Yuichi Sasaki

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 study for designing an ESL-cancelling circuit for shunt capacitor filters based on the biot-savart law

In general, insertion loss of a shunt capacitor filter at higher frequencies than its resonant frequency is deteriorated by equivalent series inductance (ESL) of the shunt path. There are some reports on circuits to improve the deterioration by cancelling the ESL by mutual inductance between coupled loops. However, a theory-based design equation is not clearly shown in these reports. On the other hand, another report derived recently that mutual inductance between vertically-stacked coupled square loops can be expressed in a relatively simple equation by applying the Biot-Savart law. In this study, a design process based on the equation for an ESL-cancelling circuit using vertically-stacked coupled square loops is proposed. A test circuit for a 10-μF shunt capacitor filter including a 30-mm microstrip line in its shunt path, which is equivalent to ESL of 10.5 nH, is designed and fabricated with an FR4 substrate. The measured results showed 30-dB improvement of insertion loss at several ten MHz. Moreover, the results were comparable to, or even better than, those of the directly-connected shunt capacitor filter.

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.