Shuichi Nitta

Effect of a shielding plane connected to ground plane of a PCB in EMI reduction

Effect of a shielding plane used for suppressing emission from a PCB is experimentally studied in this paper. The shielding plane is connected to some points of a ground plane contained in the PCB. In many cases of products, cables extend out of the shielding area and signal traces exist outside of this area. These cables and signal traces cancel the effect of shielding the devices inside of the shielding area. Moreover, in these cases, an extended shielding plane increases radiation level from the PCB.

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.

Study on electromagnetic interference of multiconductor twisted‐pair wire circuit: The case of two‐cored twisted‐pair wires

The purpose of this study is to clarify the mechanism of electromagnetic interference of a multiconductor twisted-pair wire circuit. In this study, two-cored (n = 2) twisted-pair wire is treated and a simple model of twisted-pair wire is proposed. Using the proposed twisted-pair wire model, crosstalk between twisted-pair wires is predicted. Based on the calculated and experimental results it is shown that both inductive and capacitive coupling must be taken into account in order to accurately predict the crosstalk between twisted-pair wires. For inductively coupled induced voltages, the same technique that is used for the parallel wires has been used; but a new technique is proposed for calculation of capacitively coupled voltages.

Prediction of noise reduction effect of ferrite beads on electromagnetic emission from a digital PCB

To reduce power supply noise such as power bounce and GND bounce, ferrite beads are usually inserted between the power supply and V/sub cc/ terminal of an IC by trial and error. An analytical approach on noise reduction effect of ferrite beads has not been established yet, referring to the catalog data on ferrite beads. In this paper, the noise reduction effect of ferrite beads on electromagnetic interference (EMI) is analytically discussed. Resonance characteristics of a digital circuit with ferrite beads are calculated and noise reduction effects are predicted in this paper. Near field EMI spectra are predicted and are compared with measured results. With respect to peak level of EMI spectra, predicted results coincide with measured results within an error of 4 dB.

The influence of heat sink on noise susceptibility of IC

This study discusses the influence of a heat sink (in the case that a heat sink is a plain conductor) on noise susceptibility of an IC. Paying attention to the capacitive coupling between adjacent PCBs (printed circuit boards), the equivalent model of capacitive coupling in the case of the existence of a heat sink is proposed. The induced noise voltage on an IC lead is predicted by applying the finite element method to the prediction of the capacitance between a noise source and a heat sink, and the predicted results are compared with the measured results. It is concluded that prediction method is practically useful below the 100 MHz, as the predicted results coincide with measured results within 2 dB below 50 MHz and within 5 dB below 90 MHz.

A Study on Characteristics of Electromagnetic Waves Propagating Through the Space Between Overlapped Metal Plates

The characteristics of electromagnetic (EM) waves propagating through the space between overlapped metal (conductive) plates and electrically conductive parts, which usually exists around a metal shielded box, are discussed in this study. The authors developed a method for measuring the current density distribution on the interface between the overlapped and energized metal plates. Using this method, the authors estimated that the general area of the electrically conductive parts is less than about 10 × 10 mm2. Thus, the space between overlapped metal plates and electrically conductive parts is frequently expected to be extremely thin for the width and short in the direction of EM wave propagation. In this case, it was confirmed that the extremely thin and short space can be regarded as a rectangular waveguide for the propagation of EM waves.

The influence of the instruction codes on radiated near-magnetic-fields

It has been said that the radiated electromagnetic emission (EMI) spectra from the computer change with the kind of the program executed on the computer. In this study, as a first step to investigate the influence of program on EM, the influence of instruction codes executed on a CPU on radiated near-magnetic-field is clarified by experiments and investigation on the timing chart of a CPU. It is concluded that the frequencies having peaks of near-magnetic-field spectra are observed on every frequency obtained by dividing the clock frequency by the number of clocks required for one instruction execution.

a case study on A5000

This study is about the method of obtaining stable clock pulse against incident noise by applying a PLL (phase locked loop) noise reduction circuit which the authors propose. In the proposed circuit, clock pulse is distributed without timing-skew by distributing common reference voltage to the voltage comparators included in the PLL noise reduction circuits. Further, stable clock pulse against large incident noise is realized by adding to PLL both a low-pass-filter with two different kinds of bandwidth and an edge detector of the phase variation caused by noise.

PLL noise reduction circuit to stabilize the disturbed clock pulse due to noise

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.

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

In this study, the influence of the location of a ground plane on the induced noise (crosstalk) on a twisted-pair-wire (TPW) by parallel lines is experimentally and theoretically discussed by paying attention to capacitive coupling between the TPW and the parallel lines. The capacity is obtained by applying the finite element method (FEM) to the calculation of electric field intensity. It is confirmed that calculated results are in good agreement with experimental results within 1 dB. It is concluded that the closer the TPW is to ground plane, the smaller the induced noise on the TPW becomes.