Rainbow-electronics MAX3646 Manual do Utilizador descarregar pdf (Página 8)

MAX3646

Average power is regulated using APC, which keeps

constant current from a photodiode coupled to the

laser. Peak-to-peak power is maintained by compen-

sating the modulation current for reduced slope effi-

ciency (h) of laser over time and temperature:

AVG

= I

/ρ

MON

P-P

= η x I

MOD

Modulation compensation from bias increases the mod-

ulation current by a user-selected proportion (K) need-

ed to maintain peak-to-peak laser power as bias

current increases with temperature. Refer to Maxim

Application Note HFAN-02.21 for details:

K = ∆I

MOD

/ ∆I

BIAS

This provides a first-order approximation of the current

increase needed to maintain peak-to-peak power.

Slope efficiency decreases more rapidly as tempera-

ture increases. The MAX3646 provides additional tem-

perature compensation as temperature increases past

a user-defined threshold (T

155Mbps to 622Mbps SFF/SFP

Laser Driver with Extinction Ratio Control

8 _______________________________________________________________________________________

MAX3646

IN+

IN-

OUT-

OUT+

INPUT BUFFER

DATA

PATH

MOD

MODSET

APCSET

APC

APCFILT1 APCFILT2

BIAS

ENABLE

TX_FAULT

TX_DISABLE

SAFETY LOGIC

AND

POWER DETECTOR

BC_MON

PC_MON

SHUTDOWN

x268

PULL

= 45k

Ω

xKxTC

T > T

BIAS

MOD

ENABLE

x1/2

MODTCOMP

TH_TEMP

MODBCOMP

BIAS

Figure 4. Functional Diagram

1 2 3 4 5 6 7 8 9 10 11 12 13 14

155Mbps to 622Mbps SFF/SFP 1

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