84314AY www.icst.com/products/hiperclocks.html REV. C JANUARY 27, 2005
9
Integrated
Circuit
Systems, Inc.
ICS84314
350MHZ, CRYSTAL-TO-3.3V/2.5V LVPECL
FREQUENCY SYNTHESIZER W/FANOUT BUFFER
V
CC
- 2V
50Ω 50Ω
RTT
Z
o
= 50Ω
Z
o
= 50Ω
FOUT
FIN
RTT = Z
o
1
((V
OH
+ V
OL
) / (V
CC
– 2)) – 2
3.3V
125Ω 125Ω
84Ω 84Ω
Z
o
= 50Ω
Z
o
= 50Ω
FOUT FIN
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
FIGURE 3B. LVPECL OUTPUT TERMINATIONFIGURE 3A. LVPECL OUTPUT TERMINATION
drive 50Ω transmission lines. Matched impedance techniques
should be used to maximize operating frequency and minimize
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 variations.
TERMINATION FOR 3.3V LVPECL OUTPUTS
APPLICATION INFORMATION
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS84314 provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
CC
, V
CCA
, and V
CCO
should be individually connected to the power supply
plane through vias, and bypass capacitors should be
used for each pin. To achieve optimum jitter performance,
power supply isolation is required.
Figure 2
illustrates how
a 10Ω resistor along with a 10µF and a .01µF bypass
capacitor should be connected to each V
CCA
pin.
POWER SUPPLY FILTERING T ECHNIQUES
FIGURE 2. POWER SUPPLY FILTERING
10Ω
V
CCA
10µF
.01µF
3.3V
.01µF
V
CC
