Enabling Millimeter Computing - IEEEewh.ieee.org/r5/central_texas/cas_ssc/meetings/2011/...Enabling...

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University of Michigan 1

Enabling Millimeter Computing

Dennis Sylvester

University of Michigan

Joint work with David Blaauw

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1950 1960 1970 1980 1990 2000 2010 20200.01

0.1

1

10

100

1000

10000

100000

Infla

tion

Adju

sted

Pric

e (1

000s

of U

SD)

Bell’s Law Mainframe

Mini Computer

Personal Computer

Workstation

Smartphone

Laptop

[Bell et al. Computer, 1971, Bell, ACM, 2008]

New class of computing

systems every decade

3 3

3


Bell’s Law – Corollary Mainframe

Mini Computer

Personal Computer

Workstation

Smartphone

100x smaller every decade [Nakagawa08]

Laptop

1950 1960 1970 1980 1990 2000 2010 2020100m

110

1001k

10k100k

1M10M

100M1G

10G100G

1T10T

Size

(mm

3 )

4 4

4

University of Michigan 4 1950 1960 1970 1980 1990 2000 2010 2020

100m1

101001k

10k100k

1M10M

100M1G

10G100G

1T10T

Size

(mm

3 )Bell’s Law – Production Volume

Mainframe

Mini Computer

Personal Computer

Workstation

Smartphone


1 per Enterprise

1 per Company

1 per Professional

1 per person 1 per Family

1 per Engineer

Laptop

5 5

5

University of Michigan 5 1950 1960 1970 1980 1990 2000 2010 2020

100m1

101001k

10k100k

1M10M

100M1G

10G100G

1T10T

Size

(mm

3 )Bell’s Law – Production Volume

Mainframe

Mini Computer

Personal Computer

Workstation

Smartphone


mm-Scale Computing

1 per Enterprise

1 per Company

1 per Professional

1 per person

Ubiquitous

1 per Family

1 per Engineer

Laptop

Ubiquitous

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mm-Computing: Application Areas

Medical Surveillance and micro robotics

mm-Scale Computing

Infrastructure

Textiles

Environment

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1998 2000 2002 2004 2006 2008 2010 20120.1

1

10

100

1000

10000

100000Si

ze (m

m3 )

Where Are We?

[Pister99]

[Sylvester11]

[Blaauw10]

[Pister01]

Mica2Dot

[Park06]

[Roggen06]#

Timeline

[Nakagawa08]

[Hill03]

[Chee08]

Mica2mote

[Hollar00]

Goal - 1mm3 complete sensor

Kris Pister coins “Smart Dust” term

Intel mote#

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Why aren’t we further along? Long device lifetime vs.

small form factor The 3 most important

things in miniaturization: Power, Power, Power

Circuits just are not there yet

101 102 103 104 105 106 107 108 109 101010p

100p1n

10n100n

1µ10µ

100µ1m

10m100m

110

1001k

decade

hour

Powe

r Bud

get,

W

Desired Lifetime, s

minute

weekday

yearmonth

1 mm3 Harvester

9 9

9


Status of Miniature Sensors Where are we now? 1cc in the research labs 30-50cc commercial motes

Goal: 1mm3 sensor node 1000x improvement Enables host of new applications Tiny wireless sensor nodes that

can be distributed anywhere and everywhere

Challenge: battery size

10,238:1 5hrs of lifetime

1:1 5 years of lifetime

~10,000x

10 10

10


Battery Trends New battery chemistries

are rare Li-ion ≤7%/year expected

improvement (energy density)

Energy capacity limited by safety and cost

1956 Eveready Alkaline Battery ~72mAh

1992 Rechargeable

Alkaline Battery

2000 mAh

1989 Lithium

Iron Disulfide Battery

3100 mAh

1896 Columbia Dry Cell

Zinc Carbon Battery

2005 LSD NiMH

Battery 2300 mAh

1961 Nickel

CadmiumBattery

1100 mAh

1960 Zinc

Carbon Battery

1100 mAh

[Broussely04]

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Energy Harvesting

µW/cm3

Photovoltaic (outside)

15,000#

Air flow 380

Vibration 200

Temperature 40#

Pressure Var. 17

Photovoltaic (inside)

10#

[Courtesy: Jan Rabaey, S. Roundy]

Microturbine

Air Flow

Solar

Capacitive Vibration

Harvesting

Capacitive Vibration

Harvesting

Temperature Gradient

Piezoelectric

# fundamental metric is µW/cm2

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Harvesting Improvements Limited Energy harvester efficiency gains are modest Fundamentally limited by harvesting source

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Microsystem functions include sensing, processing, storage, and transmission All components must be re-examined to fit within power

envelope defined by power sources and power management

mm3: How Do We Get There

Sensors and Front End

Microprocessor Memory

Wireless Communication

Power Management

Wakeup Controller

Antenna

Power Sources

MEMS Sensors

Wakeup Controller /

Timers

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Past Michigan Sensor Designs

Phoenix 2 Design (2010) - 0.18 µm CMOS

- Commercial ARM M3 Core - Solar harvesting / PMU

-28 µW/MHz

Subliminal 2 Design (2007) - 0.13 µm CMOS

- Study variability effects - 3.5 µW/MHz

Subliminal 1 Design (2006) -0.13 µm CMOS -investigate Vmin

-2.60 µW/MHz

Phoenix 1 Design (2008) - 0.18 µm CMOS

- Minimize sleep current - 2.8 µW/MHz / 30pW sleep power

processor

memory

244µm

305µm

122µm

181µm

processor

memory

244µm

305µm

122µm

181µm

IOPM (2011) - 0.18 µm CMOS

- MEMS/CDC - Solar / PMU

- Wireless comm

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Microsystem functions include sensing, processing, storage, and transmission All components must be re-examined to fit within power

envelope defined by power sources and power management

mm3: How Do We Get There

Sensors and Front End

Microprocessor Memory


Power Management

Wakeup Controller

Antenna

Power Sources

MEMS Sensors

Wakeup Controller /

Timers

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100p

1n

10n

100n

1µ

10µ

100µ

1m

Powe

r Con

sum

ptio

n (W

)

Time (min)0 20 40 60

100 ms

1 ms

Why Timers Are So Important

Power consumptions in various modes of ULP sensor

1

Base Station

Sensor Node

IdleSensor measure

TX / RX

Asymmetric RF communication does not require precise timing

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100p

1n

10n

100n

1µ

10µ

100µ

1m

Powe

r Con

sum

ptio

n (W

)

Time (min)0 20 40 60

100 ms

1 ms



1

Base Station

Sensor Node

IdleSensor measure

TX / RX

Meas. 10%

TX/RX 11%

Idle 79%

Energy 0.91 µJ/hr

Asymmetric RF communication does not require precise timing

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100p1n

10n100n

1µ10µ

100µ1m

Powe

r Con

sum

ptio

n (W

)

Time (min)

100p1n

10n100n

1µ10µ

100µ1m

0 20 40 60

0 20 40 60

IdleSensor Measure Synch. Mismatch

TX / RX

Timer



1

Sensor Node

Sensor Node

Asymmetric RF communication does not require precise timing Symmetric RF communication requires precise timing Energy penalty for mismatch can dominate energy budget

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100p1n

10n100n

1µ10µ

100µ1m

Powe

r Con

sum

ptio

n (W

)

Time (min)

100p1n

10n100n

1µ10µ

100µ1m

0 20 40 60

20 40 60

Mismatch (1s)

0


TX / RX

Timer



1

Sensor Node

Sensor Node


20 20

20


100p1n

10n100n

1µ10µ

100µ1m

Powe

r Con

sum

ptio

n (W

)

Time (min)

100p1n

10n100n

1µ10µ

100µ1m

0 20 40 60

20 40 60

Mismatch (1s)

0


TX / RX

Timer



Synch. Mismatch

97%

Energy 103 µJ / hr

1

Sensor Node

Sensor Node


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Keeping Time with Picowatts Crystal oscillators bulky and

power hungry RC oscillators preferable,

exhibit accuracy vs. power tradeoff

Low power commercial crystal oscillator ~120nW

[Ref: Micro Crystal Switzerland RV-2123-C2]

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exhibit accuracy vs. power tradeoff

Vin Vs

Vclk

ML1

MS1

MS2

MS3

MS4

MS5

MS6MC1

INV1 INV2

TINV

Vinv

Vin Vs Vout

MC2

vx

MI1

MI2

MI3

MI4Gate leakage

current based timer <1pW, < 1Hz@300mV

But…. 1400ppm Jitter 1600ppm/ºC



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exhibit accuracy vs. power tradeoff Still a need for improved

accuracy at ~nW

Multi-stage Gate Leakage Timer with

Temperature Compensation

660pW power

but… 275ppm jitter 31ppm/ₒC temp variation



V(Q

)

Stage 1

Stage 2

V(Q

)

Stage 3

V(Q

)

Time

MP MZ

Q

Vout

To Next Stage

From Prev. Stage

Stage1

Stage2

S

R

Q

SR Latch

StageN

Level Conversion

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Previous Voltage Reference Designs

36nW design

Voltage references used in regulators, timers, radios Previous work Consumes 100-1000X more power Typically needs higher supply voltage

Reasons: transistors in saturated region (power & headroom)

0.4 0.6 0.8 1.0 1.2 1.410-1310-1210-1110-1010-910-810-710-610-510-410-310-210-1

previous designs 2T voltage reference

Powe

r [W

]

Minimum functional Vdd [V]

3 orders of magnitudeimprovement

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pW Voltage Reference

-20 0 20 40 60 80175.0

175.1

175.2

175.3

175.4

175.5

175.6

0.5 1.0 1.5 2.0 2.5 3.0 3.5175.0

175.1

175.2

175.3

175.4

175.5

175.6

Vdd=0.5V TC=3.4ppm Vdd=1.2V TC=3.6ppm Vdd=3.3V TC=3.0ppm

V ref[m

V]

Temperature[oC]

V ref[m

V]

Vdd[V]

Temp=-20oC LS= 0.022%/V Temp=20oC LS= 0.033%/V Temp=80oC LS= 0.029%/V

VDDmin = 0.5V Power = 2.3pW TC=19.4ppm/oC LS=0.033%/V PSRR = -70dB at

100kHz Area = 1350µm2

Vss

VssM1

M2

Vdd

Vref3.3/60

1.5/60

New design achieves Ultra-low power down to 2.2pW at

Vdd=0.5V Good TC, LS, PSRR, excellent footprint,

power

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Tightening Variability

↓ TC and Vout spread by 9.6X and 9.8X 25 dies: TC<50ppm, ±0.36% Vout

166 168 170 172 174 176 178 1800

50100150200250300350400

µ=176.0mVσ=0.32mV<+-0.36%

before trimmingafter 1pt trimming

TC [p

pm/o C]

Vout [mV]

<50ppm/oC

µ=29ppm/oCσ=11ppm/oC

1-pt temp trimming over 25 dies

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1.5 mm3 Intraocular Pressure Monitor Continuous IOP monitoring Wireless communication Energy-autonomy Device components Solar cell Wireless transceiver Cap to digital converter Processor and memory Power delivery Thin-film Li battery MEMS capacitive sensor Biocompatible housing

[Haque, Wise]

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IOP Monitor Block Diagram

Cross sectional view of microsystem

Thin-filmSolid-StateLi Battery

CapacitivePressureSensor

Top Chip

3

Top Power

Management Unit

WirelessTransceiver

BottomPower

Management Unit

Bottom Chip

Bottom Wakeup

Controller

Processor Capacitance to Digital ConverterSRAM

Top WakeupController

Biocompatible Housing

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Usage Model Example

CDC converts pressure to a digital value Stores IOP data to a memory mapped location



Top Chip

3

Top Power

Management Unit

WirelessTransceiver

BottomPower

Management Unit

Bottom Chip

Bottom Wakeup

Controller




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Usage Model Example

Processor extracts medical information from IOP data Stores its result into SRAM



Top Chip

3

Top Power

Management Unit

WirelessTransceiver

BottomPower

Management Unit

Bottom Chip

Bottom Wakeup

Controller




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Usage Model Example

User wirelessly queries microsystem Responds by retrieving and transmitting data



Top Chip

3

Top Power

Management Unit

WirelessTransceiver

BottomPower

Management Unit

Bottom Chip

Bottom Wakeup

Controller




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Standby Mode

Energy harvesting and low-load power management Data stored in SRAM



Top Chip

3

Top Power

Management Unit

WirelessTransceiver

BottomPower

Management Unit

Bottom Chip

Bottom Wakeup

Controller




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IOP Transmitter

80 100 120 140 160 180 2001E-7

1E-6

1E-5

1E-4

1E-3

0.01

0.1

Tran

smit

Bit E

rror R

ate

Transmit Distance, mm

Main radio challenge: very small coils FSK receiver with

dual-resonator LC tanks Transmitter sends 1

bit (100ns), drawing from 1.6nF decap, recovers droop (~100us) then sends another bit Transmit media is 0.5

mm saline + air Transmitter: 4.7nJ/bit,

improves upon prior implantable work

10-6 bit error rate at 10cm transmit

distance

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Power Delivery and Management Battery powers CDC and wireless TRx Isolated local TRx power supply prevents catastrophic VDD drop CDC and TRx designed with high-VTH thick-tOX IO devices and

no bias currents for low leakage during standby mode

VSOLARV0P45

µP &SRAM WUC

CDC TRx

V3P6

PMUBOT

SCVR

PMU TOP

Bottom Chip Top Chip

PowerSupply

Isolation

VTRx3P6

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VSOLARV0P45

µP &SRAM WUC

CDC TRx

V3P6

PMUBOT

SCVR

PMU TOP


PowerSupply

Isolation

VTRx3P6

Power Delivery and Management 8:1 Switch Cap Voltage Regulator (SCVR) delivers 0.45 V µP is power gated in standby mode and uses logic devices SRAM and WUC use IO devices for low standby leakage SCVR clock is reduced to 50 Hz clock in standby mode

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Power Delivery and Management Solar cell connected when open circuit VSOLAR exceeds V0P45

Check voltage on solar cell with small replica Compare using clocked comparator

SCVR up-converts solar energy to recharge battery

VSOLARV0P45

µP &SRAM WUC

CDC TRx

V3P6

PMUBOT

SCVR

PMU TOP


PowerSupply

Isolation

VTRx3P6

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Power Sources

0.07 mm2 solar cell 0.18 μm CMOS No post-processing 5% solar efficiency

Cymbet thin-film Li battery 1 mm2 custom size 1μAh capacity 40μW peak power

PSUB

p+n+n+

DNW

PW

0.0 0.1 0.2 0.3 0.4 0.5 0.60

5

10

15

20

25

30

P = 13.7µW/mm2

η = 5.48%

VOC = 0.54V

Voltage, V

Curre

nt, µ

A/m

m2

ISC = 26µA/mm2

0

5

10

15

Powe

r, µW

/mm

2

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SCVR Measurements

75% efficiency with 90 nW processor load in active mode 40% efficiency with 72 pW load in standby mode

20 40 60 80 100 120 140 160

30

40

50

60

70

80Ef

ficie

ncy,

%

Load Power, nW

75% efficiency

Switching losses

Conduction losses

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Active Mode PowerCDC 7.0 µWTransceiver 47.0 mW

• µP @ 100 kHz 90.0 nW

Energy/Day

6.3 µJ

1.7 µJSCVR 116.9 nW 2.2 µJ

Standby Mode PowerCDC 172.8 pWTransceiver 3.3 nW

• WUC 62.0 pW

SCVR 174.8 pW• 4kb SRAM 9.8 pW

Energy/Day14.9 µJ

846.7 nJ15.1 µJ

5.2 µJ

Time/Day19.2 sec

134.4 µsec

19.2 sec19.2 sec

Time/Day24 hours24 hours

24 hours24 hours

24 hours

134.8 µJ

285.1 µJ

IOP Monitor Power Consumption Measure IOP every 15 minutes DSP with 10k processor cycles @ 100 kHz per measurement Daily wireless transmission of 1344b raw IOP data

5.3 nW average power 1 month lifetime with no harvesting

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PMU Measurements

Energy autonomous operation with 1.5 hours of sunlight or 10 hours of indoor lighting per day

0 440 450 460 470 480 490 5000

10

20

30

40

50

60

70

80

Char

ge P

ower

, nW

VHARVEST, mV

IndoorAverage Power of

IOP Monitor = 5.3 nW

Sunny

Cloudy

Recharge Power Delivered to Battery = 80 nW

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Leveraging Ideas for Other Domains 3D NTC

Centip3De, 7-layer 128-core system with stacked DRAM NTC: 5-10 GOPS/W general

purpose in 130LP

ULP DSP FFT accelerator with record

energy efficiency (ISSCC11)

15.8nJ/FFT @ 240MS/s

Aggressive pipelining to drive down Vmin and Emin

Minimize leaky memory

20M 40M 60M 80M 100M15n16n17n18n19n20n21n22n

0.36V

0.33V

0.3VM

easu

red

ener

gy p

er F

FT [J

]

Measured clock frequency [Hz]

Measured at 27oC proposed FFT

0.27Vdesign point (simulated)vdd=275mV

X

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1mm3 Platform

Battery and Solar Harvesting

Processor

Memory

Timer

MotionDetect

Imager


ImagingSolar

Harvesting

Processingand Wireless

New Applications

Biology

Pika

Medicine

ICP

Security

Conclusions Applications of mm-scale computing are endless and often

unimaginable today But first the hardware must get there

Power minimization is paramount Few nW power budget Re-think entire sensor

system from bottom up

For the next decade: nanowatt challenge Trickle up effect to

servers, mobile platforms

Acknowledgements: Many UM grad students

Enabling Millimeter Computing - IEEEewh.ieee.org/r5/central_texas/cas_ssc/meetings/2011/...Enabling...

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