Filtering the LCD or camera link

AN3141

6/14

Doc ID 17004 Rev 1

3

Filtering the LCD or camera link

The filter choice is made according two parameters:

●

Bandwidth, to keep the signal integrity in case of digital signals

●

Rejection at the frequency to attenuate, i.e. at RX frequencies of mobile phone

LCD and camera link clock frequency is in the range of 10 - 50 MHz, and the digital signal is

a wide band spectrum signal. Consequently, bandwidth of the filter needs to be in the range

of 200 MHz to keep good signal integrity.

As shown before (see Figure 2), the filter must reject the mobile phone reception

frequencies: GSM to W-CDMA gives frequencies from 869 MHz to 2.17 GHz.

In this frequency range attenuation needs to be as high as possible to limit the emissions of

the digital link.

Three types of device have been developed by STMicroelectronics to ensure good signal

integrity:

●

EMIF10-LCD02F3, 10-line version, (or EMIF07-LCD02F3, 7-line version)

●

EMIF08-LCD04M16,

●

EMIF10-LCD03F3 (or EMIF07-LCD03F3)

These devices offer a bandwidth of 200 MHz, as shown in Figure 6, Figure 7 and Figure 8.

Attenuation at RX frequencies are not the same:

●

EMIFxx-LCD02F3 is an RC type filter and provides attenuation of -25 dB at 900 MHz.

●

EMIF08-LCD04M16 is an LC filter and provides attenuation of -35 dB at least on RX

band, which is better than the RC type filter.

●

EMIFxx-LCD03F3 is an LC type filter and provides attenuation of -50 dB on RX band -

better than the RC type filter.