TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 7

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

Figure 5
V.2.1 - Black level locking
Figure 6
The video signal is applied to Pin 27 through the
coupling capacitor ”C27”. Since the sync pulse
amplitude is generallyequal to 1/3 of V
to 1V) and in order to obtain a good precision of the
black level, the sync pulse should be amplified by
a coefficient of - 14 before being applied to the
comparator ”C1”.
This comparator will charge the ”C27” capacitor as
long as V
line flyback interval ”T
”C27” capacitor is nil for one T
I
the middle of the back porch.
Figure 7
C
V
/I
N
D
-5 A
V
(2V)
is calculated such that the locking occurs at
S1
I
C
Composite Sync.
S1
V
S1
Output Signal
> V
V
PP
N
0
Video
Signal
Video
V
Input
S1
t
S
will stabilize at V
r
” if the average charge of
Level
Black
C27
t
V
r
H
27
t
1
Sync
Level
period.
=
t
I
r
C
2
V
t
PP
+
CC
S
N
t
+
(i.e. 66mV
r
during the
I
I
t
C
D
S
-14
+
= constant
T
t
H
S’
I
V
D
V
PP
N
t
t
= 2V
The V
is : 14
must be equal to V
i.e. : 14
It follows that :
substituting T
are standard and constant values) into above
equation :
V.2.1.1 - Application
At I
- With C27 = 220nF, V
- Due to transposition on amplifier stage, the black
TEA2028 - TEA2029 APPLICATION NOTE
which yields 0.8% maximum error in black level
with respect to V
time
level voltage on Pin 27 is equal to 2V.
C
C1
= 5 A
S1
I
D
C27
I
producedby I
C27
C
I
I
C
D
V
t
I
A
S1
C
t
H
= 6.23V
1
I
= 64 s, t
I
I
D
14
C
D
= 31 A
N
=
= 2V at the beginning of retrace
S1
t
t
5 52
Frame Sync.
A
1
220
during the time interval ”t1”,
=
D
r
S
t
during the line trace which
= 12 s, t
S
will be
V
T
= 16mV
P
H
t
R
V
N
2
t
R
= 2V
t
S
S
= 4.7 s (which
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