Costas Psychalinos

0.5-V fractional-order companding filters

Novel configurations of fractional-order filter topologies, realized through the employment of the concept of companding filtering, are introduced in this paper. As a first step, the design procedure is presented in a systematic algorithmic way, while in the next step, the basic building blocks of sinh-domain and log-domain integrators are presented. Because of the employment of metal-oxide-semiconductor MOS transistors operated in the subthreshold region, the derived filter structures offer the capability for operation in an ultra-low-voltage environment. In addition, because of the offered resistorless realizations, the proposed topologies are reconfigurable, in the sense that the order of the filter could be chosen through appropriate bias current sources. The performance of the derived fractional-order filters has been evaluated through simulation and comparison results using the Analog Design Environment of the Cadence software and MOS transistor parameters provided by the Taiwan Semiconductor Manufacturing Company TSMC 180-nm complementary MOS CMOS process. Copyright

Fractional-order filters based on low-voltage DDCCs

This paper presents the design and implementation of fractional-order filters based on promising CMOS structure of Differential Difference Current Conveyor (DDCC), which was designed and fabricated using the 0.35µm CMOS AMIS process. The derivation of the filters has been achieved using a second-order approximation of the corresponding fractional-order transfer functions. The filters offer the benefit of low-voltage (?500mV) operation as well as the requirement of grounded passive elements. In addition, a technique for the quick derivation of high-order filters has been introduced. The simulation and experimental results prove the attractive performances of the proposed filters.

Multiple Input Single Output Universal Biquad Filter with Current Feedback Operational Amplifiers

A novel Multiple Input Single Output (MISO) universal biquad filter topology realized using Current Feedback Operational Amplifiers (CFOAs) is introduced in this paper. With regards to the corresponding already published MISO universal biquads with CFOAs, the proposed topology simultaneously offers the benefits of employing only grounded capacitors, absence of any imposed constraint related to the values of input signals, and orthogonal adjustment between the quality factor and resonant frequency of the filter. The operation of the proposed biquad has been verified through experimental results by utilizing the commercially available AD844 CFOA discrete component.

Harmonic oscillators realized using current amplifiers and grounded capacitors

New configurations of harmonic oscillators, realized using current amplifier blocks and only grounded capacitors, are introduced in this article. The proposed configurations are based on a grounded inductor simulator scheme and on a loop constructed from first-order sections, respectively. Comparison with the already published topologies shows that the new configurations have attractive characteristics concerning their implementation in integrated form. Copyright

Realization of log-domain high-order transfer functions using first-order building blocks and complementary operators

High-order log-domain filters could be easily designed by using the functional block diagram (FBD) representation of the corresponding linear prototype and a set of complementary operators. For this purpose, lossy and lossless integrator blocks have been already introduced in the literature. Novel first-order log-domain highpass and allpass filter configurations, which are fully compatible with the already published integrator blocks, are introduced in this paper. These are realized using integration and subtraction blocks or a novel differentiation configuration. As a result, a complete set of first-order building blocks would be available for synthesizing any arbitrary high-order transfer function. In order to verify the correct operation of the proposed structures, the performance of the introduced highpass filters was evaluated through simulation results. In addition, a fifth-order log-domain bandpass filter was designed and simulated using one of the introduced first-order highpass filter configurations. Copyright

Low-Voltage Log-Domain Complex Filters

Two systematic methods for designing low-voltage log-domain complex filters are introduced in this paper. The first one is based on the transposition of the signal flow graph representation of the linear-domain complex leapfrog prototype filter to the corresponding one in the log-domain. The last one is based on the transposition of the wave equivalents of the elements of the complex passive prototype filter to the corresponding log-domain complex equivalents. Both transpositions are performed by employing an appropriate set of complementary operators that facilitates the derivation of low-voltage log-domain filter configurations. Two design examples are given, where a 12th-order log-domain complex transfer function is realized in order to fulfill the Bluetooth specifications. The derived log-domain filter structures operate at a single 1.2-V-power supply-voltage, and their behavior was evaluated through simulation results. In addition, a comparison concerning important quality factors of both of the proposed structures is performed, and the obtained results are further discussed.

Log-domain wave filters

A systematic method for designing log-domain wave filters is presented. Wave filters simulate topologically and functionally passive doubly terminated LC ladder prototype filters of low sensitivity. The design in the log-domain is based on a transposition of the signal flow graph (SFG) that corresponds to the wave equivalent of elementary two-port blocks in the linear domain, to the corresponding log-domain SFG. This is achieved by using an appropriate set of complementary operators, in order to preserve the linear operation of the whole circuit. Simulation results of a fifth-order low-pass and a fourth-order bandpass log-domain wave filter are given, using HSPICE. The proposed circuits are suitable for low-voltage operation and in high-frequency applications.

Design of Sinh-Domain filters using complementary operators

A new systematic method for designing Sinh-Domain filters is introduced in this paper. This is achieved by employing an appropriate set of complementary operators, in order to transpose the conventional functional block diagram representation of each linear operation to the corresponding one into the Sinh-Domain. The proposed method offers the benefits of facilitating the design procedure of high-order Sinh-Domain filters and of the absence of any restriction concerning the type and/or the order of the realized filter function. As an example, a third-order Sinh-Domain leapfrog filter is designed by employing the proposed set of operators. Two possible realizations are given and their performance has been evaluated and compared through simulation results. Copyright

Log-domain filtering by simulating the topology of passive prototypes

A systematic method for designing log-domain filter structures that simulate the topology of the corresponding passive prototypes is introduced in this paper. This has been achieved by transposing the i-/spl upsi/ characteristic equation of each passive element in the linear domain, to the corresponding one in the log domain. The transposition has been done in such a way that, the current that flows through the terminals of the passive element in the linear domain sustains its value in the corresponding log-domain configuration. In this way the linear operation of the whole filter is preserved. With regard to the voltage at each terminal of the passive prototype, this is logarithmically compressed in order to achieve filtering in the log domain. Following the above considerations, the log-domain equivalents of all passive elements of the prototype filter were derived. Having established the equivalents, the procedure for designing high-order log-domain filters is quite facilitated. The validity of the proposed technique is demonstrated through simulation results for a fifth-order elliptic low-pass filter.

Modular log-domain filters realized using wave port terminators

Log-domain wave filters that simulate the passive LC ladder prototype filters are introduced in this paper. The proposed circuits are constructed from the wave equivalents of the reactive elements corresponding to those in the prototype circuit. The wave equivalent circuits are obtained by using a novel log-domain wave port terminator. The wave equivalent of a capacitor in a shunt branch was chosen as an elementary building block for creating high-order filters. The wave equivalent circuits of all other reactive elements in a shunt or in a series-branch connection can be readily obtained using the elementary building block plus some inverters. This way the derived high-order filter configurations are modular. A design example of a third-order elliptic low-pass filter is given, and the performance of the filter was verified by simulation.