general description the max3266 is a transimpedance preamplifier for 1.25gbps local area network (lan) fiber optic receivers. the circuit features 200na input-referred noise, 920mhz bandwidth, and 1ma input overload. the max3267 provides a pin-for-pin compatible solu- tion for communications up to 2.5gbps. it features 500na input-referred noise, 1.9ghz bandwidth, and 1ma input overload. both devices operate from a +3.0v to +5.5v single sup- ply and require no compensa tion capacitor. they also include a space -saving filter connection that provides positive bias for the photodiode through a 1.5k ? resistor to v cc . these features allow easy assembly into a to-46 or to-56 header with a photodiode. the 1.25gbps max3266 has a typical optical dynamic range of -24dbm to 0dbm in a shortwave (850nm) configuration or -27dbm to -3dbm in a longwave (1300nm) configuration. the 2.5gbps max3267 has a typical optical dynamic range of -21dbm to 0dbm in a shortwave configuration or -24dbm to -3dbm in a long- wave configuration. applications gigabit ethernet 1gbps to 2.5gbps optical receivers fibre channel features 200na input-referred noise (max3266) 500na input-referred noise (max3267) 920mhz bandwidth (max3266) 1900mhz bandwidth (max3267) 1ma input overload +3.0v to +5.5v single-supply voltage max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans ________________________________________________________________ maxim integrated products 1 out- gnd filter 1 2 8 7 gnd out+ n.c. in v cc so top view 3 4 6 5 max3266 max3267 0.01 f photodiode 1.5k v cc v cc gnd filter in 0.1 f out+ out- 0.1 f c filter 400pf 100 ? max3266 max3267 limiting amplifier typical application circuit 19-4796; rev 1; 6/00 part max3266 csa max3266c/d 0? to +70? temp. range pin-package 8 so dice* evaluation kit available * dice are designed to operate over a -40? to +140? junction tem- perature (tj) range, but are tested and guaranteed at t a = +25?. pin configuration ordering information max3267 csa max3267c/d 0? to +70? 8 so dice* max3267esa -40? to +85? 8 so max3267e/d dice* for free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. for small orders, phone 1-800-835-8769.
ps max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics?ax3266c/max3267c (v cc = +3.0v to +5.5v, t a = 0? to +70?, 100 ? load between out+ and out-. typical values are at t a = +25?, v cc = 3.3v, source capacitance = 0.85pf, unless otherwise noted.) (note 1) 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. supply voltage (v cc - gnd) .................................-0.5v to +6.0v in current..............................................................-4ma to +4ma filter current......................................................-8ma to +8ma voltage at out+, out- ...................(v cc - 1.5v) to (v cc + 0.5v) continuous power dissipation (t a = +70?) 8-pin so (derate 6.7mw/? above +70?)..................533mw storage temperature range .............................-55? to +150? operating junction temperature (die) ..............-55? to +150? processing temperature (die) .........................................+400? lead temperature (soldering, 10s) .................................+300? max3267 max3266 max3267 max3266 max3267 max3266 max3266 max3267 max3266 power-supply rejection ratio (psrr) 50 db output referred, f < 2mhz, psrr = -20log ( ? v out / ? v cc ) 19 76 transimpedance linear range 40 ?p-p 30 low-frequency cutoff 44 khz 750 920 1100 small-signal bandwidth 1530 1900 2420 mhz peak-to-peak, 0.95 < linearity < 1.05 -3db, input 20? dc 6.6 input-referred rms noise 485 655 na 200 dc input overload ac input overload 1.0 map-p 0.65 ma 192 256 so package (note 2) die, packaged in to-56 header (note 2) parameter min typ max units filter resistor 1220 1500 1860 ? output impedance 48 50 52 ? transimpedance 1540 1900 2330 ? supply current input bias voltage 0.69 0.83 0.91 v 26 50 ma 2260 2800 3400 conditions single ended (per side) differential, measured with 30?p-p signal (40?p-p for max3267) maximum differential output voltage 185 250 415 mvp-p input = 1map-p max3266 max3267 input-referred noise density 11.0 pa/(hz) 1/2 (note 2) deterministic jitter 12 50 ps (note 3) max3266 max3267
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans _______________________________________________________________________________________ 3 note 1: source capacitance represents the total capacitance at the in pin during characterization of noise and bandwidth parame- ters. figure 1 shows the typical source capacitance vs. reverse voltage for the photodiode used during characterization of to-56 header packages. noise and bandwidth will be affected by the source capacitance. see the typical operating characteristics for more information. note 2: input-referred noise is calculated as rms output noise / (gain at f = 10mhz). noise density is (input-referred noise) / bandwidth . no external filters are used for the noise measurements. note 3: deterministic jitter is measured with the k28.5 pattern applied to the input [00111110101100000101]. peak-to-peak, 0.95 < linearity < 1.05 so package (note 2) differential, measured with 40?p-p signal power-supply rejection ratio (psrr) 50 db output referred, f < 2mhz, psrr = -20log ( ? v out / ? v cc ) transimpedance linear range 40 ?p-p low-frequency cutoff 24 khz small-signal bandwidth 1515 1900 2550 mhz -3db, input 20? dc deterministic jitter 14 50 input-referred rms noise 485 668 na (note 2) dc input overload ac input overload 1.0 map-p 0.65 ma ps parameter min typ max units filter resistor 1210 1500 1865 ? input-referred noise density 11.0 pa/(hz) 1/2 output impedance 47.7 50 52.1 ? transimpedance ? supply current input bias voltage 0.67 0.83 0.97 v 26 53.2 ma 1470 1900 2355 conditions single ended (per side) maximum differential output voltage 155 250 430 mvp-p input = 1map-p (note 3) electrical characteristics?ax3267e (v cc = +3.0v to +5.5v, t a = -40? to +85?, 100 ? load between out+ and out-. typical values are at t a = +25?, v cc = 3.3v, source capacitance = 0.85pf, unless otherwise noted.) (note 1)
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 4 _______________________________________________________________________________________ 50 60 55 70 65 75 1m 10m 100m 1g 10g frequency response max3266/67-03 frequency (hz) transimpedance (db) max3267 max3266 740 890 840 790 940 990 1040 1090 0 25 50 75 100 max3266 bandwidth vs. temperature max3266/67-07 junction temperature ( c) bandwidth (mhz) c in is source capacitance presented to die, including package parasitic, pin diode, and parasitic interconnect capacitance. c in = 1.5pf c in = 1.0pf c in = 0.5pf 1500 1700 1800 1900 2000 2100 2200 2300 2400 -50 -25 0 25 50 75 100 max3267 bandwidth vs. temperature max3266/67-08 junction temperature ( c) bandwidth (mhz) 1600 c in is source capacitance presented to die, including package parasitic, pin diode, and parasitic interconnect capacitance. c in = 1.5pf c in = 0.5pf c in = 1.0pf 0 100 50 150 200 250 300 350 -50 0 -25 25 75 50 100 output amplitude vs. temperature max3266/67-09 ambient temperature ( c) amplitude (mv) 170 180 190 200 210 220 230 240 250 0 255075100 max3266 input-referred noise vs. temperature max3266/67-01 junction temperature ( c) input-referred noise (na) c in = 1.5pf c in = 1.0pf c in = 0.5pf c in is source capacitance presented to die, including package parasitic, pin diode, and parasitic interconnect capacitance. 350 400 450 500 550 600 650 -50 75 0 -25 25 50 100 max3267 input-referred noise vs. temperature max3266/67-02 junction temperature ( c) input-referred noise (na) c in is source capacitance presented to die, including package parasitic, pin diode, and parasitic interconnect capacitance. c in = 1.5pf c in = 1.0pf c in = 0.5pf 100 20 10 0 10 100 1000 deterministic jitter vs. input amplitude max3266/67-04 peak-to-peak amplitude ( a) peak-to-peak jitter (ps) 40 30 60 70 50 80 90 max3266 max3267 0 300 200 100 400 500 600 700 800 900 1000 1 10 100 1000 input-referred rms noise current vs. dc input current max3266/67-05 differential dc input current ( a) input-referred noise (na) max3267 max3266 60 63 62 61 64 65 66 67 68 69 70 -50 -25 0 25 50 75 100 small-signal transimpedance vs. temperature max3266/67-06 ambient temperature ( c) transimpedance (db) max3266 max3267 typical operating characteristics (v cc = +3.3v, t a = +25?, max3266/max3267 ev kit, source capacitance = 0.85pf, unless otherwise noted.)
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 160ps/div eye diagram (input = 10 ap-p) max3266/67-10 4mv/div input: 2 7 -1 prbs 160ps/div eye diagram (input = 1map-p) max3266/67-11 30mv/div input: 2 7 -1 prbs 80ps/div eye diagram (input = 20 ap-p) max3266/67-12 5mv/div input: 2 7 -1 prbs name function 1 v cc supply voltage pin pin description 2 n.c. no connection. not internally connected. 3 in amplifier input 4 filter provides bias voltage for the photodiode through a 1.5k ? 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. 5 gnd ground 6 out- inverting output. current flowing into in causes v out- to decrease. 7 out+ noninverting output. current flowing into in causes v out+ to increase. 8 gnd ground typical operating characteristics (continued) (v cc = +3.3v, t a = +25?, max3266/max3267 ev kit, source capacitance = 0.85pf, unless otherwise noted.) -150 -100 -50 0 50 100 150 -200 -100 -150 -50 0 50 100 150 200 dc transfer function max3266/67-14 input current ( a) output voltage (mvp-p) max3267 max3266 80ps/div eye diagram (input = 1map-p) max3266/67-13 30mv/div input: 2 7 -1 prbs _______________________________________________________________________________________ 5
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 6 _______________________________________________________________________________________ detailed description the max3266 is a transimpedance amplifier designed for 1.25gbps fiber optic applications. figure 2 is a func- tional diagram of the max3266, which comprises a trans- impedance amplifier, a voltage amplifier, an output buffer, an output filter, and a dc cancellation circuit. the max3267, a transimpedance amplifier designed for 2.5gbps fiber optic applications, shares similar architecture with the max3266. transimpedance amplifier the signal current at the input flows into the summing node of a high-gain amplifier. shunt feedback through r f converts this current to a voltage with gain of approx- imately 2.2k ? (1.0k ? for max3267). schottky diodes clamp the output voltage for large input currents, as shown in figure 3. voltage amplifier the voltage amplifier converts single-ended signals to differential signals and introduces a voltage gain. output buffer the output buffer provides a reverse-terminated volt- age output. the buffer is designed to drive a 100 ? dif- ferential load between out+ and out-. the output current is divided between internal 50 ? load resistors and the external load resistor. in the typical operating circuit, this creates a voltage-divider with gain of 1/2. the max3266 can also be terminated with higher out- put impedances, which increases gain and output volt- age swing. for optimum supply-noise rejection, the max3266 should be terminated with a differential load. if a single- ended output is required, the unused output should be similarly terminated. the max3266 will not drive a dc- coupled, 50 ? grounded load. voltage amplifier transimpedance amplifier output buffer output filter out+ 50 ? 50 ? out- v cc r f v cc lowpass filter 1.5k filter in gnd dc cancellation circuit disable max3266 figure 2. max3266 functional diagram 0.50 0.95 0.80 0.65 1.10 1.25 1.40 1.55 1.70 1.85 2.00 02 1 345 max3266/67 fig01 reverse bias (v) capacitance (pf) figure 1. typical photodiode capacitance vs. bias voltage
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans _______________________________________________________________________________________ 7 output filter the max3266 includes a one-pole lowpass filter that limits the circuit bandwidth and improves noise perform- ance. dc cancellation circuit the dc cancellation circuit uses low-frequency feed- back to remove the dc component of the input signal (figure 4). this feature centers the input signal within the transimpedance amplifier? linear range, thereby reducing pulse-width distortion on large input signals. the dc cancellation circuit is internally compensated and therefore does not require external capacitors. this circuit minimizes pulse-width distortion for data sequences that exhibit a 50% duty cycle. a duty cycle significantly different from 50% will cause the max3266 to generate pulse-width distortion. dc cancellation current is drawn from the input and creates noise. for low-level signals with little or no dc component, this is not a problem. amplifier noise will increase for signals with significant dc component (see typical operating characteristics ). applications information optical power relations many of the max3266 specifications relate to the input signal amplitude. when working with fiber optic receivers, the input is usually expressed in terms of aver- age optical power and extinction ratio. figure 5 shows relations that are helpful for converting optical power to input signal when designing with the max3266. optical power relations are shown in table 1; the defini- tions are true if the average duty cycle of the input data is 50%. optical sensitivity calculation the input-referred rms noise current (i n ) of the max3266 generally determines the receiver sensitivity. to obtain a system bit error rate (ber) of 1e-12, the snr ratio must always exceed 14.1. the input sensitivi- ty, expressed in average power, can be estimated as: where is the photodiode responsivity in a/w. input optical overload the overload is the largest input that the max3266 accepts while meeting specifications. the optical over- load can be estimated in terms of average power with the following equation: overload ma dbm log = ? ? ? ? ? ? 10 1 2 1000 sensitivity ir r dbm ne e = + () ? () ? ? ? ? ? ? ? ? 10 14 1 1 21 1000 log . amplitude output (large signals) time output (small signals) figure 3. max3266 limited output figure 4. dc cancellation effect on input amplitude input from photodiode time input (after dc cancellation)
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 8 _______________________________________________________________________________________ optical linear range the max3266 has high gain, which limits the output when the input signal exceeds 30?p-p (40?p-p for max3267). the max3266 operates in a linear range for inputs not exceeding: layout considerations use good high-frequency design and layout tech- niques. the use of a multilayer circuit board with sepa- rate ground and power planes is recommended. connect the gnd pins to the ground plane with the shortest possible traces. noise performance and bandwidth will be adversely affected by capacitance at the in pin. minimize capaci- tance on this pin and select a low-capacitance photodi- ode. assembling the max3266 in die form using chip and wire technology provides the best possible perform- ance. figure 6 shows a suggested layout for a to header. the so package version of the max3266 is offered as an easy way to characterize the circuit and become familiar with the circuit? operation, but it does not offer optimum performance. when using the so version of the max3266, the package capacitance adds approxi- mately 0.3pf at the input. the pc board between the max3266 input and the photodiode also adds parasitic capacitance. keep the input line short, and remove power and ground planes beneath it. 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 max3266, combined with an external capacitor, can be used to reduce this noise (see the typical application circuit ). current gen- erated 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 = 100mvp-p, c pd = 0.85pf, r filter = 1.5k ? , and i noise selected to be 100na (1/2 of the max3266? input noise): c filter = (100mv)(0.85pf) / (1500 ? )(100na) = 570pf wire bonding for high current density and reliable operation, the max3266 uses gold metalization. connections to the die should be made with gold wire only, using ball- bonding techniques. wedge bonding is not recom- mended. die thickness is typically 15mils (0.375mm). linear range ar r dbm e e = + () ? () ? ? ? ? ? ? 10 30 1 21 1000 log figure 5. optical power relations po pi p avg time optical power parameter average power extinction ratio optical power of a 1 p1 r e p avg symbol relation p avg = (p0 + p1) / 2 r e = p1/p0 p1 = 2p avg (r e ) / (r e + 1) optical power of a 0 p0 p0 = 2p avg / (r e + 1) signal amplitude p in p in = p1 - p0 = 2p avg (r e ) / (r e + 1) table 1. optical power relations
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans _______________________________________________________________________________________ 9 figure 6. suggested layout for to-56 header case is ground top view of to-56 header c filter v cc photodiode max3266/max3267 out+ out- chip topographies 0.050" (1.25mm) 0.030" (0.75mm) gnd out- filter input v cc gnd out+ 0.050" (1.25mm) 0.030" (0.75mm) gnd out- filter input v cc gnd out+ max3266 max3267 transistor count: 320 substrate connected to gnd
max3266/max3267 1.25gbps/2.5gbps, +3v to +5.5v, low-noise transimpedance preamplifiers for lans 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 2000 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information soicn.eps
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