ICS84021 Datasheet, PDF (11/14 Pages) Integrated Circuit Systems – 260MHZ, CRYSTAL-TO-LVCMOS / LVTTL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS84021
260MHZ, CRYSTAL-TO-LVCMOS / LVTTL
FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS84021 provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V , V , and V
DD DDA
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 2 illustrates how
a 24Ω resistor along with a 10µF and a .01µF bypass
capacitor should be connected to each V_DDA pin.
V
DD
V_DDA
3.3V
.01µF 24Ω
.01µF
10µF
FIGURE 2. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS84021 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown
in Figure 3 below were determined using a 25MHz, 18pF
parallel resonant crystal and were chosen to minimize the
ppm error. The optimum C1 and C2 values can be slightly
adjusted for different board layouts.
X1
18pF Parallel Cry stal
XTAL2
C1
22p
XTAL1
C2
22p
Figure 3. CRYSTAL INPUt INTERFACE
84021AY
www.icst.com/products/hiperclocks.html
11
REV. A NOVEMBER 7, 2003