19-2281; Rev 2; 5/03 2.7Gbps Laser Driver with Modulation Compensation 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 50Ω 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. Features ♦ 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 ♦ Current Monitors ♦ ESD Protection Ordering Information PART TEMP RANGE PINPACKAGE PKG CODE MAX3863EGJ MAX3863E/D* -40°C to +85°C 32 QFN G3255-1 -40°C to +85°C Dice — *Dice are designed and guaranteed to operate from -40°C to +85°C, but are tested only at TA = +25°C Applications 25 MODMON 26 BIASMON 27 VCC 29 MODSET 30 BIASMAX 3.2Gbps Data Communications 31 EN TOP VIEW 32 RTEN WDM Transmission Systems 28 MODCOMP Pin Configuration SONET and SDH Transmission Systems Add/Drop Multiplexers 24 MDMON 2 23 MD DATA- 3 22 VCC VCC 4 21 MODN VCC 5 20 MOD CLK+ 6 19 VCC CLK- 7 18 BIAS VCC 8 17 FAIL MK- 16 MK+ 15 VCC 14 PWC- 13 APCSET Covered by U.S. patent number 5,883,910. Other patents pending. PWC+ 12 MAX3863 9 Long-Reach Optical Transmitters 1 APCFILT2 11 Section Regenerators VCC DATA+ APCFILT1 10 Digital Cross-Connects THE EXPOSED PAD MUST BE SOLDERED TO GND ON THE CIRCUIT BOARD. ________________________________________________________________ Maxim Integrated Products 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. 1 MAX3863 General Description MAX3863 2.7Gbps Laser Driver with Modulation Compensation 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 ...........-55°C to +150°C Storage Temperature Range .............................-55°C to +150°C Continuous Power Dissipation (TA = +85°C) 32-Pin QFN (derate 21.2mW/°C above +85°C) ...............1.3W Processing Temperature (die) .........................................+400°C Lead Temperature (soldering, 10s) ................................ +300°C 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 = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 40mA, TA = +25°C, unless otherwise noted.) (Notes 1, 9) PARAMETER TYP MAX UNITS (Note 2) 58 85 mA f = 100kHz, 100mVP-P (Note 10) 40 dB Power-Supply Threshold Output enabled 2.8 V Single-Ended Input Resistance Input to VCC Power-Supply Current Power-Supply Noise Rejection SYMBOL ICC PSNR CONDITIONS 60 Ω 4 100 mA APC open loop, IBIAS = 100mA, TA = +25°C -15 +15 APC open loop, IBIAS = 4mA, TA = +25°C -20 +20 Bias-Current Setting Range Bias-Current Setting Error 40 50 EN high Bias Off-Current IBIAS to IBIASMON Ratio 34 APC open loop, 10mA ≤ IBIAS ≤ 100mA (Note 3) Bias-Current Temperature Stability Modulation-Current Setting Error APC open loop, 25Ω load, TA = +25°C Modulation Off-Current EN high Modulation-Current Temperature Stability APC open loop (Note 3) IMOD to IMODMON Ratio K = ∆IMODC/∆IBIAS IMD APC Loop Time Constant tAPC VMDMON to IMD Ratio 2 RMDMON = 4kΩ EN and RTEN Input High VIH EN and RTEN Input Low VIL FAIL Output High VOH Source 150µA FAIL Output Low VOL Sink 2mA ppm/°C 80 -15 +15 % 0.1 mA +480 ppm/°C 53 mA/mA -480 46 0 30 (Notes 3, 4) mA/mA 7 1 4mA ≤ IBIAS ≤ 10mA (Note 3) APC Open Loop mA 46 +480 MD Pin Voltage Monitor Photodiode Current Range % 0.1 ±390 38 K 40 -480 APC open loop, 4mA ≤ IBIAS ≤ 100mA (Note 3) Modulation-Current Setting Range Modulation Compensation Range MIN 4 1.5 mA/mA 1.75 V 2000 µA 1000 ±390 0.8 1.0 µs mA 1.2 mV/µA 0.8 V 0.4 V 2.0 V 2.4 _______________________________________________________________________________________ mA V 2.7Gbps Laser Driver with Modulation Compensation (VCC = +3.15V to +3.6V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 40mA, TA = +25°C, unless otherwise noted.) (Notes 1, 9) PARAMETER Single-Ended Input (DC-Coupled) Single-Ended Input (AC-Coupled) Differential Input Swing SYMBOL VIS CONDITIONS Input Data Rate RLIN Turn-Off Delay from EN MAX At low VCC - 1.0 VCC - 0.1 At high VCC + 0.05 VCC + 0.4 At low VCC 0.4 VCC 0.05 DC-coupled 0.2 2.0 AC-coupled 0.2 1.6 UNITS V V NRZ (Note 3) Input Return Loss TYP VCC VIS VID MIN At high (Notes 3, 5) 3.2 f ≤ 2.7GHz 17 2.7GHz < f ≤ 4GHz 14 EN = high (Note 3) VP-P Gbps dB 1.0 µs Setup Time tSU Figure 2 (Note 3) 90 ps Hold Time tHD Figure 2 (Note 3) 90 ps Pulse-Width Adjustment Range ZL = 25Ω (Notes 3, 6) Pulse-Width Stability PWC+ and PWC- open (Notes 3, 6) Differential Pulse-Width Control Input Range For PWC+ and PWC- (Notes 3, 7), VCM = 0.5V Differential Mark Density 0% to 100%, VMK+ - VMK- Differential Mark-Density Voltage to Mark-Density Ratio Output Edge Speed Output Overshoot Random Jitter Deterministic Jitter ±185 ±220 -1.0 ps ±18.5 ps 1.0 V ±0.85 V 15.5 tR, tF δ ZL = 25Ω (20% to 80%) (Notes 3, 6) 50 V/% 85 ps psRMS ZL = 25Ω (Note 3) ±7 (Notes 3, 6) 0.8 1.3 Data Rate = 2.7Gbps (Notes 3, 8) 8 40 Data Rate = 3.2Gbps (Notes 3, 8) 10 40 % psP-P Specifications at -40°C 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 = 500Ω (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 25Ω load when no input is applied. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: _______________________________________________________________________________________ 3 MAX3863 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted. See Typical Operating Circuit.) MAX3863 toc01b 52ps/div ELECTRICAL EYE DIAGRAM (IMOD = 7mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID) OPTICAL EYE DIAGRAM (IMOD = 40mA, DATA RATE = 2.5Gbps, PATTERN 213 - 1 + 80CID) OPTICAL EYE DIAGRAM (IMOD = 40mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID) MAX3863 toc03a 58ps/div 65 60 55 50 14 12 3.2Gbps 10 8 2.7Gbps 6 4 0 40 -20 0 20 40 TEMPERATURE (°C) 60 80 200 100 0 -100 -200 2 45 300 PULSE-WIDTH ADJUST (ps) 70 16 MAX3863 toc05 75 PULSE-WIDTH ADJUST vs. DIFFERENTIAL VPWC DETERMINISTIC JITTER vs. IMOD DETERMINISTIC JITTER (psP-P) MAX3863 toc04 80 58ps/div MAX3863 toc06 SUPPLY CURRENT (ICC) vs.TEMPERATURE (EXCLUDES BIAS AND MODULATION CURRENTS) -40 MAX3863 toc03b 52ps/div MAX3863 toc02b 52ps/div 52ps/div 4 ELECTRICAL EYE DIAGRAM (IMOD = 7mA, DATA RATE = 2.7Gbps, PATTERN 213 - 1 + 80CID) MAX3863 toc02a ELECTRICAL EYE DIAGRAM (IMOD = 80mA, DATA RATE = 3.2Gbps, PATTERN 213 - 1 + 80CID) MAX3863 toc01a ELECTRICAL EYE DIAGRAM (IMOD = 80mA, DATA RATE = 2.7Gbps, PATTERN 213 - 1 + 80CID) SUPPLY CURRENT (mA) MAX3863 2.7Gbps Laser Driver with Modulation Compensation -300 5 15 25 35 45 55 IMOD (mA) 65 75 85 -0.8 -0.6 -0.4 -0.2 0 0.2 VPWC+ - VPWC- (V) _______________________________________________________________________________________ 0.4 0.6 0.8 2.7Gbps Laser Driver with Modulation Compensation MODULATION CURRENT vs. MODULATION SET RESISTOR 180 160 10 100 120 IBIAS (mA) VMODMON (mV) IMOD (mA) 140 MAX3863 toc09 1000 MAX3863 toc08 200 MAX3863 toc07 100 BIAS CURRENT vs. BIASMAX SET RESISTOR MODULATION MONITOR VOLTAGE vs. MODULATION CURRENT 100 80 10 60 40 20 0 1 1 10 1 5 100 20 RMODSET (kΩ) 50 80 65 1 0.1 IMOD (mA) IBIAS (mA) 150 2.5 VMDMON (V) 1 200 3.0 MAX3863 toc11 250 0.1 100 100 DIODE-CURRENT MONITOR VOLTAGE vs. MONITOR DIODE CURRENT 10 MAX3863toc10 300 10 RBIASMAX (kΩ) MONITOR DIODE CURRENT vs. APCSET RESISTOR BIAS MONITOR VOLTAGE vs. BIAS CURRENT 2.0 1.5 1.0 0.5 50 0 0.01 0 0 0.1 10 20 30 40 50 60 70 80 90 100 10 1 100 0 1000 0.5 RAPCSET (kΩ) IBIAS (mA) COMPENSATION (K) vs. RMODCOMP -5 MAGNITUDE S11 (dB) 100 PSNR (dB) K (mA/mA) 2.5 SINGLE-ENDED S11 vs. FREQUENCY 80 60 40 0.1 2.0 0 MAX3863 toc14 120 1 1.5 IMD (mA) POWER-SUPPLY NOISE REJECTION vs. FREQUENCY MAX3863 toc13 10 1.0 MAX3863 toc15 VBIASMON (mV) 35 MAX3863 toc12 0.1 -10 -15 -20 -25 -30 20 -35 0 0.01 0.01 0.1 1 RMODCOMP (kΩ) 10 100 -40 0.1 1 10 100 FREQUENCY (kHz) 1000 10,000 0 1 2 3 4 5 FREQUENCY (GHz) _______________________________________________________________________________________ 5 MAX3863 Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted. See Typical Operating Circuit.) 2.7Gbps Laser Driver with Modulation Compensation MAX3863 Pin Description PIN NAME 1, 4, 5, 8, 14, 19, 22, 27 VCC 2 DATA+ Data Input, with On-Chip Termination 3 DATA- Complementary Data Input, with On-Chip Termination 6 CLK+ Clock Input for Data Retiming, with On-Chip Termination 7 CLK- Complementary Clock Input for Data Retiming, with On-Chip Termination 9 APCSET 10 APCFILT1 APC Loop Filter Capacitor. Short to ground to disable the correction loop through the monitor diode. 11 APCFILT2 APC Loop Filter Capacitor 12 PWC+ Input for Modulation Pulse-Width Adjustment. Connected to GND through RPWC. 13 PWC- Complementary Input for Modulation Pulse-Width Adjustment. Connected to GND through RPWC. 15 MK+ Voltage Proportional to the Mark Density. MK+ = MK- for 50% duty cycle. Positive Supply Voltage Monitor Diode Current Set Point 16 MK- Voltage Inversely Proportional to the Mark Density 17 FAIL Alarm for Shorts on Current Set Pins and APC Loop Failure Conditions, Active Low 18 BIAS Laser Diode Bias Current Source (Sink Type) to Bias the Laser Diode. Connect to the laser with an inductor. 20 MOD 21 MODN 23 MD 24 MDMON 25 MODMON 26 BIASMON Monitor for Bias Current. Voltage developed from IBIAS mirrored through an external resistor. MODCOMP Couples the Bias Current to the Modulation Current. Mirrors IBIAS through an external resistor. Open for zero coupling. 28 6 FUNCTION 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. 29 MODSET External Resistor to Program IMODC (IMOD = IMODS + IMODC) 30 BIASMAX External Resistor to Program the Maximum IBIAS 31 EN 32 RTEN 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. _______________________________________________________________________________________ 2.7Gbps Laser Driver with Modulation Compensation MAX3863 VCC A - TOKO FSLB2520-330K B - MURATA BLM11HA601SPT A A B B VCC PATTERN GENERATOR VCC DATA+ 50Ω DATA+ DATA- 50Ω DATAMAX3863 VCC 50Ω MODN 0.1µF VCC CLK+ 25Ω 0.1µF APCFILT1 CLK+ OSCILLOSCOPE 50Ω MOD 50Ω 50Ω VCC CLK- 50Ω CLK- BIAS RTEN EN 15Ω 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. 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. 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 1kΩ. 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. 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 _______________________________________________________________________________________ 7 MAX3863 2.7Gbps Laser Driver with Modulation Compensation 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 4kΩ resistor at the MDMON output. Resistors for BIASMON and MODMON are 100Ω. The minimum voltage at the monitor pins must be 2.1V for compliance. I VBIASMON = BIAS × 100Ω 40 I VMODMON = MOD × 100Ω 45 APC Filter I VMDMON = MD × 4kΩ 4 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 0.01µF. 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. 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 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 (η) using the equations in Table 1. 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 CLK- tSU tHD DATAVIS = 0.1V TO 0.8V DATA+ (DATA+) - (DATA-) IMOD VID = 0.2VP-P TO 1.6VP-P 7mA TO 80mA Figure 2. Required Input Signal, Setup/Hold-Time Definition and Output Polarity 8 _______________________________________________________________________________________ 2.7Gbps Laser Driver with Modulation Compensation PARAMETER SYMBOL Average Power Extinction Ratio Optical Power of a 1 Optical Power of a Zero Optical Amplitude Laser Slope Efficiency Modulation Current Threshold Current RELATION PAVG re PAVG = (P0 + P1)/2 re = P1/P0 P1 P1 = 2PAVGre/(re + 1) P0 P0 = 2PAVG/(re + 1) PP-P PP-P = P1 - P 0 η η = PP-P/IMOD IMOD IMOD = PP-P/η ITH P0 at I ≥ ITH Bias Current IBIAS IBIAS ≥ ITH + IMOD /2 Laser to Monitor Transfer ρMON IMD/PAVG 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 × PAVG re − 1 × η re + 1 • • • • VD—Diode bias point voltage (1.2V typ) RL—Diode bias point resistance (5Ω typ) L—Diode lead inductance (1nH typ) RD—Series matching resistor (20Ω typ) I VCC − MOD × (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 × (RD + RL ) > LP (RD + RL ) Keep the peak voltage droop less than 3% of the peakto-peak amplitude during the maximum CID period t. The required time constant: −t For AC-coupled diodes: 2.8% = 1 − e τ = 35 × t I IBIAS = ITH + MOD 2 The required compensation factor is then: I K = MOD2 IBIAS2 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: − IMOD1 − IBIAS1 τ If τ = LP/25Ω, and t = 100UI = 40ns, then LP = 35µH. Place a good high-frequency inductor of 2µH on the transmission line to the laser. Then you can place a low-frequency inductor of 33µH at a convenient distance from the driver output. Programming the Bias Current Once the value of the compensation factor is known, the fixed portion of the modulation current is calculated from: I MODS = I MOD − K × 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, 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 10.0µA/mA, then setting IMD for 500µA 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 MAX3863 Table 1. Optical Power Relations MAX3863 2.7Gbps Laser Driver with Modulation Compensation VCC VCC RTEN 25Ω VCC MODN 1 MUX DATA DATA D D Q MOD 0 IMOD CD RD CLK CLK BIAS VCC APCFILT1 5Ω BIASMON x200 CURRENT MONITOR Vbg IMODS IMD x5 Vbg CAPC MD ∑ + IMODC IBIAS APCFILT2 x200 MODMON MDMON VCC 500pF Vbg - RMODSET RMODCOMP RBIASMAX RAPCSET EN 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 +25°C. IBIASMAX = 200 × 1.2V RBIASMAX 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 +25°C. IMD = 5 × 10 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 +25°C. 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. 1.2V RAPCSET ______________________________________________________________________________________ 2.7Gbps Laser Driver with Modulation Compensation IMOD1 MAX3863 LASER POWER VCC IMOD2 P1 T1 T2 50Ω 50Ω DATA+ PAVG DATA- P0 IBIAS1 IBIAS2 LASER CURRENT Figure 4. Laser Power vs. Current for a Change in Temperature I MOD = I MODS + K × I BIAS 1.2V I MODS = 200 × R MODSET 5 K = 200 × 500 + R MODCOMP GND Figure 5. Equivalent Input Circuit 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. 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 IMOD GND Figure 6. Equivalent Output Circuit failure of a Maxim product could create a situation where personal injury or death may occur. ______________________________________________________________________________________ 11 2.7Gbps Laser Driver with Modulation Compensation MAX3863 Typical Operating Circuit VCC VCC RBIASMON 4kΩ DATA- 50Ω DATA- VCC 25Ω 0.1µF VCC VCC MOD MAX3863 25Ω 0.1µF 20Ω APCSET BIASMAX MD RAPCSET CAPC 0.01µF RBIASMAX PWC1kΩ RPWC MODCOMP BIAS RMODCOMP CLK- MODSET 50Ω RMODSET CLK+ APCFILT2 50Ω PWC+ CLK- LP 25Ω MODN APCFILT1 MAX3892 10Gbps SERIALIZER CLK+ LP MODMON DATA+ RMODMON 100Ω BIASMON 50Ω MDMON DATA+ RTEN EN RMDMON 100Ω REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE ___________________Chip Information TRANSISTOR COUNT: 1786 PROCESS: Bipolar DIE SIZE: 81mil × 81mil PACKAGE SIZE: 5mm ✕ 5mm 12 ______________________________________________________________________________________ 2.7Gbps Laser Driver with Modulation Compensation BP23 GND BP24 MODMON BP25 BIASMON BP26 VCC BP27 GND BP28 MODCOMP BP29 MODSET BP30 BIASMAX BP31 EN BP32 RTEN BP33 GND VCC BP34 BP22 MDMON DATA+ BP35 BP21 MD DATA- BP36 VCC BP37 BP20 GND VCC BP38 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 GND BP11 MK- BP10 MK+ BP9 VCC BP8 GND BP7 PWC- BP6 PWC+ BP5 APCFILT2 BP4 APCFILT1 BP3 APCSET BP2 GND BP1 VCC BP44 81mil ______________________________________________________________________________________ 13 MAX3863 Chip Topography 2.7Gbps Laser Driver with Modulation Compensation MAX3863 Pad Coordinates NAME PAD COORDINATES (µM) NAME PAD COORDINATES (µM) GND BP1 169, -122 GND BP23 1675, 1630 1515, 1630 APCSET BP2 327, -122 MODMON BP24 APCFILT1 BP3 465, -122 BIASMON BP25 1374, 1630 APCFILT2 BP4 591, -122 VCC BP26 1248, 1630 1077, 1630 PWC+ BP5 717, -122 GND BP27 PWC- BP6 913, -122 MODCOMP BP28 906, 1630 GND BP7 1109, -120 MODSET BP29 780, 1630 VCC BP8 1235, -120 BIASMAX BP30 654, 1630 MK+ BP9 1361, -120 EN BP31 528, 1630 MK- BP10 1500, -120 RTEN BP32 390, 1630 GND BP11 1660, -120 GND BP33 205, 1630 FAIL BP12 1797, 50 VCC BP34 45, 1501 BIAS BP13 1795, 225 DATA+ BP35 45, 1375 VCC BP14 1795, 351 DATA- BP36 45, 1249 MOD BP15 1795, 477 VCC BP37 45, 1123 MOD BP16 1795, 603 VCC BP38 45, 997 MODN BP17 1795, 729 GND BP39 47, 776 MODN BP18 1795, 855 VCC BP40 47, 551 VCC BP19 1795, 981 VCC BP41 47, 425 GND BP20 1795, 1107 CLK+ BP42 47, 299 MD BP21 1797, 1328 CLK- BP43 47, 173 MDMON BP22 1797, 1454 VCC BP44 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. 14 ______________________________________________________________________________________ 2.7Gbps Laser Driver with Modulation Compensation 32L QFN.EPS 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 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX3863 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.)