ICS843004I-04 Datasheet, PDF (8/14 Pages) Integrated Circuit Systems – FEMTOCLOCKS-TM CRYSTAL/LVCMOS-TO- 3.3V LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS843004I-04
FEMTOCLOCKS™ CRYSTAL/LVCMOS-TO-
3.3V LVPECL FREQUENCY SYNTHESIZER
TERMINATION FOR 3.3V LVPECL OUTPUT
The clock layout topology shown below is a typical ter-
mination 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. There-
fore, 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 maxi-
mize operating frequency and minimize signal distor-
tion. 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 compat-
ibility across all printed circuit and clock component pro-
cess 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
843004AGI-04
www.icst.com/products/hiperclocks.html
8
REV. A FEBRUARY 15, 2006