TDA8841

Manufacturer Part NumberTDA8841
DescriptionI2C-bus controlled PAL/NTSC TV processor
ManufacturerPhilips Semiconductors
TDA8841 datasheet
 


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Page 12/68:

FUNCTIONAL DESCRIPTION

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Philips Semiconductors
2
I
C-bus controlled PAL/NTSC/SECAM TV
processors

FUNCTIONAL DESCRIPTION

Vision IF amplifier
The IF-amplifier contains 3 ac-coupled control stages with
a total gain control range which is higher then 66 dB. The
sensitivity of the circuit is comparable with that of modern
IF-IC’s.
The video signal is demodulated by means of an
alignment-free PLL carrier regenerator with an internal
VCO. This VCO is calibrated by means of a digital control
circuit which uses the X-tal frequency of the colour
decoder as a reference. The frequency setting for the
various standards (33.4, 33.9, 38, 38.9, 45.75 and 58.75
2
MHz) is realised via the I
C-bus. To get a good
performance for phase modulated carrier signals the
control speed of the PLL can be increased by means of the
FFI bit.
The AFC output is generated by the digital control circuit of
the IF-PLL demodulator and can be read via the I
For fast search tuning systems the window of the AFC can
be increased with a factor 3. The setting is realised with the
AFW bit. The AFC data is valid only when the horizontal
PLL is in lock (SL = 1)
Depending on the type the AGC-detector operates on
top-sync level (single standard versions) or on top sync
and top white- level (multi standard versions). The
demodulation polarity is switched via the I
AGC detector time-constant capacitor is connected
externally. This mainly because of the flexibility of the
application. The time-constant of the AGC system during
positive modulation is rather long to avoid visible variations
IDENT
VIDEO IDENT
Fig.6 CVBS switch and interfacing of video ident
December 16, 1997
of the signal amplitude. To improve the speed of the AGC
system a circuit has been included which detects whether
the AGC detector is activated every frame period. When
during 3 field periods no action is detected the speed of the
system is increased. For signals without peak white
information the system switches automatically to a gated
black level AGC. Because a black level clamp pulse is
required for this way of operation the circuit will only switch
to black level AGC in the internal mode.
The circuits contain a video identification circuit which is
independent of the synchronisation circuit. Therefore
search tuning is possible when the display section of the
receiver is used as a monitor. However, this ident circuit
cannot be made as sensitive as the slower sync ident
circuit (SL) and we recommend to use both ident outputs
to obtain a reliable search system. The ident output is
supplied to the tuning system via the I
The input of the identification circuit is connected to pin 13
(S-DIP 56 devices), the “internal” CVBS input (see Fig.6).
2
C-bus.
This has the advantage that the ident circuit can also be
made operative when a scrambled signal is received
(descrambler connected between pin 6 (IF video output)
and pin 13). A second advantage is that the ident circuit
can be used when the IF amplifier is not used (e.g. with
built-in satellite tuners).
The video ident circuit can also be used to identify the
selected CBVS or Y/C signal. The switching between the
2
C-bus. The
2 modes can be realised with the VIM bit.
VIM
13(24)
17(29)
CVBS-INT
CVBS-EXT
12
Tentative Device Specification
TDA884X/5X-N2 series
2
C-bus.
TO LUMA/SYNC PROCESSING
TO CHROMA PROCESSING
+
+
10(20)
11(21)
38(54)
Y/CVBS-3
CVBS-2
C
CVBS-1
OUT
OUT
(26)