84320AY-01
www.idt.com
REV. D JULY 26, 2010
11
ICS84320-01
780MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER
V
CC - 2V
50
Ω
50
Ω
RTT
Z
o = 50Ω
Z
o = 50Ω
FOUT
FIN
RTT =
Z
o
1
((V
OH + VOL) / (VCC – 2)) – 2
3.3V
125
Ω
125
Ω
84
Ω
84
Ω
Z
o = 50Ω
Z
o = 50Ω
FOUT
FIN
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 50
Ω transmission lines. Matched imped-
FIGURE 5B. LVPECL OUTPUT TERMINATION
FIGURE 5A. LVPECL OUTPUT TERMINATION
ance techniques should be used to maximize operating
frequency and minimize signal distortion.
Figures 5A and
5B 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.
TERMINATION FOR LVPECL OUTPUTS