Wireless power transfer 2007_3_slide

Design Solutions for Multi-Object Wireless Power Transmission Sheet

Based on Plastic Switches

M. Takamiya, T. Sekitani, Y. Miyamoto, Y. Noguchi, *H. Kawaguchi, T. Someya and T. Sakurai

University of Tokyo*Kobe University

2

OutlineWireless Power Delivery for Ubiquitous Electronics

Wireless Power Transmission Sheet (WPTS)

Key Circuit Technologies for WPTS(1) Mixed Circuit of MEMS Switches and Organic

FETs with Two Frequencies for Shared Coil

(2) Multiple Activation Technique of Small TX-Coils for Position Adjustment-Free WPT

(3) OFET Level-Shifters with Adaptive Biasing

Summary

3

Ubiquitous Electronics

Solar cellsReplacement cost Dark environment

Batteries

HealthcareSafety & Security

Convenience

WelfareEntertainment

1,000~10,000 Electronic devices

How can we power them ?

Issues

4

Power Transmission with Electromagnetic Induction

Advantage

Magnetic fields

TX-coil

RX-coil

I1dI1V2 dt

= M

Wireless power transmission provides the mobilityfor RX-coil.

DrawbackDisplacement degrades the power transmission efficiency.

5

Power Transmission Efficiency Loss

Efficiency ~ 0.1% Efficiency ~ 60%30cm2 X 1 coil 1 inch2 X 64 coils

1 inch2

TX-coil

RX-coil

1 large TX-coil Many small TX-coils

TX

RX

Segmentation and selective activation of TX-coils prevent the efficiency loss.Position detection of the RX-coil is required.

6

Position Detection of RX-Coilw/o RX-coil with RX-coil

TX-coil

RX-coil

FrequencyTX

vol

tage

Scan TX-coils and monitor the TX voltage change at a given frequency.

7







Summary

8

Device Structures of WPTS

RX-coil

MEMS switchesfor power transmission

Organic FETs (OFETs)for RX positiondetection

21 cm

21 cm

TX-coil array

8 x 8 array (1-inch pitch)

Speed On-resistanceSwitchMEMSOFETs

~ 1Hz> 100Hz

< 10Ω> 1kΩ

Printable switches provide the low costsolution for the large-area applicationssuch as WPTS.

Printable

Complementary

9

Wireless Power Transmission Sheet

8 x 8 TX-coil array

21 cm

Embedded in the floorMEMS switchesOFETs

10

TX-coil array

RX-coil

25.4 mm

5-mm distance between RX-and TX-coils

Power Transmission to LEDs

38 LEDs13.56 MHz

TX RX

(Without OFETs)

11

Power Transmission to LEDs

12

Plastic MEMS switches

10 mm x 20 mm, 4 Hz (max)

13







Summary

14

Shared coil sheet reduces the fabrication cost and increases the position detection efficiency.

Shared Coil Sheet

MEMS switchesfor power transmission (PT)

OFETs forRX positiondetection (PD)

TX-coil array

This workPrevious work [1]

Coil

Coil

MEMS

OFET

for PT

for PD

[1] T. Sekitani, et al., IEDM2006.

15

Mixed Circuits of MEMS and OFETs for Shared Coil

On

MEMS switch

Off

+

0V13.56 MHzfor power

transmission

RXTXf1 =3.5 MHzfor positiondetection

VMON

CP

Unit circuits for 8 x 8 array

Monitor for PD

Mixed circuits of MEMS switches and OFETs with two different frequencies enabled the shared coil.

to distinguish 2 frequencies

C1

16

Frequency for Position Detection

5

4

3

2

1

6

0Frequency (f1) (MHz)

0 10 155

WithoutRX-coil

Maximumfrequencyfor OFETs

V MO

N(V

)

WithRX-coil

3.5

Measured

3.5 MHz was used due to the speed limitation of OFETs.

17

Position Detection with Shared Coil

33% voltage change is acceptable for the position detection, while 91% was achieved with separate coils [1].

b - ab = 33%

Without RX-coil With RX-coil

a b

0.2

0.1

0-0.1

-0.2

0.3

-0.30

Time (ns)500250 750 1000 1250

f1 = 3.5 MHz

V MO

N(V

)Measured

18







Summary

19

Exact Position Adjustment was Required

TX-coil pitch = 1 unit = 25.4 mm

y

TX RX

Previous work [1]

Spectrumanalyzer

TX RX

200 mW 100μm distance

Pow

er e

ffici

ency

(%)

50

40

30

20

10

60

0Displacement (y) (unit)

0 0.4 0.6 0.8 10.2

Displacement of TX/RX coils with the same diameter rapidly reduces the power efficiency.

Next TX-coilshould beselected

20

Multiple Activation Technique of Small TX-Coils

4x4y

4 unit

TXRX

1x1y

Ref[1]y

TX RX TX

3x3y

2x2y

Pow

er e

ffici

ency

(%)

5040302010

60

0

Ref

Displacement (y) (unit)0 0.4 0.6 0.8 10.2

1x1

2x23x3

4x4

RX RXTX

Single

Same

Multipleactivation

Differentdiameter

Conv. Proposed

21

Position Adjustment-Free WPT

3 x 3 coils activation is the best design choice, because the minimum efficiency determines the specification of WPTS.

0

Pow

er e

ffici

ency

(%)

50

40

30

20

10

60

0 Ref[1] 1x1 2x2 3x3 4x4

max

minave.

Best choice

Activated number of TX-coils

22







Summary

23

Levelshifters

VDD = 1V ~ 5V

Silicon VLSIfor controller

Why OFET Level Shifters?

CostsHigh voltage tolerant silicon IC

OFETsHighLow

MEMSOFETs

VDD = 40V ~ 100V

Wireless power transmission sheet

Design target: OFET level-shifters from 5 V to 40 V

24

OFET Level Shifters

SF SF SFOut5 V

0 VIn 40 V

0 V

pMOS-only design

Gain = 2.6

40 V

In

Out

Vadap

40 V

InOut

Bias

Source followerSingle amp

Adaptive biasing is required to deal with PVT variations.

25

OFET Level Shifters with Adaptive Biasing

SF SF SF Out

5 V0 V

In

40 V

SF SF SF

+-

+-

2.5 V

20 V20 V

2.5 V

20 VIn

Out

Vadap Vadap

Original

Replica

Adaptive biasing requires high gain diff. amp.

26

3 Differential Amps with Different Loads

Diode-connectedload

Current-sourceload (proposed)

Triode load

In

Out

Inb

Outb

-30V -30V

In

Out

Inb

Outb

In

Out

Inb

Outb

The gain of three amplifiers are compared at fixed power.Identical

40 V

& DepletionEnhancement

pMOS with back gate

27

Gain Comparison of Differential Amps

0 10 20 30 400

10

20

30

40

In (V)

Inb,

Out

, Out

b(V

)

Inb

Out Outb

Diode load(G = 0.6)

CS load(G = 15)Triode load(G = 4.5)

G: Gain @ In=20 VSimulated

Current-source load achieved the highest gain.

28The high gain derived from the large rO.

Output Impedance(rO) of Driver and Each Load

0 10 20 30 400

2

4

6

8

Out (V)

I D(μ

A)

Diode load(rO = 0.20MΩ)

CS load(rO = 11MΩ)

Triode load(rO = 1.9MΩ)

10

12

14

Driver(rO = -10MΩ)

1/rO

rO @ In=20 V

Out

20VVP

ID

Out

ID

-30V

Out

ID

Out

ID

Simulated

29

Measured Differential Amps40V

InOut

20VOutb

0 10 20 30 400

10

20

30

40

In (V)

Out

, Out

b(V

)

Out

OutbGain = 6.4

4.9 mm

2.9 mm

8000/50

4000/50

16000/50

Diff. amp with the current-source loads enabled by the back-gatedOFETs achieved the 2.3 times gain of [4].

[4] N. Guy, et al., ISSCC2006.

30

Measured Adaptive Biasing

22.2 mm

6.4 mm

The high gain diff. amp contributes to the successful feedbackcontrol. In (V)

Out

(V)

0 3020 4010

20

10

0

30

40SF

+-

20 V

OutIn

31

SummaryWireless power transmission sheet with plastic MEMS switches and organic FETs.

Mixed circuit of MEMS and OFETs with two frequencies reduces the number of coil sheets.

Multiple activation technique of small TX-coils frees the users from position adjustment.

OFET level-shifters with the current-source loads bridge the operation voltage gap between silicon VLSIs and OFETs/MEMS.

32

Expected Applications of WPTS

In the wall

TV on a wall

In the table

Vacuum cleanerHome-carerobot In the floor

Ambientillumination

Cell-phone & PC

Wireless power transfer 2007_3_slide

Documents

multiple activation

key circuit

outlinewireless

plastic mems

ofet level

power efficiency

ofet level

tx rx