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1 mhz C 8 ghz, 60 db logarithmic detector/controller ad8318 rev. 0 in fo rmation furn ishe d by an al o g d e v i ces is believed to be accurate and r e liable. how e ver, no resp on sibili ty is assumed by analo g devices fo r its use, nor for an y i n fri n geme nt 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 res u l t from i t s use. specifications s u bject to cha n ge wi th o u t no tice. no licen s e is g r an te d by implicatio n o r o t h e r w ise un d e r any paten t o r paten t righ ts o f an alog d e v i ces . trade m arks and re gistered trade m arks are the property of their respective owne rs. one technolog y way, p.o . box 9106, norwood, ma 02062-9106, u.s.a. t e l: 781. 329. 4 700 www.analog.com fax: 781. 326. 87 03 ? 2003 analog de vices, i n c. al l r i ght s r e ser v ed . features w i de bandwi dt h: 1 mhz t o 8 ghz high ac cur a c y : 1.0 db ov er 5 5 db r a nge (f < 5.8 gh z) s t abilit y ov er temper a t ur e: 0 .5 db l o w noise measur ement/c o ntr o ller output vout p u ls e r e sponse time 10/1 2 ns ( f all/rise) int e gr a t ed t e m p er a t ur e senso r small f ootprint csp pack age p o w e r- down f e a t ure: <1. 5 mw a t 5 v single -sup ply oper a t ion: 5v @ 68 ma f a bric a t ed usin g high speed si g e pr oc ess applic ati o ns rf tr ansmitt e r p a setpoin t c o n t r o l and le v e l monit o ring rssi measur e m en t in base st a t ions , wl an, r a dar gener a l descripti o n the ad8318 is a dem o d u l a tin g loga r i thmic a m p l if ier , ca p a b l e of acc u ra t e l y con v er tin g a n rf in p u t sig n al t o a c o r r es p o n d in g de cib e l-s c ale d ou t p ut v o l t a g e . i t em plo y s t h e p r og r e s s i v e co m p r e ssio n t e chniq u e o v er a c a s c ad e d am plif i e r cha i n, e a ch s t a g e o f w h i c h is eq ui p p ed wi th a d e t e c t o r ce ll . t h e devi ce ca n be us ed in m e as urem en t o r con t r o l l er m o de . the ad8318 ma in ta in s acc u ra t e log co nfo r ma n c e fo r sig n als o f 1 mh z t o 6 gh z a nd p r o v ides us ef u l o p era t io n t o 8 gh z. the i n p u t ra n g e is typ i cal l y 60 db (r e: 50 ? ) wi t h er r o r les s tha n 1 db . th e ad8318 has a 1 0 n s r e s p o n s e tim e tha t enab les rf b u rs t dete c t ion to b e y o nd 60 mhz. t h e d e vice p r o v i d es un p r eced en t e d loga ri th m i c i n t e r c e p t s t a b il i t y v e r s us a m b i en t t e m p era t ur e con d i t io ns. a 2 mv/k s l o p e t e m p era t ur e s e n s o r output i s a l s o prov i d e d f o r a d d i t i on a l s y ste m m o n i tor i n g . a sin g le su p p ly o f +5 v is r e q u ir e d . c u r r en t co n s u m p t ion is typ i cal l y 68 ma. p o w e r co n s um p t io n decr e a s e s t o <1.5 mw w h en t h e de vice is dis a b l e d . the ad8318 can b e co nf igur ed t o p r o v ide a con t r o l v o l t a g e t o a v g a, such as a p o w e r a m plif ier o r a m e asur e m en t o u t p ut, f r o m p i n v o u t . si n c e t h e o u t p u t can b e us e d fo r co n t r o l l er func ti onal bl oc k di a g ram temp sensor gain bias slope det det det det inhi inlo iv vout iv vset clpf temp vpsi enbl tadj vpso cmop cmip 04853- 001 fi g u r e 1 . a p plic a t ion s , sp e c ia l a t t e n t io n h a s b e en p a i d t o mini mi ze wideb a n d n o is e . i n t h is m o d e , t h e s e t p o i n t co n t r o l v o l t a g e is ap p l i e d t o v s e t . t h e f e e d b a c k l o o p t h r o u g h a n r f a m plif ier is clos e d vi a v o u t ; t h e o u t p ut o f w h ich r e gu l a t e s t h e am plif ier s ou t p ut t o a ma g n i t ude co r r es p o ndin g t o v set . the ad8318 p r o v ides 0 v t o 4. 9 v o u t p u t c a p a b i li ty a t t h e v o ut p i n, s u i t a b le f o r co n t r o l l er a p p l ic a t io n s . a s a m e as ur em e n t devi ce , v o ut i s e x t e rn all y co n n e ct ed t o v s et t o p r o d uce a n o u t p u t v o l t a g e v ou t t h a t is a de cr e a sing lin e ar -i n- db f u n c t i on o f t h e r f in p u t sig n a l am pli t ude. the loga r i t h mic s l o p e is n o minal l y ? 25 mv/db , b u t can be ad j u s t e d b y s c al in g t h e fe e d b a ck v o l t a g e f r o m v o u t t o t h e v s et i n t e r f ace . the in t e r c ep t is +20 dbm (r e: 50 ? , c w in p u t) usin g t h e inhi i n p u t. t h es e p a ra met e rs a r e v e r y st abl e ag ai n s t supply an d te m p e r a t u r e v a r i a t i o n s . the ad8318 is fa b r ica t e d o n a s i g e b i p o la r i c p r o c es s an d is a v a i la b l e in a 4 mm 4 mm, 16-p i n lfcs p p a c k a g e , f o r t h e o p era t i n g t e m p er a t ur e ra n g e o f C40 o c t o +85 o c.
ad8318 rev. 0 | page 2 of 24 table of contents specifications ...................................................................................3 absolute maximum ratings ..........................................................6 esd caution ................................................................................6 pin configuration and functional descriptions ........................7 typical performance characteristics ............................................8 general description .................................................................... 11 using the ad8318 ........................................................................ 12 basic connections ................................................................... 12 enable ........................................................................................ 12 input signal coupling ............................................................. 12 output interface ....................................................................... 13 setpoint interface ..................................................................... 13 temperature compensation of output voltage .................. 13 temperature sensor ................................................................. 14 measurement mode ................................................................. 14 device calibration and error calculation ............................ 15 selecting calibration points to improve accuracy over a reduced range ......................................................................... 16 variation in temperature drift from device to device ...... 17 temperature drift at different temperatures ...................... 17 setting the output slope in measurement mode ................ 17 response time capability ...................................................... 18 controller mode ....................................................................... 18 characterization setups and methods .................................. 20 evaluation board .......................................................................... 21 outline dimensions ..................................................................... 23 ordering guide ........................................................................ 23 revision history 7/04revision 0: initial version
ad8318 rev. 0 | page 3 of 24 specifications v p = 5 v, c lpf = 220 pf, t a = +25 c, 52.3 ? termination resistor at inhi, unless otherwise noted. table 1. parameter conditions min typ max unit signal input interface inhi (pin 14) and inlo (pin 15) specified frequency range 0.001 8 ghz dc common-mode voltage vpos C 1.8 v measurement mode vout (pin 6) shorted to vset (pin 7), sinusoidal input signal f = 900 mhz 500 ? at tadj to gnd input impedance 957 || 0.71 ? || pf 1 db dynamic range t a = +25 c 57 db ?40 c < t a < +85 c 48 db maximum input level 1 db error C1 dbm minimum input level 1 db error C58 dbm slope ?26 C24.5 ?23 mv/db intercept 19.5 22 24 dbm output voltagehigh power in p in = C10 dbm 0.7 0.78 0.86 v output voltagelow power in p in = C40 dbm 1.42 1.52 1.62 v temperature sensitivity p in = C10 dbm 25 c t a +85 c +0.0011 db/ c ?40 c t a +25 c +0.003 db/ c f = 1.9 ghz 500 ? at tadj to gnd input impedance 523 || 0.68 ? || pf 1 db dynamic range t a = +25 c 57 db ?40 c < t a < +85 c 50 db maximum input level 1 db error C2 dbm minimum input level 1 db error C59 dbm slope ?27 C24.4 ?22 mv/db intercept 17 20.4 24 dbm output voltagehigh power in p in = C10 dbm 0.63 0.73 0.83 v output voltagelow power in p in = C35 dbm 1.2 1.35 1.5 v temperature sensitivity p in = C10 dbm 25 c t a +85 c +0.0011 db/ c C40 c t a +25 c +0.0072 db/ c f = 2.2 ghz 500 ? at tadj to gnd input impedance 391 || 0.66 ? || pf 1 db dynamic range t a = +25 c 58 db ?40 c < t a < +85 c 50 db maximum input level 1 db error C2 dbm minimum input level 1 db error C60 dbm slope ?28 C24.4 ?21.5 mv/db intercept 15 19.6 25 dbm output voltagehigh power in p in = C10 dbm 0.63 0.73 0.84 v output voltagelow power in p in = C35 dbm 1.2 1.34 1.5 v temperature sensitivity p in = C10 dbm 25 c t a +85 c ?0.0005 db/ c C40 c t a +25 c +0.0062 db/ c
ad8318 rev. 0 | page 4 of 24 parameter conditions min typ max unit f = 3.6 ghz 51 ? at tadj to gnd input impedance 119 || 0.7 ? || pf 1 db dynamic range t a = +25 c 58 db ?40 c < t a < +85 c 42 db maximum input level 1 db error C2 dbm minimum input level 1 db error C60 dbm slope C24.3 mv/db intercept 19.8 dbm output voltagehigh power in p in = C10 dbm 0.717 v output voltagelow power in p in = C40 dbm 1.46 v temperature sensitivity p in = C10 dbm 25 c t a +85 c +0.0022 db/ c C40 c t a +25 c +0.004 db/ c f = 5.8 ghz 1000 ? at tadj to gnd input impedance 33 || 0.59 ? || pf 1 db dynamic range t a = +25 c 57 db ?40 c < t a < +85 c 48 db maximum input level 1 db error C1 dbm minimum input level 1 db error C58 dbm slope C24.3 mv/db intercept 25 dbm output voltagehigh power in p in = C10 dbm 0.86 v output voltagelow power in p in = C40 dbm 1.59 v temperature sensitivity p in = C10 dbm 25 c t a +85 c +0.0033 db/ c C40 c t a +25 c +0.0069 db/ c f = 8.0 ghz 500 ? at tadj to gnd 3 db dynamic range t a = +25 c 60 db ?40 c < t a < +85 c 58 db maximum input level 3 db error 3 dbm minimum input level 3 db error C55 dbm slope C23 mv/db intercept 37 dbm output voltagehigh power in p in = C10 dbm 1.06 v output voltagelow power in p in = C40 dbm 1.78 v temperature sensitivity p in = C10 dbm 25 c t a +85 c +0.028 db/ c C40 c t a +25 c ?0.0085 db/ c output interface vout (pin 6) voltage swing vset = 0 v; rfin = C10 dbm, no load 1 4.9 v vset = 2.1 v; rfin = C10 dbm, no load 1 25 mv output current drive vset = 1.5 v, rfin = C50 dbm 60 ma small signal bandwidth rfin = ?10 dbm; from clpf to vout 600 mhz output noise rf input = 2.2 ghz, C10 dbm, f noise = 100 khz, clpf = 220 pf 90 nv/ hz
ad8318 rev. 0 | page 5 of 24 parameter conditions min typ max unit fall time input level = off to C10 dbm, 90% to 10% 10 ns rise time input level = C10 dbm to off, 10% to 90% 12 ns vset interface vset (pin 7) nominal input range rfin = 0 dbm; measurement mode 2 0.5 rfin = C65 dbm; measurement mode 2 2.1 v logarithmic scale factor C0.04 db/mv bias current source rfin = ?10 dbm; vset = 2.1 v 2.5 a temperature reference temp (pin 13) output voltage t a = 25 c, r l = 10 k ? 0.57 0.6 0.63 v temperature slope C40 c t a +85 c, r l = 10 k ? 2 mv/ c current source/sink t a = 25 c 10/0.1 ma power-down interface enbl (pin 16) logic level to enable device 1.7 v enbl current when enabled enbl = 5 v <1 a enbl current when disabled enbl = 0 v; sourcing 15 a power interface vpsi (pins 3, 4), vpso (pin 9) supply voltage 4.5 5 5.5 v quiescent current enbl = 5 v 50 68 52 ma vs. temperature C40 c t a +85 c 68 ma supply current when disabled enbl = 0 v, total currents for vpsi and vpso 260 a vs. temperature C40 c t a +85 c 350 a 1 c ontroller mode 2 (gain = 1) for other gains, see measure ment mode section of the data sheet.
ad8318 rev. 0 | page 6 of 2 4 absolute maximum ratings table 2. p a r a m e t e r r a t i n g supply voltage: vpso, vpsi enbl, vse t volt age input pow e r (singl e-ended, re: 50 ? ) internal power dissip a tion ja 1 maximum junction temperature operating tem p erature range storage temperature range lead temperature range 5.7 v 0 to vp 12 dbm 0.73 w 55 c/w 125 c C40 c to +85 c C65 c to +150 c 260 c 1 with package die paddle sold ered to thermal pads with vias conne cti n g to i nne r and b o ttom l a yers s t r e s s es a b o v e t h os e lis t e d u n de r a b s o l u t e m a xi m u m r a tin g s m a y ca use pe rm a n en t d a ma g e t o t h e devi ce . t h is i s a st re ss r a t i ng on ly ; f u nc t i ona l op e r a t ion of t h e de v i c e a t t h es e o r an y o t her co n d i t io ns a b o v e t h os e in di ca t e d i n t h e o p era t io na l s e c t io n o f t h is sp e c i f ica t ion is n o t i m plie d . e x p o su re to ab s o lute ma x i m u m r a t i ng c o ndi t i ons for ext e n d e d p e r i o d s ma y a f fe c t de vice r e l i ab ili t y . esd caution esd (electrostatic discharge) sensitive device. ele c tros tatic charg e s 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 circu i try, permanent dama ge may occur on devices subjected to high energy electrostatic discharges. theref ore, prop er esd precautions a r e recommended to avoid perform a nce degradation or l o ss of functiona l ity.
ad8318 rev. 0 | page 7 of 2 4 pin conf iguration and fu nctional descri ptions 04853-002 12 cmip 11 cmip 10 tadj 9 vpso 1 cmip 2 cmip 3 vpsi 4 vpsi 13 temp 8 cmop 14 inhi 7 vset 15 inlo 6 vout 16 enbl 5 clpf ad8318 f i g u re 2. 16-l e ad l e ad f r a m e ch ip s c al e p a ck ag e (lfcs p ) ta ble 3. pi n f u nct i on d e s c ri pt i o ns pin no. mnemonic function 1, 2, 11, 12 cmip d evic e c o mmon (i nput s y stem gr ound). 3, 4, 9 vpsi, vpso p o sitiv e supply v o ltage f o r the d evic e i n put sy stem: 4.5 v to 5.5 v ( v oltage on all pi ns sh ould b e equal) . 5 clpf l oop f i lter cap a citor . 6 vout m e asur emen t and c o n t r o ller output. 7 vse t s e tpoin t i n put f o r c o n t r o l l er m o de , or f eedbac k i n put f o r m e asur emen t m o de . 8 cmop devic e c o mmon ( o utput s y st em gr ound). 10 t a dj t e mpera tur e c o mpensa tion a d justmen t . 13 temp t e mpera tur e sensor o utput. 1 4 i n h i rf i n put. nominal input r a nge: ?60 dbm to 0 db m r e : 50 ? ; ac - c oupled rf input. 15 inl o rf c o mmon f o r inhi; ac - c oupled rf c o mmon. 16 enbl d evic e enabl e . c o nnec t to vpsi f o r nor m al ope ra tion. connec t pin to gr ound f o r disable mode . p a d d l e i n ter n ally c o nn ec ted to cm i p , solder to gr ound.
ad8318 rev. 0 | page 8 of 2 4 typical perf orm ance cha r acte ristics v p = 5 v , t = +25 c, C40 c, +85 c; c lp f = 220 pf ; t ad j = 500 ?; un l e s s o t h e r w is e n o te d . c o l o rs: +2 5 c bl a c k ; C 4 0 c blu e ; + 8 5 c re d 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ? 4 5 ? 35 ?25 ? 15 ?5 5 1 5 04853-003 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) fi g u r e 3 . v ou t and l o g c o nformanc e vs . input a m plitude at 900 mhz, t y pic a l d e v i ce 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ? 4 5 ? 35 ?25 ? 15 ?5 5 1 5 04853-004 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) fi g u r e 4 . v ou t and l o g c o nformanc e vs . input a m plitude at 1. 9 g h z, t y pic a l d e v i ce 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ? 6 5 ? 55 ?45 ? 35 ? 2 5 ? 15 ? 5 5 1 5 04853-005 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) fi g u r e 5 . v ou t and l o g c o nformanc e vs . input a m plitude at 3. 6 g h z, ty p i c a l d e v i c e , t ad j = 5 1 ? 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 04853-006 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) ?65 ? 55 ? 4 5 ? 35 ?25 ? 15 ?5 5 1 5 fi g u r e 6 . v ou t and l o g c o nformanc e vs . input a m plitude at 5. 8 g h z, ty p i c a l d e v i c e , t ad j = 1 0 00 ? 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ? 5 5 1 5 04853-007 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) fi g u r e 7 . v ou t and l o g c o nformanc e vs . input a m plitude at 2. 2 g h z, t y pic a l d e v i ce 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ? 4 5 ? 35 ? 2 5 ? 15 ?5 5 04853-008 p in (dbm) v out (v ) 4.5 ?4.5 ?3.6 ?2.7 ?1.8 ?0.9 0 0.9 1.8 2.7 3.6 e rror (db) fi g u r e 8 . v ou t and l o g c o nformanc e vs . input a m plitude at 8 ghz, t y pic a l d e v i ce
ad8318 rev. 0 | page 9 of 2 4 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ?5 5 1 5 04853-009 p in (dbm) e rror (db) f i gure 9. d i s t ributi on of e rror o v e r t e mpe r atu r e a f ter a m bi ent nor m al iz at io n v s . input a m pl it ude at 90 0 m h z f o r at l e as t 70 d e v i c e s 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ?5 5 1 5 04853-010 p in (dbm) e rror (db) f i g u re 10. d i s t r i but i on of e r r o r at t e m p er at u r e a f ter a m b i ent nor m al iz at io n v s . input a m pl it ude at 19 00 m h z f o r at le as t 7 0 d e v i ces 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ?5 5 1 5 04853-011 p in (dbm) e rror (db) f i g u re 11. d i s t r i but i on of e r r o r at t e m p er at u r e a f ter a m b i ent nor m al iz at io n v s . input a m pl it ude at 2.2 gh z f o r at le as t 70 d e v i c e s 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ?5 5 1 5 04853-012 p in (dbm) e rror (db) f i g u re 12. d i s t r i but i on of e r r o r at t e m p er at u r e a f ter a m b i ent nor m al iz at io n v s . input a m pl it ude at 3.6 gh z f o r at le as t 70 d e v i c e s 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ?5 5 1 5 04853-013 p in (dbm) e rror (db) f i g u re 13. d i s t r i but i on of e r r o r at t e m p er at u r e a f ter a m b i ent nor m al iz at io n v s . input a m pl it ude at 5.8 gh z ( t ad j = 1000 ? ) fo r a t l e a s t 70 d e v i c e s 4.5 ?4.5 ?3.6 ?2.7 ?1.8 ?0.9 0 0.9 1.9 2.7 3.6 ?65 ? 55 ? 4 5 ? 35 ?25 ? 15 ?5 5 04853-014 p in (dbm) e rror (db) f i g u re 14. d i s t r i but i on of e r r o r at t e m p er at u r e a f ter a m b i ent nor m al iz at io n v s . input a m pl it ude at 8 gh z f o r at l e as t 7 0 d e v i ces
ad8318 rev. 0 | page 10 of 24 04853-015 j2 ?j 2 j0.5 ?j0.5 j0.2 ?j0.2 0 0.2 0.5 1 2 start frequency = 0.1ghz stop frequency = 8ghz j 1 ?j 1 5.8ghz 8ghz 3.6ghz 2.2ghz 1.9ghz 0.9ghz 0.1ghz f i gure 15. input i m pedance v s . f r eque nc y ; no t e r m inat io n r e sisto r on in hi 0.07 0 0.01 0.02 0.03 0.04 0.05 0.06 1.4 1.5 1.6 1.7 1.8 04853- 016 v enbl (v) supply current (a) decreasing v enbl increasing v enbl f i gure 16. sup p l y current v s . e n abl e v o ltag e 04853-017 20ns per horizontal division vout gnd 200mv/vertical division pulsed rf input 0.1ghz, ?10dbm f i g u re 17. v ou t p u ls e r e s p ons e tim e . p u ls ed r f input 0. 1 gh z, C 10 d b m; c lpf = o p en 10k 1k 100 10 1 3 10 30 100 300 1k 3k 10k 04853-018 frequency (khz) n o ise spec tr a l d e n s ity ( n v/ h z ) ?40dbm ?20dbm ? 10dbm 0dbm rf off ?60dbm f i gure 18. no ise s p ec tr a l d e ns it y of o u tput; c lpf = o p en 1k 100 10 1 3 10 30 100 300 1k 3k 10k 04853-019 frequency (khz) noise spectral dens ity ( n v/ hz) f i gure 19. no is e s p ec tr a l d e ns it y of o u tput buffer (from clpf to vou t ); c lpf = 0 . 1 f 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ? 5 5 1 5 04853-020 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) f i g u re 20. o u t p ut v o lt ag e st ab il it y v s . sup p ly v o lt ag e at 1 . 9 g h z w h en v p v a ri es by 10%, m u l t iple d e v i c e s
ad8318 rev. 0 | page 11 of 24 gene ral description the ad8318 is a 9-s t a g e dem o d u l a tin g loga r i thmic a m p l if ier , w h ich p r o v ides rf m e a s ur e m e n t and p o w e r am plif ier co n t r o l f u n c tio n s. the desig n is simi lar t o th e ad8313 l o ga r i thmic det e c t o r /c on trol ler . h o w e v e r , th e ad8318 in p u t f r eq uen c y r a nge i s e x te nd e d to 8 g h z w i t h 6 0 d b dy n a m i c r a nge. o t he r im p r o v emen t s i n cl ude: r e d u ce d in t e r c ept va r i ab i l i t y v e rs us t e m p e r a t ur e , in cr ea sed d y n a mic ra n g e a t h i g h er f r eq ue n c i e s , l o w n o i s e m e a s ur em en t a n d co n t r o ll e r o u t p u t (v o u t ) , ad j u s t a b le lo w-p a s s co r n er f r e q uen c y (clp f), t e m p er a t ure s e n s o r o u t p u t (t emp), n e ga ti v e tra n sf e r fun c ti o n s l o p e f o r h i gh e r a c cura c y , a nd 10 n s r e sp on s e t i m e fo r rf b u rst de te c t io n ca p a b i li ty . a b l oc k dia g ra m is s h o w n in fi g u r e 2 1 . temp sensor gain bias slope det det det det inhi inlo iv vout iv vset clpf temp vpsi enbl tadj vpso cmop cmip 04853- 021 f i g u re 21. bl ock d i ag r a m a f u l l y dif f er en t i a l desig n , usin g a p r o p r i et a r y hig h sp e e d s i g e p r o c es s, ext e nds hig h f r eq uen c y p e r f o r ma n c e . i n p u t inhi r e cei v es t h e sig n al w i t h a lo w f r e q uen c y im p e dan c e o f n o minal l y 1200 ? in p a ral l e l wi th 0.7 pf . the maxim u m in p u t wi th 1 db log-co nfo r ma n c e er r o r is typ i cal l y 0 dbm (r e: 50 ? ). the n o is e s p ec tral den s i t y r e f e r r ed t o th e in p u t is 1.15 nv/ hz , w h i c h is eq ui valen t t o a v o l t a g e o f 118 v r m s in a 10. 5 gh z b a n d - wid t h, o r a n o is e p o w e r o f C66 db m (r e: 50 ? ). this n o is e sp e c t r a l d e ns i t y s e t s t h e l o we r l i m i t of t h e dy n a m i c r a nge. h o w e v e r , th e lo w-end acc u rac y o f th e ad8318 is enhan c e d b y sp e c ia l l y sh a p ing t h e de mo du l a t i ng t r ans f e r char ac te r i st ic to p a r t i a l l y c o m p e n s a te for e r rors d u e to i n te r n a l noi s e. t h e i n pu t s y s t e m c o m m o n pi n , c m i p , prov i d e s a q u a l it y l o w i m p e da n c e co nn ecti o n t o t h e p r i n t e d ci r c ui t b o a r d (pcb) g r o u n d t h r o ug h t h e us e o f fo ur p a cka g e pin s . th e p a cka g e p a dd le , w h ich is in t e r n a l ly co n n e c t e d t o t h e cm ip p i n, sh o u ld als o b e g r o u n d e d t o t h e pcb t o r e d u ce t h er mal im p e dan c e f r o m t h e die t o t h e p c b . the loga r i t h mic f u n c t i on is a ppr o x ima t e d i n a p i e c e w is e fashion b y 9 cas c ade d g a in st a g es. (f o r a m o r e co m p reh e n s iv e expla- n a ti o n o f th e loga ri th m a p p r o x im a t i o n , p l ea se r e f e r t o th e ad8307 da t a sheet, a v ailab l e a t w w w .a nalog.com.) th e c e l l s ha v e a n o mina l volt age ga in o f 8.7 d b e a ch, an d a 3 db b a nd w i d t h of 10.5 gh z. u s ing p r e c isio n b i asi n g, t h e ga i n is st a b i l i z e d o v er t e m p era t ur e and s u p p l y va r i a t i o n s . since t h e c a s c ade d gain s t a g es a r e dc-cou ple d , t h e o v eral l dc ga in is hig h . an o f fs et co m p en sa t i o n loo p i s i n c l ud ed t o co rr ect f o r o f fse t s wi th in t h e cas c ade d ce l l s. a t t h e o u t p u t o f e a ch o f t h e g a in st a g es, a s q ua r e -l a w det e c t o r ce l l is us ed t o r e c t if y th e sig n al . the rf sig n al v o l t a g es ar e co n v er t e d t o a f l uc t u a t in g dif f er en t i al c u r r en t ha v i n g a n a v era g e va l u e t h a t i n cr e a s e s wi t h sig n al le vel. a l o n g w i t h t h e ni n e gain st a g es and de te c t o r cel l s, a n addi tio n al det e c t o r is in c l uded a t th e in p u t o f the ad8318, al t o g e th er p r o v idin g a 60 db d y na mic ra n g e . af t e r th e det e c t o r c u r r en t s a r e s u mm e d and f i l t er e d , t h e f u n c t i on i d log 10 (v in /v int e r c ep t ) is fo rm e d a t t h e sum m in g n o d e , w h er e i d is t h e i n t e r n a l ly s e t dete c t o r c u r r en t, v in is t h e i n put s i g n a l vol t age, and v int e r c ep t is t h e i n ter c ep t v o l t a g e (i .e ., w h e n v in = v int e r c ep t , t h e o u t p ut v o l t a g e wo u l d b e 0 v , if i t w e r e c a p a b l e o f go in g t o 0 v).
ad8318 rev. 0 | page 12 of 24 using the ad8318 basic connections the ad8318 is s p ecif ie d f o r o p era t io n u p t o 8 gh z, as a r e s u l t lo w im p e dan c e su p p ly p i n s w i t h ade q u a t e is ol a t io n b e t w e e n f u n c tio n s a r e ess e n t ial . i n the ad8318, th e tw o p o si ti v e s u p p l y p i n s , vps i and vpso , m u st b e co nne c t e d to t h e s a m e p o ten t ia l. the vps i p i n b i as es t h e in p u t ci r c ui t r y , w h i l e t h e vpso b i as es t h e lo w n o is e ou t p ut dr i v er fo r v o u t . s e p a r a te co mm o n s a r e als o in c l ude d in th e de vice . cmo p is us ed as t h e co mm o n f o r t h e output d r ive r s . a l l c o m m on s shou l d b e c o n n e c t e d to a l o w i m p e d a nc e g r o u nd p l a n e. a p o w e r s u p p l y v o l t a g e o f between 4.5 v and 5. 5 v s h o u ld b e a p p l ie d t o vps0 a nd vps1. 100 pf a n d 0.1 f p o w e r s u p p l y deco u p lin g ca p a ci t o rs sh o u ld b e co nn ec t e d c l os e t o eac h p o w e r s u pp l y pi n . ( t h e t w o a d j a c e n t v p s 1 pi ns c a n s h are a p a i r of deco u p lin g ca p a ci t o rs bec a us e o f th eir p r o x imi t y . ) 0 4853-022 12 cmip 11 cmip 10 tadj 9 vpso 1 cmip 2 cmip 3 vpsi 4 vpsi 13 temp 8 cmop 14 inhi 7 vset 15 inlo 6 vout 16 enbl 5 clpf ad8318 c7 100pf c8 0.1 f v s c1 1nf c2 1nf 499 ? (see text) c6 100pf c5 0.1 f v s r1 52.3 ? temp out rf input v s vout f i gure 22. bas i c connec t ions the p a ddle o f t h e ad8318 s lf cs p p a c k a g e is in t e r n al l y co nnec t e d t o c m ip . f o r o p ti m u m th e r m a l a n d e l ectri c al p e r f o r ma n c e , the p a ddle sh o u ld be s o lder e d t o a lo w im p e dan c e gr o u n d p l a n e . enable t o enab le the ad8318, th e e n bl p i n m u s t be p u l l ed hig h . t a k i n g e n b l lo w wil l p u t t h e ad8318 in s l e e p m o de , r e d u cin g c u r r en t co n s um p t io n t o 260 a a t am b i en t. th e v o l t a g e on e n b l m u s t be gr ea t e r th a n 2 v be (~1.7 v) t o e n a b le the device. w h en enab le d t h e de vices dra w s les s t h a n 1 a. w h e n t h e e n bl pi n i s pu l l e d l o w , t h e pi n s o u r c e s 1 5 a . the ena b l e in t e r f ace has hig h in p u t im p e dan c e . a 200 ? re s i st or is p l ace d in s e r i es wi t h t h e e n bl in p u t f o r adde d p r o t ec tion. f i gur e 23 dep i c t s a sim p lif i e d s c h e ma tic o f the e n a b le in t e r f ace . 04853-023 enbl cmip vpsi 2 v be 2 v be discharge enable 40k ? 200 ? 40k ? f i g u re 23. e n bl int e r f ace inpu t sig n al coupling the rf in p u t t o th e ad8318 (i nhi) is sin g le-en d e d and m u s t be ac-co u p l ed . inl o (in p u t co mm on) s h o u ld be ac-co u p l ed t o g r o u n d (s ee f i gu r e 22). s u g g es t e d co u p lin g ca p a c i t o rs a r e 1 nf cera mic 040 2 s t y l e c a p a ci t o rs f o r in p u t f r eq uen c ies o f 1 mh z t o 8 g h z. the co u p ling c a p a ci t o rs s h o u ld b e m o u n t e d clos e t o t h e inhi and inlo p i n s . th es e ca p a c i t o r val u es ca n be in cr e a s e d t o lo w e r th e in p u t s t a g e s h i gh - p a s s cu t o f f f r eq ue n c y . t h e h i gh - p as s co rn e r i s se t b y th e in p u t co u p lin g ca p a c i t o rs and the in t e r n al 1 0 pf hig h - pa s s ca pa c i t o r . t h e d c v o l t a g e o n i n h i a n d in l o w i ll be ab out on e d i o d e volt age d r op b e l o w v ps i . the s m i t h c h a r t in f i gur e 15 sho w s th e ad831 8 s in p u t im p e dan c e vs. f r e q uen c y . t a b l e 4 lis t s t h e r e f l e c t i o n co ef f i - cien t and i m p e d a n c e a t s e le c t f r e q uen c ie s. f o r f i gur e 15 a nd t a b l e 4, t h e 52.3 ? in p u t t e r m in a t io n r e sist o r w a s r e m o v e d . a t dc, th e r e sis t a n c e is typ i cal l y 2 k ? . a t f r e q u e n c i e s u p t o 1 gh z, t h e im p e da n c e is a p p r o x ima t e d as 1000 ? || 0.7 p f . the rf i n p u t pi n s a r e co u p le d to a n e tw o r k g i ven b y t h e sim p lif i ed s c h e ma tic in f i gur e 24. 04853-024 vpsi 2k ? a = 8.6db 20k ? 20k ? current gm stage inlo inhi offset comp 10pf 10pf first gain stage f i gure 24. input inter f ace w h i l e t h e i n p u t ca n b e r e ac t i v e l y ma t c h e d , in ge n e ra l t h is is n o t n e ces s a r y . an ext e r n al 52.3 ? sh u n t re s i stor ( c onne c t e d o n t h e sig n al si de o f t h e i n p u t co u p lin g c a p a ci t o rs, s e e f i gur e 22) co m b in es wi t h t h e re l a ti v e l y hig h in p u t im p e d- a n c e to g i ve an ade q u a te b r o a db a nd 50 ? ma tch.
ad8318 rev. 0 | page 13 of 24 t a bl e 4. i n p u t i m p e danc e f o r s e l e c t f r e q u e nc y s11 f r equenc y mhz real imaginar y impedanc e ? (s eries) 100 0.918 ?0.041 927-j491 456 0.905 ?0.183 173-j430 900 0.834 ?0.350 61-j233 1900 0.605 ?0.595 28-j117 2200 0.524 ?0.616 28-j102 3600 0.070 ?0.601 26-j49 5300 ?0.369 ?0.305 20-j16 5800 ?0.326 ?0.286 22-j16 8000 ?0.390 ?0.062 22-j3 outpu t i n t e rface the v o u t p i n is dr i v en b y a pnp o u t p u t st a g e. an in ter n a l 10 ? r e sis t o r is place d in s e r i es w i t h t h e e m i t t e r fol l o w er o u t p ut an d th e v o ut p i n . t h e ri se tim e o f th e o u t p u t i s lim i t e d m a i n l y b y th e s l ew on cl p f . th e f a l l time is a n rc limi ted s l ew g i v e n b y t h e lo ad ca p a c i t a n c e an d t h e p u l l -do w n r e sist ance a t v o u t . ther e is a n in ter n al p u l l -do w n r e sis t o r o f 350 ?. an y r e sis t i v e lo ad a t v o ut is p l ace d in p a ra l l e l wi th t h e in t e r n al p u l l -do w n re s i stor an d prov i d e s a d d i t i on a l d i s c h a r g e c u r r e n t . 04853-025 + 0.2v 150 ? 200 ? ? 10 ? vout vpso clpf cmop f i g u re 25. o u t p ut inter f ac e setpo i nt i n terfa c e th e v se t input drives the hi gh impedance (250 k ? ) input of an internal op amp . the v se t volta g e appe ars across the in tern al 3.13 k ? resistor to gen e rate i se t . when a portion of v out is applied to vse t , the feedback loop forces ?i d log 10 (v in /v in te r c e p t ) = i se t . if v se t = v out /x, t h en i set = v out /(x 3.13 k ? ). t h e result is v out = (?i d 3. 13 k? x) log 10 (v in /v in te r c e p t ) 04853-026 3.13k ? i set cmop v set f i g u re 26. v s e t int e r f ace the s l o p e is g i ven b y Ci d x 3.13 k ? = C500 mv x. f o r exa m p l e , if a r e sis t o r divider t o g r o u n d is us e d to g e n e ra t e a v set vol t age of v ou t /2, t h e n x = 2. th e s l op e wil l b e s e t t o C1 v/de cade o r C50 mv /db . temperature compensa t i on of o u t p ut voltage the ad8318 f u n c tio n al i t y in c l udes th e ca p a b i l i ty t o ext e r n al l y t r im t h e tem p era t ur e dr if t. a t t a chin g a g r o u n d - re f e re nc e d re s i s t or to t h e t ad j p i n al t e r s a n in t e rn al curr en t , w h i c h work s to mi ni mi z e i n te rc e p t dr i f t v s . te m p e r a t u r e. a s a r e su l t , t h e t ad j re s i stor c a n b e opt i m i z e d f o r op e r a t i o n at dif f er en t f r e q uen c ies. 04853-027 2k ? i comp ~0.4v tadj 2v internal v f i g u re 27. t a dj in t e r f ace a r e sis t o r , n o minal l y 500 ? fo r o p t i mal t e m p era t ur e co m p en s a t i o n a t 2.2 gh z in p u t f r eq uen c y , is co nn ec t e d bet w een th i s p i n a n d gr o u n d (s ee f i gur e 22). t h e v a l u e o f t h is r e sist o r p a r t ia l l y det e r m i n e s t h e m a g n i t ud e o f a n a n a l og co r r e c t i o n co ef f i cien t, w h ich is em plo y e d t o r e d u ce in t e r c ept dr if t. t a b l e 5 lis t s r e c o mmende d r e sis t o r s fo r o t h e r f r e q uen c ies. t h ese r e s i s t o r s h a v e been ch osen t o p r o v i d e t h e be s t o v e r all t e m p era t ur e dr i f t b a s e d o n m e as ur em e n ts o f a di v e rs e p o pu l a t i on of d e v i c e s . the r e l a t i o n s h i p b e t w e e n o u t p u t t e m p era t ur e dr if t a nd f r e q u e nc y i s not l i ne ar a n d c a n n ot b e e a s i ly m o d e l e d. a s a r e su l t , exp e r i m e n t a t io n is r e q u ir e d t o ch o o s e t h e co r r e c t t ad j r e sis t o r a t f r e q uen c ies n o t l i s t e d in t a b l e 5.
ad8318 rev. 0 | page 14 of 24 t a b l e 5. r e co mmende d t ad j resi st o r s f r equenc y r e c o mmen d e d t adj 900 mh z 500 ? 1.9 mh z 500 ? 2.2 gh z 500 ? 3.6 gh z 51 ? 5.8 gh z 1 k ? 8 gh z 500 ? temperature sensor the ad8318 in ter n al l y g e n e ra t e s a v o l t a g e tha t is p r o p o r tio n al- t o -a bs ol u t e-tem p era t ur e (v pt a t ). t h e v pt a t v o lt ag e i s m u lt ip l i e d b y a fac t o r o f 5, r e s u l t in g in a + 2 mv/ c o u t p u t a t t h e temp p i n. the o u t p u t vol t a g e a t 27 c is ty p i cal l y 600 mv . an emi t t e r fol l o w er dr i v es th e temp p i n, as s h own i n f i gu r e 28. 04853-028 1k ? 4k ? cmip internal vpsi temp f i g u re 28. t e mp s e ns or in ter f ac e the i n t e r n al p u l l -do w n r e sis t ance is 5 k?. th e tem p er a t ur e s e ns or h a s a sl o p e of + 2 m v / c. the t e m p s e ns or o u t p u t wil l var y wi th o u t p u t c u r r en t d u e t o in cr e a s e d die te m p er a t ur e. o u tp u t lo ads less t h a n 1 k? wi l l dra w e n ou g h c u r r e n t f r om t h e output st age c a u s i n g t h i s i n c r e a s e to o c c u r . an o u t p ut c u r r en t o f 10 ma wi l l r e s u l t i n t h e v o l t a g e o n th e tem p s e n s o r t o in cr eas e b y 1.5 c, o r ~3 mv . t o g e t t h e b e st p r e c isio n f r o m t h e tem p era t ur e s e n s o r , en s u r e tha t s u p p l y c u r r en t t o ad8318 rema in s fairl y co n s tan t (i . e ., n o he a v y l o a d d r iv e ) . measurement mode w h en t h e v ou t vo lt age or a p o r t i o n of t h e v ou t vol t age i s fe d b a ck t o v s et, t h e de vice op era t es in m e as ur e m e n t m o de . a s s e en in f i gur e 2 9 , th e ad8318 has a n o f fs et v o l t a g e , a n e g a ti ve slo p e, an d a v ou t m e a s ur em en t i n t e r c e p t gr ea t e r th a n i t s i n p u t sig n al ra n g e . 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 2.5 2.0 1.5 1.0 0.5 0 ?0.5 ?1.0 ?1.5 ?2.0 ?65 ? 60 ?55 ? 50 ?45 ? 40 ?35 ? 30 ?25 ? 20 ?15 ? 10 ?5 0 5 04853-029 p in (dbm) intercept error (db) v ou t (v) error 25 c v out 25 c range for calculation of slope and intercept f i g u re 29. t y pic a l o u t p ut v o lt ag e v s . input sig n al the output volt age versus inpu t signal volt age of the ad8318 is l i near-in-db over a multidec ade range. the equatio n for thi s functio n is of t h e form v out = x v slo p e/dec log 10 ( v in / v int e rc e p t ) (1) = x v slope/db 20 log 10 ( v in / v i n tercept ) (2) where: x is t h e fe edbac k factor i n v set = v out /x v int e rc e p t is expressed in v rms . v slope/ dec is no minally C500 mv/decade or ?25 mv/db. v int e rcep t expressed i n dbv is t h e x-ax is i n terc ept of the line ar -i n- db tr a n sfer funct i o n s h o w n in f i gur e 29. v int e rcep t is +7 dbv (+20 db m, re: 50 ? or 2.239 v rms ) for a sinusoidal inpu t signal. th e slope of the transfer fu nctio n ca n be incre a s e d to accomm od ate various con v erte r mv per d b (lsb per d b ) requireme n ts. however, incre a si ng t h e slope may reduc e the dyna mic ra nge. th is is due to the li mita tio n of the mi ni mu m a nd max i mu m o u tp ut vo ltag es, d e te rmin ed by the c h osen sc aling factor x. th e m i n i mu m value fo r v out is x v off s e t . an offset voltage, v offse t , of 0.5 v is inter n ally a d ded to t h e detector signal. v out(m i n) = ( x v offset ) t h e ma xi mum output volta g e is 2.1 v x, and cannot exceed 400 mv below the positive supply.
ad8318 rev. 0 | page 15 of 24 v out(m a x ) = (2.1 v x ) when x < ( v p C 400 mv)/(2.1 v) v out(m a x ) = ( v p C 400 mv) when x ( v p C 400 mv)/(2.1 v) wh en x = 1, th e typical output vo ltage s w ing is 0.5 v to 2.1 v. the output volt age sw ing can b e modeled by us ing t h e equ a t i ons above and restri cted by the follo wing equation: v out(m i n) < v out < v out(m a x) for the case w h en x = 4 and v p = 5 v ( x v offset ) < v out < ( v p C 400 mv) (4 0.5 v) < v out < (2.1 v 4) 2 v < v out < 4.6 v for x = 4, slope = ?100 mv/db ; v out can sw in g 2.6 v, a nd usable dy n a m i c r a nge will be r e duce d to 26 db fr o m 0 dbm to C26 db m. the slope is v e ry stable ver sus process and te mperature variatio n . when base-10 logarithms are used , v sl ope / de c a de represents the v olts/decade. a dec a de corresponds to 20 db, v sl ope / de c a de /20 = v sl ope / db represents the s l ope i n volts/ d b. as note d i n t h e equatio n s abov e, the v out volt age h a s a neg a t i ve slope. this is al so the correct sl op e polarity to control the g a i n of ma ny po wer a m plifi e r s a nd o t her vga s in a nega ti ve fee d b a ck co nfigur at io n. s i nce bo th t h e sl o p e an d i n ter c e p t var y slig htly wit h frequency , it is reco mme n d ed to refer to t h e spec ifica t ion pages for applic atio n specif ic va lues for slope and int e rcept. althoug h demo dula ti ng log a m ps respond to i n put sig n al voltage, not i n p u t sig n al power, it is cus t omary to discuss the ampl itu d e of high frequency signal s in terms o f power. in this case, the charac teristic im pedance of the syste m , z o , must be know n to conv e r t voltages to th eir correspon d i n g power levels. star ti ng w i t h th e defi ni tio n s o f dbm an d dbv, p(dbm) = 10 log 10 (v rms 2 /(z o 1 mw)) (3) v(dbv) = 20 log 10 (v rms /1 v rms ) (4) expanding equ a tio n 3 gives us: p(dbm) = 20 log 10 (v rms ) ? 10 log 10 ( z o 1 mw) (5) an d giv e n equ a tio n 4, w e ca n r e wr ite equ a t i o n 5 as p(dbm) = v(dbv) ? 10 log 10 (z o 1 mw) (6) for example, p in te r c e p t for a sinusoidal inp u t signal expressed i n t e rms of db m (dec ibels referre d to 1 mw), in a 50 ? system is: p int e rcep t (dbm) = v int e rcep t (dbv) C 10 log 10 (zo 1 mw) (7) = +7 dbv ? 10 log 10 (50 10 -3 ) = +20 dbm further in formatio n on the in tercept variation d e pen d en ce upon waveform can be fo und in the ad8313 and ad8307 dat a sheets . ad8318 data sheet spec ifications for slope and intercept hav e be en c a lcu l ate d base d on a best str a ig ht line fit using mea s ured da ta i n th e ?10 db m to ?50 dbm range (see figure 29). device calibration and error calculation th e me as ur e d t r a n sf er fun c tio n o f t h e ad8318 a t 2.2 gh z is s h o w n in fi g u r e 3 0 . th e f i g u r e s h o w s plo t s o f b o t h o u tp ut vo l t age ve rsus i n p u t p o we r and c a l c u l a t e d er r o r v e r s us in p u t p o w e r . a s t h e in p u t p o w e r va ries f r o m ? 65 db m to 0 db m, t h e output v o lt a g e v a r i e s f r om 2 v t o ab out 0 . 5 v . 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 2.5 2.0 1.5 1.0 0.5 0 ? 0.5 ? 1.0 ? 1.5 ? 2.0 ? 6 5 ? 60 ? 5 5 ? 45 ? 4 0 ? 35 ? 3 0 ? 25 ? 2 0 ? 15 ? 5 0 5 04853- 030 p in (dbm) intercept pin 1 pin 2 v out (v ) error ( d b) v out +25 c v out ?4 0 c v out +85 c error +25 c error ? 4 0 c error +85 c v out 2 v out 1 vout ideal = slope (p in ? intercept) slope = (vout 1 ? vout 2 )/(pin 1 ? pin 2 ) intercept = pin 1 ? (vout 1 /slope) error (db) = (vout vout ideal )/slope f i g u re 30. t r ans f er f u nc t i on at 2 . 2 g h z b e ca us e s l o p e and in t e r c ep t v a r y f r o m de vi ce to de v i ce , b o a r d-l e vel ca lib r a t ion m u st b e p e r f o r m e d to a c hie v e hig h acc u rac y . w e can r e wr i t e t h e e q u a t i o n fo r o u t p u t v o l t a g e f r o m t h e p r e v i o u s s e c t ion usin g a n in t e r c ep t exp r ess e d i n dbm v ou t = slo p e ( p in C in t e r c e p t ) (8)
ad8318 rev. 0 | page 16 of 24 i n ge n e ra l, t h e c a li b r a t ion is p e r f o r m e d b y a p ply i n g t w o k n own sig n al lev e l s t o t h e ad8318 s in p u t an d m e as ur in g the co r r es p o n d in g o u t p ut v o l t a g es. the cal i b r a t ion p o in t s a r e ge ne r a l l y cho s e n to b e w i t h i n t h e l i ne ar - i n - d b op e r a t i n g r a nge of t h e de vice (s e e f i gur e 30). c a lcu l a t ion o f s l o p e a nd i n t e r c ept is do ne usin g t h e e q u a t i o n s slo p e = ( v ou t 1 ? v ou t 2 )/( p in1 C p in2 ) (9 ) in t e r c e p t = p in1 ? v ou t 1 / slo p e (10) on ce sl o p e and in t e r c e p t h a v e b e e n cal c ula t ed , a n eq ua t i o n ca n b e wr i t t e n w h ich w i l l a l lo w ca lc u l a t ion o f a n (u n k n o wn) i n p u t p o w e r b a s e d on t h e o u t p ut v o l t a g e o f t h e det e c t o r . p in (unkn o wn) = v ou t (m e a s u r e d)/ slo p e + in t e r c e p t (11) u s i n g th e e q ua ti o n f o r t h e i d ea l o u t p u t v o l t a g e ( 7 ) a s a r e f e r e n c e , t h e log co nfo r ma n c e er r o r o f t h e m e as ur e d da t a can b e calc u l a t ed: er r o r (db) = ( v ou t (me a s u re d) ? v ou t (i d e al ) )/ slo p e (12) f i gur e 30 in cl u d es a plo t o f t h e er r o r a t 25c, t h e tem p era t ur e a t w h ich t h e log a m p is ca l i b r a t e d . n o t e t h a t t h e e r r o r is n o t zer o . t h i s i s beca use th e log a m p does n o t pe rf ectl y f o llo w th e i d eal v ou t ve rsu s p in eq ua ti o n , ev en w i t h i n i t s o p e r a t i n g r e gi o n . th e e r r o r at t h e c a l i b r at i o n p o i n t s ( ? 12 dbm and ? 52 db m in this cas e ) wi l l , h o w e ver , b e e q u a l to zer o b y def i ni t i o n . f i gur e 30 als o in cl udes er r o r plo t s fo r t h e o u t p u t v o l t a g e a t ?40c an d +85 c. th es e er r o r plo t s a r e calc u l a t e d usin g t h e slo p e an d in t e r c ep t a t 25c. thi s is co n s ist e n t w i t h c a lib r a t ion i n a mas s -p r o d u c t io n e n v i r o nm en t w h er e cal i b r a t i o n a t te m p e r a t u r e i s not pr a c t i c a l. selecting calibratio n po ints to impro v e accuracy over a reduced rang e i n s o m e a p pli c a t io n s v e r y hig h acc u rac y is r e q u ir e d a t j u st on e p o we r l e vel or ove r a re d u c e d i n put r a nge. f o r e x am pl e, i n a w i r e le s s tra n sm i t t e r , th e a c cura c y o f th e h i gh po w e r a m p l i f i e r (hp a ) will be m o s t cr i t ical a t o r c l ose t o f u ll p o w e r . f i gur e 31 s h o w s th e s a me m e asur ed da t a as f i g u r e 30. n o tice tha t acc u rac y is v e r y hig h f r o m ?10 db m t o ?3 0 db m. b e lo w ?30 dbm t h e er r o r in cr e a s e s t o a b o u t ?1 db . th is is b e ca us e t h e calib r a t ion p o in ts ha v e be en c h a n g e d t o ?14 db m an d ?26 db m. 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.6 0.4 0.2 2.5 2.0 1.5 1.0 0.5 0 ?0.5 ?1.0 ?1.5 ?2.0 ?2.5 ?65 ? 60 ?55 ? 45 ?40 ? 35 ?30 ? 20 ?10 ? 5 0 5 04853-031 p in (dbm) pin 1 pin 2 v out (v ) e rror (d b) error +25 c error ?40 c error +85 c v out +25 c v out ?40 c v out +85 c vout 2 vout 1 f i g u re 31. o u t p ut v o lt ag e and e r r o r v s . p in wi th 2 - p o i n t cal i b r a tio n a t C1 0 db m and C 30 d b m c a l i b r at i o n p o i n t s s h o u l d b e c h o s e n t o s u i t t h e ap p l i c at i o n a t h a n d . i n g e n e r a l , t h o u g h , t h e c a l i b r a t i o n p o i n t s s h o u l d ne v e r b e ch os en in t h e n o nli n e a r p o r t io n o f t h e log a m p s tra n sf er f u n c tion (a bo v e ?5 dbm o r b e lo w ?60 db m in this cas e ). f i gur e 32 s h o w s h o w cal i b r a t ion p o in ts can be ad j u s t e d t o i n c r e a s e dy n a m i c r a nge, b u t a t t h e e x p e ns e of l i ne ar it y . i n t h is cas e t h e ca l i b r a t ion p o i n ts fo r slo p e an d i n ter c ep t a r e s e t a t ?4 dbm an d ?60 dbm. t h es e p o in t s a r e a t t h e end o f t h e d e v i c e s l i ne ar r a nge. o n c e ag ai n a t 2 5 c , we s e e an e r ror of 0 db a t t h e cal i b r a t io n p o in ts. n o t e als o t h a t t h e ra n g e o v er whic h t h e ad8 318 ma in t a in s an er r o r o f < 1 db is ext e n d ed t o 60 db a t 25c and 58 db o v er t e m p era t ur e . th e dis a d v a n t a ge o f t h is a p p r o a ch is t h a t li n e a r i t y su f f ers, es p e c i al l y a t t h e t o p end o f t h e i n p u t ran g e . 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 60 ?55 ? 50 ?45 ? 40 ? 3 5 ? 30 ? 2 5 ? 20 ? 1 5 ? 10 ? 5 0 5 04853-038 p in (dbm) v out (v ) 2.5 ? 2.5 ? 2.0 ? 1.5 ? 1.0 ? 0.5 0 0.5 1.0 1.5 2.0 e rror (db) v out +25 c v out ?40 c v out +85 c error +25 c error ?40 c error +85 c 58db dynamic range ( 1db error) f i g u re 32. d y n a mic rang e e x tens ion by choos ing cal i br a t ion p o i n t s that a r e c l os e to th e e n d of th e li ne ar range a n ot he r w a y of pre s e n t i n g t h e e r ror f u nc t i on of a l o g am p det e c t o r is sh o w n in f i gur e 33. i n this cas e , t h e db er r o r a t h o t and cold te m p er a t ur es is c a lc u l a t e d wi t h r e sp e c t t o t h e
ad8318 rev. 0 | page 17 of 24 o u t p ut v o l t a g e a t am b i e n t. this is a k e y dif f er e n ce in com p a r is o n t o th e p r evio u s p l o t s. u p t o n o w , al l er r o rs ha v e been c a lc u l a t e d w i t h r e s p ec t t o t h e id eal tra n s f e r fun c ti o n a t a m b i en t . w h en we us e t h is al t e r n a t i v e t e chniq u e , t h e er r o r a t am b i en t becom e s b y def i ni tion eq ual t o 0 (s ee f i gur e 33) . t h i s w o uld be vali d i f th e dev i ce tra n sf e r fun c tio n pe rf ectl y fol l o w e d t h e i d e a l v ou t = s l o p e (p in-i n t er cep t ) eq ua tio n . h o w e ver since a log a m p in p r ac t i ce wi l l n e ver p e r f e c t l y f o l l o w t h is e q u a t i on (esp e c ia l l y o u tsid e o f i t s li n e a r o p era t in g ran g e), t h i s pl ot te nd s t o ar t i f i c i a l ly i m prove l i ne ar i t y a n d e x te nd t h e dy n a m i c r a nge. t h i s pl ot i s a u s e f u l to o l for e s t i m a t i ng t e m p e r a t u r e d r ift a t a pa r t i c ul a r po w e r l e v e l w i th r e s p ect t o th e (n o n -ideal) out p ut v o ltag e a t am b i en t. h o w e v e r , t o ac hiev e this le vel o f acc u r a c y in a n e nd a p pl ica t ion w o u l d re q u ir e ca l i b r a t i o n a t m u l t i p le p o in ts in t h e d e vice s o p era t i n g ra n g e . 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 60 ?55 ? 50 ?45 ? 40 ? 3 5 ? 30 ? 2 5 ? 20 ? 1 5 ? 10 ? 5 0 5 04853-032 p in (dbm) v out (v ) 2.5 ?2.5 ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 1.0 1.5 2.0 e rror (db) v out +25 c v out ?40 c v out +85 c error +25 c wrt v out error ? 4 0 c wrt v out error +85 c wrt v out f i gure 33. e rror v s . t e m p er ature w i th res p ec t to o u tput v o ltag e at 2 5 c d o e s no t t a k e i n to a c c o unt t r a n sfer f u nct i o n s no nli n ea ri ties a t 25 c v a ri at i o n in t e mp erat ure d r i f t f r o m d e v i ce to device f i g u re 3 4 show s a pl ot of output vo lt age a n d e r ror f o r m u lt ipl e ad8318 devices, m e as ur ed in t h is cas e a t 5.8 g h z. the co n c e n t r a t io n of b l ack er r o r plo t s r e p r es en ts t h e p e r f o r ma n c e o f th e po p u la ti o n a t 25 c (s lop e a nd i n t e r c ep t has b e en cal c ul a t ed f o r e a c h devi ce ). th e r e d a n d b l ue pl o t s o f e r r o r i n d i c a t e t h e me a s u r e d b e h a v i or of a p o pu l a t i on of d e v i c e s ove r t e m p era t ur e . this s u g g es ts a rang e o n t h e dr if t ( f r o m de vice t o de vice) o f 1.2 db . 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 55 ?45 ? 35 ? 2 5 ? 15 ? 5 5 1 5 04853-050 p in (dbm) v out (v ) 2.0 ?2.0 ?1.6 ?1.2 ?0.8 ?0.4 0 0.4 0.8 1.2 1.6 e rror (db) f i g u re 34. o u t p ut v o lt ag e and e r r o r v s . t e mpe r at u r e ( + 2 5 c , C 4 0 c, and +8 5c ) of a p o pu la t i on of d e v i ces m e as ur ed at 5. 8 gh z temperature drift at different temperatures f i g u re 3 5 show s t h e l o g sl op e a n d e r ror ove r tem p e r a t u r e f o r a 5.8 gh z in p u t sig n al . er r o r d u e t o dr if t o v er t e m p era t ur e con s is t e n t l y r e ma i n s w i t h i n 0.5 db , an d onl y b e g i n s t o exce e d t h is limi t w h e n t h e am b i en t tem p er a t ur e dr o p s b e lo w ? 20 c. f o r a l l f r e q uen c ies w h en u s in g a r e d u ce d t e m p er a t ur e ra n g e hig h er m e as ur e m e n t acc u rac y is achie v ab le. 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 ?65 ? 60 ?55 ? 50 ?45 ? 40 ? 3 5 ? 30 ? 2 5 ? 20 ? 1 5 ? 10 ? 5 0 5 04853-039 p in (dbm) out 2.5 ? 2.5 ? 2.0 ? 1.5 ? 1.0 ? 0.5 0 0.5 1.0 1.5 2.0 e rror (db) v (v ) vapc +25c vapc 0c error ?10c vapc ? 4 0 c vapc +70c error ?20c vapc +85c error +25 c error 0 c vapc ?20c error +85 c vapc ? 1 0 c error ?40c error +70 c f i gure 35. t y pic a l d r if t at 5.8 gh z fo r v a ri ous t e mper atu r es setti ng th e outpu t s l ope in measurement mode t o o p er a t e i n me as ur emen t mo de , v o u t m u s t b e co nne c t e d to v s et . this y i elds t h e n o m i na l lo ga r i t h mic sl op e of a ppro x i m a t ely ? 2 5 m v / d b . t h e output s w i n g co r r esp o n d in g to t h e sp e c if ie d i n p u t ran g e wi l l t h e n b e a p p r o x ima t e l y 0.5 v t o 2.1 v . the s l o p e and o u t p u t s w ing
ad8318 rev. 0 | page 18 of 24 ca n b e i n cr e a s e d b y placin g a resisto r divider b e tw e e n v o u t an d v s e t ( i . e . , one re s i stor f r om v o u t to v s e t an d o n e r e sis t o r f r o m v s et t o co mm on). f o r exa m p l e , if tw o eq ual r e sis t o r s a r e us ed (e .g., 10 k?/1 0 k?), th e s l o p e wil l do ub le t o a pprox i m a t el y ? 50 mv /db . the in p u t i m p e dan c e o f v s e t is a p p r o x ima t e l y 500 k?. s l o p e s e t t in g r e sis t o r s sho u ld be k e p t b e lo w ~50 k? to p r e v en t t h is i n p u t i m p e dan c e f r o m a f fe c t in g t h e r e s u l t i n g s l op e . w h en i n cr e a sin g t h e s l o p e , t h e ne w o u t p ut v o l t a g e ra n g e cann ot exce e d t h e o u t p u t v o l t a g e swi n g c a p a b i li ty o f th e o u t p u t st a g e . ref e r t o t h e m e as ur emen t m o de s e c t ion of th e da ta sh ee t . 04853-033 vout ad8318 50mv/db vset 10k ? 10k ? f i gu r e 3 6 . i n cr ea si ng th e s l o p e response time capability the ad8318 has a 10 n s r i s e /fal l time c a p a b i l i ty (10% C 90%) f o r in p u t p o w e r sw i t chin g b e tw e e n t h e n o is e f l o o r and 0 dbm. this c a p a b i li ty ena b les rf b u rst m e a s ur em e n ts a t r e pe ti ti o n ra t e s t o b e y o n d 60 mh z . i n m o s t m e a s ur e m e n t a p p l ic a t ion s , th e ad8318 wil l ha v e a n ext e r n al c a p a ci t o r co nne c t e d to c l pf to p r o v ide addi t i o n a l f i l t er in g fo r v o u t . h o w e v e r , th e us e o f th e c l p f ca pa ci t o r s l o w s t h e r e s p o n se t i m e as do es st r a y ca p a ci t a n c e on v o ut. f o r a n a pplica t ion r e q u ir i n g m a xi m u m r f b u r s t d e t e cti o n ca pa b i li t y , th e clp f c a pa ci t o r p i n s h o u ld b e lef t un co nne c t e d . i n this cas e , t h e in teg r a t ion f u n c tion is p r o v ided b y t h e 700 ff o n -c hi p c a p a ci t o r . ther e is a 10 ? in t e r n a l r e sist o r in s e r i es wi t h t h e o u t p ut dr i v er , a n ex ter n a l 40 ? b a ck-ter mina t i n g r e sisto r sh ou ld b e a dde d i n s e r i es a t t h e o u t p u t w h e n dr iving a 50 ? co axia l ca b l e . t h e b a ck - t e r m ina t in g r e sis t o r sh o u ld be place d c l os e t o the v o ut p i n. the ad8318 has th e dr i v e c a p a b i li ty t o dr i v e a 50 ? lo ad a t the e n d of t h e c o a x i a l c a bl e or t r ans m i s s i on l i ne w h e n b a c k t e r m ina t ed . s e e f i gur e 37. the cir c ui t dia g ra m in f i gur e 37 s h o w s t h e ad8318 us ed wi th a hig h sp e e d com p a r a t o r cir c ui t. the 40 ? s e r i es r e sis t o r a t t h e o u t p u t o f th e ad8318 com b in es wi th an in t e r n al 10 ? t o p r o p erl y ma t c h t o t h e 50 ? i n pu t o f t h e com p ara t o r . 04853-040 pulsed rf input 1nf +5v 40 ? 100 ? 100 ? 50 ? 50 ? 1nf 52.3 ? inhi inlo vout vpos gnd ad8318 vset adcmp563 +5v ? 5.2v ?5.2v v ref = 1.8v?1.2v 50 ? 50 ? comparator output ad8318 output f i g u re 37. a d 8 3 1 8 o p er at ing w i t h t h e hig h spe e d a d c m p5 63 co mp ar ato r 04853-041 0 100 200 300 400 500 600 700 800 time (ns) ad8318 output comparator output pulsed rf input ? 50db ? 30db ?20db ?10db f i gur e 3 8 . p u l s e r e sp o n se o f ad831 8 and c o m p ar at or for rf p u l s e s o f v a r y ing a m pl it ude s f i gur e 38 s h o w s th e r e s p on s e o f th e ad8318 and the co m p a r a t o r f o r a 500 mh z p u ls ed sin e wa v e o f va r y in g a m p l i t udes. the o u t p u t l e v e l o f th e ad8318 is t h e sig n al s t r e n g t h o f t h e i n p u t sig n a l . f o r a p plic a t ion s w h er e t h es e rf b u rst s are ve r y s m a l l, t h e out p ut l e vel w i l l not c h ange b y a la rge am o u n t . u s in g a com p a r a t o r is b e n e f i cia l b e ca us e i t wil l t u r n the o u t p u t o f t h e log am p in t o a limi t e r - li k e sig n al . contr o ller mode the ad8318 p r o v ides a con t r o l l er m o de f e a t ure a t t h e vo u t p i n . u s i n g v set for t h e s e t p oi n t volt age, i t i s p o ss i b l e f o r th e ad8318 t o co n t r o l s u bsy s t e m s , s u ch as p o w e r a m plif iers (p a s ) , va r i a b le ga i n am plif iers (v g a s), o r va r i a b le v o l t a g e a t t e n u a t o r s (vv a s) tha t ha ve ou t p u t p o w e r tha t in cr eas e s mo n o t o nical l y wi t h r e s p ec t t o th eir ga in co n t r o l sig n al . t o o p er a t e i n con t r o l l er m o de , t h e li nk b e tw e e n v s et an d v o u t is b r ok e n . a s e t p oin t v o l t a g e is a p plie d to t h e v s et in p u t; v o u t is co nne c t e d t o t h e ga in con t r o l t e r m ina l o f t h e v g a and t h e dete c t o r s rf i n p u t is con n e c te d to t h e o u t p ut o f t h e v g a (usua l ly usin g a d i r e c t io na l co u p ler a nd s o me add i t i o n a l a tten u a t io n). b a s e d on t h e def i n e d r e la ti o n s h i p be tw ee n v ou t a nd t h e rf i n p u t sig n al w h en t h e de vice is in m e as ur em en t m o de , th e ad8318 wi l l ad j u s t t h e volt age on v o u t ( v ou t i s now an e r ror am pl i f i e r out p ut ) un t i l t h e le ve l a t t h e rf i n p u t cor r es p o n d s t o t h e a p plie d v set . w h en t h e ad8318 o p er a t es in con t r o l l er m o de , th er e is n o def i n e d r e l a t i o n shi p b e tw e e n v set and v ou t vol t age ; v ou t wi l l s e t t le to a va l u e t h a t r e su l t s i n t h e co r r e c t in pu t s i g n a l l e v e l ap p e a r i n g at i n h i / i n l o . i n o r d e r f o r this o u t p u t p o w e r co n t r o l lo o p t o b e s t a b le , a g r o u n d -r efer en ce d c a p a ci t o r m u s t b e co nn e c t e d t o t h e c fl t pi n . this c a p a ci t o r in t e g r a t es t h e er r o r sig n al (w hich is ac t u al l y a c u r r en t) t h a t is p r es en t w h en t h e lo o p is n o t b a l a n c e d .
ad8318 rev. 0 | page 19 of 24 04853-034 rfin vga/vva gain control voltage directional coupler attenuator inhi vset inlo clpf vout ad8318 52.3 ? 1nf c flt 1nf dac f i gur e 3 9 . ad83 18 c o ntr o ll er mo de decreas i ng v se t , whic h co r r e spo nds to de ma n d i n g a hig h er signal from the vga, wi ll te nd to incre a se v out . the gain control voltage of the vg a mu st ha ve a pos i ti v e sens e th at is incre a si ng ga in control voltage incre a ses g a i n . the basic co nnec tio n s f o r o p era t in g t h e ad83 18 as a n a n alog co n t r o l l er wi t h th e ad8367 a r e s h o w n in f i gure 40. the ad83 67 is a lo w f r eq uenc y t o 500 mh z v g a wi th 45 db o f d y na mic ra n g e . this co nf igura t io n is v e r y simi la r t o t h e o n e sh own in f i gur e 39. the ga in o f th e ad8367 is co n t r o l l ed b y th e v o l t a g e a p p l ie d t o th e g a in p i n. this v o l t a g e , v gai n , is s c a l e d li n e a r -i n- db w i t h a sl op e of 2 0 m v / d b a n d r u ns f r om 5 0 m v a t C 2 . 5 d b of g a i n , up t o 1.0 v a t +42. 5 db . the in co min g rf sig n al t o th e ad8367 has a va r y in g a m p l i t ude le v e l ; r e ceivin g a nd de m o d u l a tin g i t wi th t h e lo w e s t p o s s ib le er r o r r e q u ir es tha t t h e sig n al l e v e l s b e o p t i mize d fo r t h e hig h e s t sign al-t o-n o ise ra tio (s n r ) f e e d in g in t o t h e a n alog-t o-d i gi tal co n v er t e r s (ad c ). t h is can be acco m p lish e d b y usin g a n a u t o ma tic ga in co n t r o l (a gc) lo o p . i n f i gur e 4 0 th e v o l t a g e o u t p u t o f th e ad8318 is us ed to m o dif y th e gain o f th e ad8367 un til t h e in comin g rf sig n al p r o d uces an o u t p u t v o l t a g e tha t is e q u a l to t h e s e tp oi n t volt ag e v set . 04853-047 +3v inpt vout vpos gnd gain ad8367 vga hplf rf input signal rf output signal +5v vset clpf inhi vpos gnd ad8318 vout inlo r1 1k ? 1nf 1nf 0.1 f c flt 100pf 100mhz bandpass filter 174 ? r2 261 ? r hp 100 ? c hp 100pf dac +v set setpoint voltage 57.6 ? f i gure 40. a d 8 3 1 8 o p er at ing i n control l er mod e to pr o v i d e autom a ti c g a in c o ntrol f u nc t i onalit y in co mbin ation with the ad8367 this a g c lo o p is ca p a b l e o f con t r o l l in g sig n a l s o v er ~45 db d y na mic ran g e . the o u t p u t o f t h e ad8367 is desig n e d t o dr i v e lo ads 20 0 ?. a s a r e s u l t , i t is n o t n e ces s ar y t o us e th e 53.6 ? r e sis t o r a t t h e in p u t o f t h e ad8318; t h e n o minal in p u t im p e dan c e o f 2 k? is s u f f icien t . i f t h e ad8367 s o u t p ut is t o b e dr i v i n g a 50 ? lo ad , such as an os ci l l os co p e o r sp e c t r um a n a l y z er , a sim p le r e sist i v e divider n e tw o r k can be us e d . n o te tha t t h e di vider us ed in f i gur e 40 has a n in s e r t io n los s o f 11.5 db . f i g u re 4 1 show s t h e t r ans f e r f u n c t i on of output p o we r ve rsu s v set v o l t a g e f o r a 100 mh z sin e wa ve a t ?40 db m in t o t h e ad836 7. 0 ?60 ?55 ?50 ?45 ?40 ?35 ?30 ?25 ?20 ?15 ?10 ?5 1.2 ? 1.2 ? 1.0 ? 0.8 ? 0.6 ? 0.4 ? 0.2 0 0.2 0.4 0.6 0.8 1.0 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 04853- 048 v set (v) error (db) p out (d bm) f i gur e 4 1 . ad83 67 output p o w e r vs . ad8 318 s e tp oi nt v o lta g e i n o r der f o r th e a g c lo o p t o r e ma in lo ck e d , the ad8318 m u s t t r ack t h e e n v e l op e o f t h e v g a s o u t p ut si g n al a nd p r o v ide t h e n e c e s s a r y v o l t a g e le v e l s t o th e ad8 367 s ga in co n t r o l in p u t. f i gur e 42 s h o w s an os cil l os co p e s c r e en sh o t o f th e a g c lo o p dep i c t e d in f i gur e 40. a 50 mh z sin e wa ve wi t h 50 % am m o d u l a tion is a p p l ied t o t h e ad8367. the output s i g n a l f r om t h e v g a i s a c o nst a n t e n vel op e s i ne wa ve w i t h an am pli t ude co r r esp o ndin g t o a s e t p o i n t vol t a g e a t t h e ad8318 o f 1.0 v . f i gure 42. o s ci ll oscope s c r e enshot s h o w i n g a n a m mod u lated input si gnal to the ad836 7 . the ad83 18 tr acks the en v e lo p e o f thi s i n p u t s i g n al and a p pl ies t h e a p propr i at e vo l t ag e t o ens u r e a c o ns t a nt out p ut fr om the ad83 67 .
ad8318 rev. 0 | page 20 of 24 t h e 45 d b co n t r o l ra n g e is co n s t a n t f o r th e ran g e o f v set v o l t a g es. th e in p u t p o w e r lev e l s t o th e ad8367 m u s t be o p t i mi ze d to achie v e t h i s ra n g e. i n f i gur e 43 t h e mini m u m an d max i m u m i n put p o we r l e vel s are show n v s . s e tp oi n t vol t age. 10 ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.2 1.3 1.4 1.5 04853-049 v set (v) p in (dbm) maximum input level minimum input level f i g u re 43. s e t p oi nt v o lt ag e v s . input p o we r . o p t i m a l s i g n al leve ls m u s t be used to a c hi eve the full 4 5 db dyn a mi c r a ng e c a p a bi liti e s of the a d 83 6 7 . i n so m e c a se s , i t m a y be f o u n d th a t i f v gai n is >1.0 v i t ma y ta k e a n un usuall y lo n g tim e f o r th e a g c loo p t o r e co v e r ; th a t i s , th e o u t p u t o f th e ad8318 wil l r e ma in a t an a b n o r m al l y hig h val u e and t h e g a i n w i l l b e s e t to i t s ma x i m u m l e vel. a vol t age d i v i de r i s p l ace d betw e e n th e o u t p u t o f the ad8318 and t h e ad8367 s gain p i n t o ens u r e tha t v gai n wil l n o t excee d 1.0 v . i n f i gur e 40, c hp and r hp a r e conf igur ed t o r e d u ce os cil l a t ion an d d i s t or t i on du e to h a r m on i c s a t h i g h e r g a i n s e tt i n g s . s o me addi t i o n a l f i l t er in g is r e co m m e n de d b e tw e e n t h e o u t p ut o f t h e ad8367 an d t h e in p u t o f th e ad8318. this wil l h e l p t o decr eas e th e o u t p u t n o is e o f th e ad836 7, whic h ma y r e d u ce t h e d y na mic ra n g e o f th e lo op a t hig h er ga in s e t t in gs (smal l er v set ). resp on s e t i m e a nd t h e am o u n t o f sig n a l in teg r a t io n a r e co n t r o l l ed b y c fl t th i s fun c t i o n ali t y i s a n alogo u s t o th e fe e d b a ck c a p a ci t o r a r o u n d a n i n t e g r a t in g a m pl if ier . w h i l e i t is p o s s i b le t o us e l a rg e ca p a ci t o rs fo r c fl t , in m o st a p plic a t ion s val u es un der 1 nf wi l l p r o v ide s u f f i cien t f i l t er i n g. c a li b r a t io n in c o n t r o l l er m o de is simi la r t o t h e m e t h o d us e d in m e a s ur e m en t m o de . a si m p le tw o-p o in t ca l i b r a t io n can b e don e by a p p l y i n g t w o k n ow n v set vol t a g es o r d a c c o des an d m e as ur in g t h e ou t p ut p o w e r f r o m t h e v g a. slo p e an d in t e r c ep t c a n th e n b e c a l c ul a t ed w i th th e f o ll o w i n g e q ua t i o n s . slo p e = ( v set 1 ? v set 2 )/( p ou t 1 ? p ou t 2 ) (13) in t e r c e p t = p ou t 1 ? v set 1 / slo p e (14) v set = slo p e ( px ? in t e r c e p t ) (15) m o r e info r m a t io n o n a g c a p plica t ion s can b e fo un d i n t h e ad8367 d a ta sh eet. character i zation setups and m e thods the g e n e ral ha rd wa r e co nf igur a t io n us e d f o r th e ad8318 c h a r ac t e r i za tio n is s h o w n in f i g u r e 45. th e p r ima r y s e t u p us e d fo r cha r ac t e r i za t i on wa s me asur emen t mo de. t h e c h a r a c t e ri za ti o n boa r d i s si m i la r t o th e cus t o m er ev al ua ti o n b o a r d w i th th e e x c e p t i o n t h a t th e r f in h a d a r o s e n b e r g e r s m a co nn ec t o r a nd r10 was c h a n g e d t o a 1 k? r e sis t o r t o r e m o v e ca b l e c a p a ci t a n c e f r o m t h e b e n c h cha r ac t e r i za t i o n s e t u p . slo p e an d in t e r c ept w e r e calc u l a t e d usin g lin e a r re g r e s s i on f r om ? 5 0 d b m to ? 1 0 d b m . t h e sl op e a n d i n te rc e p t are u s e d to ge ne r a te a n i d e a l l i ne. l o g c o nfor m- a n c e er r o r is t h e dif f er en ce f r o m t h e ide a l li n e and t h e m e as ur e d o u t p ut v o l t a g e fo r a g i v e n t e m p er a t ure in db . f o r addi t i o n a l info r m a t ion o n t h e e r r o r ca lc u l a t io n, r e fer to t h e d e vice c a l i b r a t io n an d er r o r c a lc u l a t io n sectio n . t h e h a rdw a re c o n f i g u r a t i o n f o r pu l s e re sp ons e me a s u r e - m e n t r e plac e d t h e 0 ? s e r i es r e sis t o r o n t h e v o ut pi n w i t h a 40 ? r e sis t o r a nd t h e clp f pi n was lef t op en. pu ls e r e s p o n s e time was m e as ur e d usin g a t e k t r o nix tds51504 d i gi tal ph os ph o r o s cillosco pe . b o th c h a n n e ls o n th e sco p e had 50 ? t e r m ina t ion s e lec t ed . the 10 ? in t e r n al t o th e o u t p ut in t e r f ace a nd t h e 40 ? s e r i es r e sis t o r a t t e n u a t e t h e o u t p u t r e s p o n s e b y 2. rf in p u t f r eq uen c y was 1 00 mh z wi t h ?10 dbm a t t h e in pu t o f t h e de vic e . th e r f b u rs t was g e n e ra t e d u s i n g s m t 0 6 w i th th e p u l s e o p t i o n w i th a pe ri od o f 1.5 s, a wid t h o f 0.1 s, a nd a p u ls e dela y o f 0.04 s. th e output re sp ons e w a s t r i g ge re d u s i n g t h e v i d e o o u t f r om t h e s m t06. ref e r to f i gur e 44 f o r a n o v er vie w o f th e t e s t s e t u p . 04853- 046 video out rf out ?7dbm r and s smt06 tektronix tds51504 ch1* ch3* trigger vout gnd 5v ad8318 vpos vset inhi inlo 40 ? 52.3 ? 1nf 1nf *50 ? termination 3db splitter f i gur e 4 4 . p u l s e r e sp o n se m e a s ur em ent t e st setup t o m e as ur e n o is e s p e c t r al den s i t y , t h e e v al u a t i on r e place d t h e 0 ? r e sis t o r in s e r i es wi t h t h e v o ut pin w i t h a 1 f dc b l oc ki n g c a pa ci t o r . t h e c a pa ci t o r w a s u s ed beca u s e th e fs ea ca nn ot han d le dc v o l t a g es a t t h e rf in p u t. the clp f p i n w a s lef t o p e n fo r da t a col l e c te d fo r f i gur e 18. f o r f i gur e 19 a 1 f ca p a ci t o r was place d betw e e n clp f an d g r o u n d . th e la rg e ca p a c i t o r f i l t er e d t h e n o is e f r o m t h e det e c t o r s t a g es o f t h e log a m p . n o is e sp e c t r al den s i t y m e as ur em en ts w e r e made using r&s sp ec tr um a n al y z er fs ea an d r & s s m t06 sig n al gen e r a t o r . th e sig n al ge ne r a tor s f r e q u e nc y w a s s e t t o 2 . 2 g h z . t h e sp e c t r u m an a l y z e r h a d a s p an of 1 0 hz , re s o lut i on b a nd w i d t h of 50 h z , video ban d wid t h o f 50 h z , and a v er a g e d the sig n al 100 tim e s. d a t a was ad j u s t e d t o acco un t f o r the dc b l o c kin g ca p a c i t o r im p e da n c e o n t h e o u t p u t a t lo w e r f r eq uen c ies.
ad8318 rev. 0| page 21 of 24 evaluation board table 6. evaluation board (rev a) configuration options component function default conditions tp1, tp2 supply and ground connections not applicable sw1 device enable: when in position a, the enbl pin is connected to vp and the ad8318 is in operating mode. in posit ion b, the enbl pin is grounded through r3, putting the device in power-down mode. the enbl pin may be exercised by a pulse generator connected to j3 with sw1 in position b. sw1 = a r3 = 10k (size 0603) r1, c1, c2 input interface: the 52.3 ? resistor in position r1 combines with the ad8318's internal input impedance to give a broadband input impedance of around 50 ? . capacitors c1 and c2 are dc blocking capacitors. a reactive impedance match can be implemented by replacing r1 with an inductor and c1 and c2 with appropriately-valued capacitors . r1 = 52.3 ? (size 0402) c1 = 1 nf (size 0402) c2 = 1 nf (size 0402) r2 temperature sensor interface: the te mperature sensor output voltage is available at j1, via the current limiting resistor, r2. c4 temperature compensation interf ace: the internal temperature compensation resistor is optimized for an input signal of 2.2 ghz when c4 is 1 k ? . this circuit can be adjusted to optimize performance for other input frequencies by changing the value of the resistor in position c4. note that the designation c4 on the evaluation boa rd is a typographical error as this pad will always be populated with a resistor. this error will be corrected on the rev b revision of the board. c4 = 500 k ? (size 0603) r7, r8, r9, r10 output interfacemeasurem ent mode: in measurement mode, a portion of the output voltage is fed back to pi n vset via r7. the magnitude of the slope of the vout output voltage response may be increased by reducing the portion of vout that is fed back to vset. r10 can be used as a back- terminating resistor or as part of a single-pole low-pass filter. r7 = 0 ? = (size 0402) r8 = open (size 0402) r9 = open (size 0402 r10= 0 ? (size 0402) r7, r8, r9, r10 output interfacecontroller mode: in this mode, r7 must be open. in controller mode, the ad8318 can cont rol the gain of an external component. a setpoint voltage is applied to pin vset, the value of which corresponds to the desired rf input signal level applied to the ad8318 rf input. a sample of the rf output signal from this variable-gain component is selected, typically via a directional co upler, and applied to ad8318 rf input. the voltage at pin vout is applied to the gain control of the variable gain element. a control voltage is applied to pin vset via r9 and r8. the magnitude of the control voltage ma y optionally be attenuated via the voltage divider comprised of r8 and r9 , or a capacitor may be installed in position r8 to form a low-pass filter along with r9. r7 = open (size 0402) r8 = open (size 0402) r9 = 0 ? (size 0402) r10 = 0 ? (size 0402) c5, c6, c7, c8, r5, r6 power supply decoupling: the nominal supply decoupling consists of a 100 pf filter capacitor placed ph ysically close to the ad8318, a 0 ? series resistor and a 0.1 f capacitor placed nearer to the power supply input pin. c6 = 100 pf (size 0402) c7 = 100 pf (size 0402) c5 = 0.1 f (size 0603) c8 = 0.1 f (size 0603) r5 = 0 ? (size 0603) r6 = 0 ? (size 0603) c9 filter capacitor: the low-pass corner freq uency of the circuit that drives pin vout can be lowered by placing a capacitor between clpf and ground. c4 = open (size 0603)
ad8318 rev. 0 | page 22 of 24 04853-035 12 cmip 11 cmip 10 tadj 9 vpso 1 cmip 2 cmip 3 vpsi 4 vpsi 13 temp 8 cmop 14 inhi 7 vset 15 inlo 6 vout 16 enbl 5 clpf ad8318 c7 100pf c9 open c8 0.1 f v s tp1 vp c1 1nf c2 1nf c4 499 ? (see text) c6 100pf c5 0.1 f v s r5 0 ? r1 52.3 ? v s sw1 r3 10k ? tp2 gnd j5 vset j3 enbl j2 inhi j1 temp j4 vout r7 0 ? r9 open r10 0 ? r8 open r2 1k ? r6 0 ? f i g u re 45. ev aluat i on b o a r d s c h e m a t i c (r ev a ) 04853-036 f i g u re 46. co mpon ent sid e lay o ut 04853-037 f i g u re 47. co mpon ent sid e s ilk s c r e e n
ad8318 rev. 0| page 23 of 2 4 outline dimensions 16 5 13 8 9 12 1 4 2.25 2.10 sq 1.95 0.75 0.60 0.50 0.65 bsc 1.95 bsc 0.35 0.28 0.25 12 max 0.20 ref seating plane pin 1 indicato r top view 4.0 bsc sq 3.75 bsc sq 0.60 max 0.60 max 0.05 max 0.02 nom 0.80 max 0.65 typ pin 1 indicato r 1.00 0.85 0.80 coplanarity 0.08 0.25 min exposed pad (b o t t om view) compliant to jedec standards mo-220-vggc f i gure 48. 1 6 -l ead l e ad f r a m e ch ip s c a l e p a ck ag e [lfcs p ] (c p - 1 6 ) di me nsio ns sho w n i n mi ll im e t e r s ordering guide ad83 18 prod ucts temperature p a ckage package descri ption package outlin e ordering qnty. ad8318acpz-r eel7 1 C40c to +85c 16-lead lfcsp cp-16 1500 ad8318acpz-w p 1, 2 C40c to +85c 16-lead lfcsp cp-16 64 a d 8 3 1 8 - e v a l e v a l u a t i o n boar d 1 z = pb- f re e pa rt . 2 wp = wa ff le pa ck.
ad8318 rev. 0 | page 24 of 24 notes ? 2004 analo g de vices, inc. all rights reserve d . tra d em arks and registered tra d ema r ks are the prop erty of their respective owners . d04853C0C 7/04(0)

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