Performance and power dissipation analysis for CCD memory systems

Transcription

1 Pefomance and powe dissipation analysis fo CCD memoy systems Buoughs Copoation Piscataway, New Jesey ABSTRACT n CCD memoy systems a tadeoff exists between the fequency at which the memoy system is opeated and the powe dissipation. The highe the fequency of opeation, the lowe is the sevice time and the highe is the powe dissipation. A close look at the initial cost of the CCD memoy system and the cost of maintaining these memoy systems will show that the cost of maintenance fo a yea is nealy equal to the initial cost. This high cost necessitates an analysis of the CCD memoy system design fo sevice time and powe dissipation. n this analysis thee diffeent states called the Access, Refesh, and dle states ae defined fo a CCD memoy system. Each state is chaacteized by a fequency and five diffeent modes of opeations ae defined depending on the elation between the fequencies. Aveage sevice time and powe dissipation equations ae then deived and each mode is analyzed. Contay to the nonnal belief that the powe dissipation inceases with access fequency, it is shown that fo cetain modes the powe dissipation is constant and is independent of fequency. Finally, a figue of meit is defined and the diffeent modes ae compaed. at low fequencies. The situation would be still wose at highe fequencies. ee we will analyze some aspects of the CCD's petaining to thei use in a memoy system design. The analysis will show the tadeoffs of opeating and using diffeent devices and an insight into the design of the chip. CCD CP PARAMETERS Most common types of CCD chips being designed ae of the closed loop shift egiste type. Theefoe, we will analyze such a chip. A typical chip will have S shift egistes with Nt cells in each shift egiste (Figue 1). The design of the device will detemine the efesh time (t ), which is the maximum allowable time befoe which a new efesh cycle must be stated. Usually a efesh amplifie is available afte evey N cells, and Nt is an intege multiple of N n with N and iftreg. 9 dle Fequency f i Refesh Fequency f Access Fequency fa NTRODUCTON n the last few yeas, extensive wok has been done on Chage Coupled Devices (CCD's). These devices have a potential of becoming basic building blocks to constuct memoies fo digital computes. Many papes ae available that analyze and popose designs fo the basic component and its layout on the chip.l- Vey little analysis is available on the use of the chip in a memoy system. t is pedicted that the cost/bit fo CCD memoy systems will be 15 to 3me/bit i and powe dissipation of 2 uw /bit. Using a ule of th:umb of 1 me/uw /yea fo the opeation of semiconducto memoy systems stated by Moton, 5 it is evident that the initial cost and the opeating cost fo a yea ae equal fo CCD memoy systems even when opeated :'it = No. of cells between Refesh.A::l;l::':::ie:::, t = o. of cells in a Shift Regis"':e S = Total numbe of Shift Registes Figue -Schematic of a closed loop shift egiste type CCD chip 381

2 382 National Compute Confeence, 1976 Chip Paamete Symbo:' Typical Values St.at Shift Registes t No. of Cells between Refesh ft.jjlp. N Refesh Time 2msec. and above TABLE -Vaious Chip Paametes and Thei Typical Values Refesh complete and Nt being powes of two. Some typical values fo S, Nb N and t ae given in Table. MODES OF OPERATON With the above mentioned basic paametes fo the chip a memoy system can now be designed to opeate in thee diffeent states. The thee states ae the Access state when the data is being accessed (ead o witten) fom the chip, dle state in which the chip is doing nothing and the Refesh state in which the data in the shift egiste is being efeshed. * The thee states can be chaacteized by having thee diffeent fequencies: Access fequency fu dle fequency fl and Refesh fequency fo By definition, a memoy system can be in the Access state and Refesh state at the same time if the fequencies fo these two states ae the same. A state tansition diagam fo the thee states is shown in Figue 2. n evaluating the pefomance of the chip, the following assumptions will be made: (1) The efesh state has pioity ove both the access and idle state, wheeas the access state has pioity ove the idle state. (2) The data tansfe in a shift egiste is always initiated fom the bit addessed as the fist bit. This is not always necessay and diffeent assumptions can be teated as special cases and the analysis pusued hee modified accodingly. (3) A new access fo data is not made when a pevious access is pending. This assumption implies a buffe in which all the equests to the memoy system ae stoed and seviced with some scheduling stategy. (4) Thee is an equal pobability that the efesh, idle o access states ae stated at any bit in the shift egiste. (5) The powe dissipation is popotional to the fequency at which the data cells ae being moved. 6 Notice that the powe dissipation of ---- * The Access state may be futhe divided into an Aligning state and a Tansfe state. Pesently, we will not make any distinction and the analysis made hee can be easily extended to that case. Access not complete Access Request & :l.efesh complete Refesh not complete Figue 2-State and tansition diagam fo the diffeent states of CCD memoy opeation the peipheal cicuity, dives and the shift egiste aay is a function of the fequency. 1 (6) The efeshing and accessing can be done simultaneously, if, and only if, the efeshing fequency (f) and the accessing fequency (fa) ae the same. This implies that the inteface to the CCD memoy system always tansfes o eceives data at the same fequency. (7) Once a data tansfe is stated all the bits in a shift egiste must be tansfeed. By choosing diffeent values fo the thee fequencies fa, f and fb the chip and hence, the memoy system can be opeated in five diffeent modes (Table ) equiing one, two, o thee clocks. Notice that the numbe of clocks equied is an indication of the complexity of contol equied by the memoy system and, theefoe, in some sense defines the cost fo contol cicuity. The five modes of opeation and thei implications ae tabulated in Table. Mode 5 is the most geneal mode of opeation and the othe modes can be consideed as a limiting case of this mode. Fo example, mode 3 can be consideed as a limiting case of mode 5, when fl tends to fo Befoe evaluating the diffeent modes, the implications of the modes of opeation on a memoy system design ae qualitatively discussed. n a semiconducto memoy system design some maj o paametes of inteest ae: (a) powe dissipation which influences the cost of maintaining the memoy, (b) access and sevice times which influence the pefomance of the system, ( c) the inteface equiements such as, the data width and data ate, and (d) the contol complex-

3 Pefomance and Powe Dissipation Analysis 383 MODE FREQUENCY METOD OF OPERATON Continuous Refesh 1 f = f = f. Most common mode of opeation in the nea futue. a 2.uU-st Refesh Possible low access fequency due to inteface equiements. 3 f.j f a f. = f Possible high Access ate. Useful when the memoy is expected to emain idle fo a lage pecentage of the time. 4 f a := f Zeo idle fequency is possible. Minimum access fequency detemined by the lowest allowable efesh fequency. 5 f.jfi.j f a Zeo idle fequency possible. nteface equiement of low access fequency can be satisfied. T ABLE -Possible Modes of Opeations fo a CCD Chip ity which detemines the difficulty and the amount of ovehead involved in the design of the memoy system. Mode 1 is a continuous mode of opeation in which all the bits ae moving all the time and has the simplest contol cicuity. This will be the most common mode of opeation in the ealy systems. Mode 2 equies two fequencies and, theefoe, has a contol complexity highe than Mode 1. One method of opeating in Mode 2 would be to use low idle and access fequencies and high efesh fequency. Such a mode is applicable when an extenal device with low data ate is intefaced with CCD's and eal time tansfes ae made. Also, when memoy is opeated in a 'vetical mode',7 as is ecommended fo CCD device,s it is necessay to shift the bits at a low fequency. Mode 3 of opeation has equal idle and efesh fequency and eithe low o high access ate. The contol complexity is the same as in Mode 2. t is necessay that f (=f i ) >N/t' ntuitively, such a design is attactive only when the memoy system is expected to emain in the idle mode fo a high pecentage of the time. Mode 4 of opeation is again as complex as Mode 2 and Mode 3 and can be opeated with bust efesh and zeo idle fequency. Finally, Mode 5 is the most geneal mode of opeation and will have the maximum contol complexity. A pactical application of this would be: (1) when the system is idle most of the time, (2) the extenal equiement necessitates low data ate, and (3) bust efesh is to be used to efesh the memoy. The analysis late will show that only some of these modes ae advantageous fom the pefomance and powe dissipation consideations. On the following pages, equations fo Mode 5 of opeation will be developed. Then the equations fo the othe modes of opeation will be detemined as a limiting case of Mode 5. ANALYSS OF SERVCE TME Sevice time is defined as the time elapsed between the moment a equest is made to the memoy fo some infomation to the moment when all the infomation is deliveed. When a equest is made to a CCD memoy system fo paticula infomation, the bits in the shift egistes have to be shifted until the shift egiste is positioned at bit 1 unde the ead/wite cicuit. The time equied to do this will be called the access time (ta). Once the shift egiste has been positioned then the

4 384 National Compute Confeence, 1976 data may be tansfeed and the time equied to tansfe the data will be called the tansfe time (tt). The sevice time (ts) is the time equied to sevice a equest and is given by ts=ta +tt and the aveage value of sevice time (t 8 ) ts=ta+tt Assume that ta is a andom vaiable and can be detemined as a sum of thee andom vaiables given below. Then X = andom vaiable that epesents time spent in efeshing when a sevice equest is made. Xa = andom vaiable that epesents time spent in aligning the shift egiste to bit 1 when a sevice equest occus. Xd = andom vaiable that epesents time lost when a sevice equest cannot be satisfied because the efesh cycle has to be stated befoe all the bits in the shift egiste ae tansfeed. ta=x+xa+xd and because Xn Xa and Xd ae independent andom vaiables, we have ta=x+xa+xd We have to detemine the values of Xn Xa and Xd. The pobability density function of X is given in Figue 3. Fom the figue X _.!(N ) f t The value fo Xa is simple to calculate and is given by is [fo lage Nt] To calculate X d, notice that if a equest aives at a time when the shift egiste is at position N, then the minimum time equied to access and tansfe the block is given by Nt+ (Nt-X) 2Nt-X fa fn Because the pobability that a equest occus at any' paticula bit is the same, the expected value of Xd is (Figue 4) deived as Notice that fo lage values of Nt (! Nt-i) «i Nt2 and 2Nt«3Nt2 Xd(Nt)2 + 3N t N 6t fa 2tffa Then the aveage value of ta is ta= Nt +[(N)2 +1(N t )2 + 3N t N J ' 2fa 2t f 3 fa faf Fo a shift egiste of length Nt and tansfe fequency fa - Nt tt=t;:- Theefoe, the aveage value of the sevice time is ANALYSS OF POWER DSSPATON n CCD's powe dissipation is popotional to the fequency.6 Amelio l gives equation fo the aveage powe dissipated (P d) on chip fo a data fequency f as Pd=2N (O.2x 1- l2 )f whee Pd is the powe dissipated due to a shift egiste of N bits being shifted at a fequency f. N N f _;J ':7ime --+ Figue 3-Pobability density function of X Figue 4-Pobability density function fo Xd when a sevice equest is made at bit position x

5 Pefomance and Powe Dissipation Analysis 385 Because the CCD electodes have a lage capacitive load, the powe dissipated in the dives is much lage and is given by 'whee C is the capacitive load, and V is the voltage applied. We will epesent the constant of popotionality between powe dissipation and fequency as K. Usually the powe dissipation due to the dives is much 1<;11'"-1'"..., t11<;1tl "'.L.a._....L t11 nnxt1'"... _ Y"""""_'" ni<;l<;lin!'ltim nllp """... t.fl t.np nift o.joj...,t"'_... _ ""..._ egiste aay and hence, K = CV2. Then if t t 2, t3... tn ae diffeent time intevals in which fequencies f17 f2'... fn ae applied to the chip, the aveage powe dissipation is given by " K tlfl +t2f "tnfn u -- tl + t tn The thee diffeent states of the CCD memoy systems will detemine thee diffeent time intevals and thee diffeent fequencies. These ae: (1) Total time spent in efesh state (T) and efesh fequency fo (2) Total time spent in idle state (Ti) and idle fequency fi. (3) Total time spent in access state (Ta) and access fequency fa. Then the aveage powe dissipation (Pd) is given by Pd=KfT+fiTi +fa'l\ T+Ti+Ta To detemine the aveage values fo the diffeent times we will conside a basic peiod as the time fom the beginning of one Refesh cycle to the beginning of the next Refesh cycle. Then - N T=f; The emaining time in a cycle is the sum of the total idle time and the total sevice time. Theefoe Ta+Ti=( t - ) 1\=( t - ) -1\ To detemine the aveage total time spent in sevicing equests (1\) assume that in any given cycle thee is a possibility of maximum of s accesses. Then let p (j) = pobability that j accesses ae made (j=, 1,2... s) The aveage time spent when one access is made is aleady detemined and is given by at and, theefoe, T. (.) 3Nt a= J P J -fj=o a s Let Q= Lj p(j) j=o ntuitively Q epesents the aveage numbe of equests pe peiod. Then and T - - 3NtQ a- o.c "'.La Adding the vaious tems and eaanging gives the aveage powe dissipation fo mode 5 of opeation as j\=k{f i + N (l_ fi)+ 3N t Q (1- fi)} t f 2t fa This geneal analysis fo aveage sevice time and powe dissipation can now be applied to each mode of opeation. ANALYSS OF DFFERENT MODES n this section we will analyze each mode of opeation. The sevice time and powe dissipation equations fo the diffeent modes deived fom the analysis of geneal Mode 5 ae given in Table. The gaph in Figue 5 denotes the aveage sevice time and powe dissipation fo Mode 1 of opeation and the gaphs in Figues 6 to 1 denote the pecentage impovement in aveage powe dissipation and pecentage degadation in sevice time fo Modes 2 to 5 ove that of Mode 1 of opeation. Mode 1 will be the most usual mode of opeation in the nea futue. A plot of access fequency vs sevice 2 1 '\ 1. <>' "- "'..'>, "- t ,'".,..., : "- (l,'" 3..z. "- <;.';' 2 " f 1 t "- "- Q 5 "- " 1..5 O.L 2 " V.<'.5 3 f a (ME) 8 1 Figue 5-Gaph of sevice time and powe dissipation vs. access fequency fo mode 1 of opeation.3.1 CD 8.: +' '". 'M :< p..

6 386 National Compute Confeence, 1976 i', MODE, FREQUENCY 1 SERVCE TME POWER DSSPATON REMARKS --", ,- 1 f' f' '/ 't - t 3 N ;+'7\ +9 N t N Kf ' Puwe Dissipation diectly j e= =L i 2f + 2t 3f J a popotional to fequency! ;-.---t , i 2, f J f 13N 1 {if N2 } "5N N} K {fa + Nt: [1 _;:]} V a t 7 t / t i -2f +-2t f Mode ey little advantage ove 1 fo both sevice time 1- -, -. - L a o powe dissipation! a 1 a 1 =f' " ",2 ",2 f,. 1 : 1 = f. 1 Values of fi=l to 3Mcycles/ sec. ae advantageous fom both sevice time and powe dissipation consideations f!j.!,!, 5 i f, a 1 f a = f! f /.f/f, a 1! 1 Same as Mode 1 Seme as Mode 2 Fo fi = and a given value of Q, the powe dissipation is constmt Fo f, = and a given value + _ fi_t 3NtQ. _:-J f Q., 1 the powe dissipation t LL f;j 2tlL 1S constant. No advantage } ove Mode 4 unless f f due to inteface equienents T ABLE -Sevice Time and Powe Dissipation Equations fo Diffeent Modes of Opeation time is given in Figue 5. The dominating facto fo sevice time in the equation given in Table is 3N t /2fa. At small values of access fequency (fa= 2Kz) the contibution due to the second tem is quite high (about 4 pecent), wheeas at modeate values (fa = Mz) it is about 1 pecent and at high values it is negligible (less than 1 pecent). The second tem can be deceased by inceasing t. N has no appeciable influence on the sevice time. The powe dissipation is seen to be diectly popotional to fequency. Again, fo Mode 2, the dominant tem fo sevice time is 3N t/2fa. The powe dissipation equation shown in Table has two tems. The fist tem is the same as Mode 1 and the second tem can be made negative by making fa>f. Figue 6 shows the pecentage impovement in powe dissipation and pecentage degadation in sevice time ove Mode 1 vs the access fequency fo diffeent values of fo The esults show that eithe the degadation in sevice time is quite high o powe dissipation impovement is quite low. A simila analysis fo vaious values of N will show the same conclusion. Theefoe, this mode of opeation has little advantage ove Mode 1. The sevice time equation fo Mode 3 is the same as that fo Mode 2 but the powe dissipation equation is diffeent. Figue 7 shows the pecentage impovement in powe dissipation and pecentage degadation in sevice time vs the access fequency fo vaious values of Q. Sevice time is independent of Q but the impovement in powe dissipation is educed as Q inceases. The diffeence in P d impovement between the lowest and the highest value of Q is quite small and is of the ode of 1 to 15 pecent. Note that thee is a apid impovement in powe dissipation fom 1 to 5Mz and then the impovement tapes off. The wost case sevice time degadation is about 8 pecent. Theefoe, a good cut-off point fo this mode of opeation is aound 5Mz when the sevice time degadation is about 5 pecent. The vaiation of pecentage impovement in powe dissipation and degadation in sevice time vs the access fequency fo vaious values of f is shown in Figue 8. t shows that high values of f ae disadvantageous fom both powe dissipation and sevice time point of view. Geneally, this mode is bette than Mode 2 of opeation.

7 Pefomance and Powe Dissipation Analysis 387 Powe Dissipation _ - _ - - Sevice Time n 'l ct P, l Ol '] Ol l A 6 Q) /l.t l 4 Qj!B P- o * 2 Nt N = 64 t = 2.Omsec. / /" /' /" /" /' / - -- f = \CO f =.5 f = 2.Q 25 [ fpc (M:!:) )J Figue 6---Pecentage impovement in powe dissipation and pecentage degadation in sevice time vs access fequency fo mode 2 of opeation n the Mode 4 of opeation the aveage sevice time equation is the same as Mode 1. Physically, this is undestandable due to two easons: the idle fequency moves the infomation bits without doing any useful wok and thee is an equal pobability of a sevice equest at any bit. Powe dissipation equation has two tems, one popotional to the fequency fi and the othe a constant. By making fi zeo, and if the diffeent paametes of a chip (e.g. Na, tn etc.) ae given, then powe dissipation is only dependent on Q and is independent of the access fequency. Notice that inceasing t educes the powe dissipation. This is again physically undestandable, since the chip will have to be efeshed less egulaly. The powe dissipation also can be deceased by deceasing N o Nt. Notice that the second tem can neve be negative. Theefoe, the minimum value of powe dissipation occus when fi=o. Because the most inteesting point is fi =, we will futhe analyze this mode at this opeating point. With fi = the powe dissipation fo Mode 4 and Mode 5 ae the same. Figue 9 shows the pecentage impovement in powe dissipation and pecentage degadation in sevice time vs the access fequency fo vaious values of Q fo Modes 4 and 5. The pecentage impovement in powe dissipation inceases as access fequency inceases. ncease in the value of Q deceases the pecentage powe dissipation. Fo smalle values of access fequency (fa = 1 to 3Mz) the slope of the powe dissipation cuve is quite high (4) wheeas at highe values it is small (2). The powe dissipation impovement fo values of fa geate than 3.5 to 4Mz is maginal. Theefoe, an optimal point of opeation is fa=3mz fo small values of Q and fa=4.5 to 5Mz fo lage values of Q. Finally, the following obsevations can be made: (1) t is possible to opeate a memoy system at the highest possible fequency with about 9 pecent impovement in powe dissipation ove Mode 1 of opeation. (2) t is advisable to make the time between efeshing (t) as lage as possible both to decease the aveage powe dissipation and sevice time.

8 388 National Compute Confeence, 1976 l'el l Powe Dissi?ation Sevice Time 12j Nt"" 128 N 64 f1'= Mz \:.--= :?o msec. o.! +' til Po -l '! A :s: o p.,.9 1 f3 6 Q=1 Q= Sevice Time fo all values of Q O _ _._ _------,_------_------_, _------,_------_ o f" (Mz) Figue 7-Pecentage impovement in powe dissipation and pecentage degadation in sevice time fo vaious values of Q fo mode 3 of opeation 14 / 1 /..." Powe dissipation / f = o., Sevice Time / 12 N = t Sevice time /' gphs fo f = 3., 5., N = 64 Rnd 8. Mz ae vey nea the,,/ x-;-.x::'s to Q = 8 ecod.,,/' t = 2 msec.,,/ 1 1 S -l '! +' 8 Cl f =.2 Po -l '! f =.5.,; t A 8 f =1. 8 C) Ql '! f =2. p., '! -l +' +' 6 6 til '" \:: til CD bo ii > A f = _ f=o f = Figue 8-Pecentage impovement in powe dissipation and pecentage degadation in sevice time vs access fequency fo vaious values of ft fo mode 3 of opeation

9 Pefomance and Powe Dissipation Analysis p.. > o * 'Powe Dissipation Sevice Time / ,/ Nt = 1?8 N!, = 1?8 t =?msec. f = lmz Se'Vl.C. e Time _- Mode Sevice tle fo!' Mode 4 is sae as that fo Mode 1 and theefoe, thee is no degadation in sevice time. O _----_ _----_----._----._----_,_----,, o t22 2 :lp., (; 4 2 'l 8 <g l > Q) Cfl l.-l.p tv ' co bo Q) A *- Figue 9-Pecentage impovement in powe dissipation and pecentage degadation in sevice time fo mode 4 and mode 5 of opeation (3) The inteesting modes of opeation ae deived by making idle fequency zeo. This is intuitively valid because moving the bits in a shift egiste duing idling does not have any advantage eithe fom pefomance o fom powe dissipation viewpoint. COMPARSON OF DFFERENT MODES n this section we will compae the diffeent modes of opeation. To make a compaison we will define a figue of meit (Fgm) as the numbe of possible sevices pe unit time pe unit powe dissipation. _ 1... " gm -aveage sevice time x aveage powe dissipation Thus, a mode that has highe Fgm is bette than one that has a lowe Fgm. n Figue 1 we daw a gaph of Fgm vs. Access fequency fo vaious modes. The typical values chosen fo N b N nand t ae 128, 64 and 2msec. The Refesh fequency, wheneve it is diffeent fom Access fequency is chosen as 1Mz. The Mode 1 and Mode 2 ae independent of Q, wheeas Modes 3, 4, and 5 ae dependent on Q and, theefoe, gaphs ae dawn fo vaious values of Q. Mode 2 has the wost Fgm fo all access fequencies and, theefoe, is the wost mode of opeation. Mode 1 has a typical Fgm of about 5 and is constant ove all fequencies. Fo values of fa> 1Mz Modes 3 and 4 and Mode 5 ae bette than Mode 1 fo all values of Q up to 1. Fo fa=lmz and values of Q=1,5, Mode 1 of opeation is bette than Mode 3. Also, fo Q= 1 Mode 1 is bette than Mode 4 o Mode 5. But notice that fo Q= 1 Mode 3 is the best mode of opeation fo small values of fa. At highe values of fa Mode 4 is the best mode, closely followed by Mode 5 fo all values of Q. The Fgm fo Modes 3, 4 and 5 is educed as Q inceases. The eduction fo Modes 4 and 5 is much highe than that fo Mode 3. Table V lists the vaious modes and a qualitative compaison of these modes with espect to contol complexity and cost of design. CONCLUSONS Memoy systems built with CCD's ae shown to have thee states of opeation: The Access state, Refesh state and dle state and each state has a fequency associated with it. Thee diffeent modes of opeation ae defined and aveage sevice time and aveage

10 39 National Compute Confeence, 1976 o oj 1\=128 N",= 64 f",=l.mz Mode 4, Q=l. de 5, Q=l j i :B +' { ' i :>: '" <.; '" ll() Mode 1 and de 2 ae independent of Q 1 Figue lo-figue of meit vs access fequency fo vaious modes of opeation TABLE V-A Qualitative Compaison of Diffeent Modes of Opeation MODE ltn? ':!..C'!<':9 (" 1"'1'1\ l1'p ('\T 1 REQURED COMPLEXTY cos' OF DESGN RE1ARKS Minimum Minimum Simplest mode of opeation 2 Modeate 2 Modeately Low Lowe than Mode 4 Wost mode of opeation if f. 3 2 Modeately igh Modeate Fo small f (f <lmz) A good modeaof aopeation 4 2 if fi igh if fi Fo f ) OOz the best a 1 if f. = Low if f. = Low if f. = mode of opeation 5 3 if f. Best mode of opertion Maximum Maximum except fo mode 4 2 if f. = 1.

11 Pefomance and Powe Dissipation Analysis 391 powe dissipation equations fo a geneal case of opeation ae deived. Equations fo each mode ae then deived as a limiting case of these geneal equations. The diffeent modes ae analyzed individually and, finally, a compaison between the diffeent modes is made by defining a figue of meit. An inteesting esult deived is that the powe dissipation is constant and is independent of Access fequency fo Modes 3 and 4 when they ae opeated with fi = o. Mode 4 is shown to be the best mode of opeation. A simple qualitative compaison is finally made fo the cost of implementation. ACKNOWLEDGMENT would like to thank D. Bob Woo fo extensive discussions duing the development of this wok, M. Paul White fo comments that impoved the quality of the pape, and Maie Golden fo typing this pape. REFERENCES 1. Amelio, G. F., "Chage Coupled Devices fo Memoy Applications," AFPS Confeence Poceedings, Vol. 44, May 1975, pp Canes, J. E. and W. F. Kosonocky, "Chage Coupled Devices fo Compute Memoies/; AFPS Confeence Poceedings, Vol. 43, May 1974, p Collins, D. R., J. B. Baton, D. C. Buss, A. R. Kinetz, S. E. Schoede, "CCD Memoy Options," 1973 EEE Solid-State Cicuits Confeence, p vatil1, R. R. and. D. Fankel, "Electonic Disks in the 198's," Compute, Febuay 1975, p Moton, J. A., "Stategy fo Memoy System Technology," EEE Tansactions on Magnetics, Septembe 1971, pp Fench, B. T., "Designes Guide to Chage Coupled Devices," EDN, Jan. 2, 1972, pp R. Papenbeg, Applications Using ntel's K Chage Coupled Device, Application Notes, ntel Copoation, 365 Bowes Avenue, Santa Claa, Calif ntel 16,384 Bit CCD Seial Memoy, Specification Sheet, ntel Copoation, 365 Bowes Avenue, Santa Claa, Califonia 9551.

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