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Figure 3: Simplified schematic of Rx outputs
Rx Signal Detection and Squelch
The Rx circuitry has the ability to detect the presence of an optical signal at its input. The Rx signal detect
status may also be polled on a per-channel basis through the digital interface. Using the squelch
enable pin, SQEN, the OPTO-FireTM may be configured to shut down the Rx outputs when an optical
signal of a programmable strength is not present on a given channel. This feature eliminates chatter that
may be problematic for downstream components and reduces power dissipation on channels that are
enabled but not in use. The Rx outputs remain back terminated to 50 Ω when squelched.
Built In Test (BIT) and Diagnostics
A number of diagnostic and BIT features are provided by the OPTO-FireTM . Features include real-time
measurement of transmitted and received optical power from each channel, die temperature, bias
settings, signal detection, and fault status information. Access to these features is provided through a
serial digital interface.
Temperature Sensor
A digital thermometer integrated within the OPTO-FireTM ’s transceiver IC allows readout of the die
temperature with a resolution of ~2 C. The temperature sensor is calibrated over the full operating
temperature range of the module.
Transmitter Signal Strength Indicator (TSSI)
The unique construction of the OPTO-FireTM allows the average optical power from each element of the
VCSEL array to be independently monitored. In addition to using this information internally to control the
Tx modulation characteristics, the module provides a Transmitter Signal Strength Indicator (TSSI) for
each channel through the digital interface. The TSSI is calibrated over the full operating temperature of
the module based on the optical power coupled into the user’s fibre (i.e. the fibre into which the module’s
pigtail is coupled).
Receiver Signal Strength Indicator (RSSI)
The Rx circuitry includes a means to measure the average optical power coupled into the photo detectors.
The resulting Receiver Signal Strength Indicator (RSSI) is calibrated over the full operating temperature
range of the module relative to the power in the user’s fibre (i.e. the fibre into which the module’s pigtail is
coupled).
Digital Interface
A two-wire I2C digital interface is provided to the micro controller allowing access to BIT and diagnostic
information. For space applications in which the radiation hardness of the internal micro controller is
found to be inadequate, the OPTO-FireTM may be configured to use an external controller. In this case,
the module is manufactured without the internal micro controller and a four-wire SPI interface is provided
for direct communication with the transceiver IC.
Provisional Data Sheet
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