XRT91L80 View Datasheet(PDF) - Exar Corporation
Part Name
Description
MFG CO.
'XRT91L80' PDF : 45 Pages View PDF
xr
REV. P1.1.0
PRELIMINARY
XRT91L80
2.488/2.666 GBPS STS-48/STM-16 SONET/SDH TRANSCEIVER
3.8 External Loop Filter
As shown in Figure 13, there is an internal charge pump used to drive an external loop filter and external
VCXO. The charge pump current is fixed at 250uA. Figure 14 is a simplified block diagram of the external loop
filter and recommended values.
FIGURE 14. SIMPLIFIED DIAGRAM OF THE EXTERNAL LOOP FILTER
VCXO
300pF
4.02kΩ
1uF
CPOUT
3.9 Transmit Serial Output Control
The 2.488/2.666 Gbps transmit serial output is avaliable on TXOP/N pins. The transmit serial output can be AC
or DC coupled to an optical module or electrical interface. A simplified AC coupling block diagram is shown in
Figure 15.
FIGURE 15. TRANSMIT SERIAL OUTPUT INTERFACE BLOCK
TXOP
TXON
XRT91L80
STS-48/
STM-16
Transceiver
0.1µF
0.1µF
Optical Module
Optical Fiber
NOTE: Some optical modules integrate AC coupled capacitors within the module. If so, the external AC coupled capacitors
are not necessary and can be excluded.
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