ISSCC 2008 / SESSION 15 / TD: TRENDS IN SIGNAL AND POWER TRANSMISSION / 15.4
15.4

A 107pJ/b 100kb/s 0.18µm Capacitive-Coupling
Transceiver for Printable Communication SheetLechang Liu1, Makoto Takamiya1, Tsuyoshi Sekitani1,
Yoshiaki Noguchi1, Shintaro Nakano1, Koichiro Zaitsu1,
Tadahiro Kuroda2, Takao Someya1, Takayasu Sakurai1
1

University of Tokyo, Tokyo, Japan, 2Keio University, Yokohama, Japan

Low-power wireless communications between electronic objects
scattered over tables, walls and ceiling will form an infrastructurenecessary for wireless sensor networks and ambient intelligence. A
data edge-signaling scheme and DC power-free pulse detector allow
the realization of a low energy/bit transceiver for use in a communication sheet [1], as shown in Fig. 15.4.1(a), which allows the creationof infrastructure for ambient electronics when used together withthe wireless power transmission sheet [2].
An overview of the whole communication system is shown in Fig.
15.4.1(b). By combining meter-scale wired communication and μmscale wireless capacitive coupling communication, the sheet offers acommunication method that enables multiple electronic objects scattered over the sheet to communicate contactlessly with each other,by establishing communication paths without cumbersome physicalconnections. In this application differential signaling is required,because there is no common ground among the TX sheet, the communication sheet and RX sheet. Since the information transmitted
over the sheet is confined in a small space close to ad hoc routed
paths, the system is free from issues related with radio frequency
band allocation. The communication route is dynamically formed
using plastic MEMS switches, and an organic nonvolatile memory
stores the routing information [1]. As illustrated in Fig. 15.4.1(c), thecommunication sheet is composed of 8×8 units and every unit consists of four pads. The communication between two units is achievedby turning on the adjacent two MEMS switches and the top tworouting switches. Thus, only four switches are required for point-topoint communication.
The device structure of the communication sheet is shown in Fig.
15.4.2. It consists of five low-cost printed sheets [1]: a 16×16 9.7mm2
pad array for capacitive coupling, two 9×8 MEMS-switching matrices for differential signal routing, a 9×8 organic nonvolatile memory
array for routing information storage and a 8×8 position-sensing coilarray [2]. The communication between the pad of the TX/RX and thepad on the sheet is similar to conventional chip-to-chip communication. In the sheet communication system, however, the available
maximum effective inductance is about 10μH and the worst caseparasitic capacitance is 50pF, which are different from chip-to-chipcommunication. If the received signal is large enough so that thepower consumption of receiver can be ignored, the power-consumption of the whole system is only determined by the transmitter. Theenergy-consumption of capacitive coupling and inductive coupling
can be approximated by CV2 and LI2, respectively. For the given
parameters, the energy-consumption of capacitive coupling is lower
than inductive coupling at less than 3.5MHz. In this application thetypical data rate is 100kb/s and therefore capacitive coupling
instead of inductive coupling [1] is used.
For capacitive coupling, a key constraint to consider is that when along string of “1’s” and “0’s” is passed through a high-pass filter, thesignal experiences the “zero wander” effect. Conventionally, feedback control is introduced to generate a complementary signal tocompensate the decaying signal [3]. The input NRZ (Non-ReturnZero) signal is converted into a return-to-VDD/2 signal pulse to avoid
this constraint. Figure 15.4.3 shows the schematics of the proposedtransmitter and receiver. The modulated data is achieved by switching the input data and the output of the half-VDD generator [4]. The
driver stage of the half-VDD generator has zero power dissipation
with half-VDD signals. The edge detector is used to generate theswitching signal for the selector by detecting both the rising andfalling edge of the input data. Compared to previous synchronous
circuits [5], asynchronous circuits have no global clocks and theoperation is triggered by signal transitions, potentially having theadvantages of low power dissipation. To detect a small signal, an292

amplifier and a comparator is often used in the first stage of thereceiver to amplify the received signal for the next demodulation.
The major disadvantage of this topology is large DC power dissipation that occurs even for no AC input. In the transmitted signal of
the communication sheet, the circuit spends long periods of timewith no AC signal. Power dissipated in these periods is wasted. Apulse detector can alleviate this problem by having essentially zero
power dissipation for no AC input. Two unbalanced inverters areused to detect the rising edge and falling edge, respectively, and thedetection results are level-shifted to VDD. As shown in Fig. 15.4.3, if
the gate input of the pulse detector is a positive pulse and the bias
input is a negative pulse, the corresponding data edge can bedetected. To tune the sensitivity of proposed pulse detector, a variable bias voltage (VDD/2-ΔV) for the source input of the pulse detector
is used.
A test chip was designed and fabricated in 0.18μm 1P6M CMOS andthe micrograph is shown in Fig. 15.4.4(a). The measured performance is summarized in Fig. 15.4.4(b). The developed data edge signaling and the DC power-free pulse detector enable 107pJ/b energyconsumption at 100kb/s. Figure 15.4.5 shows the measured waveforms at 100kb/s and the eye diagram at the maximum data rate of
8Mb/s. Figure 15.4.6(a) shows the simulated dependence of the RXpower consumption on the data transition probability at 100kb/s.
For the 50% data transition probability, the power consumption of
the receiver can be reduced by 30%, which shows the advantage ofthe proposed data edge signaling scheme over the previous synchronous signaling scheme [5]. To increase the sensitivity of the receiver, the bias voltage (VDD/2-ΔV) of the pulse detector in Fig. 15.4.3
should be reduced but the power consumption will be increased.
Figure 15.4.6(b) shows the measured ΔV dependence of the RX
power consumption and the minimum detectable RX voltage. The
tradeoff between the power and the RX sensitivity is tuned by ΔV.
The high RX sensitivity is required to compensate the voltage reduction due to horizontal displacement of the RX pads and the distance
between RX pads and the pads of the communication sheet. The
measured minimum ΔV for different displacement and distance ofthe pads to achieve the 100kb/s communication is illustrated in Fig.
15.4.6(c). For the normal 75μm distance, which is equal to the sheet
thickness and corresponds to 52pF coupling capacitance, the sheet
can operate with up to 3.75mm displacement. The maximum tolerable displacement was 7.5mm, which corresponds to the 77% of thepad size. Figure 15.4.7 shows a comparison with the state-of-art
communication systems. The power-consumption of thecommunication sheet is lower than conventional wirelesscommunication systems. Thus the communication method presented, which combines the mobility of wireless communication and thelow-power performance of wireline communication simultaneously,bridges the gap between wire-line and wireless communication.
Acknowledgements:
This work is partially supported by CREST, JST, and MEXT.
References:[1] T. Sekitani, et al., “Communication Sheets using Printed Organic
Nonvolatile Memories,” IEDM, Paper 9.3, Dec. 2007.
[2] M. Takamiya, et al., “Design Solutions for Multi-Object Wireless Power
Transmission Sheet Based on Plastic Switches,” ISSCC Dig. Tech. Papers, pp.
362-363, Feb. 2007.
[3] T. J. Gabara and W. C. Fischer, “Capacitive Coupling and Quantized
Feedback applied to Conventional CMOS Technology,” IEEE J. Solid-State
Circuits, vol. 32, pp. 419-427, Mar. 1997.
[4] S. Fujii, et al., “A 50μA Standby 1MW × 1b/256KW × 4b CMOS DRAM,”
ISSCC Dig. Tech. Papers, pp. 266-268, Feb. 1986.
[5] K. Kanda, D. D. Antono, K. Ishida, and T. Sakurai, “1.27Gb/s/pin 3mW/pin
Wireless Super-Connect (WSC) Interface Scheme,” ISSCC Dig. Tech. Papers,
pp. 288-289, Feb. 2003.
[6] R. Palmer, et al., “A 14mW 6.25Gb/s Transceiver in 90nm CMOS for Serial
Chip-to-Chip Communications,” ISSCC Dig. Tech. Papers, pp. 440-441, Feb.
2007.
[7] I. D. O’Donnell, and R. Brodersen, “A 2.3mW Baseband Impulse-UWB
Transceiver Front-End in CMOS,” IEEE Symp. on VLSI Circuits, pp. 200-201,June, 2006.
[8] J. R. Bergervoet, et al., “A WiMedia-Compliant UWB Transceiver in 65nm
CMOS,” ISSCC Dig. Tech. Papers, pp. 112-113, Feb. 2007.
[9] M. Simon, et al., “An 802.11a/b/g RF transceiver in an SoC,” ISSCC Dig.
Tech. Papers, pp. 562-563, Feb. 2007.

• 2008 IEEE International Solid-State Circuits Conference

978-1-4244-2011-7/08/$25.00 ©2008 IEEE

ISSCC 2008 / February 5, 2008 / 3:15 PM0

Pad array for capacitive coupling

71
M

M

M0M

M

M

M

M

M

M

M

TX sheet
TX LSI9 x 8 MEMS
switchesfor Data7(a)M:MEMS switch
M :Organic memory

RX sheet
RX LSI(c)4 pads on
TX/RX sheet Communication
sheet

9 x 8 MEMS
switchesfor Datab

Wireless
capacitive coupling
between 16 pads

PadData
Datab

MEMS
MemoryCommunication
sheet for routing

8 x 8 coils forposition detection(and powertransmission)

Figure 15.4.1: Communication sheet. (a) Bird’s-eye photo. (b) Principle ofoperation. (c) Circuit schematic.

Bias1RXPulse detector to detect
rise edge of Datain
Bias2TXRX

Level Shifter
0.7 mmEdge detector
Delay

Datain
Bias
1Data
Datab

0.4 mm

25 μm

Pulse detector to detect
fall edge of Datain

Figure 15.4.3: Schematic of transceiver with data edge signaling and DC
power-free pulse detector.

0 1 0 1 0 1 0 1 1 0DataIn
Datain45 μm

0.8Equals to 52pF
1500.40.2002550

10075(a)Dataout

Rxin

Dataout

100kb/s

1.60.40.80.200.1500.3

ΔV in pulse detector (V)(b)

Figure 15.4.5: (a) Measured waveforms at 100kb/s. (b) Eye diagram at maximum data rate of 8Mb/s.

0.6

1.20.4

Dataout

Minimum ΔV (V)
0.300

125

Data transition probability (%)

Rxin
RX

−30%

0.6

RX power (μμW)

Txout

(a)

100kb/s1.0(b) 8Mb/s (max)
Txout

(b)
39 μm

Figure 15.4.4: (a) Chip micrographs and layout of TX and RX. (b) Performancesummary.
RX power (a.u.)(a) 100kb/s (typ)0.4 mm55 μmBias
2Bias : V /2 generator, Bias : (V /2−DD −ΔV) generator
DD
12TX

Supply Voltage
Typ
Data RateMax
Communi- Capacitive 150μμm
Couplingcation
Distance Wireline
60cm
Alignment Tolerance 7.5mm
TX
9.73μμW
PowerRX0.97μμW@100kb/s
Total
10.7μμW
Energy per bit
107pJ/b
TX
2475μμm2
Core Area
RX
975μμm2

Dataout

Bias
10.18μμm
CMOS
1.8V
100kb/s
8Mb/s

TechnologyDistance (μμm)

TX

Communication
sheet

Figure 15.4.2: Device structure of communication sheet.

Minimum detectable
RX voltage (V)Detectedposition

9 x 8 organic
nonvolatile memory

0.85 mm(b)9.7 mm
3.0 mm

20 cm

1MEMS switch array

16 x 16 pads
for capacitive
coupling

20 cm

0.285
0.270

1000.25575

100kb/s

50250

1.25 2.5 3.75 5.0

6.25 7.5

Displacement (mm)(c)

Figure 15.4.6: (a) Simulated dependence of the RX power consumption on
data transition probability. (b) Measured ΔV dependence of RX power consumption and minimum detectable RX voltage. (c) Measured minimum ΔV for
different displacement and distance of the pads.

Continued on Page 614

DIGEST OF TECHNICAL PAPERS •29315

Communication energy per bit(J/b = W/b/s)

ISSCC 2008 PAPER CONTINUATIONS

10n

Wireless
1n
Impulse UWB [7]100p

WLAN [9]OFDM UWB [8]This work

Wireline

10p

SerDes [6]1p0.1110100Communication distance (m)Figure 15.4.7: Comparison with the state-of-art wireless and wireline communications.

614• 2008 IEEE International Solid-State Circuits Conference

978-1-4244-2011-7/08/$25.00 ©2008 IEEE