January 21 - 24, 2003Kitakyushu International Conference CenterKitakyushu, Japan

January 21 - 24, 2003Kitakyushu International Conference CenterKitakyushu, Japan

IEICE IPSJACM SIGDAIEEE CASJEITA

Kitakyushu City Kitakyushu Convention Bureau

ASIAS KYUSHU Promotion Committee for Fukuoka System LSI R&D Hub

In Corporation with:Supported by:

STARC JIEP

Sponsored by:

http://www.aspdac.com

PROCEEDINGS

ASP-DAC 2002/VLSI 2002 Best Papers

Best Paper Award:

Floorplan Evaluation with Timing Driven Global Wireplanning, Pin Assignment and Buffer/WireSizingC. Albrecht, A. B. Kahng, Ion Mandoiu, A. Zelikovsky – Univ. of California, San Diego, USA

Best Student Paper Award:

Mode Selection and Mode dependency Modeling for Power Aware Embedded SystemsDeixin Li, Pai H. Chou, Nader Bagherzadeh – Univ. of California, Irvine, USA

Honorable Mention Award:

Desing of On-chip Test Pattern Generator without PPSN. Ganguly, Sikdar, P. Pal Chaudhuri – Bengal Engineering College, Howrah, India

Design Contest Award:

High-sensitivity and Wide-dynamic-range Position Sensor Using Logarithmic-response and Cor-relation CircuitYusuke Oike, Makoto Ikeda, Kunihiro Asada – University of Tokyo, Japan

x

xx

VLSI Design 2002 Conference Awards

Technical Paper Awards

Best Paper Award

“Floorplan Evaluation with Timing Driven Global Wireplanning, Pin Assignment and Buffer/Wire Sizing”

C. Albrecht, A. B. Kahng, Ion Mandoiu, and A. Zelikovsky University of California at San Diego, USA

Best Student Paper Award

“Mode Selection and Mode Dependency Modeling for Power Aware Embedded Systems”

Deixin Li, Pai H. Chou, and Nader Bagherzadeh University of California at Irvine, USA

Honorable Mention Award

“Design of On-Chip Test Pattern Generator without PPS”

N. Ganguly, B. K. Sikdar, and P. Pal Chaudhuri Bengal Engineering College, Howrah, India

Design Contest Award

Best Design

“High-Sensitivity and Wide-Dynamic-Range Position Sensor Using Logarithmic-Response and Correlation Circuit”

Yusuke Oike Dept. of Electronic Engineering, The University of Tokyo, Japan

Makoto Ikeda and Kunihiro Asada VLSI Design and Education Center, The University of Tokyo

High-sensitivity and Wide-dynamic-range Position Sensor

Using Logarithmic-response and Correlation Circuit

Yusuke Oike, Makoto Ikeda and Kunihiro Asada

Dept. of Electronic Engineering (VLSI Design and Education Center), The University of Tokyo

7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JapanTel: +81-3-5841-6771, Fax: +81-3-5800-5797e-mail: fy-oike,ikeda,asadag@silicon.u-tokyo.ac.jp

Abstract| A high-sensitivity and wide-dynamic-

range position sensor has been designed and success-

fully tested. The sensor can acquire the position

of projected light in strong background illumination

without saturation since this sensor has a log-response

and correlation circuit. Minimum sensitivity in terms

of the ratio of the projected light to the background

illumination is 0.036. The sensor integrates 64 � 64

pixels on a 4.8 mm � 4.8 mm die of a 0.5 � m CMOS

3-metal 1-poly-Si process.

I. Introduction

3-D measurement system has a wide variety of appli-cation �eld such as robot vision, computer vision andposition adjustment. In 3-D measurement system, thesensor detects the position of projected light on the sen-sor plane. The conventional image sensors and positionsensors such as [1, 2] detect positions of peak intensityto acquire the positions of projected light. This methodhas some diÆculties when a target object is placed in anon-ideal environment such as a strong background illu-mination. Correlation technique[3] is one of the solutionsto the diÆculties. The correlation sensor can suppressthe background illumination to obtain a high sensitivity.Its dynamic range is, however, limited by the linear dif-ference circuit due to the voltage signal saturation. Itis not applicable for a strong contrast image in outdoorenvironment without optical neutral-density �lters.In this study, we have developed and tested a high-

sensitivity and wide-dynamic-range position sensor. Thiscan be realized using a logarithmic-response circuit sothat the correlation circuit can detect the position of pro-jected light without saturation.

II. Circuit Realization

Fig.1 illustrates the pixel structure of the high-sensitivity and wide-dynamic-range position sensor usinglogarithmic-response and correlation circuit. It consistsof a logarithmic-response photo detector circuit, an am-pli�er of the photo current swing, a sample and hold cir-cuit, an analog multiplier for correlation, an integratorand a source follower circuit. Fig.2 shows a schematic ofthe pixel. The logarithmic-response circuit realizes wide-

LaserTarget

laser beam

Pulse generator

pixel

output

Fig. 1. Pixel structure.

PD

preamp

ref_sw

sigref

sync1sync1sync2

vbp

rst

sel

out

read

_out

Vsig

Vref

C1

Fig. 2. Schematic of a pixel.

dynamic-range photo detection. Photo current IPD(t)generates the voltage Vsig(t) at the node sig as follows:

Vsig(t) = � log IPD(t) (1)

Here � stands for the charactaristics of the pre-ampli�er.At the sample and hold circuit, the signal ref sw synchro-nized with 2f0 generates the voltage Vref (t) at the noderef when the modulation frequency of projected light tobe detected is f0. The di�erential voltage �Vsig(t) be-tween Vsig(t) and Vref (t) is multiplied by the externaldi�erential signal �Vsync(t) between Vsync1 and Vsync2for correlation. The output current Iout(t) is integratedat capacitance C1 and results in the output voltage Vout(t)as follows:

Vout(t) =

Z t

t�T

Ib ���Vsig(�)

2�

��Vsync(�)

2d� (2)

where T is frame time and � is a gain factor of the mul-tiplier. The voltage Vout(t) increases monotonously andthe pixel is activated only when the voltage Vsig(t) hasthe frequency to be detected.

Fig. 3. Microphotograph of the sensor.

TABLE ISummary of the position sensor.

Process 0.5 �m CMOS 3-metal 1-poly-Si

Chip size 4.8 mm � 4.8 mm

Num. of pixels 64 � 64 pixels

Pixel size 40.0 �m � 40.0 �m

Photo diode size 10.15 �m � 28.45 �m

Fill-Factor 18.05 %

III. Experimental results

Fig.3 shows a microphotograph of the sensor. The sen-sor is fabricated in 0.5�m CMOS 3-Metal 1-Poly-Si pro-cess. Table I shows a summary of the sensor.Fig.4 shows the minimum laser intensity on the target

objects versus the background intensity when the sensorcan acquire the position of the laser beam. We also showexamples using an image sensor without correlator (b)and the conventional correlation sensor[3] (c) in Fig.4.The measurement system is composed of the fabricatedsensor, a laser pointer (wavelength 635nm), a light pro-jector for background illumination, a luxmeter. In thismeasurement system, the modulation frequency is 1kHz,the maximum frequency of the laser, and the frame in-terval is 5ms. This experimental result shows that thepresent sensor can suppress the background illuminationand acquire the position of the projected light in a strongbackground illumination. For example, the laser intensitycan be about 3�104lx in outdoor environment, where thebackground intensity is about 1�105lx in summer season.In addition, this result shows the sensor doesn't saturateand the suppression is e�ective in various background il-luminations.Fig.5 shows acquired images of scanning laser spot for 3-

D measurement at two background illuminations, 1600lxand 28000 lx. The 3-D measurement system is composedof the fabricated sensor, a laser with mirrors and a PCwith digital I/O boards. In this measurement, the ac-quired images have 12 � 12 positions of scanning laserspot projected on a sphere-shaped object. 3-D range mapcan be calculated from this acquired image and the po-sitions of the sensor and the projected light source usingtriangulation.

103

102

103

104

105

104

105

106

(a)

(b)

(c)

Fig. 4. Minimum laser intensity on target objects: (a) theproposed position sensor, (b) the conventional image sensor, (c)the conventional correlation sensor.

Fig. 5. Acquired images for 3-D measurement: laser intensity isabout (a) 400 lx, (b) 1900 lx and max. background intensity isabout (a) 1600 lx, (b) 28000 lx.

IV. Conclusions

A high-sensitivity and wide-dynamic-range positionsensor using logarithmic-response and correlation circuithas been developed and successfully fabricated in 0.5�mCMOS 3-metal 1-poly-Si process. The sensor can acquirethe position of projected light in strong background il-luminations. The fabricated sensor has a 64 � 64 pixelarray. Minimum sensitivity in terms of the ratio of theprojected light to the background illumination is 0.036.The suppression is e�ective in wide range of the back-ground intensity.

Acknowledgements

The VLSI chip in this study has been fabricated in thechip fabrication program of VLSI Design and Education Cen-ter(VDEC), the University of Tokyo with the collaboration byHitachi Hokkai Semiconductor Ltd. and Dai Nippon PrintingCorporation.

References

[1] M. de Bakker, P. W. Verbeek, E. Nieuwkoop and G. K. Steen-voorden, \A Smart Range Image Sensor," Proc. of EuropeanSolid-State Circuits Conference, pp.208-211, 1998.

[2] T. Nezuka, M. Hoshino, M. Ikeda and K. Asada, \A SmartPosition Sensor for 3-D Measurement," Proc. of Asia South-Paci�c Design Automation Conference, pp.21-22, 2001.

[3] A. Kimachi and S. Ando, \Time-Domain Correlation ImageSensor: First CMOS Realization and Evaluation," Transduc-ers '99, pp.958-961, June 1999.

High sensitivity is realizedin wide dynamic range of backgroundHigh sensitivity is realizedin wide dynamic range of background

Multiple light system can be realizeddue to high selectivity

High-Sensitivity and Wide-Dynamic-Range Position Sensor

Using Logarithmic-Response and Correlation Circuit

High-Sensitivity and Wide-Dynamic-Range Position Sensor

Using Logarithmic-Response and Correlation Circuit

Yusuke Oike, Makoto Ikeda, and Kunihiro Asada

Department of Electronic Engineering, and VLSI Design and Education Center (VDEC),

University of Tokyo, JAPAN

1

7

5 6

Safe light projection for human eyesSafe light projection for human eyesAvailability in various backgounds

9Target object Reproduced wire frame

laser pointer

mirrors PC

fabricated sensor

target object

14100 5 10 15 20 25 30 35 40 45

1412

1414

1416

1418

1420

1422

1424

1426

1428

Num. of Data

Ran

ge (

mm

)

256

x 25

6 pi

xels

64 x

64

pixe

ls

Accuracy of 3-D Measurement

Measured Range Map

3-D Measurement SystemMeasurement result of a float panel

Application to 3-D Measurement System

Max. error : 14.6mm at a distance of 1418mm

Accuracy of ±0.5% (with 64×64 pixels)

Strong background illumination (28 klx)Weak projected laser beam (1.6 klx)

The proposed sensor realizes both :Availability in various backgounds

Measurement Environment

The proposed sensor can detect the positions clearly, which can't be detected by the conventional sensors 8

Laser beam is projected at ① Laser beam is projected at ②

Images acquired by CCD camera

Images acquired by the proposed position sensor

Projected at strongerbackground illumination

Another peakintensity exists

High-Sensitivity Position Detection

1 2

pulsegenerator

(a)(b)

laserthe proposed sensor

CCD camera

target object

backgroundillumination～60klx

The intensity of background illumination at ①

The intensity of projected laser beam

60klx

4klx

①

②

when the laser beam is projected at stronger backgrounds

when peak intensities exist at other places

The conventional sensors can't detect the position ...

The proposed sensor can detect the positions clearly, which can't be detected by the conventional sensors

102 103 104 105 106 107 108

Background intensity (lx)

Min

imum

lase

r in

tens

ity to

be

dete

cted

(lx

)

102

103

104

105

106

107

108SBR=0dB

SBR=-10dB

SBR=-20dB

(a)

(b)

(c)

experimental result

DR=46dB (SBR < -10dB)

DR=13dB (SBR < -10dB)

the proposed sensor

the conventionalcorrelation sensor

standard sensor

Wide Dynamic Range

High Sensitivity

indoor outdoor

Performance Evaluation SBR: Signal-to-Background Ratio = 10 log(Elaser/Ebg)

Sensitivity of position detection

(a) The proposed position sensor

(b) The conventional correlation sensor

(c) Standard sensor

High suppression ratio at even harmonics of the correlation frequency

High selectivity is realized using a set of even-harmonics frequencies

0.4

0.5

0.6

0.7

0.8

0.9

1.01

0.8

0.6

0.4

0.2

0

-0.2

-0.4

-0.60 2k1k(f0) 3k 5k 7k 9k4k 6k 8k 10k

Modulation frequency of projected laser beam (Hz)

the correlation frequency

Out

put v

olta

ge (

V)

Sup

pres

sion

rat

io

experimental result

Multiple light system can be realizeddue to high selectivity

Minimum SBR* : -14.4dBDynamic Range : 46dB (SBR < -10dB)

*

High sensitivity...........Wide dynamic range..

Dynamic range is limited due to the voltage saturation

High-sensivitiy and wide-dynamic-range position sensor is required

3

Motivation3-D measurement system using triangulation-based light projection method

This method can realize high accuracyA range map can acquired by simple calculation

<advantage>

This method needs a scanning light sourceA target object and a measuremenet environment are limited

<disadvantage>

High-sensivitiy and wide-dynamic-range position sensor is requiredHigh sensivitiy should be realized in wide range of background illumination

Required Performance of Position Detection

High Speed High Accuracy High Sensitivity Wide Dynamic Range

Compensation for the disadvantages of the active 3-D measurement method

calculating

camera

laser scanning

reflection

laser position

target object The features of the active 3-D measurement method

High performance position sensor can realize advanced 3-D measurement

2

Introduction

3-D measurement system using triangulation-based light projection method

The sensor detects the reflection positon of projected light (position detection)

The distance is calculated using triangulation principle

High performance position sensor can realize advanced 3-D measurement

PROCESS

row

sel

ect a

nd r

eset

shi

ft re

gist

er

column parallel comparator

64×64 pixels

4.8mm

4.8m

m

Designed and Fabricated Sensor

Microphotograph of the sensor

The pixel layout

Supply Voltage

Measurement Results

Specifications

Min. SBR3.3V-14.4dB

Dynamic Range 46dB (SBR<-10dB)Range Resolution ±5% at 1400mmPower DissipationFrame Rate

400mW at 200fpsMax. 2000fps (f0=10kHz)

ProcessChip Size

0.5µm CMOS process4.8mm×4.8mm

Num. of Pixels 64×64 pixels

Pixel Size 40µm×40µmPhoto Diode

Num. of Trans. 114k transistorsFill Factor 18.05%

10.15µm×28.45µmn+-dif and p-sub

photo diode

Sensing Process TIMING DIAGRAM

PULSEGENERATOR

RST

SYNC1

SYNC2

REF_SW

SW

reset correlation

integration

(a)

(b)

(c)

(d)

(e)

(a)(b)(c)(d)(e)

5kHz, 1nA ( in DC 1nA)5kHz, 1nA ( in DC 2nA)5kHz, 1nA ( in DC 3nA)5kHz, 1nA ( in DC 1nA + 100Hz 1nA)DC, 1nA

0 0.2m 0.4m 0.6m 0.8m 1.0m 1.2m 1.4m 1.6m 1.8m

Time (sec)

Vcmp

Vol

tage

(V

)

0.6

0

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

Vou

t

Vout(t) =

Vout ≧ Vcmp

∫

Photo current is generated by input signal

Vref is generated at S&H circuit and multiplied by Vsync

The output of multiplier is integrated

Comparison between Vout and Vcmp

Vsig(t) = αlogIPD(t)α: a gain factor of pre-amplifier

IPD : photo current

T : frame intervalVo : bias voltage of integrator

Vcmp : the reference voltage of comparator

Iout(τ) dτ 1 t

t-TC0

Vref(t) = Vsig(t- )2f01

Ib : bias currentVsync : external signals synchronized with the correlation frequency

Iout(t) = Ibκ∆Vsig(t)

2tanh tanhκ∆Vsync(t)

2

+ Vo

Input signal has the correlation frequency f0

Input signal doesn't have the correlation frequency f0

The output of multiplier is always positive valueThe voltage of integrator is monotonously increasing

The voltage of integrator fluctuates

The voltage of integrator remains constant

Integrated voltage: Vout(t)

Especially, input signal is only background illumination

Input signal with the correlation frequency ⇒monotone increasing

Input signal withoutthe correlation frequency⇒remaining constant

Proposed Sensing Scheme

LaserTarget

laser beam

Pulse generator

pixel

output

Vcmp

PD

D

log

Schematic of the pixel

PD

IPD

preamp

log-response amplifierphoto diode

analog multiplier

sample&hold

source followerreadout

integrator

ref_sw

sigref

sync1sync1sync2

vbp

rstsw

Vrst

sel

out

read

_out

To comparator

Vsig

Iout

Vref

Vout

C0

Modulated laser beam is projected on the target object

Logarithmic suppression at photo diode

The input signal is multiplied by the external signals

The output of multiplier is integrated

Projected lightis detected

Input signal hasno projected light

The previous input singal is subtractedfrom the current input signal

Sensing Scheme

with integration without integration

4

Applicaton of 3-D measurement

Robot VisionComputer VisionRecognition SystemPosition Adjustment3-D Modeling SystemVirtual Reality

3-D Duplicating

Robot Vision

Strong laser beam projection is dangerousSystem should be available in various background illuminations

Advanced application can't be realized by the reasons as follows: