Low Passband Sensitivity Research Articles

Robust Digital Filter Structures: A Direct Approach

One of the many contributions of Prof. Fettweis was the invention of wave digital filters. These filters are obtained from classical RLC filters, in particular doubly terminated lossless two-ports, by using some transformations. Namely, the voltages and currents in the circuit elements are transformed into wave-variables and then a bilinear transformation is performed. If the wave transformation is performed appropriately it results in a realizable digital filter structure which furthermore enjoys a number of robustness properties such as low passband sensitivity, low roundoff noise, and freedom from limit cycle oscillations. Prof. Fettweis and his colleagues also showed that these properties are due to the inheritence of passivity properties from the continuous-time domain into the digital filter domain. Subsequent to this landmark work, a number of researchers worked on the problem of obtaining robust digital filter structures without starting from continuoustime circuits. One of these is the structurally bounded or structurally passive class of digital filters. These structures are based on inducing structural passivity directly into the implementation and are therefore simpler, both conceptually and from a practical viewpoint. They are also more general and lead to new structures which have no natural connection to electrical circuits. This paper gives an overview of some of these developments.

A Multipurpose PV System Integrated to a Three-Phase Distribution System Using an LWDF-Based Approach

This paper presents a multipurpose photovoltaic (PV) system using a lattice wave digital filter (LWDF)-based control approach. The multipurpose PV system is developed for integrating the active power to the distribution system with variable PV insolation and compensating the nonlinear loads connected at point-of-common coupling. The PV system is multifunctional; therefore, it serves various purposes. It injects the active power of solar PV array to the grid. It mitigates harmonics of loads and provides grid currents balancing. The PV system incorporates a PV array, a boost converter, a voltage-source converter (VSC), a nonlinear load, and a distribution system. The boost converter is utilized for maximum power extraction from PV array using an incremental-conductance-based maximum power point tracking technique. To control the grid-tied VSC, a LWDF-based control approach is proposed. In addition, this approach is able to produce the desired sinusoidal fundamental component of load current to estimate the grid reference currents. The aim is to implement this control as it has many properties like low-pass band sensitivity, good dynamic response, and reduction in a dc-offset noise error. The varieties of experimental results are presented to validate the control of a PV system.

New adaptive complex IIR filters and their application in OFDM systems

In this article, very low sensitivity variable complex filter (VCF) sections are developed. They have two important advantages: extremely low passband sensitivity and independent tuning of the bandwidth and the central frequency over a wide frequency range. The first advantage provides resistance to quantization effects, while the second one gives a better digital signal processing quality and extends the area of possible applications of the developed filters. Based on the proposed VCF sections an adaptive complex system is designed which demonstrates very fast convergence and low computational complexity. This system is applied for narrowband interference cancellation in multiband orthogonal frequency division multiplexing receivers and wideband noise cancellation in OFDM receivers. It is experimentally verified that a better signal-to-noise ratio and signal-to-interference ratio can be achieved using the proposed adaptive complex filtering scheme.

Ladder derived switched-current decimators and interpolators

Switched-current elliptic decimators and interpolators based on bilinear-transformed low-sensitivity ladder structures are proposed. The combination of polyphase networks and doubly terminated ladder structures preserve low passband sensitivity and maximizes time for settling by operating at the lower sampling frequency. The decimators are derived via a z-domain multirate transformation procedure. Two different types of decimator architectures, finite-impulse response (FIR)-infinite-impulse response (IIR) cascade (FIC) and multiple feed-in (MFI) are presented and compared. The complementary IIR-FIR cascade (IFC) and multiple feed-out (MFO) interpolator structures are obtained by direct transposition, which avoids the need for redesign. A third-order elliptic low pass filter is used as prototype for deriving the decimators and interpolators. The circuits are verified by SCNAP4 and HSPICE simulations.

Feasible designs for high order switched-current filters

Fully balanced Euler integrators featuring S/sup 2/I cells and common-mode rejection are used to realise ladder derived switched-current filters, based on modified left- and right-decomposition matrix methods. The usual problems of large silicon area, high sensitivity and component spreads, encountered in very high order designs, are overcome by minimising the input circuitry and by adopting modified approximation and prototype ladder manipulation techniques. The example of a 6th order modified left-UL bandpass filter demonstrates improved sensitivity, and a 21st order elliptic lowpass filter achieves a spread of 13.63, while preserving low passband sensitivity.

Ladder decompositions for wideband SI filter applications

Methods for designing switched-current ladder filters for wideband applications are presented. By performing UL-LU and LU-UL decompositions on the z-domain matrix description of a bilinear transformed passive ladder, filter structures are derived which preserve low passband sensitivity even for large relative bandwidths. Derivation procedures are outlined and illustrated by the example of a 5th order lowpass UL-LU filter and a 10th order LU-UL bandpass. The switched-current filters are realised using Euler-type integrators based on S3I cells. A comparison of the properties of different structures demonstrate the advantages of the UL-LU and LU-UL methods.

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

AbstractThe 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.

A new family of biquads with applications to MOSFET-C filters

A new family of RC-active biquadratic building blocks are proposed in this communication. These biquads are especially designed for MOSFET-C applications, since they achieve a complete MOS nonlinearity cancellation. The proposed circuits can realize all the generic transfer functions such as lowpass, highpass, bandpass, band-rejection, and allpass. They also enjoy low passband sensitivities with respect to passive elements. The gain-bandwidth product-sensitivity is investigated too. An example of a high Q-bandpass filter is given with its Monte-Carlo simulation to verify its sensitivity performance.

Proposed MOSFET-C continuous time biquadratic building blocks with high-order implementation

Abstract A novel family of MOSFET-C continuous-time biquadratic building blocks is proposed in this paper. The proposed family realizes all generic transfer functions such as lowpass, highpass, bandpass, band rejection, and allpass. It achieves a complete MOS non-linearity cancellation and does not require the use of fully balanced op.-amps. The proposed blocks enjoy low passband sensitivities. A Monte Carlo analysis was done to verify the sensitivity performance. An example of bandpass filter with comparative study is given. The maximum dynamic range is adjusted using SPICE. All the design steps are matched with the 3.5 μm CMOS design rules. Then the proposed biquads are implemented to realize a transmission zeros bandpass filter of twelfth order.

Brief communication, Novel drift-free fully differential switched capacitor filter based on the simulation of ladder structures

A novel fully differential drift-free switched capacitor (SC) filter is introduced in this paper. The proposed structure is based on the synthesis of the state variable equations that describe LC ladder filters. Consequently the proposed fully differential SC filter enjoys the low pass-band sensitivities inherited from the simulation of LC-ladder structures, in addition to acquiring the advantages of fully differential circuits.

Bounded Complex and Lossless Bounded Complex Transfer Functions and their Applications

The concepts of structural boundedness and structural losslessness are known to be the keys behind the realization of low passband sensitivity digital filters implemented using real arithmetic. A generalization of these concepts leads to bounded complex and lossless bounded complex transfer functions, which are shown to play a similar role in the realization of low passband sensitivity digital filters with complex coefficients. Various filter realization strategies are pointed out, which involve the interconnection of complex lossless building blocks, thereby assuring the structural passivity property in the realization. Some design examples are included to verify the low sensitivity properties.

Very low sensitivity realization of IIR digital filters using a cascade of complex all-pass structures

A new realization of recursive digital filters based on a cascade of complex all-pass structures is proposed. The cascade realization ensures low stopband sensitivity, whereas the all-pass sections, being structurally bounded, guarantee low passband sensitivity. The proposed structure can exactly realize any elliptic transfer function, and it is easy to derive the multiplier coefficients associated with this structure from the original transfer function expression. To reduce the computational complexity, some of the coefficients are rounded to integer values and an optimum approximation to the original transfer function is obtained by using a minimax optimization procedure. Several examples show that the proposed structure requires significantly fewer bits than other known cascade-form realizations. Another advantage of the proposed structure is that it is free of overflow oscillations.

Generalized approach to sampling rate alteration in wave digital filters

Generalized arrangements (wave-flow diagrams) for sampling rate alteration in wave digital filters (WDFs) are proposed and analyzed. By this new approach, the number of degrees of freedom of the resulting so-called multirate WDF is not reduced in relation to that of the reference circuit. Advantages of the earlier multirate WDF's, such as improved loss performake for a given filter structure, increased dynamic range, and low passband sensitivity for coefficients, are preserved. Necessary and sufficient realiiability conditions for the generalized multirate WDF's are also presented. It is assumed that the reference filter is lossless, reciprocal, and rational in its complex frequency 4. An example of a fifth-order WDF for sampling rate increase is given.

Design of doubly-complementary IIR digital filters using a single complex allpass filter, with multirate applications

It is shown that a large class of real-coefficient doubly-complementary IIR transfer function pairs can be implemented by means of a single complex allpass filter. For a real input sequence, the real part of the output sequence corresponds to the output of one of the transfer functions <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G(z)</tex> (for example, lowpass), whereas the imaginary part of the output sequence corresponds to its "complementary" filter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H(z)</tex> (for example, highpass). The resulting implementation is structurally lossless, and hence the implementations of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G(z)</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H(z)</tex> have very low passband sensitivity. Numerical design examples are included, and a typical numerical example shows that the new implementation with 4 bits per multiplier is considerably better than a direct form implementation with 9 bits per multiplier. Multirate filter bank applications (quadrature mirror filtering) are outlined.

Switched capacitor filters with a row dominant nodal admittance matrix

AbstractStray capacitance insensitive switched capacitor filters are studied, whose nodal admittance matrix is row‐dominant for arbitrary capacitor values. Such filters have low passband sensitivities, because their transfer function is intrinsically bounded by 1, as is the case for LC‐filters. Furthermore, row‐dominant filters have the additional advantage that internal voltages are bounded by one, and reach this bound at each attenuation zero, which ensures optimal dynamic range. However, we show that the attenuation zeros of row‐dominant filters are located at the frequencies z2 with (z2)m = 1, where m is smaller than or equal to the number of operational amplifiers. Therefore, such filters are not suitable for conventional filter applications. Two examples of such filters are given.

A new approach to the realization of low-sensitivity IIR digital filters

A new implementation of an IIR digital filter transfer function is presented that is structurally passive and, hence, has extremely low pass-band sensitivity. The structure is based on a simple parallel interconnection of two all-pass sections, with each section implemented in a structurally lossless manner. The structure shares a number of properties in common with wave lattice digital filters. Computer simulation results verifying the low-sensitivity feature are included, along with results on roundoff noise/dynamic range interaction. A large number of alternatives is available for the implementation of the all-pass sections, giving rise to the well-known wave lattice digital filters as a specific instance of the implementation.

Optimal design of linear phase FIR digital filters with very flat passbands and equiripple stopbands

A new technique is presented for the design of digital FIR filters, with a prescribed degree of flatness in the passband, and a prescribed (equiripple) attenuation in the stopband. The design is based entirely on an appropriate use of the well-known Reméz-exchange algorithm for the design of weighted Chebyshev FIR filters. The extreme versatility of this algorithm is combined with certain "maximally flat" FIR filter building blocks, in order to generate a wide family of filters. The design technique directly leads to structures that have low passband sensitivity properties.

Flowgraph synthesis of Darlington - Cauer switched- capacitor filters

The Darlington-Cauer method of transfer function synthesis is proposed for the exact realization of low passband sensitivity SC filters directly from z -domain specifications. The Darlington-Cauer technique is unattractive for passive realizations due to its reliance upon ideal transformers; however, such elements are simple to realize in SC form. The resulting circuits are completely parasitic free. The use of balanced output operational amplifiers results in an economical realization.

Very low sensitivity FIR filter implementation using 'structural passivity' concept

The concept of structurally bounded or structurally FIR filter implementation is introduced, as a means of achieving very low passband sensitivities. The resulting filter structures, called FIRBR structures, can easily be transformed into very low-sensitivity passive two-dimensional FIR filter structures. From a layout point of view, the new structures are not any more complicated than the well-known cascade form. The FIRBR structures do not depend, for synthesis, upon continuous-time filter circuits.

Passivity properties of low-sensitivity digital filter structures

A general representation of a class of low passband sensitivity digital filter structures is proposed. The proposed representation for a transfer function of order <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> consists of an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(N + 1)</tex> -pair memoryless system terminated at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> -pairs by delays. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(N + 1)</tex> -pair system contains only adders and multipliers, and is described by an orthogonal transfer matrix. The set of terminating delays can be looked upon as an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</tex> -pair system with transfer matrix <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">z^{-1}{\bf 1}</tex> . Certain wave digital filter structures, Gray-Markel lattice structures and the coupled-form biquadratic section belong to the general form advanced here. Several properties satisfied in these special cases are derived in a unified manner using the generalized representation. Also, a quantization scheme that makes the structure free from zero-input limit cycles even under time-varying conditions is advanced, unifying similar such results independently reported for the above well-known structures.