CA2214667A1 - Time delay and integration sensor - Google Patents

Abstract

A time delay and integration charged coupled device which includes a charge transfer unit, a reset unit, a horizontal shift register and a plurality of cell columns. Each of the cell columns includes a plurality of cell-units connected in series therebetween, defining a downstream flow of charge towards said horizontal shift register. Each of the cell-units includes a photo-cell and at least one buffer-cell, located underneath the photo-cell. The charge transfer unit controls the device by transferring charge downstream between any of the cells and transferring charge from the cells columns to the horizontal shift register. The reset unit resets the photo-cells after charge accumulated therein is transferred therefrom. The device provides control of the exposure time of the photocells, by utilizing the buffer cells as intermediate storage ofcharges from the photo-cells, thus enabling reset of the photocells.

Description

TIME DELAYAND INTEBRATION SENSOR
Avigdor ROSENBERG and Hillel AVNI

FIELD OF TllE I~IYENTION
The present invention relates to Time Del~y ar~d Integration Charged Coupled Devices.
BAC~KGROIJND OF THE INYENTION
Ti~ne Delay and Integration~TDI) Chargecl Coupled Devices (CCC~) ~re known in the art A TDI C;CD sensor consists of a number of lines, also oalled stages, of photocells, also called pixels. ~ight, either reflected ~rorn or o generated by an object, hits the photocell and ~enerates ch~rges in the photocells. Reference is now made to Fi~. 1A ~vhich is a sche,~l~lic diagram of ~ prior art TDI CCC) sensor, gener~lly referenced 100. Sensor t00 inclucles a plurality of photocells, generally referenced 102 arranged in a two dimensional array, having a pluralit~ of lines 104 ancl columns 106. Sensor 100 also includes a horizontal shift register 112 place~ and connected to the bottom cellof each of the ~olumns.
The main principle acoor;Ji"g to ~hich sensor 100 operates is accumulating and shifting charges in synchronization with the move Tlent of an o~ject 110. ~Vhen phol4c~11 1 02f is exposed to object 110, charge is generated ~o and contained in the photocell 102f. As the obJect moves to photocell 102e, t~e charge, ~ccumulated in photocell 10~fl is transferred to photocell 102e and at the same time, char~e from photocell 102~ is transferred to photocell 102d.
Then, the photocell 102e is exposed to the light coming from object 110, ~rhiçh Gauses additional charge to be generated and accumulated in photocell 102e.
25 As the object moves to photocell 102d, the charge, ~ccumulated in photocell 102e, is transferred to photocell 102d, and so on through photocells 102c and 10~b. Fin~lly, the oharge ~ccumulated In photocell 102b, representing L
~xposures of photo~ells to the object 110, where L is the number of rows in sensor 100, is l,c,n~r~r,~cl to 1 horizontal shift re~istercell 112a and then shi~ted out to the output.
It will be appreua~ed that the same c~curs in each of the colllmns.
The photo~ells 102 Of each ine 104 l,~nsfi~,a the accumulated ch~ge to the s photo¢ells of the next line, at ~he s3me time, in sequence with the moYernent of t~e object 110. The charges previously accumulated by one line are added to the newly generat~d charges of the next line, while the object moved from one line to the next. Thus, at the botto~n of the array a line of an image of the object is fonned, ac~umulated by a I tlte lines of the array. For that reason, a TDI
10 sen~or ~asically provides a s n~itivity which is its number of ~ta~es times nwre than a linear (or single line), sensor. Due to ~s incre~sed sen~iitivity, a TDI
image sensor has many 3ppli,atio"s, where a single line senso~s sensitivity is not enough, such as in~ pection of fast n~oving andJor dark web, reconnai~sance, and ~he like. I
Reference is novv made to Fig. 1~ which is a gener~lized timing diagram of a conventional ~DI sensor 100. Line 140 represents an object mo~vement sy,,chrunka~;un si~nal which goes high each tirne the object 110 moves to the next photocell row. Line 142 represents a signal which is high during vertical oharge transfers and low du~ing the time that the photooells areexposed. ~ine 144 represents a signal ~rhich is high during the hori~vr,L~l shmsof horizontal shi~ register 112.
Vertical ch~rge tran~fers from the photocell 102f (Fig. 1A) of one row to the photoGell 102e of the lext row must be perfor~ned in a synchronous manner to the relative moveme 1t between the sensor 100 and the object 1 10. If ~s the spacing between photocell- in th~ direction of movement (spacing betweenthe rows) is ~, then the charse tr~nsfer frnm row to ro~v must occur each time the object mo~ed ~ distance of ~Y on the sensor plane. Gonsider a certain point on the objeGt, which is lexposed to photocell 102f at a predetennlned ~nor"enl, as an ex~",F'e AftPr the point tra\reled the distance of ~Y on the image plane, the ch~rge accumula~ed from the point by the ph~tocell 102f of 1.

roul 104f is transferred to the photo~ell 102e of the next row 104e, and the point is now e~posed ~seen~ by th~ t photocell of row 104e. The cl,~ryes transferred ~rom ~ow 104f are aco~lmulatPd with new light generated Gharges at row 104e, belong to the same point of he obJect 110. This operation of charge transfer from row to row, synchloni~e~l to tl-e object's relative movement on the image piane, is continued until the cl~arges of that point reach the horizontal shift register (HSR) 112, at the bo~tom of the array. At the HSR, the char~es of the photocells of the row ~re quic~ly shifted out to the output 130. If the TDI senso-has L stages, then at the cutput of the TDI, ~e get a signal representing o elements of the object, seen ~y elements of the sensor, accumul~ted L ~imes.
Thus a TDI sensor can th~oreffcally be L times more sensitive than a conventional Linear CCD sensor. The synchronization of the vertical row to row char~e transfer, to the object rnoYement ~n be done by using a shaFt encoder or by other mean~, depending lon the application.
Unlike a Unear CCD sensor, conventional ~l senso~s do not have electronlc exposure control, ~ue to the fact that charges are continl~ously accurnulated. Thus, photocells eannot be held in reset.
TEXP jS the time period in which a predetermined photooell is exposed to light, thus, accumul~ting charge. in ~ convelltional TDI C;CD sensor, TEX~ jS20 the tlrne between two suoc~sive lines In other word~ p is the time that takes an o~ject to tr~vel a distance, on the image plane, equal to the sp~cing between two ~uccessive rows of the sensor 100.
It will be appreciated that the n~in chara~teristic of the conventional TDI mechanism is based onlsynchron;zation to distanoe ~nd displacement.
~i ~/Vhere tlle relative veloclty of tl~e object is not wnstant, the time that the o~ject requires to travel a fixed distanc~ is na~ constant ~nd depends on ~/elocity.
I lence, the i"Legralion time TEXP Of the photocells of the conventional TDI $ensor ~ill vary as the velocty of the object varies. Thus, the charg~ ~enerated in photooells will valy with ~ change in the velocity and not only ~s a factor of the brightness of the cbject.

In applic~tions which involve moving webs i~ Ispe~tion, a defect which should be detected is sometimes 2 variation in the webs' shade. Varia~ion in O~ltpUt sign~l, due to t~e web's speed change, can look like an actual defect.
This is true with Linear, single line, sensor tw.
s A conventional way of solving the problem of signal v~ria~iun due to speed variation, when using Linear sensors, is by using an ele~tronic exposure time. By applying a const~nt exposure time, shorter than the minimum time beh~.,cn successive lines (which is at the maximum speed of the object), the photoce~ls' int~?gration time i~ constant, regardless of the object's speed.
Another method for ove~ "i"~ this problem utilizes compen~dLion to tl~e output signal, by measuring the speed of the object's relative mo~ement andchanging gain ac¢ordingly. Yet another method uses mechanical or LCD
shuffers. It will be appreciated that these above rnethods are usually problematic because of their complexity of implen,er,l~tions, because of the large dynamic ranse required when the speed range is big, because of the compens~tion precision needed, and the like.
Conventional TDI sensors do not have an eleGtronic exposure control fe~hlre. This makes the T~l sensor d fficult and so",eti,r,es in~possible to use in applioations where the object's speed, relative to the sensor, varies. A
disadvantage of the prior TDI sensors is that they are in~apable of overcoming ~he blooming effect, which occur$ when c~arge accumulated in the photocell exceeds a pre~eterrnined level.
Exposur~ ~or,trol can be incorporated in a TDI with Interline Transfer (IL) archite~ture. It ulill be ~ppreciated that the interline transfer architecture 2s suffers from a partial fill factor, ~Nhich is a substantial disadvantage. Thi$
technique is disclosed in the following article, incorporated herein by reference:
Stacy R. KAMAZ al, "Novel Inlt~ e Transfer CCD Array for Near-ln~rared Applications", SPIE, Vol. 2416, p 10~116.

SUMMARY OF THE PRESENT INVENTION
It is an obje~t of the present invention to provide a novel T~l CCD
sensorwhich overcomes the dlsadvantages of the prior art.
It is a further objeot of the present inYention to provide a novel ~DI
s CCD sensor with exposure control, having a fill factor of nearly 100% Of the im~ged object. The incorporation of exposure control in the present invention, enables the sensor to ~e us~d in applicalions where the relati~e speed of the imaged object is not constant, as well as in other TC~I and line scan a~FI ~tions requiring electronic shuttering.
o There is thus provided, ;n accordance with the present In~rention, a tirne delay and integration charged coupled device ;ncluding a charge transfer unit, a reset unit, a horizontal shi~t re~ister and at least one cells column. The cells oolumn includes a plura~ity of cell-uni~s connected in series therebetween, definin~ a doulnstream flow of charge to-vards the horizontai shi~t register. Each of the cell-units includes a photo~ell, generating char~e when in the presence of light, and ~t least one buffer~ell for storing charge whe~ein the photo-cell and the at least ane buffer-~ell are connected in series thereb~tween.
The ~harge transfer unit is connected to e~ch of the photocells and the buffer Gells, controlling the device by transferring ch~rge do~,,sl,~n~
between any of the cells and transferring charge from the cells ¢olumns to the horizontal shi~ register. The reset ~Init provides rese~ting the photo-cells, affe~
charge accumula~ed in the photo-cells is tr~nsferrea therefrom, According to a further aspect of the inve -i~ion the vertical length of the cell-units equals twice the verffcal length of the photo-cells.
Accordin3 to another aspect of the inventionl the vertical length of the cell-units is substantially similar to the vertic~l len~th of the photo-cells.
The device, accor~ 3 t~ a pref~rred embodiment of the invention, includes cell-units whioh include two ~llffer-cells.

Each of the cell~ colurnns may also include an additional photo-cell, connected in series to the horizon~al shi~ register, The device, according to a pr~rened embodiment of the invention, includes cell-units which in~lude a single buffer~ells.
A ~ell-unit for inGorporating in a TDI CCD comprising a photo-cell, generating and accumulating charge when in the prêsence o~ light, and at least one buffer~ell far storing charge, ~aid ~hoto-cell and said at least one buffer-cel~ being connected in series.
Accordi,)g to another aspeGt of the ;n~lention, there is provided a time lO delay and integrat;on char~ed caupled device ~hich includes a ch~r~e transferunit, a reset unit, a horizontal stiift register, at least one cells oolumn includin~ a plurality of cell-units connec~ed in series, definin~ a downstream flow of charge towar~s the hori~ontal shift register.
Each of the cell-units includes a photo-cell, generatin3 charge when 15 in the presen~e of light and a buffer-cell, for storing charge, located underne~th the photo-cell, connected to the photo-cell.
The charge ~ransfer unTt Is connected to each of the photocells and the buffer-cells, ~ntrolling the device by transferring charge in a ~cle~,led cell-unit from a photo-cell of the selected cell-unit to a kuffer-Gell of the selected 20 cell-unit. The charge transfer further controls the device by tran~ferring charge downstream betwe~n the buffer-cells towards the horizontal shi~t register. The reset unit resets the pho~o-cells a~er charge ac~umulated in the photo-cells i~
transferred therefrom.
The reset unit can reset each the cells column, individually.
Alternatively, the reset unit resets in~ividual rows of the cell-units.
According to another aspect of the in~lention, there is provided a cell-unit for inGorporating in a TDI CCD including a photo-cell, generating and awumulating charge ~hen in the p~ence of light, and at lea~t one bu~er-cell for storing charge The buffer-cell is located benea~ the photo-cell.

According to yet a further ~spect of the invention, there is thus provided a method for operating a ~DI CCD device, the TDI CCD deYiGe including a plurality of cells column~, each of the cell-columns including a plurality of cell-units, ea~h of the cell-units inGluding a photo-cell and a buffer-cell connected thereto, lo~ated undeme~th the photo-cell, each of the buffer-cells of the cell-units bein~ connected in series, definin~ a do~vnstre~mstructure which ends in a shift-register, the rnethod includes the step of repeating the followin~ steps:
enabling exposure to the pho~o-cells, o deteGting light received from an object. thereby producin~ charge by the photo-cells, transferring charge in each the oell-unit from the photo-cells to the ~uffer-cells, disabling exposure to the pho~o-cells, an~
s transferring charge do~nsl,eam beh~een the buffer-cells, towards the shift-register.
In accordance with another ~spect of the invention, there is provided a method for operating a TDI CCD device, the TDI CCD devi¢e including a pluralty of ~ells columns, each of the cell-columns including a pll~rality of cell-units connec~ed in series, each of the cell-units including a photo-Gell ~nd a buffer-cell connected in series, the last cell-llnit of ea~h of the cells columns being connected to ~ shffl-register. ~he rnethod includes the step of repeating ~he following steps:
enablin~ detection of light received from an object. thereby producing 2~ charge by the photo-cells, transferring char~e in each the cell-unit from the photo-cells to the buffer-cells, -tran~.,i"g charge out from the b~ffer cell of the last cell-unit to the shi~-register, disabling the ~et~ction of l;ght to the photo-cells, and transferring charge doumstream be~Neen the ~uffer-cells towards the shi~-reglster, from a buffer-cell of a selected cell-~nK to a photo-cell of a sllbsequent cell-unit In accordance with another aspect of the invention, there is pro~rided a method for operating a TDI CCD device, the T~l CC~) device in~luding a plu~ality of cells columns, each of the cell-columns including a plurality of 10 cell-units and a and a last cell-unit, each of the cell-~n;ts including a photo-cell and a buffer-cell connected in series, e~ch of the last cell-units including a photo-cell and being further conne~ted to ~ shift-register. The method includes the step of repeating the ~ollowing steps:
enabling detect;on of light received from an object, thereby producing 15 charge by the photo-cells, transferring Gharge in e~Gh the cell-unit from the photo-cells to the b~ffer-cells, transferrin~ charge from each the last cell-unit to the shift-re~ister, disabling the detection of light to the photo-cells, and transferring charge downstream between the cell-units towards the shift-register, from a buffer~ell of a selected cell-unit to a photo~ell of a subsequent cell-unit, In accordance with a fll~ther aspe~ of the invention, there is provided a rnethod for operating a TDI CCD device, the Tl~l CCD device including a 25 plurality of cells columns, each of the ~ell-columns including a plurality ofcell-units connected in series, each of the cell-units includin~ a photo-~ell, a first buffer-cell, conneeted in series to the photo-cell ~nd a second buffer-cell connected in series to the first l~uffer cell, the last cell-unit of each of the cells columns being ~onnected to a shi~-register. The method includes the step ~f repeating the following steps:
enabling detection of light receh~ed frorn an object, thereby producin~
charge by the pho~cells, transrei,i"g charge ;n e~ctl the cell-unit from the plloto-cells to the first buffer cells, disabling the d~L~liun of light to the photo-cells, transferring charge d~u"~ m between the ce!l-units towards the shil~re~ister, fron~ a second buffer-cell of a selected cell-unK to a photo-cell of a 0 subsequent cell-unit, transferring charge in each the cell-unit from the first buffer~ells to the second buffer~ells. and transret~ g ch~rge out from the second buffer cell of the last cell-unit ~ the shift-register, Each of the above methods can also include the steps of transferrin~
charge out from the shift-register, resetffng the photo~cells, enabling exposur by disablin~ reset to the photo-cells and disabling exposure by enabling re$et to ~he photo cells.

CA 02214667 1997-09-0~

BRIEF DESCRIPTION OF ~HE ~RAWINGS
The present invention w;ll be understood and appreci~led more fully from the following detailed de~cription ~aken in oonjunction with the drawings in which:
s Fig. 1A which is a scheilla~ic diagram of a prior art TDI CCD sen~or;
Fig. 1B which is a schematic timin~ diagranl of a conventional TDI
sensor of Fig. 1A;
Fig. 2A is ~ schenl~Lic illus~l~lion of a TDI CCD sensor, constn~ted and operative in accordance with a preferred embodiment of the invention;
~ig. ZB is ~ schematic electrical illustration of the TDI CCD sensor of Fi3. 2A and its reset mech~nism;
Fig. 3 is a schematic timin~ illu~tr~tion of the TDI CCD sensor of Fi~s.
2A and 2B, operative in acwrdance with ~ pre~erred embo~iment of the inventian;
Fig, 4A is a schematiç illu~ tion of a TDI CCD sensor, constru~ted ~nd operative in accordance w~h another pr~:fe"~d embodiment o~ the invention;
Fig. 4B is a schem~tic electrical illu~tr~tion of TDI CC~ s~nsor of Fig.
4A;
Fig, 4C is a schematic illustration of TDI CCD sensor, constructed and operative in accordance with a further preferred embodiment of the invention~
Fi~. 5 wllich is a schematic timing illustration of the devi~e of Figs. 4A
and 4B, operative in accordance with a further preferred ernbodiment of the 2s invention;
Fig, 6 is a schematic illustration of a TDI CCD s~nsor, constructed and operative in aooordance ~vith a yet another pl~rt:lled embodiment of the invention;

-Fig. 7 is a sdlen~alic illustration of ~ ¢ell-unit, constructed and operative with anotiler preferred em~odiment of the present invention;
Fig. 8 is a ~ree dinlensional schel"~lic illustration of a TDI sensor and a shift re~ister, ¢onstructed in ~c~ordance with yet a further prt:f~l,ed s embodiment of the present invention;
Fig. 9 is a schematic flow ~hart ill~t,~Lion of a metho~ ~or operating the TDI CCD sensor of Fig. 2A, operative in accordance ~vith yet another pr~ d embodiment of the present invention;
Fig, 10 is a schematic flow chart inustration of a method for operatin~
0 tt~e TC)I CCD sensor of Fig. 4A, operative with ac~ordance with yet a further embodiment of the present invention;
Fig. 11 is a schenlatic illustration of a nlultiple timing dia3ram, for operatin~ TDI CCD sen~or of Fig. 8, in accordance with another p~eferred embodiment of the present inventlon; and lS Fig. 12 is a schematic flow chart illustration of a method for operating the device of Fig. 8, operative with ~cordance with yet another preferred embodiment of the present invention.

-DETAILED DESCRIPTION OF ~t~t~i~ED EMBODIMENTS
l~eferenoe is now made to Figs. 2A, and 2B. Fig. 2A is a schematic illu~ r, of a T~l CCD sensor, generally ,~er~nced 200, oonstruGted and operative in accordance with a pre;f~:"~d embodiment of the invention. Fig. 2B
5 is a schematio el~ical illus~ldtion of TDI CCD sensor 200 and i~s reset mechanisn,. Sensor 200, also called single buffer sensor, includes a plurality of photocell rows, gener~l~y refetenced 2~0, a'nd a plurali~y of b~ffer ¢ell rows, gener~lly referenoed 212 (individually ,~r~nced by sumxes A, ~ etc.~ and a llorizontal shift re~ister 232. Eqch of the photocell rows 210 includes a plurality 0 of photoceils, generally reference~ ~02 (individually referenced by suffixes ~, B
etG.), and aesocl~ted vertical charge transfer electrodes 203. Each of the buffer cell rows 212 includes a plurality of buffer cells, generally referenced 204, and associated vertical charge transfer electrodes 705 (individually referenced by su~xes A, B etc.), wherein each buffer cell 20~ is covered so that it can not beaflected by light. Electrodes 203 and 205 are only shown in Fig. 2B.
The photocel~s 202 generate charge when exyosed to light. The charge in each photocell 202 is then l,~ns~er,~d to the adjacent dow.l~al"
buffer cell 204. According ~o the present e%ampleT the charge transfer is perFormed by applying potentials in the appropriate timing to the CCD
~o electr~des of a predete~mined photocell 202 and adjaoent downstream buffer ~ell 204.
~ ach ,~hotocell 20~ has an assoo~.ated reset mechanism 214, which m~y be constructed in a horizontai structu ~, a vertical structure and the like.BasiGally, it consists of a transfer 3ate 216 (Fig. 2B1 and reset drain 218, to drain the charges from the photocell~ to the reset potential Vr. ~ocor~ing to the present example, the reset ~ates of all photocells are Gon,r"only controlled ~y TLR timing signal 220. 1 he reset structure can be used also for anti blooming, and for stage seleetion.
The reset structure can be used also for anti-bloomin~ by provlding 30 the reset drain 218 with an anti-blooming potential, so that when a photocell has excess charge, the t~nsfer gate ~16 is tumed on ~nd excess charges are drained away.
AGcording to the present example, the buffer ~ 04 i$ used for inte""edi~ storage of the char~e gener~ted at photocell 20~, which enables s reseffing the photocell 202 and shi~ing the charge to the next photocell at appropriate time. Acco~ding to the present example, the vertical length of a buffer cell ~Y2 is made to be smaller than the vertical length of a photocell ~Y, so as to ,n;,~ i e possible undersampling (not complete coverage) of the object in the Y direction, which can happen when applying short ex~osure periods, and o slow speed.
Referen~e is also made to Fig. 3 which is a schematic timing illustration of a TDI CCD sensor 200, operative in accord~n~e with a preferred embodiment of the invention.
Line 25~ represents the synchronization signal with regard to the S relative movement between the sensor 200 and the detected object. Line ~54 represents the exposure-reset sequence of the phot~cells wherein TEXP. jS ~n exposure period. Line Z56 r~preserll-~ the ~e~uence in which charge is transferred frorn ~ photo~ell to ~n ~djacent dowl,s~-ean7 buf~er cell, generallyreferenoed T~)B Line 258 ,~pr~ser,l~ the sequence in which charge is 20 transferred from the buffer cell to adjacent downstream photocell, generally referenced T,l~. Line 260 represent the sequence in which charge is tran~ferred frorn ~ the last buffer cell Z12E, to the horizontai shi~ register, TL~SR- Line 26Z represents the time in which charges a~ shrF'~ed trom the horizontal shi~ register 232 to output ~34.
The synchronization signal 25~ is determinecl according to the relative movement between the sensor 200 and the de~,,ted object.
TLR represented by line 254, is the signal which is used to reset the photocells 202, wherein high repr~sent a re~et command and low represents an exposure command to accumulate charge. A~er TLR goes low, Gharge is ~ransfer~ed fron~ ~ buffer oell to the adjacent dow~ am ph~lucell. This charge transfer is performed at a time perio~ represented by T~G~ re~renced 258.
A~Ler the exros~re period TeXp, charge is trar~-~r~"~d from a predetermined photocell to the adjacen~ downstream buffer cell, represented by Tc "~, 5 referen~ed 256.
The time between the falling ed3e Of TLR ~nd the begl""i"~ ~rising edge) of rC~ S the actual eYrosure time TEXP, After the charge ~"~re:r ~rom a photocell 202 to a buffer cell 204 has been completed, ~epresented by the falling edse of TC-~ TLR goes high ~nd the photw~ll 202 is reset. Rese~ting the O photocell is perforrned by draining the charge in photocell 202 to a Vr reset potential ~2. The photooell 202 is held in reset until the obj~ct completes passing the distance of ~Y=~Y~ l ~Y2, on the irnage plan~, which is ~he verticalspacing between ~No adjacent photocells.
Then, after the next rising edge o~ the obJect movement s synchronization signal 2~2, TLR goes low, i.e. reset is disabledr ch~rge is trans~erred from a bufler cell 204 to a next adja~ent ~ownstream photoGell 202.
At the same time this photocell begins to gener~te and accumulate more char~es, caused due to light coming from the de~ected o~jeGt.
Thus, while the object moves vertically from the top to the bottom of ~o the sensor, it is exposed to all of the photocells 202 in a column of the sensor 200, The accumulated charges are l~nsfer,~;d from one photoeell to ~n adjacent ~uffer cell, and further to the next photocell as the object moves fromone photocell to the next photocell on the ima~e plane of the sensor 200, 2~ adding the charges of one photocell to the charges of the next photacell. Thus, the oharge ~rom last buffer cell, at the bottom of array 230 havln~ N photocells, a~riving at the horizontal shffl register 232, represents N times of exposures of the object to photocell 202. The total expasure equals N time~ the applied exposure time multiplied by the size of a photocell of ~Y1 by ~C (Fig. 2A), ~o wherein ~( is the width of a photocell.

CA 02214667 1997-09-0~

The charge transfer from the last buffer row of the array to the horizontal shift register 232 can be controlled sep~rately and is done during the time T~ H~;R- This transfer can be performed at the same time with the other trans~er T~c~ from the buffers to photocells or it can be performed just a~er t~e s lrdnsrer Tc~ from the photocells to buffers. The horizontal shift of the charges, in the holicunl~l shrft register (HSR) Z32, to output 234 can be perhorrned affer the TLE~tH8R transfer.
It will be appreclated that a reset mechanism can be adapt~d to reset the buffer cells as well.
0 Sensor 200 ov~lL;on~es the dis~dvantage of tl~e prior art ~y controlling ~he photocells' exposure tims period, thus, eliminating the affect of variable relative veloci~y, of the detected object.
The present inYention provides a ~ill factor which is near to 100%.
Reference is now made to Flgs. 4A and 4B. Fig. 4A is a schematic 711ustrqtion of a T~l CCD s~nsor, gene~ally reference~ 400, constructed and operatNe in accordance with another preferred embodiment of the invention.
Fig. 4B Is a schematic ele~trical illust~ n of TDI CCD sensor 400 and its reset mechanism. Sensor 400, also called dual buffer sensor, includes a plurality of cells columns, generally referenced 420 (individually referenced by suffixes A, B
etc ) and a honzontal shifl register 432. Each column 420 includes a plurality of cell-units 430 (individually referenced by suffixes A, B etc.), wherein e~ch cell-un~ includes a phctocell 402, ~ first buffe~ ~ell 404 and ~ second buffer cell 406. The ~ensor ~00 also inclldes vertical charge transfer electrodes 403 (indNidually referenced by suffixes A, B etc.), ~sso~ ~ with the photocells 4~Z
and the buffer cells 404 and 4û~ (~ach of which is individually referenced by su~xes A, B etc.) and a reset meclldrlr~rll 408, for resetting the photocell 40~.
According to the present invention, each ~irst and second buffer cells 404 and 406, in a cell-unit 430, includes a charge shift mechar,i~.l, which provides independent timing of Gharge t, dnsf~r.

CA 022l4667 l997-09-05 Ac~o~ding to the present embodirnent, the vertiGal length ~Y of a ~ phot~c~ll 402 is equal to the combined vertical length of ~ first buffer cell 404 and a second buffer cell 40~. In other wordg, the vertical lengt~ of a cell-unit430 is equal to ~ice the vertical hei~ht ~Y of photocell 402~ The timing of the 5 charge transfer between the different cells is periodic, synchronized to relative rnovement between the sensor400 and the detected obje¢t.
It will be noted that the structure of a reset rnechanism is not limi~ed to vertical structures, According to altemate aspects of the in~rention, the structure of the reset mecilanisr" can be either horizontal, co-nbined vertical o and hori~ontal and the like.
Reference is also made to Fig. 4C whioh is a schematiG illuslr~ of TDI CCD sensor, generally referen~ed 450 and its reset mechanism, constructed ~nd operative in accord~noe with a further preferred embodiment of ~l~e invention.
IS rDI CCD sensor ~50 is a dual buffer type CCD, ~ener~lly similar to T~l CCD sensor 400 (Fig. 4A) with an altemate structured reset mech~nism.
Photo-cell row 452A is followed by a first row of buffer-cells 454A and a secondrow of buffer-cells 456A. Photo-cell row 452B is followed by a first row of buffer-cells 454B and a second row of buffer-cells 456B.
The reset electrode strudure is horizontal wherein each electrode controls a row of ~ells. In the preser~t exan,;-'~, reset electrode ~60A resets phot~cell row 452A and reset electrode 460B resets photo-cell row 452B. 1~ will be noted that such a reset structure enables sta~e sel~tion for ~ontrolling.
exposure time. In the present example, if electrode 460B maintain~ reset to photo-cell row 45ZB then, ~ny row precedin~ row 452B, such as photo~ell row 452P., is substantially disabled. In such a case, charge transfened from ph~to-cell row 452A ~la buffer-cell rows 4s4A ~nd 4s6A will be drained when arriving at photo-cell row 4~2B.

-CA 022l4667 l997-09-05 Reference is also made to Fig. 5 which is a scher"~tic timing illustration of device 400, operatlve in accord~nce with a further pler~r,~d embodiment of the in~ention.
Line 502 represents the synchroni~lion signal with regard to the 5 relatiYe movement between the sens~r 400 and the d~tect3d object. Line 504 repre~ents the exposure-reset sequence of the ph-loc~l's wherein TrXp is an ex3osure period. Line 50B represents the sequence in which ch~rge is transferred fro~n a photocell to a first ~uffer cell of the same cell-unit, generally referenced TC ~B, or 526. Line 508 represenb the sequence in which charge is 10 ll~s~err~d from a flrst buffer cell to a second buffer ~ell, of the same cell-unlt, generally referenoed r~ 32 or S28. Line S10 r~,~r~sents the sequence in which charge is trans~erred from second buffer cell of one unit to a photocell o~ an adi~cent downstream cell-unit, generally referenced T~2~C or 530. Line 512 represents the sequenGe in which charge is transferred from a first buffer cell to :~ second buffer cell, irl the last cell-unit 430a, generally rerer~,lced TL~1~LE2 or 532. Line 514 represen[~ the se~uence in which charge is transferred from a second buffer cell, in the last cell-unit 430a, to the horizont~l shift registerTL~2/,~SR ~or 432), generally referenced 534. Lir~e 516 represents the time In which Ghar~es are shifted from the horizont~l shffl re~ister 432 to output 434, 20 generally referen~ed 636.
Object movement synchroniz~tion signal 602 goes high after the object completes a displacement of ~' on the image plane. This is the beginning of a line period. TLR then goes low and the photocells begin to ~ccumulate li~ht generated charges. ~fter Tu, goes lov~/, the charge, stored or 2s example in buffer cell 40~a, is tran~ferred to the next ve~i~ally adj~cent photocell 40~b, durin~ time period T~2~C- At the same time or later, the chargesstored at the first bul~er cell 404a are tran~rt!"~J to the second buffer cell 406a of the 6ame cell-unit 430, accordlngly, during time period T~3"ez-The charges transferled from second bufFer cell~ 406a to the 30 photocells 402b are added to the light generated char~es in photooell 402b.

-~fter the required exposure time Tr~Xpl the cbar~es accumulated in a predetermined photocell 402b are tran~ ,ed, during To~1, to the next vertically adjacent downstream first buffer cell 404b. First buffer cell 404b stores the charge, while reset is applied ~o the photooell 402b, indi~ted by the T,f~ high s state.
The exposure time of the pllot~celis is actually the time between the falling edge of T", and the rising edge Of TC-~B1- The photocells are he]d in reset, by TLR~ until the beginning of the next line period, a~ter the object moYed the distance of ~Y on the image (sensor) plane. Then the reset is disabled again, 0 the chalges held at second buffer cell 406b are transferred into the next adjacent dawnstream photocell 40~c of the next cell-unit in the column 420b and the photocell accum~lates new li~ht generated charges together with the charges transferred frorn the adjacent second buffer.
The light generated Ghar~es l~pr~senlillg the o~ect, ,~reviously lS detected by the previ~s photoceli in ~ pr~d~ ;,led colun~n, are transferred through first buffer cell 404 and second buffer ce]l 406 to the next photocell 402, dllring the time perio~ in which object rnoves from a predeterrnined photocell to the next downstream photocell in a predetermined column 420, on the image plane. For example, in photocell 402c the newly light generated charges are 20 added to ~he charges accum~lated by the previo~s photooell 402b, This process go~s on until the charges representing the detected o~ject reach the first buffer cell 404x oF the last cell-unit 430a, The char~e transf-ers from the first bLrffer oell ~04x to the second ~uffer cell 406x, at T,,3~ 2.
The charge transfer~ from the second buffer cell 406x to the horizontal shm 25 re~ister (HSR) 432, at TL~2~H~;R According to one aspect of the invention, .L~2 and TLBZ-~HS~ Gan be sequenced at the san~e time, as indicated ~y referenGe numerals 53~a and 534a (Fig. 5).
According to ~nother aspect of the ;nvention T,~ L32 ~nd T,B~ .HSR,l can be sequenced, earlier, after Tc ~"" as indicated by reference n~merals 532b 30 and 534b The transfer of charge, in all of the columns 420 at the last cell-unit 430a, to the horizontal shif~ register (HSR) 432 and further to the output 434 is sequenced affer the vertical charge t~nsfer fr~m the second buffer cell 404x, ineach column, to the HSR 432. Thus, if the sensor 400 h~s N photocells in a column 420 then the output will rep~esent o~ject expo~ed N times the appliecl s exposure time, by photocelJs of size ~Y by ~)(.
The advantage of the double buffer archite~ture over the single buffer ~rchi~e~lure is that there is no unde,~ g of an object in the double buffer a,chi~ re. The sensor ~00 covers a detected object in full coverage, in the direction of movernent.
o IReference is now m~de to Fi~. ~ which is a schematic illusl,~lion of ~
TDI CCD sensor generally referenced 600 con~tructed and operati~e in accordance with a yet ~nother prer~ d ernbo,li"lent of the inven~ion. Sensor 60Q includes horizontal shiff register 632 and a plurality of ~ells columns generally ~esignated 630 which includes a plurality of cell-uni~s 620 and a lastlS photo~ell 610L. Each of the cell-units includes ~ photocell generally designated ~10 (individllally referenced by suffixes A B etc.), and at le~st one buffer cell, generally designated 61~ (individually referenced by suffixe~ A B etc.). In the present exarnple, units 620 include a single buffer c~ll.
According to the present embodiment, ~he charge generated and accumulated in the last photoGell 610L is transrer~ed directly to horizontal shift register 632, th~s eliminating any delay Gaused by further transferring to illle,~r,ediate buffers orwasteo~CCD area.
Reference is now ma~e ~ Fjg 7~/hiChis a sche",alic illustration of a cell-unit generally referenced 7$0 constr~cted and operative with another 2s preferl~d embodiment of the present invention.
Cell-un~ 750 includes a photo cell 752 and a buffer cell 754 ~vhich is located beneath photo cell 752. It will be noted that cell-unit 750 also includes electrodes ~hich are operative to shffl charges from the photc cell 752to the buffer cell 754 as ~vell as ele~trodes to shr~ char~es from bufFer cell 754 to next adja~ent buffer cell 754 and a reset mechanism.

lg_ Photo cell 72 detects light thereby producing charge. At the end of the charge producing ope~(ion, the charge is transferred clownwards to buffers 754. ~hen the charges are b~risf~"~d from the ~uffer cells 764 forwards, to the next adjacent buffer~ell 754 Which l;es underneath the next 5 a~ljacent pho~u~ll 752.
An advant~ge of the present embodimen~ is that placing the buffer cell 754 underneath the photo-cell 762""axi"lizes the exposure area of cell-unit750 and ",i"i."iGes the silicon area.
Another advantage of the present embodirnent is that on~e the o charge is transf~rred from the phot~cell to the buffer ~ell, it n~ longer has to be transferred to ~nother photo-cell, as will ~e described hereinbelow, thus simplifying the charge transfer timing.
Reference is now made to ~ig. 8 which is a three dimension~l schem~tic illustration of a TDI CC~ sensor, g~nerally referenced 700 and a shffl15 re~ister, generally referenced 730, constructe~ in accordance with yet a further preferred embodiment of the present invention.
TDI CCD sensor 700 indudes a plurality of cell-units 702, 708, 714, 718 and 72B, which are generally similar to oell-unit 750 of Fig. 7.
Cell-unit 702 includes a pho~o ~ell 704 and a bufFer c~ll 706. Cell-unit 708 includes 8 photo cell 710 and a buffer cell 712 Cell-unit 714 includes a photo cell 71S and buffer cell 716. Cell-unit 71$ includes a photo cell 720 and a buffer cell 72~ Shi~ register 730 includes four cells: 732, 734, 736 and 738.
The photo cells 7M, 710, 715 and 720 detect light and produce charge accordingly, during an eXposure time period. When the exposure time 2~ period elap~es, the charge is transferred downward to the resp~ctive buffer oell.
Accordin~ly, the charge acoumula~ed in each of the photo cells 704, 710, 715 and 720 is tr~nsferred downward~ to buffer cell 706, 712, 71B and 722, respectively, and the photocells are held in reset until the next exposure period begins.

Then, the charge is ll~n~r~"ed one level ~ownwards. This means that the charge of buffer cell 722 is transferred to cell 732 of the shffl register 730, the charge of buffer 716 is then transr~ d to the buffer cell 722, the charge ~f buffer cell 71~ is tr~ r~rltd to buffer ~ell 71~ and th~ charge of buffer s cell 706 is tfansferred to bu~er cell 712. It will be noted th~t the charge transfers between the buffer cell~ are performed in cascade.
When the buffer cells transfer char~e therebetweenl the photo cells c~n be subjected to light thereby producing more charge. VVhen the buffer ~ells have finished lran~r~"i"g charge therebetween, then charge which is now o produGed in the photo cells can be transferred to the buffer cells ~nd accumulated there ~ogether with ~h~rge tr~nsferred frorn previous cells.
The following is a description of the detection of an object which rnoves alon~ the cell-units 70Z, 708, 714 ancl 718. First, the obiect faces photo cell 702, whereas photo cell 704 generates charge when detectin~ light received 15 from the object. When the object has rnoved towards cell-unit 710, the chargegenerated in photo cell 704 is transferre~ to buffer cell 706 and further transferred to buffer cell 712 The object is now facing cell-unit 708, whereas photo cell 710 produces charge upon detection of light received from the object.When the object has moved towards cell-unit 714 the charge generated ~y photo cell 710 is l,a"s~"~d to buffer cell 712 which adds this char~e to the charge received ~rom buffer cell 706. Then, the charge acc~lrnulated in buffer cell 712 is transfenred to buffer cell 716.
When t~e object faces ~ unit 71~, photo cell 715 generates char~e when detecting light received from the object. Wherl the object has moved towards cell-unit 718 then the charge, generated by photo cell 715, is lr~nsfened to buffer cell 716 which adds it to the charge received from buffer cell 71~. Then the charge acGumulated in buffer cell 716 is transferred to buffer cell 722.
When the obje~t f~ces cell-unit 718, then, photo cell 720 gener~e~

3~ charge when dete~ting light recei~ed from the o~ject. When the object is no longer facing cell-unit 718 then, the char~e ~enerated by photo cell 720 is sr~rr~d to buffer cell 7Z, which adds it to the charge received from buffer cell 716. buffer cell 722 now include the total charge generated ~y photo ceils 704, 710, 715 and 720, which relates to the image of the object as detected by each of these buffer cells. Fir~ally, the charge accumul~ted in buffer cell 7~2 is transferred to cell 732 of shift re~ister unit 730.
It will ~e noted that the same operation occurs in the rest of the columns of TDI CCD sensor 700 and at that time, all of the buffer cells of the ~ast row (the row of ce11-unit 718~, transfer their charges to the respective cells lO 732, 734, 736 and 738. ~t this point the ~harges ~re transferred in holi,unl~l rnanner towards the right to a storage unit not shown) for further pr~cessing.
I~eference is now made to Fig. 9 which is a schematic flow chart i~lustration of a method for operating the TDI CCD sensor of Fig. 2A, operative in a~cordance with yet another preferred embodiment of the present invention.
s In step 800, the photo-cells of device 200 are activated, so as to enable them detectin3 light, received from an object, thereby producing charge.
In step 802, the charge, accumulated in each photo cell is transferred to the adjacent assoGiated cell. For most of the photo-cells, the adj~cent cell is the adjacent buffer cell. A~cordingly charge from photo cell 210A is t~ar,-~r~r ~d to buffer cell 21~A. It will be noted that in TDI sensors, according to the present invention, which do not have buffer cells after the last photo cell, such as device 600 of Fig. ~, the adiacent ~ell of the last photo~ell is the respectiYe cell in the s~lift register. In these cases, charge fronl the last pl~oto-cell is transferled to the shift-register.
2s It \Nill be notecl that if the T~l structure includes buffers cells a~er the last photo~ell, then, the charge from ~is last photo-cell is transferred to the respective shiK register cell after passing through these buffer cells.
In step 804 the photo-cells of device 200 are deactivated. It will be noted that such activatin~ or deacti~ating as in steps 804 and 800, can be Implernented by applying ~ predetermined oon~l~nl voltage onto the photo-cells, enabling and disablin~ reset to the photo-cell~ and the like.
In step 80~, the charge In each of the buffer cells is tr~nsferred to the next photo oell. Accor~li.,gly the charge from buffer cell 212~ is tran~rred to s the nex~ photo cell which is photo cell ~10B. The adjacent cell of the last buffer cell is the respective cell in the shift reglster. Accordingly cha~ge from buffer-cell 212E is transferred to the shift-register 23~.
In step 808, the charge is shifted out of the shift-register Reference is now made to Fig. 10 which is a schematic flow chart 0 illustration of a metho~ for operating the Tl:)l CCD sensor 400 of Fig. 4A, operative ~vith a~ordance with yet a ~rther embodinlent of the present invention, In step 8~0, photo cell Pj is activ~ted,50 as to dete~ light received from an object, thereby producing charge.
In step 852, ch~rge is transferred from buffer-cell BS~COND,I- tc phot~cell Pl to be accumlllated with newly photo generated charge. Ac~r~i"g to the present example, the charge contalned in ~uffer-cell 406A is Iransrerled to photo cell 402B.
In step 854, charge is transferred firom buffer cell BFIRS~i to the next 20 adjacent associated buffer cell BS~OND,I In the present ex~mple, ch~rye is transferred from buffer-cell 404A to buffer-cell 406A.
In step 856, the charge produced by the photo cell Is l~sn4f~rled from the photo cell Pj to the next cell. For most phot~cells, the next cell is the ~djacen~ associated buffer cell l3F~RST,I- For example, the charge from photo-cell 25 4~ZA iS ~I-an3rt~ d to ~uffer cell 402B.ln step 858, the photo-cells of device 4~0 are deactivated.
In step 8~0, the photo~lls of device 400 ~re rese~

In step 8621 the ch~rge from the last buffer~ell is tr~nsferred to the respective shiFt-re~ister cell after. In the present exarnple, the charge is tl~ns~r~e~d from buffer cell 40~X to the shi~-register 432.
In step 864~ the char~e from the buffer~ell RtlR~T,LASr is tr~nsferred to buffer-cell BSECOND~A6T In the present ex~mple, the charge is ~nsfer,~d from buffer~ell 404X to buffer-cell 406X.
Then, the method is re,ue~led from step 850 whereas the photo cell P~1 pr~duces ch~r~e and adds this newly produced charge to the charge which was previously transferred from buffer cell BSEWNDI thereby ac~umulating o charge.
In step 8~6, the charge located in the shi~-resi~ter cell is transferred out ~o a storage unit, to be further processed and displayed.
It will be noted that steps of this method ~n be executed in a different order wherein, for example, step~ 862 and 864 are performed before step 852. For further explanation refer to Fig. 5.
Reference is now made to Fig. 11 which is a schematic illustration of a multiple timing diagranl, for op6r~ g TDI CCD sensor 700 of Fig. 8, in accordance with another pref~rred embodiment of the present invention, Dia~ram gO0 l~pr~ser~l the timing which is provided by a ~ontroller, 20 representing the rnovement of an object which is detected by the TDI CCD
sensor 700. Tlme period g10 is a signal which represents that the ob~ect is now facing selected cell-units.
Diagram 902 represents the exposure and reset timing of th~ photo cell-unit in \,vili~h TEXP jS the time period in which a photo çeil of the selected 2s cell-unit is operatNe to generate charge Llpon ~etection of light received from the o~je~t. Time period 912 is followed by a re$~t time period TRES~ 914 w~ler~in the photo Gell of the selecto!d cell-unit is reset.
t)iagram 904 represents the timing of transf~rli"g charge from the ph~to cells to the buffer cells in a ~.EIeGl~d oell-unit. In ~ime period 91~ the -2~

charge generated by a photo cell is transfer,~d to a buffer cell located beneaththe photo cell. This time period is located, in time, at the very end of the exposure time period 912 TEXP . It ~uill be noted that the charge that is transferred from the photo cell to the buffer ~ell is added to the charge already 5 present in the buffer cell.
Diagram 906 ~~,r~ser,l~ the tinling of the buffer to bu~er charge tr~nsfer. In time period 918 charge is transferred from a buffer to the next buffer down the s~me column.
I~iag~m 908 represents the timing of the horizontal shffl regisbr 10 THSR In time period 920 the charge located in each of the cells of the hori~ont~l shift re~ister 730 Is transferred out to be proGessed and displayed by i",ag;"g hardware and software.
Reference is nollu made to Fi~. 12 which is a sche~ lic Flow ch~rt illustration of a method for oper~ting the deYice 700, operative with aCço~al~Ce5 with yet another preferred embodirnent of the present invention.
In step 870, photo cell P~ is activated, so i~s to detect light received from an object, ~ereby produGing charge.
In step 872, the charge produced by the photo cell Pl is tr~nsferred therefrorn t~ the buffer-cell Bj of the same cell-unit, In the present example, ~o charge accumulated in photo cell 710 is ll~nsr~rlc~d to ~ffer-cell 712.
In step 874, the photocells P, are deactivated.
In step 876 charge contained in the buffer-cell ~l is transfe~ed to the next adjacent buffer cell Bh,. ~t the s~me time, char~e contalned in the last bufFer-cell BLAST jS t,~nsr~l,ed to the respective $hrft-register cell. In the present 2~ example, the char~e is tran~e, red from buffer cell 722 to shift-register cell 732, In step 878, reset is applied to photo cell Pj. As stated above, the unique structure provided by the present inYention enables resetti"g the photo-cells, thereby reducing blooming e~ect.

-~5-It will be nated that steps 878 and 876 can be pe, rur~ned simultaneously and generally in no parbcular order with respect to eaGh other.
In step 880, the charge located in the shift-register cell is t,~ ,red out, to ~e further processed and displayed.
It will be app,~;aLed by persons skilled in the art that the present invention is not limited to what has been particularly shown and des~
hereinabove. Rather the scope of the present invention is defined by the claims which follow.

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A time delay and integration charged coupled device (TDI CCD) comprising;
a charge transfer unit;
a reset unit;
a horizontal shift register; and at least one column of cells comprising a plurality of cell units connected in series, defining a downstream flow of charge towards said horizontal shift register, wherein each of said plurality of cell units comprises a photo-cell, generating charge when in the presence of light, and at least one buffer-cell for storing charge, said photo-cell and said at least one buffer-cell being connected in series, wherein said charge transfer unit, which is connected to each of said photocells and said buffer cells, controls said device by transferring charge downstream between any of said cells and transferring charge from said at least one column of cells to said horizontal shift register, and wherein said reset unit resets each of said photo-cells after the charge accumulated in each of said photo-cells is transferred therefrom.

2. A device according to claim 1 wherein:
each of said cell units has a first vertical length, each said photo-cells has a second vertical length, and said first vertical length equals twice said second vertical length.

3. A device according to claim 1 wherein:
each of said cell units has a first vertical length, each said photo-cells has a second vertical length, and said first vertical length is substantially similar to said second vertical length.

4. A device according to claim 1 wherein each of said cell units comprises two buffer-cells.

5. A device according to claim 2 wherein each of said cell units comprises two buffer-cells.

6. A device according to claim 1 wherein said at least one column of cells further comprises an additional photo-cell connected in series to said horizontal shift register.

7. A device according to claim 1 wherein each of said cell units comprises a single buffer-cell.

8. A cell unit for incorporating in a TDI CCD comprising a photo-cell, generating and accumulating charge when in the presence of light, and at least one buffer-cell for storing charge, said photo-cell and said at least one buffer-cell being connected in series.

9. A time delay and integration charged coupled device (TDI CCD) comprising:
a charge transfer unit;
a reset unit;
a horizontal shift register; and at least one column of cells comprising a plurality of cell-units connected in series, defining a downstream flow of charge towards said horizontal shift register, wherein each of said plurality of cell-units comprises a photo-cell, generating charge when in the presence of light, and a buffer-cell, for storing charge, located underneath said photo-cell, connected to said photo-cell, wherein said charge transfer unit, which is connected to each of said photocells and said buffer-cells, controls said device by transferring charge in a selected cell-unit from a photo-cell of said selected cell-unit to a buffer-cell of said selected cell-unit, wherein said charge transfer further controlling said device by transferring charge downstream between said buffer-cells towards said horizontal shift register, wherein said reset unit resetting each of said photo-cells after the charge accumulated in each of said photo-cells is transferred therefrom.

10. The time delay and integration charged coupled device according to claim 8 wherein said reset unit resets each of said at least one column of cellls, individually.

11. The time delay and integration charged coupled device according to claim 9 wherein said reset unit resets individual rows of said cell-units.

12. A cell-unit, for incorporating in a TDI CCD, comprising a photo-cell, generating and accumulating charge when in the presence of light, and at least one buffer-cell for storing charge, said at least one buffer-cell being located beneath said photo-cell.

13. A method for operating a TDI CCD device, the TDI CCD device including a plurality of cell columns, each of the cell-columns including a plurality of cell-units, each of the cell-units including a photo-cell and a buffer-cell connected thereto, located underneath the photo-cell, each of the buffer-cells of the cell-units being connected in series, defining a downstream structure which ends in a shift-register, the method comprising the step of:
repeating the following steps:
enabling exposure to said photo-cells;
detecting light received from an object, thereby producing charge by said photo-cells;

transferring charge in each said cell-unit from said photo-cells to said buffer-cells;
disabling exposure to said photo cells; and transferring charge downstream between said buffer-cells, towards said shift-register.

14. A method for operating a TDI CCD device, the TDI CCD device including a plurality of cell columns, each of the cell-columns including a plurality of cell-units connected in series, each of the cell-units including a photo-cell and a buffer-cell connected in series, the last cell-unit of each of the cell columns being connected to a shift-register, the method comprising the step of:
repeating the following steps:
enabling detection of light received from an object, thereby producing charge by said photo-cells;
transferring charge in each said cell-unit from said photo-cells to said buffer-cells;
transferring charge out from the buffer cell of said last cell-unit to said shift-register;
disabling said detection of light to said photo-cells;
transferring charge downstream between said buffer-cells towards said shift-register, from a buffer-cell of a selected cell-unit to a photo-cell of a subsequent cell-unit.

15. A method for operating a TDI CCD devioe, the TDI CCD device including a plurality of cell columns, each of the cell-columns including a plurality of cell-units and a last cell-unit, each of the cell-units including a photo-cell and a buffer-cell connected in series, each of the last cell-units including a photo-cell and being further connected to a shift-register, the method comprising the step of:

repeating the following steps:
enabling detection of light received from an object, thereby producing charge by said photo-cells;
transferring charge in each of said cell-unit from said photo-cells to said buffer-cells;
transferring charge from each of said last cell-unit to said shift-register;
disabling said detection of light to said photo-cells; and transferring charge downstream between said cell-units towards said shift-register, from a buffer-cell of a selected cell-unit to a photo-cell of a subsequent cell-unit.

16. A method for operating a TDI CCD device, the TDI CCD device including a plurality of cells columns, each of the cell-columns including a plurality of cell-units connected in series, each of the cell-units including a photo-cell, a first buffer-cell. connected in series to the photo-cell and a second buffer-cell connected in series to the first buffer cell, the last cell-unit of each of the cell columns being connected to a shift-register, the method comprising the step of:
repeating the following steps:
enabling detection of light received from an object, thereby producing charge by said photo-cells;
transferring charge in each said cell-unit from said photo-cells to said first buffer-cells;
disabling said detection of light to said photo-cells;
transferring charge downstream between said cell-units towards said shift-register, from a second buffer-cell of a selected cell-unit to a photo-cell of a subsequent cell-unit; and transferring charge in each said cell-unit from said first buffer-cells to said second buffer-cells; and transferring charge out from the second buffer cell of said last cell-unit to said shift-register.

17. The method according to claims 13, 14, 15 or 16 further comprising the step of transferring charge out from said shift-register.

18. The method according to claims 13, 14, 15 or 16 further comprising the step of resetting said photo-cells.

19. The method according to claims 13, 14, 15 or 16 wherein said step of enabling exposure comprises the step of disabling reset to said photo-cells.

20. The method according to claims 13, 14, 15 or 16 wherein said step of disabling exposure comprises the step of enabling reset to said photo-cells.