Compact quadrature oscillator with voltage and current outputs using only single VDTA and grounded capacitors

Transcription

1 Indan Jurnal f Pure & Appled Physcs Vl. 55, Aprl 07, pp Cmpact quadrature scllatr wth vltage and current utputs usng nly sngle VDTA and grunded capactrs Wrapng Tangsrrat* Faculty f Engneerng, Kng Mngkut s Insttute f Technlgy Ladkrabang, Bangkk 050, Thaland Receved Nvember 05; revsed 30 December 06; accepted 5 February 07 A pssble desgn f the cmpact snusdal quadrature scllatr usng sngle vltage dfferencng transcnductance amplfer (VDTA) and nly tw grunded capactrs has been presented. The presented quadrature scllatr prvdes the fllwng attractve prpertes: () cannc frm and resstr less structure; () avalablty f the explct quadrature vltage utputs and current utputs; () electrnc cntrllablty f the scllatn frequency (ω 0 ); and (v) lw actve and passve senstvtes. T supprt the valdty f the scllatr, PSPICE smulatn results have als been prvded. Keywrds: Vltage dfferencng transcnductance amplfer, Quadrature scllatr, Dual-mde peratn, Resstrless crcut, Electrncally tunable Intrductn The vltage dfferencng transcnductance amplfer (VDTA) s the recently defned cntrllable actve buldng blck, and ncreasngly beng used n numerus applcatns. In the mre recent wrks, ts applcatns and advantages especally n the synthess f actve flters -6 and snusdal scllatrs 7-9 have ncreased cnsderably as they have been fund t be able t prvde the electrnc tunng thrugh the transcnductance gan g m f the VDTA, and reduce the number f the passve cmpnents used fr ther crcut realzatns 0. Snusdal quadrature scllatrs,.e., generatrs prducng tw dentcal snusdal utput sgnals equally n ampltude and frequency but havng 90 phase shfted, are very frequently used n wde scpe f electrnc engneerng applcatns. Fr ths reasn, a number f vltage and current-mde snusdal quadrature scllatrs have been already realzed by utlzng the advantages f dfferent types f versatle actve buldng blcks 9,-7. Hwever, the prevusly quadrature scllatrs suffer frm ne r mre f the fllwng dsadvantageus features: () They emply mre than ne actve crcut buldng blck 9,-,5-6. () They use any external passve resstrs, whch s nt cannc and resstrless structure -0,-7. () They d nt prvde electrnc cntrllablty t ther crcut parameters -5,8,4-5 *E-mal: drwrapng@yah.cm (v) The passve cmpnents used n ther realzatn are flatng, whch s nt cnvenent fr ntegrated crcut mplementatn -5,9-0,-3,5. (v) They cannt generate vltage-mde and currentmde quadrature sgnals smultaneusly 9,-3. In ths paper, a smple scheme fr the realzatn f the snusdal quadrature scllatr wth vltage and current utputs has been cnsdered. T perfrm a cmpact and resstrless quadrature scllatr, the crcut s based n the use f a sngle VDTA and nly tw grunded capactrs. When cmpared t the already reprted wrks 9,-7, the prpsed dual-mde quadrature scllatr exhbts the fllwng salent characterstcs: uses nly ne actve element and tw grunded capactrs, a resstrless desgn, dual-mde peratn,.e., vltage and current quadrature utputs, hgh-mpedance current utputs, electrnc adjustment f the frequency f scllatn, and lw senstvty perfrmance. The characterstcs f the crcut are studed n detal and demnstrated thrugh the PSPICE smulatn wth acceptable results. Crcut Descrptns The electrcal symbl f the VDTA s shwn n Fg.. Its deal characterstc can be descrbed by the fllwng matrx: p vp n v n = z gmf gmf 0 0 v zc x vz ()

2 TANGSRIRAT: COMPACT QUADRATURE OSCILLATOR WITH VOLTAGE AND CURRENT OUTPUTS 55 where g mf and g ms are the frst and secnd transcnductance gans f the VDTA, respectvely. In general, bth transcnductance gans are cntrllable electrncally by the external DC bas currents. Accrdng t abve descrbng-relatns, the dfferental nput vltage (v p -v n ) s cnverted t currents at the termnals z ( z ) and zc ( zc ), respectvely, by the transcnductance g mf, and the crrespndng vltage drp at the termnal z s cnveyed t currents at the termnals x ( x ) by the transcnductance g ms. The pssble CMOS realzatn f the VDTA s shwn n Fg., whch actually cnssts f tw ntercnnected Arbel-Gldmnz transcnductances 8. Each f them realzes tw ndependent electrncally tunable transcnductance gans g mf and g ms. Ther values can be apprxmated as, respectvely: g g g g g 3 4 mf + g + g g3 + g4 () g g g g and + g5 + g6 g7 + g8 where W g I C L (3) = Bµ x s the transcnductance value f the -th MOS transstr ( =,,, 8), I B s the bas current f the MOS M, µ s the free carrer mblty n the channel, C x s the gate-xde capactance per unt area, and W and L are the channel wdth and length f the transstr M, respectvely. A realzatn scheme fr a cmpact snusdal quadrature scllatr wth explct vltage and current utputs s shwn n Fg. 3. The cnfguratn s cannc n cmpnent cunt, snce t cnssts f merely ne VDTA and tw grunded capactrs. It shuld be nted that the tw quadrature current utputs and exhbt hgh-nput mpedances that permt the ease f cascadng, and bth capactrs C and C are grunded that s partcularly benefcal frm the vewpnt f ease f mnlthc ntegratn. A rutne crcut analyss f Fg. 3 yelds the fllwng results. The vltage transfer functn f the frst transcnductance stage f the VDTA s gven by: T ( s) F V ( s) g V ( s) sc mf = = (4) and that f the secnd transcnductance stage s: V ( s) TS ( s) = = (5) V ( s) sc Fg. Crcut representatn f the VDTA Hence, the lp gan f Fg. 3 can be expressed as: Fg. CMOS mplementatn f the VDTA

3 56 INDIAN J PURE & APPL PHYS, VOL 55, APRIL 07 gmf T ( s) T ( s) = (6) F S s CC Fr snusdal scllatns, the lp gan s set t unty at s = jω. Ths, alng wth Eq. (6), gves the fllwng characterstc equatn fr Fg. 3: s CC gmf 0 + = (7) Frm Eq. (7), the scllatn frequency can als be btaned as: g g ω = π f = (8) mf ms CC Fr smplcty, f g m = g mf = g ms and C, = C = C, then the parameter ω n Eq. (8) turns t: f gm = (9) πc Ths means that the frequency f scllatn f can be tuned electrncally by means f g m thrugh adjustng the external bas currents I B = I BF = I BS. Als frm Fg. 3, the tw marked quadrature vltages (v and v ) and currents ( and ) are related as, respectvely: v jωc = v (0) jωc and = () whch are ensured that the utput vltages and the utput currents are n quadrature sgnals. Fg. 3 Prpsed dual-mde quadrature scllatr 3 Trackng Errr Analyses and Senstvty Study The practcal characterstcs f the VDTA takng nt accunt the trackng errrs f the devce can be expressed as: p vp n v n = z βf gmf βf gmf 0 0 v zc x 0 0 βs 0 vz () where β F and β S are respectvely the nn-deal transcnductance gans f the VDTA, whch devate frm ther deal values by trackng errrs ε F and ε S, where ε F, ε S <<. Therefre, cnsderng the effects f the VDTA nn-dealtes defned n Eq. (), the mdfed ω f the prpsed quadrature scllatr n Fg. 3 can be wrtten as: β β g g F S mf ms ω = (3) CC It s clearly seen frm Eq. (3) that the ω value s slghtly affected by the transcnductance trackng errrs f the VDTA. Hwever, these devatns can be cmpensated by pre-dstrtn f the transcnductance gans (g mf and/r g ms ) f the VDTA. The senstvty f the ω fr the scllatr n Fg. 3 wth respect t ts actve and passve cmpnents can be derved as : ω ω ω ω Sg = S mf g = S S ms β = F β = (4) S and S ω ω = S = (5) C C Frm Eqs (4) and (5), all the actve and passve senstvtes are wthn 0.5 n abslute value, whch s an advantageus feature f the prpsed canncal scllatr. 4 Effects f Parastc Impedances In rder t cmplete nn-deal analyss, t s useful t cnsder the parastc elements f the VDTA devce used n the quadrature scllatr f Fg. 3. Includng the crrespndng termnal parastc elements, the practcal mdel f the VDTA can be shwn 5 n Fg. 4. It s seen that there are the parastc resstances and capactances (R p //C p ), (R n //C n ), (R z //C z ), (R x //C x )

4 TANGSRIRAT: COMPACT QUADRATURE OSCILLATOR WITH VOLTAGE AND CURRENT OUTPUTS 57 appearng n parallel cnnectn at the crrespndng termnals f the VDTA. Typcally, these parastc resstances and capactances are n the rder f several MΩ and pf, respectvely. Cnsderng these parastc, the scllatr gven n Fg. 3 s then mdfed t Fg. 5, where R = (R p //R x ), C = (C //C p //C x ) and C = (C //C z ). Hwever, n practce, the values f the external capactrs C and C can be cnsdered t be suffcently larger than the parastc capactance values,.e., C >> (C p //C x ) and C >> C z. As a result, t becmes bvus that C C and C C. Therefre, the ttal mpedance at the termnal p (Z ) s apprxmated t: Z R (6) R Cs + The actn f Z at the termnal p f the actual VDTA lmts the perfrmance f the scllatr at the lwfrequency range. Accrdng t Eq. (6), the peratng frequency range can be easly defned as: Fg. 4 Practcal mdel f the VDTA ncludng ts termnal parastc mpedances Fg. 5 Prpsed quadrature scllatr f Fg. 3 cnsderng the termnal parastc mpedances f the VDTA f >> (7) π ( R / / R ) C p x In a smlar analyss, the frequency restrctn stemmed frm the z-termnal parastc mpedance (Z ) can als be defned as: f >> (8) π R C z 5 Smulatn Results and Dscussn The prpsed quadrature scllatr wth vltage and current utputs n Fg. 3 was smulated usng PSPICE prgram. In smulatns, the CMOS-based VDTA crcut gven n Fg. was used wth the TSMC 0.5 µm CMOS prcess technlgy, and ±.5 V vltage supply. The aspect rats f the MOS transstrs are ndcated n Table. As an example, the prpsed quadrature scllatr n Fg. 3 was desgned t btan the scllatn frequency f = 95 khz. By usng Eq. (9), the desgned cmpnent values were calculated as: g m = g mf = g ms = 0.6 ma/v (I B = I BF = I BS = 00 µa) and C = C = C = nf. Fgure 6 shws the smulated steady-state wavefrms f quadrature utputs (v, v ) and (, ). The smulated f was measured as apprxmately 97 khz, where the quadrature utputs dfferent n phase by 86. Fgure 7 shws the smulated frequency spectrums f the quadrature utput wavefrms, where the values f the crrespndng ttal harmnc dstrtn (THD) at all the utputs were arund.46 %. Als frm the smulatn results, the ttal pwer cnsumptn was fund t be.09 mw. Fr the abve desgned values, the electrnc cntrl prperty f f wth a varable I B s dsplayed n Fg. 8. Obvusly, the f s vared frm apprxmately 30 khz t 66 khz fr I B, varatn frm 0 µa t 300 µa, respectvely. A cmparsn results Table Transstr aspect rats used n the CMOS VDTA crcut f Fg. Transstrs W/L (µm/µm) M - M 5.75/0.5 M 3 - M 4, M 9 M 0 0.3/0.5 M 5 M /0.5 M 7 M 8 3.3/0.5 M - M 5./0.5 M 3 4.5/0.5 M 4 5.5/0.5 M 5 8/0.5 M 6 3./0.5 M 7 - M 8.8/0.5

5 58 INDIAN J PURE & APPL PHYS, VOL 55, APRIL 07 Fg. 6 Smulated steady-state wavefrms f quadrature utputs (a) utput vltages v and v and (b) utput currents and Fg. 7 Smulated frequency spectrums f quadrature utputs (a) utput vltages v and v and (b) utput currents and

6 TANGSRIRAT: COMPACT QUADRATURE OSCILLATOR WITH VOLTAGE AND CURRENT OUTPUTS 59 Reference Number f actve element Table Cmparatve study f the prpsed quadrature scllatr n Fg. 3 wth the prevus desgns Number f R + C Grunded elements nly Electrnc tunng fr the prpsed cmpact quadrature scllatr desgned n ths wrk and the prevusly reprted nes 9,-7 s summarzed n Table. 6 Cnclusns Ths paper prpses a crcut desgn fr a cmpact resstrless snusdal quadrature scllatr. The prpsed dual-mde quadrature scllatr features the Dual-mde quadrature utputs Technlgy Supply vltages (V) THD (%) Ttal pwer cnsumptn (mw) [9] VDTA = 0 + yes yes n TSMC 0.8-µm ± N/A [] CCII = yes n n AD844 ± N/A N/A [] DVCC = n n n TSMC 0.35-µm ± N/A 3.7 [3] CDBA = 3 + n n n AD844 ±.58 N/A [4] CDBA = 4 + n n n AD844 ±.95 N/A [5] CDBA = 3 + n n n AD844 ±.94 N/A [6] CCCDBA = + yes yes n TSMC 0.8-µm ±.00 N/A [7] GCFTA =, VF = + yes yes n PR00N, NP00N ±.67 N/A [8] DVCC = yes n n 0.5-µm CMOS ±.5.00 N/A [9] CDTA = 4 + n yes n MIETEC 0.5-µm ±.5.00 N/A [0] CFTA = + n yes n MIETEC 0.5-µm ±.5 N/A N/A [] CDTA = yes yes n PR00N, NP00N ± N/A [] CDTA = + n yes n 0.7-µm CMOS N/A 0.6 N/A [3] CDTA = + n yes n MIETEC 0.5-µm ± N/A [4] FDCCII = + yes n n TSMC 0.8-µm ± FDCCII =, 3 + yes n yes [5] CDBA = 3 + n n yes Macr-mdel N/A N/A N/A [6] CDTA = + yes yes yes MIETEC 0.5-µm ±.5 N/A N/A [7] CCTA = + yes yes yes PR00N, NP00N ± N/A Ths wrk VDTA = 0 + yes yes yes TSMC 0.5-µm ± Ntes: N/A = Nt Avalable, CCII = Secnd-Generatn Current Cnveyr, DVCC = Dfferental Vltage Current Cnveyr, CDBA = Current Dfferencng Buffered Amplfer, CCCDBA = Current Cntrlled Current Dfferencng Buffered Amplfer, GCFTA = Generalzed Current Fllwer Transcnductance Amplfer, UGVF = Unty-Gan Vltage Fllwer, CDTA = Current Dfferencng Transcnductance Amplfer, CFTA = Current Fllwer Transcnductance Amplfer, FDCCII = Fully- Dfferental Secnd-Generatn Current Cnveyr. Fg. 8 f varatn wth I B fllwng salent benefts smultaneusly : () uses nly ne VDTA and tw grunded capactrs, whch s a canncal and resstrless cnfguratn; () prduces vltage-mde as well as current-mde quadrature utputs explctly; () prvdes hghutput mpedance quadrature currents, thus permt the feature f cascadablty; (v) ffers an electrnc tunng f the scllatn frequency; and (v) has lw actve/passve senstvty perfrmance. It has been shwn by PSPICE prgram that the smulatn results agree well wth the theretcal cnclusns. Acknwledgment Ths wrk s supprted by the Faculty f Engneerng, Kng Mngkut s Insttute f Technlgy Ladkrabang (KMITL). The authr als wuld lke t thank Ms Sastaprn Thengjt fr perfrmng the crcut smulatns. References Yesl A, Kacar F & Kuntman H, Rad Eng, 0 (0) 63. Prasad D, Bhaskar D R & Srvastava M, Indan J Pure Appl Phys, 5 (03) Yesl A & Kacar F, Radengneerng, (03) 06.

7 60 INDIAN J PURE & APPL PHYS, VOL 55, APRIL 07 4 Satansup J, Pukkalanun T & Tangsrrat W, Crcuts Syst Sgnal Prcess, 3 (03) Satansup J & Tangsrrat W, Mcrelectrn J, 45 (04) Jerabek J, Stner R & Vrba K, Rev Rum Sc Technl, 59 (04) Prasad D & Bhaskar D R, ISRN Electrn, 0 (0) d: 0.540/0/ Herencsar N, Stner R, Ktn J, Msurec J & Vrba K, Elektrn Elektrtech, 9 (03) Prasad D, Srvastava M & Bhaskar D R, Crcuts Syst, 4 (03) Blek D, Senan R, Blkva V & Klka Z, Rad Eng, 7 (008) 5. Mnhaj N, Int J Electrn, 94 (007) 663. Maheshwarang S, Mhan J & Chauhan D S, J Crcuts Syst Cmput, 9 (00) Tangsrrat W & Pstchalermpng S, Frequenz, 6 (007) 0. 4 Tangsrrat W, Pukkalanun T & Surakampntrn W, Act Passve Electrn Cmpn, (008) Tangsrrat W, Prasertsm D, Pyatat T & Surakampntrn W, Int J Electrn, 95 (008) 9. 6 Khateb F, Jakla W, Kubanek D & Khatb N, Analg Integr Crcuts Sgnal Prcess, 74 (03) Herencsar N, Vrba K, Ktn J & Lahr A, Int J Electrn, 97 (00) Maheshwarang S & Chaturved B, Int J Crcuts Ther Appl, 39 (0) Keskn A U & Blek D, IEE Prc Crcuts Devces Syst, 53 (006) 4. 0 Lahr A, IEICE Electrn Exp, 6 (009) 35. Tangsrrat W & Tanjaren W, Indan J Pure Appl Phys, 48 (00) 363. Jakla W, Srpruchyanun M, Bajer J & Blek D, Rad Eng, 7 (008) Jn J & Wang C, Int J Electrn Cmmun (AEU), 66 (0) Hrng J W, Hu C L, Chang C M, Chu H P, Ln C T & Wen Y H, ETRI J, 8 (006) Maheshwarang S & Khan I A, J Act Passve Electrn Dev, (007) Lahr A, Analg Integr Crcuts Sgnal Prcess, 6 (009) Lahr A, Rad Eng, 8 (009) 5. 8 Arbel A F & Gldmnz L, Analg Integr Crcuts Sgnal Prcess, (99) 43.