Umesh Kumar

On the importance, realisation, experimental verification and measurements of active-R and active-C filters

Abstract Active-R filters are an offshoot of active-RC filters where the internal dynamics of an operational amplifier (OA) is employed in the elimination of external capacitors with several significant advantages. Some advanced level active-R topologies are discussed from the design point of view and in terms of greater flexibility over filter parameters. A few filter circuits are designed and their performance experimentally verified. Components simulation by an OA: R method is also performed and tested. A technique for realisation of a 20 A biquad is used to generate different types of filter functions which are experimentally verified. To overcome the difficulties of switched capacitor filters, a design method avoiding these but retaining the advantages of monolithic implementation with filter parameters set by ratios of capacitors, is used and termed active-C filters. Experimental verifications and measurements on designed active-C filters are presented.

Sterically hindered selenoether ligands: palladium(II) complexes as catalytic activators for Suzuki–Miyaura coupling

2-Hydroxy/(benzyloxy)-3,5-di-tert-butyl benzaldehyde reacts with PhSeCH2CH2NH2 resulting in a sterically hindered selenoether ligand (Schiff base) [2–HO–3,5–(C(CH3)3)2–C6H2–CN–(CH2)2SePh] (L1)/[2–PhCH2O–3,5–(C(CH3)3)2–C6H2–CH2–NH–(CH2)2SePh] (L2). The reactions of L1 and L2 with Na2PdCl4 in methanol and acetone–water mixture at room temperature have resulted in complexes [PdCl (L1-H)] (1) and [PdCl2(L2)] (2)], respectively. Both the complexes and their ligands have been characterized with 1H, 13C{1H} and 77Se{1H} NMR spectroscopy. The molecular structures of complexes 1 and 2 have been determined with single crystal X-ray diffraction. The Pd–Se bond lengths in 1 and 2 are 2.370(1) and 2.366(1) A, respectively. The geometry around palladium in both the complexes is nearly square planar. Complexes 1 and 2 (0.1 mol% Pd) have been found efficient as catalysts for Suzuki–Miyaura C–C coupling reactions in the presence of K2CO3 in ethanol. The catalysis in water with complex 1 in the presence of K2CO3 was found feasible but with low conversion (up to 40%). The efficiency of 1 in carrying out the coupling is marginally better than that of 2.

A New High Performance Realization of Hyperchaotic Modified Canonical Chua Circuit Using JFETs

A new implementation of hyperchaotic modified canonical Chua circuit using junction field-effect transistors (JFETs) is proposed. The design is based on a source coupled JFET circuit to approximate a smooth cubic non-linearity and a two-terminal negative resistance element containing a p-n-p silicon transistor and an n-channel JFET. The realization is supported by Orcad Pspice simulation and numerical MATLAB results. The hyper-chaotic nature is confirmed by two positive Lyapunov exponents associated with the attractor which is a fractal with a Lyapunov dimension between 3 and 4.

High‐performance ac preamplifier

A simple bandpass amplifier is presented which exhibits a very high gain, selectivity, and input impedance. The amplifier has a very narrow bandwidth and a high Q factor.