2
The product also oers digital diagnostics using the 2-
wire serial interface dened in the XFP MSA. The product
provides real time temperature (module and laser), supply
voltage, laser bias current, laser average output power and
received input power. The digital diagnostic interface also
adds the ability to disable the transmitter (TX_DIS), power
down the module, monitor for module faults and monitor
for Receiver Loss of Signal (RX_LOS). Transmitter disable,
interrupt, power down/reset, receiver loss of signal and
module not ready are also hard wired pins on the 30-pin
right angle connector.
Installation
The HFCT-721XPD can be installed in any XFP port regard-
less of host equipment operating status. The HFCT-721XPD
is hot-pluggable, allowing the module to be installed
while the host system is operating and on-line. The clip-on
heatsink is designed to clip on to the XFP cage without a
module present.
Upon insertion, the transceiver housing makes initial
contact with the host board XFP cage, mitigating potential
damage due to Electro-Static Discharge (ESD). Once fully
inserted into the XFP cage, the top surface of the XFP
module makes contact with the heatsink through a cutout
in the top of the cage ensuring an eective thermal path
for module heat.
Functional Description
Transmitter Section
The transmitter section includes a 1310 nm DFB (Distrib-
uted Feedback Laser) light source, a transmitter driver
circuit and a signal conditioner circuit on the TX data
inputs. (see Figure 1) Optical connection to the transmit-
ter is provided via a LC connector. The optical output is
controlled by a custom IC that detects the laser output via
the monitor photodiode. This IC provides both dc and ac
current drive to the laser to ensure correct modulation,
eye diagram and extinction ratio over temperature, supply
voltage and operating life.
TX_DIS
Asserting pin 5, TX_DIS, will disable the transmitter optical
output. The transmitter output can also be disabled and
monitored via the two-wire serial interface.
Eye Safety Circuit
Under normal operating conditions laser power will be
maintained below Class 1 eye-safety limits. Should a
catastrophic laser fault occur and optical power become
uncontrolled, the micro-controller will detect the fault,
shut down the laser, power down the module and assert
the hard-wired MOD_NR ag. The TX_FAULT output in the
2-wire serial interface will also be asserted.
Figure 1. Transceiver Functional Diagram
PIN
Laser
RF
driver
CW
driver
Optical receptacles
Electrical connector
Mon. PIN
ROSA
TOSA
EEPROM
Micro
controller
A/D
ESA
Heat sink
Analog
signal
conditioners
Main housing
Analog bus
Digital 10
Gb/s electrical
I/O
Digital low
speed bus or
signal
Analog signal
Power
supply
control
TIATIA
+3.3V
Signal
Conditioner
Signal
Conditioner
