STV6889 datasheet(33/56 Pages) STMICROELECTRONICS

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STV6889

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Figure 5. Horizontal PLL1 block diagram

Figure 6. Horizontal oscillator (VCO) schematic diagram

9.3.3

Voltage controlled oscillator

The VCO makes part of both PLL1 and PLL2

loops, being an “output” to PLL1 and “input” to

PLL2. It delivers a linear sawtooth. Figure 6 ex-

plains its principle of operation. The linears are ob-

tained by charging and discharging an external ca-

pacitor on pin CO, with currents proportional to the

current forced through an external resistor on pin

, which itself depends on the input tuning volt-

age VHO (filtered charge pump output). The rising

and falling linears are limited by VHOThrLo and VHO-

ThrHi thresholds filtered through HOscF pin.

At no signal condition, the VHO tuning voltage is

clamped to its minimum (see section 6.4 - page

10), which corresponds to the free-running VCO

frequency fHO(0). Refer to subsection 9.3.1 for formu-

la to calculate this frequency using external com-

ponents values. The ratio between the frequency

corresponding to maximum VHO and the one corre-

sponding to minimum VHO (free-running frequen-

cy) is about 4.5. This range can easily be in-

creased in the application. The PLL1 can only lock

to input frequencies falling inside these two limits.

PLL

INHIBITION

SHAPER

Low

High

LOCK

COMP

CHARGE

PUMP

VCO

HOSC

(I²C)

INPUT

INTERFACE

Sync

V-sync (extracted)

(I²C)

DETECTOR

Polarity

V-sync

Extracted

REF1

(I²C)

PLL1

HPLL1F RO CO HOscF

HPOS

HPosF

PLL1Pump

H/HVSyn

HLckVBk

Blank

HLock

PLL1InhEn

Flip-Flop

4 I0

(PLL1 filter)

from charge pump

VCO discharge

control

HOscF

HPLL1F

VHO

VHOThrHi

VHOThrLo

VHOThrHi

VHOThrLo

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