STV0196 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STV0196' PDF : 23 Pages View PDF
STV0196B
FUNCTIONAL DESCRIPTION (continued)
The natural frequency and the damping factor may be calculated by the following formulas :
fn
=
ωn
2π
=
Fs
2π
√βK0Kd
where β is programmed by the timing register
: β = 2beta_tmg.
K0 is the constant of the VCO
:
K0
=
∆f
226
.
Kd is the phase detector ; its value depends on : Kd = 0.977m2 (in Mode A),
the roll-off value and on the power of the signal. or Kd = 0.564m2 (in Mode B).
where m is the programmed reference level
(see AGC part), reset value : m = 24
Fs is the symbol frequency, ∆f is the half range of the VCO
Therefore fn = 19.2 10−6 ⋅ m ⋅ Fs ⋅ √∆f2beta_tmg (Mode A)
or
fn = 14.6 10−6 ⋅ m ⋅ Fs ⋅ √∆f2beta_tmg (Mode B)
√ The
damping
factor
is
:
ξ
=
α
2
K0Kd
β
with α = 2 alpha_tmg + 12
or
ξ
=
0.247
⋅
m ⋅ √∆f ⋅ 2 alpha_tmg
√2beta_tmg
(Mode A)
or ξ =
0.188 ⋅ m ⋅ √∆f ⋅ 2alpha_tmg
√2beta_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 ).
8/23
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