Crosstalk Reduction Research Articles

Full-wave characterization of the crosstalk reduction effect of an additional grounded track introduced between two printed circuit tracks

Crosstalk between tracks on printed circuit boards can degrade the signal quality in electronic circuits and systems. An additional track, grounded at regular intervals, may be introduced between the interfering tracks to reduce the unwanted coupling. Analysis techniques for this geometry have thus far all used a quasi-TEM approach for the characterization of the coupled transmission lines, which starts failing progressively as the frequency rises. In this paper, a full-wave spectral domain analysis which includes the effects of dispersion and loss, is presented. The method produces accurate results over a wide frequency range, and is particularly useful for the faithful prediction of high frequency signal distortion.

Methods for crosstalk measurement and reduction in dense WDM systems

We propose a scheme for the monitoring and reduction of crosstalk arising from the limited stop-band rejection of optical bandpass filters in dense WDM systems. The optical carrier at each wavelength is modulated with a subcarrier tone unique to that wavelength. The level of crosstalk from a given channel can be determined by measuring the power of the corresponding tone. Crosstalk from other channels can be cancelled in a linear fashion by weighting and summing the photocurrents of the desired channel and several adjacent interfering channels. Alternatively, in nonlinear crosstalk cancellation, decisions are made on the interfering signals, and these decision are weighted and summed with the photocurrent of the desired channel. For example, assuming an optical filter having a Gaussian passband, the channel density can be increased from 20 to 30%, depending on the number of adjacent channels detected. The signal-to-interference ratio can be increased by 10-20 dB and the system can achieve a BER<10/sup -9/ under conditions where, without interference cancellation, the signal-to-interference ratio would be less then 10 dB.

Beat induced crosstalk reduction against wavelength difference between signal and four-wave mixing lights in unequal channel spacing WDM transmission

The reduction in the beat induced crosstalk caused by four-wave mixing (FWM) as a function of the wavelength difference between the signal light and FWM light is experimentally elucidated for wavelength division multiplexing (WDM) transmission employing unequal channel spacing. Experimental results show that the wavelength difference must be 2.7 times the bit rate in order to reduce the beat induced crosstalk due to FWM even if direct intensity-modulation whose power spectrum is extended by laser chirping is employed.

Substrate crosstalk in BiCMOS mixed mode integrated circuits

A comparison of several crosstalk reduction schemes using two-dimensional device simulation and measurements on silicon has shown that while SOI based processes provide high isolation from crosstalk, fully junction isolated wells can provide equal or better crosstalk immunity at a lesser expense. Simple guard ring substrate contacts appear to be the technique best suited for preventing cross-talk at high operating frequencies. A lumped parameter equivalent circuit has also been developed to simulate fully junction isolated wells in SPICE.

Design of multiwavelength optical communication systems based on an integrated waveguide amplifier compensator

We theoretically analyze the performance of longhaul multichannel optical communication systems based on an integrated WDM power level compensator. By placing an array of Er/sup 3+/-Yb/sup 3+/ co-doped silica waveguides in parallel between a demultiplexer/multiplexer pair and preceeding it by an EDFA, we demonstrate the possibility of transmitting eight unequally spaced WDM channels over long distances, without electronic regenerators and using span lengths as high as 50 km. This technique allows substantial reduction of both four-wave mixing crosstalk and gain peaking.

Nonuniform FDTD formulation for the analysis and reduction of crosstalk on coupled microstrip lines

The finite difference time domain (FDTD) formulation for nonuniformly meshed computational space with inhomogeneous lossy dielectrics is presented and discussed. The use of the nonuniform mesh allows for the analysis of practical geometries with modest computer resources. The selection of FDTD parameters in both time and spatial domains, and its influence on the numerical results is also addressed. Comparisons of numerical results with available measured data show good agreement. This FDTD formulation is applied to study the minimization of crosstalk between coupled microstrip lines. Different techniques are investigated to reduce the coupling, such as an air notch, a PEC doping, a PEC cover, and some related combinations. The numerical analysis of this study shows that the best techniques for crosstalk reduction with only one specific cover height and a limited range for the other microstrip line parameters, is obtained by applying the combination of a PEC doping and a PEC cover.

Modeling and reduction of crosstalk on coupled microstrip line structures and multichip modules: An FDTD approach

The finite difference time domain modeling technique is used to model the near end and far end crosstalk on coupled microstrip structures used in multichip modules. The lines are terminated in lumped resistors which closely, but not exactly, match the lines. One line is excited by a Gaussian voltage pulse produced by a Thévenin equivalent voltage source. It is shown that adding dielectric strips in the substrate below the conducting lines will reduce the peak crosstalk by as much as 80%. Eight different configurations are modeled consisting of dielectric strips with different dielectric constant combinations. All configurations are modeled with and without a metal case in order to make sure that the crosstalk reduction persists when the structure is enclosed in a metallic enclosure (this would be the case for multichip modules). The results show that using dielectric strips with the smallest possible dielectric constant reduces crosstalk the most. © 1996 John Wiley & Sons, Inc.

Minimum crosstalk switchbox routing

As technology advances, interconnection wires are placed in closer proximity, and circuits operate at higher frequencies. Consequently, reduction of crosstalks between interconnection wires becomes an important consideration in VLSI design. In this paper, we studied the gridded switchbox routing problem with the objectives of satisfying crosstalk constraints on the nets and minimizing the total crosstalk among all of the nets. We proposed a new approach to the problem which utilizes existing switchbox routing algorithms and improves upon the routing results by re-assigning the horizontal and vertical wire segments to rows and columns, respectively, in an iterative fashion. This approach can also be applied to the channel routing problem with crosstalk constraints. To re-assign the horizontal and vertical wire segments effectively and optimally, a new mixed integer linear programming formulation and effective techniques for reducing the number of variables and constraints in the ILP formulation are presented. The novelty of the ILP formulation together with the techniques for reducing the number of variables and constraints in the formulation enable us to obtain excellent results for all the circuits we tested.

Cross-talk analysis and reduction in fully parallel matrix–matrix multipliers

Analog optical processors that calculate a product of two matrices in a single clock cycle are analyzed for cross talk. It is determined that the sidelobes from the sinc function corresponding to the individual pixels of the spatial light modulator that encodes the first matrix are the main source of the cross talk. This cross talk can be reduced substantially by the use of an apodizing function for individual pixels of the spatial light modulator. This scheme for cross-talk reduction is verified by computer simulation. Initial experimental results are presented that demonstrate the gray-scale performance of the matrix-matrix multiplier as well as sidelobe suppression with apodization.

Interferometric noise reduction in crosstalk corrupted optical WDM and TDM switching fabrics

Interferometric noise due to crosspoint crosstalk in optical WDM and TDM switching fabrics is substantially reduced by manipulation in the time and/or wavelength domains. Furthermore, providing sufficient discrete wavelengths are available, or sufficient time compression can be realized, almost all noise may be eliminated at the expense of additional equipment. Practical realizations of the proposed scheme are discussed. >

Optimum design for polarization crosstalk reduction in a polarization maintaining optical fiber of PANDA profile

AbstractThis paper investigates theoretically the polarization‐maintaining optical fiber with a circular stress‐applying part (PANDA fiber) with a high design accuracy and ease of fabrication, with a view to realizing a low crosstalk polarization‐maintaining optical fiber for coherent optical sensing. In general, two orthogonal polarization modes exist in a polarization‐maintaining fiber. Due to the coupling between these two modes, the transmission of a polarized wave is difficult. The infinitesimal polarization component caused by this coupling is called the minor component. The cause of generation of the minor component is confirmed theoretically as the generation of the off‐diagonal term in the relative permittivity tensor. In the past, the off‐diagonal terms have been neglected in the optical fiber in which symmetry is maintained.In this paper, the off‐diagonal terms of the relative permittivity tensor appearing in a PANDA fiber with symmetry are investigated. The effect of the structural characteristics of the PANDA fiber on the crosstalk degradation is analyzed. It is found that the improvement of the polarization crosstalk by 20 to 35 dB is expected with a modal birefringence of less than one‐half the previous case, by making the normalized stress‐applying part half‐spacing 2.83 and the normalized stress‐applying part diameter 0.44.

A positron emission tomograph designed for 3/4 mm resolution

Two factors of the design for a positron tomograph affect the magnitude of the tomograph spatial resolution: the gamma ray detector width and the analogue measurement of the scintillator location. In the tomograph design reported here the analogue measurement is eliminated and the detector transaxial width factor is reduced to 3/4 mm. The analogue measurement is eliminated by transmitting the scintillation light from each individual scintillator through optical fibers to four photomultipliers (PMT's); the identities of the PMT's then provide a digital address for the scintillation location. Plastic scintillators are used to provide enough scintillation light for transmission through the optical fibers. Bonuses from the use of plastic scintillators are first, the reduction of the scintillator dead time to about 10 nsec, second, a large reduction of crosstalk between neighboring scintillators, third, the reduction of resolution loss from off-axis gamma rays and, fourth, the ability to sample the axial image at one-eighth the axial resolution distance of 2.5 mm. The designed tomograph incorporates 20 rings. Two of the 32 tomograph 20-ring modules have been constructed to measure the resolution and other characteristics of the tomograph. >

Frequency and phase swept holograms in spectral hole-burning materials

A new hologram type in spectral hole-burning systems is presented. During exposure, the frequency of narrow-band laser light is swept over a spectral range that corresponds to a few homogeneous linewidths of the spectrally selective recording material. Simultaneously the phase of the hologram is adjusted as a function of frequency-the phase sweep function. Because of the phase-reconstructing properties of holography, this recording technique programs the sample as a spectral amplitude and phase filter. We call this hologram type frequency and phase swept (FPS) holograms. Their properties and applications are summarized, and a straightforward theory is presented that describes all the diffraction phenomena observed to date. Thin FPS holograms show strongly asymmetric diffraction into conjugated diffraction orders, which is an unusual behavior for thin transmission holograms. Investigations demonstrate the advantages of FPS holograms with respect to conventional cw recording techniques in freq ncymultiplexed data storage. By choosing appropriate phase sweep functions, various features of holographic data storage can be optimized. Examples for cross-talk reduction, highest diffraction efficiency, and maximal readout stability are demonstrated. The properties of these FPS hologram types are deduced from theoretical considerations and confirmed by experiments.

Recording of 6000 holograms by use of spectral hole burning

Experiments verifying a new method of storing spectral hole-burning holograms, which yields reduced cross talk as compared with standard spectral hole-burning holograms, have been conducted. Results demonstrating the reduced width of this type of hologram in both frequency and the applied electric-field dimension are presented. Analytic solutions for the spectral width and diffraction efficiency of these holograms are presented. Using this exposure technique, we have recorded 6000 holograms in a single spectral hole-burning sample.

Performance driven spacing algorithms using attractive and repulsive constraints for submicron LSI's

This paper proposes one-dimensional spacing algorithms that minimize [maximize] the degree of separation [proximity] among the specified elements of a given integrated circuit layout. Number of problems on chip and MCM systems such as poor performance, higher crosstalk, lower yield etc. are related to the degree of separation [proximity]. The proposed algorithms utilize the attractive [repulsive] constraints to shrink [expand] the distances among the specified elements while keeping the layout free of any design rule errors. The spacing problem is reduced to a parametric linear programming problem and a network simplex algorithm is proposed for solving it. The proposed algorithms are implemented into a system called PERFECT for performance enhancement and crosstalk reduction. Given a routed design, PERFECT minimizes delay due to the coupled capacitance, which could contribute as much as 50-75% to the interconnect delay in near future. PERFECT utilizes the repulsive constraints between interconnect segments for the purpose. The experimental results show a significant delay improvement and the crosstalk reduction for submicron technologies. >

Sandwich enzyme membranes for amperometric multi-biosensor applications: improvement of linearity and reduction of chemical cross-talk

Amperometric thick-film multisensors for the simultaneous determination of glucose and sucrose are described. The enzymes glucose oxidase and invertase are immobilized in a matrix made from aqueous poly(vinylacetate) dispersions. Sandwoch membranes are obtained by printing two or more membrane layers on top of each other. This technique effects the elimination of interferences, such as ascorbic acid, and enables the enlargement of the linear ranges of determination for glucose and sucrose. In addition, catalase, either co-immobilized with glucose oxidase or used in a separate cover membrane, can be used to improve the linearity and to eliminate chemical cross-talk between electrodes of multibiosensors.

Multichannel frequency-selective switch employing an arrayed-waveguide grating multiplexer with fold-back optical paths

The optimized configuration of an N-channel frequency-selective 2/spl times/2 switch based on an arrayed-waveguide grating (AWG) (2N+1)/spl times/(2N+1) multiplexer is proposed that offers significant crosstalk reduction and loss-imbalance equalization. The optimization is achieved by employing fold-back optical paths instead of loop-back paths. A switch constructed with a silica-based AWG 16/spl times/16 multiplexer demonstrates coherent crosstalk of less than -30 dB in the transmitting frequency-division-multiplexed (FDM) channels; the gain in optimization is more than 15 dB. The largest loss-difference among the seven FDM channels is simultaneously reduced from 4.5 dB to 1.6 dB. These improvements will extend the cascadable number of nodes in all-optical FDM networks. >

Reduction of four-wave mixing crosstalk in WDM systems using unequally spaced channels

Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A technique to design the channel frequency allocation in order to minimize the crosstalk due to FWM is presented. It is shown that suitable unequal channel separations can be found for which no four-wave mixing product term is superimposed on any of the transmitted channels. This is obtained at the expense of some expansion of the system bandwidth. Simulations are presented to show the effectiveness of this technique in a 10-channel, 10-Gb/s per channel, system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Measurement and simulation of crosstalk reduction by discrete discontinuities along coupled PCB traces

Crosstalk among interconnects and printed-circuit board (PCB) traces is a major limiting factor of signal quality in high-speed digital and communication equipment. The paper evaluates coupled surface microstrip transmission lines with periodical loading and coupling. The situation may represent stray coupling and loading of digital buses due to connector pins, plated through holes at connector slots, and stubs as well as the input capacitance of active devices. This paper shows that discrete periodical coupling along coupled surface microstrip transmission lines may be used to reduce far-end crosstalk. An expression is given to calculate the discrete coupling capacitance to achieve optimum far-end crosstalk reduction. The reduction of far-end crosstalk is verified by measurements, and the good agreement between the simulated and measured data is shown. On the other hand, discrete loading does not significantly reduce near-end crosstalk, but will introduce additional ringing in the time domain. >

Reduction of cross talk in an acousto-optic switch by means of dilation

It is demonstrated that cascaded (dilated) acousto-optic switches exhibit greatly reduced interport and interchannel cross talk. In our experiments, a pair of monolithic polarization-independent acousto-optic switches were joined to simulate the bar and cross states of a dilated switch consisting of a 2 × 2 matrix of subswitches. Reduction of bar- and cross-state extinctions and sidelobe levels confirmed the supposition that leakage of order ∊ in a one-stage device decreases to order ∊2 in dilated devices.