRESHOLD LEAK

PGATE LEAK

65nm tech. Node

VTH=0.15VDIBL coeff.=0.2

1

2

3

4

5

0No

rmal

ized

del

ay

Delay

T.Sakurai

Delay fluctuation gets worse in lower VDD

Fluc

tuat

ion

in d

elay

[%]

VTH=0.15V

0 0.5 1VDD [V]0

102030405060708090

100

)(

)(

)(

fast

Del

ayfa

stD

elay

slow

Del

ay VTH0.1V

VTH0.05V

T.Sakurai, “Panel on Reshaping EDA for Power,” DAC, 2003

Yield degradation

T.Sakurai

Delay fluctuation in logic

n1nfluctuatiodNormalize

n deviationstandarddelayPath

n averagedelayPath

nfluctuatioNormalized

deviationstandarddelayGate averagedelayGate

CMOS VLSI design, Baifukan, 1989. ISBN4-563-03450-9 C3055

Path delay

Gate

T.Sakurai

IOFF fluctuation due to VTH variation

VTH0 : averageVTH: standard deviation

• Within-die VTH variation is normal dist.

D. Frank, et al. Proceedings of the IEEE, 89 (2001) 259

sV10ln

0OFFOFF

TH

eII

VGS

log(IOFF)

IOFF0

VTHIOFF

VTH0 0

10-7

average

average: <IOFF>

Q.Liu, T.Sakurai, T.Hiramoto, “Optimum Device Consideration for Standby Power Reduction Scheme Using Drain-Induced Barrier Lowering,” JJAP. pp. 171 ・ 175, Apr. 2003.

T.Sakurai

Average and standard deviation of IOFF

2

VTH

2VTH

20THTHTH

s10ln

21

0OFF

TH2

VV

VTH

sV10ln

0OFFTHTHTHOFFOFF

eI

dVe2

1eIdVVf)V(II

s10ln

VTHIOFF

boundLower:0VVboundUpper:3VV

theory.distNormal:s210lnVV

0THTH

VTH0THTH

2VTH0THTH

Average

Standard deviation

Equivalent VTH shift

T.Sakurai

Leakage increase by intra-chip VTH variation

<IOFF> is much smaller than the worst case.

1.0

1.5

2.0

2.5

3.0

<IO

FF>/

I OFF

0

0 10 20 30 40 50-50

-40

-30

-20

-10

0Normal dist.

s (mV/dec) 60 80 100

VTH (mV)

<VTH

> - V

TH0 (

mV)0VV

boundLower

3VVboundUpper

s210lnVV

theory.distNormal

0THTH

VTH0THTH

2VTH0THTH

Normal dist.

Upper bound (3)

Upper bound (3)

Inter-chip VTH variability is important!

T.Sakurai

Coping with variability by adaptive circuitWhat to monitor

Leakage current, Speed, Logic thresholdTemperature

How to monitorReplica circuit, Actual circuit

What to controlFrequency , VDD, Body bias

How to controlAnalog, Digital, Software

Granularity of control Chip level , Block level, Transistor level

T.Sakurai

Self-Adjusting Threshold-voltage Scheme(SATS)

VBBN

Self- Sub- Bias

Circuit (SSB)

Leakage Sensor

leak

VGN1 Pwell

ON/OFF

low Vth large leakage SSB ON deepVBB high Vth

high Vth little leakage SSB OFF shallow VBB low Vth• control VTH to adjust leakage current• compensate VTH fluctuation

T. Kobayashi, and T. Sakurai, "Self-Adjusting Threshold-Voltage Scheme (SATS) for Low-Voltage High-Speed Operation," in Proc. IEEE 1994 CICC, pp.271-274, May 1994.

Leakage, Replica, Body bias, Analog, Chip level

T.Sakurai

VTCMOS (Variable Threshold CMOS)

Kobayashi, CICC‘94, pp.271-274. Kuroda, ISSCC’96, pp.166-167.

p-well

ILEAK,LCM

WLCM

Leakage Current Monitor (LCM)

"L"

chip

WCHIP

on / off

Self-Substrate Bias (SSB)

-3.0

-2.0

-1.0

0.0

V TH (

V)

V BB

(V)

0.2

0.3

0.4

0.5

0.6

- 0.2 - 0.1 0 0.1VTH (V)

0.2

VTH with control

VTH without control

VBB

ILEAK,CHIP

1

2

CHIP

LCM

CHIP,LEAK

LCM,LEAK

WW

WW

II

W2

W1

T.Sakurai

Body Bias Control to Minimize Fluctuation

16MbitDRAM

Speech Codec

Multiplexer

MPEG-4 VideoCodec

HostI/F

DRAM

I/F

PLLCamI/F

DisplayI/F

Pre-filter

VTVT

VT VT

T=27℃

-0.1 0 0.1 0.2 0.3 0.4 0.5(|VTH .p|+VTH.n )/2 as processed (V)

VTCMOS in active mode

VTCMOS in standby mode

Conv. CMOS

I DD.

leak

(A

)1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

Variable Threshold-voltage CMOSCourtesy of Toshiba Corp.

T.Sakurai

Measured benefit of VTCMOS

I DD

.leak

(A)

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

-0.1 0 0.1 0.2 0.3 0.4 0.5

Tj=70C

(|VTH .p|+VTH.n )/2 as processed (V)

Tj=27C

-0.1 0 0.1 0.2 0.3 0.4 0.5(|VTH .p|+VTH.n )/2 as processed (V)

VTCMOS in active mode

VTCMOS in standby mode

Conv. CMOS w/o body bias control

I DD

.leak

(A)

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

T.Sakurai

Power-on-Shunt Circuit

VT_p

VT_nLogicVT circuit

RD Q

RCounter

enableOSC.

Reset

C

R

VDD

GND

Controller

T.Sakurai

Layout of VTCMOS

Leaf cell w/oP/N-tap.(removed by MDP)

VDD

vnsu

b

vpsu

b

nwellpwell

Advantage no library re-design realized by MDP(Mask Data Processing) and

P&R possibly lower area penalty (minimum 4%)

Disadvantage P/N-taps are not close to transistors

VDD

VSS

VDD

VSS

T.Sakurai

Effect of substrate noise on

Kuroda, ISLPED’96, pp.309- 312.

8x8mm2, 188k gates 0.3 µm n-well, 2-layer metal VTCMOS

n+

n-welln-subp-sub

n+

n+

p+

p+

p+

(a) one substrate-contact

p-sub

n-welln-subp-sub

p-sub n-sub

p-sub n-sub

n-sub

(b) 400 substrate-contacts

T.Sakurai

Jitter measurement

(a) one substrate-contact with noise

(b) 400 substrate-contacts without noise

T.Sakurai

500µs

n-well

p-sub

Active Standby

2V

0V

-2V

4V

n-well

p-sub

2V

0V

4V

-2V

Standby Active0.5µs

Measured VBB waveform in VTCMOS

T.Sakurai

Power penalty of VTCMOS itself is smallIDD

impact ionization

ISUB ~ 0.1% IDD

IPUMP 2≒ ～ 3 Isub

PUMP

IPUMP ~ 0.2 ～ 0.3% IDD (at active)

ILCM ~ 1µA (always)ECV2 ~ 5µF x (3V)2 = 0.05µJ (active <-> standby) eg. MPU: ‘Idle’<->’On’ w/ timer interruption of every 25ms P ~ 2µW

LCM

ILCM

T.Sakurai

Speed-Adaptive Threshold-Voltage (SA-Vt) CMOS

Miyazaki, ISSCC’00, pp.420- 421. Miyazaki, ISLPED’98, pp.48- 53.

220MHz, 1.5-1.8V, 320-380mW, 30A, 4.3MTr

Speed, Replica, Body bias, Digital, Chip level

T.Sakurai

Digital control in adaptive body bias

Phase Detector & Counter

Resistor Network

Bias AmplifierCUT

Delay

Phase Detector & Counter

Resistor Network

Bias AmplifierCUT

Delay

21 sub-sites with separate body bias for each sub-site

J. Tschanz, J. Kao, S. Narendra, R. Nair, D. Antoniadis, A. Chandrakasan, and V. De, “Adaptive Body Bias for Reducing Impacts of Die-to-Die and Within-Die Parameter Variations on Microprocessor Frequency and Leakage,” ISSCC, Paper 25.7, 2002.

5-bit counter

VREF

VCCA

+- VBP

fCritical path

Phase detector

Circuit block (CUT)

VCC

VSS

VBP,ext

VBN,ext

PD

Bias selector

2R 2R 2R 2R 2R 2R

R R R R

Rf

R

5-bit counter

VREF

VCCA

+- VBP

fCritical path

Phase detector

Circuit block (CUT)

VCC

VSS

VBP,ext

VBN,ext

PD

Bias selector

2R 2R 2R 2R 2R 2R

R R R R

Rf

R

Speed, Replica, Body bias, Digital, Block level

T.Sakurai

Software control of adaptive body bias

Conventional

VDD=0.5VVTHlow=0V94% f/2 operation

Norm

aliz

ed p

ower

VTH-hopping

K.Nose, M.Hirabayashi, H.Kawaguchi, S.Lee and T.Sakurai, "VTH-Hopping Scheme to Reduce Subthreshold Leakage for Low-Power Processors," JSSC, pp.413-419, Mar. 2002.

0

0.5

1PLEAK

PDYNAMIC

VTH is dynamically changed by means of back-gate bias.Workload, Actual, Body bias, Software, Chip level

T.Sakurai

Schematic of VTH-hopping

VTH controller

Freq. control

CONT

fCLK or fCLK/2

VBSP2

Target processor

VTH-hopping(VTHlow&VTHhigh)

Power control block

VBSP1

VBSN2

VBSN1

VTHlow_Enable

VTHhigh_Enable

VDD

GND

VBSN

VBSP

T.Sakurai

Multiple Threshold Voltage CMOS with Body Bias

Yamashita, ISSCC’00, pp.414- 415.

450MHz,1.8V, 8.3M logic gate +20M RAM Tr.

T.Sakurai

Drain leakage

-1 -0.5 0 0.510 -3

10 -2

10 -1

100

VBS [V]

Norm

aliz

ed I D

[A]

Body bias decreases subthreshold leakage

GIDL

VTH,MAX= x VBS,MAX

VBS,MAX

T.Sakurai

Performance increase with body-bias control

Perf

orm

ance

incr

ease

with

bod

y bi

as c

ontr

ol

VDD [V]Condition: keep leakage power at 100ºC with lowest VTH (VTH=0.15VDD) constant

0.5 0.6 0.7 0.8 0.9 1 1.1 1.21.0

1.2

1.4

1.6

1.8

2.0

VTH0.1V

VTH0.05V

T.Sakurai

Performance increase with body-bias control

Perf

orm

ance

incr

ease

with

bod

y bi

as c

ontr

ol

VDD [V]Condition: keep leakage power at 100ºC with lowest VTH (VTH=0.15VDD) constant

0.5 0.6 0.7 0.8 0.9 1 1.1 1.21.0

1.2

1.4

1.6

1.8

2.0

VTH,MAX0.1V

VTH,MAX0.05V

VTH,MAX0.15V

VTH,MAX0.2V

T.Sakurai

Why a group other than circuit solve the problem?Circuit side:

We are the most power-aware people who worked hard on this... without success though and worn out.

To System group:1) Most of software is power-negligent instead of power-aware although only system level can know performance-power tradeoff.2) Give us required performance-tag in protocols.

To Device group:1) First off, come up with non-leaking switch device anyway.2) High-k, low-k and high-µ are great weapon for lower power. 3) Device has not been optimized for power although device guys think it is.

D SC

T.Sakurai

Approaches for active leakage control

DS2GSBS0THGSTHGS

s/VVLEAK

VVVVVVV10I THGS

Source Drain

Main gate VGS

2nd gate VGS2

Body

Double gate transistor

Negative VGS Body bias

Double gate

DIBL

Subthreshold swing

T.Sakurai

The headache is not foreever

1 10 10010 -1

10 0

10 1

10 2

10 3Re

lativ

e le

akag

e po

wer

Scaling variable:

Per gate

Per chip with Tr. Count 1

Per chip with Tr. Count 2

90nmVDD=1V, VTH=0.15V

T.Sakurai

Let’s search for global optimumwith collaboration among levels

Local optima

Global optimumApproaches

log

(PO

WER

)