Technology of Q 2500 colour TV set
Technology of Q 2500 colour TV set
Technology of Q 2500 colour TV set
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<strong>Technology</strong> <strong>of</strong> Q <strong>2500</strong> <strong>colour</strong> <strong>TV</strong> <strong>set</strong>3.2 DVB Board3.2.1 OverviewThe DVB decoder is able to convert DVB signalsthat are transmitted free to air via satelliteinto the appropriate analogue audio and videosignals, which are then fed to the signal processing<strong>of</strong> the <strong>TV</strong> chassis.For the conversion <strong>of</strong> the L band signal derivedfrom LNC or a multiswitch, the combituner<strong>of</strong> the satellite unit Sat 6 is designed asan assembly <strong>set</strong> or retr<strong>of</strong>it <strong>set</strong> for the Q <strong>2500</strong>chassis. It also supports the interface to anintegrated online module.AnalogueAV progr.CVBSSound-ZFor L-R27 MHzVCXO2+2 MBSDRAMDVB-DecoderSatelliteantennaAnalogue/Digital-Sat.-TunerI-SignalQ-SignalAGCI2C-BusDVBI2C-Bus<strong>TV</strong>ADCQPSK,FECI2C-BusDemux,DescramblerAV-DecoderV-EncoderControllerAudio -DACRGBS-Video toScart-MatrixAudio L-R toScart-MatrixLNC-ControlDISEqC2+2MBDRAM1+1MBFlash128 kBEAROM2x RS 232 to<strong>TV</strong>-Controller andOnline-ModulSat 6The following block diagram shows the principalarchitecture <strong>of</strong> the Sat 6 and DVB decoder.The interface between Sat 6 and theDVB decoder is formed from quasi-analogue Iand Q signals, the AGC signal, the IIC busand a port used for DISEqC. The IQ signalsare derived in the satellite tuner by quadraturemixing <strong>of</strong> the second IF (479.5 MHz) in thebase band. The AGC signal provides amplitudecontrol <strong>of</strong> the IQ outputs <strong>of</strong> the tuner. Asthe Sat 6 unit is able to process analogue anddigital signals, both the DVB controller and the<strong>TV</strong> controller have access to the tuner and theLNC supply. The switching <strong>of</strong> the IIC busesused for this is achieved by the <strong>TV</strong> controllerdriven by the Sat 6 unit.The processing <strong>of</strong> DVB signals from the tunerbase band interface to the analogue output isachieved by two high integration chips. Thefirst is the front-end component S<strong>TV</strong>0299B(ST microelectronics) that digitises the IQ signalscoming from the tuner by means <strong>of</strong> dualADCs, demodulates them (carrier and pulseextraction) and carries out Forward Error Correction.The second component is the MPEG-2 demultiplexer-, decoder-, backend- and controllerchip STi5500 (ST Microelectronics),which demultiplexes the MPEG-2 transportbeam, feeds the selected audio and videocomponents to the MPEG-2 decoder for decompression,decodes them and then convertsthem into analogue output signals. TheSTi5500 also has an integrated 32-bit RISCDocument Q <strong>2500</strong> 46 © Loewe ProCollege
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