11

Phase

comparator

output

R5

R4

Vcc1

Figure 3 : Line Oscillator

Line

Flyback

Sync pulse

Output

Current

Vc

Integrated

Flyback

Figure 4 : Phase Comparator

13

12

Vcc1

Vc

SL2

ST1

Figure 5

The oscillator thresholds are internally fixed by

resistors. The discharge of the capacitor depends

on the internal resistor R4. The control voltage is

applied on resistor R5.

The sync-pulse drives the current in the compara-

tor. The line flyback integrated by the external net

work gives on pin 13 a saw tooth, the DC offset of

this saw tooth is fixed by VC. The comparator

output provides a positive current for the part of the

signal on pin 13 greater than to VC and a negative

current for the other part. When the line flyback and

the video signal are synchronized, the output of the

comparator is an alternatively negativeand positive

current. The frame sync-pulse inhibits the compa-

rator to prevent frequency drift of the line oscillator

on the frame beginning.

TDA8218

6/9