SLK2511C_13 Datasheet, PDF (9/22 Pages) Texas Instruments – OC-48/24/12/3 SONET/SDH MULTIRATE TRANSCEIVER

SLK2511C
www.ti.com............................................................................................................................................................................................ SLLS886 – DECEMBER 2008
LOOP TIMING MODE
When LOOPTIME is high, the clock synthesizer used to serialize the transmit data is bypassed and the timing is
provided by the recovered clock. However, REFCLK is still needed for the recovery loop operation.
LOSS OF LOCK INDICATOR
The SLK2511C has a lock detection circuit to monitor the integrity of the data input. When the clock recovery
loop is locked to the input serial data stream, the LOL signal goes high. If the recovered clock frequency deviates
from the reference clock frequency by more than 100 ppm, LOL goes low. If the data stream clock rate deviates
by more than 170 ppm, loss of lock occurs. If the data streams clock rate deviates more than 500 ppm from the
local reference clock, the LOL output status might be unstable. Upon power up, the LOL goes low until the PLL is
close to phase lock with the local reference clock.
LOSS OF SIGNAL
The loss of signal (LOS) alarm is set high when no transitions appear in the input data path for more than 2.3µs.
The LOS signal becomes active when the above condition occurs. If the serial inputs of the device are
ac-coupled to its source, the ac-couple capacitor needs to be big enough to maintain a signal level above the
threshold of the receiver for the 2.3µs no transition period. Once activated, the LOS alarm pin is latched high
until the receiver detects an A1A2 pattern. The recovered clock (RXCLK) is automatically locked to the local
reference when LOS occurs. The parallel data (RXDATAx) may still be processed even when LOS is activated.
SIGNAL DETECT
The SLK2511C has an input SIGDET pin to force the device into the loss of signal state. This pin is generally
connected to the signal detect output of the optical receiver. Depending on the optics manufacturer, this signal
can be either active high or active low. To accommodate the differences, a polarity select (PS) pin is used. For
an active low, SIGDET input sets the PS pin high. For an active high, SIGDET input sets the PS pin low. When
the PS signal pin and SIGDET are of opposite polarities, the loss of signal state is generated and the device
transmits all zeroes downstream.
MULTIPLEXER OPERATION
The 4-bit parallel LVDS data is clocked into an input buffer by a clock derived from the synthesized clock. The
data is then clocked into a 4:1 multiplexer. The D0 bit is the most significant bit and is shifted out first in the serial
output stream.
DEMULTIPLEXER OPERATION
The serial 2.5 Gbps data is clocked into a 1:4 demultiplexer by the recovered clock. The D0 bit is the first bit that
is received in time from the input serial stream. The 4-bit parallel data is then sent to the LVDS driver along with
the divided down recovered clock.
Copyright © 2008, Texas Instruments Incorporated
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