All-pass Networks Research Articles

Simplified Modeling of a Multipole Amplifier Using All-Pass Network Functions

This paper presents a system model for the representation of amplifiers that cannot be accurately characterized by a classical two pole transfer function. The effects of higher order poles are modeled by an all-pass function added to the conventional two pole model. The accuracy of the model is demonstrated by comparing the results for a typical CMOS amplifier to those obtained from device level simulations using SPICE. This model can be easily implemented in a standard simulator and is shown to achieve fast simulation time. This model is expected to have application in system level modelling of mixed-signal circuits using conventional SPICE simulators.

Current-Mode First-Order Allpass Filter Employing Single Current Operational Amplifier

A current-mode first-order allpass filter configuration is proposed. The presented circuit uses a single current operational amplifier (COA), a resistor and a capacitor, which are of minimum number. High output impedance of the proposed filter enables the circuit to be cascaded without additional buffers. The proposed circuit is insensitive to parasitic input capacitances and input resistances due to internally grounded input terminals of COA. It does not impose any component matching constraint in analog signal processing circuits. Non-ideal effects of COA to the first-order allpass network are also investigated. To demonstrate the performance of the proposed filter a new current-mode quadrature oscillator is given as an application example. The theoretical results are verified with PSPICE simulations using a new realization of fully differential CMOS COA.

A Tunable Active Phase Shifter Using a Thin Film Ferroelectric Capacitor

This paper describes an active phase shifter with a large amount of variable phase. We propose a design that has second-order all-pass network characteristics and that uses a tunable ferroelectric capacitor. The transmitted phase is changed by varying the capacitance of a ferroelectric capacitor. A computer simulation is presented that shows that the network, even with markedly non-ideal transistors, can provide a true all-pass response over the frequency band of interest (100 MHz–400 MHz). These simulated results demonstrate an analog tunability of about 200° with a gain variation of about 3 dB at 300 MHz—when using a Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) capacitor with a tunability of 2:1. The simulation performed at 300 MHz because the physical layout of the real life circuit will be done mostly with the discrete components. As the self resonance frequency of most of the discrete components lies in the few hundreds of MHz range, our preferred frequency is a practical one to deal with. The simulation also predicts a flat band gain of approximately 10 dB with ± 2 dB of gain ripple.

2.4 GHz continuously variable ferroelectric phase shifters using all-pass networks

Continuously variable ferroelectric (BST on sapphire) phase shifters based on all-pass networks are presented. An all-pass network phase shifter consists of only lumped LC elements, and thus the total size of the phase shifter is kept to less than 2.2 mm /spl times/ 2.6 mm at 2.4 GHz. The tunability (C/sub max//C/sub min/) of a BST interdigital capacitor is over 2.9 with a bias voltage of 140 V. The phase shifter provides more than 121/spl deg/ phase shift with the maximum insertion loss of 1.8 dB and the worst case return loss of 12.5 dB from 2.4 GHz to 2.5 GHz. By cascading two identical phase shifters, more than 255/spl deg/ phase shift is obtained with the maximum insertion loss of 3.75 dB. The loss figure-of-merit of both the single- and double-section phase shifters is over 65/spl deg//dB from 2.4 GHz to 2.5 GHz.

A tunable all-pass MMIC active phase shifter

This paper describes a novel structure for a monolithic-microwave integrated-circuit active phase shifter based on a bridge all-pass network. The design procedure has been developed, leading to a fixed-frequency circuit with large tunable phase variation, associated to a low-gain ripple, and requiring nearly no design optimization. Simulated results predicted an analog tunable 180/spl deg/ phase variation, at 5-GHz operation frequency. The circuit was implemented using GEC-Marconi pseudomorphic high electron-mobility transistor H40 technology, and measured results validated the proposed design method and circuit structure.

An analog sampled-data DSB to SSB converter using recursive Hilbert transformer for accurate I and Q channel matching

The realization of a complete double-sideband (DSB) to single-sideband (SSB) converter using switched-capacitor techniques is presented. The proposed approach employs a recursive Hilbert transformer to achieve efficient SSB modulation. The design of the Hilbert transformer through structurally all-pass networks allows good dynamic range and small sensitivity to capacitance ratio errors. The sampling rate of the output SSB signal is reduced by a factor of two, so that the Hilbert transformer and the following circuitry work at half of the input sampling rate, reducing circuit complexity and power consumption, without loss of information. Experimental laboratory results obtained with a prototype realization using discrete components are presented. Practical aspects pertaining to a monolithic implementation in complementary metal-oxide-semiconductor (CMOS) technology are considered.

Selective Digital Filters with Linear Phase

Summary A method for synthesis of digital bandpass and bandstop filters obtained by parallel connection of two allpass networks, is considered. A procedure is based on allpass network linear phase approximation at three levels in mini-max sense, which enables obtaining of selectivedigital filters in form of elliptic filters with linear phase in both passband and stopband.

Current-mode all-pass filters using current differencing buffered amplifier and a new high-Q bandpass filter configuration

A new configuration realizing first-order canonical current processing all-pass filters based on current differencing buffered amplifier, a recently introduced active element, is proposed. Using this configuration, two types of first-order current-mode all-pass filters are derived. They employ only a single active element and a bare minimum number of passive components. No component-matching constrains are required. Because of the high performance of the current differencing buffered amplifier, they are suitable for wideband applications. The derived filters are cascadable because of their high output impedances and they use fewer active and/or passive components compared to their previously reported counterparts. As an application of the proposed first-order all-pass networks, a new current-mode high-Q bandpass filter, which offers a number of advantages over its counterparts, is also given.

The application of all-pass filters in the design of multiphase sinusoidal systems

The design of even and odd phase sinusoidal systems using all-pass networks is presented. The all-pass network has the unique characteristic of unity gain at all frequencies and a frequency-dependent phase relationship between output and input. It produces up to 180° phase shift which allows the easy implementation of multiphase systems. The network is implemented using the widely available operational amplifier which results in low harmonic distortion, low frequency error, large output voltage swing and low output impedance from a simple structure. The operating frequency is limited only by the gain–bandwidth product of the op-amp.

An MMIC active phase shifter using a variable resonant circuit [and MESFETs

This paper describes a monolithic-microwave integrated-circuit (MMIC) active phase shifter using a variable resonant circuit with a large amount of variable phase. We first propose a novel active phase-shifter configuration that uses a variable resonant circuit with second-order all-pass network characteristics. Phase can be changed with a constant amplitude by varying the capacitance or the inductance of the resonant circuit. Next, an experimental MMIC active phase shifter with input active matching is presented. A phase shift of over 100/spl deg/ and an insertion loss of 4/spl plusmn/1 dB are obtained from 2.2 to 2.8 GHz. The chip size is less than 1.0 mm/sup 2/. Finally, an experimental 360/spl deg/ MMIC active phase shifter is presented. Over the bandwidth of 40 MHz at 2.44 GHz, the insertion gain is 2.0/spl plusmn/0.7 dB and the phase error is within /spl plusmn/4/spl deg/ when measured in 30/spl deg/ steps.

An integrable 60-Hz notch filter

Previous configurations of continuous-time 60-Hz notch filters were difficult to integrate on a silicon chip because of the large component values required. A new method based on first-order all-pass networks has been introduced that lends itself more to integration. These networks use time constant multiplication circuitry to achieve large time constants using resistors and capacitors that can be integrated. With this new configuration, a 60-Hz notch filter with notch attenuation exceeding -60 dB can be implemented on a silicon chip.

Stereophonic signal processor

A frequency-dependent linear audio signal processor takes source signals S in input signals and provide directionally spread directionally encoded output signals. The processor directionally encodes with constant gain magnitude frequency components of the source signal S to-and-fro across a predetermined directional stage P" as frequency increases such that at least three predetermined positions within the stage P", the directional encoding has substantially zero perceived phasiness. The processor may be a frequency-dependent rotation matrix for stereo input signal and may be a unitary network using a feedback path around parallel identical all-pass networks in series with a rotation matrix and a feedforward path bypassing the all-pass networks. Successive frequencies of positioning of source signal S at a predetermined position P within the stage P" are preferably spaced approximately uniformly on a logarithmic or Bark Frequency scale. Several sources S may have individually adjustable spreads while sharing common processor.

Design of computationally efficient elliptic IIR filters with a reduced number of shift-and-add operations in multipliers

In this paper, a new design method for elliptic IIR filters that provides the implementation of half of the multiplication constants with few shifters and adders is proposed. An IIR filter, when derived by the bilinear transformation from an elliptic minimal Q-factor analog prototype, has its z-plane poles on the circle that is orthogonal to the unit circle and has the center on the real axis of the plane. Due to this property, the center of the circle can be used as a parameter for the representation of a pole, whereas the second parameter is the radius of the pole. It is shown in this paper that the center of the circle is uniquely determined by the frequency for which the filter attenuation is 3 dB. This result is used for the realization based on the parallel connection of two all-pass networks. It is shown that all second-order all-pass sections can be implemented with one common multiplication constant determined by the center of the circle. The design method is presented that, by an appropriate distribution of a margin in the filter performance, predetermines the value of the common constant according to the desired number of shift-and-add operations. This way, half of the multipliers are replaced with a limited number of shifters and adders. Conventional computer programs for IIR elliptic digital filters can be used. The direct approach for the distribution of the z-plane poles among two all-pass functions is developed. The application and efficiency of the proposed design method are demonstrated by examples.

Comparison of single- and dual-element frequencycontrol in a CCII-based sinusoidal oscillator

An active-RC oscillator which consists of two cascaded CCII-based first-order allpass networks with unity overall feedback is described. The oscillation frequency may be controlled by means of one or two grounded capacitors. Experimental results are reported which establish the relative merits of single- or dual-element control of frequency for this oscillator.

Study on a tuning-free network for the rf accelerating cavity

Applying a bridged-T type all-pass network to a resonator described as a parallel circuit, the output voltage of the resonator shows a band-pass feature over a certain frequency range, while the input impedance is always constant against frequency. This feature is considered to realize the ferrite-loaded tuning-free rf accelerating cavity. It has several merits such as a simple cavity structure without bias windings, an easy operation without feedback control of the bias current, applying new ferrite with favorable rf characteristics and so on. The accelerating system is applicable to a proton-synchrotron for radio therapy or a cooler-synchrotron for nuclear physics studies in a multi-GeV region. This paper presents a theory of the system, the characteristics of the new ferrite, which is currently developed, and design studies of the network based on preliminary measurements of an equivalent lumped circuit.

A simple technique for the design of MMIC 90° phase-difference networks

In this paper, a simple technique for the design of broadband 90/spl deg/ phase-difference networks, using balanced and unbalanced all-pass network topologies, is presented. In the developed method, the element values of the structures are calculated as function of two design variables: Q/sub 0/ and r. Utilizing this approach, a 90/spl deg/ phase shifter has been realized, having less than 2/spl deg/ phase error and better than 0.5 dB amplitude error in the operating band from 0.7 to 3.5 GHz.

EXSHOF-II: Active filter design, from approximation function to graphic display of the circuit

This paper presents an expert-system-based package for active filter synthesis, called EXSHOF-II. It starts with approximation function and ends with graphic display of the complete filter circuit. The package is an improved and enhanced version of its mother EXSHOF ( EX pert system based S ynthesis of H igh O rder F ilter). EXSHOF-II gives quantitative and qualitative help at various stages of filter design. Besides the Butterworth, Chebyshev and Elliptic functions which were considered in EXSHOF, the inverse Chebyshev function is also included in EXSHOF-II. For choosing particular approximation EXSHOF-II gives the order of the transfer function. The group delay characteristics of all four approximation functions are plotted on the screen by EXSHOF-II. This aids the user to make a proper choice of an approximation function. Like its mother, EXSHOF-II also considers four high-order structures. The filtering requirement in EXSHOF-II can be directly input on the attenuation characteristics, making the system more user-friendly. The circuit implementation has been done using nine different biquadratic active RC building blocks. The delay requirement can be easily satisfied by cascaded all-pass second-order networks.

Switched bandstop filters

AbstractA new prototype network is derived for a class of allpass networks from which, by a simple switch operation, a cascaded element bandstop filter results. an explicit solution for element values is obtained for the even‐ and odddegree solutions of arbitrary degree. the performance of various degrees is investigated and experimental results are presented for a fifth‐degree suspended substrate stripline bandstop filter operating over a narrow band at 10 GHz.

Design of digital allpass networks based on the eigenvalue problem

AbstractThis paper presents a new method of the phase design for the digital allpass network utilizing the eigenvalue problem. The proposed design method considers the phase error between the phase response of the allpass network to be realized and the ideal phase response. The design problem is formulated as an eigenvalue problem based on the Remez algorithm. By calculating the eigenvector corresponding to the maximum eigenvalue, the filter coefficients are determined and the optimal approximate solution is obtained by iterative calculation.In the design method, the eigenvector corresponding to the maximum eigenvalue is calculated to determine the filter coefficients so that the phase error is minimized. Consequently, the convergence of the design algorithm is guaranteed. Usually, the optimal approximate solution is obtained by several times of iterations. The error‐ratio of the phase characteristics can be set arbitrarily, and the stability of the filter is ensured.Finally, the method is extended to the phase design for the digital allpass network with complex coefficients, several design examples are shown, and the usefulness of the proposed design method is demonstrated.

A recursive orthogonal wavelet device

A design for a one-dimensional (1-D), 2-D recursive orthogonal wavelet consisting of a parallel connection of a delay and allpass network is presented. There have been some methods to obtain wavelet functions from perfect reconstruction filter banks following an investigation by Mallat of the relation between wavelet transform and filter banks. These methods are based mostly on an FIR filter. A method based on IIR filters has never been investigated. IIR digital filter has fewer orders than FIR digital filters to realize the same specification and satisfies the orthogonal condition of the orthogonal wavelet by using both parallel connection of some delays and an allpass filter. Furthermore, a maximum number of zeros are placed at aliasing frequencies in the lowpass filter as a way of obtaining the regularity of the wavelet. Finally, some design samples of discrete scaling and wavelet functions are presented.