ICS84329 Datasheet, PDF (10/19 Pages) Integrated Circuit Systems – 700MHZ, LOW JITTER, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
ICS84329
700MHZ, LOW JITTER, CRYSTAL-TO-3.3V
DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER
CRYSTAL INPUT AND OSCILLATOR INTERFACE
The ICS84329 features an internal oscillator that uses an external
quartz crystal as the source of its reference frequency. The
oscillator is a series resonant, multi-vibrator type design. This
design provides better stability and eliminates the need for large
on chip capacitors.Though a series resonant crystal is preferred,
a parallel resonant crystal can be used. A parallel resonant mode
crystal used in a series resonant circuit will exhibit a frequency
of oscillation a few hundred ppm lower than specified. A few
hundred ppm translates to KHz inaccuracy. In general computing
applications, this level of inaccuracy is irrelevant. If better ppm
accuracy is required, an external capacitor can be added to a
quartz crystal in series to XTAL_IN. Figure 5A shows how to
interface with a crystal.
Figures 5A and 5B show various crystal parameters which are
recommended only as guidelines. Figure 5A shows how to inter-
face a capacitor with a parallel resonant crystal. Figure 5B shows
the capacitor value needed for the optimum ppm performance
over various series resonant crystal frequencies. For IA64/32
platforms which required a Raltron Parallel Resonant Quartz
crystal part #AS-16.66-18-SMD-T-M1, a 7pF series capacitor can
be used to better the ppm accuracy.
ICS84329
XTAL_OUT
XTAL_IN
FIGURE 5A. CRYSTAL INTERFACE
NOTE: For crystal frequencies higher than 17MHz,
a series tuning capacitor is required for proper operation.
FIGURE 5B. Recommended tuning capacitance for various series
resonant crystals.
30 _10.000
25
20
15
10
5
12.000
14.318
16.000
20.000
24.000
0
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Series Resonant Crystal Frequency (MHz)
84329AV
www.icst.com/products/hiperclocks.html
10
REV. D DECEMBER 15, 2004