Showing papers on "Bessel filter published in 2002"

Stochastic models for capturing image variability

Abstract: We review a result in modeling lower order (univariate and bivariate) probability densities of pixel values resulting from bandpass filtering of images. Assuming an object-based model for images, a parametric family of probabilities, called Bessel K forms, has been derived (Grenander and Srivastava 2001). This parametric family matches well with the observed histograms for a large variety of images (video, range, infrared, etc.) and filters (Gabor, Laplacian Gaussian, derivatives, etc). The Bessel parameters relate to certain characteristics of objects present in an image and provide fast tools either for object recognition directly or for an intermediate (pruning) step of a larger recognition system. Examples are presented to illustrate the estimation of Bessel forms and their applications in clutter classification and object recognition.

Bessel discrete variable representation bases

Abstract: Discrete variable representation (DVR) basis sets on the radial half-line, based on Bessel functions, are presented. These are Hankel transforms of the eigenfunctions of the particle in a spherical box in k space, but there is no box or bound on the radial variable r. The grid points extend to infinity on the r axis. The DVR functions are exactly orthonormal and exactly satisfy the interpolation properties usually associated with DVR functions. The exact matrix elements of the kinetic energy are computed, and the use of the Bessel DVR functions in radial eigenvalue problems is illustrated. The phase space or semiclassical interpretation of the Bessel DVR functions is presented, and variations on these functions, corresponding to alternative boundary conditions in k space, are discussed. An interesting feature of Bessel DVR functions is that they are based on a finite basis representation that is continuously infinite.

Direct generation of bessel beams

Abstract: Two implementations are identified to create a Bessel beam directly, i.e. without the spatial filtering of an initially Gaussian beam. The first implementation is based on a resonator configuration whose lowest-loss transverse mode is a Bessel beam. Numerical simulation to corroborate the geometrical optical arguments is presented. The second implementation is based on the theorem that the angular-plane wave spectrum of a Bessel beam is composed of a cone of wave vectors. This cone is also generated through a phase-matching condition in a four-wave mixing process. This leads to the conclusion that anti-Stokes radiation generated in a nonlinear material will leave the substrate under the form of a Bessel beam.

Low-Voltage Continuous-Time Filter Based on a CMOS Transconductor with Enhanced Linearity

Abstract: Summary The proposed design of a low-voltage continuous time filter is based on a CMOS transconductor with enhanced linearity. The compensation principle is used for the reduction of transconductor non-linear distortions. The discussed transconductor consists of two transconductors connected in parallel. The input transistors of the first transconductor are working in the triode region, while the input transistors of the further one are in the saturation. A fifth-order 1 MHz low-pass Bessel filter is synthesized and simulated using transconductors. The supply voltage is equal to +2.5 V. A tuning system of the filter is also simulated and discussed. A comparison shows that the discussed filter provides a higher linearity (from 4 to 9 dB) than the known circuits with the exception of filters based on the amplifier with degeneration. But it is noted that the last approach is difficult to use for the low-voltage application, because the voltage drop on the degeneration resistors limits the possible decrease of the voltage supply.

Computation of Bessel and Airy functions and of related gaussian quadrature formulae

Abstract: Procedures are described for the high-precision calculation of the modified Bessel function Kν(x), 0 < ν < 1, and the Airy function Ai(x), for positive arguments x, as pre-requisites for generating Gaussian quadrature rules having these functions as weight function.

A 2.5-V, 0.35 /spl mu/m CMOS transconductance-capacitor filter with enhanced linearity

Abstract: A CMOS transconductance-capacitor (G/sub m/-C) filter with enhanced linearity for low-voltage applications is presented. The proposed design is based on a transconductance amplifier with enhanced linearity. For the elimination of the amplifier harmonic level the compensation principle is used. The transconductor consists of two amplifiers connected in parallel. The input transistors of the first transconductor are working in the saturation region, while the input transistors of the other one are in the triode region. The device was realized as a balanced fifth-order 1MHz low-pass Bessel filter in 0.35/spl mu/m CMOS technology. The filter operates with a low supply voltage of +2.5 Volt. A comparison shows that the discussed filter provides a higher linearity (from 3 to 8 dB) than known circuits with the exception of the filter based on a degenerated transconductor. But it is noted that there are some difficulties to use the last approach for low-voltage application.

CMOS R-MOSFET-C fourth-order Bessel filter with accurate group delay

Abstract: A fully differential R-MOSFET-C fourth-order Bessel active lowpass filter employing passive resistors and current-steering MOS transistors as a variable resistor is proposed. The implementation relies on the tunability of the current-steering MOS transistors operating in triode region which counteract the concert deviation of resistance in integrated circuit manufacturing technology in order that the group delay of the Bessel active filter can be realised accurately. A 0.75 /spl mu/s group delay 520 kHz fourth-order Bessel lowpass filter based on a passive doubly terminated RLC prototype was designed and fabricated using 3.3 V power supply and 0.5 /spl mu/m CMOS technology. Chip test results demonstrate better than 65 dB THD with a 100-kHz, 1.65-Vpp input signal, frequency tuning range of more than ten decades from 0.6 kHz to 550 kHz, chip area of 0.32 mm/sup 2/ and power consumption of 13.3 mW.

Second-Harmonic Generation of Bessel Beams in Lossy Media

Abstract: We present a further analysis for the second-harmonic generation of Bessel beams in lossy media. The emphasis is put on the effect of absorption to the radial pattern of the second-harmonic beam. It is shown that within the absorption length of the second harmonic, the Bessel second-harmonic beam approaches limited diffraction in the radial direction and behaves as in the case of lossless media.

An optical thin film Bessel filter for 40Gbit/sec -100GHz spacingD-WDM system

Abstract: It is difficult to employ conventional Butterworth filters in 40 Gbit/sec applications with 100 GHz-spacing due to their strong group delay dispersions. This paper shows design, fabrication and measurements of a thin film Bessel filter applicable for 40 Gbit/sec VSB signals, and compares the results to a typical Butterworth filter. This Bessel filter has very low dispersion because of its flattened group delay, and in turn, this allows VSB signal filtering with minimal linear distortions

Iir filter design

Abstract: Infinite impulse response (IIR) filters require fewer delay elements, adders, and multipliers for a given frequency response. Therefore, they are more efficient than finite impulse response (FIR )filters. The disadvantage of IIR filters is their nonlinear phase response. A non-constant group delay means that all frequencies do not experience the same delay. Thus, impulses containing components with a wide range of frequencies will be distorted when passed through an IIR filter. Most IIR filters are designed using an analog filter model. Analog filter models are the familiar Butterworth, Chebyshev, Cauer, Inverse Chebyshev, and Bessel types. Bessel models are not converted into digital filters. The advantage of a Bessel response in an active or passive linear filter is the constant group delay, at the expense of a poor skirt response. FIR filters can produce a constant group delay with far superior skirt response, so they are used where group delay is important.

Fully Differential 4th-order Bessel Filter Accurately Designed with Group Delay

Abstract: This paper presents a fully differential R MOSFET C 4th order Bessel active low pass filter with group delay adjusted by tuning the channel transconductance of CMOS transistors worked in weak inversion regionThe tuning can counteract the deviation of resistor in the manufacture of integrated circuit,therefore the group delay of Bessel active filter can be designed and realized accurately The active filter can be synthesized according to the state equation of passive filterComputer simulation of 4th order Bessel low pass filter with 0 75μs group delay indicate that the proposed circuits are both effective using 3 3V?0 5μm CMOS technology,and suitable for integration