
STV9432
15/18
Locking Condition Time Constant
(@ 4035)
This register provides the AS[2:0] and BS[2:0]
constants used by the algo part of the PLL (see
Figure 6
). These two constants as well as the
phase error (err(n)) give the new value (Dn) of the
high frequency signal division. Consequently,
AS[2:0] and BS[2:0] fix the pixel clock frequency.
These two constants are used only in locking con-
dition, if the phase error is inferior to a fixed value
during at least 4 scan lines. If the phase error
becomes superior to the fixed value, the PLL is
not in locking condition but in capture process. In
this case, the algo part of the PLL uses the other
constants AF[2:0] and BF[2:0] from the next regis-
ter.
Capture Process Time Constant
(@ 4036)
The choice between these two time constants
(locking condition or capture process) allows to
decrease the capture process time by changing
the time response of the PLL.
8.5.2 - How to choose the time constant value
The time response of the PLL is given by its char-
acteristic equation which is:
(x - 1)
2
+ (
)
.
(x - 1) +
Where:
[6:1]
.
2
A -11
and
(LD[6:1] = value of the LINE DURATION register,
A = value of the 1st time constant, AF or AS and
B = value of the 2
d
time constant, BF or BS).
As can be seen, the solution depends only on the
LINE DURATION and the TIME CONSTANTS
given by the I
2
C registers.
Table 3
Valid Time Constants Examples
B \ A
0
= 0
= 3
.
LD[6:1]
.
2
B - 19
If (
ble and its response is as shown in Figure 15.
If (
)
2
- 4
, the response of the PLL is as
shown in Figure 9. In this case the PLL is stable if
> 0.7 damping coefficient.
Table 3
gives some good values for A and B con-
stants for different values of the LINE DURATION.
Figure 8. Time Response of the PLL/
Characteristic equation solutions (with real
solutions)
)
2
- 4
and 2
< 4, the PLL is sta-
Figure 9. Time Response of the PLL/
Characteristic
equation
complex solutions)
solutions
(with
Notes: - Table meaning: N = No possible capture - No stability, Y = PLL can lock.
- Case of A[2:0] = 1 (001) and B[2:0] = 4 (100):
α
β
+
β
α
3 LD
=
β
α
β
+
β
0
≥
α
β
–
α
β
+
β
0
≤
τ
PLL Frequency
Input Frequency
f
1
f
0
t
f
1
f
0
t
PLL Frequency
Input Frequency
f
1
f
0
t
f
1
f
0
t
1
2
3
4
5
6
0
YYYY
YYYY
YYYY
YYYN
YNNN
NNNN
NNNN
1
YYYY
YYYY
YYYY
YYYN
YNNN
NNNN
NNNN
2
NYYY
YYYY
YYYY
YYYN
YNNN
NNNN
NNNN
3
NNNY
YYYY
NYYY
(1)
YYYY
YYYN
YNNN
NNNN
NNNN
4
NNNN
YYYY
YYYN
YNNN
NNNN
NNNN
5
NNNN
NNNY
YYYY
YYYN
YNNN
NNNN
NNNN
6
NNNN
NNNN
NYYY
YYYN
YNNN
NNNN
NNNN
7
NNNN
NNNN
NNNY
YYYN
YNNN
NNNN
NNNN
LD[6:1]
Valid Time Constants
8
N
16
Y
24
Y
32
Y