A Ve sa ile Senso In e ace o P og ammable
Vision Sys ems-on-Chip
A. Rod íguez-Vázquez 1, G. Liñán, E. Roca, S. Espejo and R. Domínguez-Cas o
Ins i u o de Mic oelec ónica de Se illa − CNM-CSIC
Edi icio CICA-CNM, C/Ta ia s/n, 41012- Se illa, SPAIN
ABSTRACT
This pape desc ibes an op ical senso in e ace designed o a p og ammable mixed-signal ision chip. This chip has
been designed and manu ac u ed in a s anda d 0.35µm n-well CMOS echnology wi h one poly laye and i e me al
laye s. I con ains a digi al shell o con ol and da a in e change, and a cen al a ay o 128 x 128 iden ical cells, each
cell co esponding o a pixel. Die size is 11.885 x 12.230mm2 and cell size is 75.7µm x 73.3µm. Each cell con ains 198
ansis o s dedica ed o unc ions like p ocessing, s o age, and sensing. The sys em is o ien ed o eal- ime, single-chip
image acquisi ion and p ocessing. Since each pixel pe o ms he basic unc ions o sensing, p ocessing and s o age, da a
ans e ences a e ully pa allel (image-wide). The p og ammabili y o he p ocessing unc ions enables he ealiza ion o
complex image p ocessing unc ions based on he sequen ial applica ion o simple ope a ions. This pape p o ides a
gene al o e iew o he sys em a chi ec u e and unc ionali y, wi h special emphasis on he op ical in e ace.
1. INTRODUCTION
Al eady in 1997, o ecas s ega ding he nex wa e o In oTech Inno a ion [1] an icipa ed ha high-pe o mance senso s
would shape he i s decade o he 3 d millenium. Thus, while in he 1980s inno a ions we e ocused on c ea ing
p ocesso -based compu e “in elligences”, and in he 1990s on ne wo king hose in elligences oge he wi h lase -
enabled bandwid h, inno a ions du ing his decade will mos likely be ocused on adding sensing and ac ua ing “o gans”
o hese de ices and ne wo ks.
In his a ea we ha e a lo o lea n om na u e. The close in eg a ion, o in e ac ing sensing, p ocessing and ac ing
subs uc u es ea u ed by na u al beings p o ides an endless sou ce o inspi a ion o hese new gene a ions o senso ial
in elligences [2]. Exploi ing his sou ce o inspi a ion may lead o e olu iona y changes in he concep ion and
implemen a ion o hese sys ems.
Thus, he ex ensi e usage o digi al p ocessing in oday’s con en ional a chi ec u es 2 is o eseen o be complemen ed in
he u u e wi h an inc eased usage o pa allel analog p ocesso s capable o ope a ing concu en ly and in close
in e ac ion wi h he senso y ci cui s. The inal a ge is o ealize comple e senso y/p ocessing (and ac ua ing) sys ems in
a single chip h ough he sma syne gy o senso s, analog p ocessing and digi al p ocessing s uc u es.
In his sense, du ing he las ew yea s signi ican ad ances ha e been made ega ding he implemen a ion o Vision
Chips; i.e. chips which a e capable o acqui ing images and p ocessing hem using ci cui s embedded in he same silicon
subs a e in which he image is cap u ed − called ocal-plane p ocessing.
The design o hese chips can be unde aken ollowing wo al e na i e app oaches:
• Pick up a speci ic ask and i s model and implemen i on silicon. This is he usual way, leading o e y use ul, ask-
speci ic sma senso s [3] [4].
• Make gene al-pu pose mixed-signal image p ocessing de ices [5]. Tha is, de ices which, h ough p og amming,
can be employed o ealize a my iad o image p ocessing asks, simila o he possibili y ea u ed by he ubiqui ous
on Neumann digi al p ocesso .
The chip epo ed co e ed in his pape , called ACE16k, belongs o his second g oup. I has a Single-Ins uc ion-
Mul iple-Da a a chi ec u e (SIMD) and includes some o he mos ele an ea u es o he Cellula Nonlinea /Neu al
Ne wo k Uni e sal Machine (CNNUM) pa adigm [6]. O he chips, also belonging o his g oup, ha e been epo ed in
1. [email protected]; phone: +34 95 5056666; ax: +34 95 5056686
2. These con en ional a chi ec u es employ analog blocks only a he on -end sec ions, while all p ocessing is ealized in he
digi al domain. The o e all sequence o ope a ions is: Sensing − A/D Con e sion − Digi al-P ocessing − D/A Con e sion)
Senso s and Came a Sys ems o Scien i ic, Indus ial, and Digi al Pho og aphy Applica ions IV,
Mo ley M. Blouke, Ni in Sampa , Rica do J. Mo a, Edi o s, P oceedings o SPIE-IS&T Elec onic
Imaging, SPIE Vol. 5017 (2003) © 2003 SPIE-IS&T · 0277-786X/03/$15.00
38
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he las yea s [7]−[17], e c. Some o hem do no ha e senso y capabili ies, hey a e jus concei ed as p og ammable co-
p ocesso s; o he s a e only designed o black-and-whi e image p ocessing; and o he s a e designed o e y la ge
densi y, bu ea u e e y small analog accu acy in he in e nal p ocessing.
This pape p esen s he new mul i-mode op ical senso which is used a he senso y pa o he chip ACE16k. The
p esen ed pixel has he capabili y o acqui ing isual in o ma ion in e y di e en illumina ion condi ions since i
p o ides bo h, linea in eg a ion and loga i hmic comp ession sensing schemes.
2. ACE16k ARCHITECTURE
ACE16k ollows he SIMD-CNNUM pa adigm. As shown in Fig. 1, Single Ins uc ion Mul iple Da a sys ems consis o
an a ay o iden ical P ocessing Elemen s (PE) which execu e he same ins uc ions a he same ime. Ins uc ions a e
execu ed on da a which a e locally de ined, a he PE le el, while he ins uc ion sequence is issued by a con ol uni
sha ed by all he PEs in he a ay. Mos commonly, he communica ion ne wo k among PEs is es ic ed o he nea es
neighbo s.
In he case o low-le el 1 image p ocessing, whe e he same ope a ion sequence is applied o all he p ocesso s in he
a ay, he mos s aigh o wa d mapping be ween images and chips consis s o using one p ocessing elemen pe pixel,
hus p o iding a e y compac , and e icien way o de ining algo i hms.
ACE16K implemen s mos o he ele an unc ional ea u es o he CNNUM [6] pa adigm, namely:
• non-linea dynamic coupling among he elemen a y p ocessing uni s, also called cells,
• local, dis ibu ed memo ies o s o age o in e media e images,
• local, dis ibu ed logical p ocessing,
• inco po a ion o global, chip-le el s uc u es o s o age o ins uc ions and con ol o algo i hmic p ocessing
lows.
Thus, ACE16k is capable o ope a ing as a lexible, use -p og ammable algo i hmic p ocesso ; a kind o isual
mic op ocesso [5]. A he ha dwa e le el, he ins uc ion se o such a mic op ocesso includes se ing he alues o he
s engh s o he cell in e connec ions, called in e connec ion empla es which de ine he ac ual low-le el image
p ocessing ask o be execu ed; also implies econ igu ing he in e connec ion opology o he s uc u es inco po a ed a
cell le el, hus con olling da a lows and basic ci cui con igu a ion; and a anging local analog and digi al ope a ions
be ween locally-s o ed images, which allows o he execu ion o bo h pixel-wise bina y in e sion in black and whi e
images, o ins ance, and image-wise ope a ions - g ay-scale combina ions o wo images by linea a i hme ic ope a ions.
The a chi ec u e o he sys em is depic ed in Fig. 2(a). He e, a ious unc ional subs uc u es a e iden i ied:
• A senso y/p ocessing co e, which consis s o an a ay o iden ical PEs. These PEs ha e embedded ci -
cui s uc u es o op ical sensing, p og ammable analog p ocessing (designed o a ound 7bi accu acy), p og am-
mable bina y p ocessing, local memo y and signal low econ igu a ion.
1. This e e s o he p ocessing ealized a he ea ly s ages o he low, whe e he amoun o da a o p ocess has e y la ge dimen-
sionali y, , whe e is he numbe o ows in he a ay o pixels, and is he co esponding numbe o columns. This
low-le el p ocessing s age is c i ical o educing he dimensionali y o he da a o subsequen p ocessing s ages.
Fig. 1. Typical SIMD A chi ec u e
PE PE
PE
PE PE PE
PE
PE
PE PE PE
PE
PE PE
PE
PE
PE PE
PE
PE
PE
Con olle
Ins uc ion
Bus
PE
NM×NM
128 128×
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• A ing o bo de cells used o es ablish spa ial bounda y condi ions o image p ocessing, and se e al bu e s d i -
ing analog and digi al signals o he a ay.
• A p og amming block, which con ains se e al SRAM digi al memo ies used o s o e he algo i hms o be execu ed
by he chip.
• A block o I/O image low con ol and o ma con e sion1. 128 Digi al o Analog (DAC) and Analog o Digi al
(ADC) con e e s, one pe column, which cons i u e a digi al I/O po o images.
• Digi al blocks o au oma ic add essing o ows and columns du ing image I/O p ocesses.
The chip uses a 32-bi bidi ec ional da a bus o image communica ion pu poses, and se e al add ess buses o he
di e en blocks wi hin he p og amming memo y. The I/O in e ace ollows e y simple hand-shaking p o ocols. Table 1
summa izes he main cha ac e is ics o he p o o ype.
ACE16k is concei ed o be used in wo al e na i e ways. Fi s , whene e he images o be p ocessed a e di ec ly
acqui ed by he op ical inpu module o he chip [5]; and second, as a con en ional image co-p ocesso wo king in
pa allel wi h a digi al hos ing sys em which p o ides and ecei es he images in elec ical o m.
3. PHYSICAL FOUNDATIONS FOR LIGHT SENSING IN CMOS
Pho o-de ices a e he elemen s which allow o he combina ion o senso y and p ocessing planes in a single chip.
Se e al possibili ies o he a chi ec u e o he pho osenso exis , howe e , all o hem ely on he same physical
phenomenon, he pho oelec ic e ec . Co alen bonds holding he elec ons a hei a omic si es in he la ice can be
b oken by an inciden adia ion i he ene gy o he inciden pho on is g ea e han he silicon band gap. Since his ene gy
le el is abou , hose pho ons wi h wa eleng hs below could be, heo e ically, powe ul enough o
exci e ca ie s om he alence band in o he conduc ion one, hus p oducing he pho o-gene a ion.
Un o una ely, no all he pho ogene a ed ca ie s a e de ec ed. Recombina ion phenomena make he numbe o c ea ed
pai s o dec ease e y as . Typical ca ie li e imes in s anda d CMOS echnologies a e in he o de o o
and, he e o e, e icien mechanisms o collec hem be o e hey ecombine mus be p o ided. The simples me hod o do
his consis s o using e e se biased diodes. I pho o-gene a ion occu s wi hin he deple ed quasi-neu al egion o he p-
n junc ion, he buil -in junc ion po en ial will quickly sepa a e elec ons and holes. These ca ie s o m a cu en whose
alue can be quan i ied by he ollowing exp ession [18],
(1)
1. F om digi al o analog and ice e sa.
128 x128
PEs A ay
P og amming Block
32b Digi al Da a Bus
Mem. Con ol. Bus
Memo y
Con ol
Add essing
Ci cui y
I/O
Con ol
2 x 128 S/H Bank
128 DA-AD Bank
Figu e 2. A chi ec u e and mic opho og aph o ACE16k.
Analog
Coe . Bus
Digi al
Ins uc ion
Bus
(a) (b) 11.885mm
12.230mm
1.124eV 1.1µm
0.1µs10µs
Iph
ηqP
i
⋅⋅
hυ⋅
--------------------
=
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whe e, is he quan um e iciency, is he elec on cha ge, is he densi y o powe o he inciden ligh , and is
he ene gy o one pho on wi h equency .
The quan um e iciency igu e, , exp esses he quo ien be ween he numbe o gene a ed pai s and he numbe o
inciden pho ons wi h a ce ain equency .
(2)
which is always lowe han uni y in he isible and in a ed po ion o he spec um.
The numbe o cha ges pho ogene a ed by an inciden ligh wi h a powe and a wa eleng h de ec ed du ing a gi en
ime in e al by using a pho osenso o a ea and a quan um e iciency is gi en by [20],
(3)
whe e is a physical cons an de ined as and is a unc ion o he wa eleng h o he
inciden ligh .
The o al amoun o elec ical cha ge de ec ed is simply ob ained as,
(4)
while he equi alen cu en p oduced wi hin his in e al is,
(5)
Mos usually, he pho ogene a ed cu en is con e ed in o an equi alen ol age alue by using one o he ollowing
me hods; he in eg a ion o he pho ogene a ed cu en on o a p e iously ini ialized capaci o , o he ans o ma ion o he
Technology ST Mic oelec onics 0.35 µm 5M-1P
Design S yle Full Cus om (Analog Co e) and S anda d Cells (Digi al I/O
block)
Package Ce amic QFP144
# o Cells 16384 (128 x 128 A ay)
# o T ansis o s 3,748,170
# o T ansis o s pe cell 198
Cell Size 75.7 µm x 73.3 µm
Cell Densi y 180 cells/mm2
Pixel Signal Swing [0.6, 1.4]V (P og ammable)
Weigh Signal Swing [2.15, 2.95]V (P og ammable)
Accu acy o Analog P ocessing
Blocks ~1%
Time-Cons an -linea . con ol.- ~160ns
Time-Cons an -CT Dynamics- ~0.8µs
I/O Mas e Clock 32 MHz
Powe Supply 3.3V +/- 10%
Powe / Speed / A ea Figu es 0.33x1012OPS, 0.18 x1012OP/J and 3.8x109 OPS/mm2
# o Analog Ins uc ions in mem. 32
# o Digi al Ins uc ions in mem. 64 x 64 Con igu a ions
Die Size 11885.0 µm x 12230 µm
Table 1. ACE16k Cha ac e is ics
ηqP
ihυ⋅
υ
ηυ
ηυ() no. o de ec ed cha ges
no o inciden pho ons
--------------------------------------------------------
=
P0λ
Tin
∆Aηλ()
n∆AP
0Hξλ() Tin
∆⋅⋅⋅ ⋅=
HHhc⋅()
1–
=ξλ() ληλ()⋅≡
Qph qn∆⋅ Aξλ() Tin
∆⋅⋅[]P0qH⋅⋅⋅==
Iph Qph Tin
∆()
1–
×Aξλ()⋅[]P0qH⋅⋅⋅==
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cu en in o a ol age by d i ing some kind o esis i e load. In any case, a emp s o linea ly co e he huge ange o
illumina ions exis ing in eal li e scenes1 − 6 o 8 decades − will always ail due o he undamen al limi s imposed by
noise loo and powe supply le el.
An in e es ing possibili y o expand he senso dynamic ange − by enouncing o linea i y − consis s o using a non-
linea I-V con e sion block wi h a comp essi e-like cha ac e is ic.
Among all he possible non-linea ans e unc ions, a e y sui able one o isual signal comp ession is he loga i hmic
unc ion. I s sui abili y comes om he e idence [21] ha pho o- ecep o s in he human e ina exhibi a loga i hmic- ype
esponse o ligh s imulus which p o ides a wide dynamic ange o ope a ion.
We will see in he nex sec ions how o exploi he pho o-sensi i e de ices exis ing in s anda d CMOS echnologies o
ob ain a mul i-mode pho osenso .
4. THE MULTIMODE OPTICAL SENSOR
4.1. Senso Schema ic
Fig. 3 shows he a chi ec u e o p oposed senso which can be di ided in o h ee blocks. The i s one, a i-s a e eadou
bu e , is used o con ol he communica ions among he senso and o he s blocks in he CNNUM cell − basically he
LAM module. Senso eadou s a e con olled by he global p og amming signal ROPT − which co esponds o one bi in
a Swi ch Con igu a ion Regis e SCR.
The second pa o he senso is he ci cui y de o ed o he ansduc ion o he pho o-gene a ed cha ges in o ei he a
cu en o a ol age le el. The use has he possibili y o selec ing he pho o- ansduc ion mechanism by means o
con igu a ion signals , which a e also s o ed in he SCR, as will be explained la e .
The hi d block includes he op ical senso i sel and wo con igu a ion swi ches used o selec one ou o he h ee
a ailable pho osenso s. The selec ion o he senso is ca ied ou by o he SCR p og amming signals called DW and WS.
4.2. In eg a ion Modes
In in eg a ion modes, he senso p o ides an ou pu ol age which linea ly depends on he in ensi y o he inciden ligh .
Independen ly o he ac ual pho osenso selec ed, he sensing p ocedu e is always he same. Fi s o all, a e u ned
o by making LOG1=LOG2=1. A e wa ds, swi ch p echa ges he in e nal node a o he use -de inable ol age
VPCH. Finally, swi ch is u ned o and he pho ogene a ed cu en cha ges o discha ges he pixel capaci o
.
Fig. 4 shows he h ee di e en con igu a ions o linea in eg a ion.
Fig. 4(a) shows he equi alen schema ic o he i s in eg a ion mode. I uses he N-Well/P-Subs pho odiode ( ) as
ligh sensi i e de ice. The P-Di /N-Well diode is annulled by making signal WS=0, while he bipola ansis o is also
o by he same signal since i o ces . Then, i is easy o ob ain ha ,
1. In humans, sepa a e he gla e limi om he sco opic h eshold.~200dB
Fig. 3. Rep esen a ion o he Mul imode Pixel. Schema ic.
Ou pu
ROPT LOG2
LOG1
VLOG
VPCH
PCH
VNWELL
WS
DW
Ms1
Ms2
Ms3
Ms4
Ms5
MLOG2
MLOG1
P-Subs.
p
+
n
-
n
+
WS
Ms2
VNWELL
DW
Ms1
a
p
--
DWS
DDW
Bip
LOG1 LOG2 PCH,,
Ms1 2,
Ms5 4,
Ms3
Ms3 Iph
Cpix
DWS
VBE 0=
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(6)
whe e is he sensing a ea o he N-Well/P-Subs pho odiode, is he powe o he inciden ligh pe a ea uni , and
.
Fig.4(b) shows he senso schema ic when he P-Di /N-Well pho odiode is used. By se ing WS=1, DW=0 and
o he supply le el, we ensu e ha he N-Well/P-Di diode emains e e se biased, and ha he e ical
bipola ansis o is OFF. Only he ca ie s collec ed by he P-Di /N-Well junc ion will con ibu e o he pho ocu en
yielding,
(7)
Finally, Fig. 4(c) shows he schema ic o he senso when WS=DW=1. In his case, he base o he e ical BJT emains
in open ci cui . Pho ogene a ed mino i y ca ie s in he base-emi e junc ion p oduce an emi e -base cu en which is
ampli ied by he ansis o e ec . In his case, he ou pu is simply gi en by
(8)
The use o linea sensing schemes is limi ed o images whe e he exis ing dynamic ange is ela i ely na ow. The nex
sec ion shows how he p oposed mul i-mode senso can be con igu ed o pe o m di e en log-comp ession sensing
schemes.
4.3. Loga i hmic Comp ession wi h T ansis o -based Loads
Loga i hmic- ype sensing has he ad an age o p oducing images in which he di e ence be ween pixels only depends on
he di e ence in op ic con as and no on global illumina ion condi ions. Then, senso s exhibi a wide dynamic ange
DR. Howe e , he p ice o be paid o ha DR inc ease is a educ ion o he con as in he image − mos ly due o he log
unc ion.
To be e unde s and he ad an ages o log comp ession ision i is necessa y o iden i y he e y basic na u e o he
in o ma ion ha is p ocessed by ision sys ems. Excep in some e y special cases, his in o ma ion is a con as le el. In
hose si ua ions whe e ansmission e ec s on he medium can be neglec ed, he ligh in ensi ies o e he objec a e he
p oduc o he i adiance and he e lec ance o i s su ace a his poin .
The esponse o a linea senso ocusing o objec poin is always p opo ional o he i adiance a his
poin and he e lec ance o he su ace a his poin , hus,
Fig. 4. A ailable Con igu a ions o In eg a ion Modes.
Ou pu
ROPT
VLOG
MLOG2
MLOG1
VPCH
Ms3
Cpix
VNWELL
VNWELL VNWELL
DW=1
WS=0
DW=1
WS=1
LOG2=
1
LOG1=
1
PCH
WS=1
DW=0
Iph
Iph Iph
a
aa
a
a) b) c)
DWS
DDW
Bip
TR
Tin
VaVPCH IPh
Cpix
----------Tin
–V=PCH Tin
Cpix
----------AWS ξWS λ()⋅[]P0qH⋅⋅⋅×–=
AWS P0
ξλ() λη
WS λ()⋅≡
VNWELL
VaVPCH IPh
Cpix
----------Tin
+VPCH Tin
Cpix
----------ADW ξDW λ()⋅[]P0qH⋅⋅⋅×+==
VaVPCH βTin
Cpix
----------ADW ξDW λ()⋅[]P0qH⋅⋅⋅–=
Eρ
OLin xy,() xy,()
Exy,() ρxy,()
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(9)
whe eas ha o a loga i hmic senso is
(10)
Hence, wo di e en egions o a su ace wi h di e en e lec ances and , bu he same i adiance
would p oduce a di e en ial ou pu signal gi en by,
(11)
in he linea case while o he loga i hmic senso i would be,
(12)
As i can be seen, in his la e case, he di e en ial ou pu signal does no depend on he i adiance bu on he di e ence
be ween he e lec ances. Ob iously, his is no ue o he linea senso , whe e he di e en ial ou pu signal also
depends on he common i adiance le el. Hence, he same de ails − poin s wi h he same le el o − in an inpu image
migh no be dis inguishable in linea senso s because o he i adiance le el which could e en make he senso o be
o e -exposed -sa u a ed.
Fig. 5 illus a es he ou pu images p o ided by linea and loga i hmic sensing schemes when cap u ing a wide dynamic
ange day-ligh scene. I is seen how, a he expense o a loss o con as , he log- ype acqui ed image gi es in o ma ion
abou a eas which couldn’ be iden i ied in he linea ly acqui ed one.
Mos log- ype epo ed CMOS image senso s exploi he loga i hmic ela ionship exis ing be ween he cu en and he
ga e o sou ce ol age when MOS ansis o s ope a e in he sub h eshold egime. This p ope y is used in ou senso as
ollows.
Fig.6 shows he con igu a ions a ailable o his ype o log-sensing in he p oposed ci cui . No ice ha he ese
ansis o has been emo ed om he schema ic since log-mode acquisi ions wo k in con inuous ime − he ou pu
ol age co esponds o he equilib ium poin o d i ing he non-linea esis i e load wi h he pho ogene a ed cu en . On
he o he hand, he selec ion o he ac i e load mus be p ope ly done acco ding o he senso choice. Assuming ha he
d ain o sou ce cu en o a sa u a ed PMOS ansis o − bulk e minal connec ed o − wi hin i s sub h eshold egion
is app oxima ely gi en by1 [22],
1. The de ini ion o he pa ame e s in his exp ession can be ound in [22].
OLin xy,()Exy,()ρxy,()⋅=
OLog xy,()Log ρxy,()Exy,()⋅[]=
ρx1y1
,() ρx2y2
,() E
∆OLin E∆ρ⋅=
∆OLin Log ρ1
()Log ρ2
()–=
ρ
Fig. 5. Example o Log-Type Visual Acquisi ion. a) No mal Linea ly Acqui ed Image. b) Log-Type
(a) (b)
Ms3
Vdd
44 P oc. o SPIE Vol. 5017
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i can be ound ha he s eady s a e ou pu ol ages a e gi en by he se o exp essions displayed in Fig.6.
In addi ion o he loss o con as p oduced by he loga i hmic unc ion, i is also obse ed ha he exp essions o he
ou pu ol age con ain se e al echnological pa ame e s ela ed o he load ansis o . Un o una ely, misma ching
phenomena make hose pa ame e s o a y om pixel o pixel and, consequen ly, he Fixed Pa e n Noise (FPN) igu es
in hese kind o senso s a e wo s han hose o hei linea coun e pa s.
An in e es ing al e na i e which pa ially sol es his p oblem consis s o using co ela ed-double sampling echniques
[23] a he pixel le el by exploi ing he econ igu a ion and algo i hmic capabili ies o he CNNUM cell. Howe e , i
may equi e adding new modules o he cell and he execu ion o a ce ain numbe o addi ional ope a ions, hus slowing-
down he p ocessing.
In he nex sec ion we will p esen a log senso which does no use any ansis o load and ha , consequen ly, exhibi s
be e FPN igu es.
4.4. Loga i hmic Comp ession in he Pho o- ol aic Mode
The idea o using he pho odiodes in he pho o- ol aic mode is ela i ely ecen . Up o ou knowledge, i was i s
in oduced and es ed by D . Ni e al. in 1994 [24]. Expe imen al esul s demons a ed ha his kind o senso s exhibi a
e y wide dynamic ange and good uni o mi y FPN pe o mances.
The basic concep in oduced by his sensing scheme consis s o using a pho odiode in an open ci cui con igu a ion, and
o le i o each i s s eady s a e.
In ou case i wo ks as ollows.
Suppose he ci cui in Fig.6(b). I no esis i e load is connec ed o node a and he ci cui is allowed o achie e i s s eady
s a e, he cha ge conse a ion p inciple imposes ha he cu en lowing om VNWELL o node a, ha is 1, mus
be equal o ha lowing h ough he diode. Assuming a ypical exponen ial exp ession o he diode cu en yields,
Fig. 6. A ailable Con igu a ions o S anda d Log.Comp ession Modes.
MLOG2
MLOG1
DW=
1
WS=
0
LOG2=
0
LOG1=
1
WS=
1
DW=
0
Iph
Iph
(a)
MLOG2
MLOG1
LOG2=
1
LOG1=
0
(b)
VLOG VLOG
VLOG
MLOG2
MLOG1
VNWELL
DW=
1
WS=
1
LOG2=
0
LOG1=
1
Iph
(c)
VLOG
VLOG
VLOG
VNWELL
VNWELL
Va
np2
VLOG VT0M2
npM2
1–


Vdd
–npM2
UTLn
AWS ξWS λ()⋅P0qH⋅⋅⋅
ID0M2
----------------------------------------------------------------
–– Fig. 3(a)
VLOG VT0M1
npM1
1–


Vdd npM1
UTLn
ADW ξDW λ()⋅P0qH⋅⋅⋅
ID0M1
-------------------------------------------------------------------
++ +
npM1
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Fig. 3(b)
npM2
VLOG VT0M2
npM2
1–


Vdd
–npM2
UTLn βADW ξDW λ()⋅P0qH⋅⋅⋅
ID0M2
-------------------------------------------------------------------
–– Fig. 3(c)













=
IDS ID0e
npVSVG
–VT0np1–()Vdd
––
npUT
---------------------------------------------------------------------------------



⋅=
ISIph
+
P oc. o SPIE Vol. 5017 45
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which shows a log- ype ela ionship be ween he pixel ou pu ol age and he ligh in ensi y.
The main ad an age o his log-comp ession scheme is ha he ob ained exp ession is simple , i in ol es only a ew
e ms, han hose on Fig.6, and consequen ly, i s ope a ion is in insically mo e obus agains cell- o-cell disc epancies.
4.5. Layou
The mul i-mode senso desc ibed in his pape has been included in o he cell used by he ACE16K [25] p o o ype.
Fig.7(a) shows he layou o he senso in he ACE16K chip. The N-Well in which he senso is laid-ou is
. A silicided p o ec ion a ea has been de ined all a ound he sensing a ea in o de o a oid a loss o
sensi i i y o he senso . In addi ion, all he econ igu a ion swi ches a e PMOS ype and laid-ou in a di e en NWELL
o isola ion pu poses. Finally, as can be seen in Fig. 7(b), all me al laye s con ain a hole jus in he a ea unde which he
senso is placed in o de o allow he ligh o di ec ly each he sensing a ea.
5. CONCLUSIONS
A new mul imode op ical senso a chi ec u e o he op ical in e ace o Focal Plane A ay P ocesso s chips ha e been
p esen ed. The senso o e s he possibili y o selec ing he ac ual ligh -sensi i e de ice as well as he mechanism o
ansducing he pho ogene a ed cha ges. Bo h linea and log comp ession acquisi ion modes a e a ailable, making he
senso e y sui able o i in o e y di e en illumina ion condi ions.
6. ACKNOWLEDGMENTS
This wo k has been pa ially unded by CE P ojec IST-1999-19007 (DICTAM) and ONR P ojec N000140210884.
7. REFERENCES
1 P. Sa o, “Senso s: The Nex Wa e o In oTech Inno a ion”. Ins i u e o he Fu u e, 1997 Ten-Yea Fo ecas .
2 B. Roska and F. We blin, “Ve ical In e ac ions Ac oss Ten Pa allel, S acked Rep esen a ions in he Mammalian Re -
ina”. Na u e, No. 410, pp. 583-587, Ma ch 2001.
3 C. Koch and H. Li (Eds.), Vision Chips, Implemen ing Vision Algo i hms wi h Analog VLSI Ci cui s. IEEE P ess, 1995.
1. is he sa u a ion cu en o he diode.IS
VaVNWELL nUTLn
Iph IS
+
IS
--------------------



+=
9.8µm9.8µm×
Senso s Swi ches
T i-s a e Bu e
Fig. 7. Layou Views. a) The senso . b) The Cell in ACE16K.
(a) (b)
46 P oc. o SPIE Vol. 5017
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