A refined classification of single amplifier filters

It is shown that Single Amplifier Biquads (SAB's) may be grouped into two major categories, the Enhanced Negative Feedback (ENF) and the Enhanced Positive Feedback (EPF). These two major classes of circuit are related by the complementary transformation and hence exhibit identical sensitivity performance. In the extreme, the ENF class degenerates to the familiar Negative Feedback (NF) class while the EPF class reduces to the Positive Feedback (PF) case where the op amp is connected in a unity-gain configuration. Depending on the order of the RC feedback network, each class includes two subclasses with different sensitivity performance. The paper examines in detail the ‘enhanced feedback’ mechanism, and investigates the optimum design of the Deliyannis—Friend circuit and its complement the Sallen and Key positive feedback configuration.     

Multiloop feedback unsymmetrical active filters using quads

In this paper, a general design procedure for high order unsymmetrical active filters is presented using a special configuration of quads. Quads are 4th order subsection blocks using biquads in a special manner. It is shown that the determination of network parameters is not dependent on frequency range, and that the design procedure is simpler than other multiloop feedback (MF) topologies. The transmission zeros of the transfer function are derived directly from the zeros of the biquadratic blocks and thus feedforward or summation techniques are not required.     

Output feedback control strategy of parallel hybrid filters

In this paper, the authors propose a novel control strategy of active hybrid filters. The adopted hybrid filter consists of an active filter and a passive filter connected in parallel. The power rating of the converter is reduced compared with simple active filter. The control is introduced to allow active filtering of load harmonics and active damping of passive filter connected in parallel with the active filter. When connected in power grid, the complete system is adjusted to prevent risk of resonance as well as harmonic filtering. A complete modeling of the system is achieved using a simple structure and effective corrector is developed. An important characteristic of the proposed control scheme is that it results in a simple static output feedback controller. Complete simulation of the system validates efficiency of the control law.     

Generation and classification of single amplifier filters

A unified approach is presented for generating configurations for circuits containing one operational amplifier together with RC elements and capable of realizing a general second-order voltage transfer function. Systematic application of the generation procedure leads to various single amplifier biquads with the known circuits, as well as some new ones, obtained as special cases. The insight gained from the generalized approach as well as the results of a general sensitivity analysis (including the effects of the amplifier limited bandwidth) offer a method for categorizing and classifying single amplifier filters. The different filter classes are illustrated and compared with the aid of extensive design tables. General equations for the effect of the amplifier limited bandwidth are also given.     

Current-mode multiple-loop feedback filters using dual-output OTAs and grounded capacitors

A systematic method is presented for the generation, analysis and synthesis of current-mode continuous-time multiple-integrator-loop all-pole filters using dual-output operational transconductance amplifiers and grounded capacitors (DO-OTA-GC). The general theory based on a multiple-loop feedback model is formulated. A number of architectures including canonical realizations are developed, with particular emphasis on high-order configurations. A sensitivity analysis method is also given and parasitic effects on the structures are discussed. The general formulations are verified by direct analysis of the generated individual circuits. Design examples are also presented. © 1997 by John Wiley & Sons Ltd.     

Elimination of limit cycles in direct form digital filters using error feedback

The elimination of zero-input limit cycles in direct form filter sections using either a rounding or a magnitude truncation fixed-point quantizer is considered. the well-known criterion of Chang is reformulated for second-order filter sections in a more practical form using the bilinear transformation. This enables graphical interpretation and quantitative analysis of the possible error feedback solutions for different pole locations. The synthesis of limit-cycle-free error feedback for second-order filter sections is addressed in detail and several solutions are proposed. the error feedback coefficients are constrained to power-of-two values or to symmetric values so that the implementation is efficient, e.g. with signal processors. Different limit-cycle-free solutions are discussed with design examples and their round-off noise properties are compared. The absence of limit cycles is related to the round-off noise properties of the filter section. the main conclusion of the paper is that when the EF coefficients are appropriately chosen, low round-off noise and the absence of limit cycles can always be accomplished at the same time. A particularly close correlation between limit cycles and roundoff noise is demonstrated with a rounding quantizer: a limit-cycle-free implementation always guarantees low roundoff noise. For most complex conjugate pole locations the converse relation also holds, i.e. low round-off noise implies the absence of limit cycles.     

A family of modular fully differential witched capacitor filters for simulating ladder filters

The switched capacitor filters proposed in this paper are based on the simulation of LC ladder filters through the state variable equations. They include all-pole and finite transmission zero, lowpass filters, bandpass and highpass filters. the introduced family of filters has a fully differential structure; consequently it has the advantages of improved power supply and common mode rejection ratios and extended dynamic range. Since the proposed family of filters simulates LC ladder filters, it inherits their low passband sensitivities. One of the main advantages of this family of filters is that it has a modular structure composed of key and auxiliary circuits. This modular structure results in easier design and implementation procedures in VLSI fabrication. the double-sampling concept is applied to the introduced modular blocks, which is essentially needed in high-frequency applications. A comparison with similar published work available in the literature is presented and illustrative examples are given.     

传统LC滤波器与新型阻尼滤波器的比较

输出滤波器多采用传统的LC无阻尼滤波器,该滤波器电路结构因无阻尼,在输出端极易产生振荡分量而严重影响电器性能。阻尼滤波器由于采用改进了的电路结构:用一电容与电阻串联之后与另一电容并联构成的组合电路来取代传统LC无阻尼滤波器的滤波电容,并通过计算与计算机仿真,合理选择参数,使电路具有适当阻尼比的同时,系统损耗较小,抑制振荡效果显著,增加了系统的稳定性,改善了系统的性能。将2种滤波器利用仿真进行研究分析,用实例证明新型阻尼滤波器的有效性且电路结构简单、成本低。     

A predistortion technique for RC-active biquadratic filters

A general method of forcing the transfer function of a biquadratic active filter to have poles/zeros in the desired locations is presented. Examples of the required calculations are shown. an example predistortion of a Thomas-Tow section has been performed, and the resulting predistorted natural frequency and selectivity are presented graphically for a wide range of q-factors and amplifier gain-bandwidth products. the technique has also been applied to the point-by-point predistortion of a digitally tuneable filter. the general predistortion method has been used to obtain estimates of frequency and selectivity errors in non-predistorted filters. the expression for relative q errors agrees with previous high-q approximations of this error.     

A simplified design-oriented analysis of switched-capacitor active filters

The method presented in this paper provides a simplified approach to obtain the z-domain equivalent circuit of an SC active filter by one-for-one substitution of each basic SC element with its z-domain equivalent admittance, if a specific terminal condition is met. Then, traditional circuit analysis techniques can be used to derive the z-domain transfer function of the filter. This method makes the analysis and the design of the SC active filter simple and similar to the S-domain method. Two application examples are given.     

A control strategy for active filters using quasi‐instantaneous positive sequence extraction filters

A novel control strategy for active filters, employing quasi‐instantaneous positive sequence extraction of utility voltage, can be useful in harmonic polluted and/or imbalanced utility voltage. In this paper, the authors examined its transient response, its performance under the change of fundamental frequency of utility voltage and its performance under utility voltage with harmonics and unbalance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(1): 54–65, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10307     

A closed-loop selective harmonic compensation for active filters

This paper proposes a control algorithm for parallel active power filters, based on current-controlled pulsewidth-modulated converters, which allows precise compensation of selected harmonic currents produced by distorting loads. The approach is based on the measurement of line currents and performs the compensation of the selected harmonics using closed-loop synchronous frame controllers. Thanks to the closed-loop operation, full compensation of the desired harmonics is achieved even in the presence of a significant delay in the current control. Thanks to the selective approach, active filter interactions with possible dynamic components of the load are minimized. Moreover, the complexity of the synchronous frame controllers is overcome using equivalent stationary frame controllers. Experimental results confirm the theoretical expectations     

Acoustic-optic filters

Optical filters are an important building block in the next generation of optical communication systems. Optical networks seem to be headed towards densely packed wavelength-division multiplexing (WDM) systems. These WDM systems require optical filters for the purpose of wavelength selection and switching. Numerous optical filters have been proposed including acousto-optical filters, electro-optical filters, and Fabry-Perots. Acoustically tunable optical filters (ATOFs) are considered promising. ATOFs are not only an important WDM device; they have great potential in many other applications such as optical spectroscopy. The acousto-optic tunable filter has a unique combination of desirable properties. These properties make it a potentially important building block     

A novel representation for two-pole feedback amplifiers

A novel representation of the response of two-pole feedback amplifiers is discussed which is useful both for pedagogical and design purposes. The presented approach allows the parameters of an open-loop amplifier to be appropriately related to the closed-loop requirements such as bandwidth and settling time     

A class of digitally programmable nth‐order filters

A family of new high‐order filters capable of providing all filter functions without changing the circuit topology is proposed for integrated circuit applications. The proposed filters are based on simple active elements, namely, digitally controlled current amplifiers (DCCAs) and unity gain voltage buffers (VBs). Gains of DCCAs are digitally programmed to adjust the coefficients of transfer functions. R2R ladders are also utilized to increase the tuning flexibility of the proposed filters. A filter replicating the famous KHN biquad is extended to realize general nth‐order filters. Comparison with the recent works shows that the proposed approach results in more efficient realizations compared with its counterparts based on other current‐mode active elements. Experimental results obtained from a fourth‐order filter implemented using devices fabricated in a 0.35‐µm CMOS process are provided. Copyright © 2011 John Wiley & Sons, Ltd.     

A simple derivation of the spectral transformations for IIR filters

A simple method is given for deriving the spectral transformations for infinite-impulse response (IIR) filters, which can be used to transform a prototype low-pass (LP) digital filter to another LP, high-pass (HP), bandpass (BP), or band-stop (BS) digital filter with prescribed passband edge(s) and the same tolerances as those of the prototype. The method is based on a combination of bilinear transformation with the analog frequency transformation and is simpler-conceptually, as well as from the calculation point of view-than the conventional method based on all-pass transformation functions.