Motoshi Tanaka

Correspondence of Common- and Differential-Mode Components on EM Radiation from Surface Microstrip Line Structure

It has been demonstrated that a common-mode (CM) current can dominate the EMI processes up to 1 GHz, despite the fact that a CM current is smaller than a differential-mode (DM) current. However, this description is insufficient to describe behavior above 1 GHz. In this paper, the correspondence of CM and DM components for total electromagnetic (EM) radiation from a printed circuit board (PCB) with surface microstrip line, which is commonly used in microwave integrated circuits, at gigahertz frequency is studied experimentally and With finite-difference time-domain (FDTD) modeling. In order to characterize the EM radiation, the frequency response of the CM current, the electric field near the PCB, and the electric far field are investigated. First, the frequency response of the CM current, near and far-fields for the PCB with an attached feed cable are compared up to 5 GHz. Although the CM current decreases above a few gigahertz, near and far electric fields increase as the frequency becomes higher. Second, in order to distinguish between CM and DM radiation at high frequency, the frequency response and the angle pattern of the fit-field from a PCB without the feed cable are discussed. The results show that radiation up to 1 GHz is related to the CM component. However, depending on polarization and PCB geometry, radiation may be bominated by the DM rather than the CM component. The results indicate that the DM component may be more significant relative to the CM component, and the increase in EM radiation can not be predicted from only the frequency response of CM current. Therefore, identifying the dominant component is essential for suppressing the EM radiation. This study is a basic consideration to realize a technique which is effective on the suppression of the EM radiation from the PCB with an attached feed cable.

An equivalent circuit model for predicting EM radiation from a PCB driven by a connected feed cable

An equivalent circuit model for predicting electro- magnetic (EM) radiation from a printed circuit board (PCB) driven by a connected feed cable is proposed and demonstrated. The equivalent circuit model is based on consideration of concepts of CM antenna impedance and distributed constant circuit to the conventional mechanisms of current- and voltage-driven. Good agreement between the predicted and measured results shows validity of the equivalent circuit model. The proposed model can predict and explain frequency response of CM current with engineering accuracy, and also express the intermediate state of the current-driven and the voltage-driven. It is demonstrated that outline of the frequency response of EM radiation from the PCB driven by the connected feed cable can be predicted up to 18 GHz. This study suggests basic method and consideration to establish methods predicting an EM radiation from the PCB driven by the connected feed cable.

PCB Structure with a Guard Band for Suppressing Electromagnetic Radiation

Electromagnetic (EM) radiation from a feed cable attached to a printed circuit board (PCB), which is commonly encountered electromagnetic interference (EMI) problem at high-speed electronic PCB designs, is investigated by experimental and finite-difference time-domain (FDTD) modeling. In this paper, we propose and demonstrate a guard-band structure as a method for suppressing the EM radiation from a PCB with a feed cable. A signal trace is located between two ground traces (guard-band: GB). Four different cross-sectional PCB structures, which are commonly used in microwave integrated circuits as typical structures, are used to compare the guard-band structure. Frequency response of common-mode (CM) current, electric field near a PCB, and far electric field (radiated emission) are investigated as characteristics of the EMI. Results show that the shield structure is effective in suppressing the CM current at lower frequency. However, structures in which a conductive plate exists near the signal trace yield resonances with high level peak on CM current, near and far-field. On the other hand, the guard-band structure is more effective than other structures in suppressing the EM radiation in the considered frequency range. Therefore the guard-band will be effective for high-density PCB packaging with high-speed traces.

Radiated emission from a PCB with an attached cable resulting from a nonzero ground plane impedance

In this paper, radiated emission from a PCB with an attached cable resulting from a nonzero ground plane impedance is studied experimentally and with FDTD modeling. Frequency responses of the CM current, the electric field near the PCB, and the electric far field are investigated. First, the effect of a thin wire to mimic an interconnected ground wire is discussed. Comparing the cases with and without the thin wire, the difference is only at the resonance frequency, and there is no change on the magnitude of the CM current. Second, the effect of a termination on EMI coupling-path that results from the nonzero ground plane impedance is discussed. When the terminating resistor is smaller than the nonzero impedance, EMI antenna is driven as current-driven. Therefore, for relatively low impedance load such as 51 /spl Omega/, EMI antenna is driven as voltage-driven at lower frequency. As the terminating resistor is larger, the CM current becomes larger at lower frequencies (10/spl sim/100 MHz). This indicates that a high impedance load such as a logic IC results in larger radiation at lower frequency.

A Study on the Effect of Grounded Conductive Sheet Placed over PCB for Electromagnetic Noise Shielding

The effect of a grounded conductive sheet placed over a PCB with a microstrip line on the electromagnetic noise shielding is discussed experimentally and with FDTD modeling. The grounding position of the sheet, which is connected with the ground plane of PCB, is changed. In results, the resonance frequency is shifted by the grounding position, and reducing the resonance of the input impedance should make a more effective shielding for EM noise radiation below 1 GHz.

Estimation of spatial distribution of electromagnetic noise radiated from PCB

This study aims to clarify the frequency characteristics of the spatial distribution of electromagnetic noise inside a distance of 3 m around a printed circuit board (PCB) by simulation and experiment. It is also shows that the finite difference time domain method (FDTD method) is a useful tool to estimate the frequency characteristic of the spatial distribution for the electric and magnetic field around the PCB. By comparison between the electric and magnetic near field spectrum above the printed line by simulation, these spectra are shown to have differences in the resonance frequency: when the characteristics of the electric and magnetic field strength at 60 ns after the excitation is calculated, the electric field is decreased, the magnetic field is not decreased, as the distance from PCB is farther. From the characteristics of particular frequencies, the electric field spectrum at 3 MHz, i.e, clock pulse, is decreased, whereas the magnetic field is not decreased. The electric and magnetic field strength at the resonance frequency, 417 MHz, is decreased in inverse proportional to the square of the distance. It is also clear that the low frequency magnetic field strength may be superior to higher frequency.

Effect on electromagnetic radiation by conductive plane placed near a PCB

The suppression and/or radiation effects of electromagnetic noise with a conductive plane shielding near a PCB with a microstrip line are discussed. The distance d between the PCB and the conductive plane, the plane size, and the grounding position on the plane are varied. The magnetic near-field is measured by a shielded-loop probe. The input impedance is also measured, and calculated by the FDTD method. In results, the distance d /spl ges/ 8 mm is more suitable to reduce the effect of the electromagnetic coupling, and changing the conductive plane size and the grounding position change the shielding effect on the magnetic field.

Experiment and estimation by FDTD-method on the close field noise from a printed line model

A modeling on emission and propagation of undesired electromagnetic noise from a printed line on a PCB, in terms of the close field noise for MHz range is simulated by FDTD method. The relationships with frequency characteristics of estimated line impedance, current waveform and measured result are discussed.

Programmable composite noise generator (P-CNG) and its application to the opinion test on TV picture degradation

We have newly developed a programmable composite noise generator (P-CNG) which can easily control noise parameters such as average power, time-based amplitude probability distribution (APD), average zero crossing rate, occurrence frequency distribution and burst duration. A composite noise is made by the combination of some Gaussian noises, each of which has different amplitude RMS and duration. Using the P-CNG, the influence of composite noise on TV picture degradation is evaluated by opinion tests. Five simple composite noise models with some kinds of APD are used, in which value of other parameters such as average power is constant. The experimental results show that the envelope and APD of composite noises do not largely influence mean opinion scores.

A study on magnetic near-field noise and EMI of LED light bulb

The magnetic near-field noise of two types of LED bulbs with and without a switching circuit in the AC/DC converter was measured in a shielded room, and compared. The field strength of the noise was larger at the top of the bulb. And the strength in the case of the bulb with the switching circuit was larger than that in the case without one below 150 MHz, which might be caused by a switching operation. Secondly, an EEG as an example of biomedical signal was measured using the same bulbs. The EEG amplitude in the case of the bulb with the switching circuit became larger than that without one. Harmonics components of 50 Hz were observed in the spectrum, which would be resulting from the EMI of the LED bulb. These results indicate that the distance between the bulbs and EUT for measurements should be noted.