Howard Heck

Substrate integrated waveguides optimized for ultrahigh-speed digital interconnects

This paper reports an experimental and computational study of substrate integrated waveguides (SIWs) optimized for use as ultrahigh-speed bandpass waveguiding digital interconnects. The novelty of this study resides in our successful design, fabrication, and testing of low-loss SIWs that achieve 100% relative bandwidths via optimal excitation of the dominant TE/sub 10/ mode and avoidance of the excitation of the TE/sub 20/ mode. Furthermore, our optimal structures maintain their 100% relative bandwidth while transmitting around 45/spl deg/ and 90/spl deg/ bends, and achieve measured crosstalk of better than -30 dB over the entire passband. We consider SIWs operating at center frequencies of 50 GHz, accommodating in principle data rates of greater than 50 Gb/s. These SIWs are 35% narrower in the transverse direction and provide a 20% larger relative bandwidth than our previously reported electromagnetic bandgap waveguiding digital interconnects. Since existing circuit-board technology permits dimensional reductions of the SIWs by yet another factor of 4:1 relative to the ones discussed here, bandpass operation at center frequencies approaching 200 GHz with data rates of 200 Gb/s are feasible. These data rates meet or exceed those expected eventually for proposed silicon photonic technologies.

Computational and experimental study of a microwave electromagnetic bandgap structure with waveguiding defect for potential use as a bandpass wireless interconnect

As clock rates continue to rise, problems with signal integrity, cross-coupling, and radiation may render impractical the baseband metallic interconnects presently used in computers. A potential means to address this problem is to use bandpass wireless interconnects operating at millimeter-wave center frequencies. We have conducted experimental and finite-difference time-domain (FDTD) computational studies scaled to a 10 GHz center frequency of single-row and double-row waveguiding defects within an electromagnetic bandgap structure. Our initial experimental results scaled to 10 GHz have verified the feasibility of achieving an approximately 80% bandwidth with excellent stopband, gain flatness, and matching characteristics. When scaled to millimeter-wave center frequencies above 300 GHz, this technology appears feasible of supporting data rates in the hundreds of Gb/s.

Modeling and mitigating AC common mode conversion in multi-Gb/s differential printed circuit boards

Techniques for quantifying and minimizing the impact of differential signal phase skew created by the non-homogeneous nature of FR4 PCBs are presented. Experimental results that allow modeling and simulation at multi-Gb/s signaling rates are developed and used to estimate the impact to voltage and timing margins at 5-10 Gb/s as a function of PCB trace length. A design approach for mitigating the impact is discussed, and results from a manufacturability study are used to assess the effectiveness of the approach.

Impact of FR4 dielectric non-uniformity on the performance of multi-Gb/s differential signals

Phase skew in high speed differential signals caused by local spatial variation in dielectric constant is presented. A simple mathematical model that allows estimation of the impact on multi-Gb/s signaling links is developed, along with HSpice models that correlate to frequency domain measurements. Options for mitigating the impacts are also discussed.

Modeling requirements for transmission lines in multi-gigabit systems

As computer clock speeds continue to increase at a rate dictated by Moores Law, the system buses must also scale in proportion to the processor speed. As data rates approach 8 to 10 Gb/s, the traditional methods used to model transmission lines start to break down and become inadequate for the proper prediction of signal integrity. Specifically, the approximations made in traditional transmission line models, while perfectly adequate for slower speeds, violate conservation of energy principles and produce non-causal waveforms in the time domain responses. This work is discuss the problems associated with accurately predicting transient responses at multi-gigabit data rates and provide a simple and practical solution that accurately predicts transient responses for multi-gigabit channel design.

Full Characterization of Substrate Integrated Waveguides from S-Parameter Measurements

A complete methodology to characterize substrate integrated waveguide (SIW) structures from S-parameter measurements is presented. We determined the complex propagation constant, the characteristic impedance of a homogeneous section of waveguide, and the efficiency of different adapters used to launch the signals into the waveguide. After a detailed analysis, it is observed that the most significant losses in an SIW are associated with the adapters since a low insertion loss is presented in a homogeneous section of waveguide

Advances in hyperspeed digital interconnects using electromagnetic bandgap technology: measured low-loss 43-GHz passband centered at 50 GHz

We have performed a computational and experimental study of a promising new wireless interconnect for high-speed digital circuits employing linear defects in electromagnetic bandgap structures at 50 GHz center frequency. Our recent results confirm the scalability of this technology. We found that employing low-loss dielectrics can maintain the approximately 80% bandwidth with excellent stopband, gain flatness, and matching characteristics previously observed at 10 GHz. When further scaled to millimeter-wave center frequencies above 300 GHz (to leverage emerging silicon transistor technology), EBG wireless interconnects should be able to support data rates in the hundreds of Gbit/s, assuming the availability of suitable low-loss dielectrics.

On the analysis of the PCB integrated waveguides

Traditional planar transmission lines, even built on a low loss dielectric substrate, exhibit prohibitive attenuation at millimeter-wave frequencies [1]. It creates serious roadblocks for using them in digital channels at millimeter-wave frequencies [2]. An alternative is hollow rectangular waveguides integrated to a PC board as guide structures. Millimeterwave integrated waveguides have special features causing their performance to be quite different from traditional centimeter-wave waveguides. Specifically, issues associated with building hollow waveguides in a conventional FR4 PC board introduce non-ideal attributes and manufacturing variations to the structure. As a result, the PCBWs are not just metal pipes anymore. Hence for realistic sensitivity and performance estimates of PCBW based digital channels one needs to define manufacturing non-idealities and variations and include them in the PCBW models to be analyzed by a full-wave method.

A study of a microwave electromagnetic bandgap structure with waveguiding defect for potential use as a bandpass wireless interconnect

We have performed a computational and experimental study of a promising new wireless interconnect technology for high-speed digital circuits employing linear defects in electromagnetic bandgap structures. Our initial experimental results scaled to 10 GHz have verified the feasibility of achieving an approximately 80 % bandwidth with excellent stopband, gain flatness, and matching characteristics. When scaled to millimeter-wave center frequencies above 300 GHz (to leverage emerging silicon transistor technology), the wireless interconnects reported in this letter should be feasible of supporting data rates in the hundreds of gigabits per second, assuming the availability of suitable low-loss dielectrics.