19-1601; rev 2; 11/05 ________________general description the max3665 low-power transimpedance preamplifier for 622mbps sdh/sonet applications consumes only 70mw at v cc = 3.3v. operating from a single +3.3v or +5.0v supply, it converts a small photodiode current to a measurable differential voltage. a dc cancellation circuit provides a true differential output swing over a wide range of input current levels, thus reducing pulse-width distortion. the differential outputs are back-terminated with 50 ? per side. the overall transimpedance gain is nominally 8k ? . for input signal levels beyond approximately 50?p-p, the amplifier will limit the output swing to 250mv. the max3665? low 55na input noise provides a typical sensitivity of -33.2dbm in 1300nm, 622mbps receivers. the max3665 is designed to be used in conjunction with the max3676 clock recovery and data retiming ic with limiting amplifier. together they form a complete 3.3v or 5.0v 622mbps sdh/sonet receiver. in die form, the max3665 is designed to fit on a header with a pin diode. it includes a filter connection that pro- vides positive bias for the photodiode through a 1.5k ? resistor to v cc . the device is available in an 8-pin ?ax package. ________________________applications sdh/sonet receivers pin photodiode preamplifiers and receivers regenerators for sdh/sonet ____________________________features ? +3.3v or +5.0v single-supply operation ? 55na rms input-referred noise ? 70mw power consumption at v cc = 3.3v ? 8k ? gain ? 450 a peak input current ? 260ps (max) deterministic jitter ? differential output drives 100 ? load ? 470mhz bandwidth max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet max3665 max3676 limiting amp r filt 1.5k ? v cc 50 ? 50 ? 0.01 f 0.1 f 0.1 f 3.3v clk data out+ out- gnd 3.3v c filt clock and data recovery filt in __________________________________________________typical application circuit part max3665eua -40? to +85? temp range pin-package 8 ?ax evaluation kit available _______________ordering information pin configuration appears at end of data sheet. note: dice are designed to operate over a -40? to +140? junction temperature (t j ) range, but are tested and guaranteed at t a = +25?. max3665e/d (see note) dice ?ax is a registered trademark of maxim integrated products, inc. ________________________________________________________________ maxim integrated products 1 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.
max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet 2 _______________________________________________________________________________________ absolute maximum ratings dc electrical characteristics (v cc = +3.3v ?0% or +5.0v ?0%, 100 ? load between out+ and out-, t a = -40? to +85?. typical values are at v cc = +3.3v, t a = +25?, unless otherwise noted.) ac electrical characteristics (v cc = +3.3v ?0% or +5.0v ?0%, 100 ? load between out+ and out-, source capacitance = 0.5pf, t a = -40? to +85?. typical values are at v cc = +3.3v, t a = +25?, unless otherwise noted.) (notes 1 and 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. note 1: ac characteristics are guaranteed by design. note 2: measured with a 3-pole filter at the output. c in = 0.5pf, i in = 0, c filt = 1000pf. note 3: psrr = -20log ( ? v out / ? v cc ). v cc ........................................................................-0.5v to +6.5v continuous current at in ....................................................?ma voltage at out+, out- ...................(v cc - 1.5v) to (v cc + 0.5v ) voltage at filt ...........................................-0.5v to (v cc + 0.5v) continuous power dissipation (t a = +85?) 8-pin ?ax (derate 4.5mw/? above +85?) ...........295mw operating junction temperature (die) ..............-55? to +150? processing temperature (die) .........................................+400? storage temperature range .............................-55? to +150? lead temperature (soldering, 10s) .................................+300? i in = 0 i in = 0 to 10? p-p i in = 0 to 300? i in = 450? p-p differential output i in = 300? conditions ma 21 30 i cc supply current % ? v 0.8 0.95 v in input bias voltage gain nonlinearity k ? 1.5 r filt filter resistor mv p-p 260 450 v out(max) maximum output voltage k ? 78 z 21 small-signal transimpedance v v cc - 0.15 output common-mode voltage mv ? ? v out differential output offset ? 48 50 52 z out output impedance (per side) units min typ max symbol parameter -3db with i in = 5? relative to gain at 10mhz 2 13 - 1 prbs with 100 cids conditions khz 20 40 mhz 404 470 bw -3db small-signal bandwidth low-frequency cutoff 100 260 ps j d deterministic jitter units min typ max symbol parameter rms noise referred to input i n 55 72 na power-supply rejection ratio psrr f < 1mhz, differential referred to output, ? v cc = 30mv p-p (note 3) 36 47 db
max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet _______________________________________________________________________________________ 3 0 30 20 10 50 40 90 80 70 60 100 -40 -20 0 20 40 60 80 100 input-referred noise vs. temperature max3665 toc01 junction temperature (?) rms noise current (na) c in = 1.5pf c in = 0.5pf c in = 1pf c in is source capacitance presented to die. iincludes package parasitic, pin diode, and parasitic interconnect capacitance. 79 78 10k 100k 1m 10m 100m 1g 77 75 76 73 74 71 70 72 69 small-signal gain vs. frequency max3665 toc02 frequency (hz) gain (db) 0 15 10 5 25 20 45 40 35 30 50 -40 -20 0 20 40 60 80 100 pulse-width distortion vs. temperature (input = 100 a p-p ) max3665 toc03 ambient temperature ( c) pwd (ps) v cc = 3.3v v cc = 5.0v 100 1000 0 50 150 100 200 250 0.1 1 10 input-referred noise vs. dc input current max3665 toc04 dc input current ( a) rms noise currnent (na) source capacitance = 0.5pf 400 450 425 500 475 550 525 575 -40 0 20 -20 40 60 80 100 bandwidth vs. temperature max2665 toc07 ambient temperature (?) bandwidth (mhz) v cc = 3.3v or 5.0v 7400 7600 7500 7800 7700 8000 7900 8100 -40 0 20 -20 40 60 80 100 small-signal transimpedance vs. temperature max3665 toc05 ambient temperature ( c) transimpedance ( ? ) v cc = 3.3v v cc = 5.0v 0 15 10 5 25 20 45 40 35 30 50 -40 -20 0 20 40 60 80 100 pulse-width distortion vs. temperature (input = 450 a p-p ) max3665 toc06 ambient temperature ( c) pwd (ps) v cc = 3.3v v cc = 5.0v 0 40 20 100 80 60 140 120 160 0 150 200 50 100 250 300 350 400 450 data-dependent jitter vs. input signal amplitude max3665-08 peak-to-peak amplitude ( a) peak-to-peak jitter (ps) v cc = 3.3v v cc = 5.0v __________________________________________typical operating characteristics (v cc = +3.3v, includes off-chip filter, see figure 3b, t a = +25?, unless otherwise noted.) -0.20 -0.17 -0.18 -0.19 -0.15 -0.16 -0.11 -0.12 -0.13 -0.14 -0.10 -40 -20 0 20 40 60 80 100 output common-mode voltage (referenced to v cc ) vs. temperature max3665 toc09 ambient temperature ( c) common-mode voltage (v) v cc = 3.3v v cc = 5.0v
________________ detailed description the max3665 is a transimpedance amplifier designed for 622mbps sdh/sonet applications. it comprises a transimpedance amplifier, a paraphase amplifier with cml differential outputs, and a dc cancellation loop. figure 1 shows a functional diagram of the max3665. transimpedance amplifier the signal current at in flows into the summing node of a high-gain amplifier. shunt feedback through r f converts this current to a voltage. diodes d1 and d2 clamp the output voltage for large input currents. max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet 4 _______________________________________________________________________________________ _____________________________typical operating characteristics (continued) (v cc = +3.3v, includes off-chip filter, see figure 3b, t a = +25?, unless otherwise noted.) 150 200 300 250 350 400 -40 0 -20 20 40 60 80 100 differential output amplitude vs. temperature (input = 450 a p-p ) max3665 toc10 ambient temperature ( c) peak-to-peak amplitude (mv) v cc = 5.0v v cc = 3.3v eye diagram (input = 10 a p-p ) 15mv/div max3665-11 200ps/div input: 2 13 - 1 prbs contains 100 zeros eye diagram (input = 450 a p-p ) 50mv/div max3665-12 200ps/div input: 2 13 - 1 prbs contains 100 zeros paraphase amp 1.5k ? v cc v cc v cc r2 50 ? r1 50 ? r5 r6 r4 r3 r7 reference amp out- out+ filt in d2 d1 q2 q3 max3665 r f v cc q5 q4 dc cancellation amp v cc q1 gnd _____________________pin description name function 1 v cc +3.3v or +5.0v supply voltage 2 in signal input (from photodiode) pin 3 n.c. no connection. not internally con- nected. 4 filt on-chip resistor for filtering photodiode supply voltage 7 out- inverting voltage output. current flow- ing into in causes v out- to decrease. 6 out+ noninverting voltage output. current flowing into in causes v out+ to increase. 5, 8 gnd ground figure 1. functional diagram
paraphase amplifier t he paraphase amplifier converts single-ended inputs to differential outputs, and introduces a voltage gain. this signal drives a differential pair of transistors, q2 and q3, which form the output stage. resistors r1 and r2 provide back-termination at the output, absorbing reflections between the max3665 and its load. the differential outputs are designed to drive a 100 ? load between out+ and out-. they can also drive higher output impedances, resulting in increased gain and output voltage swing. dc cancellation loop the dc cancellation loop removes the dc component of the input signal by using low-frequency feedback. this feature centers the signal within the max3665? dynamic range, reducing pulse-width distortion on large input signals. the output of the transimpedance amplifier is sensed through resistors r3 and r4 and then filtered, amplified, and fed back to the base of transistor q4. the transistor draws the dc component of the input signal away from the transimpedance amplifier? summing node. connect a 400pf or larger capacitor (c filt ) between filt and case ground for to header, die-mounted oper- ation. increasing c filt improves psrr. the dc cancel- lation loop can sink up to 300? of current at the input. the max3665 minimizes pulse-width distortion for data sequences that exhibit a 50% mark density. a mark density other than 50% causes the device to generate pulse-width distortion. dc cancellation current is drawn from the input and adds noise. for low-level signals with little or no dc component, this is not a problem. preamplifier noise will increase for signals with a significant dc component. ___________ applications information the max3665 is a low-noise, wide-bandwidth transim- pedance amplifier that is ideal for 622mbps sdh/ sonet receivers. its features allow easy design into a fiber optic module, in three simple steps. step 1: selecting a preamplifier for a 622mbps receiver fiber optic systems place requirements on the band- width, gain, and noise of the transimpedance preampli- fier. the max3665 optimizes these characteristics for sdh/sonet receiver applications that operate at 622mbps. in general, the bandwidth of a fiber optic preamplifier should be 0.6 to 1 times the data rate. therefore, in a 622mbps system, the bandwidth should be between 375mhz and 622mhz. lower bandwidth causes pat- tern-dependent jitter and a lower signal-to-noise ratio, while higher bandwidth increases thermal noise. the max3665 typical bandwidth is 470mhz, making it ideal for 622mbps applications. the preamplifier? transimpedance must be high enough to ensure that expected input signals generate output levels exceeding the sensitivity of the limiting amplifier (quantizer) in the following stage. the max3676 clock recovery and limiting amplifier ic has an input sensitivity of 3.6mv p-p , which means that 3.6mv p-p is the minimum signal amplitude required to produce a fully limited output. therefore, when used with the max3665, which has an 8k ? transimpedance, the minimum detectable photodetector current is 450na p-p . it is common to relate peak-to-peak input signals to average optical power. the relationship between opti- cal input power and output current for a photodetector is called the responsivity ( ), with units amperes per watt (a/w). the photodetector peak-to-peak current is related to the peak-to-peak optical power as follows: i p-p = (p p-p )( ) based on the assumption that sdh/sonet signals maintain a 50% mark density, the following equations relate peak-to-peak optical power to average optical power and extinction ratio (figure 2): average optical power = p avg = (p0 + p1) / 2 extinction ratio = r e = p1 / p0 peak-to-peak signal amplitude = p p-p = p1 - p0 max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet _______________________________________________________________________________________ 5 power time p0 p1 p avg figure 2. optical power definitions
max3665 therefore, p avg = p p-p (1 / 2)[(r e + 1) / (r e - 1)] sensitivity is a key specification of the receiver module. the itu/bellcore specifications for sdh/sonet receivers require a link sensitivity of -27dbm with a bit error rate (ber) of 10 -10 . there is an additional 1db power penalty to accommodate various system losses; therefore, the sensitivity of a 622mbps receiver must be better than -28dbm. although several parameters affect sensitivity (such as the quantizer sensitivity and preamplifier gain, as previ- ously discussed), most fiber optic receivers are designed so that noise is the dominant factor. noise from the high- gain transimpedance amplifier, in particular, determines the sensitivity. the noise generated by the max3665 can be modeled with a gaussian distribution. in this case, a ber of 10 -10 corresponds to a peak-to-peak signal amplitude to rms noise ratio (snr) of 12.7. the max3665? typical input-referred noise, i n , (bandwidth- limited to 470mhz) is 55na rms . therefore, the minimum input for a ber of 10 -10 is (12.7 55na) = 699na p-p . rearranging the previous equations in these terms results in the following relationship: optical sensitivity (dbm) = 10log[(i n / )(snr)(1/2)(r e + 1) / (r e - 1)(1000)] at room temperature, with r e = 10, snr = 12.7, i n = 55 na, and = 0.9a/w, the max3665 sensitivity is -33.2 dbm. for worst-case conditions, noise increases to 72na and sensitivity decreases to -32.1 dbm. the max3665 provides 5.1db margin over the sdh/sonet specifications, even at +85?. the max3665? overload current (i max ) is greater than 450? p-p . the pulse-width distortion and input current are closely related. if the clock recovery circuit can accept more pulse-width distortion, a higher input current might be acceptable. for worst-case responsivity and extinction ratio, = 1a/w and r e = , the input overload is: overload (dbm) = -10log (i max )(1 / 2)(1000) for i max = 450?, the max3665 overload is -6.5dbm. step 2: designing filters the max3665? noise performance is a strong function of the circuit? bandwidth, which changes over temper- ature and varies from lot to lot. the receiver sensitivity can be improved by adding filters to limit this band- width. filter designs can range from a one-pole filter using a single capacitor, to more complex filters using inductors. figure 3 illustrates two examples: the simple filter provides moderate roll-off with minimal compo- nents, while the complex filter provides a sharper roll- off. parasitics on the pc board will affect the filter char- acteristics. refer to the max3665 ev kit data sheet for a layout example of the filter shown in figure 3b. supply voltage noise at the cathode of the photodiode produces a current i = c photo ( ? v/ ? t), which reduces the receiver sensitivity. c photo is the photodiode capacitance. the filt resistor of the max3665, combined with an external capacitor (see typical operating circuit ) can be used to reduce this noise. the external capacitor (c filt ) is placed in parallel with the photodiode. current generated by supply noise is divided between c filt and c photo . the input noise current due to sup- ply noise is (assuming the filter capacitor is much larger than the photodiode capacitance): i vc rc noise noise photo filt filt = ()( ) ()( ) 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet 6 _______________________________________________________________________________________ max3665 c1 5pf 22nh 22nh r l 100 ? a) simple, 1-pole, 530mhz filter 50 ? 50 ? max3665 4pf 5pf r l 100 ? b) 3-pole, 515mhz filter 50 ? 50 ? 1.2pf 1.2pf refer to the max3665 ev kit data sheet for the filter layout example. figure 3. filter design examples
if the amount of tolerable noise is known, then the filter capacitor can be easily selected: for example, with maximum noise voltage = 100mv p-p , c photo = 0.5pf, r filt = 1.5k ? , and i noise selected to be 6na (1/10 of max3665 input-referred noise): figure 4 shows the suggested layout for a to-46 header step 3: designing a low-capacitance input noise performance and bandwidth are adversely affected by stray capacitance on the input node. select a low-capacitance photodiode and use good high-fre- quency design and layout techniques to minimize capacitance on this pin. the max3665 is optimized for 0.5pf of capacitance on the input?pproximately the capacitance of a photodetector diode sharing a com- mon header with the max3665 in die form. photodiode capacitance changes significantly with bias voltage. with a +3.3v supply voltage, the reverse voltage on the pin diode is only 2.5v. if a higher voltage supply is available, apply it to the diode to significantly reduce capacitance. take great care to reduce input capacitance. with the ?ax version of the max3665, the package capaci- tance is about 0.3pf, and the pc board between the max3665 input and the photodiode can add parasitic capacitance. keep the input line short, and remove power and ground planes beneath it. packaging the max3665 into a header with the photodiode provides the best possible performance. it reduces parasitic capacitance to a minimum, resulting in the lowest noise and the best bandwidth. wire bonding for high current density and reliable operation, the max3665 uses gold metallization. make connections to the die with gold wire only, and use ball-bonding tech- niques (wedge-bonding is not recommended). die-pad size is 4 mils square. die thickness is 16 mils. v cc and ground use good high-frequency design and layout tech- niques. the use of a multilayer circuit board with sepa- rate ground and v cc planes is recommended. take care to bypass v cc and to connect the gnd pin to the ground plane with the shortest possible traces. c = 0.1 filt () () () () ? ? ? ? ? ? = ?? ?? 05 10 1500 6 10 5 6 12 4 . / . nf c = v filt noise ()( ) ()( ) c ri photo filt noise max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet _______________________________________________________________________________________ 7
max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet 8 _______________________________________________________________________________________ top view of to-46 header photodiode is mounted on c filt . case is ground. v cc filt in c filt c vcc out+ out- gnd photodiode max3665 figure 4. suggested layout for to-46 header
max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet _______________________________________________________________________________________ 9 ___________________pin configuration ___________________chip topography 1 2 3 4 8 7 6 5 gnd out- out+ gnd filt n.c. in v cc max3665 max top view transistor count: 443 substrate connected to gnd gnd in filt in v cc out+ out- gnd 0.05" (1.27mm) 0.03" (0.76mm)
max3665 622mbps, ultra-low-power, 3.3v t ransimpedance preamplifier for sdh/sonet 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 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. 8lumaxd.eps package outline, 8l umax/usop 1 1 21-0036 j rev. document control no. approval proprietary information title: max 0.043 0.006 0.014 0.120 0.120 0.198 0.026 0.007 0.037 0.0207 bsc 0.0256 bsc a2 a1 c e b a l front view side view e h 0.60.1 0.60.1 ?0.500.1 1 top view d 8 a2 0.030 bottom view 1 6 s b l h e d e c 0 0.010 0.116 0.116 0.188 0.016 0.005 8 4x s inches - a1 a min 0.002 0.95 0.75 0.5250 bsc 0.25 0.36 2.95 3.05 2.95 3.05 4.78 0.41 0.65 bsc 5.03 0.66 6 0 0.13 0.18 max min millimeters - 1.10 0.05 0.15 dim package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .)
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