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FX-700 Low Jitter Frequency Translator

Vectron International • 267 Lowell Road, Hudson, NH 03051 • Tel: 1-88-VECTRON-1 • Web: www.vectron.com

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

8983_VECTRON

06/17/02

12:13 PM

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