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120 db range (3 na to 3 ma) dual logarithmic converter adl5310 rev. a information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent 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. tel: 781.329.4700 www.analog.com fax: 781.326.8703 ? 2004 analog devices, inc. all rights reserved. features 2 independent channels optimized for photodiode 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 the adl5310 1 low cost, dual logarithmic amplifier converts input current over a wide dynamic range to a linear-in-db output voltage. it is optimized to determine the optical power in wide-ranging optical communication system applications, including control circuitry for lasers, optical switches, atten- uators, and amplifiers, as well as system monitoring. the device is equivalent to a dual ad8305 with enhanced dynamic range (120 db). while the adl5310 contains two independent signal channels with individually configurable transfer function constants (slope and intercept), internal bias circuitry is shared between channels for improved power consumption and channel matching. dual converters in a single, compact lfcsp package yield space-efficient solutions for measuring gain or attenuation across optical elements. only a single supply is required; optional dual-supply operation offers added flexibility. the adl5310 employs an optimized translinear structure that use the accurate logarithmic relationship between a bipolar transistors base emitter voltage and collector current, with appropriate scaling by precision currents to compensate for the inherent temperature dependence. input and reference current pins sink current ranging from 3 na to 3 ma (limited to 60 db between input and reference) into a fixed voltage defined by the vsum potential. the vsum potential is internally set to 500 mv but may be externally grounded for dual-supply opera- tion, and for additional applications requiring voltage inputs. 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 ? figure 1. the logarithmic slope is set to 10 mv/db (200 mv/decade) nominal and can be modified using external resistors and the independent buffer amplifiers. the logarithmic intercepts for each channel are defined by the individual reference currents, which are set to 3 a nominal for maximum input range by connecting 665 k resistors between the 2.5 v vref pins and the irf1 and irf2 inputs. tying vrdz to vref effectively sets the x-intercept four decades below the reference current typically 300 pa for a 3 a reference. the use of individually optimized reference currents may be valuable when using the adl5310 for gain or absorbance measurements where each channel input has a different current- range requirement. the reference current inputs are also fully functional dynamic inputs, allowing log ratio operation with the reference input current as the denominator. the adl5310 is specified for operation from C40c to +85c. 1 us patents: 5,519,308.
adl5310 rev. a | 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 ................................................................ 14 relative and absolute power measurements .......................... 15 characterization methods ......................................................... 16 evaluation board ............................................................................ 17 outline dimensions ....................................................................... 20 ordering guide ........................................................................... 20 revision history 9/04data sheet changed from rev. 0 to rev. a changes to ordering guide .......................................................... 20 11/03revision 0: initial version
adl5310 rev. a | page 3 of 20 specifications vp = 5 v, vn = 0 v, t a = 25c, r ref = 665 k?, and vrdz connected to vref, unless otherwise noted. table 1. parameter conditions min typ max unit input interface pins 1 to 6: inp1 and inp2, irf1 and irf2, vsum specified current range, i pd flows toward inp1 pin or inp2 pin 3 n 3 m a input current min/max limits flows toward inp1 pin or inp2 pin 10 m a reference current, i ref , range flows toward irf1 pin or irf2 pin 3 n 3 m 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 ? v sum , v iref ? v sum ?20 +20 mv logarithmic outputs pin 15 and pin 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 12 to 14 and 17 to 19: out2, scl2, bin2, bin1, scl1, and out1 input offset voltage ?20 +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 ? 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 ?5.5 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 r e v. a | pa ge 4 of 20 absolute maximum ratings table 2. p a r a m e t e r r a t i n g supply voltage v p ? v n 12 v input current 20 ma internal power dissipation 500 mw ja 35c/w 1 maximum junction temperature 125c operating temperature range C40c to +85c storage temperature range ? 65c 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. 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.
adl5310 r e v. a | pa ge 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 vr ef v rdz com m com m vn eg out1 vr ef vpos vpos vn eg vn eg 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 photocurrent 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 . these pins are usually grounded. for more details, 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 r e v. a | pa ge 6 of 20 typical performance characteristics vp = 5 v , vn = 0 v , r ref = 665 k?, t a = 25c, unles s o t h e r w is e n o t 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 inp (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 r e v. a | pa ge 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, ?5v +5v, ? 5 v +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 = 0c, 70c mean + 3 at 70c 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 = 25 c 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 ? 4 0c mean + 3 at +85 c 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 r e v. a | pa ge 8 of 20 ?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) 04415-0-015 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 inp (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 r e v. a | pa ge 9 of 20 ?25 ?20 ?15 ?10 ?5 0 5 10 15 20 25 v re f drift (mv ) ? 4 0 ? 30 ?20 ? 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 ? 4 0 ? 30 ?20 ? 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 ?5 0 0 50 100 150 200 i z drift (pa) ? 4 0 ? 30 ?20 ? 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 ) ? 4 0 ? 30 ?20 ? 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) ? 4 0 ? 30 ?20 ? 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. a | 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. a | 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 p i n 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 o p era t io na l a m plif iers. t r a n sist o r q1 co n v er ts i pd t o a co r r es p o n d in g loga r i thmic v o l t a g e , as s h o w n in e q ua tio n 1. a f i ni t e p o si 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 fo r t h e usua l cas e o f a sin g le-su p ply v o l t a g e . this is in t e r - nal l y s e t t o 0.5 v , o n e-f i f t h o f th e 2.5 v r e f e r e n c e v o l t a g e tha t a p p e a r s o n p i 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 b o t h 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 nom i n a l l y 1 6 k ; t h i s vo lt age i s not i n te nd e d a s a ge ne r a l b i a s so 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 ea c h c h a n n e l n eed s t o be a d j u s t ed t o m a i n ta i n th e i n t e r c e p t v a lu e. a l s o note t h a t t h e c o l l e c tor - e m i t te r volt age s of q 1 and q 2 a r e 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 ca us e er r o rs a t la rge 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 gen 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 va l u es o v er a s e ver a l-de cade r a n g e ca n b e us e d wi t h a slig 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 b i p o la r j u n c t i o n t r a n sis t o r (bjt) 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 ?35c 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 . i t is a p p a r e n t tha t this o u t p u t s h o u ld be 0 f o r i pd = i ref and w o u l d n eed t o swin g n e ga ti v e f o r smal ler val u es o f in p u t cu rr e n t . t o a v o i d th i s , i ref w o u l d n e e d t o b e as sma l l as t h e smal les t val u e o f i pd . a c co r d in g l y , a n o f fs et vol t a g e is adde d to v lo g t o s h if t i t u p wa r d b y 0.8 v wh en vrdz is dir e c t l y c o nne c te d to v r e f . th i s move s t h e i n te rc e p t to t h e l e f t b y fou r decades (a t 200 mv/decade), f r o m 3 a t o 300 pa: i lo g = i y log 10 ( i pd / i int c ) ( 4 ) w h er e i int c is t h e o p era t io nal val u e o f t h e in t e r c ep t c u r r en t. b e ca us e val u es o f i pd < i int c r e s u l t in a n e ga ti v e v lo g , a n e g a t i v e su p p ly of su f f i c i e n t v a l u e is re qu ire d to ac c o mmo d a t e t h is si t u a t io n.
adl5310 rev. a | page 12 of 20 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) lowers this slope and results in an overall scaling uncertainty. this is due to the variability of the on-chip resistors compared to the off-chip load. as a con- sequence, 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 = ?0.5 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 degrades 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 do 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 operational amplifier 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 increasing the slope voltage v y , the buffer can be used to implement multipole, 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. a | 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 t ha t is, 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 va r i o u s n o n e s s en t i al co m p o n en ts, as expla i n e d n e xt. 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 i n 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 cco 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 era l l n o is e in cr e a s e s w h en usin g v e r y lo w va l 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, b e ca us 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 . i n addi t i o n , e a ch in p u t a n d r e fer e n c e p i n (inp1, inp2, irf 1 , and i r f 2 ) h a s a c o m p e n s a t i on ne t w or k m a d e up of a s e r i e s re s i stor and c a p a c i tor . t h e j u nc t i on c a p a c i t a nc e of t h e photo - d i od e alo n g w i th th e n e t w o r k ca pa ci ta n c e o f th e boa r d a r t w o r k a r o u n d t h e in p u t sys t em cr e a t e s a p o le t h a t va r i es wide l y wi t h in p u t c u r r en t. th e r c n e tw o r k s t a b i l izes t h e sys t em b y sim u l- t a ne ou sly re d u c i ng t h i s p o l e f r e q u e nc y and i n s e r t i n g a z e ro to co m p en s a t e a n addi t i o n a l p o le in h e r e n t in t h e in p u t sy st em. i n gen e ra l, t h e 1 nf , 1 k n e tw o r k ha n d les a l m o st a n y ph o t o d io de in t e r f ace . i n si t u a t io n s w h er e la rg er ac t i v e a r e a ph o t o d io des a r e us e d , o r w h en lo n g in p u t t r aces a r e us e d , t h e ca p a ci t o r val u e m a y n eed t o be i n cr ea sed t o e n s u r e s t a b il i t y . al th o u gh th e s i gn al a n d r e fer e n c e in p u t sys t em s a r e simi la r , addi t i o n al ca r e is re qu i r e d to e n su re st abl e op e r a t i o n of t h e re f e re nc e i n put s a t t e m p era t ur e ext r em es acr o s s t h e f u l l c u r r en t ra n g e o f i rf1 ( i rf2 ). i t is r e co mm en de d t h a t f i l t er co m p o n en ts o f 4.7 nf a n d 2 k? s h o u ld be us ed f r o m p i n irf1 (irf2) t o g r o u n d . t e m p era t ur e- s t a b le co m p o n en ts s h o u ld al wa ys be us ed in cr i t ical lo ca tio n s s u ch as t h e co m p en s a t i o n n e tw o r ks; y5v - typ e chi p ca p a ci t o rs a r e t o b e a v o i de d d u e t o t h eir p o o r t e m p era t ur e s t a b ili t y .
adl5310 rev. a | page 14 of 20 t h e opt i on a l c a p a c i tor f r om lo g 1 ( l o g 2 ) to g r ou nd f o r m s a sin g le-p ole , lo w-p a ss f i l t er in co m b ina t io n wi t h t h e 5 k r e sis- t a n c e a t t h is p i n. f o r exa m ple , w h en usin g a c fl t o f 10 nf , th e 3 db co r n er f r e q uen c y is 3.2 kh z. s u ch f i l t er in g is us ef u l in minimizin g th e o u t p u t n o is e , p a r t ic u l a r l y wh en i pd is sma l l. m u l t i p ole f i l t ers a r e m o r e ef fe c t i v e in r e d u cin g t h e t o t a l n o is e; exa m p l es a r e p r o v ided in th e ad8304 da ta s h eet. b e ca us e th e basic s c alin g a t l o g1 (l o g 2) is 0.2 v/decade , a n d t h us a 4 v swin g a t t h e b u f f er o u t p u t w o u l d co r r es p o n d t o 20 de cades, i t is o f t e n us ef u l t o ra is e t h e s l o p e t o mak e b e t t er us e o f th e ra il-t o-ra il v o l t a g e ra n g e . f o r ill u s t ra ti v e p u r p oses, bo th c h a n n e ls in f i gur e 34 p r o v ide a 0.5 v/decade o v eral l s l o p e (25 mv/db). th us, usin g i ref = 3 a, v lo g r u n s f r o m 0.2 v a t i pd = 3 na t o 1.4 v a t i pd = 3 ma; t h e b u f f er o u t p u t r u n s f r o m 0.5 v t o 3.5 v , co r r es p o n d in g t o a d y na mic ra n g e o f 120 db (e lec t r i cal , tha t is, 60 db o p tical p o w e r). f u r t h e r info r m a t io n o n ad j u st in g t h e slo p e a n d in t e r c ep t, usin g a n e ga t i ve su p p ly , a n d addi t i o n a l o p er a t io n s ca n b e fo un d in t h e ad8305 da ta s h eet. calibration e a c h c h a n n e l o f th e ad l5310 has a n o minal s l o p e a n d in t e r c ep t a t l o g1 (l o g 2) o f 200 mv/decade a n d 300 pa, r e s p ec ti v e l y , w h en co nf igur e d as s h o w n in f i gur e 34. th es e val u es a r e un tr imm e d a n d th e s l o p e alo n e ma y va r y b y as m u c h as 7.5% o v er t e m p era t ur e . f o r this r e as o n , i t is r e co mm en ded tha t a sim p le ca li b r a t io n b e do n e to achie v e in cr e a s e d acc u r a c y . w h i l e th e ad l5310 o f f e rs im p r o v ed s l o p e a n d in t e r c ep t ma t c hin g co m p a r ed t o a ra n d o m l y s e lec t ed p a ir o f ad8305 log a m ps, th e s p eci f i e d a c cura c y ca n o n l y be a c h i ev ed b y cal i b r a t i n g ea c h channel individ u a l ly . 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 ) e rror (db (1 0 m v / db)) 04415-0-035 calibrated error measured output ideal output uncalibrated error f i gur e 35. using 2-p o int calibr a tion to incr ease measur ement ac cur a c y f i gur e 35 s h o w s t h e im p r o v em en t in acc u rac y w h en usin g a 2- p o in t ca li b r a t io n m e t h o d . t o p e r f o r m t h is ca li b r a t io n, a p ply tw o k n o w n c u r r en ts, i 1 and i 2 , in t h e lin e a r o p era t in g r a n g e b e tw e e n 10 na a n d 1 ma. m e asur e t h e r e su l t in g o u t p u t , v 1 and v 2 , r e s p e c t i v e l y , a n d calc u l a t e t h e s l o p e m and t h e in t e r c ep t 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 ) th e s a m e ca li b r a t io n co u l d b e p e r f o r m e d wi t h tw o k n o w n opt i c a l p o we r s , p 1 and p 2 . this al lo ws f o r cali b r a t io n o f th e en t i r e m e as ur em en t sys t em w h i l e p r o v idin g a sim p lif i e d r e la ti o n s h i p be t w ee n th e i n ci d e n t o p ti cal po w e r a n d v lo g vol t age : m = ( v 1 C v 2 )/( p 1 C p 2 ) ( 9 ) b = v 1 C m p1 (10) th e un cali b r a t ed er r o r lin e in f i gur e 35 was g e n e ra t e d as s u m- in g tha t th e s l o p e o f th e m e as ur ed o u t p u t was 200 mv/decade wh en in fac t i t was ac t u al l y 194 mv/decade . c o r r ec tin g f o r this dis c r e p a n c y de cr e a s e d m e asur em en t er r o r u p to 3 db . minimizing crosstalk c o m b inin g tw o hig h -d y n a m ic-ra n ge loga r i t h mic co n v er t e rs in o n e i c ca r r i es p o t e n t ial p i t f al ls co n c er nin g cha n n e l-t o -cha nn e l 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 s t idio us s u 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 ile 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 m a tch i ng and re d u c e s p o we r c o nsu m pt i o n , i t i s a l s o a s o u r c e of 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 b e ca us 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 en co un t e r e d . b e ca us e t h e lo w f r e q uen c y n o is e a t v s u m is als 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 cr i t er io n fo r r e d u cin g t h e n o is e co n t r i b u t i o n a t t h 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 .
adl5310 rev. a | page 15 of 20 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 s t c u r r en ts f o r tw o r e as o n s. f i rs t, th e lo o p is una b le t o r e jec 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 t h e me a s u r e d re sp ons e of an i n a c t i ve ch an nel (dc 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. 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 in de- pe n d e n t c h a n n e l s c a pa b l e o f a c cu r a t e a b so l u t e o p ti c a l po 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 r e la t i v e 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 ch an nel h a s iden t i cal loga r i t h mic s l o p es a n d in t e r c ep ts, t h is ca n e a si l y b e d o ne b y d i f f e r e n c i ng t h e output s i g n a l s of e a ch ch an nel. i n r e a l i t y , cha n n e l misma 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 le v 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 al c h a n n e l cha r ac t e r i st ics. this r e q u ir es a sim p le ca lc u l a t io n o f t h e e x p e c t e d i n put l e vel for a me asu r e d l o g vol t age, fol l owe 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 t a l do ma in fo 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 w a 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 c u r r en 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 u s ed t o f e e d an opp o s i te p o l a r i t y re pl i c a of t h e c a t h o d e photo c u r re n t of p d 2 in t o cha 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 used as a n a b so l u t e p o w e r m e t e r f o r th e o p tical sign al in ciden t o n p d 2, w h i l e t h e o p p o si t e cha n n e l is us e d t o dir e c t l 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 m o dif i ed w ils on 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.
adl5310 rev. a | page 16 of 20 characterization methods th e s o l u t i o n in f i gur e 37 is n o lo n g er sub j e c t t o p o t e n t ia l 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 cha r ac t e r i st ics ca n b e ca li b r a t e d in dep e n d en t l 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 or m a nc e of t h e c i rc u i t d e pi c t e d i n f i g u re 3 7 i s show n i n 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. dur i n g th e c h a r ac t e r i za tio n o f th e ad l5310, th e device was t r e a t e d as a p r e c isio n c u r r en t-in p u t loga r i t h mic co n v er t e r , b e c a u s e i t i s i m pr a c t i c a l to ge ne r a te a c c u r a te photo c u r re n t s b y i l l u mina t i n g a ph o t o d io de. th e test c u r r en ts w e r e gen e r a te d b y usin g ei t h er a w e l l -cali b ra t e d c u r r en t s o ur ce , s u ch as t h e k e i t hley 236, o r a hig h val u e r e sis t o r f r o m a v o l t a g e s o ur ce t o t h e in p u t p i n. gr e a t ca r e is n e e d e d w h en usin g v e r y sma l l in p u t curr e n t s . f o r e x a m p l e , th e tri a x o u t p u t co n n ecti o n f r o m th e curr e n t g e n e ra t o r w a s used w i th th e gua r d ti ed t o v s u m . t h e in p u t t r ace o n t h e pc b o a r d was gua r de d b y co nn e c t i n g ad jacen t t r aces t o v s u m . 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 th es e m e as ur es a r e n e e d e d t o minimize t h e r i s k o f le aka g e curr e n t pa th s. w i th 0. 5 v a s th e n o m i n a l b i a s o n th e in p1 (inp2) p i n, a leaka g e-p a th r e sis t a n ce o f 1 g? t o g r o u n d w o u l d s u b t rac t 0.5 na f r o m th e in p u t, whic h a m o u n t s t o a ?1.6 db er r o r fo r a 3 na s o ur ce c u r r en t. a ddi t i o n al l y , t h e v e r y hig h s e ns i t iv i t y a t t h e i n put pi ns and t h e l o ng c a bl e s c o m m on ly n eed ed d u ri n g c h a r a c t e ri z a ti o n all o w 60 h z a n d r f e m i s s i o n s t o in t r o d uce s u bs t a n t ial m e as ur em en t er r o rs. c a r e f u l gua r din g t e chniq u es a r e es s e n t ial t o r e d u cin g t h e p i ck u p o f t h es e s p ur io us sig n als. a ddi t i o n a l info r m a t io n, in cl udin g t e st s e t u ps, ca n b e fo un d in th e ad8305 a n d ad l5306 da ta s h eets. 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 ?30 ? 20 ?10 0 10 20 30 ?40 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. a | page 17 of 20 evaluation board an evaluation board is available for the adl5310 (figure 40 shows the schematic). it can be configured for a wide variety of ex periments. 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 the supply pins vneg, comm, and vpos. p1 = installed p2, r1, r3, r8, r9, r17, r22, r25, r30 monitor interface. by adding 0 ? resist ors 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 appl ied 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. th e logarithmic slopes of the adl5310 can be altered using each buffers 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 vo ltage dropped across resistors r28 and r29 determines the intercept reference cu rrent 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 essent ial 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 th e 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. a | page 18 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
adl5310 rev. a | page 19 of 20 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. a | page 20 of 20 outline dimensions 1 24 6 7 13 19 18 12 2.25 2.10 sq 1.95 0.60 max 0.50 0.40 0.30 0.30 0.23 0.18 2.50 ref 0.50 bsc 12 max 0.80 max 0.65 typ 0.05 max 0.02 nom 1.00 0.85 0.80 seating plane pin 1 indica t o r to p view 3.75 bsc sq 4.00 bsc sq pin 1 indicator 0.60 max coplanarity 0.08 0.20 ref 0.25 min exposed pad (bottom view) compliant t o jedec st and ards mo-220-v ggd-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 ] 4 mm 4 mm body (cp - 24-1) d i mens ions s h o wn in millimeters ordering guide model temperature range package description package outline branding 1 adl5310acp-r2 C40c to +85c 24-lead lfcsp cp-24-1 jqa adl5310acp-reel7 C40c to +85c 24-lead lfcsp cp-24-1 jqa 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 1 bra n di n g i s a s follows: line 1 jqa line 2 lot code li n e 3 (d a t e code) d a t e code i s i n yyww form a t ? 2004 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 . c04415C0C9/04( a )

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