EG Low Voltage CMOS Fully Differential Current Feedback Amplifier with Controllable 3-dB Bandwidth

Transcription

1 EG Low olage CMS Fully Derenal Curren Feedback Ampler wh Conrollable 3dB Bandwdh Ahmed H. Madan 2, Mahmoud A. Ashour, Solman A. Mahmoud 2, and Ahmed M. Solman 3 adaon Engneerng Dep., NCT, EAEA Caro, Egyp. 2 Elecrcal Engneerng dep., German Unversy, Caro, Egyp. 3 Elecroncs and Communcaons, Faculy o Engneerng, Caro Unversy, Gza, Egyp. ABSTACT Ths paper presens a new CMS ully derenal curren eedback operaonal ampler wh conrollable 3dB bandwdh suable or analog daa processng and acquson applcaons. The FDCFA has he advanage o a wde range conrollable 3dB bandwdh ( 57MHz o 500MHz whou changng he eedback ressance hs guaranee he sably o he crcu. The FDCFA has a sandby curren o 320µA. PSpce smulaons o he FDCFA block were gven usng 0.25µm CMS echnology rom AMI MSIS and dual supply volages ±0.75. Keywords: Analog sgnal processng, lers, ully derenal, varable gan ampler. INTDUCTIN In recen years, grea neres has been devoed o he curreneedback negraed crcus operaonal amplers (CFAs [][9]. The curren eedback crcus exhbs beer perormance, parcularly hgher speed, hgh slewrae, and beer bandwdh [5], han classc volagemode opamp, whch are lmed by a consan ganbandwdh produc. The CFAs are ypcally bul by cascadng a posve curren conveyor (CCII wh a buer [6]. There are wo rends o use curren eedback opamp (CFA, he rs rend uses as a convenonal CFAs wh our ermnals devce [][9], as shown n Fg. (a, whle he second rend uses CFAs o realze operaonal ampler wh he CFA benes o ndependen ganbandwdh, as shown n Fg. (b [8][9]. In hs paper, a CMS ully derenal curren eedback ampler wh conrollable 3dB bandwdh, whose block dagram shown n Fg. 2, has been presened. The FDCFA combnes he advanages o he CFA over he opamp, and he ully derenal over he sngleended. Also, gves a wde range o conrollable 3dB bandwdh whou changng he eedback ressance, hs gves sably or he FDCFA. Fully derenal archecures mprove he perormance o analog and mxed analog/dgal sysems n erms o supply nose rejecon, dynamc range, and harmonc dsoron[9]. The FDCFA s bascally a ully derenal devce as shown n Fg. 2. The Y and Y 2 ermnals are he hgh npu mpedance ermnals whle he X and X 2 ermnals are low mpedance ones. The derenal npu volage n appled across Y and Y 2 ermnals s conveyed o a derenal volage n2 across he X and X 2 ermnals, ( n = n2. The npu curren appled o he X and X 2 ermnals are conveyed o he and 2 ermnals, (I X = I and I X2 = I 2. The and 2 are hgh mpedance oupu nodes suable or curren oupus. The and 2 ermnals are conneced o wo equal ressances l, o conver he oupu curren no npu volage or he ully derenal opamp. The derenal volage developed across and 2 are appled o he npu

2 derenal volage o he ully derenal opamp. Ths moves he hgh volage swng rom he and 2 ermnals o he ully derenal opamp whle s operang n he openloop conguraon. Ths opology has he advanages o conrollng he 3dB bandwdh o he FDCFA wh xed eedback ressance hs suppors he sably o he CFA. Also, reduces he ransmpedance requred a he and 2 ermnals, whch makes hs opology more aracve or lowvolage applcaons. The paper s organzed as ollows; n Secon II, he CMS realzaon o he lowvolage class AB FDCFA s presened. In Secon III, he small sgnal analyss o he FDCFA s gven. In Secon I, he smulaon resuls o he FDCFA are demonsraed. Concluson s gven n secon. Y F CF C X (a I X X Y CCII C l (b Fgure. CFA rends (a convenonal, (b opamp[9] x IX n2 n I X I Y I Y X X 2 Y Y 2 FDCCII 2 l l B FDpAmp Fgure 2. The FDCFA block dagram. CMS ELAIATIN F THE FDCFA

3 The CMS realzaon o he ully derenal curren eedback operaonal ampler (FDCFA s shown n Fg. 3. The crcu consss o wo mached derenal pars (M, M 2 and (M 3, M 4, wo pars o mached basng ranssors (M 5, M 6 and (M 7, M 8, class AB basng sage (M 2 o M 23, wo class AB oupu sages (M 9 o M 4 and (M 5 o M 20. The opamp consss o wo mached derenal pars (M 24, M 25 and (M 33, M 34, wo mached basng ranssors (M 26, M 35, wo mached pars o curren mrrors (M 27, M 28 and (M 36, M 37, and wo class AB oupu sages (M 29 o M 32 and (M 38 o M 4.All ranssors are operang n sauraon regon M 5 and M 6 carry equal bas currens (I B whle he equal bas curren lowng hrough M 7 and M 8 are se o I B /2.Thereore, Ι Μ5 = Ι Μ6 ( Ι Μ2 = Ι Μ4 (2 Ι Μ5 = Ι Μ3 Ι Μ4 (3 Ι Μ6 = Ι Μ Ι Μ2 (4 From equaons (3 and (4 no equaon ( yelds From equaons (2 and (5 Ι Μ Ι Μ2 = Ι Μ3 Ι Μ4 (5 Ι Μ = Ι Μ3 (6 The mached derenal pars are carryng equal derenal and common mode curren values. Thereore, X X = Y Y (7 Smlarly, he derenal pars o he opamp are carryng equal derenal and common mode curren values. There ore, = (8 To manan a good curren drve capably wh low oupu mpedance oupus, class AB oupu sages are used. Transsors (M, M 2, (M 7, M 8, (M 9, M 20, (M 3, M 32, and (M 40, M 4 orm he push pull oupu sage ranssors. The level sh crcus ormed by (M 9, M 0, (M 5, M 6, (M 29, M 30, and (M 38, M 39 are used o realze conrolled loang volage sources ha conrols he sandby curren hrough he oupu sage ranssors. The sandby curren s adjused by he basng crcu ormed o M 2, M 22, and M 23. The class AB oupu sage enables he crcu o derve he heavy ressve and capacve load wh low sandby power dsspaon and no slewng. To preven he dr n he oupu common mode (CM volage, a common mode eedback (CMFB crcu s needed. I deermnes he oupu CM volage and conrols o a speced value cm s se o zero vol. The CMFB crcu consss o ranssors M cm

4 o M cm0 as shown n Fg. 3 n addon o wo ressors ( cm and wo capacors (C cm whch are used o conrol he CM volage o he oupus (. Transsors M cm and M cm2 are employed o solae he CMFB crcu rom he basc crcu. Ths s essenal o make he npu curren o he CMFB crcu equal o zero. The CMFB crcu generaes he CM volage o he oupu sgnals a node oav va he wo equal ressors ( cm. Ths volage s hen compared o cm usng derenal ampler M cm3 and M cm4 wh negave eedback orcng oav o ollow cm. The operaon o he CMFB crcu could be explaned as ollows. Assumng he deal case o ully derenal oupu sgnals; oav = 0. Snce oav and cm are equal, he al curren o he derenal par ormed o ranssors M cm3 and M cm4 wll be dvded beween wo ranssors. Thereore, a curren wll be passed va M cm5, M cm6, and M cm7 o he oupu nodes and he curren exhbs he proper basng even when large derenal sgnals are presen. Nex consder he case when he magnude o s greaer han whch resuls n a posve CM sgnal oav. Ths volage wll cause he curren n M cm6 and M cm7 o ncreases pullng down he volages and unl oav s brough back o zero. Smlarly, n case o negave CM sgnal, he loop wll adjus he oav o be equal o CM. SMALLSIGNAL ANALYSIS The small sgnal Analyss o he crcu shown n Fg. (b, he ollowng relaons could be obaned: I =. sc sc l l.. A s A s ω ω ω ω (9 where A s he gan and ω represens he 3dB bandwdh o he opamp. Assume ha l <<< so he parallel conguraon beween l and wll resul n l.

5 DD M2 M37 M36 Mcm7 M8 Mcm6 M7 M28 M27 Mcm5 B3 Mcm2 Mcm M4 M38 CC M22 M9 M7 M5 CC CC M9 M M3 CC M29 M3 cm Av Mcm3 Mcm4 cm Ccm cm Ccm M34 M33 B2 Y M4 M3 X X M M2 Y B2 M24 M25 2 B4 Mcm8 Mcm9 Mcm0 M40 M20 M8 M2 M4 M32 M39 M30 M6 M0 M5 M6 B M23 M35 M26 SS Fgure 3. FDCFA CMS realzaon wh CMFB. Also, assume ha he pole creaed by C and l s so hgh ha s ousde he bandwdh and A s very hgh so he erm A >> and hence equaon (9 could be reduced o, I. l. Aω = s A ω l (0 The ransmpedance gan could be obaned rom (0 as ollows I = ( Assume ha he X ermnal ressance s so low ha he volage o X ermnal equals ha a he Y ermnal. So, equaon (0 could be wren as ollows: = l. Aω. s A ω l (2 So, he closed loop gan and he 3dB bandwdh could be obaned as ollows: A = A ω ω = l 3 db, (3 Where A ω s he opamp ganbandwdh produc. Equaon (3 shows ha he ω 3dB could be conrolled by load ressance l wh xed eedback ressance. Also, l used o conver he ermnal oupu curren o volage beng ampled by he ully

6 derenal opamp, hs moves he hgh volage swng rom he ermnal o he ully derenal opamp whle s operang n he openloop conguraon. Clearly or a parcular l, once s se o xed value, can be changed o vary he gan whou aecng he bandwdh. Hence, he ampler acheves a ganndependen bandwdh. In order o avod he hgh requency poles o he opamp and hereby ensure closed loop sably, he closed loop bandwdh o he CFA mus be less han he GBP o he opamp. Hence rom (3 ollows ha l mus always be less han. SIMULATIN ESULTS The perormance o he FDCFA crcu was vered by perormng PSpce smulaons wh supply volages ±0.75, he ollowng basng volages B = 0.7, B2 = 0.35, B3 =0.7, and usng 0.35µm CMS echnology parameers. Fg.4 (a, b, c shows he oupu derenal volage o varable gan ampler (GA wh deren gans or an appled AC npu volage wh value. The npu ressance, whch conrols he gans, akes values 2,, 0.5, and 0.25KΩ respecvely, eedback ressance = 2KΩ whle he bandwdh conrol ressance l akes he ollowng values (a l =0.2 KΩ, (b l =0.5 KΩ, (c l =.5 KΩ. The bandwdhs or deren l values are (a 57 MHz, (b 320 MHz, (c 530 MHz respecvely. = 0.25o2K ohm = 2K ohm n = 0.25o2K ohm FDCFA l= 0.2,0.5,.5K ohm l= 0.2,0.5,.5K ohm = 2Kohm (a 20 8 The oupu derenal volage ou [db] Gan= 2 5.0KHz 0KHz 00KHz.0M Hz 0M Hz 00M Hz.0G Hz vdb(8,9 vdb(4,5 vdb(20,2 vdb(26,27 Frequenc y (b

7 20 8 The oupu derenal volage ou [db] G a n = KHz 0KHz 00KHz.0M Hz 0M Hz 00M Hz vdb(8,9 vdb(4,5 vdb(20,2 vdb(26,27 Frequency (c.0g H z The oupu derenal volage ou [db] KHz 0KHz 00KHz vdb(8,9 vdb(4,5 vdb(20,2 vdb(26, Gan=.0M H z Frequenc y (d 0MHz 00M Hz.0GHz Fgure 4. (a Fully derenal volage ampler, Frequency response o he ully derenal volage ampler wh deren gans wh (b l =0.2kohm, (c l =0.5kohm, (d l =.5Kohm I s clear ha he GA based on he FDCFA experences no loss n bandwdh when he gan s ncreased. From he smulaons, l has been used o conrol he bandwdh o he FDCFA block or a wde range (57 MHz 530 MHz whou aecng s perormance. The npu and oupu reerred nose volages specral denses (40 n/ Hz. For n se o sep volage wh magnude 500m and requency MHz appled o he FDCFA block, he slew rae s 0 M/sec. CNCLUSIN A new lowvolage ully derenal curren eedback operaonal ampler crcu has been presened. The FDCFA has he advanages o wde range o conrollable 3dB

8 bandwdh ( 57MHz 530MHz and no need or large ransmpedance n s curren conveyor. Also, combnes beween he advanages o he CFA over he opamp and he ully derenal over sngle ended. Smulaon resuls have been gven. EFEENCES [] E. Bruun, IEEE Trans. Crcus Sys.I, Fundam. Theory Appl., 40, 275(993. [2] A. H. Madan, S. A. Mahmoud, and A. M. Solman, 3h IEEE ICECS, 600, (December 03, 2006, Nce, France. [3] E. Bruun, Anal. Inegr. Crcus Sgnal Process., ; 5,23(994. [4]. Ma, G. Palumbo, and S. Penns, IEEE Trans. Crcus Sys.II, 52, 37(2005. [5] A. M. Ismal and A. M. Solman, IEEE Trans. Crcus Sys.I, Fundam. Theory Appl., 47, 98(2000. [6] S. A. Mahmoud and A. M. Solman, Anal. Inegr. Crcus Sgnal Process., 25, 47(2000. [7] A. M. Solman, Anal. Inegr. Crcus Sgnal Process.,, 256(996. [8] S. A. Mahmoud and A. M. Solman, IEEE Trans. Crcus Sys.I, Fundam. Theory Appl., 46, 50(999. [9] S. A. Mahmoud and I. A. Awad, Anal. Inegr. Crcus Sgnal Process., 43, 6(2005.