In this paper, a compact filter based on substrate integrated coaxial line (SICL) stubs was designed using an advanced multilayer printed circuit board (PCB) substrate. This technology is convenient to implement high-density interconnect (HDI) devices, which are dedicated to mass market and require to be compact and low cost. In addition, in order to avoid parasitic effects, HDI devices need to be shielded. The laser-drilled microvias used in the low-loss advanced multilayer PCB are the assets that allow the fabrication of compacted and shielded microwave filters. Using this technology, a third-order ${X}$ -band filter based on SICL stubs was designed. The SICL topology is convenient to be used for shielded devices thanks to the outer-grounded metallization. The filter was implemented in an advanced PCB substrate composed of seven layers of Megtron 6+. The via-holes fabricated with plated through-holes or laser-drilled microvias allow implementing SICL stubs throughout the thickness of the substrate. Measurements of the ${X}$ -band filter are in a good agreement with the simulation. In comparison with other compact filters, the ${X}$ -band filter based on SICL stubs has a good footprint reduction while maintaining good electrical performances.

Compact $X$ -Band Filter Based on Substrate Integrated Coaxial Line Stubs Using Advanced Multilayer PCB Technology

This paper investigates how the longest differential via stubs in a thick multilayered printed circuit board (PCB) affect the time-domain transmission (TDT) waveform and eye diagram. A reduction scheme is also proposed to mitigate the influence of the longest differential via stubs. The manner in which the time-domain reflection noise that is generated by the longest differential via stubs affects the TDT waveform is then investigated using a lattice diagram. Formulas for step voltages on the TDT waveform are derived by analyzing the lattice diagram. Next, the effects of parameters related to the longest differential via stubs on the TDT waveform are analyzed. A high-impedance difference scheme with/without additional air-via holes is proposed to mitigate the influence of the longest differential via stubs. This mitigation scheme significantly reduces the influence of the longest differential via stubs in a thick multilayered PCB not only in the time domain (TDT waveform and eye diagram) but also in the frequency domain (differential insertion loss |S
 dd21
|). Finally, favorable comparisons between the simulations and measurements in the time and frequency domains validate the proposed analyses and mitigation scheme.

Influence and Mitigation of Longest Differential via Stubs on Transmission Waveform and Eye Diagram in a Thick Multilayered PCB

This paper presents a novel concept for microwave filter design using vias (plated through-holes) in multilayered printed circuit boards. By using the concept that vias accompanied by a sufficient number of ground vias in close proximity can be approximated as transmission lines in a certain frequency range, corresponding effective impedances and phase velocities for different configurations of vias and ground vias are deduced. By controlling these transmission-line parameters, standard microwave filter methodology is applied for the design of low-pass and bandpass Chebychev filters in the frequency range of 5–20 GHz. Measurements and full-wave simulation results are presented as validation. Advantages and limitations of the proposed method are discussed.

Chebyshev Filter Design Using Vias as Quasi-Transmission Lines in Printed Circuit Boards

This paper presents a novel form of microwave filter construction using vias (plated through holes) available in generic printed circuit boards as the main building block. It is demonstrated that for a certain arrangement of vias, the resonant behavior of via stubs can be used to create a low- or a high-pass filter using open- or short-circuited vias, respectively. These stubs are periodically cascaded, resembling an analogous implementation using transmission-line stub filters. It will be shown that such a via filter structure can achieve insertion loss lower than 0.1 dB and return loss of about -60 dB in the passband at GHz frequencies. Measurements, full-wave, and physics-based simulations are presented to verify this novel filter concept and to provide design guidelines in the frequency range from 1 to 20 GHz.

Using Via Stubs in Periodic Structures for Microwave Filter Design

Purpose




This paper aims to analyze the negative impact of surface mount (SMT) pad and imperfect via structure such as stub, pad, non-functional pad (NFP) and anti-pad on the signal integrity at 40 Gbps transmission on printed circuit board (PCB) due to impedance mismatch or discontinuity. The optimized modeling of via and SMT structures is performed to achieve minimal impedance mismatch and insertion loss less than 10 dB for six-inch full path transmission line between transmitter and receiver on PCB at Nyquist frequency 20 GHz.




Design/methodology/approach




This work is split into two phases. The first phase involves optimization of via and SMT structures in three-dimensional electromagnetic (3DEM) simulation using Hyperlynx Via Wizard and Keysight EMPro software, respectively, followed by analysis of time domain reflectometry (TDR) and insertion loss (Sdd21). Whereas, in the second phase, full path hybrid mode simulation involving vias for signal layer transition, a 6-inch PCB channel and SMT pads is performed using Keysight ADS software to observe the TDR, Sdd21 and eye diagram at 40 Gbps transmission.




Findings




Imperfect via and SMT structures have a negative effect on signal reflection and attenuation. The optimized via and SMT minimizes the impedance mismatch by 81 per cent and insertion loss by 4.5 dB, ultimately enlarging the eye diagram opening to achieve minimal data loss at receiver with 40 Gbps transmission.




Originality/value




The results of original empirical research work on signal integrity analysis that optimizes the PCB channel design to achieve 40 Gbps signal transmission are presented in this study. It serves as a reference guide for high-speed PCB layout design.

Techniques of impedance matching for minimal PCB channel loss at 40 GBPS signal transmission

Plated though-hole (PTH) vias are extensively adopted in multilayer printed circuit boards (PCBs). Unused portions of PTH vias become open stubs, which excite the resonance mode and degrade signal integrity (SI). This work investigates how open via stubs in multilayer PCBs affect the time-domain transmission (TDT) waveform and eye diagram. Exactly how time-domain reflection affects the open via stubs on TDT waveform is also studied using the lattice diagram. Additionally, the R and RL terminations of open via stubs are developed to improve SI in previous studies. Moreover, the RC termination of open via stubs is proposed to improve the performance of SI, which is the same as that of the R termination in this work. RC termination is also characterized by its nearly zero DC power consumption. Furthermore, different terminations are compared with respect to how they improve the TDT waveforms and eye diagrams.

http://ieeexplore.ieee.org/iel7/6462538/6469379/06469414.pdf

Li-Sang Liu

Papers

Influence and Mitigation of Longest Differential via Stubs on Transmission Waveform and Eye Diagram in a Thick Multilayered PCB

Influence of via stubs with different terminations on time-domain transmission waveform and eye diagram in multilayer PCBs