
ICS844251-14
FEMTOCLOCK CRYSTAL-TO-LVDS CLOCK GENERATOR
IDT / ICS LVDS CLOCK GENERATOR
9
ICS844251BG-14 REV. A NOVEMBER 19, 2012
LVDS Driver Termination
For a general LVDS interface, the recommended value for the
termination impedance (ZT) is between 90 and 132. The actual
value should be selected to match the differential impedance (Z0)
of your transmission line. A typical point-to-point LVDS design uses
a 100
parallel resistor at the receiver and a 100 differential
transmission-line environment. In order to avoid any transmission-
line reflection issues, the components should be surface mounted
and must be placed as close to the receiver as possible. IDT offers
a full line of LVDS compliant devices with two types of output
structures: current source and voltage source. The standard
termination schematic as shown in Figure XA can be used with
either type of output structure. Figure XB, which can also be used
with both output types, is an optional termination with center tap
capacitance to help filter common mode noise. The capacitor value
should be approximately 50pF. If using a non-standard termination,
it is recommended to contact IDT and confirm if the output
structure is current source or voltage source type. In addition, since
these outputs are LVDS compatible, the input receiver’s amplitude
and common-mode input range should be verified for compatibility
with the output.
LVDS Termination
LVDS
Driver
LVDS
Driver
LVDS
Receiver
LVDS
Receiver
ZT
C
ZO ZT
ZT
2
ZT
2
Figure XA. Standard Termination
Figure XB. Optional Termination