AN1751 Datasheet, PDF (1/7 Pages) STMicroelectronics – EMI Filters: Recommendations and measurements

AN1751
®
APPLICATION NOTE
EMI Filters: Recommendations and measurements
P. MERCERON AND P. RABIER
With the development of wireless telecommunications, consumer products and cellular phones are sub-
jected to Radio Frequency Interference and may generate ElectroMagnetic Interference. This is in addition
to ElectroStatic Discharge the user can apply when touching a connector like a bottom connector on a cel-
lular phone.
In the past, filtering was achieved by discrete devices (capacitors, resistors) and ESD protection was done
by discretes diodes. Cellular phone size drop and enhanced features require faster signals and more and
more integrated devices which are becoming very sensitive to ESD or EMI/RFI.
Discretes devices impose a well designed layout to minimize parasitic effect of PCB inductances while In-
tegrated Passive and Active Devices suppress most of these inductances due to very short tracks between
passives on the die itself.
Fig. 1: Frequency response comparison between discrete and IPAD™ filter.
dB
IPAD
DISCRETES
10 MHz
100 MHz
1 GHz
Discrete filter will behave like a rejection filter but the rejection frequency will be depending on parasitic in-
ductances while the IPAD filter will act like a low pass filter.
EMIF filters have three main functions, the first is of course to filter EMI/RFI, the second is to protect inputs
and outputs against ESD and the third one is to transmit data from inputs to outputs. EMIF datasheets pro-
vide data and curve measured in specific conditions. The goal of this note is to explain test conditions for
EMIF devices.
1-Frequency response
EMIF target is to pass low frequency signals and to reject frequency higher than 800MHz especially
900MHz, 1.8 and 2.4GHz.
Attenuation curve provided in specification shows :
n Simulation thanks to the Aplac (or P-Spice) tool. This is done before the die design to be sure the device
will fit customer requirements
n Measurement done on demonstration board.
September 2003 - Ed: 1
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