83PR226I-01 Datasheet, PDF (11/22 Pages) Integrated Device Technology – Programmable FemtoClock LVPECL Oscillator Replacement

83PR226I-01 Datasheet
Crystal Input Interface
The 83PR226I-01 has been characterized with 18pF parallel resonant crystals. The capacitor values shown in Figure 1 below were
determined using an 18pF parallel resonant crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
C1
27pF
XTAL_IN
C2
27pF
XTAL_OUT
Figure 1. Crystal Input Interface
Overdriving the XTAL Interface
The XTAL_IN input can accept a single-ended LVCMOS signal through an AC coupling capacitor. A general interface diagram is shown
in Figure 2A. The XTAL_OUT pin can be left floating. The maximum amplitude of the input signal should not exceed 2V and the input edge
rate can be as slow as 10ns. This configuration requires that the output impedance of the driver (Ro) plus the series resistance (Rs) equals
the transmission line impedance. In addition, matched termination at the crystal input will attenuate the signal in half. This can be done in
one of two ways. First, R1 and R2 in parallel should equal the transmission line impedance. For most 50 applications, R1 and R2 can
be 100. This can also be accomplished by removing R1 and making R2 50. By overdriving the crystal oscillator, the device will be
functional, but note, the device performance is guaranteed by using a quartz crystal.
3.3V
Ro ~ 7 Ohm
RS 43
Driv er_LVCMOS
3.3V
R1
100
Zo = 50 Ohm
R2
100
C1
0.1uF
XTAL_IN
XTAL_OUT
Cry stal Input Interf ace
Figure 2A. General Diagram for LVCMOS Driver to XTAL Input Interface
VCC=3.3V
LVPECL
Zo = 50 Ohm
Zo = 50 Ohm
C1
XTAL_IN
R1
0.1uF
50
XTAL_OUT
Cry stal Input Interf ace
R2
50
R3
50
Figure 2B. General Diagram for LVPECL Driver to XTAL Input Interface
©2017 Integrated Device Technology, Inc.
11
April 13, 2017