Essential-coupling-path models for non-contact EMI in switching power converters using lumped circuit elements

This paper proposes a simple lumped circuit modeling approach for describing noncontact EMI coupling mechanisms in switching power converters. The resulting model assumes a minimum number of noise sources and contains essential coupling paths that allow easy physical interpretations. Essentially, all capacitive couplings are represented by an equivalent noise voltage source and six coupling impedances, whereas all inductive couplings are represented by an equivalent noise current source and three coupling impedances. The resulting coupled noise appears as currents flowing into the terminals of the line-impedance-stabilization-network (LISN). The equivalent voltage source can be conveniently approximated as the switching-node-to-zero voltage, which is typically a rectangular pulse of a few hundred volts. The equivalent current source can be modeled as the current flowing around a loop containing the equivalent voltage source and parasitics such as winding capacitance of the power transformer, the snubber capacitance and connection inductances. Also, the coupling impedances can be estimated by making simplifying assumptions about the geometry of the components and tracks, or by direct measurements. Simulations and experiments verify how inductive and capacitive couplings through each path may produce substantial EMI measured by the LISN. Being based on a lumped circuit approach, the proposed model is easy to apply in practice for understanding, diagnosing and approximating EMI behaviors.     

Improving the Characteristics of integrated EMI filters by embedded conductive Layers

Discrete electromagnetic interference (EMI) filters have been used for power electronics converters to attenuate switching noise and meet EMI standards for many years. Because of the unavoidable structural parasitic parameters of the discrete filter components, such as equivalent parallel capacitance (EPC) of inductors and equivalent series inductance (ESL) of capacitors, the effective frequency range of the discrete filter is normally limited. Aiming at improving high frequency performance and reducing size and profile, the integrated EMI filter structure has been proposed based on advanced integration and packaging technologies , . Some improvements have been made but further progress is limited by EPCs of the filter inductors, which is restricted by dimension, size and physical structure. In this paper, a new structural winding capacitance cancellation method for inductors is proposed. Other than trying to reduce EPCs, a conductive ground layer is embedded in the planar inductor windings and the structural capacitance between the inductor winding and this embedded layer is utilized to cancel the parasitic winding capacitance. In order to obtain the best cancellation effect, the structural winding capacitance model of the planar spiral winding structure is given and the equivalent circuit is derived. The design methodology of the layout and area of the embedded ground layer is presented. Applying this method, an improved integrated EMI filter is designed and constructed. The experimental results show that the embedded conductive layer can effectively cancel the parasitic winding capacitance, hence ideal inductor characteristics can be obtained. With the help of this embedded conductive layer, the improved EMI filter has much smaller volume and profile and much better characteristics over a wide frequency range, compared to the former integrated EMI filter and the discrete EMI filter.     

开关电源EMI滤波器设计

分析了一种典型的开关电源电路,利用Pspice软件对其传导电磁干扰进行仿真研究,以TDK公司提供的元器件模型,提出了一种二阶无源EMI滤波器,完全消除了电路输出信号中的尖峰干扰,抑制了开关电源电路中的共模、差模噪声。同时,研究源和负载理想、非理想阻抗特性对滤波器插入损耗的影响,具有一定的意义。     

Filters with inductance cancellation using printed circuit board transformers

Capacitor parasitic inductance often limits the high-frequency performance of filters for power applications. However, these limitations can be overcome through the use of specially-coupled magnetic windings that effectively ify the capacitor parasitic inductance. This paper explores the use of printed circuit board (PCB) transformers to realize parasitic inductance cancellation of filter capacitors. Design of such inductance cancellation transformers is explored, and applicable design rules are established and experimentally validated. The high performance of the proposed inductance cancellation technology is demonstrated in an electromagnetic interference (EMI) filter design.     

Current-mode electronically tunable biquadratic filters consisting of only CCCIIs and grounded capacitors

In this paper, a current-mode (CM) analog filter for simultaneously realizing high output impedance low-pass, band-pass and high-pass analog responses besides high output impedance notch and all-pass analog filter responses with interconnection of the relevant output currents, is presented. Also, two CM filters for simultaneously providing high output impedance universal filter responses are derived from the proposed one. All of the introduced CM topologies employ a canonical number of only grounded capacitors without requiring any resistors, and do not need critical component matching conditions. All of the developed circuits have low input impedance and high output impedance resulting in easy cascadability with other CM ones. Frequency dependent non-ideal gain and parasitic impedance effects on the performance of the presented first filter are investigated as examples. In order the show the performance of the filter and verify the theory, simulations are accomplished with SPICE program.     

A Wideband Predictive “Double-$pi$ ” Equivalent-Circuit Model for On-Chip Spiral Inductors

A new wideband predictive “double-$pi$” equivalent-circuit model for on-chip spiral inductors is presented, in which the model parameters are analytically calculated with layout and process parameters. In the model, five major parasitic effects, including skin effect, proximity effect, distributed effect, substrate capacitive loss, and inductive loss, are implemented together. Considering skin effect and proximity effect simultaneously, a new equation of high-frequency resistance is proposed, and accordingly, two coupled transformer loops are developed, respectively, to calculate the network parameters of skin effect, proximity effect, and substrate inductive coupling effect independently. In order to analytically calculate substrate capacitive loss in multiturn inductors, a quasi-linear relationship between capacitive coupling effect and proximity effect is established. A series of inductors with different geometries are fabricated in two standard RFCMOS processes to verify the model. Excellent agreements have been obtained between the measured data and the proposed model within a wide frequency range. Since a clear relationship between circuit components and fabrication parameters is defined, it can precisely predict the performance of the inductors and become more flexible in RFIC design.      

Noise Source Lumped Circuit Modeling and Identification for Power Converters

In this paper, a general lumped circuit modeling method is proposed to describe the conducted electromagnetic interference (EMI) coupling mechanism for the switching power converters. The EMI characteristics of the converters can be analytically deduced from a circuit theoretical viewpoint. The shunt and series impedance insertion method is introduced to identify the differential-mode (DM) and common-mode (CM) noise impedances and voltage sources. The procedure of parameters estimation for the noise models comprises several simple measurements and is convenient to be implemented. Experimental illustrations are also included to verify the validity of the proposed method. Comparison between the measured and predicted results shows that the EMI modeling method can provide adequate prediction of the EMI feature for power-switching converters     

加固显示器抗干扰滤波器设计

着重介绍加固显示器抗干扰滤波器设计的方法与技巧。介绍了共模电流对显示器干扰的影响,提出了消除干扰源的措施,给出了滤波器电路与阻抗的关系以及抗干扰滤波器在工程设计中的注意事项,并结合实践中的实例进行设计与应用。     

Coupled-Magnetic Filters With Adaptive Inductance Cancellation

Conventional filter circuits suffer from a number of limitations, including performance degradation due to capacitor parasitic inductance and the size and cost of magnetic elements. Coupled-magnetic filters have been developed that provide increased filter order with a single magnetic component, but also suffer from parasitic inductance in the filter shunt path due to imperfectly-controlled coupling of the magnetics. In this paper, we introduce a new approach to coupled-magnetic filters that overcomes these limitations. Filter sensitivity to variations in coupling is overcome by adaptively tuning the magnetic circuit for minimum rms ripple performance with feedback based on the sensed filter output ripple. This active control enables much greater robustness to manufacturing and environmental variations than is possible in the conventional "zero-ripple" coupled-magnetic approach, while preserving its advantages. Moreover, the proposed technique also adaptively cancels the deleterious effects of capacitor parasitic inductance, thereby providing much higher filter performance than is achievable in conventional designs. The new technique is experimentally demonstrated in a dc-dc power converter application and is shown to provide high performance     

Passive cancellation of common-mode noise in power electronic circuits

It is well known that common-mode (CM) conducted electromagnetic interference (EMI) is caused by the common-mode current flowing through the parasitic capacitance of transistors, diodes, and transformers to ground in the power circuit. Because of the potential for interference with other systems it is necessary to attenuate this noise. Ordinarily this is accomplished by using a magnetic choke across the input power lines, resulting in penalties to the overall size and cost of the completed system. In order to lessen the requirement for this magnetic choke, there has been a desire to introduce noise cancellation techniques to the area of EMI. This text introduces a method of canceling the common-mode EMI by using a compensating transformer winding and a capacitor. Compared with other cancellation techniques, it is much simpler and requires no additional transistors and gate-drive circuitry since it merely adds a small copper winding and a small capacitor. By using this technique the size of the EMI filter can be reduced, especially for applications requiring high currents. In this paper, the new method for passive noise cancellation is applied to many popular converter and inverter topologies. The method, results, and ramifications of this technique are presented in order of appearance.     

D类功放输出滤波器的优化与仿真

分析了D类功放大器输出滤波器设计的必要性,并且利用巴特沃思低通滤波器的设计方法对电路参数进行优化设计;采用Filter Free软件仿真滤波器的频域特性。最终达到消除PWM信号中的开关信号和电磁干扰信号,提高效率和保真度,减小输出滤波器的体积和成本。     

Varactor-tuned combline bandpass filter using step-impedance microstrip lines

In this paper, a varactor-tuned combline bandpass filter using step-impedance microstrip lines is considered so that the absolute passband bandwidth can be maintained nearly constant within the tuning range. The difference between the odd- and even-mode characteristics of the coupled microstrip line makes it difficult to design a tunable bandpass filter with minimum degradation in passband performance. By using step-impedance microstrip lines, couplings between resonators can be controlled so that the constant bandwidth requirement could be satisfied with reasonable design parameter values. Lumped inductors are used for input and output coupling networks. Design equations are derived, and experimental results are compared with theoretical ones based on these equations.     

基于负载的有源EMI滤波器插损分析

相同的有源EMI滤波器在不同的源阻抗和负载阻抗条件下,滤波特性有很大差异。文中以电流检测电流补偿型有源EMI滤波器为例,分析了在负载分别为纯阻性、感性和容性条件下的滤波特性,并给出了有源EMI滤波器的适应条件。     

Crosstalk bandwidth and stability analysis in graphene nanoribbon interconnects

Based on transmission line modeling (TLM), and using the Nichols chart, we present a bandwidth and stability analysis, together with step time responses, for coupled multilayer graphene nanoribbon (MLGNR) interconnects that is inquired for the first time. In this analysis, the dependence of the degree of crosstalk relative stability for coupled MLGNR interconnects comprising of both capacitive and mutual-inductive couplings between adjacent MLGNR has been acquired. The obtained results show that with increasing the length or decreasing the width of the MLGNRs, the stability in near-end output increases. While, any increase in the length or width of MLGNRs, decrease the stability of far-end output. Also, by increasing capacitive coupling or decreasing inductive coupling, the near-end output becomes more stable, and the far-end output becomes less stable. Moreover, any increase in the length or capacitive coupling, decreases the bandwidth, whereas any increase in the width or inductive coupling, increases the bandwidth. Finally, transient simulations with Advanced Design System (ADS) show that the model has an excellent accuracy.     

高阻带抑制LTCC 滤波器的设计与实现*

提出了一种基于LTCC技术的新型高阻带抑制带通滤波器的实现方法.采用在并联谐振器的圆柱形电感之间引入感性耦合,在高阻带产生一个传输零点,并且能实现非常好的阻带衰减性能.本文对传统的梳状线带通滤波器结构进行改进,利用过孔的寄生电感效应,将过孔用作谐振杆,明显减小了器件的尺寸.并且通过利用空间耦合的寄生效应,实现滤波器的阻带高抑制传输零点,以满足了对特殊频点高抑制的要求.运用该方法设计了中心频率1.65 GHz,通带200MHz,带外2GHz处衰减大于60dBc的五级带通滤波器.实物测试结果和全波电磁仿真结果吻合较好.     

An EMI Resisting LIN Driver in 0.35-micron High-Voltage CMOS

This paper describes the design of a local interconnect network (LIN) integrated output driver circuit exhibiting a high degree of immunity against conducted electromagnetic interference (EMI). The transmitted signal of this driver is shaped with a predefined slope so as to reduce electromagnetic emission at higher frequencies. The effect of EMI coupling from the data bus into the driver circuit is countered using a new feedback scheme which shields the slope shaping function from the output stage. Although the output signal may be heavily corrupted by EMI, the LIN driver continues to deliver an unaltered duty cycle, which is mandatory to obtain an error-free data transmission. Measurements show that this driver circuit manages to withstand the highest levels of the direct power injection (DPI) measurements independently of the injected EMI level.     

FDTD modeling incorporating a two-port network for I/O line EMIfiltering design

Electromagnetic interference (EMI) filters are often utilized on I/O lines to reduce high-frequency noise from being conducted off the printed circuit board (PCB) and causing EMI problems. The filtering performance is often compromised at high frequencies due to parasitics associated with the filter itself, or the PCB layout and interconnects. Finite difference time domain (FDTD) modeling can be used to quantify the effect of PCB layout and interconnects, as well as filter type, on the EMI performance of I/O line filtering. FDTD modeling of a T-type and π-type filter consisting of surface-mount ferrites and capacitors is considered herein. The FDTD method is applied to model PCB layout and interconnect features, as well as the lumped element components, including the nonlinear characteristics of ferrite surface-mount parts. The EMI filters with ferrites; are included in the modeling by incorporating the time-domain Y-parameters of the two-port network into the FDTD time-marching equations. Good agreement between the FDTD modeling and S-parameter measurements supports the new FDTD algorithm for incorporating two-port networks     

Common-mode current due to a trace near a PCB edge and its suppression by a guard band

The common-mode (CM) current due to a trace near a printed circuit board (PCB) edge, and its suppression by a guard band have been studied experimentally and with finite-difference time-domain (FDTD) modeling. As the guard band, copper tape is connected along the entire edge of the ground plane. First, a PCB electromagnetic interference (EMI) coupling path that results from the nonzero impedance of the PCB ground plane is discussed. As the trace is moved closer to the PCB edge, the CM current increases. Then, the effect of the guard band on the CM current is detailed. A guard band parallel to and near a trace is most effective in suppressing the CM current. The cross-sectional magnetic field distribution at center of the PCB with and without the guard band is also calculated with FDTD modeling. The guard band decreases the magnetic field distributed on the reverse side of a PCB. These results indicate the guard band is effective in suppressing CM current. Finally, an empirical formula to quantify the relationship between the position of a trace and CM current for the case with a guard band is proposed. Calculated results using the empirical formula and FDTD modeling are in good agreement, which indicates this empirical formula should be useful for developing EMI design guidelines.     

一种具有两个传输零点的新型带通滤波器

在分析带通滤波器等效电路类型与特点的基础上,提出了一种简单的且具有两个传输零点的新型带通滤波器结构,有效解决了低介电常数多芯片组件(MCM)集成带通滤波器的性能与面积的问题.通过实际设计加工测试了一款中心频率为1.61GHz、带宽为260MHz的带通滤波器,插入损耗为0.71dB,驻波1.2,测试结果与仿真结果一致,器件整体尺寸为3.2mm×2.4mm×0.6mm.     

A new compact microstrip two-layer bandpass filter using aperture-coupled SIR-hairpin resonators with transmission zeros

A new design of a compact two-layer bandpass filter using aperture-coupled microstrip stepped-impedance hairpin resonators is proposed and investigated in this paper. The proposed filter is composed of four stepped-impedance hairpin resonators located on two stacked microstrip layers, and the couplings between the resonators on the upper layer and those on the lower one are obtained by using three coupling apertures etched on a common ground plane placed between the two layers. In addition, the use of tapped input/output couplings allow this bandpass filter to generate two independent transmission zeros. A full-wave simulator is used to design the proposed structure and calculate the aperture coupling coefficients. With this two-layer configuration, the proposed filter becomes very compact and occupies a small space. To demonstrate the proposed design, a four-order bandpass-filter prototype was designed, fabricated, and tested at 2.14 GHz. Furthermore, a single-layer filter prototype was also designed and fabricated at the same frequency band and then compared to the first one. As a result, a significant reduction of approximately 50% was achieved. These features make the proposed structure suitable for compact and high-performance circuit component designs in microwave circuits.