Naoto Oka

Influence of ground plane width on reduction of radiated emission from printed circuit boards

This paper studies the ground plane width dependence of the radiated emission suppression from a printed circuit board (PCB) with digital circuits. Measured results are shown for the variation of the radiation emission by modifying the ground plane width of the PCB. Next, the relationship between the ground plane width and the current distributions on the signal line and the PCB is discussed. It is shown that the radiated electric field calculated from the current on the PCB measured with a current probe agrees with the measured electric field strength within 4 dB. It is shown that the radiated emission is reduced by expanding the ground plane width, since the common mode current is decreased. Further, by using a two-dimensional model, the current distribution on the ground plane is treated as an equivalent current generating the scattered field by illumination of the ground plane by the signal trace current. A method based on the physical optics approximation is used for the calculation of this equivalent current. The total sum of the equivalent current distribution and the signal trace current is considered as the common mode current and the radiated field due to the latter is evaluated. In this case, the reduction of the radiated emission due to modification of the ground plane width for PCBs having a width of 5 to 20 mm can be estimated within a range of 3.7 dB. Hence, it is shown that the ground plane width dependence of the radiated emission suppression can be evaluated easily.

Differential mode noise on the PCB's signal traces converted from external common mode noise

This study experimentally clarifies the relationship between the common mode noise induced on the cable connected to the signal trace of PCB and the differential mode noise on signal trace, converted from the common mode noise, due to the unbalance of differential signal trace by applying the measurement method that Test baluns are used as a load of the cable and a signal source. In this study, S13 (Differential mode noise) and S23 (Common mode noise) are measured by the network analyzer for evaluation. Finally, the effectiveness of the common mode choke on signal trace and the shielding for the cable for both common mode and differential mode noise reduction are evaluated.

Driver/receiver IC models for simulation of normal-mode emission

The authors are developing the technology that can simulate normal-mode emission radiated from printed circuit boards. We describe the driver and the receiver IC models which are needed to simulate radiated emission. We have derived the driver and the receiver IC models. The validity of these models was confirmed by comparing measured data with the results of the simulation.

A simplified model of a common mode choke coil for 3D field simulators

We studied a CMC model with a one-turn toroidal core, which is easily used in 3D field simulators. The calculation model of a CMC differs from the actual shape, so we need to correct the CMCs characteristics. When we calculated the noise-suppressing effect of the CMC, we used relative permeability, which differs from the actual value, to approximate the actual characteristics of a CMC. From the comparison of calculated results with measurement results, the calculated results were comparable to the measurement results. We confirmed the validity of our model.

Electromagnetic field immunity test system applying array antenna technology

We examined about the electromagnetic field immunity test system applying the array antenna technology. This system is able to get the electric field uniformity and the high power electric field near the antenna, in a wideband, by the beam forming technology. We constructed an electromagnetic field immunity test system consisting of 64 elements array antenna as a prototype. In this paper, we calculated the electric field uniformity near electromagnetic field immunity test system. We measured electric distributions and compared with the calculated value and the measured value. From these results, the validity of the calculation method of the electric field uniformity near the test system was confirmed.

Surface mount shunt capacitor filters using bilateral magnetic coupling

This paper proposes shunt capacitor filters using magnetic coupling which improves the filter performance. The proposed filter structure is designed to place input/output paths parallel to shunt path from a power supply line to a ground plane. And magnetic couplings between the input/output paths and shunt path are utilized to reduce parasitic inductance of the shunt path. The proposed filter provides higher performance with almost same area compare with conventional filters. Measurement and EM simulation are used to evaluate the filter performance. As a result, the proposed filters improved the performance by 8 dB at 20 MHz compared with filters without the couplings.

A gasket-free electromagnetic shielding structure for 2.4 GHz band using folded quarter-wavelength SIW resonators

In recent years, various types of new shielding structures realizing shielding effectiveness (SE) at specific frequency band have been reported. A gasket-free shielding structure using cascaded substrate integrated waveguide (SIW) resonators is one of them. The structure consists of cascaded SIW resonators with different resonant frequencies placed on inner walls of a gap. Though the structure has an advantage of being almost free of deterioration due to its non-contact structure, miniaturization of the SIW resonators is necessary to be applied at several GHz bands. In this paper, a gasket-free shielding structure using folded quarter-wavelength (FQ)-SIW resonators is proposed and its SE is evaluated. An FQ-SIW resonator is a miniaturized SIW resonator by applying a multilayer substrate and modifying position of the coupling slits. A prototype configuration for 2.4 GHz band is designed and fabricated using a five-layered FR4 substrate. The designed FQ-SIW resonators are miniaturized to almost 1/7 of conventional SIW resonators, and the measured results of the cascaded configuration showed more than 30-dB improvement of SE at 2.4 GHz band.

A study on differential mode to common mode conversion due to asymmetric structure in differential transmission line

Recently, differential transmission lines which have low electromagnetic radiation performance are widely used for high speed digital interconnections. Though high electrical balance is required to obtain that performance, degradation of the balance may often occur from asymmetry of the structure, such as additional patterns and electrical components connected to one or both of single lines of differential transmission line. In that case, some part of differential-mode signal is converted to common-mode signal, which may often increase electromagnetic radiation from the differential transmission line. It is therefore important to reduce the differential mode to common mode conversion ratio (Scd21) by keeping the electrical balance in the design stage in order to provide low EMI equipments. In this paper, we present an equivalent circuit model to evaluate the mode conversion due to the asymmetry of structure. The additionally connected patterns and components are modeled with a shunt capacitor connected between the single line and the ground. Then, Scd21 can be expressed as a simple function of the frequency and the capacitance difference between each single line of the differential transmission line, and is independent on the position of the capacitors. The proposed model is verified by the comparison of calculated Scd21 with the experimental results, and is applicable in low EMI design of differential transmission lines.

Radiated emission from a power plane of a multilayer printed circuit board

This paper describes radiated emission from a power plane of multilayer printed circuit boards (PCBs). A multilayer PCB has power planes, ground planes and signal planes. Emission from a power plane contributes to measurement results of emission from PCB. Measurements are made of emissions from multilayer PCBs, which have various lengths power plane areas. The authors examined the influence of the power plane only on radiated emissions.

Deterioration in shield characteristics by signal lines and power lines passing through shield material

The authors are developing the technology for designing shields of electronic equipment. As a factor which deteriorates shield characteristics, we pay attention to signal lines and power lines passing through a shield material. In this paper, we describe the effects of these lines on shield characteristics.