ICS843101-312 Datasheet, PDF (10/14 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-LVPECL 312.5MHZ FREQUENCY MARGINING SYNTHESIZER

ADVANCE INFORMATION
Integrated
ICS843101-312
Circuit
Systems, Inc.
FEMTOCLOCKS™ CRYSTAL-TO-LVPECL
312.5MHZ FREQUENCY MARGINING SYNTHESIZER
RECOMMENDATIONS FOR UNUSED INPUT PINS
INPUTS:
CRYSTAL INPUT:
For applications not requiring the use of the crystal oscillator
input, both XTAL_IN and XTAL_OUT can be left floating.
Though not required, but for additional protection, a 1kΩ
resistor can be tied from XTAL_IN to ground.
LVCMOS CONTROL PINS:
All control pins have internal pull-ups or pull-downs; additional
resistance is not required but can be added for additional
protection. A 1kΩ resistor can be used.
CLK INPUT:
For applications not requiring the use of the test clock, it can
be left floating. Though not required, but for additional
protection, a 1kΩ resistor can be tied from the CLK input to
ground.
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
843101AG-312
www.icst.com/products/hiperclocks.html
10
OCTOBER 18, 2005