Block Diagram Of Transceiver
Transmitter Section
TRANSMITTER
RECEIVER
DATA+
DATA-
DATA+
PM
BIAS
TX-FAULT
TXd+
TX-DIS
TXd-
RXd+
RXd-
RXLOS
MOD_DEF(0)
MOD_DEF(2)
MOD_DEF(1)
DATA-
The
transmitter
section
consists of 1310nm FP
laser in an eye safe optical
subassembly (OSA) which
mates to the fiber cable.
The laser OSA is driven by
a LD driver IC which
converts differential input
LVPECL logic signals into
an analog laser driving
current.
TX-FAULT
TX Fault is an open collector/drain output, which should be pulled up with a 4.7K –
10KΩ resistor on the host board. Pull up voltage between 2.0V and VccT, R+0.3V. When
high, output indicates a laser fault of some kind. Low indicates normal operation. In the
low state, the output will be pulled to < 0.8V.
When sensing an improper power level in the laser driver, the SFP sets this signal
high and turns off the laser. TX-FAULT can be reset with the TX-DISABLE line. The
signal is in TTL level.
TX-DISABLE
TX disable is an input that is used to shut down the transmitter optical output. It is
pulled up within the module with a 4.7 – 10 KΩ resistor. Its states are: Low (0 – 0.8V):
Transmitter on; (>0.8, < 2.0V): Undefined; High (2.0 – 3.465V): Transmitter Disabled;
Open: Transmitter Disabled. The TX-DISABLE signal is high (TTL logic “1”) to turn off
the laser output. The laser will turn on when TX-DISABLE is low (TTL logic “0”).
TD-/+
These are the differential transmitter inputs. They are AC-coupled, differential lines
with 100Ω differential termination inside the module. The AC coupling is done inside the
module and is thus not required on the host board. The inputs will accept differential
swings of 500 – 2400 mV (250 – 1200 mV single-ended), though it is recommended that
values between 500 and 1200 mV differential (250 – 600 mV single-ended) be used for
best EMI performance.
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