Current difference buffered amplifier (CDBA) based universal inverse filter configuration is proposed. The topology can be used to synthesize inverse low-pass (ILP), inverse high-pass (IHP), inverse band-pass (IBP), inverse band-reject (IBR), and inverse all-pass filter functions with appropriate admittance choices. Workability of the proposed universal inverse filter configuration is demonstrated through PSPICE simulations for which CDBA is realized using current feedback operational amplifier (CFOA). The simulation results are found in close agreement with the theoretical results. 1. Introduction Inverse filters are commonly used in communication [1], speech processing, audio and acoustic systems [2, 3], and instrumentation [4] to reverse the distortion of the signal incurred due to signal processing and transmission. The transfer characteristics of the system that caused the distortion should be known a priori and the inverse filter to be used should have a reciprocal transfer characteristic so as to result in an undistorted desired signal. Literature review on inverse filter suggests that numerous well-established [5] methods for digital inverse filter design do exist but analog inverse filter design remained unexplored area as is evident from the limited availability of analog inverse filter circuits/design methods [6–14] until recently. However recent research trend suggests that the area is now gaining a renewed interest. A brief account of the complete literature on analog inverse filter is presented here. Reference [6] presents a general method for obtaining the inverse transfer function for linear dynamic systems and the inverse transfer characteristic for nonlinear resistive circuits using nullors. The realization procedures for the current-mode FTFN-based inverse filters from the voltage-mode op-amp-based RC filters are presented in [7, 8]. The procedure outlined in [7] is applicable to planar circuits only as it uses RC？:？CR dual transformation, whereas the method presented in [8] makes use of adjoint transformation and thus is applicable to nonplanar circuits [12]. Single FTFN based inverse filters proposed in [9–12] present inverse filters using current feedback operational amplifier (CFOA). All the circuits presented in [10, 11] provide single inverse filter function; however [12] presents a topology which can realize inverse low-pass (ILP), inverse high-pass (IHP), and inverse band-pass (IBP) filter functions by appropriate admittance choice. In [13, 14] inverse all-pass (IAP) filters have been implemented using current difference
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