AFBR-703SDDZ Datasheet, PDF (3/22 Pages) AVAGO TECHNOLOGIES LIMITED – Typical power dissipation 600mW

OPTICAL INTERFACE
LIGHT FROM FIBER
RECEIVER
PHOTO-DETECTOR
AMPLIFICATION
& QUANTIZATION
CONTROLLER & MEMORY
ELECTRICAL INTERFACE
RD+ (RECEIVE DATA)
RD– (RECEIVE DATA)
RX_LOS
RS0
RS1
SDA
SCL
MOD-ABS
LIGHT TO FIBER
TRANSMITTER
VCSEL
LASER
DRIVER &
SAFETY
CIRCUITRY
TX_DISABLE
TD+ (TRANSMIT DATA)
TD– (TRANSMIT DATA)
TX_FAULT
Figure 1. Transceiver functional diagram
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-703SDDZ 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.
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).
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