XRT91L31 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT91L31' PDF : 41 Pages View PDF
XRT91L31
REV. 1.0.2
STS-12/STM-4 OR STS-3/STM-1 SONET/SDH TRANSCEIVER
2.0 RECEIVE SECTION
The receive section of XRT91L31 include the inputs RXIP/N, followed by the clock and data recovery unit
(CDR) and receive serial-to-parallel converter. The receiver accepts the high speed Non-Return to Zero (NRZ)
serial data at 622.08 Mbps or 155.52 Mbps through the input interfaces RXIP/N. The clock and data recovery
unit recovers the high-speed receive clock from the incoming scrambled NRZ data stream. The recovered
serial data is converted into an 8-bit-wide, 77.76 Mbps or 19.44 Mbps parallel data and presented to the
RXDO[7:0] parallel interface. This parallel interface is designed for Single-Ended LVTTL operation. A divide-
by-8 version of the high-speed recovered clock RXPCLKOP/N, is used to synchronize the transfer of the 8-bit
RXDO[7:0] data with the receive portion of the framer/mapper device. Upon initialization or loss of signal or
loss of lock, the external reference clock signal of 19.44 MHz or 77.76 MHz is used to start-up the clock
recovery phase-locked loop for proper operation. In certain applications, the CDR block on the XRT91L31 can
be disabled and bypassed by enabling the CDRDIS pin to permit the flexibility of using an externally recovered
receive clock thru the XRXCLKIP/N pins.
2.1 Receive Serial Input
The receive serial inputs are applied to RXIP/N and originate from an AC coupled environement (i.e. AC-
coupled SFP). A simplified block diagram is shown in Figure 3. Since this dievice has internal pull up/pull
down biasing resitors, a 100 Ω line-to-line termination is the only resistor needed and must be installed as
close to the RXI pins as possible. See Applications note for further clarifications.
FIGURE 3. RECEIVE SERIAL INPUT INTERFACE BLOCK
Install terminators close to
RXIP and RXIN pins
RXIP
RXIN
XR T91L 31
STS-12/ STM-4
or
STS-3/ STM-1
Transceiver
XRXCLKIP
XRXCLKIN
100 Ohm
1k
( optiona)l
1k
SFP , Optical Module
Internally AC coupled
Tie unused differential input pins
to VCC and GND
Optical Fiber
15
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