Tohlu Matsushima

Verification of common-mode-current prediction method based on imbalance difference model for single-channel differential signaling system

In a differential transmission line, a large common-mode current is excited due to its asymmetry. In this paper, the authors demonstrate experimentally the common-mode current and verify the imbalance difference model that was proposed for prediction of the common-mode current reduction. Experimental results show that the reduction of common-mode current of about 20 dB is achieved by changing the position of the transmission line. In addition, the differences that are calculated using the imbalance difference model are in agreement with the measured ones within 2 dB.

Prediction of EMI from two-channel differential signaling system based on imbalance difference model

In a differential transmission line, a large common-mode radiation is excited due to asymmetry. To suppress the radiation, the differential line must be designed electrically symmetric. In this paper, the imbalance difference model, which was proposed by the authors for estimation of common-mode radiation, is extended to apply the differential signaling system. The authors focus on two pairs of differential transmission lines with asymmetric property, which consists of an adjacent return plane and signal lines which are placed close to an edge of the return plane. The authors define five transmission modes; two normal modes, two primary common modes and a secondary common mode. In these transmission modes, the secondary common mode radiation is dominant, and the authors evaluate the radiation using the imbalance difference model. To reduce the common-mode radiation, placing a guard trace which has the same potential as that of the return plane, we can control the imbalance and reduce common-mode radiation even the transmission line has asymmetry. The reduction of common-mode radiation can be estimated quantitatively by calculation of the imbalance of the transmission line.

Mode conversion and transfer characteristics of conducted disturbance to Ethernet device from power supply cable

Conducted disturbances from communication or power supply cables affect Ethernet devices. A conducted disturbance, which is generated when several switching power devices reach a communication device, degrades the quality of signal communications. In addition, a disturbance passing through an Ethernet device influences neighboring devices connected by the communication cables. Herein we propose a system to measure the propagation modes of conducted disturbances in power supply cables and Ethernet cables. The results indicate that mode conversion occurs in not only an Ethernet hub but also an AC adapter supplying DC voltage to Ethernet devices. The conducted disturbance to the AC and DC power supply cable is strongly transmitted to the Ethernet cable as the primary common mode and the differential mode. Conversion from the common mode in the power supply cable to the primary common mode in the Ethernet cable is dominant in the measured frequency range.

Impedance balance control for reduction of common mode noise in full bridge converter

In this paper, a mechanism of common mode noise generation in a full bridge converter is discussed, and a reduction method is proposed. Common mode noise is generated due to parasitic capacitors around power MOSFETs. In order to explain the mechanism of common mode generation, an equivalent circuit with the parasitic capacitors is proposed. When the circuit satisfies the impedance balance condition, the common mode noise can be eliminated. However, the impedance balance condition is time-varying because a full bridge converter changes the circuit topology during the operation of the circuit. Therefore, large capacitors are inserted for keeping the current paths dominant, and making input impedance of AC side high is applied in order to form the topology satisfying the impedance balance condition. The effectiveness of this method is verified by measurement, and the common mode current in DC side is reduced about 26 dB.

Reduction method of common-mode noise on power supply cable using floating conductor

A method to reduce common-mode current flowing on a wire harness attached to a printed circuit board is proposed in this paper. In this method, SMD inductors are placed on a power supply line and/or a ground line on a LSI package with floating conductor to control balance of impedance of the power distribution network, and the common-mode current can be reduced. The common-mode voltage is reduced about 20 dB with the package proposed in this paper.

Common-mode noise reduction using floating conductor in LSI package

The authors proposed a method to reduce the common-mode current flowing on a wire harness attached to a printed circuit board (PCB). In this method, SMD inductors are placed on a power supply line and/or a ground line on a PCB to control balance of impedance of the power distribution network, and the common-mode current can be reduced. In this paper, the authors apply this reduction method to an LSI package, and propose a new structure of the LSI package with floating conductor which is called cover metal. The common-mode voltage is reduced about 20 dB with the package proposed in this paper.

Degradation of signal integrity due to package-common-mode resonance caused by external conductive noise in power supply system

Package-common-mode resonance which is caused by a parasitic capacitance and a parasitic inductance between package and PCB grounds degrades signal and power integrity. A parasitic capacitance between a package ground and a PCB ground resonates with a parasitic inductance at ground connections, such as solder balls in a BGA package. In this paper, the authors simulate ground bounce due to the package-common-mode resonance caused by external conductive noise in a power supply system. The ground bounce degrades signal integrity of CMOS output signal. The authors demonstrated an increase in jitter of CMOS output at the package-common-mode resonance frequency.