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19-2281; Rev 2; 5/03
2.7Gbps Laser Driver with Modulation Compensation
General Description
The MAX3863 is designed for direct modulation of laser diodes at data rates up to 2.7Gbps. An automatic power-control (APC) loop is incorporated to maintain a constant average optical power. Modulation compensation is available to increase the modulation current in proportion to the bias current. The optical extinction ratio is then maintained over temperature and lifetime. The laser driver can modulate laser diodes at amplitudes up to 80mA. Typical (20% to 80%) edge speeds are 50ps. The MAX3863 can supply a bias current up to 100mA. External resistors can set the laser output levels. The MAX3863 includes adjustable pulse-width control to minimize laser pulse-width distortion. The device offers a failure monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3863 accepts differential CML clock and data input signals with on-chip 50 termination resistors. If a clock signal is available, an input data-retiming latch can be used to reject input pattern-dependent jitter. The laser driver is fabricated with Maxim's in-house second-generation SiGe process. Single +3.3V Power Supply 58mA Power-Supply Current Up to 2.7Gbps (NRZ) Operation On-Chip Termination Resistors Automatic Power Control (APC) Compensation for Constant Extinction Ratio Programmable Modulation Current Up to 80mA Programmable Bias Current Up to 100mA 50ps Typical Rise/Fall Time Pulse-Width Adjustment Circuit Selectable Data-Retiming Latch Failure Detector Mark-Density Monitor
Features
MAX3863
Current Monitors ESD Protection
Ordering Information
PART MAX3863EGJ MAX3863E/D* TEMP RANGE -40C to +85C -40C to +85C PINPACKAGE 32 QFN Dice PKG CODE G3255-1 --
*Dice are designed and guaranteed to operate from -40C to +85C, but are tested only at TA = +25C
Applications
SONET and SDH Transmission Systems
30 BIASMAX 32 RTEN
Pin Configuration
28 MODCOMP
3.2Gbps Data Communications Add/Drop Multiplexers Digital Cross-Connects Section Regenerators Long-Reach Optical Transmitters
VCC
27 VCC
WDM Transmission Systems
TOP VIEW
26 BIASMON
29 MODSET
31 EN
25 MODMON
1 2 3 4 5 6 7 8
24 23 22
MDMON MD
VCC
DATA+ DATAVCC VCC
MAX3863
21 20 19 18 17
MODN MOD
VCC
CLK+ CLKVCC
BIAS FAIL
APCFILT1 10
APCFILT2 11
PWC+ 12
PWC- 13
THE EXPOSED PAD MUST BE SOLDERED TO GND ON THE CIRCUIT BOARD.
________________________________________________________________ Maxim Integrated Products
APCSET
Covered by U.S. patent number 5,883,910. Other patents pending.
MK+ 15
MK- 16
VCC 14
9
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
2.7Gbps Laser Driver with Modulation Compensation MAX3863
ABSOLUTE MAXIMUM RATINGS
Supply Voltage VCC...............................................-0.5V to +5.0V DATA+, DATA- and CLK+, CLK- ....(VCC - 1.5V) to (VCC + 0.5V) RTEN, EN, BIAS, MK+, MK-, PWC+, PWCMODMON, BIASMON, MDMON, MODCOMP, APCFILT1, APCFILT2, BIASMAX, MODSET, APCSET Voltage.........................................-0.5V to VCC + 0.5V MOD, MODN Voltage..........................................0 to VCC + 1.5V MOD, MODN Current......................................-20mA to +150mA BIAS Current ...................................................-20mA to +150mA MD Current............................................................-5mA to +5mA Operating Junction Temperature Range ...........-55C to +150C Storage Temperature Range .............................-55C to +150C Continuous Power Dissipation (TA = +85C) 32-Pin QFN (derate 21.2mW/C above +85C) ...............1.3W Processing Temperature (die) .........................................+400C Lead Temperature (soldering, 10s) ................................ +300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC = +3.15V to +3.6V, TA = -40C to +85C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 40mA, TA = +25C, unless otherwise noted.) (Notes 1, 9)
PARAMETER Power-Supply Current Power-Supply Noise Rejection Power-Supply Threshold Single-Ended Input Resistance Bias-Current Setting Range Bias-Current Setting Error Bias Off-Current IBIAS to IBIASMON Ratio Bias-Current Temperature Stability Modulation-Current Setting Range Modulation-Current Setting Error Modulation Off-Current Modulation-Current Temperature Stability IMOD to IMODMON Ratio Modulation Compensation Range MD Pin Voltage Monitor Photodiode Current Range APC Loop Time Constant APC Open Loop VMDMON to IMD Ratio EN and RTEN Input High EN and RTEN Input Low FAIL Output High FAIL Output Low VIH VIL VOH VOL Source 150A Sink 2mA 2.4 0.4 IMD tAPC (Notes 3, 4) 4mA IBIAS 10mA (Note 3) RMDMON = 4k 0.8 2.0 0.8 30 1 4 390 1.0 1.2 K K = IMODC/IBIAS APC open loop, 25 load, TA = +25C EN high APC open loop (Note 3) -480 38 0 46 APC open loop, 10mA IBIAS 100mA (Note 3) APC open loop, 4mA IBIAS 100mA (Note 3) 7 -15 APC open loop, IBIAS = 100mA, TA = +25C APC open loop, IBIAS = 4mA, TA = +25C EN high 34 -480 390 80 +15 0.1 +480 53 1.5 1.75 2000 1000 40 SYMBOL ICC PSNR (Note 2) f = 100kHz, 100mVP-P (Note 10) Output enabled Input to VCC 40 4 -15 -20 CONDITIONS MIN TYP 58 40 2.8 50 60 100 +15 +20 0.1 46 +480 MAX 85 UNITS mA dB V mA % mA mA/mA ppm/C mA % mA ppm/C mA/mA mA/mA V A s mA mV/A V V V V
2
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2.7Gbps Laser Driver with Modulation Compensation
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.15V to +3.6V, TA = -40C to +85C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 40mA, TA = +25C, unless otherwise noted.) (Notes 1, 9)
PARAMETER Single-Ended Input (DC-Coupled) SYMBOL VIS At high At low At high Single-Ended Input (AC-Coupled) VIS At low Differential Input Swing Input Data Rate Input Return Loss Turn-Off Delay from EN Setup Time Hold Time Pulse-Width Adjustment Range Pulse-Width Stability Differential Pulse-Width Control Input Range Differential Mark Density Differential Mark-Density Voltage to Mark-Density Ratio Output Edge Speed Output Overshoot Random Jitter Deterministic Jitter tR, tF ZL = 25 (20% to 80%) (Notes 3, 6) ZL = 25 (Note 3) (Notes 3, 6) Data Rate = 2.7Gbps (Notes 3, 8) Data Rate = 3.2Gbps (Notes 3, 8) tSU tHD RLIN VID DC-coupled AC-coupled NRZ (Note 3) (Notes 3, 5) EN = high (Note 3) Figure 2 (Note 3) Figure 2 (Note 3) ZL = 25 (Notes 3, 6) PWC+ and PWC- open (Notes 3, 6) For PWC+ and PWC- (Notes 3, 7), VCM = 0.5V 0% to 100%, VMK+ - VMK15.5 50 7 0.8 8 10 1.3 40 40 85 -1.0 90 90 185 220 18.5 1.0 0.85 f 2.7GHz 2.7GHz < f 4GHz VCC - 1.0 VCC + 0.05 VCC 0.4 0.2 0.2 3.2 17 14 1.0 CONDITIONS MIN TYP VCC VCC - 0.1 VCC + 0.4 V VCC 0.05 2.0 1.6 VP-P Gbps dB s ps ps ps ps V V V/% ps % psRMS psP-P MAX UNITS V
MAX3863
Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7:
Specifications at -40C are guaranteed by design and characterization. Excluding IBIAS, IMOD, IBIASMON, IMODMON, IFAIL, and IPWC. Input clock and data are AC-coupled. Guaranteed by design and characterization. An external capacitor at APCFILT1 and APCFILT2 is used to set the time constant. For both data inputs DATA+, DATA- and clock inputs CLK+, CLK-. Measured using a 2.7Gbps repeating 0000 0000 1111 1111 pattern. For pulse width, PW = 100%: Rp = Rn = 500 (or open) or PWC+ = PWC- +0.5V. For PW > 100%: Rp > Rn or PWC+ > PWC-. For PW < 100%: Rp < Rn or PWC+ < PWC-. Note 8: Measured using a 213 - 1 PRBS with 80 zeros + 80 ones input data pattern or equivalent. Note 9: AC characterization performed using the circuit in Figure 1. Note 10: Power-Supply Noise Rejection (PSNR) = 20log10(VNOISE (on VCC)/VOUT). VOUT is the voltage across the 25 load when no input is applied.
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3
2.7Gbps Laser Driver with Modulation Compensation MAX3863
Typical Operating Characteristics
(TA = +25C, unless otherwise noted. See Typical Operating Circuit.)
ELECTRICAL EYE DIAGRAM (IMOD = 80mA, DATA RATE = 2.7Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc01a
ELECTRICAL EYE DIAGRAM (IMOD = 80mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc01b
ELECTRICAL EYE DIAGRAM (IMOD = 7mA, DATA RATE = 2.7Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc02a
52ps/div
52ps/div
52ps/div
ELECTRICAL EYE DIAGRAM (IMOD = 7mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc02b
OPTICAL EYE DIAGRAM (IMOD = 40mA, DATA RATE = 2.5Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc03a
OPTICAL EYE DIAGRAM (IMOD = 40mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID)
MAX3863 toc03b
52ps/div
58ps/div
58ps/div
SUPPLY CURRENT (ICC) vs.TEMPERATURE (EXCLUDES BIAS AND MODULATION CURRENTS)
MAX3863 toc04
DETERMINISTIC JITTER vs. IMOD
MAX3863 toc05
PULSE-WIDTH ADJUST vs. DIFFERENTIAL VPWC
MAX3863 toc06
80 75 SUPPLY CURRENT (mA) 70 65 60 55 50 45 40 -40 -20 0 20 40 60
16 14 DETERMINISTIC JITTER (psP-P) 12 3.2Gbps 10 8 6 4 2 0 5 15 25 35 45 55 65 75 2.7Gbps
300 200 PULSE-WIDTH ADJUST (ps) 100 0 -100 -200 -300
80
85
-0.8 -0.6 -0.4 -0.2
0
0.2
0.4
0.6
0.8
TEMPERATURE (C)
IMOD (mA)
VPWC+ - VPWC- (V)
4
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2.7Gbps Laser Driver with Modulation Compensation
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted. See Typical Operating Circuit.)
MODULATION CURRENT vs. MODULATION SET RESISTOR
MAX3863 toc07
MAX3863
MODULATION MONITOR VOLTAGE vs. MODULATION CURRENT
MAX3863 toc08
BIAS CURRENT vs. BIASMAX SET RESISTOR
MAX3863 toc09
100
200 180 160 140 VMODMON (mV)
1000
100 IBIAS (mA) 10 1 5 20 35 50 65 80 0.1 1 10 RBIASMAX (k) 100 IMOD (mA)
IMOD (mA)
120 100 80 60 40 20
10
1 0.1 1 RMODSET (k) 10 100
0
BIAS MONITOR VOLTAGE vs. BIAS CURRENT
MAX3863toc10
MONITOR DIODE CURRENT vs. APCSET RESISTOR
MAX3863 toc11
DIODE-CURRENT MONITOR VOLTAGE vs. MONITOR DIODE CURRENT
MAX3863 toc12
300 250 VBIASMON (mV) 200
10
3.0 2.5 2.0 1.5 1.0 0.5
150 100 50 0 0 10 20 30 40 50 60 70 80 90 100 IBIAS (mA)
0.1
VMDMON (V)
1 IBIAS (mA)
0.01 0.1 1 10 RAPCSET (k) 100 1000
0 0 0.5 1.0 1.5 2.0 2.5 IMD (mA)
COMPENSATION (K) vs. RMODCOMP
MAX3863 toc13
POWER-SUPPLY NOISE REJECTION vs. FREQUENCY
MAX3863 toc14
SINGLE-ENDED S11 vs. FREQUENCY
-5 MAGNITUDE S11 (dB) -10 -15 -20 -25 -30
MAX3863 toc15
10
120 100 80 PSNR (dB) 60 40 20
0
1 K (mA/mA) 0.1
-35 -40 0.1 1 10 100 1000 10,000 0 1 2 3 4 5 FREQUENCY (kHz) FREQUENCY (GHz)
0.01 0.01 0.1 1 RMODCOMP (k) 10 100
0
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5
2.7Gbps Laser Driver with Modulation Compensation MAX3863
Pin Description
PIN 1, 4, 5, 8, 14, 19, 22, 27 2 3 6 7 9 10 11 12 13 15 16 17 18 20 21 23 24 25 26 28 29 30 31 32 NAME VCC DATA+ DATACLK+ CLKAPCSET APCFILT1 APCFILT2 PWC+ PWCMK+ MKFAIL BIAS MOD MODN MD MDMON MODMON BIASMON MODCOMP MODSET BIASMAX EN RTEN Positive Supply Voltage Data Input, with On-Chip Termination Complementary Data Input, with On-Chip Termination Clock Input for Data Retiming, with On-Chip Termination Complementary Clock Input for Data Retiming, with On-Chip Termination Monitor Diode Current Set Point APC Loop Filter Capacitor. Short to ground to disable the correction loop through the monitor diode. APC Loop Filter Capacitor Input for Modulation Pulse-Width Adjustment. Connected to GND through RPWC. Complementary Input for Modulation Pulse-Width Adjustment. Connected to GND through RPWC. Voltage Proportional to the Mark Density. MK+ = MK- for 50% duty cycle. Voltage Inversely Proportional to the Mark Density Alarm for Shorts on Current Set Pins and APC Loop Failure Conditions, Active Low Laser Diode Bias Current Source (Sink Type) to Bias the Laser Diode. Connect to the laser with an inductor. Driver Output. AC-coupled to the laser diode. Complementary Driver Output. Connect to dummy load off-chip. Monitor Diode Connection Monitor for MD Current. Voltage developed across an external resistor from mirrored MD current. Monitor for Modulation Current. Voltage developed from IMOD mirrored through an external resistor. Monitor for Bias Current. Voltage developed from IBIAS mirrored through an external resistor. Couples the Bias Current to the Modulation Current. Mirrors IBIAS through an external resistor. Open for zero coupling. External Resistor to Program IMODC (IMOD = IMODS + IMODC) External Resistor to Program the Maximum IBIAS Modulation and Bias Current Enable, Active Low. Current disabled when floating or high. Data Retiming Enable Input, Active Low. Retiming disabled when floating or high. FUNCTION
6
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2.7Gbps Laser Driver with Modulation Compensation MAX3863
VCC A - TOKO FSLB2520-330K B - MURATA BLM11HA601SPT A VCC VCC DATA+ PATTERN GENERATOR DATA50 50 VCC VCC CLK+ CLK50 50 CLK+ CLKRTEN EN DATA+ DATAMAX3863 MODN 0.1F MOD APCFILT1 0.1F 50 VCC BIAS 15 50 50 OSCILLOSCOPE B B 25 A
Figure 1. AC Characterization
Detailed Description
The MAX3863 laser driver has two main components: a high-speed modulation driver and a biasing block with APC. The clock and data inputs to the modulation driver use CML logic levels. The optional clock signal synchronizes data transitions for minimum pattern-dependent jitter. Outputs to the laser diode consist of a switched modulation current and a steady bias current. The APC loop adjusts the laser diode bias current to maintain constant average optical power. Compensation of the modulation current can be programmed to keep a constant extinction ratio over time and temperature. The modulation output stage uses a programmable current source with a maximum current of 80mA. A high-speed differential pair switches the source to the laser diode. The rise and fall times are typically 50ps.
Mark-Density Outputs
The MK+ and MK- outputs monitor the input signal mark density. With a 50% mark density, both outputs are the same voltage. More ones cause the MK+ voltage to increase and the MK- voltage to decrease. Fewer ones than zeros cause MK- to be at a higher voltage than MK+.
Pulse-Width Control
A pulse-width adjustment range of 50% to 150% (185ps) is available at 2.7Gbps. This feature compensates pulse-width distortion elsewhere in the system. Resistors at the PWC+ and PWC- pins program the pulse width. The sum of the resistors is 1k. The pins can be left open for a 100% pulse width. A voltage also can control these pins. A differential voltage of 600mV (typ) gives 185ps of pulse-width distortion.
Optional Input Data Retiming
To eliminate pattern-dependent jitter in the input data, a synchronous differential clock signal should be connected to the CLK+ and CLK- inputs, and the RTEN control input should be connected low. The input data is retimed on the rising edge of CLK+. If RTEN is tied high or is left floating, the retiming function is disabled, and the input data is directly connected to the output stage. Leave CLK+ and CLK- open when retiming is disabled.
Output Enable
The MAX3863 incorporates an input to enable current to the laser diode. When EN is low, the modulation and bias outputs at the MOD pin are enabled. When EN is high or floating, the output is disabled. In the disabled condition, bias and modulation currents are off.
Power-Supply Threshold
To prevent data errors caused by low supply, the MAX3863 disables the laser diode current for supply voltage less than 2.7V. The power-supply threshold and
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7
2.7Gbps Laser Driver with Modulation Compensation MAX3863
the output-enable must be true to enable bias and modulation currents.
APC Loop Enable
The APC loop is enabled when an external capacitor is placed between the APCFILT1 and APCFILT2 pins. This capacitor sets the time constant of the APC loop. To open the APC loop, the APCFILT1 pin is shorted to ground. This shorts the feedback from the monitor diode and causes the bias current to rise to the maximum value set by the BIASMAX pin.
voltage to monitor diode current, use an external 4k resistor at the MDMON output. Resistors for BIASMON and MODMON are 100. The minimum voltage at the monitor pins must be 2.1V for compliance.
I VBIASMON = BIAS x 100 40 I VMODMON = MOD x 100 45 I VMDMON = MD x 4k 4
APC Filter
The APC loop keeps the average optical power from the laser constant. An external filter capacitor is used to stabilize the APC loop. The typical capacitor value is 0.01F.
APC Failure Monitor
The MAX3863 provides an APC failure monitor (TTL/CMOS) to indicate an APC loop tracking failure. FAIL is set low when the APC loop cannot adjust the bias current to maintain the desired monitor current.
Design Procedure
When designing a laser transmitter, the optical output is usually expressed in terms of average power and extinction ratio. Table 1 shows relationships helpful in converting between the optical average power and the modulation current. These relationships are valid only if the mark density and duty cycle of the optical waveform are 50%. For a desired laser average optical power (PAVG) and optical extinction ratio (re), the required modulation current can be calculated based on the laser slope efficiency () using the equations in Table 1.
Short-Circuit Protection
The MAX3863 provides short-circuit protection for modulation, bias, and monitor current sources. If BIASMAX, MODSET, or APCSET is shorted to ground, the bias and modulation output are turned off and FAIL is active.
Current Monitors
The MAX3863 features monitor outputs for bias current (BIASMON), modulation current (MODMON), and monitor diode current (MDMON). The monitors are realized by mirroring a fraction of the current and developing a voltage across an external resistor. For the specified
Laser Current Compensation Requirements
Determine static bias and modulation current requirements from the laser threshold current and slope efficiency. To use the APC loop with modulation compensation,
CLK+ VIS = 0.1V TO 0.8V CLKDATAVIS = 0.1V TO 0.8V DATA+ tSU tHD
(DATA+) - (DATA-)
VID = 0.2VP-P TO 1.6VP-P
IMOD
7mA TO 80mA
Figure 2. Required Input Signal, Setup/Hold-Time Definition and Output Polarity 8 _______________________________________________________________________________________
2.7Gbps Laser Driver with Modulation Compensation
Table 1. Optical Power Relations
PARAMETER Average Power Extinction Ratio Optical Power of a 1 Optical Power of a Zero Optical Amplitude Laser Slope Efficiency Modulation Current Threshold Current Bias Current Laser to Monitor Transfer SYMBOL PAVG re P1 P0 PP-P IMOD ITH IBIAS MON RELATION PAVG = (P0 + P1)/2 re = P1/P0 P1 = 2PAVGre/(re + 1) P0 = 2PAVG/(re + 1) PP-P = P1 - P 0 = PP-P/IMOD IMOD = PP-P/ P0 at I ITH IBIAS ITH + IMOD /2 IMD/PAVG
the current from the inductor flows to the bias input. This reduces the current through the laser diode from the average of I BIAS by half of I MOD . The resulting peak-to-peak current through the laser diode is then IMOD. See the Typical Operating Circuit. The requirement for compliance in the AC-coupled circuit: * * * * VD--Diode bias point voltage (1.2V typ) RL--Diode bias point resistance (5 typ) L--Diode lead inductance (1nH typ) RD--Series matching resistor (20 typ) I VCC - MOD x (RD + RL ) 1.8V 2 The time constant associated with the output pullup inductor and the AC-coupling capacitor, impacts the pattern-dependent jitter. For this second-order network LP usually limits the low-frequency cutoff. The capacitor CD is selected so: CD x (RD + RL ) > LP (RD + RL )
MAX3863
use information about the effects of temperature and aging. The laser driver automatically adjusts the bias to maintain the constant average power. The new bias condition requires proper compensation of the modulation current. The designer must predict the slope efficiency of the laser after its bias threshold current has changed. The modulation and bias currents under a single operating condition:
IMOD = 2 x
For AC-coupled diodes:
PAVG re - 1 x re + 1
Keep the peak voltage droop less than 3% of the peakto-peak amplitude during the maximum CID period t. The required time constant:
-t
I IBIAS = ITH + MOD 2
The required compensation factor is then:
2.8% = 1 - e = 35 x t
I K = MOD2 IBIAS2
- IMOD1 - IBIAS1
If = LP/25, and t = 100UI = 40ns, then LP = 35H. Place a good high-frequency inductor of 2H on the transmission line to the laser. Then you can place a low-frequency inductor of 33H at a convenient distance from the driver output.
Programming the Bias Current
When the APC loop is enabled, the actual bias current is reduced from the maximum value to maintain constant current from the monitor diode. With closed-loop control, the bias current will be set by the transfer function of the monitor diode to laser diode current. For example, if the transfer function to the monitor diode is 10.0A/mA, then setting IMD for 500A results in IBIAS equal to 50mA. The bias current must be limited in case the APC loop becomes open. The bias current also needs a set point in case the APC control is not used. The BIASMAX pin sets the maximum bias current. The BIASMAX current is established by an internal current regulator, which maintains the bandgap voltage of 1.2V across the external
9
Once the value of the compensation factor is known, the fixed portion of the modulation current is calculated from: I MODS = I MOD - K x I BIAS
Current Limits
To allow larger modulation current, the laser is ACcoupled to the MAX3863. In this configuration, a constant current is supplied from the inductor LP. When the MOD pin is conducting, half of IMOD is supplied from LP and half is from the laser diode. When MOD is off,
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2.7Gbps Laser Driver with Modulation Compensation MAX3863
VCC RTEN 25 VCC 1 MUX DATA DATA CLK CLK VCC IBIAS CAPC D D Q 0 MOD MODN IMOD CD RD VCC
BIAS VCC 5 x200 BIASMON MODMON MDMON CURRENT MONITOR Vbg x200 IMODS + IMODC Vbg x5 Vbg APCFILT1 APCFILT2 MD
IMD
500pF
RMODSET EN
RMODCOMP
RBIASMAX
RAPCSET
Figure 3. Functional Diagram
programming resistor. See the IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics, and select the value of RBIASMAX that corresponds to the required current at +25C. IBIASMAX = 200 x 1.2V RBIASMAX
Programming the Modulation Current
Two current sources combine to make up the modulation current of the MAX3863 as seen in Figure 3. A constant modulation current programmed at the MODSET pin and a current, proportional to I BIAS, that varies under control by the APC loop. See the Laser Current Compensation Requirements section for the desired values for IMODS and K. The portion of IMOD set by MODSET is established by an internal current regulator, which maintains the bandgap voltage of 1.2V across the external programming resistor. See the I MOD vs. R MODSET graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25C. The current proportional to IBIAS is set by an external resistor at the MODCOMP pin. Open circuiting the MODCOMP pin can turn off the interaction between IBIAS and IMOD.
Programming the Monitor Diode Current Set Point
The APCSET pin controls the set point for the monitor diode current. An internal current regulator establishes the APCSET current in the same manner as the BIASMAX pin. See the IMD vs. RAPCSET graph in the Typical Operating Characteristics, and select the value of RAPCSET that corresponds to the required current at +25C. IMD = 5 x 1.2V RAPCSET
10
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2.7Gbps Laser Driver with Modulation Compensation MAX3863
LASER POWER IMOD1
VCC
IMOD2
P1 T1 T2
50 DATA+
50
PAVG
DATA-
P0 IBIAS1 IBIAS2 LASER CURRENT
GND
Figure 4. Laser Power vs. Current for a Change in Temperature
Figure 5. Equivalent Input Circuit
I MOD = I MODS + K x I BIAS 1.2V I MODS = 200 x R MODSET 5 K = 200 x 500 + R MODCOMP
VCC
MOD
MODN
GND
Applications Information
Layout Considerations
To minimize loss and crosstalk, keep connections between the MAX3863 output and the laser diode as short as possible. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground plane to minimize EMI and crosstalk. Circuit boards should be made using low-loss dielectrics. Use controlled-impedance lines for the clock and data inputs, as well as the module output.
IMOD GND
Figure 6. Equivalent Output Circuit
Laser Safety and IEC 825
Using the MAX3863 laser driver alone does not ensure that a transmitter design is compliant with IEC825. The entire transmitter circuit and component selections must be considered. Determine the level of fault tolerance required by each application and recognize that Maxim products are not designed or authorized for use as components in systems intended for surgical implant into the body, for applications intended to support or sustain life, or for any other application where the
failure of a Maxim product could create a situation where personal injury or death may occur.
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11
2.7Gbps Laser Driver with Modulation Compensation MAX3863
Typical Operating Circuit
VCC VCC RMDMON 100 MDMON RTEN EN RBIASMON 4k BIASMON RMODMON 100 MODMON VCC LP LP 25
DATA+ DATAMAX3892 10Gbps SERIALIZER CLK+ CLK-
50 50 VCC
DATA+ DATAVCC
MODN MOD BIAS MODCOMP APCFILT1 APCFILT2 BIASMAX MODSET APCSET MD PWC-
25 0.1F
MAX3863
25 0.1F 20
50 50
CLK+ CLKPWC+
RMODCOMP
RPWC
CAPC 0.01F
REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE
___________________Chip Information
TRANSISTOR COUNT: 1786 PROCESS: Bipolar DIE SIZE: 81mil x 81mil PACKAGE SIZE: 5mm 5mm
12
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RAPCSET
1k
RBIASMAX
RMODSET
2.7Gbps Laser Driver with Modulation Compensation
Chip Topography
MAX3863
BP28 MODCOMP
BP24 MODMON
BP25 BIASMON
BP30 BIASMAX
BP29 MODSET
BP32 RTEN
BP33 GND
BP27 GND
VCC BP34 BP22 MDMON DATA+ BP35 BP21 MD
DATA- BP36 VCC BP37 VCC BP38
BP23 GND
BP26 VCC
BP31 EN
BP20 GND BP19 VCC
BP18 MODN GND BP39 BP17 MODN 81mil BP16 MOD VCC BP40 BP15 MOD VCC BP41 BP14 VCC CLK+ BP42 BP13 BIAS CLK- BP43 BP12 FAIL
VCC BP44
GND BP1
APCSET BP2
APCFILT1 BP3
APCFILT2 BP4
PWC+ BP5
PWC- BP6
MK- BP10
81mil
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GND BP11
GND BP7
VCC BP8
MK+ BP9
13
2.7Gbps Laser Driver with Modulation Compensation MAX3863
Pad Coordinates
NAME GND APCSET APCFILT1 APCFILT2 PWC+ PWCGND VCC MK+ MKGND FAIL BIAS VCC MOD MOD MODN MODN VCC GND MD MDMON PAD BP1 BP2 BP3 BP4 BP5 BP6 BP7 BP8 BP9 BP10 BP11 BP12 BP13 BP14 BP15 BP16 BP17 BP18 BP19 BP20 BP21 BP22 COORDINATES (M) 169, -122 327, -122 465, -122 591, -122 717, -122 913, -122 1109, -120 1235, -120 1361, -120 1500, -120 1660, -120 1797, 50 1795, 225 1795, 351 1795, 477 1795, 603 1795, 729 1795, 855 1795, 981 1795, 1107 1797, 1328 1797, 1454 NAME GND MODMON BIASMON VCC GND MODCOMP MODSET BIASMAX EN RTEN GND VCC DATA+ DATAVCC VCC GND VCC VCC CLK+ CLKVCC PAD BP23 BP24 BP25 BP26 BP27 BP28 BP29 BP30 BP31 BP32 BP33 BP34 BP35 BP36 BP37 BP38 BP39 BP40 BP41 BP42 BP43 BP44 COORDINATES (M) 1675, 1630 1515, 1630 1374, 1630 1248, 1630 1077, 1630 906, 1630 780, 1630 654, 1630 528, 1630 390, 1630 205, 1630 45, 1501 45, 1375 45, 1249 45, 1123 45, 997 47, 776 47, 551 47, 425 47, 299 47, 173 47, 47
Coordinates are for the center of the pad. Coordinate 0, 0 is the lower left corner of the passivation opening for pad 1.
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2.7Gbps Laser Driver with Modulation Compensation
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
32L QFN.EPS
MAX3863
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 15 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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