Efficiency of Innovative Charge Pump versus Clock Frequency and MOSFETs Sizes

Transcription

1 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, Journal homepae: Efficiency of Innovative Chare Pump veru Clock Frequency an MOFE ize Davi Matoušek 1, Jiří Hopoka 1, Onřej Šurt 2, 1 1 Department of Circuit heory, FEE CU in Praue, echnicka 2, 16627, Praue, Czech Repulic, matouav@fel.cvut.cz 2 AICentrum, a company of the watch Group, Novovorka 994, 14221, Praue, Czech Repulic Chare pump are circuit that prouce the voltae hiher than upply voltae or neative voltae. oay, chare pump ecame an interal part of the electronic equipment. he interation of chare pump irectly into the ytem allow manufacturer to fee a complex ytem with many pecific power requirement from a inle ource. However, chare pump efficiency i reuce y many phenomena. hi paper i focue on the quetion of efficiency of propoe variant of the chare pump. In thi article, the efficiency epenence on a numer of tae, output current, clock frequency an MOFE ize wa imulate y Elo. he aim of thi tuy i to etermine the MOFE ize an their influence to efficiency an the output voltae. Complex optimization of the chare pump circuit will follow in further text. Keywor: 2-phae Chare Pump, non-volatile memory, efficiency, witch ize etermination. 1. INRODUCION he Dickon Chare Pump (DCP) [1] elon to wellknown chare pump architecture. he ein equation for thi DCP are ummarize in [2]. he ifferential voltae V etween noe n an n+1 i DOI: /mr ΔV = V +1 V = V V, (1) n where V i the voltae win at each noe ue to capacitive couplin from the clock [2], V i the threhol voltae of the ioe-connecte tranfer tranitor. he optimal value of the voltae win equal to the amplitue of clock. But the tray capacitance of noe reuce voltae [2] win a follow V C n = VCLK C C, (2) + where V i the voltae win, C i the tranfer capacitance, C i the tray capacitance, V CLK i the amplitue of clock. ince the no-loa output voltae applie accorin to [2] V O IN ( V V ) V = V + N, (3) where V O i the no-loa output voltae, V IN i the input voltae, N i the numer of tae, V i the voltae win, V i the threhol voltae. he equation (3) how the output voltae in an ieal ituation when the pump i not eliverin any output loa current. he effect of the loa current i ecrie y [2] V = V I R, (4) O where V i output voltae at loa, V O i the no-loa output voltae, I i the loa current (I 0), R i the internal reitance of the chare pump. he internal reitance of the chare pump epen on the numer of tae N, tranfer capacitance C, tray capacitance C an clock frequency f [2] R ( C + C ) f = N, (5) he threhol voltae of ue tranitor ha uually the main effect to reulte value of the output voltae. It limit the DCP implementation, epecially for upply voltae lower than 1 V. herefore, u-volt application ue other architecture of chare pump [3], [4]. A chane of connection of tranfer tranitor from ioe moe to witchin moe [5], [6], [7] i enerally ue principle for threhol effect uppreion. hu the voltae rop etween two noe i not a threhol ate-ource voltae ut the aturation voltae of channel only. 260

2 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, UBJEC & MEHOD Propoe variant of the chare pump [8] ue the 2-phae clock. One cell a the aic uilin lock of thi chare pump i hown in Fi.1. he cell contain five tranitor (M 1 to M 5) an tranferrin capacitor (C ). hi cell i riven y overlappe clock inal accorin to Fi.2. Fallin ee oth clock inal tart imultaneouly. In the firt phae (CLK1 =, CLK2 = ), tranitor M 1, M 3 an M 5 are ON. hu tranferrin capacitor C i iae to upply voltae. In the econ phae (CLK1 = GND, CLK2 = GND), tranitor M 2 an M 4 are ON. hu tranitor M 2 hol ia tranitor M 5 in the iconnecte tate. ranitor M 4 connect the tranferrin capacitor C etween input (output of the previou cell) an output, now. herefore, the input voltae i increae y a voltae of tranferrin capacitor from the iae phae. In the lat phae (CLK1 = GND, CLK2 = ), all tranitor are OFF. A. Propoe ein alorithm he ein rule for initial aic parameter etimation of propoe chare pump may e ummarize to unermentione tep. For illutration, we conier thee chare pump pecification: power upply voltae = 0.7 V, minimal teay-tate output voltae V = 4 V, output loa capacitance C L = 300 pf, output current I L = 4 µa, maximal output voltae ramp-up time t r = 150 µ. input pecification numer of tae etimation (N) initial clock frequency (f CLK ) input M 5 output initial ize of tranferrin capacitor (C ) matchin W/L of ue tranitor from I-V characteritic optimal timin parameter etimation M 2 M 4 C Fi.3. Dein-flow iaram. CLK1 CLK2 M 1 Fi.1. One cell of the propoe chare pump [8]. Ue clock inal have overlappe character a i hown in Fi.2. ymol W 1 an W 2 mark with of pule oth clock inal. PER i the perio of oth clock inal. he optimal W 1, W 2 value for the et ratio etween the output voltae an reulte efficiency were etimate in the previou contriution [8] a W 1 = 24 n an W 2 = 10 n for PER = 50 n. M 3 he numer of tae: Initial etimation of numer of tae N i calculate a ratio of the output voltae V an the voltae ain of one tae V E (ieally, thi ain ha the ame value a upply voltae): V 4 N = 6 (6) V 0.7 = E he initial clock frequency f CLK: Initial clock frequency wa aume a f CLK = 20 MHz. he initial ize of tranferrin capacitor C : Value of tranfer capacitance C may e calculate from known loa capacitance C L, numer of tae N, ramp-up time t r an clock frequency f CLK [2]: CLK1 0 CLK2 W 1 W 2 0 PER Fi.2. Waveform of 2-phae clock. t t N 12 6 C = C = = 0.6 pf (7) L 6 6 t f r CLK he W/L of ue tranitor: he MOFE M 3 to M 5 an M D ue for tranfer chare houl have conuctance at leat ten time hiher than conuctance matche to the output current [2], thu their initial ize mut e etimate from I-V characteritic [8]. he MOFE M 1 to M 2 may caue loe of chare, ut thee MOFE are ue for rivin tranitor M 5 only. herefore, thee tranitor may e relatively narrow [8]. Parameter of ue tranitor are ummarize in ale

3 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, ranferrin capacitor C i realize a tranitor M C, it capacity wa calculate y erivation of I-V characteritic. M BUFA an M BUFB are tranitor from clock uffer. Moel nmo_hvt an pmo_hvt correpon to hih voltae tranitor with a relatively hih value of V. Moel nmo_na18v correpon to the native tranitor for 1.8 V technoloy. ale 1. Parameter of tranitor. ranitor W (µm) L (µm) moel M nmo_hvt M pmo_hvt M nmo_hvt M pmo_hvt M pmo_hvt M C nmo_hvt M D nmo_na18v M BUFA nmo_hvt M BUFB pmo_hvt he etimate area of the chip for the realization of propoe chare pump i lite in ale 2. where N i the numer of tae, A AGE i the area for the realization of tae, A BUFDE i the area for realization clock uffer an output etector, A OAL i the area for realization propoe chare pump with require numer of tae. he technoloical noe correpon to 100 nm. ale 2. Etimate area for the realization of the chare pump. N AAGE (µm 2 ) ABUFDE (µm 2 ) AOAL (µm 2 ) Note, that area for realization clock uffer an output etector A BUFDE ha a contant value over a numer of tae N. Namely, iniviual tae of the chare pump ue common clock uffer. he optimal timin parameter: he optimal timin parameter for clock frequency f CLK = 20 MHz were etimate in previou contriution [8] a W 1 = 24 n an W 2 = 10 n for PER = 50 n. For other value of frequency, the timin parameter mut e proportionally chane accorin to ale 3. ale 3. imin parameter for variou value of clock frequency. fclk (MHz) PER (n) W1 (n) W2 (n) B. tuy of clock frequency influence to efficiency an output voltae he aim of thi part of imulation i to etermine the influence of clock frequency to efficiency primarily an output voltae econarily. chematic iaram of imulate circuit i hown in Fi.4. hi intance i 6-tae chare pump (N=6). A numer of tae (i.e. cell) are chane for other intance only. Clock inal are uffere y tron uffer (inverter). Dioe etector ae on tranitor M D i connecte to the lat tae. Reitor R L an capacitor C L moel reitive an capacitive part of output loa. Propoe chare pump wa powere from = 0.7 V an oth clock inal ha amplitue 0.7 V, too. ymol I mark conume current. he output voltae at the loa i marke V. A numer of tae N were varie from 1 to 6, clock frequency wa et to value 10, 13.3, 20, 27, 40 MHz. Complex analye for a numer of tae varie from 1 to 6 wa performe. But in thi text, the reult for variant N = 6 wa choen. ymol I L mark reitive part of output current. I M D AGE 1 AGE 2 AGE 3 AGE 4 AGE 5 AGE 6 CLK1' CLK2' ; CLK1 CLK2 I L C L R L V Fi.4. implifie chematic iaram of the imulate chare pump for N=6. 262

4 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, Fi.5. how that efficiency increae with increain value of loa current an ecreain value of clock frequency. Increain the clock frequency lea to increain power conumption, thu efficiency ecreae with increain clock frequency. While the power conumption for iven clock frequency i relatively near a contant value an oe not vary with output current. herefore, efficiency increae with increain loa current. from power upply incluin a current of clock uffer, R L i the output loa. Efficiency i varie aout 10 % (from % at frequency 10 MHz to % at frequency 40 MHz) for the nominal value of the output current I L = 4 µa. For the ame conition, the output voltae varie from V to V. imulation reult are very imilar for another numer of tae of the chare pump. he ituation i ummarize in ale 4. ale 4. Efficiency an output voltae for a variou numer of tae at output current 4 µa. Fi.5. Efficiency a a function of IL for N=6. Fi.6. how the output voltae variation with reitive part of output current I L an clock frequency. Increain the clock frequency will increae the amount of chare tranferre over a iven time interval, thu output voltae ha a hiher value. he preence of a fixe capacitive loa lea to increain no-loa output voltae with increain clock frequency. Fi.6. Output voltae a a function of IL for N=6. otal efficiency wa calculate a ratio of the output power P in teay-tate (8) an the total conummate power from power upply P IN (9) accorin to (10) N ζ (%) V (V) to to to to to to to to to to to to Value of efficiency are relatively low ecaue propoe chare pump work at relatively low value of the power upply voltae ( = 0.7 V). C. MOFE ize influence to efficiency an output voltae he aim of thi part of imulation i to etermine the influence of MOFE ize to the efficiency an output voltae. hu ize of all tranitor were wept in the econ part of imulation. Only one parameter wa chane, ize of other tranitor (accorin to ale 1.) were left unchane. Output loa wa et to contant value R L = 1 MΩ. hee imulation were performe for 6-tae chare pump only at clock frequency 20 MHz. Next, the even option of imulation were performe to etermine the influence of tranitor imenion. Option 1: with of tranitor M 4 an M 5 wa wept from 0.5 µm to 50 µm. he ize of thee tranitor ha tron influence to oth oerve quantitie (ee Fi.7.) ecaue thee tranitor have the main effect to tranfer of chare in the firt phae (iain of C ) an the econ phae (tranferrin chare of C to output). P 2 V = V I =, (8) R L P IN = V I, (9) DD 2 PIN V ζ = 100 % = 100 %, (10) P V I R DD L where V i the output voltae in teay-tate, i the power voltae, I i the averae value of current conume Fi.7. Option 1: Efficiency an output voltae a function of W4,5. 263

5 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, Option 2: with of etector M D wa wept from 0.5 µm to 50 µm. he ize of the tranitor M D ha the primarily influence to the efficiency (ee Fi.8.) ecaue thi tranitor etermine the ratio of enery that i tranmitte to loa to the enery that i conume from the power upply. Option 6: with of tranitor M C wa wept from 6 µm to 60 µm. he optimal ize of the tranitor M C i a compromie etween efficiency an output voltae (ee Fi.11.). Influence of variation in the capacity of tranfer capacitor C ha a tron effect on the internal reitance of the chare pump (thu thi capacity ha a tron effect on the output voltae). he optimal value of C capacity for maximizin efficiency i a more complex quetion. he main role play value of C capacity for low value of C an increae power upply for hih value of C. Fi.8. Option 2: Efficiency an output voltae a function of WD. Option 3: with of tranitor M 3 wa wept from 0.2 µm to 10 µm. he ize of the tranitor M 3 ha the primarily influence to the output voltae (ee Fi.9.), ecaue thi tranitor ha inificant effect to tranfer of chare in the firt phae (iain of C ). Option 4, 5: with of tranitor M 1 an M 2 were wept from 0.2 µm to 10 µm or from 0.2 µm to 20 µm repectively. Increain with of thee tranitor lea to an increae of icharin proce effect of the tranfer capacitor C. Hence, tranitor M 1 an M 2 mut e narrowe, ee Fi.10. Fi.11. Option 6: Efficiency an output voltae a function of WC. Option 7: with of tranitor M BUFA wa wept from 1 µm to 20 µm an imultaneouly M BUFB wa wept from 5 µm to 100 µm. Maximal value of efficiency ζ = % for V = V occur for W BUFA=1 µm an W BUFB=5 µm. hi variant in t plotte ecaue ifference of value of efficiency an output voltae were relatively mall. hee tranitor mut e narrowe ecaue increae conuctance of wie tranitor lea to increae witchin current of thee uffer. 3. REUL Reult from the imulation imply poiility for optimization efficiency of propoe chare pump. Value of efficiency an output voltae are ζ = % an V = V for oriinal ize of MOFE accorin to ale 1. an loa R L = 1 MΩ. Fi.9. Option 3: Efficiency an output voltae a function of W3. Fi.10. Option 4, 5: Efficiency an output voltae a function of W1,2. 4. DICUION tuy of efficiency an the output voltae veru clock frequency an MOFE izin for propoe chare pump wa performe. Parameter of MOFE an clock cheme were choen accorin to a previou tuy [8]. Analye wa performe y Elo imulator verion he Elo i an PICE-like imulator from Mentor Graphic Corporation. he firt part of imulation emontrate that the efficiency increae with increain loa current an ecreain clock frequency. However, the epenency of the output voltae ha oppoite character, ecaue the output voltae increae with ecreain loa current an increain clock frequency. 264

6 MEAUREMEN CIENCE REVIEW, 16, (2016), No. 5, Reult from the econ part of imulation imply poiility for optimization efficiency of propoe chare pump. Effect of tranitor izin allow improvin the efficiency aout ten percent. Dimenion of tranitor M 4, M 5, M D an M C have the main effect on efficiency, M 3 ha the important effect on the output voltae. Effect of other tranitor ha preictale character an we may nelect effect on the ize of thee tranitor. Reult from thi tuy can e ue for complex optimization tuy performe in the next perio. he valiity of the preente reult i limite to pre-layout imulation. herefore, paraitic effect of hiher orer (e.. interlayer capacitance, metallic interconnection capacitance etc.) are nelecte. hee paraitic effect can have a inificant influence on attainale reult. ACKNOWLEDGMEN hi work ha een upporte y the rant No. G14/191/OHK3/3/13 of the CU in Praue. REFERENCE [1] Dickon, J.F. (1976). On-Chip hih-voltae eneration in NMO interate circuit uin an improve voltae multiplier technique. IEEE Journal of oli- tate Circuit, 11 (3), [2] Pan, F., amaar,. (2006). Chare Pump Circuit Dein. McGraw-Hill Eucation. [3] Palumo, G., Pappalaro, D. (2010). Chare pump circuit: An overview on ein trateie an topoloie. IEEE Circuit an ytem Maazine, 10 (1), [4] Matouek, D. (2014). Comparion of electe architecture of neative Chare Pump with new ein. In Raioelektronika : 24th International Conference, April 15-16, IEEE. [5] Yamazoe,., Ihia, H., Nihoni, Y. (2009). A Chare Pump that enerate poitive an neative hih voltae with low power-upply voltae an low power conumption for non-volatile memorie. In International ympoium on Circuit an ytem (ICA 2009), May 24-27, IEEE, [6] Won, O.Y., Won, R., am, W.., Kok, C.W. (2011). An overview of chare pumpin circuit for Flah memory application. In 9th International Conference on AIC (AICON), Octoer 25-28, IEEE, [7] Won, O.Y., Won, H., am, W.., Kok, C.W. (2014). On the ein of power- an area-efficient Dickon chare pump circuit. Analo Interate Circuit an inal Procein, 78 (2), [8] Matouek, D., urt, O., Hopoka, J. (2015). Chare pump ein for ue in NVM evice tet an meaurement. In MEAUREMEN 2015: 10th International Conference, May 25-28, Intitute of Meaurement cience A, Receive March 29, Accepte Octoer 07,