ICS843021I-01 Datasheet, PDF (8/15 Pages) Integrated Circuit Systems – FEMTOCLOCKS-TM CRYSTAL-TO-3.3V, 2.5V 125MHZ LVPECL CLOCK GENERATOR

ICS843021I-01
FEMTOCLOCKS™CRYSTAL-TO-3.3V, 2.5V LVPECL CLOCK GENERATOR
Termination for 3.3V LVPECL Outputs
The clock layout topology shown below is a typical termination for
LVPECL outputs. The two different layouts mentioned are
recommended only as guidelines.
FOUT and nFOUT are low impedance follower outputs that
generate ECL/LVPECL compatible outputs. Therefore, terminating
resistors (DC current path to ground) or current sources must be
used for functionality. These outputs are designed to drive 50Ω
transmission lines. Matched impedance techniques should be
used to maximize operating frequency and minimize signal
distortion. Figures 3A and 3B 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 circuit 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
Figure 3A. 3.3V LVPECL Output Termination
FOUT
3.3V
125Ω
125Ω
Z_o = 50Ω
FIN
Z_o = 50Ω
84Ω
84Ω
Figure 3B. 3.3V LVPECL Output Termination
IDT™ / ICS™ 3.3V , 2.5V LVPECL CLOCK GENERATOR
8
ICS843021AGI-01 REV. A DECEMBER 3, 2007