Cours Circuits Intégrés Analogiques / Chapitre II 29/04/2010. Outline. Polytech Montpellier ERII 4

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1 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 Polyech Monpellier ERII Design of nalog IC s Chapire I danced nalog Design echniques Pascal Noue March 010 noue@lirmm.fr nalog IC Design Flow 3 nalog IC Design Flow Specificaions Choice of he archiecure Iniial sizing (1s order models) Specificaions Choice of he archiecure Iniial sizing (1s order models) Simulaions operaing From poin, he Jus designer o be sure poin!!! of sauraions, iew: gain, inpu nex HE bandwidh, sep fabricaion cos noise, $ slew-rae, number (10-100k$) sabiliy, of sages, and oupu (analog ranges, layou is more and exper CMRR, ime C small-signal Simulaions PSRR, (few inpu weeks oupu and o sage, gain, oupu han digial oupu layou) few monhs) dynamic DC simulaions ranges, folded simulaions oupu cascode, resisance resisance, differenial and oupu curren, oupu, curren, erify cell specificaions s sabiliy, gain, echnology spreadings bandwidh, CMRR, (ariabiliy) pplicaion- and mismaches erify sysem-leel PSRR, capaciie load emperaure Specific and Power specificaions Pos-layou effecs, ayou Simulaions Supplies simulaions (DC, C, ) pplicaion- Specific Simulaions (DC, C, ) C small-signal simulaions ayou DC simulaions Pos-layou simulaions 5 6 Common Mode Rejecion Raio Design for low mismaches Noise fundamenals Characerizaion Definiion: inpu offse of a differenial amplifier is he differenial inpu olage ha leads o a zero oupu olage Symmerical power supplies!!! 1

2 Cours Circuis Inégrés nalogiques - 008/009-9/0/ Impac of offse on a simple design: high for low-inpu leels in os iin ou os RF. iin 596m 1kΩ he gain is 60 insead of 100 Offse is a random phenomenon due o: echnology spreading low frequency ariaions (die o die ; wafer o wafer ; run o run) Mismaches high frequency ariaions (deice o deice) ariabiliy ho opic coering boh preious origins affecing echnology parameers and dimensions generally following a Gaussian disribuion. Propagaion o circui behaior Example: inceriude on sauraion curren µc, / and are affeced µc Idsa ( ) gs 9 10 Gaussian disribuion basics For a large number of idenical deices he disribuion of acual (µc, /) follows a Gaussian disribuion 0.5% of he alues are more han ±3 away from he aerage alue 6 designs are hen he sandard in indusry 99.5% of yield in absence of defecs Run o run (echnology spreading) is much higher han deice o deice (mismaches) simulaions Sandard deiaions are relaed o design!!! Se of equaions can be found in he lieraure spreading increases wih he subsrae doping and he ide hickness N ( m. µm ) spreading decreases wih he area of he ransisor PMOS fabricaed in a N-well exhibis more spreading (N D >>N ) Oerall, spreading reduces wih modern echnologies (seems o saurae a around 3m.µm) 11 1 µc mismaches Similar expressions han for µc 0,0056 µm / mismaches / 1 1 / / Example: 100µm/1µm NMOS in a 0,6 µm ech. / 0,0µm 1, m 0,% 0, ,056% / % 600m µc / 50% more for a PMOS 10 imes less for MOS on he same die (mismaches) Random offse in a curren mirror 1 I I dsa 100µm ; 1µm ; eff 0,1 10µm ; 10µm ; eff 1 S µc ( ) s I. µc S / gs / Design ips arge area and eff, long gs 0,% 56 ppm 0,% 0,0% 56 ppm 0,08%

3 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 e e already sudied 13 1 nalog Some design ariabiliy flowparameers (wafer o wafer) design mus fi specificaions in he ypical case µc design mus also fi / 1 1 specificaions for all possible / µc combinaions m µm of: process (ariabiliy in process 1. / parameers and dimensions), µc 0,0056µm emperaure and µmpower / 0,0 supply 8m. µm 6 designs and ariabiliy Uncerainies ranslae in a I dsa sandard deiaion I. µc dsa /... I µc / dsa gs Random offse in a simple curren mirror arge ransisors and large eff Random offse in a differenial pair wih resisie load and symmerical supply olages od RI gmr os Spreading in load resisance I eff od os R I dsa. / Oher spreading Idsa eff / od R. I dsa I eff µc / dsa eff os os I R / dsa eff u offse can be also sysemaic due o he chosen archiecure, he bias poin, a wrong layou (sysemaic mismach) Mus be fixed by designer!!! Examples Relaed o design (layou) eff 3 eff 1 RSiou iou iin gmrsiou Common Mode Rejecion Raio Design for low mismaches Noise fundamenals Characerizaion Relaed o usage If ds > ds1 ( eff1 ) iou1 iin gou ( ) ds ds1 Common Mode Rejecion Raio, CMRR 17 Common Mode Rejecion Raio, CMRR 18 Definiion: CMRR characerizes he abiliy of a differenial amplifier o rejec he common mode d d CMRR d d - CMRR d d, d s d, d d d 0log Random CMRR in a differenial pair od RI d gmr mc id inc 0 od inc id 0 0 CMRR Impac of spreading in R inc inc /R in he curren source oupu resisance od eff inc od mc R inc id 0 gmr CMRR R R 3

4 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 Common Mode Rejecion Raio, CMRR 19 Random CMRR and offse rade-off 0 ihou R spreading, inc /(.R ) in each load resisance Impac of spreading in MOS inc I dsa od R I( R ) R R Idsa R. µc od mc R µc inc eff gmr gmr CMRR. mc R eff Design of low offse and high CMRR differenial pair eff g mr os CMRR R. R µc CMRR g R I R os m eff he lower he offse, he higher he CMRR 1. Opimize for low offse ow eff (0,1), large ransisors, mached resisors reduce spreading and curren mismach eff. Opimize for large CMRR High g m (I ) & R Sysemaic CMRR 1 Curren source oupu resisance: R Common Mode inc change bias curren inc /R inc /R equally shares beween 1 and Small-signal analysis o calculae induced oupu olage I d1 dd 3 I d I d - 1 ou Common Mode Rejecion Raio Design for low mismaches Noise fundamenals Characerizaion CMRR g g r R m m3 ds1 I bias Design for low mismaches 3 Design for low mismaches 1. Equal naure. Same emperaure 1. Equal naure. Same emperaure : 1 : 3. Increase size 3. Increase size. Minimum disance 5. Same orienaion. Minimum disance 5. Same orienaion 6. Same area/perimeer raio 7. Round shape 8. Cenroïde layou 1 6. Same s 1 1 area/perimeer s s raio : 1 : : 1 : 7. Round shape Much 8. Cenroïde layou 9. End dummies 9. End dummies 10. ipolar always beer! 10. ipolar always beer!

5 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 5 Noise consideraions 6 Common Mode Rejecion Raio Design for low mismaches Noise fundamenals Characerizaion Noise is any unwaned signal ha inerferes wih a desired signal. I can be deerminisic or random. I can be inheren o he circui iself or coming from inerferences wih he ouside world. Inerference noise is caused by an idenifiable exernal source. I can be deerminisic or random. e.g.: 50Hz hum in a loudspeaker, cellular phone inerfering wih a se, I can usually be eliminaed by proper mehods of grounding, shielding, ec (elecromagneic compaibiliy, E) Inheren noise is generaed by he circui iself. I is always random. e.g.: resisance and ransisors are noisy Differen shape of random noises are hermal, sho and flicker I can no be eliminaed (inheren) bu is effecs can be reduced by changing he circui srucure or he power consumpion. Random noise basics 7 Random noise basics 8 Uncorrelaed wih any of he sysem inpus Equialen inpu noise ime-domain analysis Null mean alue Can be represened by a olage (heenin source) or a curren (noron source) Noise is defined by a roo 1 n( rms ) ( ) mean square ( alue n ( ). d 0 Signal-o-noise raio (SNR) P s s SNR 10log 10log Pn n ( rms ) ( rms ) s 0log n ( rms ) ( rms ) Noise combinaion Differen noise sources combine as olages in series and curren in parallel no( no( 1 [ n 1( ) n ( ) ] 0 n1( rms ) n( ssuming uncorrelaed noise sources no( n1( n(. d 0 ( ). ( ). d n1 n Random noise basics 9 Random noise basics 30 Frequency-domain analysis Noise specral densiy Noise is considered only in he bandwidh of he sysem filered ou elsewhere Noise rms 100Hz for a 90Hz bandwidh? 0.1 Hz bandwidh? 10 10µ Noise Specral Densiy n( (NSD). df 0.1 f main shapes hie noise as of a resisor [ ] 10 consan specral n( 10µ ln( f ) densiy (e.g. 3.µ/ Hz) 0. 1 Flicker noise (or 1/f noise or pink noise) large conribuion in low frequencies acually inersely proporional o f 1/f noise falls off a -10d/decade wo frequency decades means noise magniude diided by en ypical NSD of a sysem as of a ransisor-based sysem 5

6 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 Inheren noise models 31 3 k J.K -1 1/f noise angen principle!!! Noise consideraions asic consideraions regarding noise in feedback sysems n1 represens he inpu noise in i, he equialen inpu noise of 1 and he oupu noise of b, ni represens he equialen inpu noise of Common Mode Rejecion Raio Design for low mismaches Noise fundamenals Characerizaion 6

7 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 Characerizaion 37 Characerizaion 38 Makes use of simulaions Define a DOE Example : error in a curren mirror Se 1 : 100 runs, 1 Sudied influences : eff ( ),, /, Iniial design : eff 0, ; /10 ; 1µm ; s µ nc Iin Idsa1 eff 8µ process : ( Idsa )? ; meani ( dsa )? process & mismach : ( )? ; meani ( )? 1 Idsa dsa s Effec of eff.1 < eff < µ nc I µ nc > 7µ ; Iin in eff eff < [10µ ; 50µ ; 100µ ; 00µ ; 500µ ; 1m ; m] Process & mismach : ( )? ; meani ( )? Effec of / : keep and eff consan / [.1 ;. ;.5 ; 1 ; ; 5 ; 10 ].8m 1 Idsa dsa 10µm.10µm ;.10µm ; Iin 8µ 10 s Characerizaion 39 0 Effec of : keep and eff consan 10µm 10µm ; Iin 8µ10µm 10 [1 ; ; 5 ; 10 ; 0] Effec of : keep / and eff consan 1 ( )? ; meani ( )? Idsa dsa s Design for low-noise: acie bridge example Design for robusness: digially programmable curren source / ; ; Iin 8µ 10 (µm ) [7 ; 0 ; 50 ; 100 ; 00 ; 500 ; 1000 ; 000] ( )? ; meani ( )? Idsa dsa Case sudy: magneomeer signal condiioning 1 heasone bridge SNR Srain gauges Reference resisors N CC IO I N > 1m R High power consumpion argeed power consumpion : 100µ (for mobile applicaions) less for auonomous sysems cc gnd cc gnd N SNR 0log 1 CC CC CC CC 1 R R 1 R R R R ( - - ) R k n n kr R ( ) kr n n n 0log n CC ( ) R 16kR. For a gien signal (/R), SNR increases wih cc and reduces wih R and 7

8 Cours Circuis Inégrés nalogiques - 008/009-9/0/010 Oupu SNR and N s noise figure 3 Oupu SNR and N s noise figure cc gnd N SNR 0log ou ( - - ) NFd SNR SNROU 0log n CC ( ) R 16kR. no ( ) ( ) kr N is necessary o reach a measurable signal N will amplify signal and noise of he n n nn Presere inpu SNR by haing an amplifier wih negligible noise conribuion < R g m > 3gm 3R I dsa Ib gm small eff eff eff and large power consumpion Example : R1kΩ and eff 0,1 Ib > eff 133µ P 3, 75m ( N) 3R N will add is own noise o he oupu N s noise figure NF d is used o characerize he loss of SNR due o he N How o reduce power consumpion? 5 Design for robusness: digially programmable curren source Design for low-noise: acie bridge example 8