EMI Suppression Filters for Digital Equipment 12/05/2004 by Murata Manufacturing Co.,Ltd.

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Catalog EMI Suppression Filters for Digital Equipment 12/05/2004

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!note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering c33e.pdf 04.5.12 1 noise sources in digital equipment 1 the electronic circuits that may raise emi noise problems use many ics which makes the process of emi noise emission very complicated to explain the emi noise phenomena simply this chapter describes how electronic circuits for example experimental circuits with only two or three ics emit emi noise

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering 1 noise sources in digital equipment effect of emi suppression filter !test circuit vcc 5v ceralock® 16mhz nfw31sp506x1e cut-off frequency 50mhz high 30Ω gnd ic2 hc04 ic1 hcu04 ic3 hc00 !board layout 3.8 signal pattern filter 10 ic3 hc00 0.3 ic1 hcu04 1.7 ceralock® ic2 hc04 4.2 10 gnd in cm !radiated noise without emi filter 60 dbµv/m 50 40 30 20 10 30 84 138 192 246 300 246 300 frequency mhz with emi filter 60 50 dbµv/m 1 this chart shows the result of the experiment for suppressing the noise radiated through a signal pattern that serves as a noise antenna normal mode noise inserting an emi suppression

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering noise sources in digital equipment vcc 5v ceralock® 16mhz nfw31sp506x1e cut-off frequency 50mhz high high 1 30Ω gnd ic1 hcu04 ic2 hc04 ic3 hc00 ic4 hc04 ground plane metal plate 1m cable 1m cable !board layout 3.8 1.7 ic1 hcu04 10 signal pattern filter 0.3 ceralock® ic3 hc00 4.2 10 gnd ic4 hc04 this diagram shows an example of the noise suppression circuit that uses the cable described in the previous experiment as an antenna for radiating common mode noise in this experiment a gnd plane is used to improve the gnd condition so that the common mode noise conducted through the gnd line can be suppressed furthermore

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering 2 suppressing emi noise emission 2 emi suppression filters using emi suppression filters 2 the emi suppression filters are connected to noise transmission lines to eliminate noise emitted from a noise source or intruded from an external device therefore the emi suppression filters can be used for both noise suppression purposes for suppression of noise emission and for improvement of noise immunity in order to prevent the noise on the filter input and output sides from being mixed with each other the emi suppression filters for suppressing noise emission should be located near the noise source and those for improving noise

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering suppressing emi noise emission 2 3 improved ground pattern as a technique for suppressing common mode noise we can consider intensification of the gnd condition when a signal return current flows through the gnd line a voltage applied to the gnd terminal causes common mode noise to suppress such voltage on the gnd terminal we must reduce the gnd impedance between the signal sending and receiving ics with attention to the high speed signal in the circuit in order to prevent noise interference between circuit blocks we must reduce the gnd impedance between individual circuit blocks so that the gnd current from individual circuit

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering 2 suppressing emi noise emission !experimental pwb influence of transmission line length these charts show the variations in noise level depending on changes in transmission line length at the same signal frequencies you can see that the noise level increases particularly at low frequencies as the transmission line is extended 29.7cm 25mhz resonator ceralock® 3.3v 7cm 5v transmission line length l=5cm 10cm 20cm 3.3v ferrite beads x=1cm 74hcu04 74lvc04 74lvc00 double-sided epoxy-glass pwb the back surface of the pwb is entirely grounded thickness t=0.8mm ε=4.7 characteristic impedance z=130Ω 2 !radiated noise and

!note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering 3 how to select and use emi suppression filters !test circuit relation between emi filters noise suppression performance and signal waveform distortion 2 vcc 5v these charts show examples of the signal waveform and harmonic spectra cause of noise measured in a circuit that uses a three terminal capacitor for a digital signal line from these measurements you can see that increasing the capacitance of the three terminal capacitor can improve the noise suppressing effect but results in large distortion of the signal waveform high measurement point 16mhz emi suppression filter gnd hc04 hc00 !relation between emi suppression filter s noise suppression

!note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering c33e.pdf 04.5.12 how to select and use emi suppression filters 3 4 examples of emi suppression filter use on conductive noise path 1 signal cable connecting section if a larger noise suppressing effect is required you should use the chip emifil® or capacitor type emi suppression filter in combination with a chip ferrite beads inductor if a relatively low noise suppressing effect is enough for the line you may use just the chip ferrite beads inductor to utilize the capacitor type emi suppression filter more effectively you must connect the gnd terminal of the emi suppression filter to a stable ground if a stable ground is not available you

!note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering 4 c33e.pdf 04.5.12 differences in noise suppressing effect caused by transmission line length current distribution change after connection of ferrite beads inductor !375mhz current distribution actual measurement focusing on the frequency shows a remarkable difference in the noise suppression effect l=5cm 75 current dbµa rms 70 mounting position 65 no filter 60 current drop large 55 50 blm 45 40 35 0 5 10 15 20 position cm l=10cm 75 current dbµa rms 70 mounting position 65 no filter 60 current drop medium 55 50 blm 45 40 35 0 5 10 15 20 position cm l=20cm 75 70 current dbµa rms 4 now the current distribution prior to connection of the

c33e.pdf 04.5.12 !note please read rating and !caution for storage operating rating soldering mounting and handling in this pdf catalog to prevent smoking and/or burning etc this catalog has only typical specifications therefore you are requested to approve our product specifications or to transact the approval sheet for product specificaions before ordering differences in noise suppressing effect caused by transmission line length measurement result on shift of ferrite beads inductor mounting position 4 !radiation noise transmission line length 20cm actual measurement these charts show the radiation noise level measurements when shifting the ferrite beads inductor to the peak current point at a frequency of 375mhz contrary to our expectation the radiation noise level measured at 375mhz is higher than the initial value to examine the cause of this phenomenon we measured the current distribution at 375mhz the charts also show the current distribution measurements when the ferrite