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120 db range (3 na to 3 ma) dual logarithmic converter adl5310 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. s p ecificatio n s subj ect to ch an 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 ? 2003 analog devices, i n c. all r i ghts r e ser v ed . features 2 ind e pend ent channels optimiz e d for photod iod e interfacing 6-decade input dynamic range law conformance 0.3 db from 3 na to 3 ma temperature-stable logarithmic outputs nominal slope 10 mv/db (200 mv/dec), externally scalable intercepts may be independently set by external resistors user-configurable output buffer amplifiers single- or dual-supply operation space-efficient 24-lead 4 mm 4 mm lfcsp low power: < 10 ma quiescent current applications gain and absorbance measurements multichannel power monitoring general-purpose baseband log compression product description th e ad l5310* lo w cos t , d u al loga r i thmic a m p l if ier co n v er ts in p u t c u r r en t o v er a wide d y na mic r a n g e to a lin e a r -in-db output vo lt age. i t i s opt i m i z e d to d e te r m i n e t h e opt i c a l p o we r i n wide-ra n g i n g o p t i ca l co mm unica t io n sy st em a p plica t io n s , in c l udin g co n t r o l cir c ui tr y f o r las e rs, o p tical swi t c h es, at t e nu at o r s , a n d a m p l i f i e r s , a s w e l l a s s y s t e m m o n i t o r i n g . t h e device is eq ui valen t t o a d u al ad8305 wi th enha n c ed d y na mic ra n g e (120 db). w h ile th e ad l5310 co n t a i n s tw o in dep e n d en t s i g n a l ch an nel s w i t h i n d i v i d u a l ly c o n f i g u r abl e t r ans f e r f u nc t i on co n s t a n t s (slo p e a n d in t e r c ep t), in t e r n a l b i as cir c ui t r y is sha r e d b e tw e e n cha n n e ls fo r im p r o v e d p o w e r co n s um p t io n a n d ch an nel m a tch i ng . d u a l c o n v e r te r s i n a s i ng l e c o m p a c t l f c s p p a cka g e yie l d s p ace-ef f i cien t s o l u t i o n s fo r m e as ur in g ga in o r a t te n u a t ion ac ro ss op t i c a l el e m e n ts . o n ly a s i ng l e su p p ly is re qu i r e d ; opt i on a l d u a l supply op e r a t i o n of f e r s a d d e d f l e x ibi l it y . th e ad l5310 em p l o y s a n o p timized tra n s l in ea r s t r u c t ur e tha t u t ili z e s th e a c cura t e loga ri th m i c r e la ti o n s h i p be t w ee n a b i po la r t r ans i stor s b a s e - e m i t t e r volt age and c o l l e c tor c u r r e n t , w i t h a p p r o p r i a t e s c alin g b y p r e c isio n c u r r en ts t o co m p en s a t e fo r t h e inh e r e n t t e m p era t ur e dep e n d en ce . i n p u t a n d r e fer e n c e c u r r en t p i n s sink c u r r en t ra n g in g f r o m 3 na t o 3 ma (limi t ed t o 60 db b e tw e e n in p u t a n d r e fer e n c e) in to a f i xe d vol t a g e def i n e d b y t h e v s u m p o t e n t ia l. th e v s u m p o t e n t ia l is in t e r n a l ly s e t t o 500 mv b u t ma y be ext e r n al l y g r o u n d ed f o r d u al-s u p p l y o p era- t i o n , a n d fo r addi t i o n a l a p plica t io n s r e q u ir in g v o l t a g e in p u ts. functional block diagram temperature compensation reference generator 451 ? 14.2k ? 80k ? 20k ? 6.69k ? 4. 99k ? comm comm vref vref vrdz vneg vsum inp2 irf2 2.5v 0.5v i log out2 scl2 bin2 log2 04415-0-001 v bias temperature compensation 451 ? 14.2k ? 6.69k ? 4. 99k ? comm vneg vsum inp1 irf1 i log out1 v out1 v out2 scl1 bin1 log1 v bias i pd1 i pd2 665k ? 665k ? fi g u r e 1 th e loga r i thmic s l o p e is s e t t o 10 mv/db (200 mv/decade) n o mina l a n d ca n b e m o dif i e d usin g ex ter n a l r e sisto r s a n d t h e in dep e n d en t b u f f er a m plif iers. th e loga r i t h mic in t e r c ep ts fo r e a ch cha n n e l a r e def i n e d b y t h e in di vid u al r e fer e n c e c u r r en ts, w h ich a r e s e t to 3 a n o mina l fo r max i m u m in p u t ra n g e b y co nn ec tin g 665 k r e sis t o r s betw een th e 2.5 v vref p i n s a n d th e irf1 a n d irf2 in p u ts. t y in g vrdz t o vref ef f e c t i v e l y s e ts t h e x-in t e r c ep t fo ur de cades b e lo w t h e r e fer e n c e c u r r en t: typ i cal l y 300 pa f o r a 3 a r e f e r e n c e . th e us e o f in di vid u al l y o p t i mize d r e fer e n c e c u r r en ts ma y b e val u a b le wh en usin g th e ad l5310 f o r ga in o r a b s o rba n ce m e as ur em en ts w h er e e a ch cha n n e l in p u t has a dif f er en t c u r r en t ra n g e r e q u ir em en t. th e r e fer e n c e c u r r en t in p u ts a r e als o f u l l y fun c ti o n al d y n a m i c i n p u t s , allo w i n g log- ra ti o o p e r a t i o n w i th th e r e f e r e n c e in p u t c u r r en t as th e den o mina t o r . th e ad l5310 is sp e c if ie d fo r o p era t io n f r o m C40c t o +85c. *us patents: 4,604,532, 5,519,308. other patents pending.
adl5310 rev. 0 | page 2 of 20 table of contents specifications..................................................................................... 3 absolute maximum ratings............................................................ 4 pin configuration and function descriptions............................. 5 typical performance characteristics ............................................. 6 general structure............................................................................ 11 theory.......................................................................................... 11 managing intercept and slope .................................................. 12 response time and noise considerations.............................. 12 applications..................................................................................... 13 calibration................................................................................... 14 minimizing crosstalk ................................................................ 15 relative and absolute power measurements .......................... 16 characterization methods......................................................... 17 evaluation board ............................................................................ 18 outline dimensions ....................................................................... 20 ordering guide........................................................................... 20 revision history revision 0: initial version
adl5310 rev. 0 | page 3 of 20 specifications table 1. v p = 5 v, v n = 0 v, t a = 25c, r ref = 665 k?, and vrdz connected to vref, unless otherwise noted parameter conditions min typ max unit input interface pins 1C6, inp1 and inp2, irf1 and irf2, vsum specified current range, i pd flows toward inp1 or inp2 pin 3n 3m a input current min/max limits flows toward inp1 or inp2 pin 10m a reference current, i ref , range flows toward irf1 or irf2 pin 3n 3m a summing node voltage internally pres et; user-alterable 0.46 0.5 0.54 v temperature drift C40c < t a < +85c 0.030 mv/c input offset voltage v in Cv sum , v iref Cv sum C20 +20 mv logarithmic outputs pins 15 and 16, log1 and log2 logarithmic slope 190 200 210 mv/dec C40c < t a < +85c 185 215 mv/dec logarithmic intercept 1 165 300 535 pa C40c < t a < +85c 40 1940 pa law conformance error 10 na < i pd < 1 ma 0.1 0.4 db 3 na < i pd < 3 ma 0.3 0.6 db wideband noise 2 i pd > 3 a; output referred 0.5 v/hz small-signal bandwidth 2 i pd = 3 a 1.5 mhz maximum output voltage 1.7 v minimum output voltage limited by v n = 0 v 0.10 v output resistance 4.375 5 5.625 k? reference output pin 7 and pin 24 (internally shorted), vref voltage wrt ground 2.45 2.5 2.55 v C40c < t a < +85c 2.42 2.58 v maximum output current sourcing (grounded load) 20 ma incremental output resistance load current < 10 ma 4 ? output buffers pins 12C14 and 17C19: out2, scl2, bin2, bin1, scl1, out1 input offset voltage C20 +20 mv input bias current flowing out of pins 13, 14, 17, and 18 0.4 a incremental input resistance 35 m? incremental output resistance load current < 10 ma; gain = 1 0.5 ? output high voltage r l = 1 k? to ground v p C 0.1 v output low voltage r l = 1 k? to ground 0.10 v peak source/sink current 30 ma small-signal bandwidth gain = 1 15 mhz slew rate 0.2 v to 4.8 v output swing 15 v/s power supply pins 8 and 9: vpos; pins 10,11, and 20: vneg positive supply voltage (v p C v n ) 12 v 3 5 12 v quiescent current input currents < 10 a 9.5 11.5 ma negative supply voltage (optional) (v p C v n ) 12 v C5.5 0 v 1 other values of logarithmic intercept can be achieved by adjustment of r ref . 2 output noise and incremental bandwidth ar e functions of input current; measured usin g output buffer connected for gain = 1.
adl5310 rev. 0 | page 4 of 20 absolute maximum ratings table 2. adl5310 stress ratings p a r a m e t e r r a t i n g supply voltage v p C v n 1 2 v input current 20 ma internal power dissipation 500 mw ja 3 5 c / w 1 maximum junction temperature 125c operating temperature range C40c to +85c storage temperature range C65c to +150c lead temperature range (soldering 60 sec) 300c 1 wi t h pa ddle soldered down . 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 lis t e d in t h e o p era t io nal s e c t io n s 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. electrostatic charges as high as 4000 v readily accumulate on the human body and test eq uipment and can discharge without detection. although this product features proprietary esd protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic disc harges. therefore, proper esd precautions are recommended to avoid performance degradation or loss of functionality.
adl5310 rev. 0 | page 5 of 20 pin configuration and f unction descriptions 24 1 2 3 4 5 6 18 17 16 15 14 13 23 22 21 20 19 7 8 9 10 11 12 pin 1 indicator top view (not to scale) adl5310 dual log amp vsum inp1 irf1 irf2 inp2 vsum scl1 bin1 log1 log2 bin2 scl2 04415-0-002 vref vrdz com m com m vneg out1 vref vpos vpos vneg vneg out2 f i g u r e 2. 24-l e ad lfcsp p i n conf ig ur at ion ta ble 3. pi n f u nct i on des c ri pt i o ns pin no. mnemonic function 1, 6 vsum guard pin. used to shield the inp1 and inp2 in put current lines, and for optional ad justment of the input summing node potentials. pin 1 and pin 6 are internally shorted. 2 inp1 channel 1 numerator input. a ccepts (sinks) photodiode current i pd1 . usually connected to photodiode anode such that photo-current flows into inp1. 3 irf1 channel 1 denominator input. accepts (sinks) reference current, i rf 1 . 4 irf2 channel 2 denominator input. accepts (sinks) reference current, i rf 2 . 5 inp2 channel 2 numerator input. a ccepts (sinks) photodiode current i pd2 . usually connected to photodiode anode such that photocurrent flows into inp2. 7, 24 vref reference output voltage of 2.5 v. pin 7 and pin 24 are internally shorted. 8, 9 vpos positive supply, (v p C v n ) 12 v. both pins must be connected externally. 10, 11, 20 vneg optional negative supply, v n . this pin is usually grounded. for detai ls of usage, see the general structure and applications sections. all vneg pins must be connected externally. 12 out2 buffer output for channel 2. 13 scl2 buffer amplifier inverting input for channel 2. 14 bin2 buffer amplifier noninverting input for channel 2. 15 log2 output of the logarith mic front-end for channel 2. 16 log1 output of the logarith mic front-end for channel 1. 17 bin1 buffer amplifier noninverting input for channel 1. 18 scl1 buffer amplifier inverting input for channel 1. 19 out1 buffer output for channel 1. 21, 22 comm analog ground. pin 21 and pin 22 are internally shorted. 23 vrdz intercept shift reference input. the top of a resi stive divider network that offsets vlog to position the intercept. normally connected to vref; may also be co nnected to ground when bipolar outputs are to be provided.
adl5310 rev. 0 | page 6 of 20 typical performance characteristics v p = 5 v, v n = 0 v, r re f = 665 k?, t a = 25c, unles s ot herwi s e not e d 0 0.2 0.4 0.6 0.8 1.0 v log (v ) 1.2 1.4 1.6 1n 10n 100n 1 10 100 1m 10m i inp (a) 04415-0-003 t a = ? 40 c, 0c, +25 c, +70 c , +85 c v in = 0v fi g u r e 3 . v lo g vs . i inp f o r m u lt iple t e mper at ur es 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 v log (v ) 1n 10n 100n 1 10 100 1m 10m i ref (a) 04415-0-004 t a = ? 40 c, 0c, +25 c, +70 c, +85 c v in = 0v fi g u r e 4 . v lo g vs . i ref f o r m u lt iple t e mper at ur es ( i inp = 3 a ) 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 v log (v ) 1n 10n 100n 1 10 100 1m 10m i inp (a) 04415-0-005 3na 30na 300na 3 a 30 a 300 a 3ma fi g u r e 5 . v lo g vs . i inp f o r m u lt iple v a lues of i ref , d e c a de steps fr om 3 na to 3 ma ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 e rror (db (1 0 m v / db)) 1.0 1.5 2.0 1n 10n 100n 1 10 100 1m 10m i inp (a) 04415-0-006 +85c +70c +25 c 0c ?4 0 c f i gur e 6. law c o nformanc e err o r vs. i inp f o r m u lt iple t e mper at ur es, normaliz ed to 25c ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 e rror (db (1 0 m v / db)) 1.0 1.5 2.0 1n 10n 100n 1 10 100 1m 10m i ref (a) 04415-0-007 +70c +85c +25 c 0c ?40 c f i gur e 7. law c o nformanc e err o r vs. i ref f o r m u lt iple t e mper at ur es, normaliz ed to 25c ( i inp = 3 a ) ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 0.8 1.0 e rror (db (1 0 m v / db)) 1n 10n 100n 1 10 100 1m 10m i pd (a) 04415-0-008 300na 30na 3na 3ma 3 a 30 a 300 a f i gur e 8. law c o nformanc e err o r vs. i inp f o r m u lt iple v a lues of i ref , d e c a de steps fr om 3 na to 3 ma
adl5310 rev. 0 | page 7 of 20 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 v log (v ) 1n 10n 100n 1 10 100 1m 10m i ref (a) 04415-0-009 3na 30na 300na 3 a 30 a 300 a 3ma fi g u r e 9 . v lo g vs . i ref f o r m u lt iple v a lues of i inp , d e c a de steps f r om 3 na to 3 ma ? 1.0 ? 0.8 ? 0.6 ? 0.4 ? 0.2 0 0.2 0.4 0.6 0.8 1.0 e rror (db (1 0 m v / db)) 1n 10n 100n 1 10 100 1m 10m i inp (a) 04415-0-010 +3v, 0v +5v, ? 5 v +5v, ?5v +12v, 0v +12v, 0v +5v, 0v +9v, 0v f i gur e 10. law c o nformanc e err o r vs. i inp f o r v a rious sup p ly condit ions ? 2.0 ? 1.5 ? 1.0 ? 0.5 0 0.5 e rror (db (1 0 m v / db)) 1.0 1.5 2.0 1n 10n 100n 1 10 100 1m 10m i pd (a) 04415-0-011 t a = 0 c, 70c mean + 3 at 70 c mean ? 3 at 70c mean 3 at 0c f i g u r e 11. law conf ormanc e e r r o r d i s t ribut i on (3 to e i t h er side of m e an) ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 0.6 0.8 1.0 e rror (db (1 0 m v / db)) 1n 10n 100n 1 10 100 1m 10m i ref (a) 04415-0-012 3 a 300 a 30 a 3ma 3 a 3ma 300na 30na 3na f i gur e 12. law c o nformanc e err o r vs. i ref f o r m u lt iple v a lues of i inp , d e c a de steps fr om 3 na to 3 ma ? 2.0 ? 1.5 ? 1.0 ? 0.5 0 0.5 e rror (db (1 0 m v / db)) 1.0 1.5 2.0 1n 10n 100n 1 10 100 1m 10m i pd (a) 04415-0-013 t a = 25c mean + 3 mean ? 3 f i g u r e 13. law conf ormanc e e r r o r d i s t ribut i on (3 to e i t h er side of m e an) ?4 ?3 ?2 ?1 0 1 e rror (db (1 0 m v / db)) 2 3 4 1n 10n 100n 1 10 100 1m 10m i pd (a) 04415-0-014 t a = ? 40c, 85c mean + 3 at ?40c mean ? 3 at ?40c mean + 3 at +85c f i g u r e 14. law conf ormanc e e r r o r d i s t ribut i on (3 to e i t h er side of m e an)
adl5310 rev. 0 | page 8 of 20 ?50 ?45 ?35 ?15 ?5 5 10 15 ?25 ?40 ?20 ?10 0 ?30 normalize d re s p ons e (db) 10k 100k 100 1k 1m 10m 100m frequency (hz) 04415-0-015 3na 30na 300na 3 a 30 a 300 a 3ma f i g u r e 15. small sig n al a c r e s p ons e , i inp to v ou t (a v = 1) (5% sine modulation, d e c a de steps f r om 3 na to 3 ma ) ?50 ?45 ?35 ?15 ?5 5 10 15 ?25 ?40 ?20 ?10 0 ?30 n o r m a l ized r espon se ( d b ) 10k 100k 100 1k 1m 10m 100m frequency (hz) 04415-0-016 3na 30na 300na 3 a 30 a 300 a 3ma f i g u r e 16. small sig n al a c r e s p ons e , i ref to v ou t (a v = 1) (5% sine modulation, d e c a de steps f r om 3 na to 3 ma ) v rms/ h z 0.01 0.1 1 10 100 100 1k 10k 100k 1m 10m frequency (hz) 04415-0-017 3na 30na 300na 3 a 30 a 300 a 3ma f i g u r e 17. spot nois e spec t r al d e ns it y at v ou t vs . f r e q ue nc y ( a v = 1) fo r i inp in d e c a de steps fr om 3 na to 3 ma 0 0.2 0.4 0.6 0.8 1.0 v out (v ) 1.2 1.4 1.6 0 2 0 4 0 6 0 8 0 100 120 140 160 180 200 time ( s) 04415-0-018 t-rise < 1 s t-fall < 1 s 300 a to 3ma t-rise < 1 s t-fall < 1 s3 0 a to 300 a t-rise < 1 s t-fall < 5 s3 a to 30 a t-rise < 5 s t-fall < 10 s 300na to 3 a t-rise < 10 s t-fall < 40 s 30na to 300na t-rise < 30 s t-fall < 80 s 3na to 30na f i gur e 1 8 . p u l s e resp o n sei inp to v ou t (a v = 1) in consecutive 1-d e c a de steps 0 0.2 0.4 0.6 0.8 1.0 v out (v ) 1.2 1.4 1.6 0 2 0 4 0 6 0 8 0 100 120 140 160 180 200 time ( s) 04415-0-019 t-rise < 80 s t-fall < 30 s 3na to 30na t-rise < 40 s t-fall < 10 s 30na to 300na t-rise < 10 s t-fall < 5 s 300na to 3 a t-rise < 1 s t-fall < 1 s3 a to 30 a t-rise < 1 s t-fall < 1 s3 0 a to 300 a t-rise < 1 s t-fall < 1 s 300 a to 3ma f i gur e 1 9 . p u l s e resp o n sei ref to v ou t (a v = 1) in consecutive 1-d e c a de steps 5.0 4.0 3.0 2.0 1.0 0 10n 100n 1 10 100 1m 10m 1n i pd (a) mv rms 04415-0-020 f i g u r e 20. t o t a l w i deband nois e v o lt ag e at v ou t vs . i inp (a v = 1)
adl5310 rev. 0 | page 9 of 20 ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 v re f drift (mv ) ?40 ? 30 ? 2 0 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-021 mean + 3 mean ? 3 f i g u r e 21. v ref d r if t v s . t e mper atur e (3 to e i ther side of mean) normaliz ed to 25c ?6 ?4 ?2 ?3 ?5 0 ?1 v y drift (mv/dec) 2 1 4 3 6 5 ?40 ? 30 ? 2 0 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-022 mean + 3 mean ? 3 f i gur e 22. slope d r if t v s . t e mper atur e (3 to e i ther side of mean) normaliz ed to 25c ?150 ?100 ?50 0 50 100 150 200 i z drift (pa) ?40 ? 30 ? 2 0 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-023 mean + 3 mean ? 3 f i gur e 23. inter c ept d r if t v s . t e mper atur e (3 to e i ther side of mean) normaliz ed to 25c ?5 ?6 ?3 1 3 5 ?1 ?4 0 2 4 ?2 v inp t drift (mv ) ?40 ? 30 ? 2 0 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-024 mean + 3 mean ? 3 f i g u r e 24. v inp t d r if t v s . t e mper atur e (3 to e i ther side of mean) normaliz ed to 25c ?6 ?5 ?3 1 3 5 6 7 ?1 ?4 0 2 4 ?2 ? v y drift (mv/dec) ?40 ? 30 ? 2 0 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-025 mean + 3 mean ? 3 f i gur e 25. slope m i smatch d r if t v s . t e mper atur e (v y1 C v y2 , 3 to e i ther side of mean) normaliz ed to 25c ? 200 ? 150 ? 100 ?50 0 50 ? i z drift (pa) 100 150 200 ?40 ? 30 ?20 ? 10 0 2 0 6 0 10 30 40 50 70 80 90 temperature ( c) 04415-0-026 mean + 3 mean ? 3 f i gur e 26. inter c ept m i smatch d r if t v s . t e mper atur e (i z1 C i z2 , 3 to e i ther side of mean) normaliz ed to 25c
adl5310 rev. 0 | page 10 of 20 0 100 200 300 400 500 600 700 count slope (mv/dec) 195 190 200 205 210 04415-0-027 f i g u r e 27. d i s t ribut i on of l o g a rit h mic slope 0 100 200 300 400 500 600 count intercept (pa) 200 100 300 400 500 04415-0-028 f i gur e 2 8 . di stri buti o n o f l o ga ri thm i c int e r c ept 0 100 200 300 400 500 600 700 count vref voltage (v) 2.48 2.46 2.50 2.52 2.54 04415-0-029 f i g u r e 29. d i s t ribut i on of v ref (r l = 100 k ? ) 0 50 100 150 200 250 300 350 400 450 count ?3 0 ?9 ? 6 3 6 9 slope mismatch (mv/dec) 04415-0-030 f i g u r e 30. d i s t ribut i on of channel-to - c hannel slope m i s m atch ( v y1 C v y2 ) 0 100 200 300 400 500 count ? 100 0 ?300 ? 200 100 200 300 intercept mismatch (pa) 04415-0-031 f i gur e 31. d i stribution of channel-to - c hannel inter c ept m i smatch (i z1 C i z2 ) 0 100 200 300 400 500 count ?3 0 ?9 ? 6 3 6 9 v inpt ? v sum voltage (mv) 04415-0-032 f i g u r e 32. d i s t ribut i on of o f f s et v o lt ag e ( v inp t C v sum )
adl5310 rev. 0 | page 11 of 20 general structure th e ad l5310 addr es s e s a wide va r i ety o f in t e r f acin g co n d i t io n s to me e t t h e ne e d s of f i b e r opt i c sup e r v i s or y s y ste m s , and i s us ef u l in ma n y n o n o p t ical a p plica t io n s . th es e n o t e s expla i n t h e s t r u c t ur e o f this uniq ue s t y l e o f tra n s l in ea r log a m p . f i gur e 33 s h o w s t h e k e y e l em en ts o f o n e o f t h e tw o iden t i cal o n -b o a r d log a m ps. q2 q1 451 ? 14.2k ? 80k ? 20k ? 6.69k ? photodiode input current bias generator temperature compensation (subtract and divide by tk) vrdz comm comm vlog vneg (normally grounded) vsum inp1 (inp2) vref iref i ref v be1 v be2 i pd v be1 v be2 44 a/dec 2.5v 0.5v 0.5v 0.5v 04415-0-033 f i g u r e 33. simplif ied s c hemat i c of sing le l o g a m p th e ph o t o d io de c u r r en t i pd is r e cei v ed a t ei th er p i n inp1 o r inp2. th e v o l t a g es a t t h es e n o des a r e a p p r o x ima t e l y e q ual t o t h e vol t a g e o n t h e ad jacen t gua r d p i n s , v s u m , as w e l l as r e fer e n c e in p u ts irf1 a n d irf2, d u e t o t h e lo w o f fs et v o l t a g e o f t h e jfet op am p s . t r ans i stor q 1 c o n v e r t s i pd to a c o r r e s p o nd- d i n g loga ri th m i c v o l t a g e , a s s h o w n i n eq ua ti o n 1. a f i n i t e posi ti v e val u e o f v su m i s n eed ed t o b i a s th e co ll ect o r o f q1 f o r th e us ual cas e o f a sin g le-su p ply v o l t a g e . this is in t e r n a l ly s e t t o 0.5 v , one - f i f t h of t h e 2 . 5 v re f e re nc e vo lt age t h a t a p p e ar s on pi n vref . b o th vref p i n s a r e in t e r n al l y s h o r t e d , as a r e bo th v s u m p i n s . th e r e sis t a n ce a t t h e v s u m p i n is n o minal l y 16 k; t h is vo lt age i s not i n te nd e d a s a ge ne r a l b i a s s o u r c e . th e ad l5310 als o s u p p o r ts th e us e o f a n o p tio n al n e ga ti v e su p p ly vol t age, v n , a t p i n v n e g . w h e n v n is 0.5 v o r m o r e n e ga ti v e , v s u m ma y be co nn ec t e d t o g r o u n d ; th us, inp1, inp2, irf1, a n d irf2 as s u m e this p o t e n t ial . this al lo ws o p era t io n as a v o l t a g e-in p u t loga r i t h mic co n v er t e r b y t h e in cl usio n o f a s e r i es r e si s t o r a t e i th e r o r bo th i n p u t s . n o t e th a t th e r e si s t o r se t t i n g i ref f o r eac h c h a n n e l wil l n eed t o be ad j u s t ed t o ma in ta in th e in t e r - cep t val u e . i t s h o u ld als o be n o t e d tha t th e col l ec t o r - emi t t e r volt age s of q 1 and q 2 are now t h e f u l l v n , a n d ef fe c t s d u e t o s e lf-h e a t i n g wi l l ca us e er r o rs a t la rg e in p u t c u r r en ts. th e in p u t-dep e n d en t v be1 o f q1 is co m p a r ed wi th th e r e f e r e n c e v be2 of a s e c o nd t r ans i stor , q 2 , op e r a t i n g a t i ref . i ref is g e n e r - a t e d ext e r n al l y t o a r e co mm en de d val u e o f 3 a. h o w e v e r , o t h e r val u es o v er a s e v e ral-de cade ra n g e ca n b e us e d wi t h a s l ig h t deg r ada t io n in la w co nfo r ma n c e. theory th e b a s e -emi t t er v o l t a g e o f a bjt (b i p ola r j u n c t i o n t r a n sis t o r ) ca n b e ex p r ess e d b y e q ua t i o n 1, w h ich imm e dia t ely sh o w s i t s basic loga r i thmic na t u r e : v be = kt / q ln( i c / i s ) ( 1 ) w h er e: i c is t h e col l e c t o r c u r r en t i s is a s c a l in g c u r r en t, ty p i ca l l y o n ly 10 C17 a kt / q i s th e th e r m a l v o l t a g e , p r o p o r ti o n al t o a b so l u t e t e m p era t ur e (pt a t), a n d is 25.85 mv a t 300 k. i s is n e ver p r e c is ely def i n e d a n d ex hi b i ts a n e v en st r o n g er tem- pe r a t u r e d e pe n d e n c e , v a r y i n g b y a f a ct o r o f r o u g hl y a b i ll i o n betw een C35c a n d +85c. th us, t o mak e us e o f th e bjt as a n acc u ra t e loga r i t h mic e l em en t, b o t h o f t h es e t e m p era t ur e dep e n d en cies m u s t b e e l imina t e d . th e dif f er en ce b e tw e e n t h e b a s e -emi t t er v o l t a g es o f a ma t c h e d p a i r of b j t s , one op e r a t i n g a t t h e photo d i o d e c u r r e n t i pd and t h e o t h e r o p era t in g a t a r e fer e n c e c u r r en t i ref , ca n b e wr i t ten as v be1 C v be2 = kt / q ln( i pd / i s ) C kt / q ln( i ref / i s ) = ln(10) kt / q log 10 ( i pd / i ref ) ( 2 ) = 59.5 mv log 10 ( i pd / i ref ) ( t = 300 k ) th e un cer t a i n, t e m p era t ur e-dep e n d en t s a t u ra t i o n c u r r en t, i s , t h a t a p p e a r s in e q ua t i o n 1 has t h er efo r e b e en e l imina t e d . t o e l imina t e t h e t e m p era t ur e va r i a t io n o f kt / q , t h is dif f er en ce v o l t a g e is p r o c es s e d b y w h a t is es s e n t ial l y a n a n alog di vider . e f f e c t ively , it put s a v a r i abl e u n d e r e q u a t i on 2 . t h e output of t h is p r o c es s, w h ich als o in v o l v es a co n v ersio n f r o m v o l t a g e mo de to c u r r e n t mo de, i s an i n te r m e d i a te, te m p e r a t u r e c o rr ect e d cu rr e n t : i lo g = i y log 10 ( i pd / i ref ) ( 3 ) w h er e i y i s an a c c u r a te, te m p e r a t u r e - st abl e s c a l i n g c u r r e n t t h a t det e r m in es t h e s l o p e o f t h e f u n c t i o n (cha n g e in c u r r en t p e r decade). f o r th e ad l5310, i y is 44 a, r e su l t in g in a t e m p era t ur e-in dep e n d en t s l o p e o f 44 a/de c ade fo r al l val u es of i pd and i ref . this c u r r en t is subs e q uen t ly co n v er t e d b a ck t o a vol t age - mo de out p ut , v lo g , s c aled 200 mv/decade .
adl5310 rev. 0 | page 12 of 20 it is apparent that this output should be zero for i pd = i ref , and would need to swing negative for smaller values of input current. to avoid this, i ref would need to be as small as the smallest value of i pd . accordingly, an offset voltage is added to v log to shift it upward by 0.8 v when vrdz is directly connected to vref. this moves the intercept to the left by four decades (at 200 mv/decade), from 3 a to 300 pa: i log = i y log 10 ( i pd / i intc ) (4) where i intc is the operational value of the intercept current. since values of i pd < i intc result in a negative v log , a negative supply of sufficient value is required to accommodate this situation. the voltage v log is generated by applying i log to an internal resistance of 4.55 k?, formed by the parallel combination of a 6.69 k? resistor to ground and a 14.2 k? resistor to pin vrdz (typically tied to the 2.5 v reference, vref). at the log1 (log2) pin, the output current i log generates a voltage of v log = i log 4.55 k? = 44 a 4.55 k? log 10 ( i pd / i intc ) (5) = v y log 10 ( i pd / i intc ) where v y = 200 mv/decade or 10 mv/db. note that any resis- tive loading on log1 (log2) will lower this slope and will result in an overall scaling uncertainty. this is due to the variability of the on-chip resistors compared to the off-chip load. consequently, this practice is not recommended. v log may also swing below ground when dual supplies ( v p and v n ) are used. when v n = C0.5 v or larger, the input pins inp1 (inp2) and irf1 (inp2) may be positioned at ground level simply by grounding vsum. care must be taken to limit the power consumed by the input bjt devices when using a larger negative supply, because self-heating will degrade the accuracy at higher currents. managing intercept and slope when using a single supply, vrdz should be directly connected to vref to allow operation over the entire 6-decade input current range. as noted in the theory section, this introduces an accurate offset voltage of 0.8 v at the log1 and log2 pins, equivalent to four decades, resulting in a logarithmic transfer function that can be written as v log = v y log 10 (10 4 i pd / i ref ) = v y log 10 ( i pd / i intc ) (6) where i intc = i ref /10 4 . thus, the effective intercept current i intc is only one ten- thousandth of i ref , corresponding to 300 pa when using the recommended value of i ref = 3 a. the slope can be reduced by attaching a resistor between the log amp output pin, log1 or log2, and ground. this is strongly discouraged given that the on-chip resistors will not ratio correctly to the added resistance. also, it is rare that one would wish to lower the basic slope of 10 mv/db; if this is needed, it should be effected at the low impedance output of the buffer amps, which are provided to avoid such miscalibration and to allow higher slopes to be used. each of the adl5310s buffers is essentially an uncommitted op amp with rail-to-rail output swing, good load-driving capabilities, and a typical unity-gain bandwidth of 15 mhz. in addition to allowing the introduction of gain, using standard feedback networks and thereby increase the slope voltage v y , the buffer can be used to implement multi-pole low-pass filters, threshold detectors, and a variety of other functions. further details on these applications can be found in the ad8304 data sheet. response time and noise considerations the response time and output noise of the adl5310 are funda- mentally a function of the signal current, i pd . for small currents, the bandwidth is proportional to i pd , as shown in figure 15. the output low frequency voltage-noise spectral-density is a function of i pd (see figure 17) and also increases for small values of i ref . details of the noise and bandwidth performance of translinear log amps can be found in the ad8304 data sheet.
adl5310 rev. 0 | page 13 of 20 applications temperature compensation reference generator 451 ? 14.2k ? 80k ? 665k ? 665k ? 20k ? 1k ? 1nf 1k ? 1nf 2k ? 4.7nf 2k ? 4.7nf 1nf 6.69k ? 12k ? 8k ? 8k ? c flt2 10 nf c flt1 10 nf comm comm vref vneg comm vref vrdz vpos vneg vsum inp2 irf2 2.5v 0.5v i log i rf2 i rf1 out2 scl2 bin2 log2 04415-0-034 v bias temperature compensation 451 ? 14.2k ? 6.69k ? 12k ? comm 5v vneg vsum inp1 irf1 i log out1 v out1 v out2 scl1 bin1 log1 v bias i pd1 i pd2 0.5log 10 ( ) i pd2 1na 0.5log 10 ( ) i pd1 1na f i gur e 34. basic c o nnec t ions for f i x e d inter c ept use th e ad l5310 is easy t o us e in o p tical s u p e r v is o r y sys t em s a n d in simi la r si t u a t io n s w h er e a wide-ra n g i n g c u r r en t is t o b e co n v er t e d t o i t s loga r i t h mic e q ui valen t , i . e . , r e p r es en t e d in de ci be l t e r m s. b a sic co nn e c tio n s fo r m e as ur in g a sin g le c u r r en t a t e a ch in p u t a r e sh o w n in f i gur e 34, w h ich a l s o in cl udes v a r i ou s none ss e n t i a l c o m p one n t s , a s w i l l b e e x pl ai ne d. th e 2 v dif f er en ce in v o l t a g e b e tw e e n t h e vref a n d in p u t p i n s inp1 a n d inp2, in co n j un c t io n wi th th e ext e r n al 665 k r e sis- tors r rf1 and r rf2 , p r o v ides 3 a r e fer e n c e c u r r en ts i rf1 and i rf2 in t o p i n s irf1 a n d irf2. c o nn ec tin g vrdz t o vref ra is es th e v o l t a g e a t l o g1 a n d l o g2 b y 0.8 v , ef f e c t i v e l y lo w e r i n g e a c h in t e r c ep t c u r r en t i intc by a f a c t or of 1 0 4 t o p o si tio n i t a t 300 pa. a wid e ra n g e o f o t h e r val u es f o r i ref , f r o m 3 na t o 3 ma, ma y be us ed . th e ef f e c t o f s u c h c h a n g e s is s h o w n in f i gur e 5 a n d fi g u r e 8 . an y t e m p era t ur e va r i a t io n in r rf1 (r rf2 ) m u s t be tak e n in t o a c co un t wh e n e s ti m a ti n g th e s t a b ili t y o f th e i n t e r c e p t . also , th e o v eral l n o is e wi l l in cr e a s e w h en usin g v e r y lo w val u es o f i rf1 ( i rf2 ). i n f i xe d-in t e r c ep t a p plica t io n s t h er e is li t t le b e n e f i t in usin g a la rg e r e fer e n c e c u r r en t, sin c e do in g s o o n l y co m p r e s s es t h e lo w c u r r en t en d o f t h e d y na mic ra n g e w h en o p era t e d f r o m a s i ng l e su p p ly . the c a p a c i tor b e twe e n v s u m and g r ou nd is st r o n g ly r e co mm en de d to minimize t h e n o is e o n t h is n o de, to r e d u ce cha n n e l-to -cha nn el cr o sst a l k, a n d to h e l p p r o v ide cle a n re f e re nc e c u r r e n t s .
adl5310 rev. 0 | page 14 of 20 in addition, each input and reference pin (inp1, inp2, irf1, irf2) has a compensation network made up of a series resistor and capacitor. the junction capacitance of the photodiode along with the network capacitance of the board artwork around the input system creates a pole that varies widely with input current. the rc network stabilizes the system by simultaneously reducing this pole frequency and inserting a zero to compensate an additional pole inherent in the input system. in general, the 1 nf, 1 k network will handle almost any photodiode interface. in situations where larger active area photodiodes are used, or when long input traces are used, the capacitor value may need to be increased to ensure stability. although the signal and reference input systems are similar, additional care is required to ensure stable operation of the reference inputs at temperature extremes across the full current range of i rf1 ( i rf2 ). it is recom- mended that filter components of 4.7 nf and 2 k? should be used from pin irf1 (irf2) to ground. temperature-stable components should always be used in critical locations such as the compensation networks; y5v-type chip capacitors are to be avoided due to their poor temperature stability. the optional capacitor from log1 (log2) to ground forms a single-pole low-pass filter in combination with the 5 k resis- tance at this pin. for example, when using a c flt of 10 nf, the 3 db corner frequency is 3.2 khz. such filtering is useful in minimizing the output noise, particularly when i pd is small. multi-pole filters are more effective in reducing the total noise; examples are provided in the ad8304 data sheet. since the basic scaling at log1 (log2) is 0.2 v/decade, and thus a 4 v swing at the buffer output would correspond to 20 decades, it is often useful to raise the slope to make better use of the rail-to-rail voltage range. for illustrative purposes, both channels in figure 34 provide a 0.5 v/decade overall slope (25 mv/db). thus, using i ref = 3 a, v log runs from 0.2 v at i pd = 3 na to 1.4 v at i pd = 3 ma; the buffer output runs from 0.5 v to 3.5 v, corresponding to a dynamic range of 120 db (electrical, that is, 60 db optical power). further information on adjusting slope and intercept, using a negative supply, and additional applications can be found in ad8305 data sheet. calibration each channel of the adl5310 has a nominal slope and intercept at log1 (log2) of 200 mv/decade and 300 pa, respectively, when configured as shown in figure 34. these values are untrimmed and the slope alone may vary by as much as 7.5% over temperature. for this reason, it is recommended that a simple calibration be done to achieve increased accuracy. while the adl5310 offers improved slope and intercept matching compared to a randomly selected pair of ad8305 log amps, the specified accuracy can only be achieved by calibrating each channel individually. 1.0 1.2 1.4 0.8 0.6 0.4 0.2 0 2 3 4 1 0 ?1 ?2 ?3 10n 100n 1 10 100 1m 10m 1n i pd (a) v log (v) error (db (10mv/db)) 04415-0-035 calibrated error measured output ideal output uncalibrated error figure 35. using 2-point calibration to increase measurement accuracy figure 35 shows the improvement in accuracy when using a two point calibration method. to perform this calibration, apply two known currents i 1 and i 2 , in the linear operating range between 10 na and 1ma. measure the resulting output v 1 and v 2 , respectively, and calculate the slope m and intercept b . m = ( v 1 C v 2 )/[log 10 ( i 1 ) C log 10 ( i 2 )] (7) b = v 1 C m log 10 ( i 1 ) (8) the same calibration could be performed with two known optical powers, p 1 and p 2 . this allows for calibration of the entire measurement system while providing a simplified relationship between the incident optical power and v log voltage. m = ( v 1 C v 2 )/( p 1 C p 2 ) (9) b = v 1 C m p1 (10) the uncalibrated error line in figure 35 was generated assum- ing that the slope of the measured output was 200 mv/decade when in fact it was actually 194 mv/decade. correcting for this discrepancy decreased measurement error up to 3 db.
adl5310 rev. 0 | page 15 of 20 minimizing crosstalk c o m b inin g tw o hig h d y na mic ra n g e loga r i t h mic co n v er t e rs in one ic c a r r i e s p o te n t i a l pi t f a l l s c o nc e r n i ng ch an nel - to - c h a n n el is ola t io n. s p e c ia l ca r e m u st b e t a k e n in s e v e ra l a r e a s t o en sur e a c c e pt abl e c r o sst a l k p e r f or m a nc e, p a r t i c u l ar ly w h e n one or b o t h cha n n e ls ma y o p era t e a t v e r y lo w in p u t c u r r en ts. f a st idio us su p- ply b y p a ss ing a l s o ne c e ss ar y for ove r a l l st ab i l i t y and c a re f u l b o ard l a y o ut are i m p o r t an t f i rst ste p s for m i n i m i z i ng c r o sst a l k . w h i l e t h e s h a r e d b i as cir c ui t r y im p r o v es cha n n e l-t o -cha nn e l ma t c hin g a n d r e d u ces p o w e r co n s um p t io n, i t is als o a s o ur ce o f c r o sst a l k t h a t m u st b e mi t i g a te d. the v s u m p i ns , w h ich are in te r n a l ly shor te d, shou l d b e b y p a ss e d wi t h a t l e ast 1 nf to g r o u n d , a n d 20 nf is r e co mm en de d fo r o p er a t io n a t t h e lo w e st c u r r en ts (<30 na). v s u m is o f p a r t ic u l a r im p o r t a n ce sin c e i t ac ts as a r e fer e n c e v o l t a g e in p u t fo r e a ch in p u t syst em, b u t w i th o u t th e ba n d w i d th li m i ta ti o n a t lo w curr e n t s th a t th e p r ima r y in p u ts in c u r . dist urb a n c es a t t h e v s u m p i n t h a t a r e w e ll w i th i n th e ba n d w i d th o f th e i n p u t a r e tra c k e d b y th e loo p a n d do n o t gen e r a te dist ur b a n c es a t t h e o u t p u t (aside f r o m t h e ge ne r a l l y m i nor p e r t u r b a t i on i n re fe re nc e c u r r e n t s c a u s e d b y v o l t a g e va r i a t io n s a t irf1 a n d irf2). f o r t h is r e as o n , t h e p o le f r e q uen c y a t v s u m , w h ich has a 16 k typ i cal s o ur ce r e sis t a n ce , s h o u ld be s e t be lo w th e minim u m in p u t sy st em b a n d w id t h fo r t h e lo w e st in p u t c u r r en t t o b e e n c o u n te re d. si nc e t h e l o w f r e q u e nc y noi s e a t v s u m i s a l s o tra c k e d b y th e loo p w i th i n i t s a v a i la b l e ba n d w i d th , th i s i s also a cri t e r i o n f o r r e d u ci n g th e n o i s e co n t ri b u ti o n a t th e o u t p u t f r o m t h e t h er mal n o is e o f t h e 16 k s o ur ce r e sis t a n ce a t v s u m . a 10 nf ca p a ci t o r o n eac h v s u m p i n (20 nf p a ral l e l eq ui valen t ) co m b in ed wi th th e 16 k s o ur ce r e sis t a n ce yie l ds a 500 h z p o le , wh i c h i s s u f f i ci e n tl y be lo w th e ba n d w i d th f o r th e m i n i m u m in p u t c u r r en t o f 3 na. r e s i d u a l c r o sst a l k dist u r b a nc e is p a r t ic u l arly p r obl e ma t i c a t t h e lo w e st c u r r en ts fo r tw o r e as o n s. f i rst, t h e lo o p is una b le t o r e je c t su m m i ng no d e d i stu r b a nc e s b e y o nd t h e l i m i te d b a ndw i d t h . s e co n d , t h e s e t t lin g r e s p o n s e a t t h e lo w e s t c u r r en ts t o a n y r e sid u a l dist urb a n c e is sig n if ica n t l y slo w er t h a n t h a t fo r in p u t c u r r en ts e v en o n e o r tw o de cades hig h er (s e e f i gur e 18). ?6 ?3 0 3 6 9 12 inactiv e channe l outp ut (mv ) 0 0.2 0.4 0.6 0.8 1.0 1.2 activ e channe l outp ut (v ) 0 0.5 1.0 1.5 2.0 2.5 time (ms) 04415-0-036 active channel output pulse, 1-decade step 3 a to 30 a inactive channel response i inp ? 100na i inp ? 10na i inp ? 30na i inp ? 3na f i gur e 3 6 . cr o ssta l k p u l s e resp o n se fo r v a r i o u s input c u r r ent v a l u es f i g u re 3 6 show s me a s u r e d re sp ons e of an i n a c t i ve ch an nel ( d c in p u t) t o a 1-de cade c u r r en t s t ep o n t h e in p u t o f t h e ac t i v e c h a n n e l f o r s e v e ral inac ti v e c h a n n e l dc c u r r en t val u es. a ddi- t i on a l s y ste m c o ns i d e r a t i o ns m a y b e ne c e ss ar y to e n su re a d e q u a te s e tt l i ng t i me f o l l ow i n g a k n ow n t r ans i e n t w h e n one or b o t h cha n n e ls a r e o p era t in g a t v e r y lo w in p u t c u r r en ts.
adl5310 rev. 0 | page 16 of 20 relative and absolute power measurements w h en p r o p erl y cali b r a t ed , th e ad l5310 p r o v ides tw o i n d e p e nd e n t ch an nel s c a p a bl e of a c c u r a te ab s o lute opt i c a l p o w e r m e as ur em en ts. of t e n, i t is desira b l e t o m e as ur e t h e rel a t i ve g a i n or ab s o r b anc e a c ro ss an opt i c a l ne t w ork el e m e n t , su ch a s an opt i c a l am pl i f i e r or v a r i abl e a t te n u a t or . i f e a ch c h a n n e l has iden tical loga r i thmic s l o p es a n d in t e r c ep ts, this ca n easil y be do n e b y dif f er en cin g th e o u t p u t sig n als o f eac h channel, i n re a l i t y , channel mis m a t ch ca n r e su l t in sig n if ica n t er r o rs o v er a wide ra n g e o f in p u t lev e l s if lef t un co m p en s a t e d . p o s t p r o c es sin g o f th e sig n al ca n be us ed t o acco un t f o r in di vid u a l cha n n e l cha r ac t e r i st ics. this r e q u ir es a sim p le calc u l a t io n o f th e exp e c t e d in p u t le v e l f o r a m e as ur e d log v o l t a g e , fol l o w e d b y dif f er en cin g o f t h e tw o sig n al le v e l s in t h e dig i tal do ma in f o r a r e la ti v e ga in o r a b s o rba n ce m e as ur em en t. a m o r e s t ra ig h t -fo r wa r d a n alog im plem en t a t i o n in cl udes t h e us e o f a cu rr e n t m i rr o r , a s s h o w n i n f i g u r e 3 7 . t h e cu rr e n t m i rr o r i s us ed t o f eed a n o p p o si t e p o la r i ty r e p l ica o f th e ca th o d e p h o t o c ur r e n t o f p d 2 in t o c h a n n e l 2 o f th e ad l5310. this al lo ws o n e c h a n n e l t o be us ed as a n a b s o l u t e p o w e r m e t e r f o r th e o p ti cal si gn al i n ci d e n t o n p d 2, wh ile th e o p posi t e c h a n n e l i s used t o d i r e ctl y co m p u t e th e log ra ti o o f th e t w o i n p u t si gn als. 5v i pd2 i in2 =i pd2 i in1 temperature compensation bias generator 1k ? 2m ? 4.7nf 1k ? 4.7nf 0.1 f 1k ? 4.7nf 1nf 1nf 0.1 f 1nf 1nf vneg comm comm vref vrdz vpos vsum inp1 pd1 ingaas pin 1k ? 4.7nf pd2 ingaas pin irf1 i log1 out1 scl1 bin1 log1 04415- 0- 037 temperature compensation comm log log log log 5v vsum 5v inp2 irf2 i log2 out2 2 * 21 ** * 2 (v) ? 0.2log 10 () scl2 bin2 log2 i in2 100pa ** 21 (v) ? 0.2log 10 () i in1 i pd2 adl5310 f i g u r e 37. a b s o lute and r e lat i ve p o wer m e as ur ement a p plic at ion u s ing modified w ilson curr ent m i rr or th e p r es en t e d c u r r en t mir r o r is a m o dif i e d w i ls o n mir r o r . o t h e r c u r r en t mir r o r im plem en t a t i o n s w o u l d als o w o rk, t h o u g h t h e mo d i f i e d w i l s on m i r r or prov i d e s f a i r ly c o nst a n t p e r f or - ma n c e o v er t e m p era t ur e . i t is es s e n t ial t o us e ma t c h e d p a ir t r a n sis t o r s w h en desig n in g t h e c u r r en t mir r o r t o minimize t h e ef fe c t s o f t e m p era t ur e g r adien t s a n d b e t a misma t ch. th e s o l u tio n in f i gur e 37 is n o lo n g er s u b j ec t t o p o t e n t ial channel mis m a t ch issu es . i n divid u a l ch an nel sl op e and i n te rc e p t c h a r ac t e r i s t ics ca n n o w be cali b r a t ed in dep e n d en tl y . th e acc u rac y was v e r i f i ed usin g a p a ir o f cali b r a t ed c u r r en t s o ur ces. th e p e r f o r ma n c e o f t h e cir c ui t dep i c t e d in f i gur e 37 is s h o w n in f i gur e 38 a n d f i gur e 39. m u l t i p le tra n sf er f u n c tio n s a n d er r o r pl ot s are prov i d e d f o r v a r i ou s p o we r l e vel s . t h e a c c u r a c y i s b e t t er t h a n 0.1 db o v er a 5-de cade r a n g e. th e d y na mic r a n g e is sl ig h t ly re d u c e d for st rong i in in p u t c u r r en ts. this is d u e t o t h e limi te d a v a i la b l e swin g o f t h e vlo g p i n a n d ca n b e r e co ver e d t h rou g h c a re f u l s e l e c t i o n of i n put and output opt i c a l t a p co u p lin g ra tios. 1.0 1.2 1.4 1.6 1.8 0.8 0.6 0.4 0.2 0 ?10 0 10 20 30 40 50 ?2 0 log 10 [i pd1 /i pd2 ] (db) output voltage (v) 04415-0-038 60 21 for multiple values of i pd1 2 when i pd1 = 100 a f i g u r e 38. a b s o rbanc e and a b s o lute p o wer t r ans f er f u nc t i ons f o r w ils on- m i rr or a d l5310 combinat ion 0 0.1 0.2 0.3 0.4 0.5 ?0.1 ?0.2 ?0.3 ?0.4 ?0.5 ? 3 0 ? 20 ?10 0 10 20 30 ?4 0 log 10 [i pd1 /i pd2 ] (db) e rror (db) 04415-0-039 40 50 60 i pd1 =1 0 a i pd1 = 100 a i pd1 =1 a f i g u r e 39. l o g conf ormanc e f o r w ils on m i rr or a d l5310 combinat ion, normaliz ed to 10 ma channel 1 input curr ent , i in1
adl5310 rev. 0 | page 17 of 20 characterization methods during the characterization of the adl5310, the device was treated as a precision current-input logarithmic converter, because it is impractical to generate accurate photocurrents by illuminating a photodiode. the test currents were generated by using either a well-calibrated current source, such as the keithley 236, or a high value resistor from a voltage source to the input pin. great care is needed when using very small input currents. for example, the triax output connection from the current generator was used with the guard tied to vsum. the input trace on the pc board was guarded by connecting adjacent traces to vsum. these measures are needed to minimize the risk of leakage current paths. with 0.5 v as the nominal bias on the inp1 (inp2) pin, a leakage-path resistance of 1 g? to ground would subtract 0.5 na from the input, which amounts to a C1.6 db error for a 3 na source current. additionally, the very high sensitivity at the input pins and the long cables commonly needed during characterization allow 60 hz and rf emissions to introduce substantial measurement errors. careful guarding techniques are essential to reducing the pickup of these spurious signals. additional information, including test setups, can be found in the ad8305 and adl5306 data sheets.
adl5310 rev. 0 | page 18 of 20 evaluation board an evaluation board is available for the adl5310, the schematic of which is shown in figure 40. it can be configured for a wide variety of experiments. the gain of each buffer amp is factory- set to unity, providing a slope of 200 mv/dec, and the intercept is set to 300 pa. table 4 describes the various configuration options. table 4. evaluation board configuration options component function default condition p1 supply interface . provides access to supply pins, vneg, comm, and vpos. p1 = installed p2, r1, r3, r8, r9, r17, r22, r25, r30 monitor interface . by adding 0 ? resistors to r1, r3, r8, r9, r17, r22, and r25, the vrdz, vref, vsum, bin1, bin2, out1, and out2 pin voltages can be monitored using a high impedance probe. vbias allows for the external bias voltages to be applied to j1 and j2. if r30 = 0 ?, vbias = vref. p2 = not installed r1 = r3 = r8 = open (size 0402) r9 = r17 = open (size 0402) r22 = r25 = r30 = open (size 0402) r5, r6, r7, r16, r18, r19, r20, r21, r31, r32, c4, c14, c15, c16, c19, c20 buffer amplifier/output interface . the logarithmic slopes of the adl5310 can be altered using each buffe rs gain-setting resistors, r5 and r6, and r18 and r19. r7, r16, r31, r32, c19, and c20 allow for variation in the buffer loading. r20, r21, c4, c14, c15, and c16 are provided for a variety of filtering applications. r5 = r19 = 0 ? (size 0402) r7 = r16 = 0 ? (size 0402) r20 = r21 = 0 ? (size 0402) r6 = r18 = open (size 0402) r31 = r32 = open (size 0402) c4 = c14 = open (size 0402) c19 = c20 = open (size 0402) c15 = c16 = open (size 0402) log1 = out1 = installed log2 = out2 = installed r2, r28, r29 intercept adjustment . the voltage dropped across resistors r28 and r29 determines the intercept reference current for each log amp, nominally set to 3 a using a 665 k? 1% resistor. r2 can be used to adjust the output offset voltage at th e log1 and log2 outputs. r28 = r29 = 665 k? (size 0402) r2 = 0 ? (size 0402) r4, r10, r11, c2, c3, c5, c6, c8, c9 supply decoupling . c2 = c5 = c9 = 100 pf (size 0402) c3 = c6 = c8 = 0.01 f (size 0402) r4 = r10 = r11 = 0 ? (size 0402) c1, c7 filtering vsum. c1 = c7 = 0.01 f (size 0402) r12, r13, r14, r15, c10, c11, c12, c13 input compensation . provides essential hf compensation at the input pins inp1, inp2, irf1, and irf2. r12 = r15 = 1 k? (size 0402) r13 = r14 = 2 k? (size 0402) c10 = c13 = 1 nf (size 0402) c11 = c12 = 4.7 nf (size 0402) iref, inpt input interface . the test board is configured to accept current through the sma connectors labeled inp1 and inp2. through-holes are provided to connect photodiodes in place of the inp1 and inp2 smas for optical interfacing. by removing r28 (r29 for inp2), a second current can be applied to the irf1 (irf2 for inp2) input (also sma) for evaluating the adl5310 in log ratio applications. iref = inpt = installed j1, j2 sc-style photodiode . provides for the direct mounting of sc-style photodiodes. j1 = j2 = open
adl5310 rev. 0 | page 19 of 20 3 2 1 3 2 1 vneg out2 out2 vpos agnd 12 3 p1 vref vbias vbias vsum inp1 out1 out1 irf1 irf2 inp2 r1 open r9 open r17 open r30 open r31 open c19 open r32 open r3 open c20 open c14 open c15 open c16 open r12 1k ? r28 665k ? r29 665k ? r13 2k ? r14 2k ? r15 1k ? c10 1nf c5 100pf c6 0.01 f c11 4.7nf c12 4.7nf c13 1nf j2 photodiode j1 photodiode c1 0.01 f c7 0.01 f r10 0 ? r19 0 ? r2 0 ? r4 0 ? c9 100pf c8 0.01 f c2 100pf c3 0.01 f r11 0 ? r16 0 ? r21 0 ? r20 0 ? r24 0 ? r27 0 ? r26 0 ? r5 0 ? r7 0 ? c4 open r8 open r23 0 ? r22 open r25 open r6 open r18 open log2 log2 log1 log1 bin2 bin1 vneg vrdz vbias vref out2 bin2 out1 log2 log1 bin1 p2 1 5 6 7 2 3 4 8 24 1 2 3 4 5 6 18 17 16 15 14 13 23 22 21 20 19 78 9 1 0 1 1 1 2 adl5310 vsum inp1 irf1 irf2 inp2 vsum scl1 bin1 log1 log2 bin2 scl2 04415-0-040 vr ef v rdz comm comm vn eg out1 vr ef vpos vpos vn eg vn eg out2 f i g u r e 40. ev aluat i on boar d s c hemat i c 04415-0-041 f i g u r e 41. component side layout 04415-0-042 f i gur e 42. component side silkscr een
adl5310 rev. 0 | page 20 of 20 outline dimensions 1 24 6 7 13 19 18 bottom view 12 2.25 2.10 sq 1.95 0.60 max 0.50 0.40 0.30 0.30 0.23 0.18 2. 5 0 r e f 0.50 bsc 12 max 0. 80 m a x 0. 65 t y p 0.05 max 0.02 nom 1.00 0.85 0.80 seating plane pin 1 indicator top view 3.75 bs c s q 4.00 bsc sq pin 1 indicator 0.60 max coplanarity 0.08 0. 20 re f 0 . 2 5 mi n co m p l i a n t t o j e d e c s t andar ds m o - 2 2 0 - v g g d - 2 f i g u r e 43. 24-l e ad l e ad f r ame chip s c ale p a ck ag e [lfcsp ] (cp - 24) d i mens ions s h o wn in millimeters ordering guide model temperature range package description package option ADL5310ACP C40c to +85c 24-lead lfcsp cp-24 ADL5310ACP-r2 C40c to +85c 24-lead lfcsp cp-24 ADL5310ACP-reel7 C40c to +85c 24-lead lfcsp cp-24 a d l 5 3 1 0 - e v a l e v a l u a t i o n b o a r d ? 2003 a n alog de vic e s , inc . a ll righ ts r e ser v ed . t r ademarks and r e gist er ed tr ademarks ar e the pr oper t y of their r e spec tiv e o w ners . c04415C0C11/03(0)

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