155Mbps to 4.25Gbps SFF/SFP Laser Driver

with Extinction Ratio Control

10

______________________________________________________________________________________

1

exceeds the programmed threshold.

2

End-of-life (EOL) condition of the laser diode. The bias current and/or the photocurrent exceed the programmed threshold.

3

Laser cathode is grounded and photocurrent exceeds the programming threshold.

4

No feedback for the APC loop (broken interconnection, defective monitor photodiode), and the bias current exceeds the

programmed threshold.

Table 1. Typical Fault Conditions

BC_MON

PC_MON

COMP

TTL

OPEN COLLECTOR

CMOS

SHUTDOWN

TX_FAULT

R

S

Q

RS

LATCH

COUNTER

60ms DELAY

POR AND COUNTER

60ms DELAY

100ns DELAY

ENABLE

ENABLE

TX_DISABLE

COMP

EXCESSIVE

APC CURRENT

SETPOINT

EXCESSIVE

MOD CURRENT

SETPOINT

1

82

Figure 5. Simplified Safety Circuit