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Laser Drive Needs
• Total laser current– ITOT = IBIAS + IMOD
• BIAS Current– Keeps ITOT > ITH (laser “on”)
– IBIAS – ITH related to speed
• Modulation (MOD) Current– Shaped by the data
– Larger IMOD gives larger signal
IBIAS
IMOD
ITOT
MAX3287 Evaluation Kit
Test Setup for Maxim board
• Tested to verify its functionality
• Two test conducted for Maxim board– DC coupled output of Maxim
board– AC coupled output of Maxim
board
• Equipment used– 5V power supply– SMA cables and connectors– Oscilloscope and function
generator
Test Results for Maxim boardDC coupled
• Near perfect open eye• Fits the compliance
mask• Signifies very low
SNR• Slight dip at the
bottom (unexplained phenomenon)
Test Results for Maxim boardAC coupled
• Again a near perfect open eye
• Low SNR • Fits the compliance
mask• The dip on bottom
disappears (mysteriously – AC coupling?)
Circuit from unstuffed part of MAX 3287 Eval board
• Remove feedback loop PD, bias adjustment PNP RED
Note: Pin 2 is really “FLTDLY”
NOT “POR” as in MAXIM data sheet.So it must be grounded.
Circuit from unstuffed part of MAX 3287 Eval board
• Remove C25 and R27 RED• Keep all other components GREEN• Use Eval board part numbers for inductors (ferrite beads)
Design elements
• Match load on OUT- with OUT+ as well as you can (R26)
• Need to be able to adjust Laser DC Bias current (R1)
• Need to be able to adjust Laser modulation current (R25)