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Can You See Me Now? — Ten-line EMI Filter Protects LCD Lines

Geneva — STMicroelectronics NV has developed an electromagnetic interference (EMI) filter for LCD driver lines. It will be used in mobile, computing and consumer applications that are subject to increasing interference from wireless applications such as cell phones and Bluetooth connections.

The EMIF10-LCD01F1 is a 10-line filter designed to replace capacitor and resistor networks, and to reject rerouted and retransmitted radiation frequencies on the lines between a graphics controller and an LCD. The part also offers protection against damage from electrostatic discharges (ESD) of up to 15 kV.

The part is based on a low-pass resister-capacitor (RC) Pi filter, repeated 10 times on silicon and with integrated zener diodes at each input and output for ESD protection. The EMIF10-LCD01F1 is rated to meet IEC61000-4-2 standard level 4 ESD requirements.

The filter is offered in a flip-chip package of the same size as the die, reducing board space and also the parasitic inductance in the leads of the device. This helps deliver superior filtering performance across a wide frequency range, from 900 MHz to 3 GHz, which makes it suitable for use in dual- to quad-band cell phones. The EMIF10-LCD01F1 offers 30 dB of attenuation at GSM and Bluetooth frequencies.

The EMIF10-LCD01F1 has been designed with line capacitances that support up 30 MHz frequencies, to avoid disturbing video signals. This means the part has little impact on the rise and fall times of video signals and imposes almost no delay.

The part is available in a 6.9mm x 6.9mm flip-chip package in normal and lead-free versions and is priced at 70 cents in quantities of 100,000.

Click here for the EMI510-LCDO1F1 data sheet.

For company information, call (781) 861-2650 or visit: www.st.com

About 85% of STMicroelectronics' integrated passive and active device (IPAD) offering consists of EMI filters for portable applications. ST Micro's newest filter, the EMIF10-LCD01F1, is the company's first EMI filter intended for video applications.

The low capacitance filters are targeting a new trend in cell phones — watching videos albeit a soccer game or movies via cell phone. Since cell phones haven't been designed to perform this function, the end result is usually a choppy version that users are straining to see, said Hary Radakichenane, product engineering manager for STMicroelectronics' IPAD group.

Maintaining signal integrity is the key to viewing videos on cell phones, according to Radakichenane. “You need an EMI filter to maintain the signal integrity so every pixel is coming together on the LCD screen — blocking any interference,” he explained.

A 10-line filter is important because it matches the number of lines to be protected against EMI in an LCD screen. However, sometimes there are up to 20 lines such as pixel driving, control, address and clock in the LCD screen, which would require two of STMicro's filters.

Using the EMIF10-LCD01F1 eliminates the need for RC networks. Typically, RC networks are used to make EMI filters for cell phones — two resistors and one capacitor per LCD line. Therefore, 10 lines would require 30 components. Depending on the size of the components being used, designers could save as much as 75% of their application space by using ST Micro's highly integrated solution, according to Radakichenane.

This product represents a breakthrough as far as EMI filters are concerned since most similar filters on the market are offered in the high capacitance (60-pF) range, versus 30 pF for STMicro's new filter. Low capacitance is also crucial to maintaining signal integrity, Radakichenane said.

STMicroelectronics is beginning a new generation of EMI filters that promises half the capacitance (15 pF) of its latest filter (EM1F10-LCD01F1). Check out the Analog ICs section of EEProductCenter.com on February 15 to see the 15 pF STMicroelectronics' filter.

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