Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setAs VPC 3230 requires four lines to determinewhether the comb filter is to be switched off,the filter operates more efficiently and morefrequently than for a two line comb filter.The vertical correction of the signal isachieved by the line interpolation in SAA4991.4.3.4 Multi-standard colour decoderLine compression/decompressionWrite to52 sThis block executes demodulation for all TVstandards - PAL, NTSC and SECAM. Additionalexternal components are no longer required.On the output of the colour decoderthere is an 8 bit wide luminance and chrominancesignal respectively in 4:2:2 format.Read from forCinema / ZoomWrite toRead from for4:3 / Panoramaon 16:9 c.r.t.s52 sThe VPC monitors the Auto S-VHS detectionby means of the colour decoder for the separatechroma line of the colour burst. If signalsare fed in from a VHS video recorder, then noburst is present on a separate chroma line.This is in turn communicated to the CCU. TheCCU switches to VHS operation. If an S-VHSrecorder is connected then a colour burst ismeasured on the chroma line on playback andthe CCU switches the VPC to S-VHS operationvia the I²C bus.4.3.5 Line compression and decompressionTo reproduce 4:3 pictures on a 16:9 c.r.t., andalso for the various zoom modes, the videosignal must be lengthened, or stretched, horizontally.For this the VPC 3230 has a linememory. Selection occurs at a slower speed,with the line beginning and end not being read(zoom, cinema)However, quicker selection is also possible.For this the start is delayed with respect to thedeflection and the selection is ended beforethe line end of the deflection (4:3 and Panoramafor the 16:9 c.r.t).Letterbox detectorFor Cinemascope or other film standards upperand lower black bars of various thicknessare visible. These black bands can be removedby various zoom functions or at leastreduced. Devices with 16:9 c.r.t.’s are alsofitted with an automatic format conversion.Depending on the thickness of the black barsthis automatic movie detection - AMD –switches between three different zoommodes. For this the Letterbox detector measuresthe luminance and chrominance componentsin the upper and lower area.If, within defined lines, luminance and chrominancevalues of less than 10% are measured,the CCU switches the deflection controller andthe display processor to the appropriate geometricalformat. As programme logos are oftenplaced on the right and left of the blackbars, no measurement takes place in thisarea.Automatic format conversion for 16:9 devices.Document Q 2500 89 © Loewe ProCollege