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| et- il34118 voice switched speakerphone circuit the il34118 voice switched speakerphone ci rcuit incorporates the necessary am plifiers, attenuators, level d e tecto r s, an d co n t ro l alg o r ith m to fo rm th e h eart o f a h i g h q u a lity hands-free speakerphone sy st em . incl uded are a m i crophone am pl i f i e r with adjustable gain and mute control, transm it and receive at t e nuat o rs whi c h operat e i n a com p l e m e nt ary m a nner, l e vel det ect ors at bot h i nput and out put of bot h at t e nuat o rs, and background noi se m onitors for both the transm it and receive channels. a dial tone detector prevents the dial tone from being attenuated by the receive background noi se m oni t o r ci rcui t . al so i n cl uded are t w o l i n e dri v er am pl i f i e rs whi c h can be used t o form a hy bri d net w ork i n conjunct i on with an ex tern al co u p lin g tran sfo r m e r. a h i g h p a ss filter can b e u s ed to filter o u t 6 0 hz n o i se in th e reseiv e ch an n e l, o r fo r o t h e r filterin g funct i ons. a c h i p di sabl e pi n perm i t s poweri ng down t h e ent i r e ci rcui t t o conserve power on l ong l oops where l oop current i s at a mi n i mu m. ordering information il34118n pl ast i c il34118dw soic t a = -25 to 7 0 c for all packages the il34118 m a y be operat e d from a power suppl y , or i t can be powered from t h e t e l e phone l i n e, requi ri ng t y pi cal l y 5.0 m a . the il34118 can be interfaced direc tly to tip and ring (through a coupl i ng t r ansform e r) for st and-al one operat i on, or i t can be used i n conjunction with a handset speech netw ork and or other features of a feat urephone. pin assignment ? im proved at t e nuat o r gai n r a nge: 52 db b e t w een transm i t and receive ? low vol t a ge operat i on for li ne-powered appl i cat i ons (3.0- 6.5 v) ? 4 po in t sig n a l sen s in g fo r im p r o v e d sen s itiv ity ? background noise monitors for both transm it and receive paths ? m i crophone am pl i f i e r gai n set by ext e rnal r e si st ors - m u t e funct i on incl uded ? c h i p di sabl e for act i v e st andby operat i on ? on bo ard filter pin n e d - ou t fo r user dein ed fu n c tio n ? dial tone detector to inhibit receive idle m ode during dial tone presence beijing estek electronics co.,ltd 1
simplified block diagram functional description introduction the fundam e nt al di fference bet w een t h e operat i on of a speakerphone and a handset i s t h at of hal f-dupl ex versus ful l - dupl ex. the handset i s ful l dupl ex si nce conversat i on can occur i n bot h directions (transm it and receive) sim u ltaneousiy. a speakerphone has hi gher gai n l e vel s i n bot h pat h s, and at t e m p t i ng t o converse ful l dupl ex resul t s i n oscillatory problem s due to the loop that exists within the system . the loop is form ed by the receive an d tran sm it p a th s, th e h y b r id , an d th e aco u s tic coupl i ng (speaker t o m i crophone). the onl y pract i cal and econom i cal sol u t i on used t o dat a i s t o desi gn t h e speakerphone t o funct i on i n a hal f dupl ex m ode - i . e., onl y one person speaks at a t i m e, whi l e t h e ot her listen s . to ach iev e th is req u i res a circu it wh ich can det ect who i s t a l k i ng, swi t c h on t h e appropri a t e pat h (transm it or receive), and switch off (attenuate) the ot her pat h . in t h i s way , t h e l oop gai n i s m a i n t a i n ed less th an u n ity. w h en th e talk ers ex ch an g e fu n c tio n , th e circu it m u st q u i ck ly d e tect th is, an d switch th e circuit appropriately.by providing speech level detectors, the circuit operates in a ?hand-free? m ode, elim in atin g th e n eed fo r a ?p u s h - to -talk ? switch . the handset , by t h e way , has t h e sam e l oop as t h e speakerphone. b u t si nce t h e gai n s are consi d erabl y l o wer, and si nce t h e acoust i c coupl i ng from t h e earpiece to the m outhpiece is alm o st non-existent (the receiver is norm a lly held against a person?s ear), oscillations don?t occur. the il34118 provides the necessary level det ect ors, at t e nuat o rs, and swi t c hi ng cont rol for a properl y operat i ng speakerphone. the det ect i on sen s itiv ity an d tim in g are ex tern ally co n t ro llab l e. addi t i onal l y , t h e il34118 provi des background n o i se m o n ito rs wh ich m a k e th e circu it in sen s itiv e to room and l i n e noi se, hy bri d am pl i f i e rs for i n t e rfaci ng t o ti p and r i ng, t h e m i crophone am pl i f i e r, and ot her associated functions. attenuators the transm it and receive attenuators are com p l e m e nt ary i n funct i on, i . e., when one i s at m a xi m u m gai n (+6.0 db ), t h e ot her i s at m a xi m u m at t e nuat i on (-46 db ), and vi ce versa. they are never bot h ful l y on or bot h ful l y off. the sum of t h ei r gai n s rem a i n s const a nt (wi t h i n a nom i n al error band of 0.1 db ) at a t y pi cal val u e of -40 db . thei r purpose is to control the transm it a nd receive paths to provide t h e hal f-dupl ex operat i on requi red i n a speakerphone. the at t e nuat o rs are non-i nvert i ng, and have a - 3.0 db (from m a x gain) frequency of 100 khz. the input im pedance of each attenuator (txi and rxi) is nom i n al l y 10 k ? (see fi gure 1), and t h e i nput si gnal shoul d be l i m i t e d t o 350 m v rm s (990 m v p-p) t o prevent di st ort i on. that m a xi m u m beijing estek electronics co.,ltd 2 et- il34118 recom m e nded i nput si gnal i s i ndependent of t h e vol um e cont rol set t i ng. the di ode cl am p on t h e i nput s l i m i t s t h e i nput swi ng, and t h erefore t h e m a xi m u m negat i v e out put swi ng. thi s i s t h e reason for v rxol and v txol speci fi cat i on bei ng defi ned as they are in the electrical characteristics. the output i m pedance i s <10 ? u n til th e o u t p u t cu rren t lim it (typically 2.5 m a ) is reached. figure 1. attenuator input stage the at t e nuat o rs are cont rol l e d by t h e si ngl e out put of t h e c ont rol b l ock, whi c h i s m easurabl e at th e c t pi n (pi n 14). w h en t h e c t pi n i s at +240 m illivolts with respect to v b , th e circu it is in the receive m ode (receive attenuator is at +6.0 db). w h en the c t pin is at -240 m illivolts with respect to v b , th e circu it is in th e tran sm it m o d e (tran s m it atten u a to r is at +6 .0 d b ). th e circu it is in an id le m ode when the c t v o ltag e is eq u a l to v b , causing th e atten u a to rs? g a in s to b e h a lfway b e tween th eir fully on and fully off positions (-20 db each). m oni t o ri ng t h e c t v o ltag e (with resp ect to v b ) is th e m o st di rect m e t hod of m oni t o ri ng t h e ci rcui t ? s m ode. the i nput s t o t h e c ont rol b l ock are seven: 2 from t h e com p arat ors operat e d by t h e l e vel det ect ors, 2 from t h e background noi se m oni t o rs, t h e vol um e cont rol , t h e di al -t one det ect or, and t h e agc ci rcui t . these seven i nput s are descri bed bel o w. level detectors there are four level detectors - two on the receive si de and t w o on t h e t r ansm i t si de. r e fer t o fi gure 2 - t h e t e rm s i n parent heses form one sy st em , and t h e ot her t e rm s form t h e second sy st em fi gure 2. l e vel detectors each lev e l d e tecto r is a h i g h g a in am p lifier with back-t o-back di odes i n t h e feedback pat h , resul t i ng i n non-l i n ear gai n , whi c h perm i t s operat i on over a wi de dynam i c range of speech levels. the sensitivity of each level detector is dete rm ined by the external resistor and capacitor at each input (tli1, tli2, rli1, and rli2). each output charges an external capacitor through a diode a nd lim iting resistor, thus provi di ng a dc represent a t i on of t h e i nput ac si gnal l e vel . the out put s have a gui ck ri se t i m e (det erm i ned by t h e capaci t o r and an i n t e rnal 350 ? resistor), and a slow decay tim e set by an internal current source and the capacitor. the capac i t o rs on t h e four out put s shoul d have t h e sam e val u e ( 1 0 % ) to p r ev en t tim in g probl em s. referring to figure 8, on the receive side, one level detector (rli1) is at the receive input receiving t h e sam e si gnal as at ti p and r i ng, and beijing estek electronics co.,ltd 3 et- il34118 t h e ot her (r li2) i s at t h e out put of t h e speaker am p lifier. on th e tran sm it sid e , o n e lev e l d e tecto r (tli2) i s at t h e out put of t h e m i crophone am pl i f i e r, whi l e t h e ot her (tli1) i s at t h e hy bri d out put . outputs rlo1 and tlo1 feed a com p arator, the out put of whi c h goes t o t h e at t e nuat o r c ont rol b l ock. li kewi se, out put s r l o2 and tlo2 feed a second co m p arato r wh ich also g o e s to th e atten u a to r c ont rol b l ock. the t r ut h t a bl e for t h e effect s of t h e l e vel det ect ors on t h e c ont rol b l ock i s gi ven i n t h e sect i on descri bi ng t h e c ont rol b l ock. background noise monitors the purpose of t h e background noi se m oni t o rs i s to distinguish speech (which consists of bursts) from background noi se (a rel a t i v el y const a nt si gnal l e vel ) . there are t w o background noi se m oni t o rs - one for the receive path and one for the transm it path. refering to figure 2, th e receive background noise m oni t o r i s operat e d on by t h e r l i1-r lo1 l e vel det ect or, whi l e t h e t r ansm i t background noi se m oni t o r i s operat e d on by t h e tli2-tlo2 l e vel det ect or. they m oni t o r t h e background noi se by st ori ng a dc vol t a ge represent a t i v e of t h e respect i v e noise levels in capacitors at cpr and cpt. the vol t a ges at t h ese pi ns have sl ow ri se t i m es (determ i ned by the external rc), but fast decay tim es. if t h e si gnal at r l i1 (or tli2) changes sl owl y , t h e v o ltag e at cpr (o r cpt) will rem a in m o re p o s itiv e t h an t h e vol t a ge at t h e non-i nvert i ng i nput of t h e m onitor?s output com p arator. w h en speech is present, t h e vol t a ge on t h e noni nvert i ng i nput of t h e co m p arato r will rise q u i ck er th an th e v o ltag e at th e i nvert i ng i nput (due t o t h e burst charact eri s t i c of speech), causing its output to change. this output is sensed by t h e at t e nuat o r c ont rol b l ock. the 36 m v offset at t h e com p arat or?s i nput keeps the com p arator from changi ng state unless the speech level exceeds the background noise by 4.0 db . the tim e co n s tan t o f th e ex tern al rc ( 4.7 seconds) det e rm i n es t h e response t i m e t o background noi se vari at i ons volume control the vol um e cont rol i nput at vlc (pi n 13) i s sensed as a voltage with respect to v b . the vol um e control affects the attenuators only in the receive m o d e . it h a s n o effect in th e id le o r tran sm it m o d e s. w h en in the receive m ode, the gain of the receive atten u a to r will b e +6 .0 d b , an d th e g a in o f th e tran sm it atten u a to r will b e -4 6 d b o n l y wh en vlc is eq u a l to v b . as vlc is reduced below v b , the gain of the receive a ttenuator is reduced, and the g a in o f th e tran sm it atten u a to r is in creased su ch th at t h ei r sum rem a i n s const a nt . c h angi ng t h e vol t a ge at vlc changes t h e vol t a ge at c t (see th e atten u a to r c ont rol b l ock sect i on), whi c h i n t u rn cont rol s t h e atten u a to rs. the vol um e cont rol set t i ng does not affect t h e m a xi m u m at t e nuat o r i nput si gnal at whi c h not i ce abl e di st ort i on occurs. the bi as current at vlc i s t y pi cal l y 60 na out of t h e pi n, and does not vary si gni fi cant l y wi t h t h e vlc vol t a ge or wi t h v cc . dial tone detector the dial tone detector is a com p arator with one side connected to the r eceive input (rxi) and the ot her i nput connect ed t o v b with a 15 m v offset (see figure 3). if the circuit is in the receive m ode, and the incom i ng signal is greater than 15 m v (1 0 m v rm s), th e co m p arato r?s o u t p u t will ch an g e , disabling the receive idle m ode. tthe receive atten u a to r will th en b e at a settin g d e term in ed so lely by t h e vol um e cont rol . th e p u r p o s e o f th is circu it is to p r ev en t th e d i al t one (whi ch woul d be consi d ered as cont i nuous noi se) from fadi ng away as t h e ci rcui t woul d have t h e ten d e n c y to swich to th e id le m o d e . by d i sab lin g th e receive idle m ode, the dial tone rem a ins at the n o r m a lly ex p ected fu ll lev e l. fi gure 3. di al t o ne detector ags the ags circuit affects th e circu it o n l y in th e receive m ode, and only when the supply voltage (v cc ) is less th an 3 . 5 v o lts. as v cc falls b e lo w 3.5 volts, the gain of the r eceive attenuator is reduced. th e tran sm it p a th atten u a tio n ch an g e s su ch th at th e sum of the transm it and receive gains rem a ins const a nt . the purpose of t h i s feat ur e is to reduce the power (and current) used by the speaker when a line- powered speakerphone i s connect ed t o a l ong l i n e, wh ere th e av ailab l e p o w er is lim ited . by red u c in g th e speaker power, the voltage sag at v cc is co n t ro lled , prevent i ng possi bl e errat i c operat i on. beijing estek electronics co.,ltd 4 et- il34118 attenuator control block the attenuator control block has the seven inputs described above: - tthe output of the comparator operated by rlo2 and tlo2 (microphone/speaker side) - designated c1. - the output of the comparator operated by rlo1 and tlo1 (tip/ring) side) - designated c2. - the output of the transmit background noise monitor - designated c3. - the output of the receive background noise monitor - designated c4. - the volume control. - the dial tone detector. - the agc circuit. the single output of the control block controls the two attenuators. the effect of c1-c4 is as follows: inputs output c1 c2 c3 c4 mode tx tx 1 x transmit tx rx y y fast idle rx tx y y fast idle rx rx x 1 receive tx tx 0 x slow idle tx rx 0 0 slow idle rx tx 0 0 slow idle rx rx x 0 slow idle x = don?t care; y = c3 and c4 are not both 0 a definition of the above terms: 1) ?transmit? means the transmit attenuator is fully on (+6.0 db), and the receive attenuator is at max. attenuation (-46 db). 2) ?receive? means both attenuators are controlled by the volume control. at max. volume, the receive attenuator is fully on (6.0 db), and the transmit attenuator is at max. attenuation (- 46 db). 3) ?fast idle? means both transmit and receive speech are present in approximately equal levels. the attenuators are quickly switched (30 ms) to idle until one speech level dominates the other. 4) ?slow idle? means speech has ceassed in both transmit and receive path. the attenuators are then slowly switched (1 second) to the idle mode. 5) switching to the full transmit or receive modes from any other mode is at the fast rate (30 ms). a summary of the truth table is as follows: 1) the circuit will switch to transmit if: a) both transmit level detectors sense higher signal levels relative to the respective receive level detectors (tli1 versus rli1, tli2 versus rli2), and b) the transmit background noise monitor indicates the presence of speech. 2) the circuit will switch to receive if: a) both receive level detectors sense higher signal levels relative to the respective transmit level detectors, and b) the receive background noi se monitor indicates the presence of speech. 3) the circuit will switch to the fast idle mode if the level detectors disagree on the relative strengths of the signal levels, and at least one of the background noise monitors indicates speech. for example, refferring to the expanded logic diagram (figure 8), if there is sufficient signal at the microphone amp output (tli2) to override the speaker signal (rli2), and th ere is sufficient signal at the receive input (rli1) to override the signal at the hybrid output (tli1), and either or both background monitors indicate speech, then the circuit will be in the fast idle mode. two conditions which can cause the fast idle mode to occu r are a) when both talkers are attempting to gain control of the system by talking at the same time, and b) when one talker is in a very noisy environment, forcing the other talker to continually override that noise level. in general, the fast idle mode will occur infrequently. 4) the circuit will switch to the slow idle mode when a) both talkers are quiet (no speech present), or b) when one talker?s speech level is continuously overriden by noise at the other speaker?s location. the time required to switch the circuit between transmit, receive, fast idle and slow idle is determined in part by the components at the c t pin (pin 14). a schematic of the c t circuitry is shown in figure 4 and operates as follows: - r t is typically 120 k ? , and c t typically 5.0 f. - to switch to the receive mode, i 1 is turned on (i 2 is off), charging the external capacitor to +240 mv above v b . (an internal clamp prevents further charging of the capacitor.) - to switch to the transmit mode, i 2 is turned on (i 1 is off) bringing down the voltage on the capacitor to -240 mv with respect to v b . - to switch to idle quickly (fast idle), the current sources are turned off, and the internal 2.0 k ? resistor is switched in, discharging the capacitor to v b with a time constant = 2.0 k ? x c t . - to switch to idle slowly (slow idle), the current sources are turned off, the switch at the 2.0 k ? resistor is open, and the capacitor discharges to v b through the external resistor r t with a time constant = r t x c t . beijing estek electronics co.,ltd 5 et- il34118 figure 4. ct attenuator control block circuit microphone amplifier the m i crophone am pl i f i e r (pi n 10, 11) has t h e noni nvert i ng i nput i n t e rnal l y connect ed t o v b , wh ile t h e i nvert i ng i nput and t h e out put are pi nned out . un lik e m o st o p - am p s , th e am p lifier h a s an all-npn out put st age, whi c h m a xi m i zes phase m a rgi n and g a in -b an d w id th . th is featu r e en su res stab ility at g a in s less th an u n ity, as well as with a wid e ran g e o f react i v e l o ads. the open l oop gai n i s t y pi cal l y 80 db (f<100 hz), and t h e gai n -bandwi d t h i s t y pi cal l y 1.0 m h z. the m a xi m u m p-p out put swi ng i s typ i cally 1 . 0 v o lt less th an v cc wi t h an out put i m pedance of <10 ? until curent lim iting is reached (t y p i cal l y 1.5 m a ). input bi as current at m c i i s t y pi cal l y 40 na out of t h e pi n. figure 5. microphone amplifier and mute the m u t i ng funct i on (pi n 12), when act i v at ed, will red u ce th e g a in o f th e am p lifier to = -3 9 d b (will r m i = 5.1 k ? ) by short i ng t h e out put t o t h e i nvert i ng i nput (see fi gure 5). the m u t e i nput has a t h reshol d of 1.5 vol t , and t h e vol t a ge at t h i s pi n m u st be kept wi t h i ng t h e range of ground and v cc . if the m u t e funct i on i s not used, t h e pi n shoul d be grounded. hybrid amplifiers th e two h y b r id am p lifiers (at hto+, hto-, an d hti), in co n j u n c tio n with an ex tern al tran sfo r m e r, provi de t h e t w o-t o -four wi re convert er for i n t e rfaci ng t o t h e t e l e phone l i n e. the gai n of t h e fi rst am pl i f i e r (hti to hto-) is set by external resistors (gain = - r hf /r hi i n fi gure 8), and i t s out put dri v es t h e second am pl i f i e r, t h e gai n of whi c h i s i n t e rnal l y set at -1.0. unlike m o st op-am ps , th e am p lifiers h a v e an al l - npn out put st age, whi c h m a xi m i zes phase m a rg in an d g a in -b an d w id th . th is featu r e en su res stab ility at g a in s less th an u n ity, as well as with a wi de range of react i v e l o ads. the open l oop gai n of th e first am p lifier is typ i cally 8 0 d b , an d th e g a in bandwidth of each am plifier is 1.0 m h z. the m a xim u m p-p output swing of each am plifier is typ i cally 1 . 2 v o lts less th an v cc wi t h an out put i m pedance of <10 ? until current lim iting is reached (typ ically 8 . 0 m a ). th e o u t p u t cu rren t cap ab ility is guarant eed t o be a m i ni m u m of 5.0 m a . the bi as current at hti i s t y pi cal l y 30 na out of t h e pi n. the connect i ons t o t h e coupl i ng t r ansform e r are shown i n t h e expanded logi c di agram (fi gure 8). the bl ock l a bel e d zbal i s t h e bal a nci ng net w ork n ecessary to m a tch th e lin e im p e d a n ce. filter th e o p e ratio n o f th e filter circu it is d e term in ed b y t h e ext e rnal com ponent s. the ci rcui t wi t h i n t h e il34118, from pi ns fi t o fo i s a buffer wi t h a hi gh i nput i m pedance (>1.0 m ? ), and a l o w out put i m pedance (<50 ? ). the confi gurat i on of t h e ext e rnal com ponent s det e rm i n es whet her t h e ci rcui t is a h i g h - p a ss filter (as sh o w n in fig u r e 8 ) , a lo w- p a ss filter, o r a b a n d - p a ss filter. fi gure 6. hi gh pass fi l t er as a high pass filter, with the com ponents shown in figure 6 the filter will keep out 60 hz (and 120 hz) hum whi c h can be pi cked up by t h e ext e rnal t e l e phone l i n es. beijing estek electronics co.,ltd 6 et- il34118 as a lo w p a ss filter (fig u r e 7 ) , it can b e u s ed to roll off the high and frequencies in the receive circuit, whi c h ai ds prot ect i ng agai nst acoust i c feedback probl em s. w i t h an appropri a t e choi ce of an i nput co u p lin g cap acito r to th e lo w p a ss filter, a b a n d p a ss filter is fo rm ed . the out put vol t a ge at v b (pin 1 5 ) is (v cc - 0.7)/ 2 , and provi des t h e ac ground for t h e sy st em . the out put i m pedance at v b is 400 ? , and i n conjunction with the external capacitor at v b , form s a low pass filter for power supply rejection. since v b bi ases t h e m i crophone and hy bri d am pl i f i e rs, t h e am ount of suppl y reject i on at t h ei r o u t p u t s is d i rectly related to th e rej ectio n at v b , as well as th eir resp ectiv e g a in s. figure 7. low pass filter the c h i p di sabl e (pi n 3) perm i t s poweri ng down t h e ic t o conserve power and/ or for m u t i ng purposes. w ith cd 0.8 vol t s , norm a l operat i on i s i n effect . w ith cd 2.0 vol t s and v cc , the ic is powered down. in t h e powered down m ode, t h e m i crophone and t h e hy bri d am pl i f i e rs are di sabl ed, and t h ei r out put s go t o a hi gh i m pedance st at e. addi t i onal l y , th e b i as is rem o v e d fro m th e filter (pin s 1 , 2 ) , th e at t e nuat o rs (pi n s 8, 9, 21, 22), or from pi ns 13, 14, and 15 (t he at t e nuat o rs are di sabl ed, however, and will not pass a signal). the input im pedance at cd is typ i cally 9 0 k ? , has a t h reshol d of 1.5 vol t s , and t h e vol t a ge at t h i s pi n m u st be kept wi t h i n t h e range of ground and v cc . if c d i s not used, t h e pi n shoul d be grounded. power supply, v b , and chip disable the power suppl y vol t a ge at v cc (pin 4 ) is to b e bet w een 3.5 and 6.5 vol t s for norm a l operat i on, wi t h reduced operat i on possi bl e down t o 2.8 vol t s . pin description pin no designation description 1 f o filter o u t p u t . ou tp u t im p e d a n ce is less th an 5 0 ? . 2 f i filter input. input im pedance is greater than 1.0 m ? . 3 c d c h i p di sabl e. a l ogi c l o w (<0.8 v) set s norm a l operat i on. a l ogi c hi gh (>2.0 v) di sabl es t h e ic t o conserve power. input i m pedance i s nom i n al l y 90 k ? . 4 v cc a suppl y vol t a ge of +2.8 t o +6.5 vol t s i s requi red, at 5.0 m a . as v cc falls from 3.5 to 2.8 volts, an agc circuit redu ces the receive attenuator gain by 25 db (when in the receive m ode). 5 hto+ out put of t h e second hy bri d am pl i f i e r. th e gai n i s i n t e rnal l y set at -1.0 t o provi de a di fferent i a l out put , i n conjunct i on wi t h hto-, t o t h e hy bri d t r ansform e r. 6 hto- ou tp u t o f th e first h y b r id am p lifier. th e g a in o f th e am p is set b y ex tern al resisto r s. 7 h t i input and sum m i ng node for t h e fi rst hy bri d am pl i f i e r. dc l e vel i s v b. 8 txo ou tp u t o f th e tran sm it atten u a to r. dc lev e l is ap p r o x i m a tely v b . 9 txi input t o t h e t r ansm i t at t e nuat o r. m a x. si gnal l e vel i s 350 m v rm s. input i m pedance is 10 k ? . 10 m c o out put of t h e m i crophone am pl i f i e r. the gai n of t h e am pl i f i e r i s set by ext e rnal resistors. 1 1 m c i input and sum m i ng node of t h e m i crophone am pl i f i e r. dc l e vel i s v b . (cont i nued) pin description pin no designation description beijing estek electronics co.,ltd 7 et- il34118 12 mut mute input. a logic low (<0.8 v) sets normal operation. a logic high (>2.0 v) mutes the microphone amplifier without affecting the rest of the circuit. input impedance is nominally 90 ? . 13 vlc volume control input. when vlc = v b , the receive attenuator is at maximum gain when in the receive mode. when vlc = 0.3 v b , the receive gain is down 35 db. does not affect the transmit mode. 14 c t an rc this pin sets the response time for the circuit to switch modes. 15 v b an output voltage v cc /2. this voltage is a system ac ground, and biases the volume control. a filter cap is required. 16 cpt an rc at this pin sets the time constant for the transmit background monitor. 17 tli2 input to the transmit level detector on the mike speaker side. 18 tlo2 output of the transmit level detector on the mike/speaker side, and input to the transmit background monitor. 19 rlo2 output of the receive level detector on the mike/speaker side. 20 rli2 input to the receive level detector on the mike/speaker side. 21 rxi input to the receive attenuator and dial tone detector. max input level is 350 mv rms. input impedance is 10 k ? . 22 rxo output of the receive attenua tor. dc level is approximately v b . 23 tli1 input to the transmit level detector on the line side. 24 tlo1 output of the transmit level detector on the line side. 25 rlo1 output of the receive level detector on the line side, and input to the receive background monitor. 26 rli1 input the receive leve l detector on the line side. 27 cpr an rc at this pin sets the time c onstant for the receive background monitor. 28 gnd ground pin for the entire ic. maximum ratings * symbol parameter value unit v cc supply voltage (pin 14) -1.0 to +7.0 v v in input voltage at cd(pin 3), mut (pin 12) -1.0 tov cc +1.0 v v v in input voltage at vlc (pin 13) -1.0 tov cc +0.5 v v v in input voltage at txi(pin 9), rxi (pin 21), fi (pin 2) -0.5 tov cc +0.5 v v tstg storage temperature range -65 to +150 c * maximum ratings are those values beyond which damage to the device may occur. functional operation should be restricted to the reco mmended operating conditions. beijing estek electronics co.,ltd 8 et- il34118 recommended operating conditions symbol parameter min max unit v cc supply voltage (pin 4) 3.5 6.5 v v in input voltage at cd (pin 3), mut (pin12) 0 v cc v i vb v b current (pin 15) 500 a v in input voltage at vlc (pin 13) 0.3 x v b v b v v in attenuator input signal voltage (pins 9, 21) 0 350 mvrms g microphone amplifier, hybrid amplifier gain 0 40 db i l load current rxo, txo pins 8,22) mco (pin 10) hto-, hto+ (pins 6,5) 0 0 0 2.0 1.0 5.0 ma t a operating temperature -25 +70 c this device contains protection circuitry to guard ag ainst damage due to high static voltages or electric fields. however, precautions must be taken to avoid applications of an y voltage higher than maximum rated voltages to this high-impedance circuit. for proper operation, v in and v out should be constrained to the range gnd (v in or v out ) v cc . unused inputs must always be tied to an appropriate logic voltage level (e.g., either gnd or v cc ). unused outputs must be left open. electrical characteristics (t a = -25 to +70 c, v cc = 5.0 v , cd = 0.8 v, unless noted) symbol parameter test conditions guaranteed limits unit min max power supply i cc v cc sypply current v cc =6.5 v, cd =0.8 v v cc =6.5 v, cd =2.0 v - - 10 1.0 ma r cd cd input resistance v cc = v cd = 6.5 v 37.5 - kk ? v cdh cd input high voltage v cc = v cd = 6.5 v 2.0 v cc v v cdl cd input low voltage v cc = v cd = 6.5 v 0 0.8 v v b v b output voltage 13.5 3.0 v attenuator (vlc = v b , unless noted) g rx g rx ? g rx1 * ? g rx2 * g rx1 ? g rx3 * receive attenuator gain ( f =1.0 khz) rx mode, rxi=150 mvrms, (v cc =5.0 v) rx mode, rxi=150 mvrms (v cc =3.5 v) gain change -v cc =3.5 v versus v cc =5.0 v agc gain change - v cc =2.8 v versus v cc =5.0 v idle mode, rxi=150mvrms range (rx to tx mode) 1.5 1.5 -0.5 - -25 49 10.0 10.0 +0.5 -15 -15 54 db v cr * volume control range rx mode, 0.3v b electrical characteristics (t a = -25 to +70 c, v cc = 5.0 v , cd = 0.8 v, unless noted) symbol parameter test conditions guaranteed limits unit min max hybrid amplifiers h vos hto - offset v hto- - v b , freedback r= 51 k ? v b - 25 v b +25 mv hb vos hto - to hto+ offset freedback r= 51 k ? v b - 37 v b +37 mv a volh open loop gain hti to hto-, f = 100 hz, v hti = 20 mv 57 - db a vclh closed loop gain hto- to hto+ -2.8 2.2 db v ht-h hto- high voltage i out =-5.0 ma, v hti =v b -1.0 v 2.8 - v v ht-l hto- low voltage i out =5.0 ma, v hti =v b +1.5 v - 375 mv v ht+h hto+ high voltage i out =-5.0 ma,v hti =v b +1.5 v 2.8 - v v ht+l hto+ low voltage i out =5.0 ma, v hti =v b -1.0 v - 562 mv level detectors and background noise monitors i th * transmit-recieve switching threshold ratio of current at rli1 + rli2 to 20 a at tli1 + tli2 to switch from tx to rx 0.8 1.2 filter fo vos voltage offset at fo v fo -v b , 220 k ? from v b to fi v b - 250 v b +25 mv i fo fo sink current v b = v fo , v fi = 0 v 112 500 a note. 1. all currents into a device pin are positive, those out of a pin are negative. algebraic convention rather than magnitude is used to define limits. * @25 c beijing estek electronics co.,ltd 11 et- il34118 expanded logic diagram beijing estek electronics co.,ltd 12 et- il34118 |
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