sta002 STMicroelectronics, sta002 Datasheet - Page 16

• Manufacturer Part Number: sta002
• Description: Starmano Channel Decoder
• Manufacturer: STMicroelectronics

STA002
The 22 bits value to be written into this register is
given by:
for example if
M_CLK = 39,02687179MHz, Fck = M_CLK/4
which is the Reset Value.
3.3.2 Loop equations
This timing loop is a second order one. The natu-
ral frequency and the damping factor may be cal-
culated by the following formulas:
where
beta_tmg:
where m is the reference value of the AGC2 loop
(see AGC2_REF register), K
tor gain and Ko is the constant of the timing NCO:
The damping factor is:
where
pha_tmg:
beta_tmg can only take value from 0 to 15; if
beta_tmg is 0 the loop reduces to a first order
one.
Alpha_tmg can take any value from 0 to 7. If both
alpha_tmg and beta_tmg are 0 then the timing
loop is open.
The timing phase detector gain K
the signal to noise ratio and is given in the follow-
ing figure:
(see par. 3.8 for the C/N definition)
K
The natural frequency and the damping factor
can be rewritten as:
16/43
D
= 0.356 for a noise free input signal.
b = 2
SYMFREQ = 790995 = (C11D3)HEX
is programmed by the timing register al-
beta_tmg-14
is programmed by the timing register
SYMFREQ
f
n
K
o
Fsym (Fsym = 1.84MHz)
= 2
K
o
2
alpha_tmg
INT
K
2
K
22
o
2
D
K
F
D
D
ck
F
F
is the timing detec-
sym
m
ck
m
2
D
22
depends on
Phase Detector Gain
Table 1 gives the natural frequency and the
damping factor for the nominal amplitude m = 22,
K
In high noise conditions the value of K
reduced up to 25% of its nominal (noise free)
value; it is recommended to start with a damping
factor, calculated without noise, greater than the
usual value of 0.7.
3.4. CARRIER RECOVERY
Also the carrier recovery is completely imple-
mented digitally and comprises a phase and fre-
quency detector, a loop filter, a NCO and a
sine/cosine look-up table.
The carrier NCO is the local oscillator for the in-
put quadrature demodulator.
3.4.1 Carrier loop registers
Carrier
(CARFLTPAR)
Internal address: 8F H
Reset Value: 57H
MSB
D
b7
= 0.356 and M_CLK = 39.02687179MHz.
(Kd)
0.3
0.2
0.1
0
f
0
n
alpha_car
0.0577
b6
loop
2.064 F
b5
F
CK
5
filter
CK
b4
2
m K
beta_tmg
m K
b3
parameter
10
D
D
b2
beta_car
2
2
beta_tmg
D97AU724
alpha_tmg
C/N(dB)
b1
D
may be
register
LSB
b0