Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setBlock diagram, VPC 3230 input interfaceAGC+6/-4,5 dBChroma72ClampADCDigital CVBSor Y signalCVBS/YAV3/Synch on Y7374InputmultiplexerAmplificationH-Synch/VGA75ClampADCdigital ChromaSystem ClockI 2271VPC 3230ReferencegenerationFrequencyDVCO150ppm78 59 62 63C 473/48920,25 MHzU5SBThe chroma signal is clamped to its middlevalue. The following automatic amplifier controlin the FBAS/Y path has a control range of-4.5 dB to +6 dB and ensures that even fordifferent input levels the FBAS/Y signal is alwaysoptimally adapted to the ADC. In thechroma branch a fixed amplification is sufficient.The FBAS/Y signal, as also the chroma signalfor Y/C operation are digitised at a cycle rateof 20.25 MHz. The resolution of the two ADCsis 8-bit. Therefore, at the output of the inputinterface there is an 8-bit wide FBAS or Y datastream and for Y/C operation also an 8 bitwide chroma data stream. Both ADCs need acorresponding reference value. This is producedinternally in the reference generationand stored externally on pin 78 by C 488/489.4.3.2 20.25 MHz clock generatorThe frequency determining 20.25 MHz QuarzX 2283 is connected to pin 62/63 of VPC3230. The clock generator is controlled fromthe synchronisation block. In normal operationthe clock generator is line frequency coupled.In the VCR mode, the line frequency couplingis switched off.Document Q 2500 86 © Loewe ProCollege