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low cost, low power 12-bit differential adc driver ad8137 rev. a 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. 326. 87 03 ? 2004 analog de vices, i n c. al l r i ght s r e ser v ed . fea t ures fully dif f erenti al extremely low power with power-down feat ure 2.6 ma quie scent supply curre nt @ 5 v 450 a in power-down mode @ 5 v high speed 110 mh z large signal 3 db bandwidth @ g = 1 450 v/s s l ew r a te 12-bit sfdr performance @ 500 khz fast settling ti me: 100 ns to 0 . 02% low input offset voltage: 2. 6 mv max low input offset current: 0. 45 a max differentia l inp u t and output differential-to-differential or s i ngle-ended-to-different ial operation rail-to-rail out p ut adjustable out p ut common- mode voltage externally adjustable gain wide s u pply voltage range: 2. 7 v to 1 2 v avail a ble in sm all soic packa g e applic a t io ns 12-bit a d c drivers portable instrumentation battery-powered applications single-ended-t o-differential converters differentia l act i ve fi lters video amplifi e rs level shift e rs 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 fi g u r e 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 ?12 ?11 ?10 ?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 f i g u r e 2. small sig n al r e s p ons e f o r v a ri ous g a ins 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 nd cos t . th e ad8137 is easy t o a p p l y , an d i t s in t e r n al co mm on-m o d e f e e d back a r c h i t ec t u r e al lo ws i t s o u t p u t co mm o n - 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. the in t e r n al f e e d back lo o p als o p r o v ides in h e r 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 gain co nf igura t io n s a r e e a si ly r e a l iz e d b y t h e ad8137. e x t e r n al f eed back n e tw o r ks co n s is t i ng o f f o ur r e sis t 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 w n fe a t ur e is b e n e f i cia l i n cr i t ica l lo w p o w e r a p plic a t io n s . the ad8137 is ma n u fac t ur ed on analog de vic e s p r o p r i eta r y s e c o nd 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 mm lfcs p . i t is ra t e d t o o p era t e o v e r t h e ext e n d e 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. a | 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 f and r g networks...................................................................................... 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 8/04data sheet changed from a rev. 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. a | page 3 of 24 specifications table 1. v s = 5 v, v ocm = 0 v (@ 25c, diff. gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c) 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. a | page 4 of 24 table 2. v s = 5 v, v ocm = 2.5 v (@ 25c, diff. gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c) 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. a | page 5 of 24 table 3. v s = 3 v, v ocm = 1.5 v (@ 25c, diff. gain = 1, r l, dm = r f = r g = 1 k?, unless otherwise noted, t min to t max = ?40c to +125c) 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. a | pa ge 6 o f 2 4 absolute maximum ra tings ta bl e 4. p a r a m e t e r r a t i n g supply voltage 12 v v ocm v s+ to v s? power dissi pati on see figure 3 input common-mode vol t age v s+ to v s? storage temperature ?65c to +125c operating tem p erature range ?40c to +125c lead temperature range (sol dering 10 s e c) 300c junction tempe r ature 150c s t r e s s es a b o v e t h os e lis t e d u n de r a b s o l u t e m a xi m u m r a t i n g s ma y c a us e p e r m a n en t dama ge t o t h e de vice . this is a s t r e s s ra tin g onl y a nd f u n c tio n al op era t io n o f t h e de vice a t t h es e o r 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 n di ca t e d in 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 plie d . e x p o sur e t o a b s o l u te max i m u m ra t i ng co ndi t i on s fo r ex ten d e d p e r i o d s ma y a f fe c t de vice r e l i ab i l i t y . thermal resist ance ja is sp e c if ie d fo r t h e w o rst - ca s e co ndi t i on s, i . e. , ja is sp e c if ie d fo r t h e de vic e s o lder e d in a cir c ui t b o a r d in s t i l l a i r . ta bl e 5. th er m a l resista n ce package type ja jc unit s o i c - 8 / 2 - l a y e r 1 5 7 5 6 c / w s o i c - 8 / 4 - l a y e r 1 2 5 5 6 c / w l f c s p / 4 - l a 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 soc i a t ed ri se in 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, whic h is t h e g l as s tran si tion t e m p era t ur e , t h e plas t i c w i l l cha n g e i t s p r o p er t i es. e v en t e m p o- ra r i l y e x ce e d in g t h is t e m p era t ur e limi t ma y chan g e t h e s t r e s s es 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 e n 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 exten d ed p e r i o d o f time can r e s u l t in cha n ge s in t h e si lico n d e vices p o t e n t ia l l y c a usin g fa i l ur e . the p o w e r dis s i p a t e d in t h e p a cka g e (p d ) i s th e s u m o f th e q u ies c en 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 q u ie s 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 ) ti m e s th e q u ies c en t c u r r en t (i s ). th e 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 on- m o d e c u r r en ts f l o w in g t o t h e lo ad , as we l l as curr e n t s f l o w i n g th r o ugh th e ext e rn al f eed ba ck n e t w 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 ter n al r e sis t o r ta p used i n t h e co mm o n -m od e f eed ba ck 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 ld b e co n s i d er ed w h en d e alin g w i t h ac si gn als. air f l o w r e d u ces ja . a l s o , m o r e m e t a l d i r e c t l y 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 holes, g r o u n d , a nd p o w e r pla n es wi l l r e d u ce t h e ja . f i gur e 3 sh o w s t h e max i m u m s a fe p o w e r dissi p a t io n in t h e p a cka g e v e rs us t h e am b i e n t t e m p era t ur e fo r t h e so i c -8 (125c/w) an d lfcs p ( ja = 70c/w) p a cka g e o n a jed e c st anda r d 4- la ye r b o a r d . ja val u es a r e a p p r 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 power 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 f i g u r e 3. m a x i m u m p o wer d i s s i pat i on vs . t e mper at ur e f o r a 4-layer boar d esd c a ution esd (electrostatic discharge) sensitive device. ele c trosta tic charg e s as high as 4000 v readily accumulate on the human body and test eq uipment and can discharge without detection. although this product features proprie - tary esd protect i on circuitry, permanent damag e may o ccur on devices subje c ted to high energy electrostatic discharges. ther efore, prop er esd precautions a r e reco mmende d to avoid performance degradation or lo ss of functionality.
ad8137 r e v. a | 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 f i gur e 4. p i n c o nfi g u r ation ta bl e 6. pi n f u nct i o n d e s c ri pt i o ns pin no. name description 1 ? i n i n v e r t i n g i n p u t . 2 v ocm an internal feedback l oop drive s the output common-mode voltage to be eq ual to the voltage applied to the v ocm pin, prov ided the amplifier s op eration remains linear. 3 v s+ positive power s u pply voltage. 4 +out positive side of the differential output. 5 ?out negative side of the differential output. 6 v s? negative power supply voltage. 7 pd power down. 8 + i n n o n i n v e r t i n g in 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 f i g u re 5 . b a s i c t e s t ci rc u 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 f i g u r e 6. capacit i ve l oad t e st cir c uit, g = 1
ad8137 r e v. a | pa ge 8 o f 2 4 typical perf orm ance cha r acte ristics u n l e ss ot he r w i s e no te d, d i f f . g a i n = 1 , r g = r f = r l, d m = 1 k?, v s = 5 v , t a = 2 5 c, v oc m = 2.5 v . ref e r t o the b a sic t e s t cir c ui t in f i gur e 5 fo r t h e def i ni t i on 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 ?12 ?11 ?10 ?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 f i gur e 7 . sm a l l si gna l f r equenc y resp o n se fo r v a r i o u s g a i n s frequency (mhz) closed- l oop gain ( d b) ?12 1 1 0 100 1000 04771-0-003 v s = 5 v s = +5 v s = +3 3 2 1 0 ?11 ?10 ?9 ?8 ?7 ?6 ?5 ?4 ?3 ?2 ?1 v o, dm = 0.1v p-p f i gur e 8 . sm a l l si gna l f r equenc y resp o n se fo r v a r i o u s p o w e r sup p l i e s 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 = ? 40 c t = +125 c t = +85c t = +25c f i g u r e 9. small sig n al f r equenc y r e s p o n s e at v a rious t e mper 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 f i g u r e 10. lar g e signal f r equenc y r e sp ons e f o r v a rious g a ins frequency (mhz) closed-loop gain (db) 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 f i g u r e 11. lar g e signal f r equenc y r e sp ons e f o r v a rious p o wer sup p lies 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 f i g u r e 12. lar g e signal f r equenc y r e sp ons e at v a rious t e m p er at ur es
ad8137 r e v. a | 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 ? f i g u r e 13. small sig n al f r equenc y r e sp ons e f o r v a rious l o a d s 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 f i g u r e 14. small sig n al f r equenc y r e sp ons e f o r v a rious 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 f i g u r e 15. small sig n al f r equenc y r e sp ons e at v a rious 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 ? f i g u r e 16. lar g e signal f r equenc y r e sp ons e f o r v a rious l o a d s 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 f i g u r e 17. lar g e signal f r equenc y r e sp ons e f o r v a rious 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 f i g u r e 18. f r equenc y r e s p ons e f o r v a rious o u t p ut a m plit udes
ad8137 rev. a | page 10 of 24 frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 ?3 ?2 ?1 0 ?7 ?6 ?5 ?4 ?1 1 ?1 0 ?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 ? f i g u r e 19. small sig n al f r equenc y r e sp ons e f o r v a rious r f frequency (mhz) distortion (dbc) ?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 f i g u r e 20. s e c o nd harmonic d i s t or t i on vs. f r equenc y and sup p ly v o l t ag e v o, dm (v p-p) distortion (dbc) ?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 f i g u r e 21. harmonic d i s t or t i on vs. o u t p ut a m plitude and supply , f c = 500 k h z frequency (mhz) closed- l oop gain ( d b) 4 3 2 1 ?3 ?2 ?1 0 ?7 ?6 ?5 ?4 ?1 1 ?1 0 ?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 ? f i g u r e 22. lar g e signal f r equenc y r e sp ons e f o r v a rious r f frequency (mhz) distortion (dbc) ?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 f i g u r e 23. thir d harmonic d i s t or t i on v s . f r equenc y and sup p ly v o lt ag e v o, dm (v p-p) distortion (dbc) ?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 harm o n i c s o l i d l i n e t h i r d h ar m o ni c d a s he d l i n e f i g u r e 24. harmonic d i s t or t i on vs. o u t p ut a m plitude and supply , f c = 2 mh z
ad8137 rev. a | 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 ? f i g u r e 25. s e c o nd harmonic d i s t or t i on at v a rious 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 ? f i g u r e 26. s e c o nd harmonic d i s t or t i on at v a rious g a 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 04771-0-030 v o, dm = 2v p-p g = 1 r f = 500 ? r f = 2k ? r f = 1k ? f i g u r e 27. s e c o nd harmonic d i s t or t i on at v a rious 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 ? f i g u r e 28. thir d harmonic d i s t or t i on at v a rious 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 04771-0-035 v o, dm = 2v p-p r g = 1k ? g = 5 g = 1 g = 2 f i g u r e 29. thir d harmonic d i s t or t i on at v a rious g a 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 ? f i g u r e 30. thir d harmonic d i s t or t i on at v a rious r f
ad8137 rev. a | 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 f i g u r e 31. harmonic d i s t or t i on vs. v ocm , 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 f i gur e 32. inpu t v o ltage noise vs. f r eque nc y frequency (mhz) cmrr (db) 20 ?20 ?10 0 10 ?50 ?30 ?40 ?70 ?60 ?80 1 1 0 100 04771-0-013 v in, cm = 0.2v p-p input cmrr = ? v o, cm/ ? v in, cm fi g u r e 3 3 . c m r r v s . fr e q u e n c y v ocm (v) distortion ( d bc) ?50 ?60 ?70 ?80 ?90 ?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 f i g u r e 34. harmonic d i s t or t i on vs. v ocm , 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 f i g u r e 35. v ocm v o ltage noise vs . f r equen c y frequency (mhz) v ocm cmrr (db) ?10 ?30 ?20 ?50 ?40 ?70 ?60 ?80 1 1 0 100 04771-0-012 v o, cm = 0.2v p-p v ocm cmrr = ? v o, dm/ ? v ocm f i g u r e 36. v ocm cm r r v s . f r e q u e n c y
ad8137 rev. a | 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 f i gur e 37. o v er drive r e c o ver y 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 f i g u r e 38. small sig n al t r ans i ent r e s p o n s e f o r v a rious f eedback capacit a nc e s 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 f i g u r e 39. small sig n al t r ans i ent r e s p o n s e f o r v a rious capa cit i ve l oads 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) f i g u r e 40. s e t t ling ti me (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 f i g u r e 41. lar g e signal t r ans i ent r e s p o n s e f o r v a rious f eedback capacit a nc e s 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 f i g u r e 42. lar g e signal t r ans i ent r e s p o n s e f o r v a rious capa cit i ve l oads
ad8137 rev. a | page 14 of 24 frequency (mhz) p s rr (db) ?5 ?25 ?35 ?15 ?45 ?65 ?55 ?85 ?75 0.1 1 1 0 100 04771-0-011 psrr = ? v o, dm/ ? v s ?psrr +psrr f i g u r e 43. psr r vs. f r equenc y 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 f i g u r e 44. v ocm smal l sig n al f r equenc y res p ons e f o r v a rious sup p ly 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 f i g u r e 45. o u tput s a t u r a t i on v o lt a g e vs. o u tput l oad frequency (mhz) outp ut imp e d ance ( ? ) 1000 100 10 1 0.1 0.01 0.01 100 10 1 0.1 04771-0-061 f i gur e 46. single -e n d ed o u tpu t impe danc e vs. f r equenc 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 f i g u r e 47. v ocm lar g e sig n al t r ans i ent r e s p ons e 320 350 ?330 ?325 ?320 ?315 ?310 ?305 ?300 345 340 335 330 325 ?40 ? 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 f i g u r e 48. o u tput s a t u r a t i on v o lt a g e vs. t e mper at ur e
ad8137 rev. a | page 15 of 24 ?0.3 0.3 ?15 10 5 0 5 10 15 0.2 0.1 0 ?0.1 ?0.2 ?40 ? 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 f i g u r e 49. o f f s e t v o ltag e vs. t e mper at ur e 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 f i g u r e 50. input bias curr ent v s . input common-m o de v o lt age , v ac m 0.10 0.40 ?3 ?2 ?1 0 1 2 3 0.35 0.30 0.25 0.20 0.15 ?40 ? 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 f i g u r e 51. input bias and o f f s e t curr ent vs. t e mper at ur 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 ?40 0 20 ? 2 0 4 0 8 0 100 60 120 04771-0-051 f i gur e 52. sup p ly cu rr ent vs. t e mper atur e v ocm (v) i v ocm ( a) 70 50 30 10 ?10 ?30 ?50 ?70 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 04771-0-056 f i g u r e 53. v ocm bias c u rr ent vs . v ocm inp u t v o ltage ?0.5 ?0.1 ?0.2 ?0.3 ?0.4 ?40 ? 20 0 2 0 4 0 6 0 8 0 100 120 04771-0-054 temperature ( c) v ocm curre nt ( a) f i g u r e 54. v ocm bias curr ent v s . t e mper atur e
ad8137 rev. a | 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 f i g u r e 55. v o, c m vs. v ocm input v o l t age pd voltage (v) p d curre nt ( a) 40 20 0 ?20 ?40 ?60 ?80 ?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 f i g u r e 56. pd cu rren t 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 ? f i g u r e 57. sup p ly curr ent vs. pd vo l 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 f i g u r e 58. p o wer - d o wn t r ans i ent r e spons 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) f i g u re 5 9 . p o we r- d o w n t u r n - o n 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) f i g u re 6 0 . p o we r- d o w n t u r n - o ff ti m e
ad8137 rev. a | page 17 of 24 theor y of opera tion the ad8137 is a lo w p o w e r , l o w cos t , f u l l y dif f er en tia l v o l t a g e f eed back am 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 o n -mo d e cir c ui tr y wi th an in t e r n al l y der i v e d co mm on- mo d e re f e re nc e vo lt age, a n d bi a s sh ut d o w n c i rc u i t r y . t h e a m p l i - f i er us es tw o fe e d b a ck lo o p s t o s e p a ra t e l y con t r o l dif f er en t i al a nd co mm on- m o d e fe e d b a ck. the dif f er en t i al ga in is s e t w i t h ext e r n a l r e sist o r s as in a t r ad i t iona l a m plif ier w h i l e t h e o u t p u t c o m m on - m o d e volt age i s s e t b y an i n te r n a l fe e d b a c k l o op , co n t r o l l ed b y an ext e r n al v oc m in p u t. this a r ch i t e c t u r e ma k e s i t e a s y to ar bi t r ar i l y s e t t h e out p ut c o m m on - m o d e volt age l e vel wi t h o u t a f fe c t ing t h e dif f er en t i a l ga 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 f i g u r e 61. block d i ag r a 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 idge w h os e o u t p u t c u r r en t is mir r o r e d t o hig h i m p e dance n o des cp and c n . t h e o u t p ut s e c t io n is t r ad i t i o na l h- b r idge dr i v en cir c ui tr y wi t h co mm on emi t t e r de vices dr i v in g n o des +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 is t h e t r a n s c on d u c t anc e o f t h e i n p u t s t a g e and c c is th e t o tal c a p a ci t a n c e o n n o de cp/cn ( c a p ac i t an ces cp an d cn 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 tan c e c c is 3.5 pf , s e t t in g the 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 ish e s an am plif ier s uni t y ga in b a ndwid t h , b u t wi t h t h e ad8137, the c l os ed-lo o p b a n d wid t h dep e n d s u p o n t h e f eed back r e sis t or val u e as w e l l ( s ee f i gur e 19). the o p en-lo o p ga in and phas e sim u l a t i o n s a r e sh own 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) f i g u r e 62. o p en-l oo p g a in and p h as e i n f i gur e 61, the co mm o n -m o d e f eedbac k a m 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 volt ag e, and b y ne g a t i ve fe e d b a ck fo r c es t h e o u t p ut co mm on- m o d e v o l t a g e t o b e e q ual to t h e volt age a p pl i e d to t h e v oc m i n put . in ot h e r word s , t h e f eed back lo o p s e r v os th e o u t p u t co mm o n -m o d e v o l t a g e t o th e volt age a p pl i e d to t h e v oc m i n put . a n i n te r n a l b i as ge ne r a tor se t s t h e v oc m le v e l t o a p p r o x ima t e l y mids u p ply , t h er efo r e , t h e o u t p u t co mm on-m o d e v o l t a g e wil l be s e t t o a p p r o x ima t e l y midsu p ply w h e n t h e v oc m in p u t is lef t f l o a tin g . the s o ur ce r e sis- t a nce o f t h e in te r n a l b i a s ge n e r a to r is la rge an d ca n b e o v er r i d- den easil y b y a n ext e r n al v o l t a g e s u p p lie d b y a s o ur ce wi th a rel a t i vely s m a l l output re s i st a n c e . t h e v oc m in p u t can b e dr i v en t o w i t h in a p p r o x i m a t e l y 1 v o f th e su p p l y ra ils wh ile m a i n ta i n - in g li n e a r o p er a t io n i n t h e co mm on- m o d e fe e d b a ck lo o p . the co mm on-m o d e f e e d back 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 ove r a w i d e f r e q u e nc y r a nge w i t h out t h e re q u i r e m e n t of t i g h t l y m a tc he d e x te r n a l c o m p o - n e n t s b e ca us e i t fo r c es t h e sig n a l co m p on e n t o f t h e o u t p ut c o m m on - m o d e vo lt age to b e z e ro e d . t h e re su lt i s ne ar ly p e r f e c t l y b a la n c e d dif f er en t i al ou t p uts o f iden t i cal a m pl i t ude a nd exac tl y 180 a p a r t in p h as e .
ad8137 rev. a | page 18 of 24 appli c a t ions anal yzing a ty pic a l a pplic a t ion with ma t c hed r f and r g ne t w orks typical connection and defi nition of terms f i gur e 63 s h 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 n e tw o r ks. th e dif f er en t i al i n p u t t e r m inals o f th e ad8137, v ap a nd v an , a r e u s e d a s s u m m i n g j u n c t i o n s. a n ext 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 u t co mmo n -m o d e v o l t a g e . the tw o output te r m i n a l s , v op and v on , move i n opp o s i t e d i re c t i o ns i n a balan c e d fas h ion in r e sp o n s e t o a n in p u t sig 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 f i gur e 63. t y pic a l c o nnec t ion the dif f er en t i al o u t p ut v o l t a g e is def i ne d as on op dm o, v v v ? = ( 1 ) c o mm on- m o d e v o l t a g e is t h e a v era g e o f t w o v o l t a g es. th e o u t p u t co mm on-m o d e v o l 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 u t 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 m a t c h e d in am pli t ude an d h o w p r ecis e l y they a r e 180 deg r ees o u t o f p h ase wi t h eac h o t h e r . i t is th e in t e r n al co m m o n -m o d e f eed back lo o p t h a t f o r c es th e sig n al co m p o n en t o f th e o u t p u t c o m m on - m o d e tow 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 cal am pli t ude a n d exac t l y 180 deg r ees o u t o f p h as e . th e ou t p u t balance p e r f o r m a 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 exter 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 loo p be eq u a l t o ea ch o t h e r . lo w f r eq uen c y o u t p u t ba lan c e is limi ted ul tim a t e l y b y the m i s m a t c h of an on - c h i p vo lt ag e d i v i d e r . o u t p u t b a lan c e is m e a s ur e d b y placin g a w e l l ma t c h e d r e sist o r divider acr o ss 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 in g t h e sig n al a t t h e di v i der s mi d p oin t wi t h t h e mag n i t ude o f t h e d i f f e r e n ti al 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 bala n c e i s eq u a l t o t h e ma g n i t ude o f t h e cha n ge in 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 ude o f t h e cha n g e i n o u t p u t dif f er en t i al- mo d e vo lt ag e : dm o cm o v v balance output , , ? ? = ( 3 ) the dif f er e n t i al neg a t i v e fe e d b a ck dr iv es t h e volt a g es a t t h e su m- mi ng j u nc t i ons v an and v ap to b e e s s e n t i a l l y e q u a l to e a c h ot he r . ap an v v = ( 4 ) the co mm on- m o d e fe e d b a ck lo o p dr i v es t h e o u t p u t co mm on- m o de v o l t a g e , s a m p led a t t h e mid p o i n t o f t h e tw o in t e r n al co mm o n -m o d e ta p r e sis t o r s in f i gur e 61, t o eq ual the v o l t a g e se t a t th 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 ) an d 2 , dm o ocm on v v v ? = ( 6 ) estima ti ng noise, gai n , an d ban d with wi t h ma t c hed f eedba c k n e t w orks es timating o u tput nois e voltage an d b a n d w i dth the t o t a l ou t p u t n o is e is t h e r o o t -su m -s qua r e d t o t a l o f s e v e ral st a t i s t i cal l y i n de p e nden t s o ur ce s. sin c e t h e s o u r ces a r e st a t i s t i - cal l y in d e p e n d en t, t h e co n t r i b u t i o n s o f eac h m u s t b e in di vid u - al ly in cl ude d i n t h e r o o t -sum-s q u a r e calc u l a t ion. t a b l e 7 lists re c o m m e nd e d re s i stor v a lu e s an d e s t i m a te s of b a n d w i d t h a n d o u t p u t 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 c l ose d -lo o p ga i n s. f o r m o st a p pl i c a t ions , 1 % res i st ors are su f f i c i en t . t a b l e 7. recommended v a lues of gai n -setti ng resist ors, a nd vo ltag e gai n f o r vari ous cl os e d - l o o p gai n s g a i n r g (?) r f (?) 3 db bandwidth (m hz) total output noise (nv/hz) 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 the dif f er en t i al o u t p u t v o l t a g e n o is e con t a i n s c o n t r i b u t i o n s f r o m t h e ad81 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 al fe e d b a ck n e t w o r ks.
ad8137 rev. a | page 19 of 24 the co n t r i b u t i on f r o m t h e in p u t v o l t a g e n o is e sp e c t r al den s i t y is co m p ut e d as ? ? ? ? ? ? + = g f n r r v vo_n 1 1 , o r e q u i v a l e n t l y , v n / ( 7 ) wher 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 ua t i o n is t h e s a m e as t h a t o f t r adi 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 in p u t c u r r en t n o is e o f e a ch in pu t is co m p u t ed 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 ne e d s t o b e t r e a t e d s e p a r a t e l y since t h e t w o in p u t c u r r en ts a r e s t a t i s t i cal l y i n de p e n d e n t p r o c es s e s. t h e c o n t r i but i o n f rom e a ch r g is co m p ut e d as ? ? ? ? ? ? = g f g r r tr vo_n k 4 3 ( 9 ) this r e s u l t c a n b e i n t u i t iv e l y vi e w e d as t h e t h er mal n o is e o f ea c h r g m u l t i p li e d b y t h e ma g n i t ude o f t h e dif f e r en t i al gain. the co n t r i b u t i on f r o m eac h r f is co m p u t ed 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 sin g le- e n d e d -t o- dif f er en tial ou t p u t t o p o log y ca n be ded u ce d f r o m the sig n al def i ni tion s an d f i gur e 63. ref e r r i n g t o f i gur e 63, (c f = 0) a n d se t t in 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 ? = ? ( 1 1 ) ? ? ? ? ? ? + = = g f g op ap an r r r v v v ( 1 2 ) s o lvi n g t h e ab o v e tw o e q ua t i o n s a n d s e t t i n g v ip to v i gi v e s th e ga in r e l a tion s h i p fo r v o, d m / v i . i g f dm o, on op v r r v v v = = ? (13) an in v e r t in g conf igura t io n wi t h the s a m e ga in ma g n i t ude can be im p l em en t e d b y sim p l y a p p l y i n g the in p u t sig n al t o v in and se t t in g v ip = 0. f o r a b a lan c e d dif f er en t i al in put, t h e ga i n f r o m v in, d m to v o, d m is als o eq ual t o r f / r g , w h er e v in, d m = v ip ? v in . fe ed ba ck fa ctor nota tion w h en w o rk in g wi t h dif f er en t i al dr i v ers, i t is con v enien t t o in - tr o d uce t h e f e e d back fac t o r , whic h is def i n e d as g f g r r r + ( 1 4 ) this n o t a tio n is co n s is t e n t wi t h co n v en tio n al f e ed back a n al ysis a n d 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 h e 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 ex 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 and v ap are e s se n t i a ll y eq ual t o ea c h o t h e r , th ey a r e bo t h eq ual t o th e a m p l i- f i er s in p u t comm on- m o d e v o l t a g e . th eir ra n g e is indic a t e d i n t h e sp e c if ic a t ion s t a b l es as in pu t co m m on- m o d e ra n g e . the volt age a t v an and v ap f o r th e co nn ec t i o n dia g r a m in f i gur e 63 ca n 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 th e comm o n - m o d e v o l t a g e p r es en t a t t h e am pli - fi e r i n p u t t e r m i n a l s . u s i n g th e n o ta t i o n , eq u a ti o n ( 1 5 ) c a n b e 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 icm 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 p u t sig n al, i . e . , 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 an d v ap mu s t s t ay w i th i n th e i r r e s p e c t i v e l i n e a r r a n g e s . c a lc ulating in put im pe da nc e the in p u t im p e dan c e o f th e circ ui t in f i gur e 63 wil l dep e n d on w h et her t h e a m plif ier is b e in g d r i v en b y a sin g le -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 i n p u t sig n als, t h e dif f er en t i a l 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 s i ng l e - e nd e d s i g n a l ( f or e x am pl e, w h e n v in i s g rou nd e d , a n d t h e i n p u t si g n a l dr i v es v ip ), t h e i n p u t im p e dan c e b e com e s ) ( 2 1 f g f g in r r r r r + ? = ( 1 9 )
ad8137 rev. a | 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 f i g u r e 64. a d 8137 d r iv ing ad7450a, 12-bit a / d con v er ter the i n p u t i m p e dan c e o f a con v en t i o n al i n ver t in g o p a m p co nf igura t io n is sim p ly r g , b u t i t is hig h er in e q ua tion 19 b e ca 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 t h e su m m i ng j u nc t i on s , v an an d v ap . this v o l t a g e p a r t ia l l y b o ot st r a p s t h e v o lt age a c ro ss t h e i n put re s i stor r g , l e a d i n g t o t h e in cr e a s e d in pu t r e sist a n c e . input common-mode swing consideratio ns i n s o me s i ng l e - e nd e d - t o - d i f f e r e n t i a l a p pl i c a t i o ns w h e n u s i n g a s i ng l e - s upply volt age, a t t e n t i o n m u st b e p a i d to t h e s w i n g of t h e i n put c o m m on- m o d e volt ag e, v ac m . c o n s ider t h e cas e in f i gur e 64, w h er e v in is 5 v p-p swin g i ng ab out a b a s e l i ne a t g rou n d a n d v refb is co nn ec ted t o g r o u nd . the in p u t sig 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 an c e . th e cir c ui t has a dif f er en t i al g a in o f 1.0 a n d = 0. 5. v icm ha s a n am pl i t u d e o f 2 . 5 v p - p and i s s w ing i ng ab out g r o u nd. u s i n g t h e r e s u l t s in e q ua ti o n 16 , th e co mm o n -m o d e v o l t a g e a t th e ad813 7 s in p u ts, v ac m , is a 1.25 v p-p signal swin g i n g a b o u t a bas e lin e o f 1 . 2 5 v . th e max i m u m n e ga t i ve excur s io n o f v ac m in this cas e is 0.63 v , w h ich e x ce eds t h e lo w e r in p u t co mm o n -m o d e v o l t a g e limi t. on e wa y t o a v o i d t h e in p u t comm on- m o d e s w i n g limi t a t i o n is to b i a s v in an d v ref a t midsu p pl y . i n this cas e , v in is 5 v p-p swi n g i n g ab o u t a b a s e li n e a t 2.5 v , a n d v ref is conn ec t e d t o a lo w-z 2.5 v s o u r ce . v ic m n o w has a n am p l i t ude o f 2.5 v p-p a n d is swin g i n g abou 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 calcula t ed t o be eq ual t o v icm b e ca us e v oc m = v icm . th er efo r e , v icm swin gs f r o m 1.25 v t o 3.7 5 v , w h ich is w e l l wi t h in t h e in pu t co mm o n -mo d e v o l t a g e limi ts of th e ad8137. an o t h e r b e n e f i t s e en b y t h is exam ple is t h a t si nce v oc m = v ac m = v ic m , n o w a s t e d c o m m on - m o d e c u r r e n t f l ow s . f i g u re 6 5 i l lu st r a te s a w a y to p r o v ide t h e lo w-z b i as v o l t a g e . f o r si t u a t io n s t h a t do n o t r e q u ir e a p r e c is e r e fer e n c e , a si m p le v o l t a g e divider wi l l s u 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 f i g u r e 65. l o w-z bia s s o ur c e a n ot he r w a y to a v oi d t h e i n put c o m m on - 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 the 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 versus closed-l oop 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 easin g c l os e d -lo o p ga in in t h e s a me wa y as a tradi t io nal 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 ga i n s gr ea t e r tha n 4, t h e b a n d wid t h ob ta in ed f o r a sp ecif ic ga in ca n b e es t i ma t e d as ) mhz 72 ( , 3 + = ? f g g dm o, db r r r v f (20) o r eq ui valen t l y , (72 mh z). this est i ma te assum e s a mi ni m u m 90 deg r e e phas e ma rg i n fo r t h e am plif ier lo o p , a co ndi t io n a p p r o a che d fo r ga in s g r e a t e r t h an 4 . l o we r g a i n s w i l l s h ow more b a n d w i d t h t h an pre d i c te d b y t h e e q ua t i o n d u e t o t h e p e a k i n g p r o d uce d b y t h e lo w e r phas e ma rg in.
ad8137 rev. a | page 21 of 24 estimating dc errors p r ima r y dif f er e n tial o u t p u t o f fs et er r o r s in th e ad8137 a r e d u e t o t h r e e ma jo r c o m p on e n 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 bet w een t h e v an an d v ap in p u t c u r r en ts in t e rac t in g wi t h t h e f eed back n e tw 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 tw e 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 in co n j un c t ion wi th 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 . t h e f i r s t output e r ror c o m p one n t i s c a l c u l a t e d a s ? ? ? ? ? ? + = 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 lt 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 cu rr e n t s . 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 tio n al misma t ch betw e e n th e tw o f eed- b a ck re s i stor s . the t o t a l dif f er en 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 c k ne t w or k w i l l st i l l f orc 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 th e r f /r g fe e d back n e t w orks a r e misma t ch e d . th e misma t c h wil l , h o w - e v e r , 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 abi l it y to re j e c t c o m m on - m o d e s i g n a l s a t t h e v an and v in in p u t t e r m inals, m u ch t h e s a m e as w i t h a fo ur -r esis to r dif f er en ce am pl i f i e r m a d 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 er r o r s wi l l als o p r o d uce a dif f er en t i al o u t p u t com p on e n t t h a t is eq 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 dif f er en c e 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 st a pplica t ion s usin g 1% r e sist o r s, th i s co m p o n en t a m o u n t s t o a d i f f e r e n ti al d c o f fse t a t th e o u t p u t tha t is smal l eno u g h t o b e ig n o r e d . driving a capaciti ve lo ad a p u r e l y ca p a c i ti v e lo ad wil l r e ac t wi th t h e bond wir e an d p i n ind u c t an ce 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 i n t h e t r ans i e n t re sp ons e a n d l o ss of ph a s e m a r g i n . o n e w a y to minimize this ef f e c t is t o p l ace a smal l r e sis t o r in s e r i es wi th eac h o u t p u t t o b u f f er th e lo ad ca p a ci tan c e . the r e sis t o r a n d lo ad c a p a c i t a nc e w i l l f o r m a f i r s t - ord e r , low - p a ss f i lte r , s o t h e re s i stor val u e sh o u ld be as smal l as p o s s ib le . i n s o me cas e s, th 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 an 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 ve r s u s c a - p a ci ti v e lo ad , and w e r e g e n e ra t e d usin g s e r i es r e sis t o r s in each o u t p ut an d a dif f er en t i a l ca p a c i t i ve lo ad . layout c o ns id er ations s t anda rd hig h sp e e d pc b l a yo u t p r ac t i ces sho u l d b e ad h e re d t o wh e n d e s i gn i n g w i th th e a d 8 137 . a so l i d gr o u n d p l a n e i s r e com m e nde d and go o d w i de b a nd p o wer sup p ly de cou p l i n g n e t w o r k s s h o u ld be p l a c ed a s c l ose as pos s i b le t o th e s u p p l y p i n s. t o m i n i m i z e st r a y c a p a c i t a nc e a t t h e su m m i ng no d e s , t h e co p p er in al l la yers un der al l traces a n d p a ds tha t co nnec t t o t h e su m m i ng no d e s shou l d b e re mo ve d. sm a l l a m o u n t s of st r a y s u mmi n g - n o d e ca p a c i t a n c e wi l l ca us e p e aking i n t h e f r e q 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 m m i n g -n ode c a pa ci ta n c e i s un a v o i d a b l e , i t s ef f e ct s c a n be co m p en s a t e d f o r b y p l acin g 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 s t h i g h sp e e d sig n a l a pplica t ion s , an d t h e y r e q u ir e a t le ast on e li ne t e r - mina t i o n . i n a n a l og a p plica t io ns, a ma t c he d r e s i st i v e t e r m i n a - tio n is g e n e ral l y p l aced a t t h e lo ad en d o f t h e lin e . this s e c t ion de a l s w i t h how to prop e r ly te r m i n a t e a s i ng l e - e nd e d i n put to th e ad8137. the in p u t r e sis t a n c e p r es en t e d b y th e ad8137 in p u t cir c ui tr y is s e e n i n pa r a ll e l w i th th e t e rm i n a t i o n r e s i s t o r , a n d i t s l o a d i n g ef f e c t m u s t b e t a k e n in t o acco u n t. th e thev enin eq ui valen t cir c ui t o f th e dr i v er , i t s s o ur ce r e sis t a n ce , an d t h e ter m ina t io n re s i st anc e m u st a l l b e i n cl u d e d in the calc u l a t ion as we l l . 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 sim u l - t a n e ou s a l ge br a i c e q u a t i ons a n d i s b e y o n d t h e s c op e of t h i s d a t a s h e e t. an i t er a t iv e s o l u tio n is al s o p o s s i b le and is sim p ler , es p e c i al ly co n s i d er in g t h e fac t t h a t st anda r d r e s i s t o r val u es a r e ge ne r a l l y u s e d . f i gur e 66 s h o w s th e ad8137 in a uni t y-ga in conf igura t io n, and w i t h t h e f o l l ow i n g d i s c u s s i on , prov i d e s a go o d e x am pl e of how t o p r o v ide a p r op er t e r m ina t io n in a 50 ? e n viro nm e n t .
ad8137 rev. a | page 22 of 24 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 f i g u r e 66. a d 8137 wit h t e rminated input the 52.3 ? t e r m ina t io n r e sis t o r , r t , i n pa r a ll e l w i th th e 1 k ? in p u t r e sis t an ce o f th e ad8137 cir c ui t, yie l ds an o v eral l in p u t r e sis t a n c e 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 e ed back lo o p s, eac h lo o p m u s t ha v e t h e s a me r g if th ey ha v e t h e s a me r f . i n t h e i n p u t (u pp er) lo o p , r g is e q ua l t o th e 1 k ? r e s i s t o r i n se ri e s w i th th e (+) i n p u t p l us th e pa ralle l co m b in a t ion o f r t a n d the s o ur ce r e sis t a n ce o f 50 ?. i n th e upp e r l o op , r g is t h er efo r e e q ua l t o 1.03 k?. the clos es t s t an - da r d val u e is 1.0 2 k? a n d is us e d f o r r g in the lo w e r lo o p . thin gs g e t m o r e co m p lic a ted w h en i t com e s t o det e r m inin g t h e fe e d b a ck r e sis t or val u es. th e am pli t ude o f t h e sig n al s o ur ce ge ne r a tor v in is tw o t i m e s t h e am p l i t ude o f i t s o u t p u t sig n al w h en ter m ina t e d in 50 ?. th erefo r e , a 2 v p-p t e r m ina t e d a m p l i t ude is p r o d uce d b y a 4 v p-p a m p l i t ude f r o m v s . t h e thev enin eq ui valen t cir c ui t o f t h e sig n al s o ur ce a n d r t mu s t b e used w h en calc ula t in g th e c l osed - l oo p g a in be ca use r g in t h e upp e r l o op i s sp l i t b e t w e e n t h e 1 k ? re s i stor an d t h e t h e v e n i n r e s i s t a n ce l o o k in g ba c k t o w a r d th e so u r c e . t h e t h ev en i n v o l t - a g e o f th e sig n al s o ur ce is g r ea t e r tha n the sig n a l s o ur ce o u t p u t v o l t a g e w h en te r m ina t e d i n 50 ? b e c a us e r t mu s t a l w a y s b e g r ea t e r tha n 50 ?. i n this cas e , r t is 52.3 ? a n d th e thev enin v o l t a g e and r e sis t an ce a r e 2.04 v p-p an d 25.6 ?, r e s p ec ti v e l y . n o w the u p p e r in p u t b r an ch can b e viewed as a 2.04 v p-p s o ur ce in s e r i es wi t h 1.03 k?. s i n c e this is t o b e a uni 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 ut is r e quir e d , an d 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?. this exa m ple sh o w s t h a t w h e n r f and r g a r e la rg e c o m p a r e d t o r t , th e ga in r e d u ctio n p r od uce d b y th e in cr ease in r g is ess e n t ia l l y can c e l le d b y th e in cr eas e in th e thev enin v o l t a g e ca us e d b y r t b e in g g r e a t e r t h an t h e o u t p u t r e sist anc e o f t h e sig n a l s o ur c e . i n ge ne r a l, as r f and r g b e co m e smalle r in t e r m ina t ed a p p l ica t i o n s , r f n e ed s t o be i n c r ea sed t o co m p e n sa t e f o r th e i n c r ea se i n r g . w h en g e n e r a t i ng t h e typ i ca l 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 ion s o n c l os ed-lo o p ga in in t o acco un t. power down the ad8137 f e a t ur es a pd p i n tha t can b e us ed t o minimize t h e q u ies c en t c u r r en t co ns u m ed w h en the device is n o t bein g us e d . pd is as s e r t ed b y a p p l yin g a lo w log i c lev e l t o p i n 7. th e thr e s h old betw e e n hig h an d lo w log i c lev e l s is no minal l y 1.1 v a b o v e t h e n e ga t i v e s u p p ly ra i l . s e e t h e s p e c if ic a t io n t a b l es fo r th e th r e s h o l d lim i t s . drivi n g a n adc wi th grea ter than 12-bit performa nce s i n c e t h e ad81 37 is s u i t a b le f o r 12-b i t sys t ems, i t is desira b 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 in a s y s t em wi t h g r e a te r t h an 1 2 - b it l i ne ar i t y . in p a r t i c u l ar , t h e e f fe c t ive n u m b e r o f b i ts, en o b , is m o s t in ter e s t in g. th e 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 can d ida t e f o r s h o w c a sin 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. f o r t h is a p plica t io n, t h e ad813 7 is s e t in a ga i n o f 2 a n d dr i v en sing le - e nde d t h ro ug h a 20 k h z b a nd- p a ss f i l t er , w h i l e t h e o u tp ut is ta k e n dif f er en tial l y t o t h e in p u t o f t h e ad76 87 (s e e f i g u r e 67). this circ u i t has mis m a t ch e d r g i m p e dan c es and, t h erefo r e , has a d c o f f s et a t th e di f f e r en ti al o u t p u t . i t is in c l ud ed as a t e s t c i r c ui t t o il l u s t r a te t h e p e r f o r mance o f t h e ad813 7. a c t u a l a p p l ic a t io n cir c u i ts sho u l d ha ve ma tche d fe e d b a ck n e t w orks. f o r an ad7 687 in p u t r a n g e u p t o ?1. 82 db fs, t h e ad8 137 p o w e r sup p ly is a si n g l e 5 v a p pl ie d t o v s+ wi th v s? ti ed 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 e s a r e in cr ease d t o +6 v a n d ?1 v . i n bo th ca s e s , t h e v oc m p i n is b i a s e d w i t h 2 . 5 v and t h e pd p i n i s le f t f l o a tin g . all v o l t a g e s u p p l i es a r e de c o u p l e d wi t h 0. 1 f c a p a c i t o rs. f i gur e 68 and f i gu r e 6 9 s h o w th e pe rf o r m a n c e o f th e ? 1 . 8 2 d b f s se t u p a n d th e ?0.4 5 db fs s e t u p , r e sp e c t i ve l y . 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 f i g u r e 67. a d 8137 d r iv ing ad7687, 16-bit 250 ksps a d c
ad8137 rev. a | page 23 of 24 frequency (khz) amp l itude (db of full s cale ) 0 ?1 0 ?2 0 ?3 0 ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?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 f i g u r e 68. a d 8137 p e r f ormanc e on sing le 5 v sup p l y , ?1.82 dbfs frequency (khz) amp l itude (db of full s cale ) 0 ?1 0 ?2 0 ?3 0 ?4 0 ?5 0 ?6 0 ?7 0 ?8 0 ?9 0 ?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 f i g u r e 69. a d 8137 p e r f ormanc e on +6 v , ?1 v sup p lie s, ?0.45 dbfs
ad8137 rev. a | 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 . 196 8) 4. 80 ( 0 . 189 0) 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) coplanarit y 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-012aa f i g u r e 70. 8-l e ad standar d small o u t line p a ck ag e [soic ] narr o w body ( r -8)d imens ions s h o w n in millimeters ( i nches ) 1 ex po s e d pa d (b o t t o m v ie w) 0.50 bsc 0.60 max pin 1 indicator 1.50 ref 0.50 0.40 0.30 0.25 min 0.45 2.75 bsc sq top view 12 max 0.80 max 0. 65 t y p seating plane pin 1 indicato r 0.90 0.85 0.80 0.30 0.23 0.18 0.05 max 0.02 nom 0.20 ref 1.90 1.75 1.60 4 1.60 1.45 1.30 3.00 bsc sq 5 8 f i g u r e 71. 8-l e ad l e ad f r ame chip s c ale p a ck ag e [lfcsp ] 3 mm 3 mm body (cp - 8-2) d imens io ns sho w n in millimet e rs ordering guide model temperature r a nge package desc ri p t i o n p a c k a g e o p t i o n b r a n d i n g ad8137yr ?40c to +125c 8-lead standard small outline package (soic) r-8 ad8137yr-ree l ?40c to +125c 8-lead standa rd small outline package (soic) r-8 ad8137yr-ree l 7 ?40c to +125c 8-lead standa rd small outline package (soic) r-8 ad8137yrz 1 ?40c to +125c 8-lead standard small outline package (soic) r-8 ad8137yrz-ree l 1 ?40c to +125c 8-lead standard small outline package (soic) r-8 ad8137yrz-ree l7 1 ?40c to +125c 8-lead standard small outline package (soic) r-8 AD8137YCP-R2 C40c to +125c 8-lead lead frame chip scale p a ckage (lfcsp) cp-8-2 hfb ad8137ycp-ree l C40c to +125c 8-lead lead fra me chip scale p a ckage (lfcsp) cp-8-2 hfb ad8137ycp-ree l7 C40c to +125c 8-lead lead fra me chip scale p a ckage (lfcsp) cp-8-2 hfb ad8137ycpz-r2 1 C40c to +125c 8-lead lead frame ch ip scale p a ckage (lfcsp) cp-8-2 hgb ad8137ycpz-reel 1 C40c to +125c 8-lead lead frame ch ip scale p a ckage (lfcsp) cp-8-2 hgb ad8137ycpz-r eel7 1 C40c to +125c 8-lead lead frame ch ip scale p a ckage (lfcsp) cp-8-2 hgb 1 z = pb-free part. ? 2004 an alog de vices, inc. all rig h ts res e rve d . trad emarks a n d regis- tered trade m arks are the property of their respective owners . d04771C0C 8/04(a)

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