general description the MAX3744/max3745 transimpedance amplifiers pro- vide a compact, low-power solution for communication up to 2.7gbps. they feature 330na input-referred noise at 2.1ghz bandwidth (bw) with 0.85pf input capaci- tance. the parts also have >2ma p-p ac input overload. both parts operate from a single +3.3v supply and con- sume 93mw. the MAX3744/max3745 are in a compact 30-mil x 50-mil die and require no external compensa- tion capacitor. a space-saving filter connection is pro- vided for positive bias to the photodiode through an on-chip 580 ? resistor to v cc . these features allow easy assembly into a low-cost to-46 or to-56 header with a photodiode. the MAX3744 and max3748a receiver chip set pro- vides an rssi output using a maxim-proprietary* inter- face technique. the MAX3744 preamplifier, max3748a postamplifier, and ds1858/ds1859 sfp controller meet all the sff-8472 digital diagnostic requirements. applications up to 2.7gbps sff/sfp optical receivers optimized for small-form-factor pluggable (sfp) optical receivers features up to 2.7gbps (nrz) data rates rssi implementation in 4-pin to46 header (MAX3744) 10ps p-p deterministic jitter for <100a p-p input current 330na rms input-referred noise at 2.1ghz bandwidth 28ma supply current at +3.3v 2ghz small-signal bandwidth 2.0ma p-p ac overload die size: 30 mils x 50 mils MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi ________________________________________________________________ maxim integrated products 1 ordering information v cc filter 4-pin to can 400pf 400pf in out+ out- gnd out+ 0.1 f 0.1 f 3.3k ? in+ v cc in- rssi disable los out- max3748a sfp optical receiver host board mod-def1 mod-def2 4.7k ? to 10k ? v cc = 3.3v MAX3744 ds1858/ ds1859 typical application circuit 19-2927; rev 1; 8/03 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ** dice are guaranteed to operate from -40? to +85?, but are tested only at t a = +25?. part temp range pin-package MAX3744 e/d -40 c to +85 c dice** max3745 e/d -40 c to +85 c dice** * patent pending
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = +2.97v to +3.63v and t a = -40? to +85?. typical values are at v cc = +3.3v, source capacitance (c in ) = 0.85pf, and t a = +25?, unless otherwise noted.) (notes 1, 2) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. power-supply voltage (v cc ) .................................-0.5v to +6.0v continuous cml output current (out+, out-) ............................................. -25ma to +25ma continuous input current (in)...............................-4ma to +4ma continuous input current (filter).......................-8ma to +8ma operating junction temperature range (t j ) ....-55? to +150? storage ambient temperature range (t stg ) ...-55? to +150? die attach temperature...................................................+400? parameter symbol conditions min typ max units supply current i cc including cml output current (i in = 0) 28 41 ma input bias voltage 1.0 v input overload (note 3) 2 ma p-p c in = 0.85pf, bw = 933mhz 206 c in = 0.85pf, bw = 2.1ghz 330 430 c in = 0.85pf, bw = 18ghz 620 c in = 0.85pf, bw = 933mhz 206 c in = 0.6pf, bw = 2.1ghz 300 380 input-referred noise i n c in = 0.6pf, bw = 18ghz 550 na rms differential transimpedance differential output, i in = 40a ave 2.8 3.5 4.5 k ? -3db, c in = 0.6pf 1.8 2 small-signal bandwidth (note 3) bw -3db, c in = 0.85pf 1.6 1.8 ghz low-frequency cutoff -3db, input current = 20a ave (note 3) 30 khz 2.1gbps, k28.5 pattern 14 31 100a p-p < input 2ma p-p 2.7gbps, 2 31 -1 pattern 24 2.1gbps, k28.5 pattern 10 16 deterministic jitter (notes 3, 5) dj 10a p-p < input 100a p-p 2.7gbps, 2 31 -1 pattern 20 ps p-p filter resistance 510 580 690 ? differential output resistance (out+, out-) 85 100 115 ? maximum differential output voltage v od input > 50a ave , output termination 50 ? to v cc (output in limited state) 220 280 400 mv p-p
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi _______________________________________________________________________________________ 3 electrical characteristics (continued) (v cc = +2.97v to +3.63v and t a = -40 c to +85 c. typical values are at v cc = +3.3v, source capacitance (c in ) = 0.85pf, and t a = +25 c, unless otherwise noted.) (notes 1, 2) note 1: die parameters are production tested at room temperature only, but are guaranteed by design and characterization from -40 c to +85 c. note 2: source capacitance represents the total capacitance at the in pad during characterization of the noise and bandwidth para- meters. note 3: guaranteed by design and characterization. note 4: input-referred noise is: note 5: deterministic jitter is the sum of pulse-width distortion (pwd) and pattern-dependent jitter (pdj). note 6: power-supply noise rejection psnr = -20log( ? v out / ? v cc ), where ? v out is the differential output voltage and ? v cc is the noise on v cc . note 7: a iiaiia a where i ii rssi range is from i a to a rssi out cm in out cm in out cm out out in = =? = = + = +? __ _ ()() 400 0 400 2 6 500 ? ? rms output noise gain at f mhz = ? ? ? ? ? ? 100 parameter symbol conditions min typ max units single-ended output common- mode minimum level (MAX3744) relative to v cc , i in = 1ma ave 540 490 mv output data transition time input > 200a p-p 20% to 80% rise/fall time (note 3) 80 140 ps frequency 1ghz 17 differential output return loss 1ghz < frequency 2ghz 10 db f < 1mhz 46 power-supply noise rejection psnr i in = 0 (note 6) 1mhz f < 10mhz 34 db rssi gain (MAX3744) a rssi (note 7) 21 a/a rssi gain stability (MAX3744) 10log(a rssi /a rssi-nom ) where a rssi-nom = a rssi at 3.3v, +25 c (note 3) 0.24 db
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi 4 _______________________________________________________________________________________ typical operating characteristics (v cc = +3.3v, c in = 0.85pf, t a = +25 c, unless otherwise noted.) 60ps/div eye diagram input = 2ma p-p , data rate = 2.7gbps 30mv/div MAX3744 toc09 2 23 -1 pattern 60ps/div eye diagram input = 2ma p-p , data rate = 2.1gbps 30mv/div MAX3744 toc08 k28-5 pattern 60ps/div eye diagram input = 20 a p-p , data rate = 2.1gbps 5mv/div MAX3744 toc06 k28-5 pattern 50 10m 10g 1g 100m frequency response 75 60 55 70 65 MAX3744 toc03 frequency (hz) gain (db) 60ps/div eye diagram input = 20 a p-p , data rate = 2.7gbps 6mv/div MAX3744 toc07 2 23 -1 pattern 200 400 300 600 500 700 800 -40 20 40 -20 0 60 80 100 input-referred noise vs. temperature MAX3744 toc01 temperature ( c) input-referred noise (na rms ) unfilter c in = 1.5pf c in = 0.85pf c in = 0.5pf 200 400 300 600 500 700 800 -40 20 40 -20 0 60 80 100 input-referred noise vs. temperature MAX3744 toc02 temperature ( c) input-referred noise (na rms ) bw = 2.1ghz c in = 1.5pf c in = 0.85pf c in = 0.5pf deterministic jitter vs. input amplitude MAX3744 toc04 input amplitude (ma p-p ) deterministic jitter (ps p-p ) 1 0.1 10 20 30 40 50 0 0.01 10 2.7gbp sonet 2.1gbps fibre channel 60 65 70 75 -40 0 20 -20 40 60 80 100 small-signal transimpedance vs. temperature MAX3744 toc05 temperature ( c) transimpedance (db ? )
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi _______________________________________________________________________________________ 5 typical operating characteristics (continued) (v cc = +3.3v, c in = 0.85pf, t a = +25 c, unless otherwise noted.) 0 1.0 0.5 2.5 1.5 3.5 4.0 -40 20 -20 40 60 100 bandwidth vs. temperature MAX3744 toc14 temperature ( c) 3db bandwidth (ghz) 3.0 2.0 080 c in = 0.6pf differential s22 vs. frequency MAX3744 toc10 frequency (mhz) s22 (db) 3500 3000 2500 2000 1500 1000 500 -25 -20 -15 -10 -5 0 -30 0 4000 MAX3744 max3745 0 20 10 40 30 60 50 70 -40 0 20 -20 40 60 80 100 supply current vs. temperature MAX3744 toc11 temperature ( c) supply current (ma) -200 -150 -100 -50 0 50 100 150 200 -100 -50 0 50 100 dc transfer function (v filt = 0v) MAX3744 toc12 input current (ma p-p ) output voltage (mv p-p ) 150 200 250 300 350 400 450 500 550 0 500 1000 1500 2000 rssi MAX3744, max3748a MAX3744 toc13 average input current ( a) max3748 rssi output ( a) t a = -40 c t a = +85 c 60ps/div eye diagram temperature = +100 c input = 20 a p-p data rate = 2.7gbps 6mv/div MAX3744 toc15 2 23 -1 prbs
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi 6 _______________________________________________________________________________________ pin description detailed description the MAX3744/max3745 are transimpedance amplifiers designed for up to 2.7gbps sff/sfp transceiver mod- ules. a functional diagram of the MAX3744/max3745 is shown in figure 1. the MAX3744/max3745 comprise a transimpedance amplifier stage, a voltage amplifier stage, an output buffer, and a direct-current (dc) feed- back cancellation circuit. the MAX3744 also includes a signal strength indicator (rssi). to provide this signal in a standard 4-pin to header, the rssi level is added to the common mode of the differential data output pins. transimpedance amplifier stage the signal current at the input flows into the summing node of a high-gain amplifier. shunt feedback through the resistor r f converts this current to a voltage. in par- allel with the feedback resistor are two back-to-back schottky diodes that clamp the output signal for large input currents, as shown in figure 2. MAX3744/ max3745 bond pad name function 1, 3 v cc supply voltage 2, 7 n.c. no connection 4 in tia input. signal current from photodiode flows into this pin. 5 filter provides bias voltage for the photodiode through a 580 ? resistor to v cc . when grounded, this pin disables the dc cancellation amplifier to allow a dc path from in to out+ and out- for testing. 6, 10 gnd supply ground 8 out- inverting data output. current flowing into in causes the voltage at out- to decrease. for the MAX3744, the common mode between out+ and out- is proportional to the average input current. 9 out+ noninverting data output. current flowing into in causes the voltage at out+ to increase. for the MAX3744, the common mode between out+ and out- is proportional to the average input current. transimpedance amplifier out+ 50 ? 50 ? out- v cc filter in dc cancellation circuit MAX3744 rssi transimpedance amplifier out+ 50 ? 50 ? out- v cc filter in dc cancellation circuit max3745 v cc r f r f figure 1. functional diagram
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi _______________________________________________________________________________________ 7 voltage amplifier stage the voltage amplifier stage provides gain and converts the single-ended input to differential outputs. dc cancellation circuit the dc cancellation circuit uses low-frequency feed- back to remove the dc component of the input signal (figure 3). this feature centers the input signal within the transimpedance amplifier s linear range, thereby reducing pulse-width distortion caused by large input signals. the dc cancellation circuit is internally com- pensated and therefore does not require external capacitors. output buffer the output buffer provides a reverse-terminated voltage output. the buffer is designed to drive a 100 ? differential load between out+ and out-. the MAX3744 must be dc-coupled to the max3748a. see figures 4 and 5. for optimum supply-noise rejection, the max3745 should be terminated with a matched load. if a single- ended output is required, the unused output should be terminated to a 50 ? resistor to v cc . the max3745 does not drive a dc-coupled, 50 ? grounded load; however, it does drive a compatible 50 ? cml input. signal-strength indicator the MAX3744 produces a signal proportional to the average photodiode current. this is added to the com- mon mode of the data outputs out+ and out-. this signal is intended for use with the max3748a to pro- vide a ground-referenced rssi voltage. applications information signal-strength indicator the sff-8472 digital diagnostic specification requires monitoring of input receive power. the max3748a and MAX3744 receiver chipset allows for the monitoring of the average receive power by measuring the average dc current of the photodiode. amplitude output (large signals) time output (small signals) amplitude input from photodiode time input after dc cancellation figure 2. MAX3744/max3745 limited output figure 3. dc cancellation effect on input out+ out- 50 ? 50 ? v cc out+ out- 100 ? v cc figure 4. equivalent output MAX3744 figure 5. equivalent output max3745
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi 8 _______________________________________________________________________________________ the MAX3744 preamp measures the average photodi- ode current and provides the information to the output common mode. the max3748a rssi detect block senses the common-mode dc level of input signals in+ and in- and provides a ground-level-referenced output signal of the photodiode current. the advantage of this implementation is that it allows the tia to be packaged in a low-cost conventional 4-pin to-46 header. the max3748a rssi output is connected to an analog input channel of the ds1858/ds1859 sfp controller to convert the analog information into a 16-bit word. the ds1858/ds1859 provide the received power informa- tion to the host board of the optical receiver through a 2-wire interface. the ds1859 allows for internal calibra- tion of the receive power monitor. the MAX3744 and the max3748a have been optimized to achieve rssi stability of better than 2.5db within the 6a to 500a range of average input photodiode cur- rent. to achieve the best accuracy, maxim recom- mends receive power calibration at the low end (6a) and the high end (500a) of the required range. optical power relations many of the MAX3744/max3745 specifications relate to the input signal amplitude. when working with optical receivers, the input is sometimes expressed in terms of average optical power and extinction ratio. figure 6 and table 1 show relations that are helpful for convert- ing optical power to input signal when designing with the MAX3744/max3745. (refer to application note hfan 3.0.0: accurately estimating optical receiver sensitivity .) optical sensitivity calculation the input-referred rms noise current (i n ) of the MAX3744/max3745 generally determines the receiver sensitivity. to obtain a system bit-error rate (ber) of 1e-12, the signal-to-noise ratio must always exceed 14.1. the input sensitivity, expressed in average power, can be estimated as: where is the photodiode responsivity in a/w and i n is rms current in amps. input optical overload the overload is the largest input that the MAX3744/ max3745 can accept while meeting deterministic jitter specifications. the optical overload can be estimated in terms of average power with the following equation: optical linear range the MAX3744/max3745 have high gain, which limits the output when the input signal exceeds 50a p-p . the MAX3744/max3745 operate in a linear range (10% lin- earity) for inputs not exceeding: linear range ar r dbm rms e e log ( ) ( ) = + ? ? ? ? ? ? ? 10 50 1 21 1000 overload ma r r dbm rms e e log ( ) ( ) = + ? ? ? ? ? ? ? 10 21 21 1000 sensitivity ir r dbm ne e log .( ) ( ) = + ? ? ? ? ? ? ? 10 14 1 1 21 1000 parameter symbol relation average power p avg p avg = (p 0 + p 1 ) / 2 extinction ratio r e r e = p 1 / p 0 optical power of a 1 p 1 p 1 = 2p avg (r e ) / (r e + 1) optical power of a zero p 0 p 0 = 2p avg / (r e + 1) signal amplitude p in p in = p 1 - p 0 ; p in = 2p avg (r e - 1) / (r e + 1) table 1. optical power relations note: assuming 50% average duty cycle and mark density.
layout considerations noise performance and bandwidth are adversely affect- ed by capacitance at the in pad. minimize capacitance on this pad and select a low-capacitance photodiode. assembling the MAX3744/max3745 in die form using chip and wire technology provides the best possible performance. figure 7 shows a suggested layout for a to header for the MAX3744/max3745. the placement of the filter cap to minimize the ground loop of the pho- todiode is required to achieve the specified bandwidth. the out+ and out- bond wire lengths should also be minimized to meet the bandwidth specification. special care should be taken to ensure that esd at in does not exceed 500v. photodiode filter supply voltage noise at the cathode of the photodiode produces a current i = c pd ? v/ ? t, which reduces the receiver sensitivity (c pd is the photodiode capaci- tance.) the filter resistor of the MAX3744/max3745, combined with an external capacitor, can be used to reduce this noise (see the typical application circuit ). current generated by supply noise voltage is divided between c filter and c pd . the input noise current due to supply noise is (assuming the filter capacitor is much larger than the photodiode capacitance): i noise = (v noise )(c pd ) / (r filter )(c filter ) if the amount of tolerable noise is known, the filter capacitor can be easily selected: c filter = (v noise )(c pd ) / (r filter )(i noise ) for example, with maximum noise voltage = 100mv p-p , c pd = 0.85pf, r filter = 600 ? , and i noise selected to be 350na: c filter = (100mv)(0.85pf) / (600 ? )(350na) = 405pf wire bonding for high-current density and reliable operation, the MAX3744/max3745 use gold metalization. connections to the die should be made with gold wire only, using ball- bonding techniques. die thickness is typically 14 mils (0.4mm). MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi _______________________________________________________________________________________ 9 po pi p avg time optical power figure 6. optical power relations top view of to-46 header v cc out+ out- case ground 400pf to 1000pf photodiode 400pf to 1000pf MAX3744 max3745 figure 7. suggested layout for to-46 header
MAX3744/max3745 2.7gbps sfp transimpedance amplifiers with rssi maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. v cc n.c. v cc in filter gnd out- out+ gnd n.c. 0.03in (0.76mm) 0.05in (1.26mm) 1 2 3 4 6 7 8 9 10 5 MAX3744 max3745 pad coordinates chip information transistor count: 301 process: sige bipolar substrate: isolated die thickness: 0.014in 0.001in chip topography pad coordinates ( m) x coordinates ( m) y 1 1.4 495.6 2 0 336 3 0 224 4 0 112 50 0 6 494.2 -1.4 7 865.2 -1.4 8 1005.2 -1.4 9 1005.2 495.6 10 490 495.6
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