High-speed Digital Interconnects Research Articles

Spectrally Accurate Causality Enforcement Using SVD-Based Fourier Continuations for High-Speed Digital Interconnects

We introduce an accurate and robust technique for accessing the causality of network transfer functions given in the form of band-limited discrete frequency responses. These transfer functions are commonly used to represent the electrical response of high-speed digital interconnects used on chip and in electronic package assemblies. In some cases, small errors in the model development lead to noncausal behavior that does not accurately represent the electrical response and may lead to a lack of convergence in simulations that utilize these models. The approach is based on Hilbert transform relations or Kramers–Kronig dispersion relations and a construction of causal Fourier continuations using a regularized singular value decomposition method. Given a transfer function, nonperiodic in general, this procedure constructs highly accurate Fourier series approximations on the given frequency interval by allowing the function to be periodic in an extended domain. The causality dispersion relations are enforced spectrally and exactly. This eliminates the necessity of approximating the transfer function behavior at infinity and explicit computation of the Hilbert transform. We perform the error analysis of the method and take into account a possible presence of a noise or approximation errors in data. The developed error estimates can be used in verifying the causality of the given data. The performance of the method is tested on several analytic and simulated examples that demonstrate an excellent accuracy and reliability of the proposed technique in agreement with the obtained error estimates. The method is capable of detecting very small localized causality violations with amplitudes close to the machine precision.

Frequency and Time-Domain Performance of LTCC Transmission Lines Fabricated Using Multiple Printing Techniques

The many advantages of low temperature co-fired ceramic (LTCC) materials are increasing their use in multi-layer systems containing multiple high-frequency / high-speed digital interconnects. Although construction of such interconnects is possible with current fabrication techniques, the loss exhibited by transmission lines at high frequencies limits their application by increasing system power consumption or requiring complex transceivers. Use of non-standard metal printing processes provides one possibility for realizing lower insertion loss desired for these interconnects. We have fabricated and evaluated representative single-ended and differential stripline transmission line structures using single, double, and mirror printing techniques for Ag metalization in DuPont 9K7 LTCC, to explore their suitability for high-frequency/high-speed applications. Discussion of analysis performed on cross-sections of these structures to determine post-firing geometry, as well as the level of fabrication control afforded over these parameters will be presented. To predict their performance for high-speed interconnects, 3D electromagnetic (3DEM) simulation models for characterizing the frequency performance of single-ended and differential structures have been also been developed. These 3DEM models have also been used in time domain simulations to verify digital signal capability by demonstrating structure performance at data rates exceeding 25 Gbps. Measurements of fabricated structures corresponding to the 3DEM models have also been performed in both the time and frequency domain and will be compared to the simulation results to confirm 3DEM model accuracy. The culmination of results from simulation and measurement will be used to present the differences, advantages, and disadvantages of each fabrication technique.

Wideband power line isolation using open stub structures

A wideband isolation topology of a power line is proposed, using open stub structures for high-speed digital interconnects. To reduce the coupled noise to the power line in the absence of a common-mode choke (CMC), which could degenerate signal integrity due to its loss and unbalanced properties, ferrite bead and open stub structures are utilised as they are suitable to the small size of commercial systems. In terms of the enhanced isolation characteristics, the induced power noise is reduced from 83 to 12 mV (86% reduction ratio) under a mobile high-definition link data transfer without data losses. Therefore, the proposed open stub structures are a very effective tool for both power integrity and signal integrity, and most importantly the cost is minimal when the CMC is removed from the high-speed digital interconnect.

A Novel Model Extraction Algorithm for Reconstruction of Coupled Transmission Lines in High-speed Digital System

This paper discusses the parameters extraction and electrical characterization in high speed digital interconnection system using layer peeling algorithm and genetic algorithm. Base on the time domain reflection (TDR) measurement, the impedance profile of the device under test (D.U.T) is first derived by layer peeling transmission line synthesis. Then, the genetic algorithm (G.A.) is employed to extract the parameter of the lumped/distributed circuits in high-speed digital circuit. This algorithm is suitable for reconstructing the physically structures of a nonuniform couple transmission lines. The system characteristic can be obtained easily by the extracted model and SPICE circuit simulation software.

Twisted differential line structure on high-speed printed circuit boards to reduce crosstalk and radiated emission

Differential signaling has become a popular choice for high-speed digital interconnection schemes on printed circuit boards (PCBs), offering superior immunity to crosstalk and external noise. However, conventional differential lines on PCBs still have unsolved problems, such as crosstalk and radiated emission. When more than two differential pairs run in parallel, a line is coupled to the line adjacent to it because all the lines are parallel in a fixed order. Accordingly, the two lines that constitute a differential pair are subject to the differential-mode crosstalk that cannot be canceled out by virtue of the differential signaling. To overcome this, we propose a twisted differential line (TDL) structure on a high-speed multilayer PCB by using a concept similar to a twisted pair in a cable interconnection. It has been successfully demonstrated by measurement and simulation that the TDL is subject to much lower crosstalk and achieves a 13-dB suppression of radiated emission, even when supporting a 3-Gb/s data rate.

On deembedding of port discontinuities in full-wave CAD models of multiport circuits

A systematic numerical methodology is proposed for the accurate deembedding of multiport discontinuities in full-wave numerical models of multiconductor microwave and millimeter-wave passive structures and high-speed digital interconnects. The discussed methodology is based on the earlier-proposed short-open calibration (SOC) procedure. The latter being a numerical analog of the experimental transmission-thru-reflection technique provides a consistent removal of the feed networks of the device-under-test over a wide range of frequencies. The treatment of multiport topologies is achieved through the continuation of the original scalar SOC method into the vector space. The new vector SOC method is easily combined with integral-equation-based method-of-moments electromagnetic-field solvers and allows for substantial flexibility in the choice of excitation mechanisms. Such commonly used method-of-moments driving schemes as ports locally backed up by a vertical conducting wall, ungrounded-internal differential ports, and via-mounted ports can be accurately deembedded within the framework of the vector SOC. Several numerical experiments are provided to validate the proposed multiport deembedding methodology and demonstrate its application.

High-speed integrated optoelectronic modulation circuit

A chip-level integrated optoelectronic modulation circuit is described for high-speed digital interconnects. This circuit is composed of an electroabsorption modulator with surface-normal operation at 1550-nm wavelengths and a high-speed electronic driver. A growth/etch/regrowth procedure is used to fabricate the multiple-quantum well modulators and the heterojunction bipolar transistors (HBTs) of the circuit on a common InP substrate. The measured bandwidth is approximately 30 GHz.

The effect of rise time upon pulse shape and cross talk in high-speed digital interconnects

A lossy model for microstrip lines has been implemented in the SPICE simulator to inestigate the effect of rise time of an input signal upon the output waeforms. The leel of ringing and pulse deformation are found to be related to the fast rise time gien the circuit layout and parameters. The limits to the speed and pulse width of an input signal hae been predicted for appropriate logic functions. Q 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 328)331, 1997. Recent advances made in high-speed digital integrated cir- cuits technology has reduced the single device switching time to a few picoseconds. However, the interconnection delay time between the devices is often significantly longer than device switching time. Therefore, in such cases one can no longer ignore the transmission-line property of the intercon- nections. Accurate modeling and simulation of the effect of the rise time of a signal traveling along the transmission lines has become very important, because changes in the rise time wx may lead to distortion of the desired logic functions 1) 3. The faster the rise time, the more ringing and distortion to the output signal will occur. Excess ringing may cause a logic error in the received signal, as the voltage level may pass through the critical logic voltage levels more than once in a single pulse. Distortion to the signal shape may also be detrimental, as the length of the pulse may either become shorter or longer than the critical length. If a series of pulses are sent and their width increases, errors in timing are likely to occur and to propagate further on through the system until the signal no longer resembles the original. It is therefore important that the fastest possible rise time is calculated, so that the interconnect can be evaluated for its suitability in a particular application, such as a high-speed digital circuit, where excess ringing may introduce severe signal distortion wx and induce an error in logic on a neighboring line 3 . The purpose of this article is to present the results of modeling work on the effect of signal rise time upon pulse shape and cross talk between neighboring lines on a high-speed inter- connection bus. All simulations in this article are carried out with the use of the example of an eight-line bus in a high-

Transient analysis of high-speed digital interconnects with nonuniform coupled lines

Transient analysis of high-speed digital interconnects with nonuniform coupled lines

Application of path integrals in modeling transmission line loss

In signal integrity applications involving the modeling and analysis of high-speed digital interconnects, it is necessary to include the effects of nonideal transmission line behavior due to, for example, the effects of ohmic, dielectric, and skin effect losses. This paper describes a new approach to this problem by employing a path integral formulation to both model lossy and nonuniform transmission line behavior. The algorithm resulting from the application of this formulation is accurate, stable, computationally efficient, and applicable to time domain modeling of interconnect in digital systems.

Synthesis of lumped models from N-port scattering parameter data

A closed form technique is described which allows the synthesis of an N-node lumped network from N-port scattering parameter (S-parameter) data. The synthesis is appropriate for networks where N is very large, for example, high speed digital interconnect networks. The resulting lumped model can be used in SPICE and other simulators. The synthesis is valid for any structure that is small with respect to wavelength. Thus it is also appropriate for synthesizing lumped models of simple discontinuities, such as step junctions and cross junctions. A description of the theory and several examples are provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

THE SHINPADS SERIAL DATA BUS

ABSTRACTThe Shipboard Integrated Processing And Display System (SHINPADS) Serial Data Bus is a high speed digital interconnect system designed to provide a real time data bus communication facility for Naval Electronic Systems. The Serial Data Bus (SDB) can be used to interconnect devices currently using Military Standard MIL‐STD‐1397 Input/Output Interfaces and it has been designed to suit the needs of Naval Combat Systems.The SHINPADS Serial Data Bus was specified with an eye to the future. A large growth margin was designed into the system, while minimizing costs, by properly distributing functions between software, firmware, and hardware. The Serial Data Bus protocol enables future evolution to Fiber Optic Transmission without impacting system software. The Serial Data Bus provides the potential for accomplishing many of the features attributed to Distributed Processing Systems. However, the accomplishment of Distributed Processing improvements can only occur through proper and enlightened system design.