Track Impedance Research Articles

A Method of Optimizing Characteristic Impedance Compensation Using Cut-Outs in High-Density PCB Designs.

The modern era of technology contains a myriad of high-speed standards and proprietary serial digital protocols, which evolve alongside the microwave and RF realm. The increasing data rate push the requirements for hardware design, including modern printed circuit boards (PCB). One of these requirements for modern high-speed PCB interfaces are a homogenous track impedance all the way from the source to the load. Even though some high-speed interfaces don’t require any external components embedded into the interconnects, there are others which require either passive or active components—or both. Usually, component package land-pads are of fixed size, thus, if not addressed, they create discontinuities and degrade the transmitted signal. To solve this problem, impedance compensation techniques such as reference plane cut-out are employed for multiple case studies covering this topic. This paper presents an original method of finding the optimal cut-out size for the maximum characteristic impedance compensation in high-density multilayer PCB designs, which has been verified via theoretical estimation, computer simulation, and practical measurement results. Track-to-discontinuity ratios of 1:1.75, 1:2.5, and 1:5.0 were selected in order to resemble most practical design scenarios on a 6-layer standard thickness PCB. The measurements and simulations revealed that the compensated impedance saturation occurs at (150–250%) cut-out widths for a 50 Ω microstrip.

Fast approach to calculate the ballastless track impedance

PurposeThe track impedance is one of the most important parameters in designing the track circuit which is widely used in the railway signal control system to detect the presence of a train. This paper aims to calculate the ballastless track impedance by taking account of the influence of reinforcement bars.Design/methodology/approachThis paper proposes a two-step decomposition approach to calculate the ballastless track impedance. The basic idea is evaluating the track impedance without the reinforcement bars by using two-dimensional (2D) finite element method (FEM), and the incremental impedance, because of the reinforcement bar, is calculated by the partial element equivalent circuit (PEEC) method.FindingsThe numerical examples show that the proposed approach can guarantee the accuracy and largely reduce the computing time, at least 20 times, compared with the direct three-dimensional (3D) FEM method.Research limitations/implicationsThe study provides a fast approach to calculate the ballastless track impedance. However, compared with the 3D FEM method, the results are less accurate because of the approximation and assumption adopted in the method. A future study should pay more attention to improve accuracy of the model.Originality/valueA fast approach is proposed to calculate the ballastless track impedance taking account of the influence of the reinforcement bars. The computing time can be largely reduced by using the method. With the proposed approach, the influence of insulation of the reinforcement bars on track impedance can be analyzed.

Investigation of a track circuit operation under conditions of saturation of the track’s impedance bonds

The article’s purpose is studying the operation of the code track circuit in the conditions of track’s impedance bonds saturation. Results. The dependences of the track receiver voltage on the asymmetry current magnitude for the insulation resistances in the winter and summer period are obtained, provided the track’s impedance bonds saturation. It is established that, due to an increase in the asymmetry current, there can be a decrease in the voltage across the track receivers below the threshold, which is a failure of the track circuit, the elimination of which requires the use of a whole range of measures. Scientific novelty consists in applying an indirect calculation method based on obtaining the coefficients of the impedance bond’s equivalent circuit for various values of the resistance modules of the magnetization circuit, which change during the magnetization of the impedance bonds magnetic core by DC. The obtained method makes it possible to perform calculations of the code track circuit normal operating mode under the conditions of the impedance bonds’ saturating. Practical significance. The proposed indirect method can be used to adjust the calculation of the track circuits operating modes, with considering the saturation of track impedance bonds.

Influence of metallization impedance on the current distribution along the conducting tracks from a FET operated in saturation

Analytical expressions are derived for the distribution of drain current per unit channel width along the source track of JEETs or MOSFETs operated in saturation. Its departure from uniformity related to the voltage drop across the track impedance is shown to be governed by the product of the FET transconductance and the track impedance. It is also found that the coordinate of the mean current flow path is independent of net current.

Calculation of PCB track impedance

The value of the controlled impedance of various track configurations is usually obtained using algebraic equations. Most of these equations, particularly those for non‐zero track thickness, have been obtained by either theoretical approximations or curve‐fitting the results of numerical solutions of the basic electromagnetic equations. With the advent of modern PCs it is now possible to calculate the impedances directly and quickly, using numerical techniques. This has the advantage of improving the accuracy of the impedance value and increasing the range of validity. Furthermore, a wider range of configurations is now possible. The paper discusses the algebraic equations and numerical solutions in more detail.

Railway track transmission line parameters from finite element field modelling : Series impedance

An electromagnetic field model for identification of rail track equivalent multiconductor transmission line distributed self and mutual series impedances is formulated, and used to illustrate the parametric behaviour of single track impedance with reference to current, frequency, track material properties and ground conductivity. Verification is demonstrated by theoretical analysis and comparison with published experimental data. The skin effect in both rails and earth is a critical phenomenon.

Electromagnetic field modelling for transmission line distributed parameters of railway track

The authors describe modelling to determine frequency-dependent distributed rail track impedance and admittance for solution by the finite element method. The equivalent transmission line track model is excited by the TEM propagation mode. Maxwell's equations are decoupled in separate two-dimensional calculations of the electromagnetic and electrostatic fields around the track. The summed stored and dissipated energies in the fields for common and differential excitation modes enable independent calculation of the self and mutual impedances and admittances.

Electric railway traction. Part 6: Electromagnetic compatibility disturbance - sources and equipment susceptibility

The railway traction environment contains many noise sources and receivers, and is considered to be EMI unfriendly because of the mixing of power, information and communications signals in space, time and frequency. Railway EMC has received much attention for 30 years following the development of converter-fed traction drives and computerised signalling systems. This article covers systems issues including the fundamentals of electromagnetic coupling, disturbance noise sources and receiver susceptibility. The article discusses EM noise sources in traction systems including: rectifier and transformer substations; track and traction line; vehicles and drives; radiative emissions (RFI); and signalling equipment. The article then discusses track and equipment susceptibility to EMI including: track and traction line impedance; traction drive impedance; track signalling system impedance; and track circuit receivers.

In situ determination of rail track electrical impedance and admittance matrix elements

A novel differential excitation technique is described for the experimental determination of the elements of rail track impedance and admittance matrices from measurements of rail voltages, and currents on a short, isolated track section. The establishment of a common earth point along the track is unnecessary, although rail breaks and driven earth rods at the feed and remote ends of the test section are required. Rail self and mutual impedance and admittance measurements are reported for a single railway track, for a frequency of 50 Hz. >

Evaluation Of Rail Track Impedance And Capacitance Using The Electromagnetic Transients Program

Time-domain electric circuit simulation packages designed for power systems ffiXS r° *2 ** *? ™*'y ***<* ^works provided the track and traction line impedance and admittance are known from basic track geometry and material properties. This paper illustrates the use of the EMTP whh^n ^ ?™** ™^ ^ obtain the track impedance and capacitance with special reference to running rail circuits. By comparison with practical measurements it ,s shown that with care, the method is suitable for track impedance, but less precise for running rail circuit capacitance.

Use Of Frequency-dependent Track Models In Traction System Simulation

This paper describes research to derive simulation models of railway traction systems with frequency-dependent track impedance characteristics. The work has been applied for both frequency and time domain modelling. Simulation results are given of traction system input impedance, short circuit current transients and harmonic interference currents in DC railway traction systems It is shown that for accuracy, wideband simulation in the time domain requires an accurate, frequency-dependent track model which is best provided using a discrete-component equivalent circuit.