FX-700 Datasheet, PDF (6/8 Pages) Vectron International, Inc – Low Jitter Frequency Translator

FX-700 Low Jitter Frequency Translator
FX-700 Theory of Operation
The FX-700 includes an integrated phase
detector, current mode charge pump,
programmable frequency dividers and VCXO.
The FX-700 will translate an input frequency
such as 8 kHz, 1.544 MHz or 19.440 MHz to
a specific output frequency which is an integer
multiple (1-16384) of the input frequency and
less than or equal to 77.760 MHz. For clock
smoothing applications, the input frequency is
typically internally divided down by a factor of
64 (2N where N = 6) by the input frequency
divider and this frequency becomes an input
to the phase detector. The integrated
frequency dividers (factory programmed)
and crystal based VCXO allows for a large
range of possible frequency translations and
clock smoothing applications.
The FX-700’s PLL is a feedback system which
forces the output frequency to lock in both
phase and frequency to the input frequency.
While there will be some phase error, theory
states there is no frequency error. The loop
filter design will dictate many key parameters
such as jitter reduction, stability, lock range
and acquisition time. The external second
order passive loop filter is a complex imped-
ance in parallel with the input capacitance of
the VCXO. The loop filter converts the charge
pump output into the VCXO’s control voltage.
VI’s loop filter design methodology involves
the calculation of the open loop gain band-
width and corresponding phase margin to
determine the optimal component values that
ensure high loop stability and acceptable lock
in time. As a rule of thumb, the VCXO gain is
typically 100 ppm/volt and the charge pump
current is typically 32 uA.
VI’s Applications Engineering staff can provide
the external loop filter component values
required to meet specific system requirements
and application
Vectron International • 267 Lowell Road, Hudson, NH 03051 • Tel: 1-88-VECTRON-1 • Web: www.vectron.com
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