ICS843020-01 Datasheet, PDF (12/20 Pages) Integrated Circuit Systems – FEMTOCLOCKS-TM 680MHZ, CRYSTAL-TO- 3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS843020-01
FEMTOCLOCKS™ 680MHZ, CRYSTAL-TO-
3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER
TERMINATION FOR LVPECL OUTPUTS
The clock layout topology shown below is a typical termina-
tion 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, terminat-
ing 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 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
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
FOUT
3.3V
125Ω
125Ω
Z_o = 50Ω
FIN
Z_o = 50Ω
84Ω
84Ω
FIGURE 4A. LVPECL OUTPUT TERMINATION
FIGURE 4B. LVPECL OUTPUT TERMINATION
843020AY-01
www.icst.com/products/hiperclocks.html
12
REV. B APRIL 14, 2005