AFBR-709DMZ datasheet(3/22 Pages) AVAGO

3 / 22 page

Figure 1. Transceiver functional diagram

Transmit Fault (TX_FAULT)

A catastrophic laser fault will activate the transmitter

signal, TX_FAULT, and disable the laser. This signal is

an open collector output (pull-up required on the host

board). A low signal indicates normal laser operation

and a high signal indicates a fault. The TX_FAULT will

be latched high when a laser fault occurs and is cleared

by toggling the TX_DISABLE input or power cycling the

transceiver. The transmitter fault condition can also be

monitored via the two-wire serial interface (address A2,

byte 110, bit 2).

Transmitter Section

The transmitter section includes the Transmitter

Optical Sub-Assembly (TOSA) and laser driver circuitry.

The TOSA, containing an Avago designed and manufac-

tured 850 nm VCSEL (Vertical Cavity Surface Emitting

Laser) light source, is located at the optical interface and

mates with the LC optical connector. The TOSA is driven

by an IC which uses the incoming differential high speed

logic signal to modulate the laser diode driver current.

This Tx laser driver circuit regulates the optical power at

a constant level provided the incoming data pattern is

DC balanced.

Transmit Disable (TX_DISABLE)

The AFBR-709DMZ accepts an LVTTL compatible trans-

mit disable control signal input which shuts down the

transmitter optical output. A high signal implements this

function while a low signal allows normal transceiver

operation. In the event of a fault (e.g. eye safety circuit

activated), cycling this control signal resets the module

as depicted in Figure 6. An internal pull up resistor dis-

ables the transceiver transmitter until the host pulls the

input low. TX_DISABLE can also be asserted via the two-

wire interface (address A2h, byte 110, bit 6) and moni-

tored (address A2h, byte 110, bit 7).

The contents of A2h, byte 110, bit 6 are logic OR’d with

hardware TX_DISABLE (contact 3) to control transmitter

operation.

LIGHT FROM FIBER

LIGHT TO FIBER

PHOTO-DETECTOR

RECEIVER

AMPLIFICATION

& QUANTIZATION

RD+ (RECEIVE DATA)

RD– (RECEIVE DATA)

RX_LOS

VCSEL

TRANSMITTER

LASER

DRIVER &

SAFETY

CIRCUITRY

TX_DISABLE

TD+ (TRANSMIT DATA)

TD– (TRANSMIT DATA)

TX_FAULT

ELECTRICAL INTERFACE

SDA

SCL

MOD-ABS

CONTROLLER & MEMORY

OPTICAL INTERFACE

RS0

RS1

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