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low cost, low power 12-bit differential adc driver ad8137 re v . b in fo rmation furn ished by an alog d e v i c e s is believed to be accurate and reliable. how e ver, n o resp on sibili ty is assume d b y a n alog de vices fo r its use, nor for an y i n fri n geme nt s of p a t e nt s or ot h e r ri ght s o f th ird parties th at may result fro m its use . s p ecificatio n s subj ec t to ch an g e witho u t n o tice. no licen s e is g r an te d by implicati o n or ot herwi s e u n der a n y p a t e nt or p a t e nt ri ghts of analog de v i ces. trademarks an d registered tra d ema r ks are the prop erty o f their respective ow ners. one technolog y way, p.o . box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4 700 www.analog.com fax: 781. 461. 31 13 ? 2005 analog de vices, i n c. al l r i ght s r e ser v ed . fea t ures f u lly dif f er enti al ex tr emely low po w e r with po w e r- down f e a t ur e 2.6 ma quie sc e n t sup p ly curre n t @ 5 v 450 a in pow e r- down mode @ 5 v high speed 110 mh z large signal 3 db bandwidth @ g = 1 450 v/s sle w ra t e 12-bit sfdr per f ormanc e @ 5 00 kh z f a st settl ing ti me: 100 ns t o 0 . 02% l o w input off s et v o ltage: 2 . 6 mv m a x l o w input off s et curr ent: 0.4 5 a ma x d i ff er entia l inp u t and output d i ff er entia l -t o - diff er ential or s i ngle - e nded -t o - dif f er entia l oper a t ion r a il-to - r a i l out p ut a d justable out p ut c o mmon-mode v o ltage ex t e rnally adjustable gain w i de s u p p ly v o ltage r a nge: 2. 7 v t o 12 v a v ai lable in sm all soic pack a g e applic a t io ns 12-bit a d c driv ers p o r t able instrumen t a t ion ba tt er y - pow e r e d ap plic a t ions single - e nded -to - dif f er entia l con v er t e rs d i ff er entia l ac t i v e fil t ers v i deo amplifi e rs le v e l shif ters func ti on a l bl ock di a g r a m 04771-0-001 ?i n 1 v ocm 2 v s+ 3 +out 4 +in 8 pd 7 v s? 6 ? out 5 ad8137 figure 1. r g = 1k ? v o, dm = 0.1v p-p frequency (mhz) normalize d clos e d -loop gain (db) 3 2 1 0 ?1 2 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 0.1 1 1 0 100 1000 04771-0-002 g = 5 g = 10 g = 1 g = 2 fig u re 2. sm a ll s i g n al r e s p ons e f o r v a r i ous g a i n s gener a l descript on the ad8137 is a lo w cos t dif f er en t i al dr i v er wi t h a ra il-t o-ra il o u t p u t tha t is ideal f o r dr i v in g 1 2 -b i t ad cs in s y s t em s tha t a r e s e n s i t i v e t o p o wer a n d cos t . the ad8137 is easy t o a p p l y , an d i t s i n t e rnal co mm o n -m o d e f eed ba ck a r c h i t e c t u r e al lo w s i t s o u t p u t co mm on- m o d e v o l t a g e t o b e con t r o l l e d b y t h e v o l t a g e a p plie d t o o n e p i n. th e in t e r n al f eed b a ck lo o p als o p r o v ides inher e n t l y b a l a nc e d output s a s wel l a s suppre ss i o n of e v e n - o rd e r h a r m on i c disto r t i o n p r o d uc ts. f u l l y dif f er en t i a l an d si n g l e -e n d e d - t o - dif f er en t i a l ga i n co nf igura t io n s a r e e a si ly r e a l iz e d b y th e ad813 7. e x te r n a l f e e d b a c k ne t w or k s c o ns i s t i n g of f o ur r e sist o r s det e r m i n e t h e am plif ier s clos e d -lo o p ga in. t h e p o w e r - do wn fe a t ur e is b e n e f i cia l in cr i t ica l l o w p o w e r a p plic a t io n s . the ad8137 is ma n u fac t ur e d o n analog de vic e s p r o p r i eta r y s e c o n d ge ne r a t i on x f c b pro c e s s , e n abl i ng i t to a c h i e v e h i g h l e vel s of p e r f or manc e w i t h ve r y l o w p o we r c o nsu m pt i o n. the ad8137 is a v a i la b l e in t h e smal l 8-lead soi c p a c k a g e and 3 mm 3 m m lf cs p . i t is r a te d to o p er a t e o v e r t h e ex te nde d ind u s t r i al t e m p era t ur e ra n g e o f ?40c t o +125c.
ad8137 rev. b | page 2 of 24 table of contents specifications ..................................................................................... 3 absolute maximum ratings ............................................................ 6 thermal resistance ...................................................................... 6 esd caution .................................................................................. 6 pin configuration and function descriptions ............................. 7 typical performance characteristics ............................................. 8 theory of operation ...................................................................... 17 applications ..................................................................................... 18 analyzing a typical application with matched r and r networks f g ...................................................................................... 18 estimating noise, gain, and bandwith with matched feedback networks .................................................................... 18 driving an adc with greater than 12-bit performance ...... 22 outline dimensions ....................................................................... 24 ordering guide .......................................................................... 24 revision history 7/05rev. a to rev. b changes to ordering guide .......................................................... 24 8/04rev. 0 to rev. a. added 8-lead lfcsp.........................................................universal changes to layout ..............................................................universal changes to product title ................................................................. 1 changes to figure 1.......................................................................... 1 changes to specifications ................................................................ 3 changes to absolute maximum ratings ....................................... 6 changes to figure 4 and figure 5................................................... 7 added figure 6, figure 20, figure 23, figure 35, figure 48, and figure 58; renumbered successive figures ........................... 7 changes to figure 32...................................................................... 12 changes to figure 40...................................................................... 13 changes to figure 55...................................................................... 16 changes to table 7 and figure 63................................................. 18 changes to equation 19 ................................................................. 19 changes to figure 64 and figure 65............................................. 20 changes to figure 66...................................................................... 22 added driving an adc with greater than 12-bit performance section ...................................................................... 22 changes to ordering guide .......................................................... 24 updated outline dimensions ....................................................... 24 5/04revision 0: initial version
ad8137 rev. b | page 3 of 24 specifications v s = 5 v, v ocm = 0 v (@ 25c, differential gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c). table 1. parameter conditions min typ max unit differential input performance dynamic performance ?3 db small signal bandwidth v o, dm = 0.1 v p-p 64 76 mhz ?3 db large signal bandwidth v o, dm = 2 v p-p 79 110 mhz slew rate v o, dm = 2 v step 450 v/s settling time to 0.02% v o, dm = 3.5 v step 100 ns overdrive recovery time g = 2, v i, dm = 12 v p-p triangle wave 85 ns noise/harmonic performance sfdr v o, dm = 2 v p-p, f c = 500 khz 90 db v o, dm = 2 v p-p, f c = 2 mhz 76 db input voltage noise f = 50 khz to 1 mhz 8.25 nv/hz input current noise f = 50 khz to 1 mhz 1 pa/hz dc performance input offset voltage v ip = v in = v ocm = 0 v ?2.6 0.7 +2.6 mv input offset voltage drift t min to t max 3 v/c input bias current t min to t max 0.5 1 a input offset current 0.1 0.45 a open-loop gain 91 db input characteristics input common-mode voltage range ?4 +4 v input resistance differential 800 k? common-mode 400 k? input capacitance common-mode 1.8 pf cmrr ?v icm = 1 v 66 79 db output characteristics output voltage swing each single-ended output, r l, dm = 1 k? v s? + 0.55 v s+ ? 0.55 v output current 20 ma output balance error f = 1 mhz ?64 db v ocm to v o, cm performance v ocm dynamic performance ?3 db bandwidth v o, cm = 0.1 v p-p 58 mhz slew rate v o, cm = 0.5 v p-p 63 v/s gain 0.992 1.000 1.008 v/v v ocm input characteristics input voltage range ?4 +4 v input resistance 35 k? input offset voltage ?28 11 +28 mv input voltage noise f = 100 khz to 1 mhz 18 nv/hz input bias current 0.3 1.1 a cmrr ?v o, dm /?v ocm , ?v ocm = 0.5 v 62 75 db power supply operating range +2.7 6 v quiescent current 3.2 3.6 ma quiescent current, disabled power-down = low 750 900 a psrr ?v s = 1 v 79 91 db pd pin threshold voltage v s? + 0.7 v s? + 1.7 v input current power-down = high/low 150/210 170/240 a operating temperature range ?40 +125 c
ad8137 rev. b | page 4 of 24 v s = 5 v, v ocm = 2.5 v (@ 25c, differential gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c). table 2. parameter conditions min typ max unit differential input performance dynamic performance ?3 db small signal bandwidth v o, dm = 0.1 v p-p 63 75 mhz ?3 db large signal bandwidth v o, dm = 2 v p-p 76 107 mhz slew rate v o, dm = 2 v step 375 v/s settling time to 0.02% v o, dm = 3.5 v step 110 ns overdrive recovery time g = 2, v i, dm = 7 v p-p triangle wave 90 ns noise/harmonic performance sfdr v o, dm = 2 v p-p, f c = 500 khz 89 db v o, dm = 2 v p-p, f c = 2 mhz 73 db input voltage noise f = 50 khz to 1 mhz 8.25 nv/hz input current noise f = 50 khz to 1 mhz 1 pa/hz dc performance input offset voltage v ip = v in = v ocm = 0 v ?2.7 0.7 +2.7 mv input offset voltage drift t min to t max 3 v/c input bias current t min to t max 0.5 0.9 a input offset current 0.1 0.45 a open-loop gain 89 db input characteristics input common-mode voltage range 1 4 v input resistance differential 800 k? common-mode 400 k? input capacitance common-mode 1.8 pf cmrr ?v icm = 1 v 64 90 db output characteristics output voltage swing each single-ended output, r l, dm = 1 k? v s? + 0.45 v s+ ? 0.45 v output current 20 ma output balance error f = 1 mhz ?64 db v ocm to v o, cm performance v ocm dynamic performance ?3 db bandwidth v o, cm = 0.1 v p-p 60 mhz slew rate v o, cm = 0.5 v p-p 61 v/s gain 0.980 1.000 1.020 v/v v ocm input characteristics input voltage range 1 4 v input resistance 35 k? input offset voltage ?25 7.5 +25 mv input voltage noise f = 100 khz to 5 mhz 18 nv/hz input bias current 0.25 0.9 a cmrr ?v o, dm /?v ocm , ?v ocm = 0.5 v 62 75 db power supply operating range +2.7 6 v quiescent current 2.6 2.8 ma quiescent current, disabled power-down = low 450 600 a psrr ?v s = 1 v 79 91 db pd pin threshold voltage v s? + 0.7 v s? + 1.5 v input current power-down = high/low 50/110 60/120 a operating temperature range ?40 +125 c
ad8137 rev. b | page 5 of 24 v s = 3 v, v ocm = 1.5 v (@ 25c, differential gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c). table 3. parameter conditions min typ max unit differential input performance dynamic performance ?3 db small signal bandwidth v o, dm = 0.1 v p-p 61 73 mhz ?3 db large signal bandwidth v o, dm = 2 v p-p 62 93 mhz slew rate v o, dm = 2 v step 340 v/s settling time to 0.02% v o, dm = 3.5 v step 110 ns overdrive recovery time g = 2, v i, dm = 5 v p-p triangle wave 100 ns noise/harmonic performance sfdr v o, dm = 2 v p-p, f c = 500 khz 89 db v o, dm = 2 v p-p, f c = 2 mhz 71 db input voltage noise f = 50 khz to 1 mhz 8.25 nv/hz input current noise f = 50 khz to 1 mhz 1 pa/hz dc performance input offset voltage v ip = v in = v ocm = 0 v ?2.75 0.7 +2.75 mv input offset voltage drift t min to t max 3 v/c input bias current t min to t max 0.5 0.9 a input offset current 0.1 0.4 a open-loop gain 87 db input characteristics input common-mode voltage range 1 2 v input resistance differential 800 m? common-mode 400 m? input capacitance common-mode 1.8 pf cmrr ?v icm = 1 v 64 80 db output characteristics output voltage swing each single-ended output, r l, dm = 1 k? v s? + 0.37 v s+ ? 0.37 v output current 20 ma output balance error f = 1 mhz ?64 db v ocm to v o, cm performance v ocm dynamic performance ?3 db bandwidth v o, cm = 0.1 v p-p 61 mhz slew rate v o, cm = 0.5 v p-p 59 v/s gain 0.96 1.00 1.04 v/v v ocm input characteristics input voltage range 1.0 2.0 v input resistance 35 k? input offset voltage ?25 5.5 +25 mv input voltage noise f = 100 khz to 5 mhz 18 nv/hz input bias current 0.3 0.7 a cmrr ?v o, dm /?v ocm , ?v ocm = 0.5 v 62 74 db power supply operating range +2.7 6 v quiescent current 2.3 2.5 ma quiescent current, disabled power-down = low 345 460 a psrr ?v s = 1 v 78 90 db pd pin threshold voltage v s? + 0.7 v s? + 1.5 v input current power-down = high/low 8/65 10/70 a operating temperature range ?40 +125 c
ad8137 r e v. b | pa ge 6 o f 2 4 absolute maximum ra tings table 4. p a r a me t e r r a t i n g supply v o ltage 12 v v ocm v s+ to v s? p o w e r di ssip a ti on s ee f i gur e 3 i n put c o mmon-m o de v o ltage v s+ to v s? stor age t e mpera tur e ?65c to +125c o p era t ing t e mper a tur e r a nge ?40c to +125c l e ad t e mper a tur e (s older i ng 10 sec) 300c junc tion t e mpe r a tur e 150c s t r e s s es a b o v e t h os e list e d u nde r a b s o l u te m a xi m u m r a t i n g s ma y ca us e p e r m a n e n t dama ge to t h e de vi ce. t h is is a st r e ss r a t i ng on ly a n d f u nc t i on a l op e r a t i o n of t h e d e v i c e a t t h e s e or a n y o t h e r con d i t io n s ab o v e t h o s e i ndic a t e d i n t h e op era t io nal s e c t io n o f t h is sp e c if ic a t io n is no t im pl ie d . e x p o sur e t o a b s o l u te max i m u m r a t i ng co ndi t i on s fo r ex tende d p e r i o d s ma y a f fe c t de vice rel i a b i l i t y . thermal resistance ja is sp e c if ie d fo r t h e w o rst - ca s e co ndi t i o n s, t h a t is, ja is sp e c if ie d fo r t h e de vice s o lder e d in a c i r c ui t b o ar d in st i l l a i r . table 5. therm a l resistance p a ck age t y pe ja jc unit soic-8/2-la y e r 1 5 7 5 6 c / w soic-8/4-la y e r 1 2 5 5 6 c / w lfcsp/4-la y e r 7 0 5 6 c / w maximum power dissipation the maxim u m s a f e p o w e r dis s i p a t io n in t h e ad8137 p a c k a g e is l i m i t e d b y t h e as soci a t ed ri se i n j u n c ti o n t e m p era t u r e (t j ) o n th e die . a t a p p r o x ima t e l y 150c, which is t h e g l as s tra n s i tio n t e m p era t ur e , t h e plas t i c chan g e s i t s p r o p er t i es. e v en t e m p o - ra r i l y exce e d in g t h is t e m p era t ure limi t ma y cha n g e t h e s t r e s s e s t h a t t h e p a cka g e exer ts o n t h e die , p e r m an en t l y s h if t i n g t h e p a ra m e tr ic p e r f o r ma n c e o f t h e ad8137. e x ceedin g a j u n c tion t e m p era t ur e o f 175c f o r a n ext e nded p e r i o d o f time can r e s u l t in c h a n g e s in the silico n de vices , p o t e n t ial l y ca u s in g fa il ur e . the p o wer dis s i p a t e d in t h e p a cka g e (p d ) is t h e s u m o f t h e q u ies c e n t p o w e r dissi p a t ion and t h e p o w e r dissi p a te d i n t h e p a cka g e d u e t o t h e lo ad dr i v e fo r al l o u t p u t s. th e quies c e n t p o w e r is t h e v o l t a g e b e tw e e n t h e s u p p l y p i n s (v s ) tim e s t h e q u i e scen t curr en t (i s ). the lo ad c u r r en t co n s is t s o f dif f er en t i al a nd co mm o n - m o d e c u r r en ts f l o w i n g t o t h e lo ad , as we l l as curr e n t s f l o w in g th r o ugh t h e ext e rn al f eed ba ck n e tw o r k s a n d t h e in t e r n al comm on- m o d e fe e d b a ck lo o p . the in t e r n al r e sis t o r ta p used i n t h e co m m o n -m o d e f eed ba c k l o o p p l a c e s a 1 k ? dif f er en t i al lo ad o n t h e o u t p u t . rms o u t p u t v o l t a g es sh o u l d b e co n s i d er ed w h en d e ali n g wi t h ac si gn als. air f lo w r e d u ces ja . a l s o , more me t a l d i re c t ly i n c o n t a c t w i t h t h e p a cka g e le ads f r o m m e t a l t r aces, t h r o ug h h o les, g r o u nd , a nd p o w e r planes r e d u ces t h e ja . fi g u r e 3 s h ow s t h e m a x i m u m s a f e p o w e r d i s s ip at i o n i n t h e p a c k a g e vs. t h e a m b i en t t e m p era t ur e f o r the so i c -8 (125c/w ) a nd lf cs p ( ja = 70c/w) p a cka g e on a jed e c s t anda r d 4-l a yer bo a r d . ja val u es a r e a p pr o x ima t io n s . ?40 ? 20 ?10 ?30 0 10 20 30 40 50 60 70 80 90 100 110 120 3.0 m a xim u m pow e r d i ssipa tion ( w ) 1.0 1.5 0.5 2.0 2.5 0 ambient temperature ( c) soic-8 lfcsp 04771-0-022 fig u re 3. m a x i mu m pow er dis s i p a t i o n v s . te mper at ur e f o r a 4-lay e r b o a r d esd caution esd (elec t r o sta t ic dischar g e) sensitiv e devic e . e l ec tr osta tic charges as high as 4000 v r e adily ac cumula te on the human body and t e st eq uipmen t and can dischar g e with out det e c t ion. although this pr oduc t f e a tur es pr oprietar y esd pr ot ec tion cir c uitr y , permanen t dama ge may oc cur on dev i c e s sub j ec ted to high ener gy elec tr o s ta tic di scharge s . theref or e , proper esd pr ecautio n s a r e r e c o m m ended to a v oid per f or man c e degrada t ion or l o ss of func tiona l it y .
ad8137 r e v. b | pa ge 7 o f 2 4 pin conf igura t ion and fu nction descriptions 04771-0-001 ?i n 1 v ocm 2 v s+ 3 +out 4 +in 8 pd 7 v s? 6 ? out 5 ad8137 figure 4. pin c o nfiguration ta ble 6. pi n f u nct i on d e s c ri pt i o ns p i n no . m n emonic description 1 ? i n in v e r t i n g in p u t . 2 v ocm an in ter n al f eed back l oop dr iv e s the output c o mmon-mode v o lt age to be equal to the v o ltage a p plied to the v ocm pin, provided the amplifier s opera tion remains l i near . 3 v s+ p o sitiv e p o w e r sup p ly v o ltage . 4 +out p o sitiv e side of the diff er en tial output. 5 ?out nega tiv e side of the diff er en tial o utput. 6 v s? nega tiv e p o w e r sup p ly v o ltage . 7 pd p o w e r d o wn. 8 + i n nonin v er t i n g i n p u t . ad8137 + ? 52.3 52.3 r l, dm 1k v o, dm + ? v ocm r f c f r f v test test signal source 50 50 04771-0-023 r g = 1k r g = 1k c f midsupply figure 5. bas i c t e s t circu i t ad8137 + ? 52.3 52.3 r l, dm v o, dm + ? r f = 1k r f = 1k r s r s v test test signal source 50 50 04771-0-062 c l, dm r g = 1k r g = 1k v ocm midsupply figure 6. cap a c i tiv e lo ad t e st cir c uit, g = 1
ad8137 r e v. b | pa ge 8 o f 2 4 typical perf orm ance cha r acte ristics u n l e ss o t h e r w i s e no te d, d i f f e r e n t i a l g a i n = 1 , r g = r f = r l, d m = 1 k?, v s = 5 v , t a = 25c, v oc m = 2.5v . ref e r to th e basic t e s t cir c ui t in f i gur e 5 fo r t h e def i ni t i o n o f ter m s. r g = 1k ? v o, dm = 0.1v p-p frequency (mhz) normalize d clos e d -loop gain (db) 3 2 1 0 ?1 2 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 0.1 1 1 0 100 1000 04771-0-002 g = 5 g = 10 g = 1 g = 2 fi gur e 7 . smal l si g n a l fr equency respo n se f o r v a ri o u s g a i n s frequency (mhz) closed- l oop gain ( d b) ?1 2 1 1 0 100 1000 04771-0-003 v s = 5 v s = +5 v s = +3 3 2 1 0 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 v o, dm = 0.1v p-p fig u re 8. sm a ll s i g n al frequ e ncy r e s p ons e f o r v a r i ous po wer s u ppl ies frequency (mhz) closed- l oop gain ( d b) 3 2 1 0 ?1 2 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 1 1 0 100 1000 04771-0-006 v o, dm = 0.1v p-p t = ? 40c t = +125 c t = +85c t = +25c fig u re 9. sm a ll s i g n al frequ e ncy r e s p ons e at v a ri ous te mpe r at ur es frequency (mhz) normalize d clos e d -loop gain (db) 3 2 1 0 ?1 2 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 0.1 1 1 0 100 1000 04771-0-004 g = 10 g = 1 g = 2 g = 5 r g = 1k ? v o, dm = 2.0v p-p fi gur e 10 . l a r g e signa l f r equency r e spo n se for v a ri o u s ga i n s frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 0 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 1 1 0 100 1000 04771-0-005 v o, dm = 2.0v p-p v s = 5 v s = +5 v s = +3 figure 1 1 . l a rge si gnal f r equ e ncy r e s p ons e fo r v a r i ous p o we r supp li es frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 ?1 1 ?1 0 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 0 1 1 0 100 1000 04771-0-007 t = +85c t = +125 c t = ? 40c t = +25c v o, dm = 2.0v p-p fig u re 1 2 . l a rg e si g n al f r equ e ncy r e s p ons e at v a ri ous t e mp er at ures
ad8137 r e v. b | pa ge 9 o f 2 4 frequency (mhz) closed- l oop gain ( d b) 3 2 1 0 ?1 ?3 ?4 ?2 ?5 ?6 ?7 ?8 ?1 0 ?1 1 ?9 ?1 2 1 1 0 100 1000 04771-0-041 v o, dm = 0.1v p-p r l, dm = 2k ? r l, dm = 1k ? r l, dm = 500 ? fig u re 1 3 . s m al l s i g n al f r equ e ncy r e s p ons e f o r v a r i ous l oads 1 1 0 100 1000 frequency (mhz) closed- l oop gain ( d b) v o, dm = 0.1v p-p 3 2 1 0 ?12 ?11 ?10 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 04771-0-008 c f = 2pf c f = 1pf c f = 0pf fig u re 1 4 . s m al l s i g n al f r equ e ncy r e s p ons e f o r v a r i ous c f frequency (mhz) closed- l oop gain ( d b) 2 1 0 ?1 ?2 ?4 ?5 ?3 ?6 ?7 ?8 ?9 ?1 1 ?1 2 ?1 0 ?1 3 1 1 0 100 1000 04771-0-042 v o, dm = 0.1v p-p v ocm = 1v v ocm = 4v v ocm = 2.5v fig u re 1 5 . s m al l s i g n al f r equ e ncy r e s p ons e at v a ri ous v ocm frequency (mhz) closed- l oop gain ( d b) 3 2 1 0 ?1 ?3 ?4 ?2 ?5 ?6 ?7 ?8 ?1 0 ?1 1 ?9 ?1 2 1 1 0 100 1000 04771-0-043 v o, dm = 2v p-p r l, dm = 2k ? r l, dm = 1k ? r l, dm = 500 ? fig u re 1 6 . l a rg e si g n al f r equ e ncy r e s p ons e f o r v a r i ous l oads 1 1 0 100 1000 frequency (mhz) closed- l oop gain ( d b) v o, dm = 2.0v p-p 3 2 1 0 ?12 ?11 ?10 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 04771-0-009 c f = 2pf c f = 1pf c f = 0pf figure 1 7 . l a rge si gnal f r equ e ncy r e s p ons e fo r v a r i ous c f frequency (mhz) closed- l oop gain ( d b) 3 2 1 0 ?1 ?3 ?4 ?2 ?5 ?6 ?7 ?8 ?1 0 ?1 1 ?9 ?1 2 1 1 0 100 1000 04771-0-044 2v p-p 0.5v p-p 0.1v p-p 1v p-p fi gur e 18 . f r equency respo n se f o r v a ri o u s output a m pli t udes
ad8137 rev. b | page 10 of 24 frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 ?3 ?2 ?1 0 ?7 ?6 ?5 ?4 ?11 ?10 ?9 ?8 1 1 0 100 1000 04771-0-037 g= 1 v s = 5v v o, dm = 0.1v p-p r f = 500 ? r f = 2k ? r f = 1k ? fig u re 1 9 . s m al l s i g n al f r equ e ncy r e s p ons e f o r v a r i ous r f frequency (mhz) distortion ( d bc) ?65 ?70 ?80 ?75 ?85 ?90 ?95 ? 100 ? 105 0.1 1 1 0 04771-0-045 v s = 5v v s = +5v v s = +3v g = 1 v o, dm = 2v p-p fig u re 2 0 . s e c o nd ha rm on ic dis t o r t i o n v s . frequ e ncy an d supply v o lt ag e v o, dm (v p-p) distortion ( d bc) ?50 ?60 ?65 ?70 ?55 ?75 ?80 ?85 ?90 ?95 ? 100 0.25 1.25 2.25 3.25 4.25 5.25 7.25 8.25 6.25 9.25 04771-0-027 f c = 500khz second harmonic solid line third harmonic dashed line v s = +5v v s = +5v v s = +3v v s = +3v figure 2 1 . ha rm on i c dis t o r ti on vs. out p ut amplitude and supply, f c = 50 0 k h z frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 ?3 ?2 ?1 0 ?7 ?6 ?5 ?4 ?11 ?10 ?9 ?8 1 1 0 100 1000 04771-0-036 g = 1 v o, dm = 2v p-p r f = 500 ? r f = 2k ? r f = 1k ? figure 2 2 . l a rge si gnal f r equ e ncy r e s p ons e fo r v a r i ous r f frequency (mhz) distortion ( d bc) ?40 ?70 ?60 ?50 ?80 ?90 ? 100 ? 110 0.1 1 1 0 04771-0-063 v s = 5v v s = +5v v s = +3v g = 1 v o, dm = 2v p-p fig u re 2 3 . t h ird h a rm oni c d i s t ort i on v s . freque ncy and s u pply v o lt ag e v o, dm (v p-p) distortion ( d bc) ?50 ?60 ?65 ?70 ?55 ?75 ?80 ?85 ?90 ?95 ? 100 0.25 1.25 2.25 3.25 4.25 5.25 7.25 8.25 6.25 9.25 04771-0-026 v s = +5v v s = +5v v s = +3v v s = +3v f c = 2mhz s e co nd h arm o n i c s o l i d l i n e t h i r d h a r m o ni c das he d l i n e figure 2 4 . ha rm on i c dis t o r ti on v s . out p ut amplitude and supply, f c = 2 m h z
ad8137 rev. b | page 11 of 24 frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-032 v o, dm = 2v p-p r l, dm = 200 ? r l, dm = 1k ? r l, dm = 500 ? fig u re 2 5 . s e c o nd ha rm on ic dis t o r t i o n at v a ri ous l oads frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-034 g = 2 g = 5 g = 1 v o, dm = 2v p-p r g = 1k ? figure 2 6 . s e c o nd ha rm on ic dis t o r tio n at va ri ous g a i n s frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-030 v o, dm = 2v p-p g = 1 r f = 500 ? r f = 2k ? r f = 1k ? figure 2 7 . s e c o nd ha rm on ic dis t o r tio n at va ri ous r f frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-033 v o, dm = 2v p-p r l, dm = 200 ? r l, dm = 1k ? r l, dm = 500 ? fig u re 2 8 . t h ird h a rm oni c d i s t ort i on at v a r i ous lo ads frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-035 v o, dm = 2v p-p r g = 1k ? g = 5 g = 1 g = 2 fig u re 2 9 . t h ird h a rm oni c d i s t ort i on at v a r i ous ga ins frequency (mhz) distortion ( d bc) ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.1 1 1 0 04771-0-031 v o, dm = 2v p-p g = 1 r f = 500 ? r f = 2k ? r f = 1k ? fig u re 3 0 . t h ird h a rm oni c d i s t ort i on at v a r i ous r f
ad8137 rev. b | page 12 of 24 v ocm (v) distortion ( d bc) ?50 ?60 ?80 ?70 ? 100 ?90 ? 110 0.5 1.0 1.5 2.5 2.0 3.5 4.0 3.0 4.5 04771-0-028 f c = 500khz v o, dm = 2v p-p second harmonic solid line third harmonic dashed line figure 3 1 . ha rm on i c dis t o r ti on v s . v oc m , v s = 5 v frequency (hz) in pu t volta ge n o ise ( n v/ hz) 100 10 1 10 100 1k 10k 100k 1m 10m 100m 04771-0-046 figure 3 2 . inp u t vo ltage no ise v s . fr eq uency frequency (mhz) cmrr (db) 20 ?2 0 ?1 0 0 10 ?5 0 ?3 0 ?4 0 ?7 0 ?6 0 ?8 0 1 1 0 100 04771-0-013 v in, cm = 0.2v p-p input cmrr = ? v o, cm/ ? v in, cm figure 33. cmrr vs. frequ e ncy v ocm (v) distortion ( d bc) ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?100 ?110 0.5 0.7 0.9 1.3 1.1 1.5 1.7 2.3 2.1 1.9 2.5 04771-0-029 f c = 500khz v o, dm = 2v p-p second harmonic solid line third harmonic dashed line figure 3 4 . ha rm on i c dis t o r ti on v s . v oc m , v s = 3 v frequency (hz) v ocm n o ise ( n v/ hz) 1000 100 10 1 10 100 1k 10k 100k 1m 10m 100m 04771-0-047 figure 35. v ocm v o lt age n o is e v s . freq u e ncy frequency (mhz) v ocm cmrr (db) ?1 0 ?3 0 ?2 0 ?5 0 ?4 0 ?7 0 ?6 0 ?8 0 1 1 0 100 04771-0-012 v o, cm = 0.2v p-p v ocm cmrr = ? v o, dm/ ? v ocm figure 36. v ocm cm rr vs. fr e q ue nc y
ad8137 rev. b | page 13 of 24 time (ns) voltage (v) 8 2 4 6 0 ?4 ?2 ?6 ?8 04771-0-016 250ns/div input 2 output g = 2 figure 37. over drive recovery time (ns) v o, dm (mv ) 100 50 25 75 0 ?25 ?50 ?75 ?100 04771-0-015 10ns/div v o, dm = 100mv p-p c f = 0pf c f = 1pf fig u re 3 8 . s m al l s i g n al tr ans i e n t r e s p ons e f o r v a r i ous f eedba ck capa cita nces time (ns) v o, dm (v ) 100 50 25 75 0 ?50 ?25 ?75 ?100 04771-0-039 20ns/div r s = 111, c l = 5pf r s = 60.4, c l = 15pf fig u re 3 9 . s m al l s i g n al tr ans i e n t r e s p ons e f o r v a r i ous c a pa cit i v e lo ads 2.0 ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 1.5 1.0 04771-0-040 amp l itude (v ) er r o r ( v ) 1d iv = 0.02% c f = 0pf v o, dm = 3.5v p-p error = v o, dm - input t settle = 110ns 50ns/div v o, dm input time (ns) figure 40. s e ttling time ( 0 .02%) 2v p-p 1v p-p time (ns) v o, dm (v ) 1.5 1.0 ?0.5 0 0.5 ?1.0 ?1.5 04771-0-014 c f = 0pf c f = 1pf c f = 0pf c f = 1pf 20ns/div fig u re 4 1 . l a rg e si g n al tr ans i e n t r e s p ons e f o r v a r i ous f eedba ck capa cita nces time (ns) v o, dm (v ) 1.5 0.5 1.0 0 ?0.5 ?1.0 ?1.5 04771-0-038 20ns/div r s = 111, c l = 5pf r s = 60.4, c l = 15pf fig u re 4 2 . l a rg e si g n al tr ans i e n t r e s p ons e f o r v a r i ous c a pa cit i v e lo ads
ad8137 rev. b | page 14 of 24 frequency (mhz) p s rr (db) ?5 ?2 5 ?3 5 ?1 5 ?4 5 ?6 5 ?5 5 ?8 5 ?7 5 0.1 1 1 0 100 04771-0-011 psrr = ? v o, dm/ ? v s ?psrr +psrr figure 43. psrr vs. freque ncy 1 1 0 100 1000 frequency (mhz) closed- l oop gain ( d b) v o, dm = 0.1v p-p 1 0 ?1 ?2 ?14 ?13 ?12 ?11 ?10 ?9 ?8 ?7 ?6 ?5 ?4 ?3 04771-0-010 v s = +3 v s = +5 v s = 5 figure 44. v ocm s m al l s i g n a l fr eque nc y r e s p ons e f o r v a ri ous supply v o lt ag e s 700 ?700 ?600 ?500 ?400 ?300 ?200 ?100 0 100 200 300 400 500 600 200 1k 10k 04771-0-049 resistive load ( ? ) s i ngle -e nde d outp ut s w ing from rail (mv ) v s+ ? v op v on ? v s? v s = +3v v s = +5v fig u re 4 5 . out p ut s a t u rat i on v o lt ag e v s . out p ut load frequency (mhz) outp ut imp e dance ( ? ) 1000 100 10 1 0.1 0.01 0.01 100 10 1 0.1 04771-0-061 figure 46. s i ngle-ended outp ut i m pedance vs. freq uen c y time (ns) v o, c m (v ) 4.0 3.0 3.5 2.5 1.5 2.0 1.0 04771-0-050 20ns/div 2v p-p 1v p-p figure 47. v ocm l a r g e sig n al tr ans i ent r e s p ons e 320 350 ?330 ?325 ?320 ?315 ?310 ?305 ?300 345 340 335 330 325 ? 4 0 ? 20 0 2 0 4 0 6 0 8 0 100 120 04771-0-065 temperature ( c) v op sw ing from rail ( m v) v on sw ing from rail ( m v) v on ? v s ? v s + ? v op fig u re 4 8 . out p ut s a t u rat i on v o lt ag e v s . tempe r at u r e
ad8137 rev. b | page 15 of 24 ?0.3 0.3 ?15 10 5 0 5 10 15 0.2 0.1 0 ?0.1 ?0.2 ? 4 0 ? 20 0 2 0 4 0 6 0 8 0 100 120 04771-0-052 temperature ( c) v os, dm (mv ) v os, c m (mv ) v os, cm v os, dm figure 4 9 . offset v o ltag e v s . te mpe r a t ure v acm (v) inp u t bias curre nt ( a) 1.2 1.0 0.6 0.8 0.4 0.2 ?0.2 0 ?0.4 0.50 1.50 2.50 3.50 4.50 04771-0-059 figure 5 0 . inp u t bi a s curre nt v s . input common-mod e voltage, vacm 0.10 0.40 ?3 ?2 ?1 0 1 2 3 0.35 0.30 0.25 0.20 0.15 ? 4 0 ? 20 0 2 0 4 0 6 0 8 0 100 120 04771-0-053 temperature ( c) i bias ( a) i os (na) i bias i os figure 5 1 . inp u t bi a s and offset cur r en t v s . tempe r atu r e temperature (c) s u p p l y curre nt (ma) 2.60 2.55 2.45 2.40 2.50 2.35 2.30 ?4 0 0 2 0 ?20 4 0 8 0 100 60 120 04771-0-051 figure 5 2 . supp ly c u rre nt v s . te mper a t ure v ocm (v) i v ocm ( a) 70 50 30 10 ?1 0 ?3 0 ?5 0 ?7 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 04771-0-056 figure 53. v ocm b i a s curre nt v s . v ocm in p u t v o l t a g e ?0.5 ?0.1 ?0.2 ?0.3 ?0.4 ? 4 0 ? 20 0 2 0 4 0 6 0 8 0 100 120 04771-0-054 temperature ( c) v ocm curre nt ( a) figure 54. v ocm b i a s curre nt v s . te mp eratu r e
ad8137 rev. b | page 16 of 24 v ocm v o, c m 5 4 2 3 0 1 ?1 ?4 ?3 ?2 ?5 ?5 ? 4 ? 3 ?2 ?1 4 3 2 1 05 04771-0-060 v s = +3v v s = +5v v s = 5v figure 55. v o, cm vs. v ocm input v o lt age pd voltage (v) p d curre nt ( a) 40 20 0 ?2 0 ?4 0 ?6 0 ?8 0 ?100 ?120 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 04771-0-057 figure 56. pd current vs. pd vo l t a g e pd voltage (v) s u p p l y curre nt (ma) 3 2 1 0 ?1 ?2 ?3 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 04771-0-058 i s + i s ? figure 5 7 . supp ly c u rre nt v s . pd vol t a g e pd ?2.0v ? 0.5v v o, dm 2 s/div v s = 2.5v g = 1 (r f = r g = 1k ? ) r l, dm = 1k ? input = 1vp-p @ 1mhz time ( s) s u p p l y curre nt (ma) 1.5 1.0 0.5 ?0.5 0 ?1.0 ?1.5 04771-0-066 fig u re 5 8 . po wer- d o wn tr ans i e n t r e s p ons e time (ns) s u p p l y curre nt (ma) 3.6 3.2 2.8 2.0 2.4 0.8 1.2 1.6 0.4 0 04771-0-024 100ns/div pd (0.8v to 1.5v) figure 5 9 . po wer- d o wn turn-on ti m e time (ns) s u p p l y curre nt (ma) 3.4 3.0 2.6 2.2 1.8 1.4 1.0 0.6 0.2 04771-0-025 40ns/div pd (1.5v to 0.8v) figure 6 0 . po wer- d o wn turn-off t i m e
ad8137 rev. b | page 17 of 24 theor y of opera tion the ad8137 is a lo w p o w e r , lo w cos t , f u l l y dif f er en t i al v o l t a g e f eed back a m p l if ier tha t f e a t ur es a ra il-t o-ra il o u t p u t s t a g e , co mm on-m o d e cir c ui tr y wi t h an in t e r n al l y der i v e d co mm o n - m o de r e fer e n c e vol t a g e, and b i a s sh utdo w n cir c ui t r y . t h e a m plif ier us es t w o fe e d b a ck lo ops t o s e p a ra te ly co n t r o l dif f er - en t i al and co mm o n - m o d e fe e d b a ck. the dif f er en t i al ga i n is s e t wi t h exter n a l r e sist o r s as in a t r adi t io na l am plif ier w h i l e t h e o u t p u t co mm o n -m o d e v o l t a g e i s se t b y a n in t e rn al f eed ba ck lo o p , co n t r o l l ed b y a n ext e r n al v oc m in p u t. this a r c h i t ec t u r e mak e s i t e a sy t o a r b i tra r il y s e t t h e o u t p u t co mm o n -m o d e v o l t a g e le ve l wi t h o u t a f fe c t in g t h e dif f er en t i al g a in o f t h e a m plif ier . ?out +in a cm v ocm c c c c cp +out ?in c n 04771-0-017 figure 6 1 . b l o c k d i agra m f r o m f i gur e 61, th e in p u t tra n s c o n d u c t an ce s t ag e is a n h - b r id g e wh o s e o u t p u t cu rr e n t i s m i rr o r ed t o hi gh i m ped a n c e n o des cp and c n . t h e ou t p u t s e c t io n is t r ad i t i o na l h-b r i d ge d r ive n c i rc u i t r y w i t h c o m m on e m it te r d e v i c e s d r iv i n g no d e s +o u t and ?ou t . t h e 3 db p o in t o f t h e am pl if ier is def i n e d a s c m c g bw = 2 w h er e g m i s th e tr a n s c o n d u ct a n ce o f t h e i n p u t s t a g e a n d c c is t h e t o t a l ca p a c i t a n c e on n o d e c p /cn ( c a p ac i t an ces c p an d c n a r e w e l l ma t c h e d). f o r th e ad8 137, th e in p u t st a g e g m is ~1 ma/ v an d t h e ca p a c i t a n c e c c is 3.5 pf , s e t t in g t h e cr os s o v e r f r e q uen c y o f t h e a m plif ier a t 41 mh z. this f r e q uen c y gen e ra l l y est a b l i s h e s a n am plif ier s un i t y ga in b a ndwid t h , b u t w i t h t h e ad8137, t h e c l os ed-lo o p bandwid t h dep e n d s u p o n t h e f e e d - b a ck r e sis t o r val u e as w e l l (s e e f i gur e 19). th e op en-l o o p ga in a nd phas e si m u l a t i o n s a r e sho w n i n f i gur e 62. frequency (mhz) 100 80 ?6 0 ?4 0 ?2 0 0 20 40 60 ? 120 ? 100 ?8 0 ? 200 ? 180 ? 160 ? 140 0.0001 0.01 0.001 0.1 1 1 0 100 04771-0-021 open-loop gain (db) phase (degrees) fig u re 6 2 . op en-lo o p g a in and ph as e i n f i gur e 61, t h e co mm o n -mo d e f eed b a c k am p l if ier a cm s a m p l e s t h e output c o m m on - m o d e vol t age, and b y ne g a t i ve fe e d b a ck fo r c es t h e ou t p u t co mm o n - m o d e v o l t a g e t o b e e q ual t o t h e v o l t a g e a p plie d t o t h e v oc m i n p u t. i n o t h e r w o r d s, th e fe e d b a ck lo o p s e r v os t h e o u t p ut co mm o n - m o d e v o l t a g e t o t h e v o l t a g e a p plie d t o t h e v oc m in pu t. an in ter n a l b i a s genera t o r se t s t h e v oc m l e vel to a ppro x i m a t ely m i dsupply ; t h e r e f ore, t h e out p ut c o m m on- m o d e vol t age w i l l b e s e t to a p pro x i m a t ely midsu p ply w h e n t h e v oc m in p u t is lef t f l o a t i n g . the s o ur ce r e sis t a n ce o f t h e in t e r n al b i as g e n e ra t o r is la rg e a nd can be o v er r i dde n e a sily b y a n ext e r n al v o l t a g e s u p p l i e d b y a s o ur ce w i th a r e la ti v e l y sm all o u t p u t r e si s t a n ce . th e v oc m in p u t ca n b e d r ive n to w i t h i n a pprox i m a t el y 1 v of t h e s u pp l y r a i l s w h i l e ma in t a inin g lin e a r o p era t i o n in th e co mm o n -m o d e fee d b a ck loo p . the co mm o n -m o d e f eedbac k lo o p in side t h e ad8137 p r o d uc es output s t h a t are h i g h ly b a l a nc e d o v e r a w i d e f r e q u e nc y r a nge wi t h o u t t h e r e quir em e n t o f t i g h t l y ma t c h e d ex t e r n al co m p o - n e n t s, b e c a us e i t fo r c es t h e sig n al co m p on e n t of t h e o u t p ut c o mmon- m o d e vol t age to b e ze ro e d . t h e re su lt is ne arly pe rf ectl y bal a n c ed di f f e r e n ti al o u t p u t s o f i d en tical a m p l i t ud e a nd exac tl y 180 a p a r t in p h as e .
ad8137 rev. b | page 18 of 24 appli c a t ions analyzing a typical a pplica t ion with matche d r f and r g networks typical connection and defi nition of terms f i gur e 63 sh o w s a typ i cal co nn e c tio n f o r th e ad8137, usin g ma tc he d e x te r n a l r f /r g net w o r ks. th e dif f er en t i al in p u t t e r m inals o f t h e ad8137, v ap a nd v an , a r e us e d as s u mming j u n c t i on s. an e x t e r n al r e fer e n c e v o l t a g e a p plie d t o t h e v oc m t e r m inal s e ts t h e o u t p ut co mmo n - m o d e v o l t a g e . th e tw o output te r m i n a l s , v op and v on , m o ve in o p p o si te dir e c t ion s in a b a l a n c e d fa shio n in r e sp o n s e t o a n in pu t si g n a l . 04771-0-055 + ? v ap v an v on v op ? + v o, dm r l, dm ad8137 c f r f r g r g c f r f v ip v ocm v in figure 63. typ i c a l c o nne ction the dif f er en t i al o u t p ut v o l t a g e i s def i ne d as on op dm o, v v v ? = (1) c o mm o n - m o d e v o l t a g e is t h e a v era g e o f tw o vol t a g es. th e o u t p ut co m m on- m o d e vol t a g e is def i n e d as 2 , on op cm o v v v + = (2) out p ut bal a n c e o u t p ut b a lan c e is a me asur e o f h o w w e l l v op and v on are ma t c h e d in a m pli t u d e and ho w p r ecis e l y they a r e 180 o u t o f p h as e wi t h each o t h e r . i t is t h e in t e r n al co mm on-m o d e f eed- b a ck l o op t h a t f o rc e s t h e s i g n a l c o m p o n e n t of t h e output c o m m o n - m o d e to w a rd s z e ro , re su lt i n g i n t h e n e ar p e r f e c t l y b a lan c e d dif f er en t i al o u t p u t s o f iden t i c a l a m pl i t ude an d exac t l y 180 o u t o f p h as e . th e o u t p u t b a lan c e p e r f o r ma n c e do es n o t r e q u ir e t i g h t l y ma t c h e d ext e r n al co m p on e n ts, n o r do es i t r e q u i r e th a t t h e f eed ba ck fa ct o r s o f ea c h l o o p b e eq ual t o ea c h ot he r . l o w f r e q u e nc y output b a l a nc e i s u l t i m a t e ly l i m i te d b y t h e m i s m a t ch of an on - c h i p vo lt age d i v i d e r . o u t p ut b a lan c e is m e a s ur e d b y placin g a we l l - m a t ch e d r e sist o r divider acr o s s t h e dif f er en t i al vol t a g e o u t p u t s and co m p a r ing t h e s i g n al a t t h e divider s mid p oin t w i t h t h e mag n i t u d e o f t h e d i f f e r e n tial o u t p u t . b y th i s d e f i ni ti o n , o u t p u t ba la n c e i s e q ual t o t h e ma g n i t ude o f t h e chan g e i n o u t p u t co mm on- m o d e v o l t a g e divide d b y t h e ma g n i t u d e o f t h e cha n g e in o u t p u t dif f er en t i al - mo d e vo lt age : dm o cm o v v balance output , , = ( 3 ) the dif f er e n t i a l neg a t i ve fe e d b a ck dr i v e s t h e v o l t a g es a t t h e su mm i n g j u nc t i ons v an and v ap t o be e s sen t iall y eq ual t o e a c h ot h e r . ap an v v = ( 4 ) the co mm o n - m o d e fe e d b a ck lo o p dr i v es t h e o u t p ut co mm on- mo de vol t age, s a m p l e d a t t h e m i d p oi n t of t h e t w o i n te r n a l co mm on-m o d e ta p r e sis t o r s in f i gur e 61, t o eq ual t h e v o l t a g e se t a t t h e v oc m t e r m ina l . this e n sur e s t h a t 2 , dm o ocm op v v v + = ( 5 ) a nd 2 , dm o ocm on v v v ? = ( 6 ) estimat i n g noise, ga in, an d ba ndwi th wi th matche d feedback n e tworks es timating o u tput nois e voltage an d b a n d w i dth the t o t a l o u t p ut n o is e is t h e r o o t -s u m -s q u a r e d t o t a l o f s e veral st a t ist i ca l l y i nde p e nde n t s o ur ce s. si n c e t h e s o ur ces a r e st a t i s t i - call y in d e pen d en t , t h e co n t r i b u ti o n s o f ea c h m u s t be in di vi d u - all y i n c l ud ed i n th e r o o t - s um -s q u a r e cal c ul a t i o n . t a b l e 7 l i s t s r e co mm e nde d resisto r va l u es and est i m a tes o f b a ndwi d t h and o u t p ut dif f er en t i al v o l t a g e n o is e fo r va r i o u s cl os e d -lo o p ga i n s. f o r mo st a p pl i c a t ions , 1 % re s i stors are su f f i c i e n t. table 7. r e com m ende d values of gain-settin g resistors, and voltage ga in for various closed-loo p g a ins ga i n r g (?) r f (?) 3 db bandw idth (mh z) t o tal o utput noise (nv/h z) 1 1 k 1 k 72 18.6 2 1 k 2 k 40 28.9 5 1 k 5 k 12 60.1 10 1 k 10 k 6 112.0
ad8137 rev. b | page 19 of 24 the dif f er en t i al o u t p ut v o l t a g e n o is e con t ain s c o n t r i b u t i o n s f r o m t h e a d 81 37 s in p u t v o l t a g e n o is e an d in pu t c u r r en t n o is e as w e l l as t h os e f r o m t h e ext e r n a l fe e d b a ck n e t w o r ks. the co n t r i b u t i on f r o m t h e i n p u t v o l t a g e n o is e sp e c t r al de n s i t y is co m p u t e d as ? ? ? ? ? ? + = g f n r r v vo_n 1 1 , o r e q ui vale n t l y , v n / ( 7 ) w h er e v n is def i n e d as t h e i n p u t - r e fer r e d dif f er en t i al v o l t a g e n o is e. this e q u a t i o n is t h e s a me as t h a t o f t r ad i t io na l o p a m ps. the co n t r i b u t i on f r o m t h e i n p u t c u r r en t n o is e o f e a ch i n p u t is co m p u t e d as ( ) f n r i vo_n = 2 ( 8 ) w h er e i n is def i ne d as t h e i n p u t n o is e c u r r en t o f o n e i n p u t. e a ch in p u t n e e d s t o b e t r e a t e d s e p a ra t e l y si n c e t h e two in p u t c u r r e n ts a r e s t a t is t i cal l y i n dep e nden t p r o c es s e s. t h e co n t r i b u ti o n f r o m ea c h r g is co m p u t e d as ? ? ? ? ? ? = g f g r r tr vo_n k 4 3 (9) this r e s u l t can b e in t u i t i v e l y vi e w e d as t h e t h er mal n o i s e o f ea c h r g m u l t i p l i e d b y t h e ma g n i t ude o f t h e dif f er en t i al ga i n . t h e co n t r i b u ti o n f r o m ea c h r f is co m p u t e d as f tr vo_n k 4 4 = (10) voltage g a in the b e ha vio r o f t h e n o de v o l t a g es o f t h e si n g le- e nde d-t o - dif f er en t i a l o u t p u t to p o lo g y ca n b e de d u ce d f r o m t h e sig n a l def i ni t i o n s an d f i gur e 63. refer r in g t o f i gur e 6 3 , (c f = 0) a n d se t t i n g v in = 0 o n e ca n wr i t e: f on ap g ap ip r v v r v v ? = ? (11) ? ? ? ? ? ? + = = g f g op ap an r r r v v v ( 1 2 ) s o lvin g t h e ab o v e tw o e q ua t i o n s a nd s e t t i n g v ip to v i gi v e s th e g a i n re l a t i onsh ip f o r v o, d m / v i . i g f dm o, on op v r r v v v = = ? ( 1 3 ) an i n v e r t in g conf igura t io n w i t h t h e s a m e gain ma g n i t u d e can b e im pl e m e n te d b y s i m p ly a p ply i ng t h e in pu t s i g n a l to v in and se t t i n g v ip = 0. f o r a b a lan c e d dif f er en t i al i n p u t, t h e ga i n f r o m v in, d m to v o, d m i s als o eq ual t o r f / r g , w h er e v in, dm = v ip ? v in . fe ed ba ck fa ctor nota tion w h en w o rking wi t h dif f er en t i al dr i v ers, i t is co n v enien t t o in t r o d uce t h e fe e d b a ck fac t o r , w h ich is def i n e d as g f g r r r + ( 1 4 ) t h i s n o ta ti o n i s co n s i s t e n t w i t h co n v en ti o n al f e ed ba ck a n al ys i s a nd is v e r y us ef u l , p a r t ic u l a r ly w h en t h e tw o fe e d b a ck lo o p s a r e not m a tc he d. inp u t com m on-mode volt age the li n e a r ra n g e o f t h e v an an d v ap te r m i n a l s e x te nds to w i t h i n a p p r o x ima t e l y 1 v o f ei t h er s u pply ra i l . sin c e v an a nd v ap are e s se n t iall y eq ual t o ea c h o t h e r , t h ey a r e bo t h eq ual t o t h e a m plif ier s i n p u t co mm o n - m o d e v o l t a g e . th eir ra n g e is indi ca t e d in t h e sp e c if ic a t io n s t a b l es as i n p u t c o mm on- m o d e ra n g e . th e v o l t ag e a t v an an d v ap fo r t h e co nne c t io n d i a g r a m in f i gur e 63 can b e exp r es s e d as = = = acm ap an v v v ? ? ? ? ? ? + + ? ? ? ? ? ? + + ocm g f g in ip g f f v r r r v v r r r 2 ) ( (15) w h er e v ac m is t h e co mm on- m o d e v o l t a g e p r es en t a t t h e a m plif ier i n p u t t e r m ina l s. u s i n g th e n o ta t i o n , eq u a t i o n ( 1 5 ) c a n be w r i t t e n a s ( ) icm ocm acm v v v ? + = 1 ( 1 6 ) or e q u i v a l e n t ly , ( ) icm ocm icm acm v v v v ? + = ( 1 7 ) w h er e v ic m is t h e co mm o n - m o d e v o l t a g e o f t h e in pu t sig n a l , th a t i s 2 in ip icm v v v + f o r p r o p er o p era t io n, t h e v o l t a g es a t v an a nd v ap m u st st a y w i th in t h ei r r e s p ecti v e lin e a r ra n g e s . c a lc ulating in put im pe da nc e the i n p u t im p e dan c e o f t h e circ ui t i n f i gur e 63 dep e n d s on w h et h e r t h e am plif ier is b e i n g d r i v en b y a sin g l e -ende d o r a dif f er en t i al sig n al s o ur ce . f o r b a lan c e d dif f er en t i al in p u t sig n als, t h e dif f er en t i al i n p u t i m p e dan c e ( r in, d m ) is sim p l y g dm in, r r 2 = ( 1 8 ) f o r a sin g le-ended sig n al (f o r exa m p l e , w h en v in i s g rou nd e d , a nd t h e i n p u t si g n al dr i v es v ip ), t h e in p u t i m p e dan c e b e co m e s ) ( 2 1 f g f g in r r r r r + ? = ( 1 9 )
ad8137 rev. b | page 20 of 24 04771-0-018 gnd v ref v refa adr525a 2.5v shunt reference ad7450a v in + v in ? vdd ad8137 + ? 8 v refb 2.5v 2 1 6 3 4 5 v ocm 1k ? 1k ? 1k ? 2.5k ? 1k ? 5v 50 ? 50 ? v in 1.0nf 1.0nf 0.1 f 0.1 f +1.88v +1.25v v acm with v refb = 0 +0.63v +2.5v gnd ? 2.5v fi gur e 64 . ad8 137 dr i v ing ad74 50 a, 1 2 - bi t a/ d co nver t e r the i n p u t im p e dan c e o f a co n v en t i o n al i n v e r t i n g o p a m p co nf igura t io n is sim p ly r g , b u t i s hig h er i n e q u a t i o n 19 b e c a us e a f r ac t i o n o f t h e dif f er en t i al o u t p u t v o l t a g e a p p e a r s a t th e s u m m i n g j u n c ti o n s , v an a nd v ap . this v o l t a g e p a r t ia l l y b o o t s t ra ps t h e vol t a g e acr o s s t h e in pu t r e sis t o r r g , le adin g t o th e in cr ea se d in p u t r e s i s t a n ce . input common-mode swing consideratio ns i n s o me sin g le - e nde d - t o - d if fer e n t ia l a p plic a t ion s w h e n usin g a sin g le- s u p ply v o l t a g e , a t ten t i o n m u s t b e p a i d t o t h e s w in g o f t h e in p u t co mm o n - m o d e v o l t a g e , v ac m . c o n s ider t h e cas e i n f i gur e 64, w h er e v in is 5 v p-p swin g i n g ab out a b a s e l i ne a t g rou n d a n d v refb is co nn e c te d to g r o u nd . the in p u t s i g n a l t o th e ad8137 is o r ig ina t in g f r o m a s o ur ce wi t h a v e r y lo w o u t p ut r e sist a n c e . th e cir c ui t has a dif f er en t i al ga in o f 1.0 a n d = 0. 5. v ic m has a n a m p l i t ude o f 2.5 v p-p a n d is swin g i n g a b o u t gr o u n d . u s in g t h e r e s u l t s in e q ua ti o n 16 , th e c o mm o n -m o d e v o l t a g e a t th e ad81 37 s in p u ts, v ac m , i s a 1.2 5 v p-p signal swin g i n g a b o u t a bas e lin e o f 1.25 v . th e maxi m u m n e ga ti v e e x c u rs io n o f v ac m in t h is cas e is 0.63 v , w h ich e x ce e d s t h e lo w e r i n p u t co mm o n - m o d e v o l t a g e li mi t. on e wa y t o a v o i d t h e i n p u t co mm o n - m o d e s w i n g limi t a t i o n is to b i a s v in and v ref a t midsu p pl y . i n t h is cas e , v in is 5 v p-p sw in gi n g a b o u t a ba s e lin e a t 2.5 v , a n d v ref is c o nn e c te d to a lo w-z 2.5 v s o u r ce . v ic m now h a s an am pl itu d e of 2 . 5 v p - p an d is swin g i n g a b ou t 2.5 v . u s in g t h e r e s u l t s in e q ua tion 17, v ac m is calc u l a t e d t o be eq ual t o v ic m beca use v oc m = v ic m . ther efo r e , v ic m swin gs f r o m 1.25 v t o 3.7 5 v , whic h is wel l wi thin t h e in p u t co mm o n -m o d e v o l t a g e limi ts o f t h e ad8 137. an o t h e r b e n e f i t s e en b y t h is exa m ple is t h a t si n c e v oc m = v ac m = v ic m , n o wast e d co mm o n - m o d e c u r r en t f l o w s. f i gur e 65 i l l u s t ra t e s a w a y to pro v i d e t h e l o w - z bi as v o lt age. f o r s i tu a t i o ns t h a t do not re qu i r e a pre c i s e re f e re nc e, a s i m p l e vo lt ag e d i v i d e r w i l l su f f i c e t o de ve lo p t h e i n p u t v o l t a g e t o t h e b u f f er . 04771-0-019 v in 0 v to 5v ad8137 + ? 8 2 1 6 3 4 5 v ocm 1k ? 1k ? 5v 1k ? 1k ? 10k ? 0.1 f 0.1 f 0.1 f 10 f + ad8031 + ? 0.1 f 5v adr525a 2.5v shunt reference to ad7450a v ref figure 65. l o w-z b i as sou r ce a n ot he r w a y to a v oi d t h e i n put c o m m o n - m o d e s w i n g l i m i t a - tio n is t o us e d u al p o w e r s u p p lies o n t h e ad81 37. i n this cas e , t h e b i asin g c i r c ui t r y is n o t r e q u ir e d . bandwidth v s . closed-loop gain the ad8137 s 3 db ban d wid t h wil l decr eas e p r o p o r tio n al l y t o in cr e a s i n g clos e d -lo o p ga i n i n t h e s a me w a y as a t r ad i t io na l v o l t a g e fe e d b a ck o p era t io na l am plif ier . f o r clos e d -lo o p gain s gr ea t e r th a n 4, t h e ba n d w id t h o b ta in e d f o r a s p eci f i c g a i n ca n b e es t i ma t e d as ) ( r r r v , f f g g dm o, db mhz 72 3 + = ? (20) o r eq ui valen t l y , (72 mh z). this est i ma te assum e s a m i ni m u m 90 phas e ma rg in fo r t h e a m plif ier lo o p , a co nd i t io n a p pr o a ch e d fo r ga in s g r e a t e r t h an f o ur . lo w e r g a i n s will s h o w m o r e ba n d w id th tha n p r ed i c t e d b y t h e e q u a t i on d u e t o t h e p e aking p r o d uce d b y t h e lo w e r phas e ma rg in.
ad8137 rev. b | page 21 of 24 estimating dc errors p r ima r y dif f er e n t i al o u t p u t o f fs et er r o r s in t h e ad8137 a r e d u e t o t h r e e ma jo r c o m p on en ts: t h e in p u t o f fs et v o l t a g e , t h e o f fs et b e tw e e n t h e v an a nd v ap in p u t c u r r en ts i n t e rac t in g wi t h t h e fe e d b a ck net w ork r e sis t an ces, and t h e o f fs et p r o d uce d b y t h e dc v o l t a g e dif f er ence b e twe e n t h e i n p u t and o u t p ut co mm o n - m o d e v o l t a g es i n co n j un c t ion wi t h ma t c hin g er r o r s in t h e fe e d b a ck ne t w or k . the f i rs t o u t p u t er r o r co m p o n e n t is c a lc u l a t e d as ? ? ? ? ? ? + = g g f io r r r v vo_e 1 , o r eq ui valen t l y as v io / (21) w h er e v io is t h e in p u t o f fs et v o l t a g e . the s e cond er r o r is calc u l a t e d as ( ) f io g f f g g g f io r i r r r r r r r i vo_e = ? ? ? ? ? ? + ? ? ? ? ? ? + = 2 ( 2 2 ) w h er e i io is def i n e d as t h e o f fs et b e tw e e n t h e two in p u t b i as c u r r en ts. the t h ir d er r o r v o l t a g e is c a lc u l a t e d as ) ( 3 ocm icm v v enr vo_e ? ? = ( 2 3 ) w h er e en r is t h e f r ac t i o n al mi sma t ch b e tw e e n t h e tw o f e e d b a c k re s i stor s . the t o t a l dif f er e n t i al o f fs et er r o r is t h e s u m o f t h es e t h r e e er r o r so u r c e s . additiona l impac t of mis m a t che s in the feedback ne twork s the i n t e r n al comm on- m o d e fe e d b a ck n e tw o r k wi l l s t i l l fo r c e th e o u t p u t v o l t a g e s t o r e m a i n b a la n c e d , ev en w h en t h e r f /r g fe e d back net w orks a r e misma t ch e d . th e misma t c h , h o we v e r , w i l l c a u s e a g a i n e r ror prop or t i on a l to t h e f e e d b a ck ne t w or k misma t ch. r a t i o-ma t c hin g er r o r s in t h e ext e r n al r e sis t o r s wi l l deg r ade t h e a b il i t y t o r e je c t co mm on-m o d e sig n als a t t h e v an a nd v in in p u t te r m i n a l s , s i mi l a r to a fou r - r e s istor di f f e r e n c e am pl i f i e r mad e f rom a c o n v e n t i on a l op am p . r a t i o - m a t c h i ng e r ror s w i l l a l s o p r o d uce a dif f er en t i al o u t p ut co m p on e n t t h a t is e q ual t o t h e v oc m in p u t v o l t a g e t i m e s t h e di f f er en ce b e tw e e n t h e fe e d b a ck fac t o r s (s). i n m o s t a p p l ic a t ion s usin g 1% r e sis t o r s, t h is co m p on e n t amo u n t s t o a dif f er en t i al dc o f fs et a t t h e o u t p ut t h a t i s s m a l l e n ou g h to b e i g nore d. driving a capaciti ve lo ad a pu rely c a p a c i t i ve l o a d w i l l re a c t w i t h t h e b o nd w i re a n d pi n ind u c t an c e o f t h e ad8137, r e su l t in g in hig h f r eq uen c y r i n g ing in t h e t r an sien t r e s p o n s e and los s o f phas e ma rg in. o n e wa y t o mini mi ze t h is e f fe c t is to place a sma l l r e sisto r in s e r i es w i t h ea c h o u t p u t t o b u f f e r th e loa d ca pa ci ta n c e . th e r e s i s t o r a n d loa d ca p a ci t a n c e wi l l fo r m a f i rs t-o r d er , lo w-p a s s f i l t e r , s o t h e r e sis t o r val u e sh o u l d b e as smal l as p o s s ib le . i n s o m e cas e s, t h e ad cs re qu i r e s m a l l s e r i e s re s i stor s to b e a d d e d on t h e i r i n put s . f i g u re 3 9 a n d fi g u re 4 2 i l lu st r a te t r ans i e n t re sp ons e v s . c a p a c i - t i ve lo ad , and wer e gen e r a te d us in g s e r i es r e sisto r s in e a ch o u t p ut an d a d i f f er en t i a l ca p a c i t i v e lo ad . layout c o ns id er ations s t a n da r d hi g h spe e d pcb la y o u t p r a c tices sh o u ld b e ad h e r e d t o wh e n d e s i gn i n g w i th th e a d 81 37 . a s o li d g r o u n d p l a n e i s r e com m e n de d and go o d w i d e b a nd p o wer sup p ly de cou p l i n g n etw o r k s s h o u ld b e p l a c e d as close a s pos s i b le t o t h e s u p p l y p i n s. t o mini mi ze st ra y ca p a c i t a n c e a t t h e s u mming n o des, t h e co p p er i n al l l a yers un der al l t r aces a nd p a ds t h a t co nn e c t t o t h e su m m i n g no d e s shou l d b e re move d. sm a l l a m o u n t s of st r a y s u mmin g-n o de ca p a ci tan c e wil l ca us e p e ak in g in t h e f r eq uen c y re sp ons e , a n d l a r g e amou n t s c a n c a u s e i n st a b i l it y . i f s o m e st r a y s u mmin g-n o de ca p a ci tan c e is u n a v o i dab l e , i t s ef f e c t s ca n b e co m p ens a t e d f o r b y p l acing smal l ca p a c i t o rs ac r o s s th e f e e d back re s i stor s . terminating a sing le-en d e d inp u t c o n t ro l l e d i m p e d a nc e i n te rc on ne c t i o ns are u s e d i n mo st h i g h sp e e d s i g n a l a pplica t ion s , an d t h e y r e q u ir e a t le ast o n e li n e t e r m in a t io n. i n a n a l og a p plic a t i o n s , a ma t c h e d r e sist i v e t e r - m i n a t i o n i s g e n e rall y p l a c ed a t th e load en d o f th e lin e . t h i s s e c t io n de a l s wi t h h o w to p r o p e r ly ter m ina t e a s i n g le -e n d e d in p u t t o t h e ad8137. the in p u t r e sis t a n ce p r es en t e d b y t h e ad8137 in p u t cir c ui tr y is s e en in p a ra l l e l wi t h t h e t e r m ina t ion r e sist o r , a nd i t s lo ading ef fe c t m u s t b e t a k e n in t o ac co u n t. th e the v eni n e q uivale n t cir c ui t o f t h e dr i v er , i t s s o ur ce r e sis t a n c e , an d t h e ter mina t i o n r e si s t a n ce m u s t all be in c l ud e d in t h e calcula ti o n a s w e ll . an exac t s o l u t i o n to t h e p r ob le m r e q u ir es s o l u t i on o f s e v e ral s i m u l t a n eo us alg e b r a i c eq ua ti o n s a n d i s bey o n d t h e sco p e o f th i s d a t a s h eet . a n i t e r a t i v e so l u ti o n i s also pos s i b l e a n d i s sim p ler , es p e c i a l ly co n s ider in g t h e f a c t t h a t s t anda r d r e sis t o r val u es a r e g e n e ral l y us e d . f i gur e 66 sh o w s th e ad8137 in a uni t y-ga in conf igura t io n, and wi t h t h e fol l o w i n g dis c us sion, pr o v ides a g o o d exa m ple o f h o w t o p r o v id e a p r op er t e r m in a t ion in a 50 ? e n viro nm e n t.
ad8137 rev. b | page 22 of 24 this exa m ple sho w s t h a t w h e n r f and r g a r e larg e co m p a r e d to r t , th e g a i n r e d u cti o n p r od uced b y th e in cr e a se in r g is es s e n t i a l l y can c e l le d b y t h e i n cre a s e i n t h e th e v enin v o l t a g e ca us e d b y r t b e i n g g r ea t e r t h a n th e o u t p u t r e s i s t a n ce o f th e sig n a l s o urce. i n g e nera l , as r f and r g be co m e sm a l l e r i n t e rm i - na te d a p pli c a t ion s , r f n e eds t o b e in cr ease d t o co m p en s a t e f o r t h e in cr ease in r g . ad8137 + ? 8 2 1 6 3 4 0v 2v p-p r t 52.3 ? 5 + ? v ocm 1k ? 1.02k ? 1k ? 1k ? 0.1 f 0.1 f +5v ?5v v in signal source 50 ? 04771-0-020 w h en g e n e r a t i ng t h e typ i cal p e r f o r ma n c e cha r ac t e r i s t ics da t a , th e m e a s ur em en t s w e r e cali b r a t ed t o t a k e t h e ef f e ct s o f th e t e r m ina t io n s on c l os ed-lo o p ga in in t o acco u n t. power down the ad8137 f e a t ur es a pd p i n t h a t ca n b e us e d to mini mi ze t h e q u i e scen t curr en t co n s um ed w h en t h e de v i ce is n o t bei n g use d . pd is as s e r t ed b y a p p l yin g a l o w log i c lev e l t o p i n 7. the thr e sh- old betw een hig h an d lo w log i c lev e ls is n o mina l l y 1.1 v a b o v e th e n e g a ti v e s u p p l y ra il . s e e th e s p eci f i c a t i o n t a b l e s (t a b le 1 t o t a b l e 3) fo r t h e t h r e s h ol d limi ts . fi gur e 66 . ad8 137 wi th te rm i n a t e d input the 52.3 ? t e r m ina t io n r e sis t o r , r t , in p a ral l el wi t h t h e 1 k? in p u t r e sis t an ce o f th e ad8137 cir c ui t, y i e l ds an o v eral l in p u t r e sis t a n ce o f 50 ? tha t is s een b y th e sig n al s o u r ce . i n o r d er t o ha v e ma t c h e d f eed back lo o p s, e a c h lo o p m u st ha v e t h e s a me r g if i t has t h e s a me r f . i n t h e in p u t (u p p er) lo o p , r g is eq ual t o t h e 1 k? r e sis t o r in s e r i es w i t h t h e ( + ) in p u t pl us t h e p a ral l e l co m b in a t io n o f r t a n d t h e s o ur ce r e sis t a n c e o f 50 ?. i n t h e upp e r l o op , r g i s t h er efo r e e q u a l t o 1.03 k?. the clos es t st anda r d v a l u e i s 1.02 k? a nd is us e d fo r r g in t h e lo wer lo o p . drivi n g a n adc wit h greater th an 12-bit performa nce since t h e ad81 37 is s u i t ab le fo r 12-b i t sys tem s , i t is desirab l e to m e as ur e t h e p e r f o r ma n c e o f t h e a m plif ier i n a s y s t em wi t h gr ea t e r th a n 12-b i t lin e a r i t y . i n pa r t i c ula r , th e ef f e cti v e n u m b e r o f b i t s, e n o b , is m o s t in t e r e s t in g. the ad768 7, 16-b i t, 250 ks ps ad c s p e r f o r ma n c e mak e s i t an idea l ca ndida te f o r s h o w casin g t h e 12-b i t p e r f o r ma n c e o f t h e ad8 137. thin gs be co me m o r e co m p l i c a ted w h en i t comes t o det e r m ini n g t h e fe e d b a ck r e sis t o r val u es. th e am pli t ude o f t h e sign al so ur ce g e n e ra t o r v in i s tw o ti m e s t h e a m p l i t ud e o f i t s output s i g n a l w h e n te r m i n a t e d i n 5 0 ? . t h e r e f ore, a 2 v p - p t e r m ina t e d a m pli t u d e is p r o d u c ed b y a 4 v p-p a m p l i t ude f r o m v s . the th e v enin e q u i vale n t c i r c ui t o f t h e sig n a l s o ur ce an d r t m u s t be use d w h en calcu l a t i n g th e c l ose d - l oo p g a i n beca use r g in t h e u p p e r lo op is s p li t b e tw e e n t h e 1 k? r e sist o r a nd t h e the v enin r e sis t a n ce lo ok in g b a ck t o w a r d t h e s o ur ce . th e t h ev e n i n v o l t a g e o f th e s i gnal s o ur ce i s gr ea t e r th a n t h e si gn al s o u r c e output v o lt age w h e n te r m i n a t e d i n 5 0 ? b e c a u s e r t m u s t al wa ys be gr ea t e r th a n 50 ?. i n th i s ca s e , r t is 52.3 ? a n d th e th evenin vol t a g e an d r e sis t a n ce a r e 2.04 v p-p a nd 25.6 ?, r e s p ecti v e l y . f o r t h is a p plic a t io n, t h e ad813 7 is s et i n a gain o f tw o a nd dr i v en s i n g l e - e n d ed th r o ugh a 20 k h z ba n d - p a s s fil t e r , wh il e th e o u t p u t i s ta k e n d i ff e r e n ti all y t o th e i n p u t o f th e a d 7 6 8 7 (se e f i gur e 67). t h is c i r c ui t ha s m i sm a t c h e d r g im p e da n c e s a n d , t h erefo r e, has a dc o f fs e t a t t h e di ff e r e n ti al o u t p u t . i t i s i n c l u d ed as a t e s t c i r c ui t to i l l u st ra te t h e p e r f o r manc e o f t h e a d 81 37. a c t u a l app l i c at i o n c i r c u i t s s h ou l d h a v e m a t c h e d f e e d b a c k n etw o r k s . f o r an ad76 87 in p u t ran g e u p to ?1. 82 db fs , t h e ad813 7 p o w e r sup p ly is a si ng l e 5 v a p pl ie d t o v s+ wi t h v s? tie d t o gr o u n d . t o in creas e t h e ad7687 in p u t r a nge t o ?0 .45 dbfs, t h e ad813 7 s u p p li es a r e in cr ease d t o +6 v a n d ?1 v . i n bo t h cases , t h e v oc m p i n i s b i a s ed w i th 2. 5 v a n d th e pd p i n is lef t f l o a t i ng. al l volt a g e s u p p l i es a r e de c o u p l e d wi th 0. 1 f ca p a c i t o rs. f i gur e 68 and f i g u r e 6 9 s h ow t h e p e r f or m a n c e of t h e ? 1 . 8 2 d b f s s e tup a n d t h e ?0.4 5 db fs s e t u p , resp e c t i vel y . n o w the u p p e r in p u t b r an ch can b e view e d as a 2.04 v p-p so ur ce in se ri e s w i th 1.03 k ? . s i n c e th i s i s t o be a un i t y- ga in a p plic a t ion, a 2 v p-p dif f er en t i a l o u t p u t is r e quir e d , and r f m u s t t h er ef o r e be 1.03 k? (2/2.04) = 1.01 k? 1 k?.
ad8137 rev. b | page 23 of 24 ad8137 + ? 1nf 1nf v ocm v s ? v s + v+ 1.0k ? 1.0k ? 20khz 33 ? 33 ? 04771-0-067 499 ? 499 ? +2.5 ad7687 gnd v dd v in gnd bpf fi gur e 67 . ad8 137 dr i v ing ad76 87 , 16 -bi t 2 5 0 k s p s adc frequency (khz) amp l itude (db of full s cale ) 0 ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 ? 100 ? 110 ? 120 ? 130 ? 140 ? 150 ? 160 ? 170 04 0 20 60 120 100 80 140 04771-0-068 thd = ? 93.63dbc snr = 91.10db sinad = 89.74db enob = 14.6 fi gur e 68 . ad8 137 p e r f o r m a nc e o n singl e 5 v suppl y , ? 1 .8 2 dbfs frequency (khz) amp l itude (db of full s cale ) 0 ?10 ?20 ?30 ?40 ?50 ?60 ?70 ?80 ?90 ? 100 ? 110 ? 120 ? 130 ? 140 ? 150 ? 160 04 0 20 60 120 100 80 140 04771-0-069 thd = ? 91.75dbc snr = 91.35db sinad = 88.75db enob = 14.4 fig u re 6 9 . a d 81 3 7 perf or ma nce on + 6 v , ? 1 v supp li es , ? 0 .4 5 dbfs
ad8137 rev. b | page 24 of 24 outline dimensions 0.25 (0.0098) 0.17 (0.0067) 1.27 (0.0500) 0.40 (0.0157) 0.50 (0.0196) 0.25 (0.0099) 45 8 0 1.75 (0.0688) 1.35 (0.0532) seating plane 0.25 (0.0098) 0.10 (0.0040) 4 1 85 5 . 00 ( 0 . 1 968) 4 . 80 ( 0 . 1 890) 4.00 (0.1574) 3.80 (0.1497) 1.27 (0.0500) bsc 6.20 (0.2440) 5.80 (0.2284) 0.51 (0.0201) 0.31 (0.0122) coplanarity 0.10 controlling dimensions are in millimeters; inch dimensions (in parentheses) are rounded-off millimeter equivalents for reference only and are not appropriate for use in design compliant to jedec standards ms-012-aa fig u re 7 0 . 8-le ad s t anda rd s m a l l out l ine p a ck ag e [soic _ n] nar r ow b o dy (r-8) dim e nsio ns sho w n i n mi ll im e t er s and (i nc he s) 1 ex po s e d pa d (b o t t o m v i e w ) 0.50 bsc 0.60 max pin 1 indicato r 1.50 ref 0.50 0.40 0.30 2.75 bsc sq top view 12 max 0.70 max 0. 6 5 t y p seating plane pin 1 indicator 0.90 max 0.85 nom 0.30 0.23 0.18 0.05 max 0.01 nom 0.20 ref 1.89 1.74 1.59 4 1.60 1.45 1.30 3.00 bsc sq 5 8 fig u re 7 1 . 8-le ad l e ad f r a m e chip sc al e p a ck ag e [lfcs p _v d] 3 mm 3 m m b o d y , v e ry th in, dua l l e ad (cp-8- 2) dim e nsio ns sho w n i n mi ll im e t er s ordering guide model t e mper a t ur e r a nge p a ck age descri ption p a ck age o p tion br anding ad8137y r ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y r-ree l ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y r-ree l 7 ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y rz 1 ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y rz -re e l 1 ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y rz -re e l 7 1 ?40c to +125c 8-l e ad standar d small o utline p a ck age (soic_n) r-8 ad8137y cp -r2 C40c to +125c 8-l e ad l e ad f r ame chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb ad8137y cp -ree l C40c to +125c 8-l e ad l e ad f r ame chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb ad8137y cp -ree l7 C40c to +125c 8-l e ad l e ad f r am e chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb ad8137y cp z - r2 1 C40c to +125c 8-l e ad l e ad f r ame chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb# ad8137y cp z - re el 1 C40c to +125c 8-l e ad l e ad f r ame chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb# ad8137y cp z - re el7 1 C40c to +125c 8-l e ad l e ad f r ame chip s c ale p a ck age (lfcsp_vd ) cp -8-2 hfb# 1 z = p b -fre e part; # d e no te s le ad -f re e , may be to p o r b o tto m mark e d . ? 2005 analo g de vices, inc. all rights reserve d . tra d em arks and registered tra d ema r ks are the prop erty of their respective owners . d04771C0C 7/05(b)

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