IDT8N3S271 Data Sheet LVPECL FREQUENCY-PROGRAMMABLE CRYSTAL OSCILLATOR
IDT8N3S271CCD
REVISION A DECEMBER 17, 2012
3 ©2012 Integrated Device Technology, Inc.
Principles of Operation
The block diagram consists of the internal 3rd overtone crystal and
oscillator which provide the reference clock f
XTAL
of either
114.285MHz or 100MHz. The PLL includes the FemtoClock NG VCO
along with the Pre-divider (P), the feedback divider (M) and the post
divider (N). The P, M, and N dividers determine the output frequency
based on the f
XTAL
reference. The feedback divider is fractional
supporting a huge number of output frequencies. The configuration
of the feedback divider to integer-only values results in an improved
output phase noise characteristics at the expense of the range of
output frequencies. Internal registers are used to hold one factory
pre-set P, M, and N configuration setting. The P, M, and N frequency
configuration supports an output frequency range from 15.476MHz to
866.67MHz and from 975MHz to 1,300MHz.
The devices use the fractional feedback divider with a delta-sigma
modul
ator for noise shaping and robust frequency synthesis
capability. The relatively high reference frequency minimizes phase
noise generated by frequency multiplication and allows more efficient
shaping of noise by the delta-sigma modulator.
The output frequency is determine
d by the 2-bit pre-divider (P), the
feedback divider (M) and the 7-bit post divider (N). The feedback
divider (M) consists of both a 7-bit integer portion (MINT) and an
18-bit fractional portion (MFRAC) and provides the means for
high-resolution frequency generation. The output frequency f
OUT
is
calculated by:
f
OUT
f
XTAL
1
PN
------------
MINT
MFRAC 0.5+
2
18
-------------------------------------+=
Frequency Configuration
An order code is assigned to each frequency configuration
programmed by the factory (default frequencies). For more
information on the available default frequencies and order codes,
please see the Ordering Information section in this document. For
available order codes, see the FemtoClock NG Ceramic-Package XO
and VCXO Ordering Product Information document.
For more information on programming capabilities of the device for
custom frequency and pull-range configurations, see the FemtoClock
NG Ceramic 5x7 Module Programming Guide.