Electrical characterization of differential stretchable transmission line

Differential transmission lines (DTL) can be synthesized by identical or different periodic structures (PS). These PS can be used not only for matching one circuit to another; also small resonators can be established serving in filters or oscillators. These new DTL - by using the proposed PS - allow characteristic impedances beyond that of classical TL and in addition at much smaller size. It is the first time that DTL structures form a real alternative for applications in MMIC design below 10 GHz.

Recent work by Intel [1,2] has shown that it is possible to reduce the loss of transmission lines through innovative routing. The “vertical trench” proposed in Intel's work [1,2] showed a 20% reduction in the differential insertion loss. In this work a detailed discussion on the reasons why this novel routing approach can reduce the loss of the differential lines as well as analysis on the design variables of and their effects on the performance of a differential transmission line employing the vertical trench is undertaken. It is also shown through simulation that similar improvements in the differential insertion loss can be obtained through simply increasing the thickness of the of metal for the differential pair.

In this paper, the problem of using guard traces for reducing crosstalk between differential transmission line pairs is investigated, both experimentally and by full-wave electromagnetic (EM) simulations. Different cases of differential lines crosstalk are treated with and without guard trace separation between the differential line pairs. Coated microstrip printed circuit board test structures including thru-reflect-line calibration standards are designed and fabricated on a high frequency laminate material, allowing direct measurement of crosstalk between adjacent differential line pairs in the absence and in the presence of guard traces stitched with vias of regular spacing. The test structures are characterized with mixed-mode scattering parameters using a physical layer test system. Different configurations (of differential line pairs) without guard trace, with floating guard traces (which are terminated and nonterminated) and with a solid guard trace separation are investigated using a High Frequency Structure Simulator (a commercial full-wave 3-D EM simulation tool). The experimental data are compared with the simulation results, and some conclusions and guidelines on the effect of guard traces for alleviating crosstalk between differential transmission lines are presented

A methodology for the harmonic-balance analysis and design of rotary-traveling wave oscillator is presented. Two different implementations are compared. The first one is the standard configuration based on a distributed transmission lines. The second one is a new configuration based on a differential nonlinear transmission line (NLTL), which enables the generation of square waveforms with reduced number of stages, while still maintaining the capability to produce multiphase signals. The possible coexistence of oscillation modes is investigated with a detailed bifurcation analysis versus practical parameters such as the device bias voltage. The phase-noise spectrum is predicted from the variance of the common phase deviation. The parameters that determine this variance are identified with the conversion-matrix approach. The two prototypes, based on a distributed transmission line and a differential NLTL, have been manufactured and characterized experimentally, obtaining very good agreement between simulations and measurements.

A viable wide-band circuit model of parallel corrugated differential transmission line is established. By solving for the even- and odd-modes in this structured differential transmission line, the equivalent capacitance, inductance, resistance, and conductance per unit length are calculated, then the characteristic impedances of differential and common signals are obtained. The S-parameters obtained from the equivalent circuit model agree well with the full-wave simulation results with a deviation of only about 0.036 dB in the frequency range of 10 GHz. Experimentally, the characteristic impedances are measured for the differential and common signals using a time domain reflectometer (TDR). The deviation between the experimental and theoretical results was less than 1.05%. Based on the equivalent circuit model, it is feasible to implement this type of structured differential line directly into real circuits.

Differential transmission lines (DTL) built as periodic structure (PS) can be composed of identical unit cells (UC). The PS can be used either for matching circuits to each other and or for realizing small resonators serving in filters or oscillators. In this paper, we propose new, integrated DTLs with possible characteristic impedances beyond that of classical TLs and - even more importantly - at much smaller size. The reduction factor of approximately 22 can be achieved. This result provides a real alternative for DTL applications in MMIC design below 10GHz

High-speed transmission line characteristics have been analyzed from the point view of many parameter's effects in huge amount of papers. As far as maintaining geometric (dimensional) similarity of transmission line configurations, i.e., shrink or expansion of cross-sectional dimension, characteristics of transmission lines are not affected by their configurations based on electromagnetism from Maxwell's equations. However, direct current resistance (DCR) and skin depth surface/bulk ratio (SBR) of metal conductor in constant transmission length are changed even if geometric similarity is maintained. There have been seen no previous studies performed from this stand point. Therefore, as a fundamental study we examined on characteristics of transmission lines with geometric similarity by focusing on the effect of DCR and SBR. Time domain reflectometry (TDR) profiles, clock pulse rise/fall times (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> /t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> ), and eye-patterns were measured on the transmission line samples with different dimensions (line width and thickness) while maintaining geometric similarity. Experimental results suggest that the surface electron behavior would be related with DCR and SBR on the characteristics of transmission lines despite experimental accuracy is still not enough. These phenomena should more care for recent printed circuit boards over 10 Gbps/pin preferably toward 20 Gbps/pin.

In recent years, with improvement in the speed of digital equipment, differential transmission lines are used abundantly in the circuit substrate. However, by using the differential lines, the number of signal wires doubles as compared with the conventional single-ended. In this paper, the authors investigated the cross-sectional shape of the trace of printed circuit board, which can reduce the cross-talk interference or improve the wiring density. The three patterns of the cross-sectional shape of the trace are examined in this paper. The one is conventional rectangular shape, which the width of the trace is longer than the thickness (low aspect ratio), and the second pattern is a shape of high aspect ratio (the thickness of the trace is longer than the width), and the last trace pattern is a shape of square. The characteristic impedances of the all three trace patterns are designed to be 100 ohm in differential mode. Also, the cross sectional area is arranged to be same among the three trace patterns in order to make the transmission loss conditions are same. As a result, we discovered that the amount of cross talks become minimum, when the cross sectional form of the trace is square. In verification of this idea, the authors simulated for three patterns of cross-sectional shapes of signal traces by the HSPICE of circuit analysis software and the HFSS of three-dimensional electromagnetic-field analysis software.

This paper presents an area-efficient differential distributed amplifier using differential coupled inductors. The artificial transmission lines of the proposed distributed amplifier are modeled as differential transmission lines, and thus, it can be easily designed compared with other area reduction techniques. The dimensions of the coupled inductors have been optimized using a gradient descent algorithm with a scalable model of the coupled inductors. The proposed amplifier was designed using 1P5M 180 nm standard CMOS technology. Post-layout simulation results demonstrated a gain of 6.9 dB and a bandwidth of 20.2 GHz with 4.9 ps Nyquist group delay variation. A core area of the proposed amplifier was 0.28 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which was the smallest value compared with previous works using similar processes.

In a differential transmission line, a large common-mode radiation is excited due to its asymmetry. In this paper, the imbalance difference model, which was proposed by the authors for estimation of common-mode radiation, is extended to apply to the differential signaling systems. The authors focus on a differential transmission line with asymmetric property, which consists of an adjacent return plane and two signal lines which are placed close to an edge of the return plane. Three orthogonal transmission modes, a normal mode, a primary common mode and a secondary common mode, are defined. Among these transmission modes, the secondary common mode is dominant in radiation, and a mechanism of the secondary common-mode generation is explained. The radiated emission which was calculated using the imbalance difference model was in good agreement with that obtained by full wave calculation.

In this paper, a new fault detection scheme based on a cumulative sum of differential positive sequence impedance component is presented for the application of relaying in the power system. The performance of the proposed method is tested for various fault conditions that usually occur in a power system by carrying simulations in MATLAB/Simulink. Along with faults at normal operating condition, several faults at extreme operating condition are also investigated to test the superiority of the method. From the simulation studies, it is observed that the proposed method produced acceptable performance in detecting all types of faults at different fault conditions.

In the field of digital electronics, devices operating in differential mode, such as LVDS, USB, and HDMI interfaces, are widely used. However, conductive interference, including electromagnetic and electrical disturbances, can degrade data transmission quality and cause device malfunctions. This study presents an analysis of the impact of an electromagnetic absorber (EA) on the time and frequency characteristics of a differential transmission line. The investigated structure is a two-conductor microstrip transmission line. The use of the EA helps reduce the propagation of electromagnetic interference (EMI) but also decreases the device's bandwidth. Specifically, the suppression of ultra-wideband interference increased from 3.52 times to 23.8 times with the EA, while the bandwidth decreased from 3 GHz to 0.5 GHz.

Via design is an important factor for signal integrity. Usually there are lots of ground vias on the PCB board at high frequencies. Transmission lines need to turn or change layer, which invariably leads to impedance discontinuity and also result in the disconnection of the signal return path. To reduce the area surrounded by the signal return path and to diminish electromagnetic radiation, ground vias are added to provide the shortest return path signal. To research the influence on the transmission parameters brought by ground vias, considerable simulation work was performed and via optimization based on the simulation results was undertaken. By adjusting the gap between ground via and edge of transmission lines and the density of the vias, parameters for high speed signals transmission lines were optimized. The relations between transmission parameters and ground via placement are plot in this paper. Moreover, for incoherent signal transmission differential pair, the gap between differential lines is not identical throughout the trace, which leads to the weak signal transmission quality at high frequency due to the non-identical coupled capacitance between the lines. Placing several ground vias at the turning and side of differential transmission lines, signal integrity is enhanced in simulation results.

Modern trends in electronics development require the design of compact and high-performance devices operating under high levels of electromagnetic interference (EMI). A promising solution for ensuring the electromagnetic compatibility (EMC) of differential transmission lines (DTLs) is the use of electromagnetic absorbers (EAs). However, the influence of the absorber thickness on the time-domain and frequency-domain characteristics of integrated DTLs remains insufficiently studied. This study employs modeling methods implemented in the software tools TUSUR.EMC and COMSOL Multiphysics. A DTL on a GaAs substrate is considered, with the EA thickness varied from 0 to 20 µm. The investigation includes an analysis of transmission and reflection coefficients, signal integrity, and propagation delays. The research aims to determine the optimal EA thickness that provides maximum interference suppression while minimizing its impact on the useful signal. The results show that an EA with a thickness of 8 µm reduces interference amplitude by a factor of 1.4, increases signal arrival time by a factor of 1.15, and decreases the level of reflected signals in the stopband to minus 13.16 dB. However, the passband width decreases from 2.41 GHz (at H = 0) to 1.03 GHz (at H = 20 µm). Thus, the use of an EA with an optimal thickness significantly improves the EMC of integrated DTLs. The obtained results can be utilized in the design of high-frequency devices with enhanced immunity to interference.

The design and development of novel microelectromechanical systems’ (MEMS) coplanar waveguide (CPW) transmission lines, using microshield and groove, are presented in the paper to operate between 5–60 GHz. The quasi-static capacitances of CPW are calculated using the conformal mapping technique to express the propagation properties, i.e., the characteristic impedance and effective permittivity. Simulation results have shown a considerable loss reduction to levels that compare favorably with the conventional CPW. These transmission lines can be widely used in the development of phase shifters, filters, and antennas, because of their advantages in loss reduction and improvement in the performance.