TDA9109N datasheet(18/32 Pages) STMICROELECTRONICS

18 / 32 page

II.2 - PLL1

The PLL1 consists of a phase comparator, an

external filter and a voltage-controlled oscillator

(VCO). The phase comparator is a ”phase fre-

quency” type designed in CMOS technology. This

kind of phase detector avoids locking on wrong

frequencies. It is followed by a ”charge pump”,

composed of two current sources : sunk and sour-

ced (typically I = 1mA when locked and I = 140

µA

whenunlocked).This differencebetweenlock/unlock

allows smooth catching of the horizontal frequency

by PLL1. This effect is reinforced by an internal

original slow down system when PLL1 is locked,

avoiding the horizontal frequency changing too

quickly. The dynamic behaviour of PLL1 is fixed by

an external filter which integrates the current of the

charge pump. A ”CRC” filter is generally used

(see Figure 7).

The PLL1 is internally inhibited during extracted

vertical sync (if any) to avoid taking in account

missing pulses or wrong pulses on phase compa-

rator.The inhibition is done by a switch located

between the charge pump and the filter (see Fig-

PLL1F

µF

4.7

µF

1.8k

Ω

Figure 7

OPERATING DESCRIPTION (continued)

ure 8). The VCO uses an external RC network. It

delivers a linear sawtooth obtained by the charge

and the discharge of the capacitor, with a current

proportional to the current in the resistor. The typi-

cal thresholds of the sawtooth are 1.6V and 6.4V.

The control voltage of the VCO is between 1.33V

and 6V (see Figure 9). The theorical frequency

range of this VCO is in the ratio of 1 to 4.5.

The effective frequency range has to be smaller

(1 to 4.2) due to clamp intervention on the filter

lowest value.

Loop

Filter

1.6V

6.4V

1.6V

0 0.875T

H TH

FLIP FLOP

(1.3V < V

< 6V)

4 I0

Figure 9 : Details of VCO

LOCKDET

COMP1

INPUT

INTERFACE

H/HVIN

High

CHARGE

PUMP

Low

PLL

INHIBITION

VCO

PLL1F

PHASE

ADJUST

I2C

HPOS

Adj.

OSC

Tramext

I2C

Forced

Frequency

Lock/Unlock

Status

HPOSITION

Figure 8 : Block Diagram

TDA9109/N

18/32

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