A Flexible EMI Measurement Sheetto Measure Electric and Magnetic Fields Separatelywith Distributed Antennas and LSI’s
Naoki Masunaga, Koichi Ishida, Zhiwei Zhou, Tadashi Yasufuku, Tsuyoshi Sekitani *,Takao Someya *, Makoto Takamiya **, and Takayasu Sakurai
Institute of Industrial Science, University of Tokyo, Japan* Quantum-Phase Electronics Center, School of Engineering, University of Tokyo, Japan** VLSI Design and Education Center, University of Tokyo, Japan
Abstract—A flexible 12cm×12cm EMI measurement sheet isdeveloped to enable the measurement of the EMI distribution onthe surface of the electronic devices by wrapping the devices inthe sheet. The sheet includes 8×8 antenna array, 2V organic
CMOS decoder, stretchable interconnects, and EMI detection
LSI’s (Large Scale Integrations) in 0.18µm CMOS. The
distributed LSI’s near the antennas enable the in-situ EMI
measurement and have a potential to improve the measurement
speed and accuracy. By changing the connection of the antenna
to the LSI, the electric and magnetic fields are successfullymeasured separately. The minimum detectable magnetic field
noise power was -70dBm and the maximum detectable noisefrequency was 1GHz. The minimum detectable electric field
noise power was -60dBm and the maximum detectable noise
frequency was 700MHz.

I. INTRODUCTION
An intra-system EMC in electronic devices (e.g. cellphones and flat panel displays) is becoming a serious problem
with the increasing density of the packaging. Fig. 1 shows atypical intra-system EMC in a cell-phone. The EMI noise
generated by a digital LSI (Large Scale Integration) degrades
the performance of an RF LSI. It is difficult to find the EMI
generation points, because the electronic devices have thecomplicated three-dimensional structures. The conventional
magnetic field probe with a X-Y scanning equipment [1] andthe integrated array of magnetic field loop antennas in a solid
board [2], however, are not applicable to the threedimensional structures. To solve the problem, an EMI
Conventional

II. FLEXIBLE EMI MEASUREMENT SHEET
Fig. 2 shows a prototype of the developed EMI
measurement sheet. Fig. 3 shows the block diagram of theEMI measurement sheet. The 12cm×12cm sheet has 4×4 PCB

12cm

ProposedProbeEMI

measurement sheet is proposed, which enables themeasurement of the EMI distribution on the surface of theelectronic devices by wrapping the devices with a sheet likethe “furoshiki”.
The details of the circuit techniques and the preliminary
measurement results of the magnetic field by the EMI
measurement sheet are shown in [3]. In this paper, theelectrical field measurement by the EMI measurement sheet is
newly demonstrated and the measured frequency
characteristics of the EMI measurement sheet for both themagnetic and electric field are shown.

Wrap

Scan

LSI

AnalogAntenna

DC to DC converter
Magnetic field probe

EMI measurement sheet

Difficult to locatethe EMI source

Easy to locate
the EMI source

9.8mm

Fig. 1. Typical intra-system EMC in a cell-phone and the proposed EMI
measurement sheet.

978-1-4244-4267-6/09/$25.00 ©2009 IEEE156

Fig. 2. Prototype of the flexible EMI measurement sheet.

Decoder (Organic CMOS)

Rubber sheet
PCB
Antenna

CMOS LSI
Stretchable
interconnects

Selector (Organic CMOS)
Fig. 3. Block diagram of the EMI measurement sheet.

array and 2 organic circuits (decoder and selector) on therubber sheet made of silicone elastomer. The PCB’s and theorganic circuits are connected by stretchable interconnects [4]including carbon nanotubes, and the whole system is covered
with a rubber sheet, which enables the sheet to be stretched.
Magnetic field noise up to 1GHzPCB LSI

Rectifier Sample/Hold

Differential amps
V1

III. EMI MEASUREMENT LSI
Fig. 4(a) shows the circuit diagram and the timing chart ofthe proposed EMI measurement LSI. The LSI has four-stage
differential amplifiers, an nMOS rectifier, sample and holdcircuits, and a comparator. The conventional integrated EMI
sensor circuits [8] have analog outputs, which is not suitablefor the array measurement. In contrast, the developed EMI
measurement LSI has a digital output, which is suitable for thearray measurement.
By changing the connection method of the antenna, theelectric and magnetic fields are measured separately [9].
When the both ends of the antenna are connected to the inputsof the differential amplifier, the magnetic field is measured,
because the differential current in the antenna is amplified. In
contrast, when the both ends of the antenna are connected tothe one input of the differential amplifier and the other inputof the amplifier is connected to the bias voltage, the electricfield is measured, because the common-mode current in theantenna is amplified.
To capture the waveform of the EMI noise up to 1GHz

Comparator
V3

OutV2

Electric field noise up to 700MHz
ResetSample

VREF CompClk(100kHz)

HoldReset
CompClkt(a)Large power EMI

Small power EMI

VV

V1
VREF

V

V3

VREF

Converted to DCt

VREF

2.9 mmVREF
Converted to DCt
V

VOUTt

Vt

VAll “H”

“L”
t

0.2mm

V2t

V

0.9 mmtV

Each PCB has a 2×2 antenna array to pick up EMI, an LSI,
and 6 stretchable interconnects. The 4 antennas share the LSI
to measure EMI. In the conventional integrated array ofmagnetic field antennas in a solid board [2], the processing
function of the measured results is not integrated in the board.
In contrast, the EMI measurement sheet has the distributed
LSI’s near the antennas for the EMI measurement. It is thefirst demonstration of the distributed in-situ EMI
measurement, which has a potential to improve themeasurement speed and accuracy.
The diameter of the loop antenna is 9.8mm. The antennas
are made on a rigid PCB, because the antennas on a flexible
film provide unstable antenna characteristics depending on themechanical bending.
When the scale of the array is large, a low-cost and largearea decoder is required to reduce the number of interconnects
and the organic transistor are suitable for the decoder [5]. In
this study, 2V organic CMOS technology enabled by the
2.1nm-thickness gate insulator (SAM[6]) and the organic
semiconductor (NTCDI[7]) for nMOS was used. The
measured organic decoder operation is shown in [3].

“L”t(b)0.9mm

Fig. 4. (a) Circuit diagram and timing chart of the proposed EMI
measurement LSI. (b) Operation of the EMI measurement LSI.

157

Fig. 5. Die microphotograph and layout of the EMI measurement LSI.

Memory module in laptop PC

accurately, bandwidth of the comparator should be 10GHz or
higher, which is not reasonable. The proposed LSI, therefore,converts the EMI noise waveform into the DC voltage by therectifier and the sample and hold circuits. The down
conversion relaxes the requirement for the speed of thecomparator and the comparator can operate at slow frequency
such as 100kHz. Fig. 4(b) shows the operation of the EMI
measurement LSI. When the EMI power is large, the sampled
voltage (V3) is higher than the reference voltage (VREF) of thecomparator and the output of the comparator (VOUT) is high.
In contrast, when the EMI power is small, V3 is lower than
VREF and VOUT is low. The VOUT is reset to high at every clock(CompClk) edge, because the comparator is a clocked
comparator. In this way, the EMI noise power is observed as afunction of VREF.
The four-stage differential amplifiers in Fig. 4(a) have again of around 80dB, which enables the measurement of themagnetic EMI noise of -70dBm which equals to 45µV at 50ohm input resistance of the amplifier.
Fig. 5 shows die microphotograph and the layout of theEMI measurement LSI. The LSI is implemented in 1.8-V,
0.18-µm CMOS process and the core area is 0.18mm2.

Antenna and LSI
for EMI measurement sheet(a)CompClk(100kHz)

Out

IV. MEASUREMENT OF ELECTRIC AND MAGNETIC FIELDS

81% highÎEMI detected

A. Comparison of Conventional and Proposed Methods
In order to demonstrate the operation of the EMI(b)

Magnetic probe

CompClk(100kHz)

Out
Memory module in laptop PC(a)

All lowÎno EMI(c)-50dBm@267MHz
Fig. 7. Measured magnetic EMI noise with the EMI measurement sheet. (a)Measurement setup. (b) and (c) show the output waveform of the developed
EMI measurement LSI with and without DUT, respectively.

(b)Fig. 6. Measured magnetic EMI noise with the conventional magnetic probe.
(a) Measurement setup. (b) Spectrum of the noise.

measurement sheet, the same magnetic EMI’s measured withthe conventional magnetic probe [1] and the developed EMI
measurement sheet are compared. DUT is a memory modulein a laptop PC. Figs. 6(a) and (b) show the photograph of themeasurement setup and the spectrum of the measured
magnetic EMI noise with the conventional magnetic probe,
respectively. The highest peak was -50dBm at 267MHz.

158

ReferenceElectric field power [dBm]0Spectrum
analyzer

Magnetic field probeorElectric field probe

Power spectrum

Signalgenerator(EMI emulator)

CompClk (100kHz)
Proposed EMI
Measurement
LSI

Swept sinusoidal
wave up to 1GHz

Oscilloscope

Sweep VREF

Fig. 8. Measurement setup in order to calibrate the frequency characteristicsof the measurement of the electric and magnetic fields in the EMI
measurement LSI.

-20-30
Hz1Gz
MH90 0 H z
M500z0 MH

30-80
650
700
750
800
850
900
Reference voltage of comparator (VREF) [mV]-30
VREF=850mV
845mV
844mV

-70-80100

200
300
500 700
Frequency [MHz]-70-10-20-30

VREF=755mV

-40
747mV
744mV

-50-60-70

200300500 700
Frequency [MHz]1000

measurement LSI with and without DUT, respectively. In Fig.
7(b), the output shows high pulse density of 81%, which
detects the EMI noise above the DUT. In Fig. 7(c), however,
the output shows include no high pulse, which detects no EMI
noise without the DUT. Thus, the proposed system
successfully detects the actual noise emitted by the memory
module in the laptop PC.

-20-60-60

Fig. 10. Measured electric field power with the EMI measurement LSI. (a)VREF dependence at different EMI frequency. (b) Frequency characteristics atdifferent VREF’s.

-10-50100MHz-50(b)0-40-40-80100(a)Magnetic field power [dBm]

Electric field power [dBm]

Magnetic field power [dBm]-10-70-30

00-60

700MHz500MHz300MHz(a)Similarly, Fig. 7(a) shows the photograph of themeasurement setup with the EMI measurement sheet. Figs.
7(b) and (c) show the output waveform of the developed EMI-50-20-80
740
745
750
755
760
Reference voltage of comparator (VREF) [mV]

50% pulse density-40-101000(b)Fig. 9. Measured magnetic field power with the EMI measurement LSI. (a)VREF dependence at different EMI frequency. (b) Frequency characteristics atdifferent VREF’s.

B. Calibration for EMI Measurement LSI
Fig. 8 shows the measurement setup in order to calibrate
the frequency characteristics of the measurement of theelectric and magnetic fields in the EMI measurement LSI.
EMI noise is emulated by using a signal generator and anantenna. The signal generator sweeps sinusoidal wave up to1GHz. The EMI noise is measured by the EMI measurement
LSI and the commercial magnetic [1] and electric [10] fieldprobes. The magnetic field probe detects power ranging from
10MHz to 3GHz within ±1dBuA/m error. The emulated EMInoise is monitored with the probe and the spectrum analyzer
to calibrate the noise power. Similar to the magnetic field

159

V. CONCLUSION
Collaboration among silicon CMOS technology, 2V
organic CMOS technology, and stretchable interconnect
including carbon nanotubes makes a stretchable EMI
measurement sheet possible, and the proposed LSI
demonstrates EMI noise measurement up to 1GHz by using
rectifier and the comparator operating at only 100kHz. Bychanging the connection of the antenna to the LSI, the electricand magnetic fields are successfully measured separately. The
minimum detectable magnetic field noise power was -70dBm
and the maximum detectable noise frequency was 1GHz. The
minimum detectable electric field noise power was -60dBm
and the maximum detectable noise frequency was 700MHz.

TABLE I PERFORMANCE SUMMARY OF THE EMI MEASUREMENT LSI

Technology

1.8V, 0.18µm CMOS

Core area

0.18mm2

Sampling frequency

100kHzPower consumption

110mW

EMI Measurement

Magnetic Electricfieldfield

Minimum detectable-70dBmnoise power
Maximum detectable
1GHz
noise frequency-60dBm
700MHzcalibration, the electric field strength is calibrated by theelectric field probe that can handle electric field from 2MHz
to 2GHz.
Fig. 9(a) shows the measured relationship between themagnetic field power and VREF at different EMI frequency in
the EMI measurement LSI. VREF increases with increasing themagnetic field power. The minimum detectable magnetic field
noise power was -70dBm. Fig. 9(b) shows the measured
frequency characteristics of the magnetic field power at
different VREF’s. The maximum detectable noise frequency
was 1GHz. Ideally, the frequency characteristics should be flat.
The magnetic field power, however, increases with increasing
the frequency, which derives from the frequency
characteristics of the amplifier in the EMI measurement LSI.
Similarly, Fig. 10(a) shows the measured relationshipbetween the electric field power and VREF at different EMI
frequency and Fig. 10(b) shows the measured frequency
characteristics of the electric field power at different VREF’s.
The minimum detectable electric field noise power was-60dBm and the maximum detectable noise frequency was700MHz.
Comparing the electric and magnetic fields measurement
shown in Figs. 9(a) and 10(a), the sensitivity of the electricfields measurement is worse than that of the magnetic fields
measurement. The difference derives from the antenna gain
difference between the electric and magnetic fields.
Key features of the developed the EMI measurement LSI
are summarized in Table I.

ACKNOWLEDGMENT
This work was partially supported by the Grant-in-Aid for
Scientific Research, Special Coordination Funds for
Promoting and Technology, NEDO, and CREST/JST.
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