Yoshiki Kayano

A method for compensating imbalance component of asymmetrical differential-paired lines due to turnoff point for SI and EMI performances

For differential-signaling system, the ideal balance or symmetrical topology cannot be established due to discontinuities at turnoff point (90-degree turn), so called bending, and hence, an imbalance component is excited. Therefore methodology and geometrical-structure for satisfying both SI and EMI performances are indispensable. In order to provide basic considerations for the realization of methods for compensating the imbalance component and suppressing the EM radiation from asymmetrical differential-paired lines, the imbalance component and EMI from the differential-paired lines with discontinuities at turnoff point were studied experimentally and with numerical modeling. The differential-paired lines with different layouts were prepared for the discussion as typical routing. In the method, the distance between the paired lines at turnoff point is narrow, and hence the difference of length between Line 1 and 2 is compensated. Therefore the suppression of imbalance component by compensating the difference of the length and suppression of EMI by narrower separation can be achieved. Firstly the mixed-mode scattering parameters are discussed, from view point of SI performance. Secondly, frequency responses of electric-field and magnetic-field near a PCB are discussed, from view point of EMI. It is demonstrated that the proposed method is suitable for improving the SI performance and suppressing the EMI. This study has successfully reported the basic characteristics of imbalance component of differential-paired lines with turnoff point.

Locally shielded differential-paired lines with bend discontinuities for SI and EMI performances

To provide the basic considerations for EM radiation from practical asymmetrical differential-paired lines with bend routing, this paper newly attempts to propose locally shielded differential-paired lines for establishing SI performance and suppressing imbalance component and EMI generated by differential-paired lines with bend (turnoff point) discontinuities. The conductive plane is placed on discontinuity region asymmetrically. The concept of locally shielded layout is based on compensation of phase-difference due to the bend discontinuities, by using electric-coupling between signal trace and a conductive plane for the shield. The proposed method is suitable for implementing on PCB, without changing layout of the differential-paired lines. To compare the effect of the locally shielded paired-lines on CM component, the |Scd21|, which is defined as the conversion from DM to CM, are evaluated. The significant suppression effectiveness of |Scd21| in the case study is achieved below 1 GHz by locally shielded differential-paired lines. Consequently, the validity of the proposed locally shielded layout is demonstrated in the case study. It is demonstrated that the proposed locally shielded layout is suitable for improving the SI performance and suppressing the CM in the case study. This study has successfully reported the basic method for suppressing imbalance component of differential-paired lines with bend discontinuities.

A study on transmission characteristics and shielding effectiveness of shielded-flexible printed circuits for differential-signaling

To provide basic considerations for the realization of method for suppressing the EMI from differential-paired lines on flexible printed circuits (FPC), the characteristics of the SI performance and shielding effectiveness (SE) of shielded-flexible printed circuits for differential-signaling are investigated in this paper experimentally and by a numerical modeling. Firstly, transmission characteristics of TDR measurement and frequency response of |Sdd21| are discussed, from view point of signal integrity. Secondly, as the characteristics of the SE performance for EMI, frequency responses of magnetic field are investigated. Although placement of conductive shield near the paired-lines decreases characteristics impedance, |Sdd21| for the “with Cu 5.5um-thickness copper shield” is not deteriorated compared with “without shield” and sufficient SE performance for magnetic fields can be established. But, thin-shield deteriorates SI as well as SE performances.

Characteristics of mode-conversion of bent differential-paired lines with different EM coupling

In order to provide basic considerations for the realization of methods for suppressing the mode-conversion and EM radiation from differential-paired lines with length mismatch, the mode-conversion in bend differential-paired lines with different EM coupling was studied with FDTD modelling. It is demonstrated that the differential-paired line with thinner dielectric substrate which can maintain narrow width of trace, is suitable for improving the SI performance and suppressing the EMI.

Investigation on characteristic impedance of transmission line in meshed-ground flexible printed circuit

A method to obtain the effective characteristic impedance of transmission line in meshed-ground FPC is investigated. Above on plenty of data, through the least square method, a relationship between the characteristic impedance and structural parameters of FPC is proposed for common design, with which it is more convenient to design the structure after getting the characteristic impedance.

A study on frequency dispersion of transmission characteristics of shielded-flexible printed circuits

In this paper, a frequency dispersion of transmission characteristics of shielded-flexible printed circuits (FPC) for differential-signaling is studied experimentally and numerical modeling. Firstly, differential-mode impedance, the mixed-mode scattering parameters and eye-diagram are discussed. Secondly, frequency dispersion of transmission characteristics is discussed by using RLGC equivalent-circuit model. The insufficient shielding performance for near magnetic field increases both the inductance and resistance. As the frequency becomes lower, DM impedance increases and propagation velocity decreases. Consequently, the frequency response has relatively large frequency dispersion.

Negative group delay characteristics of embedded transmission line with half-wavelength type F-SIR structure

Negative group delay is one of the anomalous characteristics of the metamaterial, and can be used to compensate the group delay of systems and is applicable to signal processing devices. In this paper, to achieve negative group delay with not only wide-band characteristics but also low-insertion loss, we newly propose the embedded transmission line with half-wavelength type folded-stepped impedance resonator (F-SIR) structure which has the symmetrical electric-wall at the guide center driven by differential-mode. The characteristics are discussed with numerical simulation. The concept of the proposed TL is based on the combination of resonance and anti-resonance due to open-stub resonator and F-SIR. The negative group delay and slope characteristics are achieved around anti-resonance. The insertion loss is dramatically improved compared with our previous results, which is constructed by gap and F-SIR structure. This study is a successful report that the validity of the proposed embedded TL structure is demonstrated.

Suppression of mode-conversion by DNG material placed on differential-paired lines with bend discontinuities

This paper newly attempts to propose a method for compensating the mode-conversion by double negative (DNG) material, for establishment of SI performance and suppression of imbalance (common-mode: CM) component and EMI generated by differential-paired lines with bend discontinuities. To demonstrate the impact of the DNG material on CM component, the simulated |Scd21|, which is defined as the conversion from differential-mode (DM) to CM, are evaluated. The significant suppression effectiveness of |Scd21| in the case study is achieved around 100MHz by DNG material. The suppression effectiveness at 70MHz is 10dB. It is estimated that the proposed structure is suitable for improving the SI performance and suppressing the CM in the case study. The results validate the proof of concept. The proposed method is good candidate for suppressing mode-conversion due to phase-difference.