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sy88432l 4.25 gbps transceiver with integrated fp/dfp laser diode driver and limiting post amplifier micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 m9999 - 061312 - a hbwhelp@micrel.com or (408) 955 - 1690 general description the sy88432l is a l ow power transceiver device that integrates a 4.25g bp s fp/dfb laser diode driver with a wide - sensitivity limiting post amplifier. this low power device is designed for use in fiber - optic optical m odules for multi - rate applications up to 4.25gbps. the sy88432l transmitter section can output up to 60ma of modulation current with fast rise and fall times and is designed to be ac - coupled to the laser . the transmitter output stage incorporates a t ransmit d isable feature and integrated 50 ? input impedance referenced to v cc . the receiver sections limiting post amplifier connects to a typical trans - impedance amplifier (tia) to amplify the incoming weak signal from the rosa and output s normalized rece ived data in cml format at the output. the receiver offers a wide los ( loss o f s ignal ) assert range between 8mv pp to 40mv pp differential. a programmable l oss - of - s ignal level set pin (loslvl ) sets the sensitivity of the input amplitude detection. the los or sd (s ignal - d etect) is user selectable and the los/sd signal can be fed back to the jam input to implement the squelch function that maintains output stability under a loss - of - signal condition. the receiver input should be ac - coupled. the sy88432l interf aces with micrels highly advanced optical module controller mic3003 as an easy - to - use chipset solution for csfp/sfp/ csff/ sff optical module application s . the mic3003 allows for both modulation and bias current con tro l , with a utomatic p ower c ontrol (apc) and temperature compensation. the sy88432l operates on a single 3.3v power supply and is available in a 24 lead, 4x 4mm qfn package . all support documentation can be found on micrels web site at: www.micrel.com . features ? multi - rate operation up to 4.25gbps ? single, wide range power supply: 3.3v ? 10% ? industrial t emp r ange: - 40c to +85c ? mic3003 compatible transmitter C fp/dfp laser diode driver ? modulation current up to 60ma - ac coupled laser d iode modulation - voltage controlled modulation current ? rise/fall times 65ps (typical) ? tx disable with internal 75 k? pull down resistor ? integrated 50 ? input impedance to v cc receiver C limiting post amplifier ? wide differential input range (10 mvpp C 1800mvpp) ? programmable los level (loslvl) sensitivity ? w ide los assert r ange (8 mvpp C 4 0mvpp) - with 3.5db typical electrical hysteresis ? selectable los or sd output ? ttl compatible jam inpu t with internal pull up ? low - noise cml data outputs with i ntegrated 50 ? termination impedance - rise/fall times 60ps (typical) ? low - noise cml data inputs with integrated 50 termination impedance to internal reference v re f applications ? gigabit ethernet ? fibre channel C 1fc, 2fc, 4fc ? sonet oc3/12/24/48 and with fec ? sdh stm1/4/8/16 and with fec markets ? datacom / t elecom / storage ? compact sfp/sff optical transceiver ? sfp/sff optical transceiver ? wireless backhaul
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 2 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 ordering information part number package type operating range package marking lead finish SY88432LMG 4 mm x 4mm qfn - 24 industrial 88432l with pb - free bar line indicator nipdau pb - free SY88432LMG tr (1) 4 mm x 4mm qfn - 24 industrial 88432l with pb - free bar line indicator nipdau pb - free note : 1. tr = tape and reel (1kpcs) typical application : single - ended ac - coupled configuration ( 2 ) note: 2. for reference only. please refer to the evaluation or reference board schematics for more complete information. s y 8 8 4 3 2 l m g 4 . 2 5 g b p s t r a n s c e i v e r 1 2 4 2 3 4 5 6 1 8 1 7 1 6 1 5 1 4 1 3 2 3 2 2 2 1 2 0 1 9 7 8 9 1 0 1 1 1 2 g n d _ t v c c _ t v c c _ t m o d + m o d - v c c _ t j a m l o s / s d v c c _ r r x o u t - r x o u t + v c c _ r l o s l v l g n d _ r r x i n - r x i n + g n d _ r l o s / s d _ s g n d _ t t x i n + t x i n - g n d _ t m o d s e t t x d i s m i c 3 0 0 3 l m g f i b e r o p t i c m o d u l e c o n t r o l l e r 1 2 4 2 3 4 5 6 1 8 1 7 1 6 1 5 1 4 1 3 2 3 2 2 2 1 2 0 1 9 7 8 9 1 0 1 1 1 2 v d d _ d q g p o g n d _ d r s 0 v i n / i n t c l k f b v m p d g n d _ a v d d _ a v i l d - v i l d + s h d n / t x f i n v r x r s 1 t x f a u l t t x d i s a b l e v m o d + v m o d - v b i a s c o m p r r s o u t / g p o r x l o s / t r s o u t v c c = 3 . 3 v v c c = 3 . 3 v 3 . 3 v v c c = 3 . 3 v 3 . 3 v d a t a _ i n + d a t a _ i n - 5 0 ? t r a n s m i s s i o n l i n e s d a t a _ o u t - v c c = 3 . 3 v s e r i a l d a t a s e r i a l c l k 5 0 ? l i n e s 5 0 ? t r a n s m i s s i o n l i n e s t i a d a t a d a t a _ o u t + r l o s l v l t x _ d i s a b l e
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 3 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 pin configuration 24 lead qfn (4x4mm) g n d _ t v c c _ t v c c _ t m o d + m o d - v c c _ t j a m l o s / s d v c c _ r r x o u t - r x o u t + v c c _ r l o s l v l g n d _ r r x i n - r x i n + g n d _ r l o s / s d _ s g n d _ t t x i n + t x i n - g n d _ t m o d s e t t x d i s g r o u n d e - p a d ( b o t t o m o f p a c k a g e ) p i n 1 i n d i c a t o r ( t o p o f p a c k a g e ) n o t e : e - p a d m u s t b e c o n n e c t e d t o t h e p c b g r o u n d p l a n e u s i n g t h e c o r r e c t v i a a r r a y 1 2 4 2 3 4 5 6 1 8 1 7 1 6 1 5 1 4 1 3 2 3 2 2 2 1 2 0 1 9 7 8 9 1 0 1 1 1 2 s y 8 8 4 3 2 l m g 2 4 l e a d 4 x 4 m m q f n ( t o p v i e w )
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 4 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 pin description pin number pin name type pin function 1 jam logic level input active low ttl input. determines whether the post amp output is enabled or disabled. operation when los/sd = los is selected: high = post amp output is disabled. low = post amp output is enabled. operation when los/sd = sd is selected: high = post amp output is enabled. low = post amp output is disabled. default: internally pulled - up with 25k?. can be shorted to los/sd (pin 2) to create a squelch function. 2 los/sd logic level output loss - of - signal / signal - detect. determined by los/sd_s pin setting. operation when los is selected by los/sd_s pin setting: high = when the data input amplitude falls below the threshold set by loslvl. low = when the data input amplitude rises above the t hreshold set by loslvl. operation when sd is selected by los/sd_s pin setting: high = when the data input amplitude rises above the threshold set by loslvl. low = when the data input amplitude falls below the threshold set by loslvl. 4, 5 rxout - , rxout+ cml outputs receiver differential cml outputs. unused output should be terminated 50 to v cc . 8, 9 txin+, txin - cml input s transmitter differential data cml inputs. data input signals for the laser diode driver section internally terminated with 50 to v c c . 11 modset analog input modulation current setting and control. the modulation current is set by applying a voltage between 0v and 1.2v to this pin . 5k? input impedance. 12 txdis logic level input transmit disable. control signal that enables or disables the laser diode driver outputs. high = transmitter outputs are set as follows: mod+ = high; mod - = low low = transmitter outputs enabled. default: internally pulled down with a 75k? resistor. 14, 15 mod - , mod+ transmitter output modulation cu rrent output. must be ac coupled to the laser. 19 los/sd_s logic level input los/sd output select. determines whether los or sd is selected. high = sd i s selected on the los/sd output and jam logic operation is: when jam = high ? post amplifier output is enabled . low = los i s selected on the los/sd output and jam logic operation is : when jam = low ? post amplifier output is enabled. default: internally pulled up with a 25k? resistor. 21, 2 2 rxin+, rxin - receiver inputs receiver differential data inputs. each input is internally terminated to v ref (v cc C 1.3v) with 50 resistors. inputs are ac - coupled. 24 loslvl analog input loss - of - signal level set. a resistor from this pin to v cc sets the threshold for the data input amplitu de at which los/sd will be asserted. 3, 6 vcc_r receiver positive supply rail receiver voltage supply. bypass with a 0.1uf || 0.01uf low esr capacitor as close to vcc_r pin as possible.
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 5 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 pin description pin number pin name type pin function 7, 10, 18 gnd_t transmitter ground transmitter ground. connect to the pcb ground plane. 13, 16, 17 vcc_t transmitter positive supply rail transmitter voltage supply. bypass with a 0.1uf || 0.01uf low esr capacitor as close to vcc_t pin as possible. 20, 23 , e - pad gnd_r receiver ground receiver ground. connect to the pcb ground plane. the e - pad must be connected to the pcb ground plane using a via array to transfer the heat from the package to the pcb ground plane. transmitter - laser diode driver truth table tx in+ tx in - txdis mod+ ( 3 ) mod - laser output ( 4 ) l h l h l l h l l l h h x x h h l l notes : 3 . i mod ? ? ? i mod_off when mod+ is high. 4 . assuming that laser is tied to mod+
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 6 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 absolute maximum ratings ( 5 ) supply voltage (v cc ) ................................ ... C 0.5v to +4.0v input voltage (v in ) ................................ .......... C 0.5v to v cc ttl control input voltage (v in ) ........................... 0v to v cc lead temperature (soldering, 20 sec.) .................... +260c storage temperature (t s ) ....................... C 65c to +150c operating ratings ( 6 ) supply voltage (v cc ) ................................ ..... +3.0 0v to +3.60v ambient temperature (t a ) ................................ C 40c to +85c package thermal resistance ( 7 ) still - air ( ? ja ) ................................ ............................. 50c/w junction - to - board ( ? jb ) ................................ ......... 30.5c/w notes: 5 . permanent device damage may occur if absolute maximum ratings are exceeded. this is a stress rating only and functional opera tion is not implied at conditions other than those detailed in the operational sections of this data sheet. exposure to absolute maximum ratings conditions for extended periods may affect device reliability. 6 . the data sheet limits are not guaranteed if the device is operated beyond the operating ratings . 7 . package thermal resistance assu mes exposed pad is soldered (or equivalent) to the devices most negative potential on the pcb using the recommended via pattern and size. assumes a 4 layer pcb and still a ir. transceiver dc electrical characteristics ( 8 ) v cc = 3.3v 10%, t a = - 40c to +85c. typical values are v cc = 3.3v, t a = 25c, i mod = 60ma symbol parameter condition min typ max units i cc power supply current without modulation & bias currents 90 13 0 ma v il txdis, los/sd_s, jam, input low - 0.3 0.8 v v ih txdis, los/sd_s, jam, input high 2 v cc + 0.3 v i ih txdis, los/sd_s, jam, input high v in = v cc ; note 10 20 a i il txdis, los/sd_s, jam, input low v in = 0.5v ; note 10 - 0.3 ma v oh los output high level v cc = 3.3v. ioh < 50ua 2 v v ol los output low level i ol = 2ma 0.5 v i oh los output leakage v oh = v cc 100 a laser diode driver electrical characteristics ( 8 ) v cc = 3.3v 10%, t a = C 40c to +85c. typical values are v cc = 3.3v, t a = 25c, i mod = 60ma symbol parameter condition min typ max units data rate nrz data 0.155 4.25 gbps r iin(txin ) input resistance (txin+,txin - ) 45 50 55 r iin(imod_set) input resistance (modset) 5 k v id differential input voltage swing cml inputs 3 00 8 00 mv pp v modset voltage range on modset pin 0 1.2 v v mod voltage (mod +, mod - ) note 9 v cc C 1.5 v cc v i mod modulation current ac - coupled 10 60 ma i mod_off modulation off current mod+ current when the device is disabled (txdis = high) 200 ? a j total total jitter @ 4.25gbps data rate 20 ps t pwdis pulse - width distortion i mod range 10ma C 60ma 20 ps t r , t f output rise/fall times (20% to 80%) 15 load 65 80 ps notes: 8 . specification for packaged product only. 9 . mod + and mod - are curre nt outputs. this defines the voltage range the user m ust guarantee these pins remain w ithin for proper operation . 10. txdis signal has an internal 75 k pull down resistor. for txdis: i ih = 150 a maximum. i il = 0.5 a minimum.
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 7 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 limiting amplifier electrical characteristics v cc = 3.3v 10%, t a = C 40c to +85c. typical values at v cc = 3.3v, t a = 25c; r load = 50 ? to v cc ; symbol parameter condition min typ max units los lvl los lvl voltage vcc - 1.3 v cc v v oh rx out + , rx out - high voltage v cc - 0.020 v cc - 0.005 v cc v v ol rx out + , rx out - low voltage v cc - 0.475 v cc - 0.400 v cc - 0.350 v z 0 single - ended output impedance 40 50 60 ? ? z i single - ended input impedance 40 50 60 ? ? t r , t f output rise/fall time (20% to 80%) note 1 60 120 ps t jitter deterministic random note 2 note 3 10 1 ps ps v id _2.5g differential input voltage swing note 7. see fig #1. 10 1800 mv pp v id_3.2g differential input voltage swing note 7. see fig #1. 10 1800 mv pp v id_4.25g differential input voltage swing note 7. see fig #1. 15 1800 mv pp v od differential output voltage swing note 1 600 800 950 mv pp t off los release time note 6 2 10 ? s t on los assert time note 6 2 10 ? s los al low los assert level r loslvl = 15k ?, note 4 8 mv pp los dl low los de - assert level r loslvl = 15k ?, note 4 13 mv pp hys l low los hysteresis r loslvl = 15k ?, note 5 2 3.5 6 db los am medium los assert level r loslvl = 5k ?, note 4 12 15 mv pp los dm medium los de - assert level r loslvl = 5k ?, note 4 24 33 mv pp hys m medium los hysteresis r loslvl = 5k ?, note 5 2 3.7 6 db los ah high los assert level r loslvl = 100 ?, note 4 34 40 mv pp los dh high los de - assert level r loslvl = 100 ?, note 4 65 83 mv pp hys h high los hysteresis r loslvl = 100 ?, note 5 2 4 6 db a v(diff) differential voltage gain 38 db s 21 single - ended small - signal gain 26 32 db notes : 1 . amplifier in limiting mode. input is a 200mhz square wave. 2 . deterministic jitter measured using 4.25gbps k28.5 pattern, v id = 60mv pp . 3 . random jitter measured using 4.25gbps k28.7 pattern, v id = 60mv pp . 4 . see typical operating characteristics for a graph showing how to choose a particular r loslvl for a particular los assert and its associated de - assert amplitude. 5 . this specification defines electrical hysteresis as 20log (los de - assert/los assert). the ratio between optical h ysteresis and electrical hysteresis is found to vary between 1.5 and 2 depending upon the level of received optical power and rosa characteristics. ba sed on that ratio, the optical hysteresis corresponding to the ele ctrical hysteresis range 2db - 6 db, shown in the ac characteristics table, will be 1db - 3db optical hysteresis. 6 . in real world applications, the los release/assert time can be strongly influenced by the rc time constant of the ac - coupling cap and the 50 input termination. to keep this time low, use a decoupling cap with the lowest value that is allowed by the data rate and the number of consecutive identical bits in the application (typical values are in the range of 0.001 f to 1.0 f). 7. input swing required to achieve 30% mask margin with pr bs 2 7 pattern at specified data rate. see fig #1 for differential and single - ended swing definitions.
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 8 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 transmitter C laser diode driver typical operating characteristics driver typical functional characteristics v cc = 3.3v 10%; t a = C 40c to +85c, typical values at v cc = 3.3v, t a = 25c ; r load = 25 ? to v cc ; electrical eye diagram @ 2. 5gbps prbs 2 23 , 25 ? load, 40 ma modulation time ( 100 ps /div) electrical eye diagram @ 4.2 5gbps prbs 2 23 , 25 ? load, 40 ma modulation time ( 50 ps /div) optical eye diagram @ 2.5gbps (stm16/oc48) er=11 db, mask margin = 32% time (67 ps/div)
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 9 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 receiver C limiting post amplifier typical operating characteristics v cc = 3.3 10%; t a = C 40c to +85c, typical values at v cc = 3.3v, t a = 25c; r load = 50? to v cc ; eye diagram @ 2.5gbps with vin=10mvpp time ( 100 ps /div) eye diagram @ 4.2 5gbps with vin=10mvpp time ( 50 ps /div) eye diagram @ 2.5gbps with vin=5 mvpp time ( 100 ps /div) eye diagram @ 4.2 5gbps with vin=5 mvpp time ( 50 ps /div)
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 10 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 transceiver functional block diagram
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 11 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 functional description transmitter - laser diode driver the laser driver consists of three stages which include the input buffer stage, a pre - driver stage where the modulation current is set, and the output driver stage. input buffer the input stage is internally terminated to v cc with 50 impedances. the input signals should be routed using 50 transmission lines and terminated with 50 ? impedances at the load. pre - driver / modulation control this stage is used to control the modulation current for the laser driver when an analog voltage between 0v to 1.2v is applied at the modset pin. output driver the output stage is an open - collector differential pair capable of driving modulation currents up to 60ma. it may be used single - ended or differentially. specific care must be taken to ensure that outputs are terminated correctly for either mode of operation. figure 2 and 3 show input and output stages of the driver. receiver - post amplifier the post amplifier detects and amplifies signals with data rates from 155mbps and up to 4.25 gbps with amplitudes as low as 10 mv pp . to reduce the noise at the output of the post amplifier when the input signal is absent or lower than the minimum detectable level set by los lvl , a jam pin is provided, which can be connected to los/sd output to turn off t he output buffer when los is asserted or sd is de - asserted. input amplifier/buffer figure 4 shows a simplified schematic of the input stage. the high - sensitivity of the input amplifier allows signals as small as 10 mv pp to be detected and amplified. the i nput amplifier allows input signals as large as 1800mv pp . figure 1 shows the allowed input voltage swing. small input signals below typically 12mv pp are lin early amplified with a typical 38db differential voltage gain. for input signals larger than 12mv pp , the output signal is limited to typically 800mv pp . output buffer the post amplifier cml output buffer is designed to drive 50? lines and is internally terminated with 50? to v cc . figure 5 shows a simplifie d schematic of the output stage which can be eith er ac - coupled (as shown) or dc - coupled. loss - of - signal the post amplifier generates a selectable chatter - free loss - of - signal (los) or signal detect (sd) open - collector ttl output as shown in figure 6 . los/sd is used to determine that the input amplitude is too small to be considered as a valid input. when the los function is selected (los/sd_s =0 ), los/sd asserts high if the input amplitude falls below the threshold set by loslvl and de - asserts low otherwise. i f the sd function is selected (los/sd_s=1 ), los/sd asserts low if the input amplitude falls below the threshold set by loslvl and de - asserts high otherwise. los/sd can be fed back to the jam input to maintain output stability under a loss of signal condition. jam de - asserts low the true output s ignal without removing the input signals. typically, 3db los hysteresis is provided to prevent chattering. loss/signal detect selection a p in (los/sd_s ) is provided to select between los (s et to low) or sd (set to high ) function. it also controls the int ernal circuitry of jam input to follow los/sd selection. loss - of - signal - level set a programmable los/sd level set pin ( loslvl ) sets the threshold of the input amplitude detection. connecting an external resistor between v cc and los lvl sets the voltage at l os lvl . this voltage ranges from v cc to v cc - 1.3v. the external resistor creates a voltage divider between v cc and v cc - 1.3v, as shown o n figure 7 . hysteresis the post amplifier provides typically 3 .5 db los electrical hysteresis, which is defined as 20log (vin los - assert / vin los - de - assert ). since the relationship between the voltage out of the rosa to optical power at its input is linear, the optical hysteresis will be typically half of the electrical hysteresis reported in the datasheet, but in practice, t he ratio between electrical and optical hysteresis is found to be within the range 1.5 to 1.8. thus, 3 .5 db electrical hysteresis will correspond to an optical hysteresis within the range 1.6db to 2db.
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 12 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 figure 1. transceiver v is and v id definition input and output stages figure 2 . laser diode driver input stage figure 3 . simplified laser diode driver output stage r x i n + r x i n - v i s ( m v ) 5 ( m v ) 9 0 0 ( m v ) ( r x i n + ) C ( r x i n - ) v i d ( m v p p ) 1 0 ( m v p p ) 1 8 0 0 ( m v p p )
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 13 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 figure 4 . receiver C post amplifier input structure figure 5 . receiver C post amplifier output structure figure 6 . receiver los /sd output structure figure 7 . receiver los lvl setting circuit note : recommended value for r loslvl is 15k? or less. 4 . 7 k v c c l o s / s d 2 . 8 k v c c r l o s l v l v r e f = v c c C 1 . 3 v l o s l v l
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 14 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 application hints the typical applications drawing on the front page shows how to connect the dr iver to the laser in a single - ended configuration where the mod - signal is disconnected from the laser anode and pull ed up to v cc with a resistor equal to the equivalent resistor of the load on mod+, damping resistor plu s the laser equivalent resistance. differential drive improves transition time and laser response. driving the laser differentially will also minimize th e cross talk with the rest of the circuitry on the board and especially the receiver. referring to figure 8 , the modulation current out of the driver is split between the pull - up network and the laser. if, for example, the total pull - up resistor is twice t he sum of the damping resistor and laser equivalent series resistance, only two thirds (2/3) of the modulation current will be used by the laser. to keep most of the modulation current going through the laser, it is necessary that the total pull - up resist ors a re high as possib le. one solution consists of using a combination of resistor and inductor as shown in figure 8 below . in this case, the headroom of the driver is vcc C r1 * ? i mod , where ? i mod is the portion of the modulation current that goes through the pull - up network. the coupling capacitor creates a low - frequency cut - off in the circuit, and its value must be chosen to accommodate the lowest and the highest data rates. if the value of the cap is too high, it will degrade the performance at higher data rates . i f its value is too small, it w ill not be able to hold a constant charge between the first bit and the last bit of a long string of identical bits in a low data rate application. both cases lead to higher pattern - depe nd e nt jitter in the transmitter signal. 0.01 - to - 0.1 ? f is found to be good range for all applic ations from 155mbps to 4.25gbps figure 8. transceiver laser driver stage ac - coupled differential interface n etwork
micrel, inc. sy88432l micrel inc. ? 2180 fortune drive ? san jose, ca 95131 ? usa ? tel +1 ( 408 ) 944 - 0800 ? fax + 1 (408) 474 - 1000 ? http://www.micrel.com july 2012 15 m9999 - 060512 - a hbwhelp@micrel.com or (408) 955 - 1690 package information 24 lead qfn (4 x 4 mm) micrel, inc. 2180 fortune drive san jose, ca 95131 usa tel +1 (408) 944 - 0800 fax +1 (408) 474 - 1000 web http://www.micrel.com micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in th is data sheet. this information is not intended as a warranty and micrel does not assume responsibility for its use. micrel reserv es the right to change circuitry, specifications and descriptions at any time without notice. no license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. except as provided in m icrels terms and conditions of sale for such products, micrel assumes no liability micrel products are not designed or authorized for use as components in life support appliances, devices or systems where mal function o f a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasona bly expected to result in a significant injury to the user. a purchasers use or sale of micrel products for use in life support appliances, devices or systems is a purchasers own risk a ? 2012 micrel, incorporated.

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