laser drive needs

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)

Circuit from unstuffed part of MAX 3287 Eval board

• Remove feedback loop PD, bias adjustment PNP

Circuit from unstuffed part of MAX 3287 Eval board

• Keep almost all other components• Use Eval board part numbers for inductors (ferrite beads)

Design elements

• Match load on OUT- with OUT+ as well as you can

• Need to adjust Laser DC Bias current

• Need to adjust Laser modulation current