STV9432

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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

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:

= 0

Where:

(LD[6:1] = value of the LINE DURATION register,

A = value of the 1st time constant, AF or AS and

As can be seen, the solution depends only on the

LINE DURATION and the TIME CONSTANTS

If (

and 2

< 4, the PLL is sta-

ble and its response is as shown in Figure 15.

If (

, the response of the PLL is as

shown in Figure 9. In this case the PLL is stable if

> 0.7 damping coefficient.

stants for different values of the LINE DURATION.

Figure

8.

Time

Response

of

the

PLL/

Characteristic equation solutions (with real

solutions)

Figure

9.

Time

Response

of

the

PLL/

Characteristic

equation

solutions

(with

complex solutions)

Table 3

Valid Time Constants Examples

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):

αβ

+

β

α

3LD

⋅

=

β

αβ

+

β 0

≥α β

–

αβ

+

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

B \ A

0

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

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]

8

16

24

32

Valid Time Constants

NYYY