Optimization and Design of Passive Link with Single Channel 25 Gbps Based on High-Speed Backplane

In recent years, with the development of the communication industry, the need to use Ethernet switches to transmit big data has become more urgent, and its protocol standards are iterating towards higher return loss, wider bandwidth, lower impedance fluctuations and insertion loss. Based on the research of high-speed backplane with a single channel 25 Gbps transmission rate, a novel double grounded planar strip coplanar waveguide design is presented, which significantly improved return loss to 20 dB and reduced insertion loss, which meet the loss standard of 100GBASE-KR4. The resonant cavity model of transmission line reference plane is improved by introducing vias and the parameters of vias in the reference plane are studied to reduce the impact of resonance, which improved the transmission –1 dB bandwidth to 60 GHz. Based on equivalent circuit analysis of differential vias’ joint reverse pad, the parameters related to the differential vias are studied, the impedance fluctuation is reduced to 100 ± 3 Ω, which is 70% better than the impedance fluctuation standard (100 ± 10 Ω) of 100GBASE-KR4. After optimizing the mathematical model of strip coplanar waveguide, reference plane and differential vias, we built a simulation model of the backplane passive link which met the 100GBASE-KR4 backplane Ethernet specification. In the actual test, it was found that the optimized model can improve the link performance.

Effect of Fiber Weave Structure in Printed Circuit Boards on Signal Transmission Characteristics

In this paper, we characterized and compared signal transmission performances of traces with different specifications of fiber weave. Measurements demonstrated that the dielectric constant, impedance fluctuation, and differential skew were all affected by fiber weave style. For flattened fiber weaves, the dielectric constant fluctuation reached 0.18, the impedance fluctuation amplitude was 1.0 Ω, and the differential skew was 2 ps/inch. For conventional fiber weaves, the three parameters were 0.44, 2.5 Ω, and 4 ps/inch respectively. Flattened fiber weave was more favorable for high-speed signal control. We also discussed the other methods to improve the fiber weave effect. It turned out that NE-glass (new electronic glass) fiber weave also had better performance in reducing impedance fluctuation and differential skew. Furthermore, made the signal traces and fiber weave bundles with an angle or designing the long signal line parallel to the weft direction both are simple and effective methods to solve this problem.

Numerical studies of the coda falloff rate of multiply scattered waves in randomly layered media

We study the falloff rate of the coda of acoustic signals after transmission (net forward-scattering) through a stack of thin layers (compared to the wavelength of the signal) with randomly fluctuating impedances. We find that the change in coda energy with time after the first arrival can be modeled as a decaying exponential with falloff rate c ∝ ω − 1 x − 3 / 2 σ − 1 where ω is the center frequency of a frequency band of the coda, x is the source-receiver distance, and σ is the standard deviation of the impedance fluctuation in a band centered about 2 ω. The dependence of the falloff rate of net forward-scattered coda on ω and σ is opposite to that of single back-scattered coda, and distinguishes the two types of scattering.