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quad low noise, low cost variable gain amplifier ad8335 rev. 0 in fo rmatio n furn ish e d by an alo g d e v i ces is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any i n fri n gement s of p a t e nt s or ot her ri ght s of t h i r d p a rt i e s t h at may resul t from i t s use. specifications subject to chan g e with o u t n o tice. no licen s e is g r an ted by implicatio n or ot herwi s e under any p a t e nt or p a t e nt ri ghts of analog devices. trademarks and registered trademarks are the prop erty of their respective owners. one technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4700 www.analog.com fax: 781. 326. 8703 ? 2004 analog devices, i n c. all r i ghts r e ser v ed . features low noise preamplifier (pra) vo ltage no ise = 1.3 nv/hz typical current no ise = 2.4 pa/hz typical nf = 7 db (r s = r in = 50 ?) single-ended input; v in max = 625 mv p-p active input match input snr (no ise bandwidth = 20 mhz) = 92 db vga differential output v out max = 5 v p-p, r l = 500 ? differential gain range (8 db output gain step) ?10 db to +38 db lo gain mo de ?2 db to +46 db hi gain mo de accurate linear-in-db gain control pra + vga perfo rmance ?3 db bandwidth o f 70 mhz excellent overload performance supply: 5 v power consumption 95 mw/channel (380 mw total) 65 mw/channel (pra off; 260 mw total) power-down applications medical imaging (ultrasound, gamma cameras) sonar test and measurement precise, stable wideband gain control functional block diagram 63 pip1 64 pmd1 1 pmd2 2 pip2 4 pon2 5 pop2 6 vip2 7 vin2 10 vin3 11 vip3 12 pop3 13 pon3 15 pip3 16 pmd3 17 pmd4 18 pip4 61 pon 1 60 pop1 59 vip1 58 vin 1 53 vc m 2 55 vc m 1 52 en 12 51 sp12 49 hl1 2 47 voh1 46 vol1 56 vgn1 50 sl12 54 vgn2 43 vol2 42 voh2 39 voh3 38 vol3 27 vgn3 31 sl34 25 vgn4 35 vol4 34 voh4 20 pon 4 21 pop4 22 vip4 23 vin 4 28 vc m 3 26 vc m 4 29 en 34 30 sp34 32 hl3 4 18db 18db 18db 18db vmd1 vmd2 vmd3 vmd4 interpolator interpolator interpolator interpolator 20db to 28db 20db to 28db 20db to 28db 20db to 28db atten ?48db to 0db atten ? 48db to 0db atten ?48db to 0db atten ?48db to 0db gain int gain int gain int gain int ad8335 04976-001 fi g u r e 1 . general description th e ad8335 is a q u ad va r i a b le ga in a m p l if ier (v ga) wi th lo w noi s e pre a m p l i f i e r i n te nd e d for c o st and p o we r s e ns i t ive ap p l i c at i o n s . e a c h c h a n n e l f e at u r e s a g a i n r a n g e 4 8 d b , f u l l y d i f f e r e n ti al si gn al pa th s, a c ti v e i n p u t p r ea m p li f i e r m a t c h i n g , a n d us er -s ele c t a b l e max i m u m ga in s o f 46 db a n d 38 db . i n di vid u a l ga in co n t r o ls a r e p r o v ide d fo r e a ch cha n n e l. th e p r e a m p lif i er (p ra) has a sin g le-en d e d t o dif f er en t i al ga in o f 8 (18.06 db) a n d accep t s in p u t sig n als 625 mv p-p . p r a n o is e is 1.2 nv/h z a n d t h e co m b in e d in p u t r e fer r e d v o l t a g e n o is e o f t h e pra a n d v g a is 1.3 nv/h z a t maxim u m ga in. a ssu m i ng a 2 0 m h z noi s e b a ndw i d t h ( n b w ) , t h e n y qu i s t f r eq uen c y f o r a 40 mh z ad c, th e in p u t s n r is 92 db . th e hil o p i n o p timizes th e o u t p u t s n r f o r 10-b i t a n d 12-b i t ad cs wi th 1 v p-p o r 2 v p-p f u l l -s cale (fs) in p u ts. c h an nel s 1 and 2 are e n abl e d t h rou g h t h e e n 1 2 pi n w h i l e c h an nel s 3 and 4 are e n abl e d t h rou g h t h e e n 3 4 pi n . f o r v g a o n ly a p plica t io n s , t h e pra s ca n b e p o w e r e d do wn, sig n if ica n t l y re d u c i ng p o we r c o nsu m pt i o n . th e ad8335 is a v a i la b l e in a 64-lead lead f r a m e c h i p s c ale (9 mm 9 mm) p a cka g e fo r t h e in d u s t r i al t e m p era t ur e ra n g e o f ?40c t o +85c.
ad8335 rev. 0 | page 2 of 24 table of contents specifications..................................................................................... 3 absolute maximum ratings............................................................ 5 esd caution.................................................................................. 5 pin configuration and function descriptions ............................. 6 typical performance characteristics ............................................. 7 test circuits..................................................................................... 15 theory of operation ...................................................................... 16 enable summary......................................................................... 16 preamp ......................................................................................... 17 noise......................................................................................... 17 vga.............................................................................................. 18 optimizing the system dynamic range ............................. 18 attenuator................................................................................ 18 gain control ........................................................................... 19 output stage ........................................................................... 19 vga noise .............................................................................. 19 applications..................................................................................... 20 ultrasound................................................................................... 20 basic connections ...................................................................... 21 preamp connections.................................................................. 21 input overdrive .......................................................................... 23 input overload protection.................................................... 23 logic inputs................................................................................. 23 common-mode pins ................................................................. 23 driving adcs ............................................................................. 23 outline dimensions ....................................................................... 24 ordering guide........................................................................... 24 revision history 9/04revision 0: initial version
ad8335 rev. 0 | page 3 of 24 specifications v s = 5 v, t a = 25c, r l = 500 ?, f = 5 mhz, c l = 10 pf, lo gain range (?10 db to +38 db), r fb = 249 ? (pra r in = 50 ?) and signal voltage specified differential, per channel performance, dbm (50 ?), unless otherwise noted. table 1. parameter conditions min typ max unit pra characteristics gain single-ended input to di fferential output 18 db single-ended input to single-ended output 12 db input voltage range pra output limited to 5 v p-p differential 625 mv p-p input resistance r fb = 249 ? 50 ? r fb = 374 ? 75 ? r fb = 499 ? 100 ? r fb = , low frequency value into pipx 14.7 k? input capacitance pipx (pins 2, 15, 18, 63) 1.5 pf ?3 db small signal bandwidth with r fb = 249 ? 110 mhz input voltage noise r s = 0 ?, r fb = 1.15 nv/hz input current noise 2.4 pa/hz noise figure active termination match r s = r in = 50 ?, r fb = 249 ? 7 db unterminated r s = 50 ?, r fb = 4.4 db pra + vga characteristics ?3 db small signal bandwidth unterminated: r s = 50 ?, r fb = 70 mhz matched: r s = r in = 50 ? 85 mhz slew rate lo gain, vgn = 3 v, v out = 2 v p-p 250 v/s hi gain, vgn = 3 v, v out = 2 v p-p 350 v/s input voltage noise pins vgnx = 3 v, r s = 0 ?, r fb = 1.3 nv/hz noise figure pins vgnx = 3 v, f = 1 mhz to 10 mhz active termination match r s = r in = 50 ? 7 db r s = r in = 100 ? 4.5 db unterminated r s = 50 ?, r fb = 5.0 db r s = 500 ?, r fb = 1.3 db output referred noise lo gain; vgn < 2 v 33 nv/hz hi gain; vgn < 2 v 80 nv/hz peak output voltage differential, r l 500 ? 5 v p-p output resistance f < 1 mhz, pins vohx, volx 1.2 ? common-mode level set to mid supply for pra and vga v s /2 v output offset voltage differential (v ohx?volx) full gain range ?25 5 35 mv common-mode (vohx?vcmx, volx?vcmx) ?20 0 20 mv harmonic distortion v out = 1 v p-p, lo gain, vgn = 2 v hd2 f = 1 mhz ?69 dbc hd3 f = 1 mhz ?57 dbc hd2 f = 10 mhz ?57 dbc hd3 f = 10 mhz ?55 dbc harmonic distortion v out = 1 v p-p, hi gain, vgn = 2 v hd2 f = 1 mhz ?58 dbc hd3 f = 1 mhz ?70 dbc hd2 f = 10 mhz ?55 dbc hd3 f = 10 mhz ?55 dbc output 1 db compression (o p1db) vgn = 3 v 18 dbm vgn = 3 v 8 dbvpk
ad8335 rev. 0 | page 4 of 24 parameter conditions min typ max unit two-tone imd3 distortion v out = 1 v p-p, vgn = 3 v f 1 = 1 mhz, f 2 = 1.05 mhz ?69 dbc f 1 = 10 mhz, f 2 = 10.05 mhz ?65 dbc output ip3 (oip3) v out = 1 v p-p, vgn = 3 v f = 1 mhz 33 dbm f = 10 mhz 31 dbm channel-to-channel crosstalk v out = 1 v p-p, f = 1 to 10 mhz ?80 dbc overload recovery pra or vga 10 ns group delay variation full gain range, f = 1 mhz to 10 mhz 3.0 ns gain control interface pins vgnx normal operating range 0 3 v maximum range no gain foldover 0 v s v gain range lo gain mode; (pin s hlxx = 0 v) ?10 to +38 db hi gain mode; (pins hlxx = v s ) ?2 to +46 db scale factor nominal (pins sl12 and sl34 = 2.5 v) 19.0 20.0 21.0 db/v bias current ?0.3 a response bandwidth 5 mhz response time 48 db gain change 350 ns gain accuracy pins vgnx absolute gain error 0 vgn 0.4 v 1.25 7.5 db 0.4 vgn 2.6 v, 1 ?1.25 0.2 +1.25 db 2.6 vgn 3 v ?7.5 ?1.25 db gain law conformance over temperature 0.4 vgn 2.6 v; ?40c < t a < +85c 0.75 db intercept lo gain mode; pra matched to 50 ? ?16.1 db hi gain mode; pra matched to 50 ? ?8.1 db channel-to-channel matching 0.4 v gn 2.6 v 0.15 db logic levelhilo, shutdown preamp, and enable interfaces pins hlxx, spxx, and enxx logic level high 2.75 5 v logic level low 0 1 v bias currenthilo, enable logic high 80 a logic low ?12 a input resistancehilo, enable 50 k? bias current C shutdown preamp logic high 20 a logic low 0 a input resistanceshutdown preamp 500 k? hilo response time 0.6 s enable response time 100 s power supply pins vppx and vpvx supply voltage 4.5 5 5.5 v quiescent current per channelpra and vga enabled 19 ma over temperature ?40c < t a < +85c 16 22.8 ma quiescent power per channelpra and vga enabled 95 mw quiescent current per channelpra disabled, vga enabled 13 ma quiescent power per channelpra disabled, vga enabled 65 mw quiescent current all channels enabled 76 ma disable current all channels disabled 0.8 ma psrr v gn = 0 v, all bypass capacitors removed, 1 mhz ?60 db
ad8335 rev. 0 | page 5 of 24 absolute maximum ratings t a bl e 2. p a r a m e t e r r a t i n g v o l t a g e supply v s 6 v preamp input v s vga inputs v s enable, shutdown preamp, and hilo interfaces v s g a i n v s power dissipation (4-layer jedec board (2s2p)) 2 . 4 6 w ja 2 6 . 4 c / w jc 6.8c/w operating temperature range ?40c to +85c storage temperature range ?65c to +150c lead temperature range (soldering 60 s) 300c s t r e s s es a b o v e t h os e lis t e d un der a b s o l u t e m a xim u m r a t i n g s ma y ca us e p e r m a n en t da ma g e t o t h e de vice . this is a s t r e s s r a t i ng on ly ; 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 an y o t h e r co n d i t io n s a b o v e t h os e in dica t e d in t h e o p era t io nal s e c t io n o f t h is sp e c if ica t io n is n o t im plie d . e x p o sur e t o a b s o l u t e m a x i m u m r a t i ng c o nd i t i o ns for e x te nd e d p e r i o d s m a y af fe c t de vice r e lia b i l i t y . esd caution esd (electrostatic discharge) sensitive device. electros tatic charges as high as 4000 v readily accumulate on the human body and test eq uipment and can discharge wi thout detection. although this product features proprietary esd protection circuitry, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. therefore, proper esd pr ecautions are recommended to avoid performance degradation or loss of functionality.
ad8335 rev. 0 | page 6 of 24 pin configuration and f unction descriptions pin 1 identifier 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 pmd 4 pip4 vpp4 pon 4 pop4 vip4 vin 4 com 4 vgn 4 vc m4 vgn 3 vc m3 en 3 4 sp3 4 sl3 4 hl34 64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 pmd 1 pip1 vpp1 pon 1 pop1 vip1 vin 1 com 1 vgn 1 vc m1 vgn 2 vc m2 en 1 2 sp1 2 sl1 2 hl12 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 pmd2 pip2 vpp2 pon2 pop2 vip2 vin2 com2 com3 vin3 vip3 pop3 pon3 vpp3 pip3 pmd3 gnd1 voh1 vol1 vpv1 vpv2 vol2 voh2 gnd2 gnd3 voh3 vol3 vpv3 vpv4 vol4 voh4 gnd4 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 ad8335 top view (not to scale) 04976-058 f i gur e 2. lf csp p i n c o nfigur ation t a bl e 3. p i n f u nc ti o n des c rip t i o ns pin no. mnemonic function 1 pmd2 preamp input commonch2 2 p i p 2 preamp i n p u t c h 2 3 vpp2 positive supply preampch2 4 pon2 preamp output negativech2 5 pop2 preamp output positivech2 6 vip2 vga input positivech2 7 vin2 vga input negativech2 8 c o m 2 ground p r e a m p c h 2 9 c o m 3 ground p r e a m p c h 3 10 vin3 vga input negativech3 11 vip3 vga input positivech3 12 pop3 preamp output positivech3 13 pon3 preamp output negativech3 14 vpp3 positive supply preampch3 1 5 p i p 3 preamp i n p u t c h 3 16 pmd3 preamp input commonch3 17 pmd4 preamp input commonch4 1 8 p i p 4 preamp i n p u t c h 4 19 vpp4 positive supply preampch4 20 pon4 preamp output negativech4 21 pop4 preamp output positivech4 22 vip4 vga input positivech4 23 vin4 vga input negativech4 2 4 c o m 4 ground p r e a m p c h 4 2 5 v g n 4 gain c o n t r o l c h 4 26 vcm4 common-mode decoupl i ng pinch4 2 7 v g n 3 gain c o n t r o l c h 3 28 vcm3 common-mode decoupl i ng pinch3 29 en34 enablech3 and ch4 30 sp34 shutdownpreamp3 and preamp4 31 sl34 slope decoupling pinch3 and ch4 32 hl34 hilo pinch3 and ch4 pin no. mnemonic function 3 3 g n d 4 ground v g a c h 4 34 voh4 vga output positivech4 35 vol4 vga output negativech4 36 vpv4 positive supply vgach4 37 vpv3 positive supply vgach3 38 vol3 vga output negativech3 39 voh3 vga output positivech3 40 gnd3 ground vga ch3 41 gnd2 ground vga ch2 42 voh2 vga output positivech2 43 vol2 vga output negativech2 44 vpv2 positive supply vgach2 45 vpv1 positive supply vgach1 46 vol1 vga output negativech1 47 voh1 vga output positivech1 48 gnd1 ground vga ch1 49 hl12 hilo pinch1 and ch2 50 sl12 slope decoupling pinch1 and ch2 51 sp12 shutdownpreamp1 and preamp2 52 en12 enablech1 and ch2 53 vcm2 common-mode decoupl i ng pinch2 5 4 v g n 2 gain c o n t r o l c h 2 55 vcm1 common-mode decoupl i ng pinch1 5 6 v g n 1 gain c o n t r o l c h 1 5 7 c o m 1 ground p r e a m p c h 1 58 vin1 vga input negativech1 59 vip1 vga input positivech1 60 pop1 preamp output positivech1 61 pon1 preamp output negativech1 62 vpp1 positive supply preampch1 6 3 p i p 1 preamp i n p u t c h 1 64 pmd1 preamp input commonch1
ad8335 rev. 0 | page 7 of 24 typical performance characteristics v s = 5 v , t a = 25c, r l = 500 ?, f = 5 mh z, c l = 10 pf , l o ga in ra n g e (?10 db t o +38 db), r fb = 249 ? (p ra r in = 50 ?) a n d sig n al v o l t a g e s p e c if ie d dif f er en t i al , p e r cha n n e l p e r f o r ma n c e , unles s o t h e r w is e n o t e d . ?2 0 ?1 0 0 10 20 30 40 50 gain ( d b) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-002 lo gain hi gain +85 c +25 c ?40 c fi g u r e 3 . g a i n v s . v ga i n at thr ee t e mper atur es (s ee f i gur e 49) ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 gain e rror (db) 1.0 1.5 2.0 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-003 +85 c, lo gain +85 c, hi gain +25 c, lo gain +25 c, hi gain ?40 c, lo gain ?40 c, hi gain f i g u re 4 . g a i n e r ro r v s . v ga i n at thr ee t e mper atur es (s ee f i gur e 49) ?6.0 ?4.0 ?2.0 0 2.0 gain e rror (db) 4.0 6.0 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-004 1mhz 5mhz 10mhz 20mhz f i g u re 5 . g a i n e r ro r v s . v ga i n at v a rious f r equencies (s ee f i gur e 49) 0 2 4 6 8 10 12 14 16 18 20 ?0.6 ? 0.5 ?0.4 ?0.3 ?0.2 0 0.4 ?0.1 0.1 0.2 0.3 0.5 0.6 % of units gain error (db) 04976-005 420 channels (105 units) v gain = 1.5v f i g u re 6 . g a i n e r ro r h i s t o g r a m % of units channel-to-channel gain match (db) 04976-006 ?1.0 ?0.9 ?0.8 ?0.7 ?0.6 ?0.5 ?0.4 ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ?1 . 0 ?0 . 9 ?0 . 8 ?0 . 7 ?0 . 6 ?0 . 5 ?0 . 4 ?0 . 3 ?0 . 2 ?0 . 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 5 10 15 20 25 0 5 10 15 20 25 420 channels (105 units) v gain = 1.0v v gain = 2.0v ch 1 t o c h2 ch 1 t o c h4 ch 1 t o c h3 f i gur e 7. g a in match histogr a m for v ga i n = 1 v and 2 v 0 5 10 15 20 25 30 35 40 45 % total gain scaling factor 04976-007 20.4 19.9 20.0 20.1 20.2 20.3 420 channels (105 units) 0.5v < v gain < 2.5v f i g u r e 8. g a in s c aling f a c t or his t og r a m f o r 0.5 v < v ga i n < 2.5 v
ad8335 rev. 0 | page 8 of 24 0 5 10 15 20 25 ? 16.7 ?16.6 ? 16.5 ?16.4 ?16.3 ?16.1 ?15.7 ?16.2 ? 16.0 ?15.9 ?15.8 ? 15.6 ?15.5 % total intercept (db) 04976-008 420 channels (105 units) 0.5v < v gain < 2.5v f i g u re 9 . i n te rce p t h i s t o g r a m 1m 100k 10m 100m 1g ?2 0 ?1 0 0 10 20 30 40 50 gain ( d b) frequency (hz) 04976-009 v gain = 3.0v v gain = 2.5v v gain = 2.0v v gain = 1.5v v gain = 1.0v v gain = 0.5v v gain = 0v f i gur e 1 0 . f r equenc y resp o n se fo r v a r i o u s v a l u es o f v ga i n (s ee f i gur e 49) 1m 100k 10m 100m 1g ?2 0 ?1 0 0 10 20 30 40 50 gain ( d b) frequency (hz) 04976-010 v gain = 3.0v v gain = 2.5v v gain = 2.0v v gain = 1.5v v gain = 1.0v v gain = 0.5v v gain = 0v fi g u r e 1 1 . fr e q u e n c y r e s p o n s e v s . fr e q u e n c y f o r v a r i o u s v a l u e s o f v ga i n , hil o = hi (s ee f i g u r e 49) 1m 100k 10m 100m 1g ?5 0 5 10 15 20 25 30 gain ( d b) frequency (hz) 04976-011 ?10 r s = 50 ? v in = 10mv p-p r fb = r fb = 249 ? f i g u r e 12. f r equenc y r e s p ons e f o r a t e rminated and u n terminated 50 ? s o ur c e (s ee f i gur e 49) ?100 ?9 0 ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 ?1 0 cros s t alk (db) frequency (hz) 100k 10m 1m 100m 04976-012 v out = 1v p-p v gain = 3v v gain = 2v v gain = 1v v gain = 1v v gain = 2v v gain = 3v f i gur e 13. channel-to - c hannel cr o ssta l k vs . f r equenc y fo r va r i o u s va l u e s o f v ga i n group delay (ns) frequency (hz) 100k 10m 1m 100m 04976-013 10 20 30 40 50 60 70 80 0 fi g u r e 1 4 . g r o u p d e l a y v s . fr e q u e n c y
ad8335 rev. 0 | page 9 of 24 ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 offset volta ge ( m v) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-014 +85 c, hi +85 c, lo ?40 c, lo ?40 c, hi +25 c, lo +25 c, hi f i gur e 1 5 . di ffer e nti a l o u tput o ffset v o l t a g e vs . v ga i n at thr ee t e mper atur es ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 offset volta ge ( m v) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-015 f i gur e 16. absolute o ffset v s . v ga i n at p i ns vohx and volx relative to p i ns vc mx 1m 100k 10m 1g 0.1 1 10 100 outp ut imp e dance ( ? ) frequency (hz) 04976-016 v in = 10mv p-p vohx volx f i gur e 17. o u tput resistanc e at p i ns vohx and volx v s . f r equenc y 1m 10m 1g inp u t imp e dance ( ? ) frequency (hz) 04976-017 10 100 1k r fb = 2.5k ? r fb = 1k ? r fb = 499 ? r fb = 249 ? r sh = 49 ? , c sh = 22pf r sh = , c sh = 0pf f i gur e 1 8 . p r ea m p input resi sta n c e vs . f r equenc y fo r va r i o u s va l u e s o f r fb ?100 ?9 0 ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 ?1 0 cros s t alk (db) frequency (hz) 100k 10m 1m 100m 04976-018 25j 50j 100j ? 75j ?50j ? 25j 0 ? 17 ? 50 ? 150 ? stop 1ghz start 100khz v in = 10mv p-p 100mhz f i g u r e 19. smit h char t s11 v s . f r equenc y , 100 k h z to 1 gh z 0 50 100 150 200 250 outp ut re fe rre d nois e (nv / hz) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-019 hilo = hi hilo = lo r s = 0 ? r fb = f i gur e 20. o u tput r e ferr ed noise v s . v ga i n (s ee f i gur e 50)
ad8335 rev. 0 | page 10 of 24 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 frequency (mhz) 0.1 10 1 100 04976-020 inp u t re fe rre d nois e (nv / hz) v gain = 3.0v r s = 0 ? r fb = f i gur e 2 1 . sho r t- ci r c ui t input referr ed no i s e vs . f r equenc y a t ma xi m u m g a i n (s ee f i gur e 50) v gain (v) 04976-021 0.1 1.0 10 100 1k 1.0 1.5 0 0.5 2.0 2.5 3.0 n o ise ( n v/ h z ) t = ? 40 c t = +25 c t = +85 c f i gur e 22. input r e ferr ed noise v s . v ga i n at thr ee t e mper atur es (s ee f i gur e 50) 10 1 100 1k 0.1 1.0 10 source resistance ( ? ) 04976-022 in pu t n o ise ( n v/ h z ) r s thermal noise alone f = 1mhz, v gain = 3v f i gur e 23. input r e ferr ed noise v s . r s 0 10 20 15 5 30 25 nois e figure (db) 40 35 50 45 60 55 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-062 f = 10mhz fi g u r e 2 4 . n o i s e fi g u r e v s . v ga i n fo r r s = r in = 50 ? ?70 ?65 ?60 ?55 ?50 ?45 ?40 ?35 distortion (dbc) 200 400 600 800 1.0k 1.2k 1.4k 1.6k 1.8k 2.0k r load ( ? ) 04976-025 f = 10mhz v out = 1v p-p v gain = 1.5v hilo = lo hd2 hd3 hilo = hi hd2 hd3 f i g u r e 25. harmonic d i s t or t i on v s . r lo a d (s ee f i gur e 50) ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 0 1 02 03 0 4 0 5 0 c load (pf) 04976-200 f = 10mhz v out = 1v p-p hilo = lo hd3 hilo = hi, hd3 hilo = hi, hd2 hilo = lo, hd2 f i g u r e 26. harmonic d i s t or t i on v s . c lo a d (s ee f i gur e 53)
ad8335 rev. 0 | page 11 of 24 ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) 04976-026 lo gain v out = 1v p-p f = 10mhz f = 5mhz f = 1mhz f i g u r e 27. hd2 v s . v ga i n at thr ee f r equencies, l o g a in (s ee f i gur e 53) ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) 04976-027 lo gain v out = 1v p-p f = 10mhz f = 5mhz f = 1mhz f i g u r e 28. hd3 v s . v ga i n at thr ee f r equencies, l o g a in (s ee f i gur e 53) ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) 04976-029 hi gain v out = 1v p-p f = 10mhz f = 5mhz f = 1mhz f i g u r e 29. hd2 v s . v ga i n at thr ee f r equencies, hi g a in (s ee f i gur e 53) ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) 04976-030 hi gain v out = 1v p-p f = 10mhz f = 5mhz f = 1mhz f i g u r e 30. hd3 v s . v ga i n at thr ee f r equencies, hi g a in (s ee f i gur e 53) ?80 ?75 ?70 ?65 ?60 ?55 ?50 ?45 ?40 ?35 distortion ( d bc) 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) 04976-031 f = 1mhz 2v p-p 1v p-p 0.5v p-p f i g u r e 31. hd2 v s . v ga i n at thr ee o u tput v o ltages, l o g a in (s ee f i gur e 53) ?90 ?80 ?70 ?60 ?50 ?40 ?30 ?20 distortion (dbc) 04976-032 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) f = 1mhz 2v p-p 1v p-p 0.5v p-p f i g u r e 32. hd3 v s . v ga i n , at thr ee o u tput v o ltages, l o g a in (s ee f i gur e 53)
ad8335 rev. 0 | page 12 of 24 ?7 0 ?6 5 ?6 0 ?5 5 ?5 0 ?4 5 ?4 0 ?3 5 distortion (dbc) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-034 f = 1mhz 2v p-p 1v p-p 0.5v p-p f i g u r e 33. hd2 v s . v ga i n at thr ee o u tput v o ltages, hi g a in, f = 1 mh z (s ee f i gur e 53) ?9 0 ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 distortion ( d bc) 04976-035 0.5 1.0 1.5 2.0 2.5 3.0 v gain (v) f = 1mhz 2v p-p 1v p-p 0.5v p-p 0 f i g u r e 34. hd3 v s . v ga i n at thr ee o u tput v o ltages , hi g a in (s ee f i gur e 53) im 3 ( d bc) frequency (mhz) 04976-036 ?9 0 ?8 0 ?7 0 ?6 0 ?5 0 ?4 0 ?3 0 ?2 0 ?1 0 0 1 1 0 100 imd3 (hi) imd3 (lo) v out = 1v p-p v gain = 3v fi g u r e 3 5 . i m d 3 v s . fr e q u e n c y 0 5 10 15 20 25 ip3 ( d bm) 30 35 40 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-037 5mhz (lo) 5mhz (hi) v out = 1vp-p f i g u r e 36. o u t p ut r e f e rr ed ip3 (oip3) v s . v ga i n ?3 0 ?2 5 ?2 0 ?1 5 ?1 0 ?5 0 5 in pu t power ( d b m ) 1.0 1.5 0 0.5 2.0 2.5 3.0 v gain (v) 04976-038 hilo = hi hilo = lo f = 10mhz f i gur e 37. input p1db (ip1db) vs . v ga i n harmoni c di s t orti on (dbc ) 04976-039 10 0 90 10 0 10 m v 50m v 10 n s f i g u r e 38. small sig n al p u ls e r e s p ons e , l o g a in ( s ee f i g u r e 51)
ad8335 rev. 0 | page 13 of 24 harmoni c di s t orti on (dbc ) 04976-039 10 0 90 10 0 10 m v 50m v 10 n s f i gur e 39. lar g e signal p u lse r e sponse , l o g a in (s ee f i gur e 51) v out (v ) time (ns) 04976-041 ?2 ?1 0 1 2 0 1 02 0 3 04 0 5 0 6 07 0 8 09 0 1 0 0 v gain = 2v c l = 47pf c l = 22pf c l = 10pf input input is not to scale c l = 0pf f i g u r e 40. lar g e sig n al p u ls e r e s p ons e f o r v a rious capacit i ve l oads, c l = 0 pf , 10 pf , 20 pf , 47 pf each o u t p ut (s ee f i g u r e 51) harm oni c di s t orti on (dbc ) 04976-042 10 0 90 10 0 40 0n s 2v 500 mv f i gur e 4 1 . g a i n resp o n se , v ga i n step ped f r om 0 v to3 v , v ou t = 2 v p -p (s ee f i gur e 51) harmonic dis t ortion (dbc ) 04976-043 10 0 90 10 0 10 0 s 1 00m v 2v f i g u r e 42. small sig n al e n able r e s p ons e (s ee f i g u r e 51) harmonic dis t ortion (dbc ) 04976-044 10 0 90 10 0 1v 2v 10 0 s f i g u r e 43. lar g e sig n al e n able r e s p ons e (s ee f i g u r e 51) harmonic dis t ortion (dbc ) 04976-045 100 90 10 0 1 s 1v f i gur e 44. p r eamp o v er drive r e c o ver y , 50 mv p -p t o 1.5 v p -p at p r eamp input (measur e d at p r eamp o u tput)
ad8335 rev. 0 | page 14 of 24 harmonic dis t ortion (dbc ) 04976-046 10 0 90 10 0 1 s 1v f i g u r e 45. v g a o v er drive r e c o ver y , 40 mv to 500 mv input , v ga i n = 2.5 v p s rr (db) frequency (hz) 100k 10m 1m 100m 04976-100 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 ?8 0 v gain = 2.5v v gain = 0v v gain = 0.5v v gain = 1.5v f i gur e 46. psrr vs . f r equenc y ( a ll b y pass c a pacit o rs remo v e d) 60 65 70 75 80 85 90 95 quie s c e n t s u p p l y curre nt (ma) ?40 ? 20 0 2 0 4 0 6 0 8 0 100 temperature ( c) 04976-047 v gain = 2.5v f i gur e 47. q u iesc ent sup p ly curr ent v s . t e mper atur e harmonic dis t ortion (dbc ) 04976-101 10 0 90 0 5 00m v 2v 1 s 10 f i gur e 4 8 h i l o resp o n se t i m e
ad8335 rev. 0 | page 15 of 24 test circuits 28 ? 237 ? 249 ? 1:1 network analyzer ad8335 18nf 22pf 50 ? in out 0.1 f 237 ? 28 ? 0.1 f 0.1 f 50 ? 49.9 ? 0.1 f 04976-048 f i gur e 49. t e st cir c uit for g a in and bandwidth measur ements 1:1 ad8335 22pf 0.1 f 0.1 f 0.1 f 49 ? 0.1 f in 50 ? spectrum analyzer 04976-050 f i gur e 50. t e st cir c uit used for noise measur ements 28 ? 237 ? 249 ? 1:1 ad8335 18nf 22pf 0.1 f 237 ? 28 ? 0.1 f 0.1 f 49.9 ? 0.1 f 50 ? in 50 ? oscilloscope 04976-049 f i gur e 51. t e st cir c uit for t r ansient measur ements 28 ? 237 ? 249 ? 1:1 network analyzer ad8335 18nf 22pf 50 ? in out 0.1 f 237 ? 28 ? 0.1 f 0.1 f 50 ? 49.9 ? 0.1 f 50 ? 50 ? 04976-052 f i g u r e 52. t e s t cir c uit u s ed f o r s11 m e as ur ement s 28 ? 237 ? 249 ? 1:1 ad8335 18nf 22pf 0.1 f 237 ? 28 ? 0.1 f 0.1 f 50 ? 0.1 f 50 ? in 50 ? spectrum analyzer 04976-051 lpf signal generato r f i g u r e 53. t e s t cir c uit u s ed f o r d i s t or t i on m e as ur ement s
ad8335 rev. 0 | page 16 of 24 theory of operation f i gur e 54 is a sim p lif i e d b l o c k dia g ra m o f a sin g le cha n n e l. e a ch ch an nel c o ns i s t s of a l o w noi s e pre a m p l i f i e r ( p r a ) fo l l o w e d b y a v g a wi th a us er -s e l ec ta b l e ga in o f 20 db o r 28 db . cha n n e ls a r e e n abl e d i n p a i r s , c h an nel s 1 and 2 and c h an nel s 3 and 4 . t h e pre a m p s are e n abl e d b y g r ou nd i n g pi ns sp x x and p o we re d d o w n b y co n n ecti n g th e m t o th e posi ti v e s u p p l y . t h e en xx p i n s a r e co nn e c t e d t o t h e p o si t i v e s u p p l y t o ena b le t h e v g a s a n d t h e o v er a l l cha n n e l. hilo co nf igur es v g a fo r a f i xe d ga in o f 20 db o r 28 db , wi th 0 v o r 5 v a p p l ied t o th e hlxx p i n s , r e s p ec ti v e l y . c h an nel s 1 and 2 sh are pi n h l 1 2 , and c h an nel s 3 and 4 sh are p i n hl34. th e hlxx p i n s a r e typ i cal l y ha r d wir e d t o ad j u s t t h e v g a ga in acco r d in g t o a n ad c r e s o l u tio n o f 12 b i ts f o r l o ga in a n d 10 b i ts f o r hi ga in. th e sig n al p a t h is f u l l y dif f er en t i al t h r o ug h o u t t o maximize sig n al swin g a n d r e d u ce e v en-o r d er dis t o r t i o n ; h o w e v e r , t h e p r e a m p lif i ers a r e desig n e d t o b e dr i v en f r o m a sin g le-en d e d sig n al s o ur ce . ga in val u es a r e r e fer e n c e d f r o m t h e sin g le-en d e d p r a in p u t t o t h e dif f er en t i al o u t p u t o f ei t h er t h e p r a o r t h e v g a. a g a i n r e f e r r i n g t o f i gur e 54, th e sys t em ga in is dist r i b u te d as liste d in t a b l e 4. t a bl e 4. c h annel g a i n di stri b u ti o n section lo nominal gain (db) hi nominal gain (db) p r a 1 8 . 0 6 1 8 . 0 6 attenuator 0 to ?48.16 0 to ?48.16 output amp 20 27.96 aggregate ?10.1 to +38.6 ?2.14 to +46.02 i n th e r e m a i n d e r o f th i s d o cum e n t , th e ga i n v a l u e s a r e r o un de d to ?10 db to +38 db fo r lo ga in m o de a n d to ?2 db to +46 db fo r hi ga in m o de. i f desir e d , e q ua t i o n 1 ca n b e us e d t o calc u l a t e t h e ga in a t val u e o f v gai n : icpt v v db db gain gn + = 20 ) ( (1) w h er e icp t = ?16.1 db f o r l o ga in m o de wi th th e p r ea m p i n put ma tche d to 5 0 ? ( r fb = 250 ?) a n d ?10.1 db f o r th e unma t c h e d in p u t cas e . f o r hi ga in m o de , t h es e n u m b ers a r e ?8.1 db a n d ?2.1 db , r e sp e c t i vely . p o w e r co n s um p t io n is 95 mw/c ha nn e l f r o m a 5 v s u p p l y , o r 380 mw f o r al l f o ur c h a n n e ls. p o w e r is dis t r i b u t e d 35% f o r th e p r a, a n d 65% f o r th e r e ma in d e r o f th e cir c ui t. t h e p r e a m p s ca n b e sh u t do wn via t h e s p 12 a n d s p 34 p i n s if a us er wa n t s t o us e t h e v g a s o n l y . h o w e v e r , t o a v o i d f eed th r o ugh a r o u n d th e p r ea m p , f eed ba c k r e s i s t o r s s h o u l d not b e i n st a l l e d. enable summary t a b l e 5 s u mma r i zes t h e ena b le/s h u t d o w n log i c a n d re su l t ing su p p ly c u r r e n t. t a bl e 5. c o n t rol p i n l o g i c and p o wer c o nsump t i o n e n 1 2 s p 1 2 e n 3 4 s p 3 4 p r a 1 2 v g a 1 2 p r a 3 4 v g a 3 4 i s h l h l o n o n o n o n 7 6 m a h h h h o f f o n o f f o n 5 2 m a l l l l o f f o f f o f f o f f 0 . 8 m a l h l h o f f o f f o f f o f f 0 . 8 m a +1 +1 +1 +1 pra 18db hilo +1 interpolator attenx 48db to 0db gain interface +1 bias output amp 20db to 28db vohx volx hlxx slxx vgnx vcm x vipx popx enxx pmd x pipx pon x vinx 04976-054 rfb r s f i g u r e 54. simplif ied block d i ag r a m of sing le channel
ad8335 rev. 0 | page 17 of 24 preamp a l th o u gh th e p r ea m p si gn al pa th i s full y d i f f e r e n ti al , th e d e si gn is o p t i mize d fo r sin g le-en d e d in p u t dr i v e a n d sig n a l s o ur ce r e sis t a n ce ma t c hin g . th us, t h e n e ga t i v e in p u t t o t h e dif f er en t i al p r ea m p lif i er p i n s pmd x m u s t be ac-g r o un ded t o p r o v ide a b a la n c e d dif f er en t i al sig n al a t t h e p r a o u t p u t s. d e t a i l e d info r m a t io n r e ga r d in g t h e p r e a m p lif i er a r chi t e c t u r e is fo un d in th e ln a s e c t io n o f th e ad8331/ad8332 da ta s h eet. th e p r e a m p lif i er co n s ists o f a f i xe d ga in a m plif ier wi t h dif f er en - ti al o u t p u t s. w i th th e n e ga ti v e o u t p u t a v a i la b l e a n d a f i x e d ga i n o f 8 (18.06 db), a n ac ti v e in p u t t e r m ina t io n is syn t h e sized b y co n n ecti n g a f eed ba c k r e s i s t o r be t w ee n th e n e ga ti v e o u t p u t a n d t h e p o si t i ve in p u t, pin pipx . this te chniq u e is w e l l k n o w n a n d re su l t s in t h e in p u t re s i st anc e sho w n in e q u a t i on 2 . ) 2 1 ( a r r fb in + = (2) w h er e a/2 is t h e sin g le-en d e d ga in, o r t h e ga in f r o m t h e p i px in p u ts t o t h e pon x o u t p u t s. sin c e t h e a m plif ier has a ga in o f 8 f rom it s i n put t o it s d i f f e r e n t i a l output , it i s i m p o r t a n t t o n o t e t h a t t h e ga in a/2 is t h e ga in f r o m pin pipx t o pin pon x , w h ich is 6 db lo w e r , o r 12.04 db (4). th e in p u t r e sis t a n ce is r e d u ced b y a n in t e r n al b i as r e sis t o r o f 14.7 k? in p a ral l e l wi th th e s o ur ce r e sis t a n ce co nn ec t e d t o p i n p i px, wi th p i n pmd x ac-g r o u n d ed . e q ua tio n 3 ca n be us ed t o calc u l a t e th e n eeded r fb fo r a desir e d r in , a n d is us ed f o r hig h er val u es o f r in . k 7 . 14 || ) 4 1 ( + = fb in r r ( 3 ) fo r e x a m p l e , t o s e t r in = 200 ?, th e val u e o f r fb is 1.013 k?. i f t h e sim p lif i ed e q ua tio n 2 is us ed t o calc u l a t e r in , th e val u e is 197 ?, re su lt i n g i n a l e ss t h an 0 . 1 d b g a i n e r ror . f a c t or s su ch a s a wide l y va r y in g s o ur ce r e sis t a n ce mig h t inf l uen c e th e a b s o l u t e ga in acc u rac y m o r e sig n if ica n t l y . a t hig h er f r e q uen c ies, t h e in p u t ca p a ci t a n c e o f t h e p r a n e e d s t o b e co n s ider e d . th e us er m u s t det e r m in e th e lev e l o f ma t c hin g acc u rac y a n d ad j u s t r fb a c c ord i n g l y . th e b a n d wid t h s (b w) o f t h e p r e a m p lif i er a n d v g a a r e a p p r o x ima t e l y 110 mh z eac h , r e s u l t in g in a cas c aded b w o f a p p r o x i m a t e l y 80 mh z . u l ti m a t e l y th e b w o f th e p r a li m i t s th e acc u rac y o f t h e syn t h e size d r in . f o r r in = r s u p t o a p p r o x ima t e l y 200 ?, th e bes t ma t c h is betw een 100 kh z a n d 10 mh z, wh er e th e lo w e r f r eq ue n c y li m i t i s d e t e rm i n ed b y th e s i z e o f th e a c - co u p lin g ca p a ci t o rs, a n d th e u p p e r limi t is det e r m in ed b y th e p r e a m p lif i er b w . f u r t h e r m o r e , t h e in p u t ca p a ci t a n c e a n d r s limi ts t h e b w a t hig h er f r e q uen c ies. inp u t imp e dance ( ? ) frequency (hz) 04976-102 10 100 1k 100k 1m 10m 50m r in = 500 ? , r fb = 2.5k ? r sh = , c sh = 0pf r in = 200 ? , r fb = 1k ? r sh = 50 ? , c sh = 22pf r in = 100 ? , r fb = 499 ? r in = 50 ? , r fb = 249 ? r sh = , c sh = 0pf r sh = 50 ? , c sh = 22pf f i g u r e 55. r in v s . f r equenc y for v a rious v a lues of r fb . e ffects o f r sh and c sh ar e als o s h o wn. f i gur e 55 s h o w s r in vs. f r e q uen c y fo r va r i o u s val u es o f r fb . n o t e tha t a t th e lo w e s t val u e , 50 ?, r in p e aks a t f r e q uen c ies g r e a t e r tha n 10 mh z. this is d u e t o th e b w r o l l -o f f o f th e p r a as m e n t io n e d e a rlier . th e r sh and c sh ne t w or k sho w n i n f i g u re 5 8 r e d u ces t h is p e a k in g. h o w e v e r , as ca n be s e en f o r la rg er r in val u es, p a rasi t i c ca p a ci ta n c e s t a r ts r o l l in g o f f th e sig n al b w bef o r e th e p r a ca n p r o d uce p e akin g a n d t h e r sh /c sh n e tw o r k f u r t h e r deg r ades t h e ma t c h. th er efo r e r sh and c sh s h o u ld n o t be us ed f o r val u es o f r in g r ea t e r tha n 50 ?. noise th e t o t a l in p u t r e fer r e d n o is e (irn) is a p p r o x ima t e l y 1.3 nv/ h z . al lo win g f o r a ga in o f 8 in th e p r ea m p , th e v g a n o is e is 0.46 nv/ h z r e f e r r ed t o th e p r a in p u t. th e p r ea m p n o is e is 1.2 nv/ h z . i t is im p o r t a n t t o n o t e t h a t t h es e n o is e va l u es in cl ude a l l a m plif ier n o is e s o ur ces, in cl udin g t h e v g a a n d t h e p r e a m p lif i er ga in r e sis t o r s. f r e q uen t ly , ma n u fac t ur er n o is e sp e c if ica t io n s excl ude ga in s e t t in g r e sist o r s, a n d t h e v o l t a g e n o is e s p e c t r al den s i t y o f a n o p a m p mig h t b e p r es en t e d as 1 nv/ hz . i n clu d i n g t h e g a i n re s i stor s re su lt s i n a m u ch hig h er n o is e sp e c if ica t io n.
ad8335 rev. 0 | page 18 of 24 f i gur e 56 s h o w s th e sim u la t e d n o is e f i gur e (nf) vs. s o ur ce r e sis t a n ce , a n d va r i o u s val u es o f p r ea m p lif i er r in f rom 5 0 ? , to 14.7 k?, t h e val u e s e en lo okin g in t o p i n s p i px w h en r fb = . a s sh o w n in t h e f i gur e , t h e minim u m nf fo r r in = 50 ? is slig h t ly le s s th a n 7 d b . n o t e th a t , f o r th i s p r ea m p li f i e r , th e n f i s o p ti m i z e d f o r th e r in f r o m 50 ? t o 200 ?; f o r r fb = , th e minim u m nf is a t a p p r o x ima t e l y 480 ?. this o p tim u m n o is e r e sis t a n ce ca n als o be calc u l a t ed b y di vidin g th e in p u t r e f e r r ed v o l t a g e n o is e b y t h e c u r r en t n o is e . 0 2 4 6 8 10 nois e figure (db) 12 14 16 r s ( ? ) 10 100 1k 04976-066 r in = 50 ? r fb = 250 ? r in = 75 ? r fb = 375 ? r in = 100 ? r fb = 500 ? r in = 200 ? r fb = 1k ? r in = 14.7k ? r fb = simulation includes noise of vga f = 1mhz f i g u r e 56. sim u lated nois e f i g u r e v s . r s fo r va r i o u s f i x e d va l u e s o f r in , ac tively matched vga a s s e en in f i gur e 54, th e basic a r c h i t ec t u r e , a n x-amp tm , co n s is ts o f a ladder a t t e n u a t o r , f o l l o w ed b y a f i xed-ga in a m plif ier wi t h s e le c t a b le in p u t st a g es. e a rlier exa m ples o f t h is a r c h i t ec t u r e a r e t o be f o un d in th e ad60x s e r i es, ad8331/ ad8332, a n d ad8367 v g a s . thr o ug h a p r o p r i eta r y , t e m p era - tu re - c om p e ns a t e d i n te r p o l a t or d e s i g n , t h e bi a s c u r r e n t s to t h e in p u t g m s t a g es a r e co n t in uo us l y s t eer e d f r o m r i g h t t o lef t (de c r e asin g a t t e n u a t io n) r e su l t in g in in cr e a sin g ga in. th e hil o (hl12 a n d hl34) ga in p i n s s e lec t o n e o f tw o o u t p u t a m plif ier n e tw o r ks co n s ist i n g o f t h e fe e d b a ck r e sist o r s, a m plif ier st age s , and b u f f e r s . optimizing the system dynamic range th e v g a o u t p u t ga in swi t c h o f 8 db (2.5) o p timizes th e v g a n o is e f l o o r f o r a 10-b i t o r 12-b i t ad c, as s u min g a f u l l -s cale ad c in p u t v o l t a g e o f 1 v p-p . a t lo w ga in th e ad c s n r s h o u ld limi t th e sys t em n o is e p e r - fo r m a n ce , w h i l e a t hig h ga in s t h e n o is e is def i n e d b y t h e s o ur ce a n d p r e a m p lif i er . th e maxim u m v o l t a g e swin g is b o un de d b y t h e f u l l -s ca le p e a k -t o-p e a k ad c in p u t v o l t a g e (typ ica l ly 1 v p-p t o 2 v p-p). th e n o is e p e r f o r ma n c e is o p t i mize d b y ad j u s t in g t h e noi s e f l o o r of t h e v g a a c c ord i n g to t h e a d c re s o lut i on . th e s n r o f a 12-b i t co n v er t e r is th eo r e tical l y 12 db bet t er tha n a 10-b i t; h o w e v e r , a p p r o x ima t e l y 8 db is typ i cal in p r ac tice , acco un tin g f o r th e 8 db ga in o p tio n o f th e ad8335. th e irn a n d t h e p o w e r co n s um p t io n o f t h e v g a a r e una f fe c t e d b y ei t h er ga in s e t t in g; t h er efo r e , o n ly t h e o u t p u t r e fer r e d n o is e (o rn ) c h a n g e s (b y 8 db) wi th o u t a f f e c t in g a n y o t h e r pa ra m e t e r s . attenuator th e a t t e n u a t o r is a n 8-s t a g e dif f er en t i al r - 2r ladder wi t h a t o t a l a t t e n u a t io n o f 48.16 db C 6.02 db p e r ta p . th e ef f e c t i v e in p u t r e sis t a n ce p e r side is 320 ? n o minal l y fo r a t o t a l dif f er en t i al r e sis t a n ce o f 640 ?. th e co mm o n -m o d e v o l t a g e o f th e a t t e n u a t o r a n d th e v g a is co n t r o l l ed b y a n a m p l if ier tha t us es th e s a m e midsu p ply vol t a g e der i ve d in t h e p r e a m p lif i er , p e r m i t t i n g dc co u p li n g o f th e p r a t o th e v g a w i th o u t i n tr od uci n g la r g e o f fs ets d u e t o co mm o n -m o d e dif f er en ces. h o w e v e r , w h en dc co u p lin g betw een th e p r a a n d v g a, a n y o f fs et f r o m th e p r a a r e a m plif ie d as t h e ga in is in cr e a s e d , p r o d ucin g a n exp o n e n t ia l l y in cr e a sin g v g a o u t p u t o f fs et. w h en t h e p r a a n d t h e v g a a r e a c - c oupl e d , t h e output of f s e t i s u n ch ange d w i t h ch ange s i n g a i n (s ee f i gur e 15). a s a r e s u l t , ac co u p lin g is r e co mm en ded f o r mo s t a p p l ica t io n s. a s ca n be s e en f r o m fi g u re 5 4 , p i n s v c mx co n n ect to t h e re sp e c t i ve mi d p oi n t s on e a ch channel and are us ed t o ac deco u p le th e co mm o n -m o d e n o de a t hig h f r eq uen c ies. i t i s ve r y i m p o r t an t t h a t a t l e ast a 0 . 1 f ca pa ci t o r be used , w i th b e t t er de co u p lin g a t hig h er f r e q uen c ies w h e n anot he r s m a l l e r ca p a ci t o r (10 nf) is co nn ec t e d in p a ral l e l . th e in t e r n al +1 b u f f er p r o v ides co r r ec t co mm o n -m o d e b i as lev e l s a n d a n y d y na mic c u r r en ts ha v e t o be a b s o rbed b y th e ext e r n al deco u p lin g ca p a ci t o rs.
ad8335 rev. 0 | page 19 of 24 gain control th e ga in co n t r o l in t e r f ace has tw o in p u ts, v gai n (p in s v g n x ) a n d v s lp (pin s s l xx). th e slo p e in p u t is in t e n d e d o n ly as a deco u p lin g p i n, a n d th e o n l y gua r a n t eed ga in s l o p e is th e 20 db/v defa u l t. h o w e v e r , if a v o l t a g e is a p plie d t o t h e v s lp in p u ts, th e ga in s l o p e ca n be in cr eas e d b y r e d u cin g th e s l o p e v o l t a g e . f o r exa m p l e , if a v o l t a g e o f 1.67 v is a p p l ied t o p i n s s l xx, t h e ga in s l o p e cha n g e s t o 30 db/v . u s e e q ua t i o n 4 t o calc u l a t e th e ga i n s l o p e . slope vslp db/v 20 v 5 . 2 = ( 4 ) v gai n v a ri e s th e ga i n o f th e v g a th r o u gh th e i n t e r p o l a t o r b y s e le c t in g t h e a p p r o p r i a t e in p u t s t a g es co nn e c t e d t o t h e in p u t at t e nu at o r . t h e n o m i n a l v gai n ra n g e f o r 20 db/v is 0 v t o 3 v , wi th th e bes t ga in-lin ea r i ty f r o m a p p r o x ima t e l y 0.5 v t o 2.5 v , w h er e t h e er r o r is typ i cal l y les s t h a n 0.2 db . f o r v gai n volt age s a b o v e 2.5 v a n d les s tha n 0.5 v , th e er r o r in cr eas e s (s ee f i gur e 4). th e val u e o f t h e v gai n v o l t a g e ca n be in cr eas e d t o tha t o f th e supply volt age, w i t h out g a i n fol d o v e r . e a c h c h a n n e l has s e p a ra t e ga in co n t r o l p i n s tha t ca n be co nn ec t e d t o a co mm o n v o l t a g e-s o ur ce s u c h as f o un d in m o s t u l t r a s ou nd a p pl i c a t i o ns . f o r c o n t ro l of i n d i v i d u a l ch an nel s , co nn ec t th e a p p r o p r i a t e ga in co n t r o l sig n al t o eac h c h a n n e l . output stage d u plica t e o u t p u t s t a g es o f t h e v g a p r o v ide a n 8 db (2.5) ga in swi t ch. th e ga in swi t ch is in t e n d e d t o o p t i mize t h e o u t p u t n o is e f l o o r f o r ei th er a 10-b i t o r 12-b i t ad c. th e v g a ga in is 20 db (10) in l o ga in m o de a n d 28 db (25) in hi ga in m o de . th e log i c s e t t in g o f th e hil o (p in s hlxx) s e lec t s betw een o u t p u t a m plif iers in cl udin g t h e ga in r e sist o r s a n d fe e d b a ck b u f f ers. 100 mh z ba n d wid t h is ma in ta in ed betw een th e a m p l if iers b y cha n g i n g t h e co m p en s a t i o n ca p a ci t a n c e as t h e ga in swi t ch es ga in s e t t in gs. p o w e r co n s um p t io n is t h e s a m e fo r ei t h er le v e l o f ga in. i n cer t a i n a p p l ica t io n s , p o w e r co n s um p t io n ca n be r e d u ced b y lo w e r i n g th e s u p p l y v o l t a g e as m u c h as p o s s i b le; h o w e v e r , th e o u t p u t d y na mic ra n g e is a f f e c t ed b y th e m o r e limi t e d swin g. th e f u l l y dif f er en tial sig n al p a th o f th e ad8335 r e s t o r es 6 db o f d y na mic ra n g e , a n d th e co mm o n -m o d e lev e l is ma in ta in ed a u to ma t i ca l l y a t ha lf t h e su p p ly vol t a g e fo r max i m u m sig n a l swin g. th e dif f er en t i al sig n al has t h e adde d b e n e f i t o f s u p p r es s- in g t h e e v en o r d er ha r m o n ics. th e o u t p u t a m plif ier is desig n e d t o dr i v e a n o mina l dif f er en t i a l lo ad o f 500 ? o r g r ea t e r ; th e sig n al swin g ca n be as la rg e as 5 v p - p dif f er en tial bef o r e c l i p p i n g o c c u rs. h o w e v e r , tha t dis t o r - tio n i n c r e a s e s b e f ore re a c h i ng t h e cl ippi ng l e vel. d i stor t i on i s sho w n i n f i g u re 2 5 t h rou g h f i g u re 3 4 f o r t y pi c a l v a lu e s of 1 v p-p o r 2 v p-p (f u l l-s c ale in p u ts f o r ma n y ad cs). th e o u t p u t is ac-co u ple d t o a dif f er en t i a l a n t i -a lias f i l t er dr i v in g a dif f er en t i al ad c. m o s t m o der n ad cs ha v e dif f er en t i al in p u ts a n d achie v e o p t i m u m p e r f o r ma n c e w h en dr i v en dif f er en t i al ly . f o r m o r e info r m a t io n, s e e t h e a p plica t io n s s e c t io n. vga noise a s w i th all x - a m p s , th e o u t p u t n o i s e o f th e v g a i s co n s ta n t wi th ga in. this ca us es th e in p u t r e f e r r ed n o is e t o in cr eas e as th e ga in is decr eas e d . this c h a r ac t e r i s t ic is desira b l e in r e cei v er a p plica t io n s w h er e wide d y na mic ra n g e in p u t sig n als a r e co m - p r ess e d wi t h a f i xe d cei l in g a n d n o is e f l o o r in to a n ad c. th e v g a o u t p u t n o is e is a p p r o x ima t e l y 33 nv/h z in lo ga in m o de a n d 2.5 tim e s hig h er tha n this, 83 nv/h z , in hi g a i n m o d e . a s th e ga i n i n cr ea se s , th e n o i s e o f th e p r ea m p li f i e r pre v ai l s a n d , a t t h e maxim u m v g a ga in, t h e o u t p u t n o is e is a p p r o x i- ma t e l y 90 nv/h z a n d 225 nv/h z f o r l o a n d hi ga in m o des, re sp e c t i vely . th e o u t p u t s n r is det e r m in e d b y t h e n o is e f l o o r a n d t h e la rg es t sig n al lev e l , typ i cal l y limi t e d b y th e fs o f th e ad c. m o d u la tio n n o is e , ess e n t ia l l y t h e n o is e in t r o d uce d b y t h e ga in co n t r o l in p u t, ca n be tr o u b l es o m e . n o r m al l y o n e t e n d s t o lo ok a t th e ma in a m plif ier sig n a l p a t h fo r n o is e , b u t a v g a is r e a l ly a m u l t i p lier w i th th e f o llo w i n g fun c ti o n ref in gain out v v v v = ( 4 ) w h er e v ref (b ias) a n d v gain (ga i n co n t r o l in t e r f ace) a r e bo th n o is e co n t r i b u t o rs un der cer t a i n co n d i t io n s . i t is th er ef o r e im p o r t a n t tha t th e ga in co n t r o l sig n als be k e p t c l ea n, es p e cial l y a t hig h er ga in co n t r o l s l o p es.
ad8335 rev. 0 | page 20 of 24 applications ultrasound th e p r ima r y a p p l ica t io n f o r th e ad8335 is m e dical u l tras o u n d . f i g u re 5 7 sho w s a s i m p l i f i e d bl o c k d i ag r a m of an u l t r a s ou nd sys t em. th e m o s t cr i t ical f u n c tio n o f a n u l tras o u n d sys t em is th e tim e ga in co n t r o l (t gc) co m p en s a tio n f o r p h ysiolog i cal s i g n a l at t e nu at i o n . b e c a u s e t h e at t e nu at i o n o f u l t r a s o u n d s i g n a l s is exp o n e n t ial wi th r e s p ec t t o dis t a n ce (tim e), a lin e a r -in-db v g a i s th e o p ti m a l so l u ti o n . k e y re qu i r e m e n t s i n an u l t r a s ou nd s i g n a l ch ai n are ve r y l o w n o is e , ac t i v e in p u t t e r m ina t io n, fast o v erlo ad r e co v e r y , lo w p o w e r , a n d dif f er en t i al dr i v e t o a n ad c. b e ca us e u l t r as o u n d machin es us e b e a m fo r m in g t e chniq u es r e q u ir in g la rg e b i na r y w e ig h t ed n u m b ers (f o r exa m p l e , 32 t o 512) o f c h a n n e ls, th e lo w e s t p o w e r a t th e lo w e s t p o s s i b le n o is e is o f k e y im p o r t a n ce . m o st m o der n machin es us e dig i t a l b e a m fo r m in g. i n t h is te chni qu e, t h e s i g n a l i s c o n v e r te d to di g i t a l for m a t i m me di a t ely fol l o w in g t h e t g c a m plif ier ; b e a m fo r m in g is do n e dig i t a l l y . t y p i ca l ad c r e s o l u t i o n in gen e ra l p u r p os e machin es is 10 b i ts w i t h s a m p l i ng r a te s g r e a te r t h an 4 0 m s p s , w h i l e hi g h e n d sys t em s us e 12 b i ts. p o w e r co n s um p t io n a n d lo w cos t a r e o f p r ima r y im p o r t a n ce in lo w-en d a n d p o r t a b le u l tras o u n d mac h in es, a n d th e ad8335 is desig n e d fo r t h es e cr i t er ia . f o r a d d i t i on a l i n f o r m a t i o n re g a rd i n g u l t r a s ou nd s y ste m s , re f e r to h o w ult r a s ou nd s y ste m c o ns i d e r a t i o ns i n f l u e nc e f ron t - en d c o m p o n en t ch o i ce , analog dialogue , v o l . 36, n o . 3, m a yCj u l y 2003. ( h t t p ://w w w .a nalog.co m/li b r a r y/a n alogdialogue/a r c hi v e s/36- 0 3 / u l t r a s ou nd / i nd e x . h t m l ) beamformer central control r x beamformer (b and f modes) color doppler (pw) processing (f mode) image and motion processing (b mode) spectral doppler processing mode display audio output tx beamformer cw (analog) beamformer lnas transducer array 128, 256 etc. elements bidirectional cable hv mux/ demux t/r switches tx hv amps multichannel tgc uses many vgas tgc time gain compensation 04976-053 vgas ad8335 f i g u r e 57. simplif ied u l t r as ound sy s t em block d i ag r a m
ad8335 rev. 0 | page 21 of 24 basic connections f i gur e 58 s h o w s th e basic co nn ec tio n s f o r th e ad8335. i n p u t sig n als en t e r f r o m t h e lef t a n d o u t p u t sig n als exi t f r o m t h e r i g h t, p r o v idin g st ra ig h t -lin e sig n a l p a t h s. of co urs e , a de vice wi t h fo ur dif f er en t i al v g a s s u ch as t h is r e q u ir es a m u l t i l a y er p r in t e d cir c ui t b o a r d . p o w e r su p p ly is ola t io n is sh o w n fo r t h e p r e a m p s, a n d fo r t h e v g a s e c t io n s . i f co m p o n en ts a r e m o un t e d t o b o t h s i d e s o f th e boa r d , th ose i n th e s i g n al p a th s h o u ld be lo ca t e d o n th e t o p , wi th p o w e r - s u p p l y deco u p lin g co m p o n en ts o n th e wir i n g side . preamp connections t o co nf igur e th e ad8335 f o r in p u t ma t c hin g a f eed bac k r e sis t o r (r fb ) is ac-co u ple d b e tw e e n pin pon x a n d pin pipx . a c co u p lin g acco mm o d a t es dis s imila r co mm o n -m o d e v o l t a g es a t th e in p u t and output p o r t s . f o r v a lu e s of r so ur c e betw een 50 ? a n d 200 ?, r fb is sim p l y 5 r so ur c e . t a b l e 6 lis t s a fe w la rg er val u es o f s o ur ce re s i stor ( o r r in ), alo n g wi t h t h e exac t val u e a n d n e a r es t s t a n da r d 1% f eed bac k r e sis t o r . f o r val u es o t h e r th ose tha n lis t ed in t a b l e 6, r fb ca n be calc u l a t ed usin g e q ua tio n 5. f o r val u es la rg er tha n 1 k ? , i t ma y be ad va n t a g eo us t o sim p l y r e m o v e r fb . t a bl e 6. f e e d b a c k resi st o r v a lu es f o r v a ri ou s i n p u t resi st anc e s r in (?) exact r fb v a l u e ( ? ) nearest standard 1% value (?) 2 0 0 1 0 1 4 1 . 0 2 k 5 0 0 2 5 8 8 2 . 6 1 k 1 0 0 0 5 3 6 5 5 . 3 6 k k 7 . 14 1 5 ) ( in in fb r r r ? = ? ( 5 )
ad8335 rev. 0 | page 22 of 24 pip2 c sh 2 22pf r fb 2 249 ? pip3 c sh 3 22 p f r fb 3 249 ? r sh 3 49.9 ? r sh 4 49.9 ? c sh 4 22p f r fb 4 249 ? 120nh f b +5v voh3 voh4 r sh 1 49.9 ? c sh 1 22pf r fb 1 249 ? vgn2 1nf* sl12 120nh fb +5v 1nf* 1nf* sl34 vgn1 h +5v l pip4 +5v pip1 vpp vpp +5v voh1 vol1 vol2 voh2 vol3 vpv vpv vol4 vgn3 vgn4 vpp vpp 1nf* 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 0.1 f 50 49 56 55 51 54 53 52 58 57 59 62 61 60 vip1 pon 1 vc m 2 pip1 63 pop1 vpp1 vin 1 en 12 vc m 1 pm d 1 vgn 1 sl12 vgn 2 sp12 com1 64 hl1 2 gnd4 vpv2 vol2 voh1 vol1 voh2 vpv4 voh3 vol3 voh4 vpv3 vol4 vpv1 gnd1 35 36 37 38 42 39 40 41 34 33 48 47 43 46 45 44 gnd3 gnd2 h +5v l 28 25 26 27 17 18 19 21 22 23 24 29 30 31 32 pm d 4 pip4 pop4 vpp4 sp34 sl34 en 34 vc m 3 vip4 vc m 4 com4 vgn 4 vin 4 vgn 3 pon 4 hl3 4 20 pmd2 pon2 pip2 com2 vip2 vin2 pop2 com3 vip3 vin3 pip3 pon3 pmd3 pop3 vpp3 vpp2 15 16 8 7 6 5 1 4 3 2 14 13 9 12 11 10 ad8335 04976-056 vpp *see text r sh 2 49.9 ? f i gur e 58. basic c o nnec t ions for r in = 50 ? th e p r ea m p pmd p i n s m u s t be ca p a ci ti v e l y co u p led t o g r o u n d . al t h o u g h t h e p r e a m p lif i er is a dif f er en t i al desig n , t h e pmd p i n s are t h e i n te r n a l i n put b i a s no d e s and are m a d e a v ai l a bl e for b y p a s s in g o n l y . th es e p i n s ma y n o t be us ed as sig n al in p u ts. th e p i px in p u ts m u s t be ca p a ci ti v e l y co u p led f r o m th e sig n al s o ur ce beca us e th ey ha v e a n o minal dc lev e l o f m o r e tha n half th e s u p p l y v o l t a g e . a c co u p lin g ca p a ci t o rs thr o u g h o u t th e cir c ui t s h o u ld be as la rg e as p o s s i b le f o r th e a p p l ica t io n. al th o u g h 0.1 f ca p a ci t o rs a r e s h o w n in f i gur e 58 (a n d us ed in m o s t pos i ti o n s i n th e ev al ua ti o n boa r d ) , v a l u e s o f th e s e ca pa ci t o r s s h o u ld be det e r m in ed b y th e a p p l ica t io n. ca p a ci t o rs us ed f o r co u p lin g pmd x a n d p i px p i n s s h o u ld be th e s a m e val u e . w h en syn t h e sizin g lo w val u es o f r in , th e ba n d w i d t h o f th e p r e a m p lif i er p r o d uces s o m e p e akin g a t t h e hig h en d o f t h e f r e q u e nc y re sp ons e . t h e opt i on a l s e r i e s r sh x/c sh x n e tw o r k sho w n i n f i g u re 5 8 f l a t te ns t h e re sp ons e ( s e e f i g u re 5 5 ) . w i t h a 50 ? s o ur ce , th e r e sis t o r a n d ca p a ci t o r val u es s h o u ld be 49.9 ? a n d 22 pf . f o r r s val u es g r ea t e r tha n 100 ?, th e n e tw o r k is n o t n e e d e d . th e cir c ui t is s t a b le in ei t h er s c ena r io . th e s t a r r e d ca p a ci t o rs in f i gur e 58 (*) o n th e v g n x p i n s ma y be r e m o v e d wh en fas t er ga in co n t r o l sig n als a r e r e q u ir ed .
ad8335 rev. 0 | page 23 of 24 input overdrive e x ce l l en t o v erlo ad be ha vio r is o f p r ima r y im p o r t a n ce in u l tra- s o un d . b o t h t h e p r e a m p lif i er a n d v g a ha v e b u i l t-in o v er dr i v e prote c t i on and qu i c k l y re c o ve r af te r an o v e r l o a d e v e n t . input ov erload protection a s wi t h a n y a m plif ier , v o l t a g e cla m p i n g p r io r t o t h e in p u ts is hig h ly r e co mm en de d if t h e a p plica t io n is sub j e c t t o hig h t r ans i e n t volt age s . a b l o c k dia g ra m o f a sim p lif i e d u l t r as o u n d t r a n s d ucer in ter f ace is s h o w n in f i gur e 59. a co mm o n t r a n s d ucer e l em en t s e r v es t h e d u a l f u nc t i ons of t r ans m it and re c e ive of u l t r a s ou nd e n e r g y . d u r i n g t h e t r a n smi t phas e , hig h v o l t a g e p u ls es a r e a p plie d t o th e cera mic e l em en ts. a typ i cal t/r (tra n s mi t/r e cei v e) swi t c h ma y co n s ist o f fo ur hig h v o l t a g e dio d es in a b r idge co nf igura t io n. a l th o u gh th ey i d eall y b l oc k tra n s m i t p u lse s f r o m th e se n s i t i v e r e cei v er in p u t, dio d e cha r ac t e r i st ics a r e n o t ide a l, a n d r e su l t in g le aka g e t r a n sien ts im p i n g in g o n t h e p i px in p u ts ca n b e pro b l e m a t i c . sin c e u l t r as o u n d is a p u ls e sys t em, a n d t i m e -o f-f l ig h t is us e d t o det e r m in e dep t h, q u ick r e co v e r y f r o m in p u t o v erlo ads is ess e n t ia l. o v erlo ad ca n o c c u r in t h e p r e a m p a n d t h e v g a. i m m e dia t e l y f o l l o w in g a tra n smi t p u ls e , th e typ i cal v g a ga in s a r e lo w , a n d th e p r a is s u b j ec t t o o v erlo ad f r o m t/r swi t c h leaka g e . w i th in cr easin g ga in, th e v g a ca n beco m e o v erlo aded f r o m s t r o n g ec h o es tha t o c c u r wi th n e a r f i e l d ec h o es a n d aco u s t ical l y den s e ma t e r i als, s u c h as bo n e . f i g u re 5 9 i l lu st r a te s an e x te r n a l o v e r l o a d prote c t i on s c he me. a p a ir o f b a ck-t o-b a ck s c h o t t k y dio d es is in st a l le d p r io r t o in st a l lin g th e ac-co u p l in g ca p a ci t o rs. al th o u g h th e b a s40 is s h o w n, ma n y typ e s a r e a v a i la b l e a n d m e r i t in v e s t iga t io n b y t h e us er . w i t h s u ch dio d es, cla m p i n g le v e l s o f 0.5 v o r les s g r e a t l y enha n c e t h e sys t em o v erlo ad p e r f o r ma n c e . pra 18db rs t ransduce r ?hv bas40-04 pmdx pipx ponx pop x optional schottky overload clamp rfb 3 2 1 +h v 04976-057 f i g u r e 59. input o v erload p r otec t i on logic inputs th e ena b le p i n s en12 a n d en34, th e p r ea m p s h u t do wn p i n s s p 12 a n d s p 34, a n d th e hil o p i n s hl12 a n d hl34 a r e al l log i c in p u ts o f th e ad8335. th e ena b le in p u ts t u r n o n a n d o f f eac h o f th e c o r r e s p o nd i n g p a i r s of ch an nel s ; t h e pre a m p sh utd o w n pi ns d o t h e s a m e fo r t h e p r e a m p lif i ers o n ly ; in p u ts hl12 a n d hl34 s e t t h e h i lo g a i n for c h an nel s 1 and 2 , and c h an nel s 3 and 4 , re sp e c t i vely . sh u t t i n g do wn t h e p r e a m p lif i ers al lo ws us e o f t h e v g a s alo n e , while r e d u cin g p o w e r co n s um p t io n. th e v g a s ca nn o t be s h u t do wn in dep e n d en t l y . th e s p x x (sh u tdo w n p r e a m p ) p i n s a r e logi c h i gh ; th us th e p i n s a r e gr o u n d ed t o e n a b le th e p r ea m p li f i e r s . th e p i n s ca n be ena b led b y co nn ec tin g t o th e s u p p l y o r t o g rou nd f o r f i x e d e n abl e or d i s a bl e, or to t h e output of a l o g i c device . b e s u r e t o c h ec k th e da ta s h eet o f th e device f o r v o l t a g e a n d c u r r en t r e q u ir em en ts. common-mode pins th e co mm o n -m o d e p i n s v c mx a r e p r o v ide d fo r b y p a s s in g t h e i n te r n a l c o m m on - m o d e re f e re nc e f o r e a ch ch an nel to g rou nd. th ey r e q u ir e a ca p a ci t o r a t eac h o f th e f o ur p i n s a n d ca n n e i t h e r be co nn ec t e d t o g e th er n o r dr i v en b y a n ext e r n al s o ur ce . driving adcs th e ad8335 v g a is desig n ed t o dr i v e 10-b i t a n d 12-b i t ad cs wi th minimal extra co m p o n en ts. b e ca us e th e ad8335 is a sin g le s u p p ly 5 v p a r t a n d ma n y o f t h e n e w e s t ad cs o p era t e f r o m a 3 v s u p p ly , dis s imi l a r co mm o n -m o d e v o l t a g es exis t b e tw e e n t h e v g a o u t p u t a n d t h e ad c in p u t. this le v e l shif t is m o st e a si ly acco mm o d a t ed b y ac co u p lin g , es p e cial l y if th e sig n al is f i l t er ed , as is th e cas e in m o s t u l tras o u n d a n d co mm unica t io n s ap p l i c at i o n s . w h en a n a n ti-aliasin g f i l t er (aaf) is cal l ed f o r , i t is ad va n t a g eo us t o im plem en t a dif f er en t i al co nf igura t io n. a f u l l y dif f er en t i al aaf r e q u ir es a p p r o x ima t e l y 1.5 t i m e s t h e n u m b er o f co m p o n en ts t h a n a sin g le-en d e d f i l t er , b e ca us e t h e co m p o n en ts t h a t in t h e sin g le-en d ed cas e a r e tied t o g r o u n d , n o w co nn ec t acr o s s th e d i f f e r e n ti al s i gn al pa th . a l th o u gh th e se ri e s co m p o n e n t s d o u b le , t h e co m p o n en t co un t fo r t h e dif f er en t i al f i l t er is m o r e e c o n o m ical wh en co m p a r ed t o sim p l y b u ildin g a p a i r of s i ng l e - e nd e d f i lte r s r e q u ir in g twice as ma n y co m p o n en ts.
ad8335 rev. 0 | page 24 of 24 outline dimensions pin 1 indicator top view 8.75 bsc sq 9.00 bsc sq 1 64 16 17 49 48 32 33 0.45 0.40 0.35 0.50 bsc 0.20 ref 12 max 0.80 max 0.65 typ 1.00 0.85 0.80 7.50 ref 0.05 max 0.02 nom 0.60 max 0.60 max 4.85 4.70 sq * 4.55 seating plane pin 1 indicator exposed pad (b o t t o m view) 0.30 0.25 0.18 * compliant to jedec standards mo-220-vmmd except for exposed pad dimension f i g u r e 60. 64-l e ad l e ad f r ame chip s c ale p a ck ag e [lfcsp ] (cp - 64) d i mens ions s h o wn in millimeters ordering guide model temperature range package description package option ad8335acpz 1 ?40c to +85c lead frame ch ip scale package (lfcsp) cp-64 ad8335acpz-reel 1 ?40c to +85c lead frame ch ip scale package (lfcsp) cp-64 AD8335ACPZ-REEL7 1 ?40c to +85c lead frame ch ip scale package (lfcsp) cp-64 ad8335-eval evaluation board with ad8335acp 1 z = pb- f ree pa rt . ? 2004 analog devices, inc. all ri ghts reserved. trademarks and registered trademarks are the prop erty of their respective owners. d04976C0C9/04(0)

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