Order Bandpass Filter Research Articles

Multivariate determination of glucose concentrations from optimally filtered frequency-warped NIR spectra of human blood serum

Glucose concentrations over the 39 - 160 mg range have been determined from 357 NIR (near-infrared) spectra of human blood serum in the spectral region from 6766 to 4003 . A frequency-warping procedure was applied to the NIR data to compress 511 spectral components into 102 in the 6766 - 4003 spectral region. Before the data compression process was carried out, the NIR spectrum of deionized water was subtracted from each of the blood serum spectra to remove the intrinsic high background absorption due to the water. PLS (partial least-squares) regression was coupled with time-domain digital Butterworth bandpass filtering in an optimization procedure. The optimization procedure was carried out over a range of centre frequencies and bandwidths for first- (two-pole), second- (four-pole) and third- (six-pole) order bandpass filters, and over a range of PLS factors. The optimal PLS model and filter parameters were determined from a sequence of three-dimensional performance response maps for different numbers of PLS factors and filter orders. As a basis for comparison, the same optimization process was carried out for a Gaussian filter design approach (i.e., Fourier filtering). Using the optimally filtered frequency-warped NIR spectral data, an SEP (standard error of prediction ) of 13.2 mg was achieved for the test (monitoring) data using 14 PLS factors and a simple first-order (two-pole) digital Butterworth bandpass filter. Keywords: diabetes mellitus, glucose, human blood serum, non-invasive monitoring, near-infrared spectroscopy, partial least squares, optimal filtering, frequency warping

Design and analysis of bilinear digital ladder filters

Methods for designing bilinear switched-capacitor (SC) ladder filters are well known. However, they cannot be directly extended to digital filters because of the delay-free loops allowed in SC filters. In the present paper, design methods for low-sensitive bilinearly transformed voltage-current ladder filters are developed. The matrix approach for SC filter design is extended to digital filters, and the delay-free loops are eliminated. Design equations for general order low-pass, high-pass, bandpass, bandstop, and allpass filters are obtained in a simple closed form. The design procedure gives a canonical number of delays and a number of distinct multipliers equal to the number of reactive elements in the prototype. A number of test filters are analyzed with respect to magnitude sensitivity, magnitude response with respect to coefficient quantization, occurrence of limit cycles, stability, quantization noise levels, and structural complexity. The results are compared to wave digital filters (WDF), and cascade-form filters. It is found that bilinear digital ladder filters (BDLF) in most cases perform better than WDFs, while they at the same time have a simpler structure.

Insensitive current-mode bandpass filter implemented from two current conveyors

Two configurations for second order bandpass filters with current transfers are introduced. The circuits, which exhibit reduced values for the active and passive insensitivities, only use four passive components and necessitate two current conveyors. SPICE simulated results, which confirm the theoretical analysis, are given and discussed for current conveyors implemented in a translinear form.

Optimum design of active filters using the generalized immittance converter

Design equations are derived for the generalized immittance converter (GIC) when embedded in an arbitrary network. The derivation is based on minimizing the dependence of the GIC transfer function on the op amps' characteristics. Equations for the optimum design of the GIC when simulating inductance and frequency-dependent negative-resistance (FDNR) elements follow as special cases. The optimized GIC's are applied in the design of bandpass filters using Gorski-Popiel's ladder embedding technique. The design procedure is presented in detail and its application is illustrated through the design of a telephone-channel bandpass filter of the twelfth order.

A New Design Procedure for Inductorless Filters

A new design procedure for realizing any second order transfer function is given. It essentially transforms the given function into an RC function with identical zeros but poles shifted to the negative real axis through suitable feedback. The configurations proposed realize the transfer functions with opposite polarities, and are suitable for cascading. One of the configurations is stiitable for adjusting the desired gain constant or accommodating the source conductance. Using this new procedure, 3rd order Butterworth low-pass and band-pass filters are realized with equal valued earthed capacitors.

A comparison of active, multiple-loop feedback techniques for realizing high order bandpass filters

This paper reviews and compares the four multiple-loop feedback techniques used to realize high-order narrow-band filters; namely: follow-the-leader feedback (FLF), primary resonator block (PRB), leapfrog (LF), and modified leapfrog (MLF) techniques. The comparison is based upon the following criteria: design ease and flexibility, sensitivity performance, insensitivity to design errors due to nonideal operational amplifiers, and tunability. In all comparisons the simple but highly sensitive cascade technique is used as a reference. Several examples are cited which indicate comparative trends in sensitivity performance. Finally the computer program used to realize minimum sensitivity FLF networks is described.

High Accuracy Analog Differentiator

A second order bandpass filter with the proper choice of damping ratio has been adapted for use as a high accuracy analog differentiator. Curves showing differentiator gain error as a function of damping ratio are given along with the gain error of the ``standard'' analog differentiating circuit. For a gain error of 1%, the differentiator bandwidth is reduced by a factor of 6 compared to the bandwidth necessary with the ``standard'' differentiating circuit. The reduced bandwidth results in lower wideband noise.