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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
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
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
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
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
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
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
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
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
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