CD-700, VCXO Based PLL
VCXO and Absolute Pull Range (APR) Specification
The CD-700’s VCXO is a varactor tuned crystal oscillator, which produces an output frequency
proportional to the control voltage (pin 1). The frequency deviation of the CD-700 VCXO is specified in
terms of Absolute Pull Range (APR). APR provides the user with a guaranteed specification for minimum
available frequency deviation over all operating conditions. Operating conditions include operating
temperature range, power supply variation, and differences in output loading and changes due to aging.
A CD-700 VCXO with an APR of +/-50 ppm will track a +/-50 ppm reference source over all
operating conditions. The fourth character of the product code in Table 6 specifies absolute Pull Range
(APR). Please see Vectron’s web site, www.vectron.com, for the APR Application Note.
APR is tested at 0.5 and 4.5 volts for a 5.0volt option and 0.3 and 3.0 volts for the 3.3volt option.
VCXO Aging
Quartz oscillators typically exhibit a part per million shift in output frequency during aging. The major
factors, which lead to this shift, are changes in the mechanical stress on the crystal and mass-loading on
the crystal.
As the oscillator ages, relaxation of the crystal mounting stress or transfer of environmental stress through
the package to the crystal mounting arrangement can lead to frequency variations. VI has minimized these
two effects through the use of a miniature AT-cut strip resonator crystal, which allows a superior mounting
arrangement. This results in minimal relaxation and almost negligible environmental stress transfer.
VI has eliminated the impact of mass loading by ensuring hermetic integrity and minimizing out-gassing by
limiting the number of internal components through the use of ASIC technology. Mass-loading on the
crystal generally results in a frequency decrease and is typically due to out-gassing of material within a
hermetic package or from contamination by external material in a non-hermetic package.
Under normal operating conditions the CD-700 will typically exhibit 2 ppm aging in the first year of
operation. The device will then typically exhibit 1 ppm aging the following year with a logarithmic decline
each year thereafter.
Divide-By Feature
The lowest available VCXO OUT1 frequency is 12.000MHz. To achieve lower frequencies, such as 1.544
or 2.048 MHz, OUT1 is divided by a 2n counter , where n=1 to 8 and is the OUT2 frequency. This results in
a divide by 2,4,8…256 and is set at the factory, so it is user selectable upon ordering only. To achieve
1.544 or 2.048MHz, a CD-700 at 24.704 MHz with a divide by 16 or a CD-700 16.384 MHz with a divide-by
8 would be used. Additional external divide-by circuits can be used to further lower or change the
frequency.
A disabled OUT2 is an ordering option.
Vectron International • 166 Glover Avenue, Norwalk, CT 06856 • Tel: 1-88-VECTRON-1• http://www.vectron.com
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