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LCD display technology EMC and ESD protection
2011-10-10 by seoer1

LCD (Liquid Crystal Display), for many users may be a term is not new, but there is history of this technology may be far beyond our imagination - in the 19th century, the Austrian botanist found in liquid crystal, that liquid crystals, a substance that also has a liquid crystal liquidity and a similar arrangement of features. In the electric field, liquid crystal molecules will produce changes in the arrangement. Thus affect its optical properties, a phenomenon called electro-optic effect. Using liquid crystal electro-optic effect, British scientists in the last century created the first piece of liquid crystal display that is LCD. Today's China LCD module manufacturer are widely used in the fixed linear liquid crystal, microscopic look at it if we will find it especially like a cotton swab. Compared with the traditional CRT, LCD is not only small and thin (the thickness of the current 14.1-inch machine may be only 5 cm), light weight, low energy consumption (1 to 10 microwatts / square centimeter), low voltage (1.5 to 6V) and no radiation, no flicker and can be matched directly with CMOS integrated circuits. Because many advantages, LCD from 1998 into the desktop applications ... ...

At present, for many popular mobile phones (especially the flip phones), the phone's color LCD, OLED display, or CMOS sensor camera module and other components, flexible circuits or through long PCB traces and connected to the baseband controller, These cables will be radiated by the parasitic antenna GSM / CDMA frequency interference. Meanwhile, high-resolution CMOS sensor and TFT module into the digital signal to work at higher frequencies, these connecting lines will act as an antenna causing EMI interference or danger may cause ESD events.

This interference with the EMI and ESD will damage the integrity of the video signal, or even damage to the baseband controller circuit. Driven by compact design trend, considering the board room, high on a cell phone frequency filtering performance and the preservation of signal integrity design constraints, discrete filters can not provide any space saving solution, but can only provide for the narrow-band attenuation filtering performance is limited, so most designers now use the integrated EMI filter.

As mobile phones and cameras and other portable devices to improve the LCD screen resolution, video signal transmission rate is also increasing, the traditional filter program has gradually reached their technical limits. In the high-resolution display and embedded with a camera phone, the signal through a specific frequency (depending on resolution) is sent from the baseband ASIC and embedded camera on the COG LCD module. The higher resolution video, data, also higher frequency of work. For example, for 30-600000 pixel camera module, the clock frequency between approximately between 6 to 12MHz. Therefore recommended that the filter (down) cutoff frequency selection from 30 to 50MHz range. As the resolution increases the number of megapixels to the clock frequency of over 60MHz, which requires the filter's cutoff frequency up to 300MHz.

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