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9.2.2
Mono
In mono sets, the signal goes via the SAW filter (position
1004 in case of QSS demodulation and 1003 in case of
Intercarrier demodulation), to the audio demodulator part of
the UOC IC7200. The audio output on pin 48 goes directly,
via the smart sound circuit (7941 for Bass and 7942 for
Treble) and buffer (7943), to the audio amplifier (AN7523 at
position 7902).
The volume level is controlled at this IC (pin 9) by a
'VolumeMute' control line from the microprocessor.
The audio signal from IC7902 is then sent to the speaker/
headphone output panel.
EXT. AUDIO
OUTPUT
EXT. AUDIO
FM
FM IF
FMR
BUFFER
INPUT
7200
SIF
SOUND
23
RF ANT.
SAW
IF
FILTER
24
DEMOD.
FM ANT.
1000
VIF
10
0265
18
TUNER
19
VISION
1
1
11
SAW
IF
FILTER
DEMOD.
1
AGC
22
Figure 9-4 .eps
9.2.3
FM radio (if present)
The FM radio uses the 10.7 MHz concept. This SIF
frequency is available at pin 10 of the tuner. Via a pre-
amplifier (TS7209 and TS7210), the signal is fed for
demodulation to either the UOC (for mono FM radio) or by the
Micronas MSP34X5 (for stereo FM radio).
9.3
Video Signal Processing
9.3.1
Introduction
The video signal-processing path consists of the following
parts:
•
RF signal processing.
•
Video source selection.
•
Video demodulation.
•
Luminance/Chrominance signal processing.
•
RGB control.
•
RGB amplifier
The processing circuits listed above are all integrated in the
UOC TV processor. The surrounding components are for the
adaptation of the selected application. The I
defining and controlling the signals.
9.3.2
RF Signal Processing
The incoming RF signal goes to the tuner (pos. 1000), where
the 38.9 MHz IF signal is developed and amplified. The IF
signals then exits the tuner from pin 11 to pass through the
SAW filter (position 1002 in case of QSS demodulation and
1003 in case of Intercarrier demodulation). The shaped
signal is then applied to the IF processor part of the UOC
(pos. 7200).
Tuner AGC (Automatic Gain Control) will reduce the tuner
gain and thus the tuner output voltage when receiving strong
RF signals. Adjust the AGC take-over point via the Service
Alignment Mode (SAM). The tuner AGC starts working when
the video-IF input reaches a certain input level and will adjust
2
this level via the I
C bus. The tuner AGC signal goes to the
tuner (pin 1) via the open collector output (pin 22) of the UOC.
The IC also generates an Automatic Frequency Control
(AFC) signal that goes to the tuning system via the I
to provide frequency correction when needed.
The demodulated composite video signal is available at pin
38 and then buffered by transistor 7201.
Circuit Description
7941
7942
7943
7902
SMART
AUDIO
SND
AMPL.
9
48
VOLUME MUTE
AUDIO SWITCH
AVL
7602
68
µP
NVM
CL 16532008_040.eps
220501
2
C bus is for
2
C bus,
L01.1E
9.3.3
Video Source Selection
The Composite Video Blanking Signal (CVBS) from buffer
7201 goes to the audio carrier trap filters (1200 and 1201) to
remove the audio signal. The signal then goes to pin 40 of
IC7200. The internal input switch selects the following input
signals:
•
Pin 40: terrestrial CVBS input
•
Pin 42: external AV1 CVBS input
•
Pin 44: external Side I/O CVBS or AV2 Luminance (Y)
input
•
Pin 45: external AV2 Chrominance (C) input
RGB/YUV _IN
INTERNAL_CVBS_IN
AV1_CVBS1_1
7802
SY_CVBS_IN
CVBS_FRONT_IN
0225-B
C-IN 45
AV2 CVBS_IN
9
Y_IN
SVHS
C_IN
SEL-MAIN-FRNT-RR
SC2-CTRL
9
10
FRONT AUDIO IN
1, 12
AV1 AUDIO IN
5, 14
AV1 AUDIO IN
3, 13
2, 15
7801
Figure 9-5
Once the signal source is selected, a chroma filter calibration
is performed. The received colour burst sub-carrier
frequency is used for this. Correspondingly, the chroma band
pass filter for PAL processing or the cloche filter for SECAM
processing is switched on. The selected luminance (Y) signal
is supplied to the horizontal and vertical synchronisation
processing circuit and to the luminance processing circuit. In
the luminance-processing block, the luminance signal goes
to the chroma trap filter. This trap is switched 'on' or 'off',
depending on the colour burst detection of the chroma
calibration circuit.
The group delay correction part can be switched between the
BG and a flat group delay characteristic. This has the
advantage that in multi-standard receivers no compromise
has to be made for the choice of the SAW filter.
9.3.4
Video Demodulation
The colour decoder circuit detects whether the signal is a
PAL, NTSC or SECAM signal. The result is made known to
the auto system manager. The PAL/NTSC decoder has an
internal clock generator, which is stabilised to the required
frequency by using the 12 MHz clock signal from the
reference oscillator of the microcontroller/teletext decoder.
The base-band delay line is used to obtain a good
suppression of cross colour effects.
The Y signal and the delay line outputs U and V are applied
to the luminance/chroma signal processing part of the TV
processor.
9.3.5
Luminance/Chrominance Signal Processing
The output of the YUV separator is fed to the internal YUV
switch, which switches between the output of the YUV
separator or the external YUV (for DVD or PIP) on pins 51-
53. Pin 50 is the input for the insertion control signal called
'FBL-1'. When this signal level becomes higher than 0.9 V
(but less than 3 V), the RGB signals at pins 51, 52 and 53 are
inserted into the picture by using the internal switches.
9.
GB 57
7200
UOC
51 53
RGB
RGB/YUV
INSERT
56 58
40
42
VIDEO
PROC.
44
V-OUT
47
L/R OUT
P
70
QSS_AM_DEM_OUT
7831
47
SOUND
DEC
4
30, 31
MAIN_OUT
SC1-IN
24,25
41, 42
CL 16532016_011.eps
CRT
PANEL
MON. OUT
7901
AUDIO
AMPL.
120401
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