general description the gd16076a is a 2.5 gbit/s laser modulator driver designed for providing a controllable drive current to an optical modulator (linbo 3 ) circuit properly bi- ased and with 25 w or 50 w characteris- tic input impedance. the gd16076a features differential ecl compatible, wide common mode range inputs (din, ndin) with loop through ter- mination capability for optimal input re- flection coefficient. the pins out and nout are open drain outputs designed for driving an external load with a characteristic impedance of: u 25 w (GD16076A-25SLP) u 50 w (gd16076a-50slp) the outputs can sink a current that can be controlled in the range 40ma - 180ma by vcip. the output voltage swing across an external load may be varied accordingly. for the 25 w version the output voltage swing may be adjusted in the range 1.0 v p-p - 4.5 v p-p . for the 50 w version, the output swing may be adjusted within the range 2.0 v p-p - 6.0 v p-p (typ.). the output current may be monitored at pin sip. the part is housed in a high speed 40 pin leaded multi layer ceramic (mlc) package. features l 2.5 gbit/s operation. l 180 ma maximum modulator current. l ecl compatible differential inputs. l power dissipation: 1.5 - 2.3 w (typ.) l available in two versions for: ?25 w (GD16076A-25SLP) ?50 w (gd16076a-50slp) l housed in a leaded 40 pin mlc package. applications l tele communications systems: ? sdh stm-16 ? sonet oc-48 l data communications. l linbo 3 modulator driver. l high current laser driver. l high-speed clock buffer. 2.5 gbit/s linbo 3 modulator driver gd16076a data sheet rev. 07 veep vee vdd nout out ndin vref din veep vsip vcip
functional details gd16076a is designed to drive external loads with a characteristic impedance of: u 25 w (GD16076A-25SLP) u 50 w (gd16076a-50slp). with din high the sink current into out will be high. in order to avoid reflections, and thereby to obtain optimum performance, connec- tions from out and/or nout must be made with a transmission line of 25 w (50 w ), terminated at the device end into a matched load. this is because out and nout are unterminated open drain outputs and effectively can be regarded as modulated current sources. the termination voltage on an output is determined by the load impedance z l (25 w or 50 w ) and the output current i out . the optimum termination voltage v cc is: v cc =v dd -2v+z l i out see: ?thermal considerations? in the sec- tion application information below. the driver output current i out can be measured as the voltage drop across a resistor r sip , internally on the chip, con- nected in between the veep pin and the sip pin. figure 1. application diagram by using an external general purpose operational amplifier, as illustrated in figure 1, the driver output current i out may be controlled accurately and inde- pendent of environmental changes. vref in figure 1 should be r sip i out , see above. the op-amp must be able to drive cip in the range veep - 1.2 v to veep +1.2 v. r sip is made of two resistors of 4 w ,as shown in figure on page 1. one of the resistors are connected to the veep pins 4 and 5, and the other to the veep pins 16 and 17. if all veep are connected, r sip is 2 w . each resistor has been dimensioned to withstand 100 ma. therefore if the output current i out is > 100 ma the veep pins on opposite sides must be connected externally in order not to damage the chip. notice that the transistors driving out and nout are susceptible to breakdown. therefore the peak voltage on out and nout should never exceed 10.0 v above veep as specified in maximum ratings . application information in this section the behaviour of gd16076a is described when used in connection with a linbo 3 mach zender interferometer, for simplicity called ?the modulator?. first the modulator and a transfer function from electrical to optical signal is derived. next a spice simula- tion of the application diagram in figure 1 is shown. in this simulation the modulator is connected to the output of gd16076a via a transmission line with a characteris- tic impedance of 25 w . finally some ther- mal properties of gd16076a are considered. the mach zender interferometer. the modulator is typically made as shown in figure 2. its function is to inten- sity modulate the incoming unmodulated light. in optical data transmission systems, cur- rent modulation of the light directly in the semiconductor laser, causes the optical signal from the laser to have chirp (fre- quency fluctuations of the light fre- quency). this degrades system performance. data sheet rev. 07 gd16076a page 2 veep vee 50 -5v -5v -5v vtt = -2v 50 1k 100nf vref 50 50 50 25 vcc vcc 25 optical in modulator optical out vdd nout out ndin din data ndata veep vsip vcip
figure 2. optical modulator with segmented transmission line. the incoming light to the modulator is an unmodulated continuous light wave, and therefore does not suffer from chirp. the signal treatment within the modulator is linear, see below. consequently the modulated light signal does not suffer from chirp. high speed optical communication systems using a mach zender interfer- ometer therefore has better system per- formance than systems using direct current modulation. characterisation of the modulator when the light enters the modulator it is split into two branches, as shown in figure 2. on the output it is combined again. the propagation delay of the light wave can be adjusted through one (or both) of the branches by applying a voltage to the substrate near the optical wave-guide. this is because the refractive index of the material changes proportional to the voltage applied to the substrate and be- cause the velocity of light is proportional to the refractive index. changing the re- fractive index in one branch therefore gives a tuneable delay variation between the two branches. thereby the light can be combined in phase, making the light pass through to the output without atten- uation, or in counter phase, thereby turn- ing off the light. typically the electrical data signal for a high-speed modulator is connected into the modulator via a transmission line, traveling along one of the optical branches. on the output the transmission line is terminated in order to obtain a good input impedance. an equivalent diagram for the modulator has been derived. the diagram was made from the physical components of the modulator (input pin, bonding wires and transmission line characteristics), and fitting the component values to mea- surements. at low modulation rates the relation be- tween the voltage applied to the modula- tor and the relative light p on the output can be described as: p vvv act off = ++ (cos(( )/)) 1 2 p ? (1) where: v act is the voltage applied to the active region v off is an offset voltage (material de- pendent) v ? is the voltage difference between the applied voltages that causes fully on and fully off light on the output respectively. from (1) some important features of the modulator can bee derived. when (v act +v off )/v ? =1thenp=0. if (v act +v off )/v ? becomes slightly larger than 1 or smaller than 1, p still ap- proximates 0 very closely. 20 % over (un- der) shoot causes p to be only 0.1. this is due to the sine transformation in (1). therefore the modulator effectively acts as a pulse shaper on the voltage v act defined above and attenuates any small over and/or undershoot in the electrical signal. however if the over and/or undershoot in the electrical signal becomes larger than approximately 1/3 v ? there will be no lim- iting effect. instead two pulses will be created on the optical output. an over- shoot of 50 % causes p to be 0.5. i.e. in- stead of only one optical output pulse a second pulse has been created. there- fore it is important to ensure that the ring- ing on the electrical signal is less than approximately 20%. the above formula works well at low modulation rates. however at high speed data rates the formula does not describe the function precisely, because the volt- age actually travels as a wave along the active part. assuming first that the velocity of light is much higher than the electrical signals propagation velocity, the voltage that any light wave actually sees, will be the aver- age of the voltages along the transmis- sion lines, taking into account that the transmission line represents a loss. now this voltage can be used as v act in the above formula. in reality the velocity of light v l is approximately c/2.2 for linbo 3 , whereas the electrical signal?s propaga- tion velocity is approximately cc 113 34 . . = where c is the velocity of light in open air. this means that instead of just averaging the voltage across the active area, the voltage that the optical wave actually sees is a function of time. this was modeled by splitting up the ac- tive area into 10 parts, see figure 2. the optical wave present at l n at time t n was present at l n+1 at time t n -d t /v l , where d t is the distance from l n to ln+1. the ef- fective voltage v act exposed to the light wave entering the active area at time t - causing the optical refractive index of the linbo 3 to change, and thereby changing the velocity of the light - therefore can be expressed as: v n v t ndt v act n i n n = + - = ? 1 1 0 (/) (2) where v n (t) is the voltage at l n . the above formulas (1) and (2) were used together with the electrical equiva- lent diagram for the modulator to make spice simulations of the behaviour of gd16076a connected to an optical modulator as shown in figure 1. data sheet rev. 07 gd16076a page 3 vcc optical wave guides in linbo 3 active area d t v;l n+1 n+1 l n v n v n v sumn delay = nd / v ti + - electrical signal input optical input segmented transmission line
simulations in figur e 3 a simulation of the application diagram in figure 1 is shown. the modu- lation current is 180 ma. the simulation shows the relative optical output power p as defined above. as shown the optical output has little ringing. rise and fall times are below 90 ps. in conclusion the above simulations have shown that gd16076a is capable of driving a mach zender interferometer with a 180 ma drive current into 25 w at 2.5 gbit/s. thermal considerations as shown in figure 1 both the modulator and the unused nout outputs are termi- nated to v cc . in order to reduce the chip power consumption it is important that v cc is kept as low as possible. if e.g. the output current is 180 ma into 25 w the voltage swing will be 4.5 v. if v cc = 4.5 v the power consumption p oc due to output current will be: p oc = (v cc -v eep -180ma 25 w ) 180ma = 900mw (3) if instead v cc = 2.5 v is used the power consumption will be only 540 mw. approximately 360 mw of p oc is con- sumed by the current source and current sense resistors, see figure on page 1 re- gardless of v cc . therefore the power consumption in the output fet?s are re- duced from 540 mw (270 mw each out- put fet) down to 180 mw (90 mw each output fet). therefore it is recommended to use the lowest possible value for v cc , which does not sacrifice the performance of the mod- ulator driver. the open drain outputs of gd16076a works down to v dd -2v. with 180 ma output current into 25 w this means that v cc can be as low as 2.5 v. figure 3. simulation of the optical output of the modulator data sheet rev. 07 gd16076a page 4 0s 0 0.5 1.0 180 ma modulation current into 25 w temperature 75.0 c o 1.0ns 0.5ns 1.5ns 2.0ns 2.5ns 3.0ns 3.5ns
pin list mnemonic: pin no.: pin type: description: din ndin 32, 32 29, 30 ecl in loop through? data inputs. out nout (out) (nout) 9, 10 11, 12 (9) (12) open drain data outputs for 25 w version GD16076A-25SLP. (data outputs for 50 w version gd16076a-50slp). vcip 6, 15 bias in driver current control input. vsip 2, 19 analogue out driver current sense output. vdd 3, 7, 8, 13, 14, 18, 21, 23, 24, 25, 26, 28, 33, 35, 36, 37, 40 (10,11) pwr ground. common for both 25 w and 50 w versions. (only 50 w version gd16076a-50slp) vee 1, 20, 22, 27, 34, 39 pwr negative supply. veep 4, 5, 16, 17 pwr negative supply. vref 38 analogue in for normal operation leave open. data sheet rev. 07 gd16076a page 5
package pinout figure 4. 25 w output version - top view figure 5. 50 w output version - top view data sheet rev. 07 gd16076a page 6 5 4 3 2 1 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 veep veep vdd vsip vee vdd vee vref vdd vdd vdd vee vdd din din ndin ndin vdd vee vdd vdd vdd vdd vee vdd vee vsip vdd veep veep vcip vdd vdd nout nout out out vdd vdd vcip 5 4 3 2 1 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 veep veep vdd vsip vee vdd vee vref vdd vdd vdd vee vdd din din ndin ndin vdd vee vdd vdd vdd vdd vee vdd vee vsip vdd veep veep vcip vdd vdd nout vdd vdd out vdd vdd vcip
maximum ratings these are the limits beyond which the component may be damaged. all voltages in table are referred to vdd (gnd). all currents in table are defined positive out of the pin. symbol: characteristic: conditions: min.: typ.: max.: unit.: v eep supply voltage note 1 v ee - 0.5 2.5 v v ee supply voltage - 7.0 0 v v o out,nout applied voltage out, nout v eep -0.5 v eep +10 v i o out,nout output current out, nout - 200 ma v i vcip output current control v eep -1.4 v eep +1.4 v v i din,ndin applied voltage din, ndin v ee -0.5 0.5 v t o operating temperature channel - 55 +150 e c t s storage temperature - 65 +175 e c note 1: veep normally connected to vee externally. dc characteristics t case =0 e cto85 e c. all voltages in table are referred to vdd (gnd). all currents in table are defined positive out of the pin. symbol: characteristic: conditions: min.: typ.: max.: unit: v eep negative supply voltage for output - 5.5 - 5.2 - 5.0 v v ee negative supply voltage - 5.5 - 5.2 - 5.0 v i veep negative supply current note 1 40 180 ma i vee negative supply current note 1 260 ma p diss,open power dissipation v eep unconnected 1.4 w p diss power dissipation note 1 2.3 w v vcip output current control voltage v eep - 1.4 v eep +1.4 v v hi din,ndin din, ndin hi input voltage v cm + 0.3 v v lo din,ndin din, ndin lo input voltage v cm -0.3 v v cm din,ndin din, ndin common mode voltage - 2.0 - 1.0 v i oh out,nout out,nout output hi current note 2, 4 - 180 - 40 ma i ol out,nout out,nout output lo current note 3 1 % note 1: r l =25 w . maximum amplitude on r l assumed (180 ma modulation current). r l connected to vdd + 2.8 v. duty cycle 50%. note 2: hi current is defined as maximum current sink. note 3: see i ol out,nout ac characteristics below. note 4: minimum specification corresponds to maximum amplitude on load. i oh out,nout depends on v cip . data sheet rev. 07 gd16076a page 7
ac characteristics t case =0 o cto85 o c. symbol: characteristic: conditions: min.: max.: unit: f max din,out maximum data i/o frequency 2.5 gbit/s t r out out rise time (20 ? 80 %) note 1 100 120 ps t f out out fall time (20 ? 80 %) note 1 100 120 ps v amp out out voltage amplitude (p-p) note 1 4.5 v d i oh out,nout relative deviation of out output hi current from current through sense resistor r sip . note 1, 2, 3 +/- 5 % i ol out,nout out output lo current relative to i hi out note 1, 4 1 % f vcs modulation frequency note 5 100 khz note 1: r l =25 w mounted at package pin ( c l <= 1pf). differential input signals with t r ,t f < 140 ps (10 ? 90 %) and amplitude > 600 mv pp assumed. note 2: defined as: d i vv kr i hi oh out sip eep sip out = -- 1( ) where k takes into account parasitic resistance within the package and the pcb, and process variations on r sip .r sip normally is 2 w (see functional details above). note 3: guaranteed up to 2.5 gbit/s. note 4: 11001100 2.5 gbit/s patterns and lower frequency patterns. for a 1010 2.5 gbit/s pattern the deviation is allowed to be +/-5%. note 5: modulation depth for current at least 5%. package pinout figure 6. package 40 pin (all dimensions are in inch) data sheet rev. 07 gd16076a page 8 note 1: leads are hot dip soldered before cutting 0.480" +- 0.006 bottom view top view side view 0.020" 0.680" +- 0.006 max 0.008" note 2: coplanarity of leads > 0.008" 0.015" +- 0.003" 0.100" +- 0.02 0.105" +- 0.011 0.040" +- 0.006 pin 1
device marking figure 7. device marking (xx = option) ordering information to order, please specify as shown below: product name: option: package type: case temperature range: GD16076A-25SLP 25 w load 40 pin straight leads tinned 0..85 o c gd16076a-50slp 50 w load 40 pin straight leads tinned 0..85 o c gd16076a, data sheet rev. 07 - date: 4 january 1999 the information herein is assumed to be reliable. giga assumes no responsibility for the use of this information, and all such information shall be at the users own risk. prices and specifications are subject to change without notice. no patent rights or licenses to any of the circuits described herein are implied or granted to any third party. giga does not authorise or warrant any giga product for use in life support devices and/or systems. mileparken 22, dk-2740 skovlunde denmark telephone : +45 4492 6100 telefax : +45 4492 5900 e-mail : sales@giga.dk web site : http://www.giga.dk please check our internet web site for latest version of this data sheet. distributor: copyright ? 1999 giga a/s all rights reserved gd16076a-xx wwyy gd16076a-xx bottom view top view
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