ICS843003 Datasheet, PDF (11/17 Pages) Integrated Circuit Systems – FEMTOCLOCKS CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS843003
FEMTOCLOCKS™CRYSTAL-TO-3.3V LVPECL
FREQUENCY SYNTHESIZER
TERMINATION FOR 3.3V LVPECL OUTPUT
The clock layout topology shown below is a typical termi-
nation for LVPECL outputs. The two different layouts men-
tioned are recommended only as guidelines.
FOUT and nFOUT are low impedance follower outputs that
generate ECL/LVPECL compatible outputs. Therefore, ter-
minating resistors (DC current path to ground) or current
sources must be used for functionality. These outputs are
designed to drive 50Ω transmission lines. Matched imped-
ance techniques should be used to maximize operating
frequency and minimize signal distortion. Figures 4A and
4B show two different layouts which are recommended
only as guidelines. Other suitable clock layouts may exist
and it would be recommended that the board designers
simulate to guarantee compatibility across all printed cir-
cuit and clock component process variations.
Z_o = 50Ω
FOUT
FIN
Z_o = 50Ω
50Ω
RTT =
1
((V_OH + V_OL) / (V_CC – 2)) – 2
Z_o
50Ω
V_CC - 2V
RTT
FOUT
3.3V
125Ω
125Ω
Z_o = 50Ω
FIN
Z_o = 50Ω
84Ω
84Ω
FIGURE 4A. LVPECL OUTPUT TERMINATION
FIGURE 4B. LVPECL OUTPUT TERMINATION
843003AG
www.icst.com/products/hiperclocks.html
11
REV. A JULY 27, 2004