Dazhao Liu

A measurement technique for ESD current spreading on a PCB using near field scanning

Electrostatic discharge (ESD) can cause interference or damage in circuits in many ways e.g., by E- or H-field coupling or via conduction paths. Although we can roughly estimate the voltage and current at the injection point during an ESD event, the real offending parameter is mostly the ESD current spreading throughout the system. Those currents can be simulated if great simplifications of the system are accepted. However, even in moderately complex systems the ability to simulate is limited by lack of models and computational resources. Independent of the complexity, but obviously not free of its own limitations is a measurement technique that captures the current as a function of time and location through the system. This article describes the proof on concept of ESD such a measurement technique that allows reconstructing the spreading current as a movie from magnetic field measurements. It details the technique, question of probe selection and how to process the data to present the current spread as a movie.

Full wave model for simulating a Noiseken ESD generator

A CST Microwave Studio model was generated to simulate the discharge current and the transient field of an ESD generator. The ESD generator is conforming to the IEC 61000-4-2 standard. Individual components of the Noiseken ESD generator (ESS-2000) were modelled, validated and combined. The complete full wave model was verified by comparing the simulated discharge current waveform and induced loop voltage with the measured results.

Fast admittance computation for TSV arrays

A fast method to calculate the admittance matrix of Through Silicon Vias (TSVs) is proposed in this paper. The silicon dioxide layers are equivalently modelled using the bound charge on the conductor surfaces as well as on the dielectric interface between the silicon dioxide and the silicon regions. Unknown surface densities of both the free and bound charge are expanded using the axial harmonics. Galerkins method is then applied to obtain the capacitance and conductance matrices. The proposed method is validated with a full-wave 2D cross-sectional analysis tool for a typical TSV pair structure. Comparisons with popular closed-form expressions are also discussed.

Probe characterization and data process for current reconstruction by near field scanning method

previously a measurement technique for ESD current spreading on a PCB using near field scanning was developed in order to connect the local ESD sensitivity to system level ESD failures in time and spatial domain. The concept of such scanning methodology is proved and several scanning results were processed. However the validation, precision and weakness of such methodology need to be further investigated before the application of such scanning methodology on complex circuit or system. This article investigates the current reconstruction by near field scanning technique and methodology. It studies the probe factors including coupling frequency response characterization and deconvolution method, spatial resolution for scanning and orthogonal-scan data combine process.

Near field probe for detecting resonances in EMC application

Resonances degrade the products EMI or immunity performance at resonance frequencies. Near field scanning techniques, like EMI scanning or susceptibility scanning determine the local behaviour, but fail to connect the local behaviour to the system level behaviour. Resonating structures form part of the coupling paths, i.e., identifying them will aid in understanding system level behaviour of products. In this article, a near field probe (patent pending) is proposed to detecting the resonances frequencies, locations or resonating structures and their Q-factors. The probe is suitable for integration into an automatic scanning system for analysing resonances of PCBs, cables, structural elements etc. The mechanism of the probe has been verified with full wave tools (CST MWS and Ansoft HFSS). Two samples of application are presented.

Modeling of Multiple Vias with a Shared Anti-Pad in an Irregular Plate Pair Using Domain Decomposition Approach

An irregular plate pair with multiple vias sharing an anti-pad is decomposed into top/bottom plate-thickness domain and parallel-plate domain whose admittance matrices are calculated by three-dimensional (3D) finite element method (FEM) and hybrid 3D/2D FEM. Combined admittance matrix algorithm is used to obtain the final admittance matrix of the plate pair including finite thickness plates. The widely-used assumption of transverse electromagnetic (TEM) modes on anti-pads is carefully investigated by comparing the combined admittance matrix algorithm with hybrid 3D/2D FEM. It is found that higher-order modes are excited on anti-pads and in practical printed circuit board, the higher-order modes can penetrate from one layer of plate pair to another layer. This may provide guidance for future research for multiple vias in a shared anti-pad.

Accurate Evaluation of Field Interactions Between Cable Harness and Vehicle Body by a Multiple Scattering Method

Interactions between cable harness and vehicle body can be calculated using the full-wave method-of-moments (MoM) formulation. Although the full-wave MoM formulation can help us to calculate these interactions with great accuracy, it can be fairly time consuming when dealing with complex wire structures. On the other hand, the conventional multiconductor transmission-line theory can be used to obtain a simple model of the interactions, but only the effect of the transmission-line (TL)-mode current can be accounted for in this method. Starting with the complete electrical field integral equations, the current on a two-conductor thin wire structure due to incident field illumination can be decomposed into TL and antenna modes. Both modes can be solved using a SPICE solver in the form of Telegraphers equations. A proposed multiple scattering (MS) method based on a hybrid of TL and surface MoM can then be used to calculate interactions between thin wire structures, such as cable harness, and conductive surfaces, such as vehicle body. A test case shows that wire current computation using the proposed MS method takes less time but reaches the same accuracy compared to the full-wave MoM.

An efficient hybrid boundary-integral and finite-element method for signal integrity analysis of multiple vias sharing an anti-pad in an infinitely-large plate pair

A domain decomposition approach, namely hybrid boundary-integral and finite-element method, is proposed for signal integrity analysis of an infinitely-large plate pair with multi-vias in a shared anti-pad. Each via structure is modeled as a multi-mode network containing top/bottom transverse electromagnetic (TEM) ports associated with vias and parallel-plate ports a little far away from the anti-pad. Coupling among parallel-plate ports of all via structures is considered by a plate-pair impedance matrix. The connection of the multi-mode networks of via structures and the impedance matrix constructs a complete noise coupling path from one via structure to another one, and the S-parameter of the entire plate pair can be steadily obtained by simply manipulating S-parameter matrices. Numerical examples are used to verify the accuracy of the approach by comparing with a full-wave solver.

Parametric study on the effect of asymmetry in multi-channel differential signaling

The effects of geometric asymmetry on the electrical performance of multi-channel differential signaling in printed circuit boards are investigated in this paper. The asymmetry, which is the origin of noise coupled through mode conversion, is difficult to control in real channel structures, where a large number of vias and traces are populated. Supported by an efficient parametric simulation tool, this paper presents the effects of the asymmetry on mode conversion and differential mode crosstalk in real multi-channel structures. This extensive parametric study was used to define design guidelines to suppress this noise coupling by adding ground vias in strategic locations.

Statistical estimation of root mean square crosstalk in SFP+ cable evaluations

A rigorous statistical estimation of the root mean square equation is proposed for near-end crosstalk simulation in SFP+ cable evaluations. This method employs the pulse response, the near-end output in the victim pair due to a single-pulse input of one bit long in the aggressor pair. This pulse response can be obtained from vector network analyzer (VNA) measurements. Thus SFP+ cable evaluations can be effectively performed using easier and more accurate frequency-domain measurements, instead of the time-domain ones defined in the specification.