PRELIMINARY
Integrated
Circuit
Systems, Inc.
ICS840001-31
F
EMTO
C
LOCKS
™ C
RYSTAL
-
TO
-
LVCMOS/LVTTL F
REQUENCY
S
YNTHESIZER
A
PPLICATION
I
NFORMATION
P
OWER
S
UPPLY
F
ILTERING
T
ECHNIQUES
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. The ICS840001-31 provides sepa-
rate power supplies to isolate any high switching noise from the
outputs to the internal PLL. V
DD
, V
DDA
and V
DDO
should be indi-
vidually connected to the power supply plane through vias, and
bypass capacitors should be used for each pin. To achieve op-
timum jitter performance, power supply isolation is required.
Fig-
ure 1
illustrates how a 10Ω resistor along with a 10μF and a
.01μF bypass capacitor should be connected to each V
DDA
pin.
3.3V
V
DD
.01μF
10Ω
V
DDA
.01μF
10μF
F
IGURE
1. P
OWER
S
UPPLY
F
ILTERING
C
RYSTAL
I
NPUT
I
NTERFACE
The ICS840001-31 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown in
Figure 2
below were determined using a 26.5625MHz, 18pF par-
allel resonant crystal and were chosen to minimize the ppm er-
ror. The optimum C1 and C2 values can be slightly adjusted for
different board layouts.
XTAL_OUT
C1
33p
X1
18pF Parallel Crystal
XTAL_IN
C2
22p
Figure 2. C
RYSTAL
I
NPU
t I
NTERFACE
840001-31AK
www.icst.com/products/hiperclocks.html
6
REV. A MAY 4, 2005
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
