TEA2029 STMICROELECTRONICS [STMicroelectronics], TEA2029 Datasheet - Page 15

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

This amplitude changing modifies the open-loop
system gain and therefore the damping coefficient
and the locking time constant.
The device will be in short time constant mode
under the following two conditions :
- VCR Mode or SCART Connector Mode :
- Transmitter search and tunning.
V.3.5 - Video identification stage
This stage will detect the coincidence between the
line sync pulse (if present) and a 2 s pulse issued
from the logic block. This 2 s pulse at line fre-
quency is positionned at the center of line sync
pulse when the first loop ” 1” is locked.
This sampled detection is stored by an external
capacitor connected to Pin 25. The video recogni-
tion status is also available on Pin 24 so as to
enable Sound Muting during station search proc-
ess and the inhibition of Automatic Frequency Tun-
ing.
V.3.5.1 - Block diagram
Figure 28
The video recognition signal is delivered by a hys-
teresis comparator.
The recognition time ”T
nal capacitor, as soon as 1 is locked :
- I
and :
- T
This mode is enabled by a low state on Pin 23.
V
In order to accelerate the capture, a ”Video Iden-
tification” stage will detect the presence or the
absence of a video signal on input Pin 27, and
deliver accordingly a signal called ”Mute”.
2 s
with C25 = 4.7nF
(which is clearly quite fast)
C25(AV)
LS
LS
23
R
= C25
< 2.1V.
= I
&
&
C
I
C25
64 s
V
2
H
AV
s
I
750 A
I
500 A
C
D
4.7nF
= 1.96 10
C25
T
R
R
” is adjustable by an exter-
25
= 1ms
i
C(25)
4.6V
5
C25
Comparator
Frame
Logic
1
Pin
24
Figure 29
V.3.6 - Characteristics of loop 1
V.3.6.1 - Locking accuracy
Let’s study the phase error ”
steady state conditions :
The open-loop gain is :
- T(p) =
- f(p) = R
If a phase step of
following would be obtained as a function of (p) :
Using the last value theorem : lim f(t) = lim p . f(p)
Let’s calculate lim
- The closed-loop gain is :
- H(p) =
that is : lim
TEA2028 - TEA2029 APPLICATION NOTE
Where :
A = 0.16mA/rd (long time constant)
A = 0.47mA/rd (short time constant)
B = 0.7kHz/V or B = 4.4 10
Where : R = Dynamic input resistance of VCO.
p 0
Line Sync.
LS
AB f p
1
Mute
Output
T p
I
I
p
f
C(25)
C(25)
1
T p
2 s
I
D
1
0
p 0
IN
2
1
=
I
p 1
C
p
1
IN
IN
ABf p
1
OUT
is applied to the input, the
p
p
V
ABf
L
4.7 s
4.6V
OUT
V
3
H
p
p
p
3
p
lim
rd/s
with Video
without Video
V
=
0
HYST
OUT
p
2 s
OUT
IN p
p
= 0.3V
AB f
-
p
V
25
IN
0
” under
15/46
0