A very compact KHN filter with multidecade tuning

A Ve y Compac KHN Fil e wi h Mul idecade Tuning Ca los Muñiz-Mon e o1, Alejand o Díaz-Sánchez1,2 Elec onics depa men s 1. Na ional Ins i u e o As ophysics Op ics and Elec onics 2. Poli echnical Ins i u e o Puebla. Puebla, MEXICO cmuniz, [email protected] Ramón González-Ca ajal Depa men o Elec onic Enginee ing School o Enginee ing, Uni e si y o Se illa Se illa, SPAIN ca ajal@g e.esi.us.es Abs ac —A e y compac implemen a ion o a mul i unc ion Ke win Huelsman Newcomb (KHN) il e ha can be equency uned almos se en decades, om 0.2 Hz o 1 Mhz, is p esen ed. Tuning is achie ed by means o high- alue, p og ammable ac i e esis o s biased using he quasi loa ing ga e (QFG) echnique and linea isa ed h ough capaci i e ga e ol age a e aging. The ci cui , ealized in a 0.5 µm s anda d CMOS echnology using only ou CMOS in e e s, six small capaci o s, six small esis o s and wo p og ammable ac i e esis o s, occupies a o al a ea o 0.02 mm2, dissipa es 3.45 mW and p esen s a dynamic ange a 0.1 % THD o 55.86. I. INTRODUCTION In low equency applica ions, such as analog p ocessing o biomedical signals, analog il e s a e used o ejec unwan ed signals, such ha la ge DC o se s gene a ed by senso s and licke o ou band noise. Addi ionally, he bandwid h o mos o he biomedical signals is in he ange o 0.1 Hz − 10 kHz and, because o he ypical equi emen s o biomedical applica ions, p og ammabili y is manda o y [1]. Un o una ely, he design o p og ammable in eg a ed il e s wi h bandwid hs below 1 kHz is no i ial, especially i o he design speci ica ions such as low noise, low dis o ion, small a ea and educed powe consump ion, mus be sa is ied. The main challenge comes om he lack o la ge ime cons an s a ailable in in eg a ed ci cui s. To o e come his p oblem, imp ac ical echniques ha e been used in he li e a u e, among hem: use o ex e nal capaci o s (addi ional ou pu pads), capaci ance mul iplica ion (coa se p og ammabili y ha is only possible wi h disc e e con ol) and echniques o cu en di ision and cu en cancella ion (p one o p esen misma ch and la ge o se componen s) [2-3]. A mo e success ul al e na i e ha eaches un il i e decades o equency uning is he companding app oach in log-domain p ocessing, whe e he inpu is comp essed, hen nonlinea ly p ocessed, and inally expanded a he ou pu , p ese ing dynamic ange (a low supply ol ages) and he o e all linea i y [4]. This app oach exploi s he exponen ial law o MOS ansis o s biased in weak in e sion and equen ly equi es de use o Mul iple Inpu T anslinea Elemen s (MITE) ealized wi h loa ing ga e ansis o s (FGT) [4, 6]. The main p oblem o all he p e iously men ioned app oaches is he huge die a ea equi ed, and he ac ha only he log-domain il e s each mul idecade uning. This wo k p oposes a e y compac and ex emely simple ealiza ion o a KHN il e (sui able o biomedical applica ions) wi h mul idecade uning ha does no equi e o log-domain p ocessing. The p oposal is based on he use o e y la ge- alued, p og ammable ac i e esis o s biased using he quasi loa ing ga e (QFG) echnique and linea isa ed h ough capaci i e ga e ol age a e aging. A cu en mode e sion o his s a egy was ecen ly epo ed in [7]. The pape is o ganized as ollows. Sec ion II in oduces he quasi ideal in eg a o used in he KHN il e syn hesis o Sec ion III. Simula ion esul s a e p esen ed in Sec ion IV. Finally, in Sec ion V some conclusions a e d awn. II. QUASI-IDEAL INTEGRATOR DESIGN Le ’s conside he quasi-ideal in eg a o shown in Fig. 1a. The CMOS in e e is conside ed o analysis pu poses as an OPAMP o gain A wi h he non-in e ing inpu connec ed o VDD/2. Rg is a p og ammable ac i e esis o con olled by he ol age Vcp. The co esponding ans e unc ion is gi en by ∞→−≈ +      + −== A CsR AA CsR V V sH g g in ou , 1 11 1 1 )( (1) The ci cui implemen a ions o he CMOS in e e and he ac i e esis o Rg a e illus a ed in igu es 1b and 1c, espec i ely. The in e e is ealized by using la ge ansis o s o educe noise and misma ch con ibu ions. Ne e heless, mo e elabo a ed ampli ie s can be employed o ob ain low ol age and/o low powe e sions o his in eg a o . Rg is a h ee ansis o e sion o he linea ised quasi- loa ing ga e esis o p oposed in [8], bu wi h he ansis o s Mp2 biased in weak, mode a e o s ong in e sion egion, always in iode mode, by he ol age Vcp. Consequen ly, he e ec i e esis ance can be uned om hund eds o kilo-ohms o he ange Wo k suppo ed by CONACyT, Mexico, unde G an I-37470-A 1-4244-1342-7/07/$25.00 ©2007 IEEE 44 Figu e 1. (a) Quasi-ideal in eg a o ealized wi h a unable ac i e esis o . (b) CMOS in e e ealiza ion. (c) QFG p og ammable esis o linea ised wi h he capaci i e ga e ol age a e aging scheme p oposed in [8]. o Gigaohms, while a capaci o o a ew pico a ads is enough o ob ain cu o equencies in he o de o he z. Th ee ansis o s a e necessa y o a oid di ec pola iza ion o he pa asi ic ac i e-subs a e diodes due o signal luc ua ions be ween he e minals o Rg, inc easing he dynamic ange [9, 10]. In addi ion, he weak-in e sion ope a ion o ansis o s Mp2 o ces Rg<<RB (whe e RB is he di usion esis ance), in o de o a oid a pa asi ic esis i e di ide [11]. The subs a e connec ion o he i s ansis o Mp2 (ma ked wi h a black iangle in Figu e 1a) should be connec ed o a d ain ins ead o a ga e o a oid unp edic able o se s due o subs a e leakage cu en s [10]. In single-ended ci cui s wi h loa ing MOS esis o s, linea isa ion can be pe o med by including in he ga e ol age a componen co esponding o he a e age o he ol ages in he e minals o he esis o [8]. This a e aging is achie ed by he small capaci o s Ca. Consequen ly, he ga e ol age o ansis o s Mp2 becomes (VA+VB)/2+Vcp. III. KHN FILTER WITH MULTIDECADE TUNING The Ke win Huelsman Newcomb (KHN) il e is a opology wi h ex eme lexibili y, good pe o mance and low sensi i i ies [12]. A ci cui app oxima ion o his il e , using he quasi-ideal in eg a o desc ibed in he p e ious sec ion, is illus a ed in Figu e 2. Wi h a s aigh o wa d analysis, he high-pass, band-pass and low-pass esponses becomes        +++        ++      + = 2 4 6 5 6 2 4 6 2 2 3 6 12 )( A AR R R R s AR R s A s R R sH HP ψψ ψ (2) Figu e 2. Tunable KHN il e ealized wi h he quasi-ideal in eg a o o Figu e 1a and he QFG p og ammable ac i e esis o wi h capaci i e ga e ol age a e aging linea isa ion o Figu e 1c.        +++        ++      +− = 2 4 6 5 62 4 62 3 6 12 )( A AR R R R s AR R s A s R R sH BP ψψ ψ ψ (3)        +++        ++ = 2 4 6 5 6 2 4 6 2 3 6 2 12 )( A AR R R R s AR R s R R sH LP ψψ ψ (4) CR g 1 = ψ (5) while he na u al equency ω n and quali y ac o Q a e: 2 4 6 5 61 A AR R R R n++= ψω (6) AR R A AR R R R Q2 1 4 6 2 4 6 5 6 + ++ = (7) F om (6) and (7) is obse ed ha he na u al equency can be uned modi ying he pa ame e ψ =1/(RGC) h ough he ol age Vcp. Mo eo e , his uning does no a ec Q. 45 Figu e 3. Layou o he p og ammable KHN il e o Figu e 2 designed in a 0.5-µm CMOS echnology. TABLE I. DESIGN DETAILS OF THE CIRCUIT OF FIGURE 2 Mn1, Mp1, Mp2 W/L (µm/µm) = 12/1.2, 71.1/1.2, 1.5/0.6 R3, R4, R5, R6 10 KΩ C, Ca, CL 1 pF, 0.1 pF, 1 pF VDD, Vcp, 3 V, Vcp ∈ (0 V, 1 V) IV. RESULTS The KHN il e o Figu e 2 was designed using BSIM3.1 models o a 0.5 µm CMOS AMI p ocess (VTHn=0.65 V, |VTHp|=0.95 V). Figu e 3 shows he layou o his il e using he design de ails summa ized in Table I. All he capaci o s a e e y small, consequen ly, he o e all ci cui occupies and a ea o only 0.02 mm2. The equency esponses o he low- pass, band-pass and high-pass signals a e illus a ed in Figu e 4. Whi a sweep o Vcp om 0 o 1 V, he cu o and cen e equencies ange goes om 0.2 Hz o 1 MHz, he e o e ea u ing a uning ange o se en decades. The simula ed To al Ha monic Dis o ions (THD) o he low-pass and high-pass signals a e shown in Figu e 5 as a unc ion o he ampli ude o he inpu signal and he uned equency. The maximum le els o dis o ion appea wi h signals o equency 0.1 Hz and ampli ude abo e 0.4 V. Howe e , he THD emains in mos o he cases below 1 % (- 40 dB) wi h signals o ampli ude below o 0.3 V. The inpu - e e ed noise spec al densi y o he low-pass signal is illus a ed in Figu e 6. The co esponding dynamic ange, o a 100 Hz-bandwid h ( uned equency) and a signal o ampli ude 100 mV (co esponding o a THD o 0.1 %) and equency 10 Hz is equal o 55.86 dB. In Table II some o he cha ac e is ics o unable il e s p oposed in he li e a u e a e summa ized and compa ed wi h he il e p oposed in his wo k. As can be obse ed, he a ea Figu e 4. Low-pass, band-pass and high-pass esponses o he KHN il e wi h a sweep o Vcp om 0 V o 1 V in inc eases o 25 mV. o he p oposed il e is only he 2 % o he a ea epo ed in e e ences [2] and [5], and he unable ange is wo decades bigge han he ange o he log-domain il e p oposed in [4]. Finally, an a e age powe consump ion o 3.45 mW was ob ained using he echnique epo ed in [13]. Ne e heless, mo e elabo a ed ampli ie s can be employed ins ead o he in e e o ob ain a be e powe consump ion. V. CONCLUSIONS A new s a egy o design low- equency, unable in eg a ed il e s has been p esen ed and e i ied by simula ion. This echnique uses la ge- alued ac i e esis o s o o e come he p incipal challenges o he p e iously epo ed s a egies in he li e a u e, allowing an ex emely compac and easy ci cui ealiza ion, wi h low ha dwa e complexi y, ully in eg a ed capaci o s and mul idecade uning capabili y wi hou using he log-domain p ocessing app oach. The s a egy can be used in o he il e opologies and scales wi h he CMOS p ocesses. Also, he powe consump ion and ol age equi emen s can be easily educed i mo e elabo a ed ampli ie s a e used ins ead o CMOS in e e s. 46 Figu e 5. Simula ed THD o he low-pass and high-pass signals as a unc ion o he ampli ude o he inpu signal and he uned equency. The equency o he inpu is one decade below o abo e o he uned equency, o he case o he low-pass and high-pass il e s, espec i ely. Figu e 6. Inpu e e ed noise o he low-pass esponse uned a 100 Hz. TABLE II. COMPARISON OF TUNABLE FILTERS IN THE LITERATURE Re e ence and CMOS p ocess Tunable ange O de Die a ea [2] (1.2 µm) 2 Hz 6 1 mm2 [4] (1.2 µm) (1 Hz – 100 kHz) 2 No epo ed [5] (0.8 µm) (50 kHz – 2.1 MHz) 3 1 mm2 [6] (0.8 µm) (25 Hz – 35 kHz) 1 0.1 mm2 * This wo k (0.5 µm) (0.2 Hz – 1 MHz) 2 0.02 mm2 * Wi hou conside wo ex e nal capaci o s o 150 pF. REFERENCES [1] J. D. B onzino, The Biomedical Enginee ing Handbook, CRC P ess Inc. and IEEE P ess, 1995. [2] S. Solis-Bus os, J. Sil a-Ma ínez, F. Mallobe i and E. Sánchez- Sinencio, “A 60 dB Dynamic Range Six h O de 2.4 Hz Lowpass Fil e o Medical Applica ions,” IEEE T ansac ions on Ci cui s and Sys ems Pa II, Vol. 47, No. 12, pp. 1391-1398, Decembe 2000. [3] J. Sil a-Ma ínez and S. Solis-Bus os, “Designs conside a ions o high pe o mance e y low equency il e s,” P oc. o he 50 h In e na ional Symposium on Ci cui s and Sys ems, ISCAS 99, Vol II, pp. 648-651, O lando, USA, June 1999. [4] B. A. 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