!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 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 1 2
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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 effect of emi suppression filter 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 filter between the ic2 output terminal and the signal pattern can remarkably suppress the noise level the emi suppression filter used in this experiment is a combination of the chip emifilŪ for the signal line and a 30 resistor so that distortion of the digital signal waveform can be suppressed !test circuit vcc 5v ceralockŪ 16mhz nfw31sp506x1e cut-off frequency 50mhz high 1 30 gn
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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 noise sources in digital equipment 1 example of suppressing radiated noise from cable 2 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 an emi suppression filter is connected to the ic2 output terminal so that the noise radiated from the signal pattern can be suppressed through these noise suppressing measures the radiation noise level can be reduced markedly
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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 2 suppressing emi noise emission 2 emi suppression filters using emi suppression filters 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 immunity s
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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 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 bloc
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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 2 suppressing emi noise emission 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 !experimental pwb 29.7cm 25mhz resonator ceralockŪ 5v 7cm 3.3v transmission line length l=5cm ferrite beads x=1cm 74hcu04 74lvc04 74lvc00 10cm 20cm 3.3v 2 !radiated noise and signal waveform actual measurement double-sided epoxy-glass pwb the back surface of the pwb is entirely grounded thickness t=0.8mm =4.7 characteristic i
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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 3 how to select and use emi suppression filters relation between emi filters noise suppression performance and signal waveform distortion 2 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 !test circuit vcc 5v measurement point 16mhz emi suppression filter gnd hc04 hc00 high 3 !relation between emi suppression filter s
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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 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 emifilŪ 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 should pr
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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 4 differences in noise suppressing effect caused by transmission line length current distribution change after connection of ferrite beads inductor now the current distribution prior to connection of the ferrite beads inductor is compared with the data after connection of the inductor to compare the current distributions our attention is focused on the data at 375mhz because we observed a remarkable difference in the ferrite beads inductor s noise suppressing effect at 375mhz when the transmission line length on the prototype experimental pwb was changed the charts above show the measurements of current distributions for individual
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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 differences in noise suppressing effect caused by transmission line length 4 measurement result on shift of ferrite beads inductor mounting position 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 beads inductor is moved away from the transmission terminal the current
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