Theory of Operation
3
The LTX-5510T amplifies, filters and digitizes the input analog signal to 12-bit precision at a 50 MS/s rate
and the LTX5515T at 100MS/s. The twelve bit digital data from each sample is combined with the state
of the four digital input channels to form a sixteen bit word. This word is converted to an 8b/10b code
and transmitted as a twenty bit word. This process is repeated at a 50 MHz for the LTX5510, resulting
in a 1 Gb/s data stream and at a 100 MHz rate for the LTX5515 resulting in a 2 Gb/s data stream. This
data is converted to an optical bitstream and transmitted via a user-supplied optical fiber to the LTX-
551XR receiver.
The LTX-551XR receives the optical bitstream and converts it to a digital signal. It then decodes and
de-multiplexes this data. Twelve bits are presented to a fast D/A converter and post amplifier which
drives the analog output port and four bits are latched and presented at the digital output ports. The
system is intended to be used with 50/125 uM or 62.5/125 uM fiber optic cable. (The LTX-551XSM is
intended for use with single mode fiber).
Upon energizing the LTX-551XT, it transmits framing characters for a few seconds so that the receiver
can determine where a valid word in the data stream begins and ends. The receiver is phase-locked
to the transmitters data rate and will remain so unless the optical signal is disrupted in some fashion
such as removing an optical fiber or power to one of the units.
