Dvb Board; Overview - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set

3.2 DVB Board

3.2.1

Overview

The DVB decoder is able to convert DVB sig-
nals that are transmitted free to air via satellite
into the appropriate analogue audio and video
signals, which are then fed to the signal proc-
essing of the TV chassis.
Analogue
AV progr.
Satellite
Analogue/
antenna
Digital-Sat.-
Tuner
LNC-Control
Sat 6
The following block diagram shows the princi-
pal architecture of the Sat 6 and DVB de-
coder. The interface between Sat 6 and the
DVB decoder is formed from quasi-analogue I
and Q signals, the AGC signal, the IIC bus
and a port used for DISEqC. The IQ signals
are derived in the satellite tuner by quadrature
mixing of the second IF (479.5 MHz) in the
base band. The AGC signal provides ampli-
tude control of the IQ outputs of the tuner. As
the Sat 6 unit is able to process analogue and
digital signals, both the DVB controller and the
TV controller have access to the tuner and the
LNC supply. The switching of the IIC buses
used for this is achieved by the TV controller
driven by the Sat 6 unit.
Document Q 2500
CVBS
Sound-ZF
or L-R
I-Signal
ADC
Q-Signal QPSK,
FEC
AGC
I2C-Bus
DVB
I2C-Bus
TV
DISEqC
2+2MB
DRAM
For the conversion of the L band signal de-
rived from LNC or a multiswitch, the combi-
tuner of the satellite unit Sat 6 is designed as
an assembly set or retrofit set for the Q 2500
chassis. It also supports the interface to an
integrated online module.
27 MHz
VCXO
Demux,
Descrambler
I2C-Bus
AV-Decoder
V-Encoder
Controller
1+1MB
Flash
The processing of DVB signals from the tuner
base band interface to the analogue output is
achieved by two high integration chips. The
first is the front-end component STV0299B
(ST microelectronics) that digitises the IQ sig-
nals coming from the tuner by means of dual
ADCs, demodulates them (carrier and pulse
extraction) and carries out Forward Error Cor-
rection. The second component is the MPEG-
2 demultiplexer-, decoder-, backend- and con-
troller chip STi5500 (ST Microelectronics),
which demultiplexes the MPEG-2 transport
beam, feeds the selected audio and video
components to the MPEG-2 decoder for de-
compression, decodes them and then con-
verts them into analogue output signals. The
STi5500 also has an integrated 32-bit RISC
46
DVB-Decoder
2+2 MB
SDRAM
Audio -
DAC
128 kB
EAROM
© Loewe ProCollege
RGB
S-Video to
Scart-Matrix
Audio L-R to
Scart-Matrix
2x RS 232 to
TV-Controller and
Online-Modul