TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 17

• Manufacturer Part Number: TEA2029
• Description: APPLICATION NOTE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

V.3.7 - Phase comparator inhibition
The phase comparator is disabled under two con-
ditions :
- During frame sync pulse (see Figure 30)
Figure 30 : On Screen Display of Time Constants
Figure 31
Inverting the line sync pulse contained within the
video signal will provide the frame sync pulses
required for the synchronization of vertical scan-
ning.
Since the current supply to comparator 1 is
controlled by the line sync pulse, the comparator
must be inhibited at the time of line sync inver-
sions so as to avoid occurence of phase errors at
the beginning of each frame.
This inhibition is activated during FRI (Frame
Retrace Inhibition) issued by frame logic circuitry.
If 1 is locked before the vertical scanning syn-
chronization occurs, (e.g. when switching be-
tween channels), and since FRI phase is not yet
correctly positioned, the 1 must be further inhib-
ited by FS signal which is the extracted frame
VIDEO
COMPOSITE
SYNC.
FRAME
SYNC. (FS)
FRAME 1
INHIBITION (FR)
FRAME
BLANKING
S INHIBITION
(normal mode)
CURRENT
SIGNAL (FRI + FS)
[VCR mode]
1 COMPARATOR
1 INHIBITION
+ 4 s
Long Time Constant
Normal Mode
- 4 s shift
N
Inhibition
Inverted Pulses for Frame Sync.
- During line scanning (see Figures 31 and 32)
TEA2028 - TEA2029 APPLICATION NOTE
sync pulse.
This inhibition will eliminate the occurrence of all
possible phase errors due to a noisy sync signal
or parasitics during the line scanning phase. It
yields excellent display stability at noisy video
signals.
f1 Inhibition in long time constant mode
(VCR = 0)
S
and S
Inhibition is activated during, frame sync, FRI
and each time line trace interval - except at
frame beginning between lines 8 and 21.
(VCR = 1)
S
In VCR mode, inhibition is disabled during line
trace since phase or frequency variations are
not taken into account instantenously.
1 Inhibition in short time constant mode
INH(LONG)
INH(SHORT)
+ 4 s
In the abscence of Frame Inhibition
Short Time Constant
INH(SHORT)
VCR Mode
= Mute . (FRI + FS + BLK . LINE
= Mute . (FRI + FS) = S
= 1
- 4 s
N
n
INH(LONG)
17/46
INH
)