TEA2028 Ver la hoja de datos (PDF) - STMicroelectronics
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TEA2028 Datasheet PDF : 47 Pages
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TEA2028 - TEA2029 APPLICATION NOTE
V.2.3 - Sync pulse detection
This function is fulfilled by comparing the inverted
video signal (VS1 + VD) whose black level is con-
stant at 2V, with the sync 50% voltage level on
Pin 26 (see Figure 10).
Comparator C4 will deliver the line sync pulse (LS)
which will be used for 3 functions :
- Horizontal scanning frequency locking : output to
ϕ1 phase comparator.
- Frame sync extraction for vertical scanning syn-
chronization.
- Detecting the presence of a video signal at circuit
input.
The LS signal in two latter functions is filtered for
noise by using combination of current generator I
and a zener diode equivalent to a capacitor.
Using this extraction technique at a very noisy
video signal yields remarkable display stability.
Figure 10
The device also provides for scanning synchroni-
zation at aerial signal attenuation of approximately
75dB, i.e. 15 to 20dB better than other sync proc-
essors.
V.3 - First Phase Locked-loop Stage ”ϕ1”
This stage is commonly called the first Phase
Locked-Loop ”ϕ1”.
Its duty is to lock the frequency and the phase of
the horizontal time base with respect to the line
sync signal.
In the absence of transmission (i.e. lack of line
sync), the horizontal scanning frequency is ob-
tained by dividing the output frequency of a VCO
device. This VCO oscillates at approximately
500kHz and uses a low frequency drift ceramic
resonator. This method eliminates the need of hori-
zontal frequency adjustment.
+
VCC
V50%
26
C4
I
VS1 + VD
V50%
+
VCC
+
i
Frame
3V Separator
Video at Pin 27
LS
+
I
LS
On Video
C Recognition Output
LS
250ns
Line Sync. Output
toward Phase Comparatorϕ1
V.3.1 - Phase locked-loop ”ϕ1” block diagram
Figure 11
Phase Comparator
LS
φ IN +
-
∆ϕ
A
i
(mA/rd)
LOW-PASS
FILTER
F(P)
ϕ1
φ OUT
1 ω S BY-32-DIVIDER ω 1 VCO
Ve
P
STAGES
B (kHz/V)
Horizontal
Frequency
Ceramic Resonator
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