Laser Drive Needs

1
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
2
MAX3287 Evaluation Kit
3
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

4
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)

5
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?)

6
Circuit from unstuffed part of MAX 3287 Eval board
Note Pin 2 is really FLTDLY NOT POR as in
MAXIM data sheet. So it must be grounded.

• Remove feedback loop PD, bias adjustment PNP RED

7
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)

8
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)