Abstract
This paper traces the history of the evolution of inverse analog filters (IAF) and presents a review of the progress made in this area to date. The paper, thus, presents the current state-of-the art of IAFs by providing an appraisal of a variety of realizations of IAFs using commercially available active building blocks (ABB), such as operational amplifiers (Op-amp), operational transconductance amplifiers (OTA), current conveyors (CC) and current feedback operational amplifiers (CFOA) as well as those realized with newer active building blocks of more recent origin, such as operational transresistance amplifiers (OTRA), current differencing buffered amplifiers (CDBA) and variants of current conveyors which, although not available as off-the-shelf ICs yet, can be implemented as complementary metal–oxide–semiconductors (CMOS) or be realized in discrete form using other commercially available integrated circuits (IC). In the end, some issues related to IAFs have been highlighted which need further investigation.
Highlights
History, Progress and UnresolvedOver the last twenty-five years, there has been considerable interest and research effort in the technical literature on the circuit realizations of inverse analog filters
Subsequent to the publication of [1], a number of authors have come up with various kinds of circuits for realizing inverse analog filters (IAF) [7–43] using a variety of active building blocks such as the four-terminal floating nullors (FTFN) [44,45], operational transconductance amplifiers (OTA) [46], current conveyors [47,48] and their many variants such as differential difference current conveyors (DDCC), second generation voltage conveyors (VCII), current feedback operational amplifiers (CFOA) [49], operational transresistance amplifiers (OTRA) [50], current differencing buffered amplifiers (CDBA) [51], current differencing transconductance amplifiers (CDTA) [52], voltage differencing transconductance amplifiers (VDTA) [53], etc
The signifThe physical meaning of the parameters H0, Q0 and ω0 is clear in the context of icance of the various coefficients of the inverse transfer functions and their influence on normal low-pass (LP) and high-pass (HP) filters, and that of H0, ω0 /Q0 (BW) and ω0 is the shapes of the corresponding frequency responses does not appear to have been elabalso clear in the case of normal band-pass (BP) and band reject (BR) filters
Summary
Over the last twenty-five years, there has been considerable interest and research effort in the technical literature on the circuit realizations of inverse analog filters. In many areas such as communication, control and instrumentation, inverse filters may be required to correct the distortions of the signals caused by the signal processors. 2. The Transfer Functions of Inverse Filters, Their Frequency Responses, the Significance of the Various Parameters and the Stability Issues. Attempt to provide the significance of the various parameters H0 , ω0 and Q0 on the shape of the frequency responses.ofWe comment upon the stability issues related toofthe
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