Integrated
Circuit
Systems, Inc.
ICS840002-01
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 ICS840002-01 provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD
, V
DDA
, and V
DDO
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 1
illustrates how
a 10Ω resistor along with a 10µF and a .01μF bypass
capacitor should be connected to each V
DDA
. The 10Ω re-
sistor can also be replaced by a ferrite bead.
3.3V
V
DD
.01μF
V
DDA
.01μF
10μF
10Ω
F
IGURE
1. P
OWER
S
UPPLY
F
ILTERING
C
RYSTAL
I
NPUT
I
NTERFACE
The ICS840002-01 has been characterized with 18pF paral-
lel resonant crystals. The capacitor values shown in
Figure 2
below were determined using a 25MHz 18pF parallel reso-
nant crystal and were chosen to minimize the ppm error.
XTAL_IN
C1
22p
X1
18pF Parallel Cry stal
XTAL_OUT
C2
22p
ICS84332
ICS840002-01
Figure 2. C
RYSTAL
I
NPU
t I
NTERFACE
840002AG-01
www.icst.com/products/hiperclocks.html
REV. B JANUARY 13, 2006
7
ICS [ INTEGRATED CIRCUIT SYSTEMS ]
