Current-Mode Circuits Based on SIMO OTA: Review and New Applications in Filters

Transcription

1 onteporary Enineerin Science, Vol., 009, no. 0, urrent-mode ircuit Baed on SMO OTA: Review and New Application in Filter Toa Dotal, Dept. of Radio Electronic, Brno Univerity of Technoloy, Purkyňova 8, 6 00 Brno, zech Republic European Polytechnic ntitute, Ltd., Ovobození 699, unovice, zech Republic dotal@feec.vutbr.cz Roan Sotner and Joef Slezak Dept. of Radio Electronic, Brno Univerity of Technoloy, Purkyňova 8, 6 00 Brno, zech Republic xotne00@tud.feec.vutbr.cz, xleza08@tud.feec.vutbr.cz Abtract The paper deal with dein of low-order R filter workin in current ode (M). A the baic buildin block, tranconductor (OTA) with inle input and ultiple output are ued. One-loop, two-loop and ulti-loop tructure are dicued. The adjoint VM-M tranforation i ued to obtain new circuit fro known VM prototype. The deined tructure are verified by Ppice iulation uin odel of OTA on tranitor level of decription. eyword: Analoue circuit, active R filter, tranconductor, current ode ntroduction laical active R filter [] baed on the voltae ode operational aplifier are widely ued in any low frequency application. However at hiher frequencie, uability of operational aplifier i liited. More uitable active block for hiher frequencie are for exaple tranconductor (OTA-) [] or it derivative uch a current differencin tranconductance aplifier (DTA) [8]. Thee coponent have followin attractive feature:

2 480 T. Dotal, R. Sotner and J. Slezak - hiher peed of the inal procein, operation at the hiher frequencie (everal MHz), - ipleentation in full interation for uin odern bipolar, MOS, BiMOS and aa technoloie, - the tranconductance paraeter ( ) can be electronically controlled by D current SET, what ive u the poibility of electronic tunin. However, the tranconductor have alo oe diadvantae. portant proble i low dynaic rane of input voltae. There i poibility of uin a linearization technique which increae the dynaic rane. The OTA baed circuit have been widely reearched in recent year ([]-[9]). Thee circuit work ainly in the voltae ode (VM), where the OTA-DSO active block (differential-input inle-output) are uually ued. Thee VM tructure are baed on voltae aplifier (ultiplier by contant), voltae interator and voltae feedback. Soe current ode circuit (filter) were publihed too, for exaple ulti-output OTA are ued in HN filter in reference []. Prore in inal procein ha hown that current ode (M) approach i better than the VM in ter of it wider bandwidth, hiher peed, lower D voltae and power biain, larer dynaic rane and iplicity in circuit ipleentation. The M network can be obtained by direct ynthei or fro the VM prototype uin the adjoint VM M tranforation [], what will be detailed dicued below. Note that the M circuit can be baed on the ae buildin block like the VM but for the current inal procein. The baic buildin block of M tructure i the current interator. Thee M block have different circuit topoloy and different active coponent are ued. n the cae of the OTA, intead of the DSO type, uin inle-input ultiple-output (SMO) type i ore uitable. Tranconductor with inle input and ultiple output The ybol of OTA-SMO i hown in Fi. a. deal OTA-SMO i voltae-controlled current ource with inle input and ultiple output. t operation i decribed by followin equation o ± o... ± on Vi, Z i Z o. () The tranconductance ( ) can be controlled externally by D current SET, what ive u poibility of electronic control of paraeter of OTA baed circuit. Note that linear relationhip between and SET i typical for MOS ipleentation operatin in weak inverion area. But it i not truth for aturation area where the relationhip between and SET i quadratic. Typical value of are in the rane of ten to hundred of μs for MOS technoloy (up to oe S for BJT). nput reitance of real OTA i very hih, fro hundred of kω to ten of MΩ. However the output reitance i aller (in the rane 50 kω - MΩ).

3 urrent-ode circuit baed on SMO OTA 48 Paraitic capacitance are very all (unit of pf). Maxial workin frequency of thee active block i everal hundred MHz. For very hih frequencie, relationhip between the paraeter and frequency i appearin. ( ). () τ The linearization technique ake the OTA able to handle input inal of the order of volt. a) V on o SET - o - on -V b) Fi.. Tranconductor OTA-SMO. a) Sybol, b) circuit diara. At firt iht, the idea of inle input OTA ive u the poibility of ipler circuit tructure without tandard differential tae at the input. However coniderin technoloy apect of thi, it i better to ue the well-known tructure of the input tae adopted fro [0]. The circuit wa little odified. nvertin input (V-) wa rounded. There i alo poibility of adjutin of the tranconductance of OTA ( ) by varyin control current SET. Furtherore for obtainin other current replica ± o with oppoite phae, ore current irror were added to input tae. The reultin circuit diara for BJT technoloy i hown in Fi. b. Siilar circuit for the MOS technoloy wa iven in []. Zero-order OTA-SMO M circuit Firtly, let uarize all OTA-SMO buildin block neceary for

4 48 T. Dotal, R. Sotner and J. Slezak realization circuit in the M. The baic zero-order buildin block i current ditributor (Fi. a), which producin n current replica ( on ) of the input current ( i ). urrent ain of thi block i exactly one. Note that at input port thi circuit can alo eulate rounded reitor Z i /. Floatin reitor eulation require two OTA. Addin a reitor at the input (Fi. b), attenuator i obtained. The current tranfer function i. () i < Reovin the neative feedback, ulti-output current aplifier or ultiplier by contant i obtained (Fi. c). The ain i ( ). (4) i ± Thi circuit can be alo ued a weihted current ditributor. t can be odified for interated circuit realization a hown in Fi. d. Note that current uer can be realized very eay by only inle node connection what coe fro current irchhof law. Thi i one of advantae of the current ode. a) b) c) d) Fi.. Zero order M circuit with OTA-SMO. a) urrent ditributor, b) current anttenuator, c) current aplifier, d) odification for for. 4 OTA-SMO current interator Baic firt-order buildin block, epecially for the M filter, i the current interator. Two circuit diara of thi block baed on the OTA-SMO are hown in Fi.. The ideal (lole) interator in Fi. a ha iple current tranfer function ( ), τ. (5) τ The loy interator in Fi. b ha tranfer function

5 urrent-ode circuit baed on SMO OTA 48 ( ), τ τ, (6) tranfer function of it odification in Fi. c i ) (. (7) V i i o... - o on a) b) c) Fi.. urrent interator with OTA-SMO. a) deal interator, b) c) loy interator. 5 Exaple of feedback loop tructure with OTA in M The circuit iven above (Fi. c) can be eneralized by the odel in Fi. 4. t conit of the inle OTA-SMO, three adittance and one loop of current feedback ( FB ). Note that iilar odel with five adittance wa firtly publihed in [5] and dicued in []. However the ipler odel in Fi. 4 i uitable for our application. Uin adjoint tranforation, voltae ode circuit dicued in [4] can be obtained. n [4] yteatic dein procedure of thee circuit baed on the autonoou network with the inle OTA-DSO and voltae feedback wa decribed and everal appropriate circuit were preented and tudied. Fi. 4. eneral M odel with one OTA-SMO and three adittance.

6 484 T. Dotal, R. Sotner and J. Slezak The eneral circuit in Fi. 4 wa ybolically analyzed uin prora SNAP. The reultin current tranfer function can be written in eneral ybolic forula i o ) ( Y Y Y Y Y Y Y Y. (8) 5. OTA firt-order circuit For the firt-order circuit, one capacitor and two reitor can be choen. hooin Y, Y, Y, the circuit realize low pa (LP) filter with the followin tranfer function ) ( ) ( ) (. (9) Another LP tructure can be obtained if Y, Y, Y. The hih pa filter (HP) i realized for ettin Y, Y and Y. Then the eneral tranfer function (8) i tranfored to ) ( ) (. (0) 5. Second-order M circuit with inle OTA The eneral tructure baed on inle OTA-SMO (Fi. 4) can be alo ued for the econd order M circuit. The iplet econd order LP i obtained by ettin Y, Y, Y, the reultin current tranfer function i ) ( ) (. () oparin () with the tandard for () 0 ) ( Q ω ω ω, () Forula for cut-off frequency and quality factor of frequency filter are ω, Q, () For iplification of the dein and for decreain of value of enitivitie, we et. Forula for value of the other coponent are very iple Q ω, Q ω. (4) Senitivitie of the filter are extreely low 0,5 Q Q p p p p S S S S S S ω ω ω ω, 0 0,5 S S Q Q. (5)

7 urrent-ode circuit baed on SMO OTA 485 A odified circuit can be obtained if another reitor i added parallel to the firt capacitor. Then Y, Y, Y, and the current tranfer function i ( ). (6) [ ( ) ] ( ) Another odified circuit i obtained for ettin Y, Y, Y. The band pa filter (BP) i realized for Y, Y and Y. For real BP, hiher value of quality factor i deired. For enurin thi, the feedback i chaned to be poitive. t correpond to witchin of the phae of the FB current FB. Then output terinal ha reveral arrow a hown in circuit diara (Fi. 5). Thi biquad wa ybolically analyzed by SNAP. Reultin current tranfer function i ( ) a. (7) b b b0 [ ( ) ] Siplification and lead to the followin dein equation. enter frequency and quality factor are ω 0, Q Senitivitie of the center frequency are very low ω o ωo ωo ωo o S S S S 0,5, 0 However the enitivitie of the quality factor are. (8) Q Q Q S S S 0, 5 Q, S Q 0,5 Q, S Q 0,5 Q S ω, (9), (0) what indicate a little dependence of Q and oe proble for dein of thi BP with larer Q. Fi. 5. Bandpa biquad baed on inle OTA-SDO. 6 Structure in current ode with two feedback loop n the chapter above we have dicued the one-loop feedback M tructure realizin everal biquad. oparable feature have the tructure with two-loop

8 486 T. Dotal, R. Sotner and J. Slezak feedback (TLF). Fi. 6 how two confiuration of thee TLF tructure uin inal flow raph (SF) odel. H H a) H H b) Fi. 6. Two-loop feedback M tructure. a) Sued feedback type, b) ditributed feedback type. Both of thee tructure include two loop conitin two current aplifier with ain F k and two ideal current interator (Fi. a) with tranfer function (). ( ) H, H, () j j The difference between thee two tructure i in the topoloy of feedback. n Fi. 6a there i the ued feedback type (SF), alo called follow-the-leader feedback canonical tructure. n the econd one (Fi. 6b), output inal i connected to the input of all interator. Thi tructure i called ditributed feedback type (DF). t i alo called invere follow-the-leader feedback. Note that in thee raph all node are current. haracteritic equation of pole can be derived fro deterinant of SF. For DF tructure (Fi. 6b), the deterinant reult in the followin polynoial for F F D ( ). () τ ττ oparin () with the denoinator of (), the dein equation are ω F, τ. () o Q F τ τ For iven ω and Q, the dein require ettin of the feedback coefficient F k and the tie contant τ j. Fro the equation () it can be eay hown that thi tructure ha very low value of enitivitie ω o ωo ωo o Q Q Q o, 0 S ω. (4) S F Sτ Sτ 0,5 j F τ j τ S ω, F S Sτ Sτ 0, 5, F F For circuit realization of the TLF tructure in the M an appropriate action i taken to odify and coplete the baic SF (Fi. 6). n Fi. 7 i hown the coplete SF of the DF-TLF tructure developed fro baic SF on Fi. 6b by copletin with all poible input ( i ) and output ( o ) current. Note that the untaed branche have the ain value equal one.

9 urrent-ode circuit baed on SMO OTA 487 H H Fi. 7. SF odel of the TLF-DF-M tructure. The SF iven in Fi. 7 can be realized by two OTA-SMO ideal current interator (Fi. a) and two OTA-SMO current aplifier (Fi. c). The reultin circuit diara i hown in Fi. 8. Sybolical analyzin in SNAP, followin dein equation are obtained ω 4, 4. (5) p Q Thi analyi alo how that the propoed circuit i able to realize ultifunctional frequency filter with tranfer function of type (LP, BP, HP). Fi. 8 decribe connection of input and output to the tructure of the filter. For exaple if the input current i i and the output current i o, LP tranfer function i obtained o ( ). (6) i 4 for input current i and output current o, BP i obtained o ( ). (7) i 4 Preented tructure in Fi. 8 can be iplified if feedback coefficient F k are et to one (F F l) or are et to the ae value F F. On the other hand the current ditributor (Fi. a) can be connected to the input of thi circuit ipleentin a coon ultiple drivin ( i, i, i, dot line in Fi. 8) to produce univeral biquadratic characteritic. More coplex tranfer function i alo obtained if the output current o, o, o and o4 in Fi. 8.are ued.

10 488 T. Dotal, R. Sotner and J. Slezak 4 o4 o i R i o o i Fi. 8. Two-loop ditributed feedback biquad in current ode. Siilar M tructure, which are copoed of two lole interator in loop with uator have been already dicued in [9] and [6]. 7 Adjoint VM-M tranforation The M circuit can be obtained fro the VM prototype uin the adjoint VM-M tranforation. The principle of thi ethod wa decribed in []. The adjoint tranforation can be alo applied in the circuit baed on the OTA. Note that after application of the tranforation, the node of input voltae are tranfored to node of output current and reverely node of output voltae are tranfored to node of input current. Alo active functional block of the prototype are replaced by adjoint counterpart. n the cae of the OTA-DSO the correpondin adjoint active block i OTA-SDO where input and output port are utually interchaned. The reultin adjoint network ha equivalent tranfer function like tranfer function of it prototype. Note that the OTA-SDO can be eneralized to OTA-SMO. The other port can be ued a the output of the hole filter (ee OTA- in Fi. 9b).

11 urrent-ode circuit baed on SMO OTA R 4 - V i4 - V i V o4 R V i - V o V o - V o a) 4 o4 R 4 i4 R o i o o i i Fi. 9. Adjoint VM-M tranforation. a) Ditributed feedback voltae ode -nd order tructure, b) Adjoint ued feedback current ode tructure. b) A an illutratin exaple, the OTA-DSO voltae ode TLF-DF tructure fro [9] (Fi. 9a) wa choen a a prototype. Applyin the adjoint tranforation, the DF-VM tructure (Fi. 6b) i tranfored to the tructure SF-M (Fi. 6a). The reultin circuit i hown in Fi. 9b. Thi ultifunctional biquad (Fi. 9b) wa detailed decribed in [7]. LP, BP, HP tranfer function can be eay realized uin different input and output. All paive eleent (R and ) are rounded, which i uitable for practical fabrication. Band reject filter or odified LP and HP filter with zero can be obtained if certain output inal are ued. 8 urrent ode ultiple loop tructure Advantae of the OTA-SMO i uperb in the current ode ulti-loop

12 490 T. Dotal, R. Sotner and J. Slezak feedback (MLF) tructure [], epecially if ore current ditribution are ued. The eneral current tranfer function of any order (n) ( ) a a... a a n n out n n 0 (8) n n inp bn bn... b b0 can be directly ipleented by one of the MLF tructure well known in the claical VM. For the M, econd canonical analo tructure follow-the-leader feedback (FLF) with output uation (FLF-OS) i the ot uitable. Bi advantae of current ode i very eay realization of uation of current by only inle node connection. The baic SF odel of FLF-OS-M correpondin to forula (8) wa preented in []. However the circuit realization of thi SF need a lot of ultiplier (ultiplication by coefficient a i, b i ) what i reaon for rearranin the tranfer function (8) to the followin for an an a bn bn ( ) bn b b n n bn n bn a... b... n bn n bn a b 0 n bn 0 n bn. (9) The odified SF correpondin to (9) i hown in Fi. 0. The ain of oe of the branche i et to one and half of the ultiplier can be oitted and replaced by direct connection. To illutrate the tructure FLF-OS-M baed on OTA-SMO, univeral 4 th -order ultifunctional (LP, BP, HP) filter wa choen. For thi cae the SF fro Fi. 0 can be rearraned to the for iven in Fi.. Fi. 0. Modified SF of the tructure FLF-OS-M. The circuit realization of thi SF (Fi. ) require four current interator (Fi. a) ipleented in branche in direct path (/) and one current ditributor ipleented in the firt node. The current ditributor can be oitted if HP output i not required. n thi cae the iplet variant hown in Fi. i obtained. Thi tructure i uitable for interated for becaue all capacitor are rounded. Four OTA with two or three current output are ipleented. To obtain other BP with ayetrical characteritic, OTA ( ) and OTA ( ) are uppleented by current output (BP A ). The BP i tandard yetrical BP of the 4 th -order. The tranfer function of BP i

13 urrent-ode circuit baed on SMO OTA 49 Fi.. The SF of the ultifunctional 4 th -order filter. i et et et et4 4 4 BP A BP BP A LP Fi.. Electronically tuned ultifunctional 4 th -order filter. The LP tranfer function i LP ( ) BP ( ) a BP o. (0) 4 i b4 b b b b0 a LP. () 4 i b4 b b b b0 n eneral forula (0) and (), the relationhip between coefficient and circuit coponent are b 4,,,, 4. () b f tranconductance are et to b a b b 0 a 0 /, /.4, 4 /6.8 () the filter can be iply electronically tuned by control current SET. Relationhip between control current SET and traconductance i linear. Siilar econd-order filter ha been preented in []. 4 9 Siulation reult n the iulation of OTA-SMO on tranitor level of decription (Fi. ), odel

14 49 T. Dotal, R. Sotner and J. Slezak of BJT are ued. n [7], thee odel are ued for realization of ulti-output current follower. Thee odel of OTA have few advantae. The firt one i linear dependence of on D control current SET ( 0. SET in the rane between 0 ua and A and for V ±.5 V). The econd one i lower input voltae offet in coparion to noncacode MOS realization. Finally, frequency bandwidth i approxiately 50 MHz. Diadvantae are lower input ipedance, frequency dependence of input ipedance and hiher power conuption. The econd order BP filter i iven in Fi. 5. t wa deined for: center frequency f MHz, axially flat (Butterworth filter) pa-band, ain - db, top-band frequency f MHz, for the iniu dapin - 5 db. Reultin coefficient of the denoinator of (7) are b 0,9449.0, b 8, , b. (4) hooin 470 pf, value of other coponent are and b 4, 5 S. (5) b., 9 S 0 The circuit fro Fi. 5 uin thee coponent value (5) and odel of OTA on tranitor level of decription (Fi. b), wa iulated by PSpice. The reultin anitude repone i hown in Fi.. 0 [db] ,0E04,0E05,0E06,0E07 f[hz],0e08 Fi.. Siulated anitude repone of the BP biquad (Fi. 5). Siilarly the two-loop ditributed feedback ultifunctional biquad fro Fi. 8 wa verified for f 0 MHz and quality factor Q. hooin nf, 4 0 S, 4 0 S ( SET SET4 500 ua) and in accordance to (5),tranconductance are et 6. S ( SET SET 5 ua). Siulated anitude repone of the filter are iven in Fi. 4. Tranfer function of type LP ( O / ), BP ( O / ), BR ( O / ) and HP ( O - O / ) are obtained. Varyin of tranconductance, value of quality factor Q and baic ain 0 are adjuted. A one can ee fro (5), (6) and (7), it i not poible to

15 urrent-ode circuit baed on SMO OTA 49 adjut Q, 0 and f independently. 5 [db] SET SET 5 ua -0 f 977 khz Q V ±.5 V R L 50 Ω SET 500 ua HP BR LP BP iulation -45 ideal cae (theoretical) -50,0E04,0E05,0E06,0E07,0E08 f [Hz] Fi. 4. Siulated anitude repone of the BP biquad fro Fi. 8. The fourth order ultifunctional filter of the FLF-OS-M tructure baed on OTA-SMO (Fi. ) wa deined for the followin pecification: axially flat Butterworth filter, LP and yetrical BP type, cut-off frequency and center frequency f f 0 MHz, iniu pa-band ain - db, top-band frequency f MHz, for the iniu dapin - 5 db. The correpondin coefficient of the denoinator of (8) are b 0, , b 6, , b, , b, , b 4. Uin dein equation () and ettin all capacitor pf, followin value of tranconductance are obtained 7,7 S,,86 S,,6 S, 4, S. The reultin Ppice anitude repone are iven in Fi. 5. f all tranconductance ( ) are varied iultaneouly, the filter can be very eay tuned. The tunin of the LP filter i hown in Fi 6. Alo BP i tuned. Decription of iulated reult of Fi. 5 and Fi. 6 i uarized in Tab.. 0 [db] ,0E04,0E05,0E06 f[hz],0e07 Fi. 5. Siulated anitude repone of the 4 th order filter (Fi. ).

16 494 T. Dotal, R. Sotner and J. Slezak 5 [db] ,0E0,0E04,0E05,0E06,0E07,0E08 f[hz] Fi. 6. Siulation of the tunin of the LP filter (Fi. ). Tab.. ontrollin the cut-off frequency by the tranconductance. urve index [S] f - db [khz] 4 5 0,,0 7,7 0,0 0, oncluion Tranconductor (OTA) with ultiple output are uitable for uin epecially in current ode circuit. Multi-output active block ive ore flexibility in dein of frequency filter. The paper decribed how to ue OTA-SMO block for realization of ulti-output current ditributor, ulti-output current interator and ulti-output current aplifier. One-loop, two-loop and ulti-loop filter tructure in current ode were dicued. Dein procedure i baed on the inal flow raph technique. n the current ode ulti-loop feedback tructure the OTA-SMO are baic buildin block. n ot of econd-order application, two or three-output active block are ufficient. The adjoint VM-M tranforation wa ued for tranforation of VM prototype to new OTA-SMO baed circuit. Deined circuit were verified in Ppice uin odel of OTA on tranitor level. Siulation confired that deined circuit are uitable for hih frequency application in video band.

17 urrent-ode circuit baed on SMO OTA 495 Acknowledeent. Reearch decribed in the paper i a part of the OST Action 080 RF/Microwave counication ubyte for eerin wirele technoloie, financed by the zech Minitry of Education by the rant no. O0906. Reearch decribed in the paper wa financially upported by the zech Minitry of Education under reearch prora MSM and zech Science Foundation under project No. 0/08/H07. Reference [] HEN, W.. The circuit and filter handbook. R Pre, Boca Raton Florida, 995. [] TOUMAZOU,., LDEY, F. J., HAH, D.. Analoue dein: The current ode approach, Peter Pererinu Ltd., London, 990. [] DELYANNS, T., SUN, Y., FDLER, J.. ontinuou-tie active filter dein, R Pre, Boca Raton Florida, 999. [4] EER, R. L., SANHEZ, S. E. Active filter dein uin operational tranconductance aplifier: a tutorial. EEE ircuit and Device Maazine, 985, vol., p [5] SUN, Y., FDLER, J.. Novel OTA- realization of biquadratic tranfer function. nternational Journal of Electronic, 99, vol. 75, p [6] SUN, Y., FDLER J.. urrent-ode OTA- realization of arbitrary filter characteritic. Electronic Letter, 996, vol., no., p [7] SUN, Y., FDLER J.. urrent-ode ultiple-loop filter uin dual-output OTA and rounded capacitor. nternational Journal of circuit theory and application, 997, vol. 5, no., p [8] AAR,., ANDAY, F., UNTMAN, H. On the realization of OTA- filter. nternational Journal of circuit theory and application, 99, vol., no., p [9] SANHEZ, S. E., EER, R. L., NEVAREZ, L. H. eneration of continuou-tie two interator loop OTA filter tructure. EEE Tran. ircuit and Syte, 988, vol. 5, no. 8, p [0] Data heet LM 700 [on line]. Available: [] BOLE, D.; BOLOVÁ, V.; OLA, Z. Univeral current-ode OTA- HN biquad. nternational Journal of Electronic, ircuit and Syte (JES), 007, vol., no. 4, p. 4-7.

18 496 T. Dotal, R. Sotner and J. Slezak [] DOSTÁL, T. Filter with ulti-loop feedback tructure in current ode. Radioeineerin, vol., no., 00, pp. -6. [] DOSTÁL, T. All-pa filter in current ode. Radioeineerin, vol. 4, no., 005, pp [4] DOSTÁL, T. On canonical tructure of AR biquadratic filter with inle tranconductor. Radioeineerin, vol. 5, no., 006, pp. -6. [5] AL-HASHM, B. urrent-ode filter tructure baed on dual-output tranconductance aplifier. Electronic Letter, vol., no., 996, pp [6] SUN, Y., FDLER J.. Structure eneration of current-ode two interator loop dual-output OTA rounded capacitor filter. EEE Tran. ircuit and Syte, 996, vol. 4, no. 9, p [7] JERABE, J., VRBA,. Dein of a frequency filter by help of paive interator with current ode eleent. Elektrorevue zech Republic nternet Journal of Eelectrical Enineerin ( 009, Vol. 009, No. 9,. -7. [8] ESN, A. U., BOLE, D., HANOLU, E., BOLOVA, V. urrent-ode HN filter eployin urrent Differencin Tranconductance Aplifier. nt. J. Electronic and ounication, 006, Vol. 60, No. 6, pp Received: May, 009