Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setOwing to the narrow bandwidth the rise timesfor colour change are very long, which appearson the screen as "washed out" transitions.a)Uin,Vinb)t4.6.2 Band width doublingIn order to increase the effectiveness of thecolour flank increase on the supply side, adoubling of the bandwidth from 4:1:1 to 4:2:2is implemented.Using a linear phase interpolation filter additionalsampling values are calculated from theavailable chroma sampling values.These calculated sampling values are insertedrespectively between two available values, bywhich means the bandwidth is doubled. In thisway, steep flanks can be transmitted moreeasily.Ampl.c)Ampl.t4.6.3 Colour flank sharpeningAn improvement of the colour transition isachieved by a dual differentiation of the originalchroma signal and the ensuing subtractionof the derived correction signal of the chromasignal.d)Uout,Voutta) U, V input of SAAb) U, V Correction signalc) U, V input + Correction signald) sharpend and limited U, VTo compensate for this deficiency, two circuitcomponents are incorporated into the SAA4979, with which short rise times can beachieved artificially, thereby improving thecolour transitions.In the circuit before these components is ademultiplexer, with which 8-bit wide parallel R-Y- and B-Y signals respectively are derivedfrom the supplied signals.tThe changes in these signals are evaluated inseparate circuits for U and V, and if a thresholdvalue specified by the software is exceededa correction value is calculated. Afterthe two derived correction signals have beencleaned of noise components, they are subtractedfrom the available chroma signals Uand V. The subtraction is implemented by inversionof the correction signals and subsequentaddition with the original signal.To avoid colour phase errors by the overshooter,it must be blocked by limiter stages.Here analogue signals are produced from therespective 8-bit wide digital R-Y and B-Y signals,which are then output at 1.8 Vss on pins46 and 48.4.6.4 Y signal pathThe peaking circuit is not used. The signal isled directly to the sampling stage. This operatesin the same way as the sampling stage inthe chroma branch.Document Q 2500 101 © Loewe ProCollege