ICS853054 Datasheet, PDF (9/15 Pages) Integrated Circuit Systems – 4:1, DIFFERENTIAL-TO-3.3V OR 2.5V LVPECL/ECL CLOCK MULTIPLEXER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS853054
4:1, DIFFERENTIAL-TO-3.3V OR 2.5V
LVPECL/ECL CLOCK MULTIPLEXER
TERMINATION FOR 3.3V LVPECL OUTPUTS
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, termi-
nating 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 mini-
mize 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 varia-
tions.
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 3A. LVPECL OUTPUT TERMINATION
FIGURE 3B. LVPECL OUTPUT TERMINATION
853054AG
www.icst.com/products/hiperclocks.html
9
REV. A JANUARY 5, 2006