A METHOD FOR CONTINUOUS TUNING OF MOSFET RC FILTERS WITH EXTENDED CONTROL RANGE

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1 Journal of ELECTICAL ENGINEEING, VOL 67 (2016), NO6, COMMUNICATIONS A METHOD FO CONTINUOUS TUNING OF MOSFET C FILTES WITH EXTENDED CONTOL ANGE Karolis Kiela omualdas Navickas In his paper a uning srucure for a MOSFET?C filers is presened. The proposed uning srucure is composed of swiched resisor banks wih volage conrolled ransisors. The volage conrolled ransisors use acive feedback wih exended conrol range for coninuous filer parameer uning, wihou degrading he oal lineariy performance of he filer. The proposed uning srucure is esed by implemening i in a second order low pass biquadraic filer cell in 65 nm CMOS echnology. The designed filer has a highly reconfigurable response, ranging from Chebyshev o Bessel, a uneable -3 db bandwidh from 10 MHz o 100 MHz and can be used for muliple sandard wireless soluions. Filer IIP3 performance is no degraded when he bandwidh is coninuously uned by 40 % wih a 1 V pp inpu. The maximum power dissipaion, including acive feedback circuis, is 17.2 mw from a 1.2 V source when he filer is uned o 100 MHz bandwidh. K e y w o r d s: coninuous uning, inegraed filer, lineariy, MOSFET-C, reconfigurable, sofware-defined radio 1 INTODUCTION The ever-growing number of wireless communicaion sandards has creaed a new rend in designs of wireless ransceivers. Modern mobile ransceivers should comply wih a muliude of exising or developing wireless sandards as he indusry shifs o he sofware-defined radio (SD) echnology [1, 2]. Due o is simpliciy, direc conversion ransceiver archiecure is bes suied for SD implemenaion [3]. The reconfigurable naure of he SD requires ha he baseband channel selecion filers, used in direc conversion archiecures, should have a high degree of filer configuraion capabiliies, mainly cenered, bu no limied o: bandwidh, power dissipaion, filer response and order. Mos of he ime, flexible channel selecion filers are based on acive-c, gm-c or curren amplifier designs [4, 5]. High bandwidh applicaions usually use gm-c filers, bu for applicaion ha require high lineariy acive-c fileraresillhebesdueoheirlargedynamicrange,alhough hey suffer from variaions in process, volage and emperaure (PVT) [6, 7]. PVT variaion problem can be parially miigaed by he use of swiched--mosfet-c circuis, where accurae ime-consans can be achieved based on duy cycle uning [7]. Due o a more digial naure of he swiching gaes, even fully synhesizable soluions for swiched--mosfet-c circuis are repored [8]. One major drawback of such filers is he need of a high frequency clock signal o implemen filer blocks wih wide bandwidhs. Moreover, a highly reconfigurable filer design, inended for SD echnology, could only be achieved by adding complex divider circuis and a dedicaed PLL, boh of which increase he complexiy and design ime of he ransceiver. Compared o acive-c filers wih fixed capacior and resisor uning seps [9], MOSFET-C filer srucures are more suied for SD ransceivers due o heir uning flexibiliy and accuracy. While high bandwidh MOSFET-C filers usually dissipae more power han oher filer ypes, precise uning mehods can reduce he oal power consumpion by opimizing he operaional amplifier biasing currens[10, 11]. Noneheless, one of he major drawbacks of coninuous MOSFET-C uning is he lineariy degradaion due o he non-linear ransisor behavior. In his work a uning mehod wih acive feedback for srucures of MOSFET-C filer is proposed, which overcomes he lineariy degradaion problem when he filer is uned over is bandwidh or seings and does no increase he noise generaion as in he case of [12]. A low pass biquadraic filer cell is designed o es he proposeduning srucure. I uses only oneype ofresisor and capacior blocks for he whole feedback chain, which reduces componen mismach variaion and enables layou re-use. 2 CICUIT DESIGN AND IMPLEMENTATION The srucure of he low pass biquadraic filer cell implemened in a fully-deferenial Tow-Thomas configuraion is shown in Fig. 1. The filer uses he same capacior uning bank for he enire srucure. The capacior bank, shown in Fig. 1, is used for coarse frequency uning and is made of n capaciors conneced in Micro and Nanosysems Design and esearch Laboraory of Elecronics faculy, Vilnius Gediminas Technical Universiy, Sauleekio al. 3-B126, LT Vilnius, Lihuania, karolis.kiela@vgu.l DOI: /jee , Prin (ill 2015) ISSN , On-line ISSN X c 2016 FEI STU

2 450 K. Kiela. Navickas: A METHOD FO CONTINUOUS TUNING OF MOSFET-C FILTES WITH EXTENDED CONTOL ANGE V in V ip C C C C V op V on C c[1] C c[ n] C f C 1 cw C n cap Fig. 1. srucure of he filer, swiched capacior bank LB fb LB fb LB fb LA + - LA + - LA + - res 1 M n sw res 1 M nx2 M nx2 sw 1x2 1 1 c[ n] c[ n] n n M 1 M 1x2 M 1x2 nx2 c[n] c[n] n n Fig. 2. The proposed uning resisor bank: SAFB srucure, DAFB srucure bias p bias pc V i+ V i- bias nc bias n M 1 M 2 M 3 M 4 M 6 M 8 M 10 Fig. 3. Acive feedback amplifier M 5 M 7 M 9 CC C CC M 12 V 0 M 11 M 13 parallel, which are conrolled by n number of C c[n] conrol bis. The capaciors, wih he excepion of C f, are made by muliplying he srucure of C 1 and doubles wih each bi. The wo-saged Miller compensaed operaional amplifier () uses a long-ailed pair as inpu and a push-pull oupu sage o achieve wide bandwidh and low power consumpion [13]. The proposed coninuous uning srucure is shown in Fig. 2. This srucure uses a single acive feedback elemen (SAFB). A furher exension o his srucure is shown in Fig. 2, where dual acive feedback elemens (DAFB) are used. One ype of srucure is used for boh filer resisors and, bu heir fixed and coninuous conrol signals are independen. The proposed coninuous uning srucure is made of fixed resisors 1 n. The series-conneced pair made of an accordingly scaled n-ype MOSFET ransisor ogeher wih a parallel conneced fixed resisor acs as he coninuous variable uning elemen. DAFB srucure MOSFET widh is doubled and he parallel conneced resisor value reduced by a facor of 2 for each branch, when comparing i o he SAFB srucure. The resisors branches are conrolled by a binary (BCD) o decimal convered digial conrol word, meaning only one branch can be acive a a ime. The high impedance resisors LA and LB are used o linearize he MOSFET. Acive feedback amplifier (), shown in Fig. 3, is used o exend he range of volage conrol for he acive uning MOSFET. Furhermore, he use of such an acive feedback configuraion removes he need of increased supply volage for MOSFET conrol, compared o only passive realizaion. I uses a high gain folded cascade srucure, wih an oupu sage used o drive he feedback resisors fa and fb. SAFB srucure conrol volage

3 Journal of ELECTICAL ENGINEEING 67, NO6, dB bandwidh (MHz) IIP3 (dbm) dB bandwidh (MHz) 22.5 IIP3 (DAFB) 20.5 IIP3 (dbm) IIP3 (SAFB) -3dB bandwidh ( SAFB) dB bandwidh ( DAFB) and resisor bank une volage V (mv) and resisor bank une volage V (mv) Fig. 4. Designed filer IIP3 and -3 db bandwidh versus coninuous conrol volage: SAFB srucure, DAFB srucure Table 1. Performance summary Bandwidh (MHz) Filer response Bessel Buerworh Chebyshev Bessel Buerworh Chebyshev 1 db ripple 1 db ripple In-band IP3 (dbm) In-band IP3 (dbm) Inegraed inpu-reffered noise (µv) rms In-band SFD (db) Power (mw) Power of coninuous uning circuis(mw) Frequency range(mhz ) Supply volage (V) 1.2 Technology (nm) CMOS 65 1 f 1 = 1 MHz, f 2 = 1.9 MHz, inpu =1 V pp; 2 f 1 = 10 MHz, f 2 = 19.0 MHz, inpu = 1 V pp; 3 SAFB srucure; 4 DAFB srucure; 5 Inegraed from 1 o 10/100 MHz V 0 can be calculaed according o V 0 = A 0 (V i+ V i ) = fbv i+ + fa (V i+ ) fb + (1) fb + fa A 0 V i = + fb fa + fb (V 0 ) (2) V i+ = LB V sw + LA V s V s ( n + LA )+ LB V r + n 0Mn nx2 LA + LB (3) n + LA + LB + n 0Mn nx2 Here, A 0 is he open-loop gain of he acive feedback amplifier; V r and V sw are common mode volage levels a nodes res and sw respecively; n and nx2 is he value of seleced resisor, including he channel resisance of series-conneced swich (SWn); 0Mn is he channel resisance of he coninuously unable MOSFET, where he resisance for he region of linear operaion can be calculaed from (4), [14]. Conrol volage for DAFB srucure canbe derivedin he samemannerasforhe SAFB srucure. 0Mn = L Wµ n C 0x ( [VGS h ] VDS 2 3 SIMULATION ESULTS ) (4) The filer was designed and simulaed in 65 nm CMOS echnology. The proposed design uses 5 fixed branches o

4 452 K. Kiela. Navickas: A METHOD FO CONTINUOUS TUNING OF MOSFET-C FILTES WITH EXTENDED CONTOL ANGE Volage ampliude response (db) 20 0 Group delay (ns) Bessel 30 Buerworh -60 Buerworh 20 Bessel -80 Chebyshev 10 Chebyshev Frequency (Hz) Frequency (Hz) Fig. 5. Phase Noise simulaion resuls a DCO and divide-by-2 oupus, when operaing a highes operaing frequency esisance (k ) c[ 5] 10 4 c[ 4] c[ 3] c[ 2] 10 3 and resisor bank une volage V (mv) Fig. 6. and resisance versus he coninuous conrol volage implemen a resisor bank wih a coninuously variable resisance from 800 o 30 kω.i occupies an area of 0.16 mm 2 excluding supply and ground lines. A filer wih a SAFB srucure occupies and area of 0.14 mm 2. Filer, designed wih a SAFB and DAFB uning srucure, in-band IP3 performance over he uned bandwidh is shown in Fig. 4 when a 1 V pp signal is applied o is inpu. Fore a SAFB uning srucure, he in-band IP3 performance is no affeced when he bandwidh is coninuously uned by 15 %. When DAFB srucure is used insead, he in-band IP3 performance is no affeced for a 40 % of he coninuous bandwidh uning range. Fig. 5 shows he volage ampliude and group delay responses of he designed filer a 10 and 100 MHz. Using eiher SAFB or DAFB coninuous uning srucures, he filer can be uned o achieve Bessel, Buerworh and Chebyshev wih 1 db in-band ripple responses. Boh SAFB and DAFB srucures can be uned o condiions shown in Fig. 5. Figure 6 shows he graphs of resisor banks and resisance versus he coninuous conrol volage. The proposed design uses 5 fixed branches o implemen a resisor bank wih a coninuously variable resisance from 800 o 30 kω. Table I gives he overall performance summary for he designed 2nd order low pass biquadraic filer wih he proposed coninuous uning srucure. 4 CONCLUSIONS A new uning srucure of resisor bank for MOSFET- C filers was proposed in his work. The srucure was esed by designing a 2-nd order low pass biquadraic filer in 65 nm CMOS echnology, wih a layou size of 0.16 mm 2. Pos layou simulaions verify ha designed filer bandwidh can be uned from 10 o 100 MHz. By using he proposed coninuous uning srucure, he designed filer response can be elecronically reconfigured o mee a broad range of responses, ranging from Bessel o Chebyshev. Furhermore, he proposed uning srucure does no degrade in-band IP3 performance when he filer is coninuously uned up o 40 % of is bandwidh and can be used for muliple sandard wireless soluions. eferences [1] GIANNINI, V. CANINCKX, J. AMICO, S. D. BASCHI- OTTO, A.: Flexible baseband analog circuis for sofware-defined radio fron-ends, IEEE J. Solid-Sae Circuis 42 (2007).

5 Journal of ELECTICAL ENGINEEING 67, NO6, [2] ISHIHAA, N. AMAKAWA, S. KAZUYA, M.:: F CMOS inegraed circui: Hisory, curren saus and fuure prospecs, IEICE ransacions on Fundamenals of Elecronics, Communicaions and Compuer Sciences 94 (2011). [3] HWANG, J. H. LEE, M. Y. JEONG, C. Y. YOO, C.: Acive-C channel selecion filer unable from 6 khz o 18 MHz for sofware-defined radio, IEEE Inernaional Symposium on Circuis and Sysems (2005). [4] KIM, B. DAEIK, K.: Low-volage curren-mode inegraor for channel selecion filer, IEICE Elecronics Express 11 (2014). [5] SOTNE,. JEABEK, J. HEENCSA, N. POKOP,. LAHII, A. DOSTAL, T. VBA, K.: FirsOrder Transfer Secions wih econnecionless Elecronically econfigurable HighPass, AllPass and Direc Transfer Characer, Journal of Elecrical Engineering 67 No. 1 (2016). [6] KUAHASHI, P. HANUMOLU, P. K. TEMES, G. C. MOON, U. K.: Design of low-volage highly linear swiched- -MOSFET-C filers, IEEE J. Solid-Sae Circuis 42 (2007). [7] TSIVIDIS, Y. BANU, M. KHOUY, J.: Coninuous-ime MOSFET-C filers in VLSI, IEEE J. Solid-Sae Circuis 21 (1986). [8] LIU, J. FAHMY, A. KIM, T. MAGHAI, N.: A fully synhesized 0.4 V 77dB SFD reprogrammable SMC filer using digial sandard cells, IEEE Cusom Inegraed Circuis Conference (2015). [9] SUNGHO, B. JEONG, S. SUNKI, M. HWANG, M. W. KYUTAE, L. TENTZEIS, E. M.: A 0.56 MHz Acive-C LPF wih Fine Gain Seps Using Binary Inerpolaed esisor Banks, IEICE ransacions on elecronics 94 (2011). [10] KOUSAI, S. HAMADA, M. ITAKUA, T.: A Novel Auomaic ualiy Facor Tuning Scheme for a Low-Power Wideband Acive-C Filer, IEICE ransacions on Fundamenals of Elecronics, Communicaions and Compuer Sciences 92, yr2009. [11] KOUSAI, S. HAMADA, M. ITO,. ITAKUA, T.: A 19.7 MHz, fifh-order acive-c Chebyshev LPF for draf IEEE n wih auomaic qualiy-facor uning scheme IEEE J. Solid-Sae Circuis. [12] ASLANZADEH, H. A. PANKATZ, E. J. SNCHEZ-SINEN- CIO, E.: A 1-V+ 31 dbm IIP3, reconfigurable, coninuously unable, power-adjusable acive-c LPF, IEEE J. Solid-Sae Circuis 44 (2009), 495. [13] ITO,. IAKUA, T.: Phase compensaion echniques for low-power operaional amplifiers, IEICE ransacions on elecronics 93 (2010). [14] SUZUKI, T. TAKAO, O. YONEYAMA, T.: Design and simulaion of 4-muliplier using linear and sauraion regions of MOSFET complemenally, IEICE ransacions on Fundamenals of Elecronics, Communicaions and Compuer Sciences 85 (2002). eceived 6 Sepember 2016 Karolis Kiela (Ing, MSc) received his Ing and MSc degrees in he Deparmen of Compuer Engineering, from Faculy of Elecronics, Vilnius Gediminas Technical Universiy (VGTU), Lihuania in 2010 and 2012 years respecively. He is currenly pursuing he PhD degree in he Deparmen of Compuer Engineering from Faculy of Elecronics, Vilnius Gediminas Technical Universiy, Lihuania. His ineress are inegraed flexible baseband circuis for sofware defined radio applicaions. He is a suden member of IEEE and IEICE. omualdas Navickas (Prof, DrHb) received he elecronics engineer degree in 1973 a Kaunas Polyechnical Insiue; candidae of echnical science (CTS) degree of USS in 1984 from Elecronics Insiue of Science Academy Belorussia, Minsk; docor of echnical sciences degree in 1993 from Lihuanian Council of Science (nosrified CTS); Docor Habiliaus of echnological sciences, in From 2004 he is a professor a Compuer Engineering Deparmen of Vilnius Gediminas echnical universiy. His curren research ineress are in he field of micro-and nanoelecronics, high-speed inegraed circui design, self-formaion processes of nano- and microsrucures. Dr Habil omualdas Navickas is auhor of 4 books, he has made more han 80 publicaions, has 8 paens. He is a senior member of IEEE.

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