The natural frequency and the damping factor may be calculated by the following formulas :

=

2

π =

2

π √

where

β is programmed by the timing register

:

∆f

2

the roll-off value and on the power of the signal.

where m is the programmed reference level

(see AGC part), reset value : m = 24

∆f is the half range of the VCO

√

or

√

The damping factor is :

ξ= α



β

with

or

ξ=

0.247

√

2

beta_tmg

(Mode A) or

ξ=

0.188

√

2

beta_tmg

(Mode B).

beta_tmg can only take value from 0 to 9 ; if beta_tmg = 0, the loop becomes a first order one.

alpha_tmg can take any value from 1 to 6 ; if both alpha_tmg and beta_tmg are null, the loop is open ; the

duty cycle of the CLKREC output is controlled by writting the timing frequency register.

The next curve shows the natural frequency for a symbol frequency of 20Mbd, in Mode A, with nominal

reference level m = 24 as a function of the VCO relative frequency half range

∆f, for different values of the

register value beta_tmg.

The followingchart gives the value of the damping factor as a function of the VCO relative range, for different

combinations of alpha_tmg and beta_tmg, noticing that the damping factor only depends on the value of

α

√β

or (2 . alpha_tmg - beta_tmg ).

FUNCTIONAL DESCRIPTION (continued)

STV0196B

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