Modern cars are widely equipped with infotainment systems that use digital, high-resolution TFT-LCD's. These LCD's can show MMI contents (navigation, climate, telephone or radio control) as well as entertainment contents (DVD or TV). Within the last years, the display resolution and hence the pixel CLK frequencies were increased from some 6.3 MHz (QVGA, 320x240) to now typically 33 MHz (WVGA, 800x480) and even above. lt is obvious that now already lower harmonics of these frequencies might interfere with the FM radio or TV reception, which is broadcast in several bands between 47 MHz to 862 MHz. The German FNV regulation lists the allocated bands for radio and television broadcast as well as for other services from 9 kHz up to 105 GHz.Car manufacturers have established internal EMC standards that combine a number of mandatory component tests. Some typical noise sources in a display application are phase-locked data transmission, presence of multiple and poor GND layers, use of single-ended lines, lack of signal conditioning, and a chain of video IC's that amplify harmonic noise as well as non-harmonic one. EMI can be reduced by a common, low impedance GND, with multiple contacts between grounded layers, and by shielding of the COG flex connector. The generation of harmonic noise must be minimized by signal conditioning of single-ended lines an the main PCB as well as inside the TFT module. A slew rate control and/or RL filtering is recommended for the video data, while sine-wave filtering works for the pixel CLK. SSC is a effective method to reduce existing EMI, especially in TFT applications where single-ended lines are used for the video data transfer. The very sensitive signal path from the TC to the COG drivers can also be optimized by the implementation of RSDS. State-of-the-art timing controllers combine RSDS outputs with SSC, thus contributing to a very low emission level of the entire display application.
EMI aspects of automotive TFT-LCD applications
2005
10 Seiten, 11 Bilder, 1 Tabelle, 12 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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