Weighted least-squares design of recursive allpass filters

A method for the design of allpass filters is described. In this method, an error reflecting the difference between the desired phase response and the phase response of the practical allpass filter is formulated in a quadratic form. The coefficients are obtained by solving a system of linear equations involving the sum of a Toeplitz and an Hankel matrix     

Noniterative WLS design of allpass variable fractional-delay digital filters

This paper presents a noniterative weighted-least-squares (WLS) method for designing allpass variable fractional-delay (VFD) digital filters. After expressing each coefficient of an allpass VFD filter as a polynomial of the VFD parameter p, we develop a noniterative technique for finding the optimal polynomial coefficients, and show that the allpass VFD filter design problem can be efficiently solved without using any iterative procedure while a closed-form solution can be easily obtained through solving a matrix equation. Compared with the existing iterative WLS method that solves a series of approximately linearized WLS minimization problems, the proposed noniterative one can yield much better design results with significantly reduced computational complexity. Moreover, the new WLS method does not involve any convergence issue.     

Minimax design of two-channel nonuniform-division filterbanks using IIR allpass filters

The design of two-channel linear-phase nonuniform-division filter (NDF) banks constructed by infinite impulse response (IIR) digital allpass filters (DAFs) in the sense of L/sub /spl infin// error criteria is considered. First, the theory of two-channel NDF bank structures using two IIR DAFs is developed. Then, the design problem is appropriately formulated to result in a simple optimization problem. Utilizing a variant of Karmarkar's algorithm, we can efficiently solve the optimization problem through a frequency sampling and iterative approximation method to find the coefficients for the IIR DAFs. The resulting two-channel NDF banks can possess approximately linear-phase response without magnitude distortion. The effectiveness of the proposed technique is achieved by forming an appropriate Chebyshev approximation of a desired phase response and then to find its solution from a linear subspace in a few iterations. Several simulation examples are presented for illustration and comparison.     

Transfer-function synthesis of allpass filters for pulse compression

The problem of approximation in the time domain may be solved by using the criterion of maximising the peak envelope of a compressed pulse. The position of allpass poles and zeros can be obtained by varying only three parameters. The new method, compared with the existing ones, gives greater pulse compression with greater range sidelobe reduction, using a simpler procedure.     

Orthogonal realization of first-order allpass filters for two-dimensional signals

An orthogonal realization for two-dimensional first-order strictly-stable allpass transfer functions is presented. It consists of two shift (delay) elements (one for each dimension) and three two-input/two-output memory-less lossless cells (i.e., elementary orthogonal rotations). We establish a one-to-one correspondence between the parameters of our orthogonal realization and those of the corresponding transfer function. A brief discussion of finite precision effects on our realization and a comparison with previous realizations are also included.     

Improved systolic allpass digital filters for very high-speed applications

An improved systolic realisation of an arbitrary-order allpass digital filter for delayed N-path digital filtering is presented. Using this method, the sampling rate at the input and output of a delayed N-path digital filter can be reduced to (T/sub m/+2T/sub a/)/(N(N-1)) (where N>or=2, and T/sub m/ and T/sub a/, respectively, represent the times for 2-input real multiplication and 2-input real addition), which is attractive for very high-speed applications.<>     

Novel first-order differential class-AB log-domain allpass filters

The first-order differential class-AB log-domain filters are proposed. They are systematically derived using the state–space synthesis procedure. It is also demonstrated that the present second filter cannot be realized without using differential class-AB type. To the best knowledge of the authors, the filters are the first log-domain first-order allpass filters in the literature. PSPICE simulations are performed using both, bipolar junction transistors (BJT) and ideal devices to confirm the theoretical analysis. Tolerable differences are observed due to BJT non-idealities such as finite-beta, non-zero ohmic junction resistances and early voltages.     

Additional generalisation scheme of active RC allpass filters

A generalisation scheme of the active RC allpass networks with one differential input operational amplifier and three RC 2-ports is presented. The 2-ports are unbalanced, but not earthed, and only the voltage transfer functions of these networks are used in this generalisation, thus making the analysis of the circuit and the circuit transfer functions considerably easier.     

MOS-only allpass filters with extended operating frequency range

Although the design of integrated filters using MOS-only circuits provides some vital advantages, these circuits are inherently prone to have limited operating frequency range. This fact leads to a poor tunability range and seriously degrades the usefulness of this class of filters. In order to address this issue, two methods are presented and detailed simulation results verifying the feasibility of the techniques are provided.     

Novel systolic array realisation of allpass digital filters for high speed applications

A novel systolic array realisation of a general allpass digital filter of any arbitrary order suitable for high speed delayed N-path recursive digital filtering applications is presented. The proposed systolic array is a purely systolic (not semisystolic) design which is also canonic in the number of multipliers, modulator in having one type of basic cell, and has nearest neighbour interconnections.<>     

Bandstop monolithic crystal filters having allpass response outside stopband

A dual-resonator monolithic crystal filter (MCF) is basically a narrowband bandpass filter. It is well known that a narrowband bandstop response can be obtained by connecting an inductor in parallel to an MCF element, however, it yields a lowpass response outside the stopband with a cutoff frequency about square root (2) times the stopband frequency. Ideally, outside the stopband, it should have an allpass characteristic. The author shows a simple method of designing a bandstop MCF filter having an allpass response outside the stopband by adding a series-connection inductor. The series inductor together with two capacitors provide the required highpass structure that complements the lowpass response to yield an allpass response.<>     

New topology for implementing bandpass,bandstop and allpass filters with CFAs

In this brief, a new filter topology based on current feedback amplifiers is presented and compared with its operational amplifier counterpart. The circuits arising from the new topology have the important advantage that access to the Z node of the current feedback amplifier is not required, as is the case with many existing current feedback amplifier filter circuits. The operation and requirements for each of the filters are described. Theoretical results and circuit limitations are discussed and verified with experimental results. In one experiment a bandpass filter with a calculated Q and centre frequency of 20 and 158.53 kHz, respectively was built using the OPA2607 dual CFAs IC. Measured results yielded a Q of 20.153 at a centre frequency of 148.62 kHz showing close agreement with theory.     

Entirely thin-film allpass coupled-cavity filters in a parallelconfiguration for adjustable dispersion-slope compensation

Conventional dispersion-slope compensation filters suffer from a fundamental tradeoff between the amount of dispersion-slope compensation and the compensation bandwidth. A novel multireflection device, composed of two coupled cavity filters in a parallel configuration is proposed that has an adjustable dispersion-slope independent of the compensation bandwidth. The device provides an adjustable dispersion-slope value between -6.7 and -35.7 ps³ over a bandwidth of 3 nm. The center wavelength is adjustable over a 10-nm range     

New insensitive notch and allpass filters with single current follower

New second-order notch and allpass filters using a single current follower are proposed. The filters use five passive RC elements. Both the active and passive sensitivities are very low. The natural frequencies and the quality factors of the proposed filters are insensitive to the current tracking error of the current follower. Simulation results which agree with the theoretical analysis are obtained.<>     

Complex notch filter design using allpass filter

Complex coefficient IIR notch filter design problems are investigated. The specification of a notch filter is first transformed into that of an allpass filter. An effective approach to the design of this desired allpass filter is developed. The realisation of the proposed notch filter is equivalent to the realisation of an allpass filter. Owing to the mirror-image symmetry relation between the numerator and denominator polynomials of allpass filters, the notch filter can be realised by a computationally efficient lattice structure with very low sensitivity     

High-output-impedance current-mode multiphase sinusoidal oscillator employing current differencing transconductance amplifier-based allpass filters

This article presents a multiphase sinusoidal oscillator using current differencing transconductance amplifier (CDTA)-based allpass filters. The oscillation condition and oscillation frequency can be orthogonally controlled. The proposed circuit provides 2n – phase signals (n≥2) that are equally spaced in phase and of equal amplitude. The circuit requires one CDTA, two resistors and one capacitor for each phase and no additional current amplifier. Owing to high-output impedances, the proposed circuit enables easy cascading in current-mode configurations. The effects of the nonidealities of the CDTA-allpass sections were also studied. The results of PSpice simulations are presented, demonstrating their consistency with theoretical assumptions.     

Interpolated LIR Mth-band filter design with allpass subfilters

We propose a new allpass-based structure for the IIR Mth-and 2Mth-band filters. These filters consist of M allpass filters and an interpolation filter (sum of two allpasses). Consequently, the proposed structure is very efficient in implementation. By choosing the allpass phase appropriately, the resulting phase response of the IIR Mth-band filter becomes approximately linear. An example is designed and compared with FIR Mth-band filters     

Single MIMO-OTA and single-grounded-capacitor-based first-order allpass filter design

A novel first-order voltage-mode allpass (AP) filter employing a single multiple-input-multiple-output operational-transconductance-amplifier (MIMO-OTA) and a single grounded capacitor is introduced in this article. Compared to the corresponding already published topologies, the offered benefits are as follows: it employs minimum number of active and passive components; the only capacitor is grounded, which is good for a monolithic integration of an IC; and the absence of any matching condition for its realisability. The performance of the proposed circuit has been evaluated through simulation results, utilising the analogue design environment of Cadence software.     

Wide-band system identification using multiple tones with allpass filters and square-law detectors

This paper introduces a method of wide-band system identification that uses a uniformly spaced set of tones with allpass filters and square-law detectors to obtain estimates of amplitude and phase at the associated discrete frequencies. The bandwidth of the detectors is on the order of the tone spacing and so can be much smaller than the overall signal bandwidth, thereby making feasible the use of low-cost analog RF integrated circuits and/or pure digital signal processing with all of its inherent advantages. Applications of this technique include equalization and compensation for fiber optic and wide-band cellular communication systems.