Browsing by Author "Danchev V.I."

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    Master equation for operational amplifiers: Stability of negative differential converters, crossover frequency and pass-bandwidth
    (2019-02-26) Mishonov T.M.; Stefanov A.A.; Petkov E.G.; Dimitrova I.M.; Danchev V.I.; Varonov A.M.
    The well forgotten master equation from the seminal article by Ragazzini, Randall and Russell [J. R. Ragazzini, R. H. Randall and F. A. Russell, ``Analysis of Problems in Dynamics by Electronic Circuits``, Proc. of the I.R.E., 35, pp. 11-19, (1947)] is recovered as indispensable tool for the analysis of contemporary circuits with operational amplifiers. This equation gives the relation between time dependent the output voltage U 0 (t) and the difference between the input voltages (U + (t) and U - (t)). The crossover frequency f 0 parameterizes the time constant τ 0 of this equation. The work of the master equation is illustrated by two typical examples: a) the stability criterion of the devices with negative impedance converters, which we consider as a new result b) the frequency dependence of the amplifiers with operational amplifiers given in the technical specifications. A simple circuit for determination of f 0 is suggested and the method is illustrated by determination of crossover frequency for the low-noise and high speed ADA4898 operational amplifier. It is concluded that for an exact calculation of the pass bandwidth of amplifiers with active filters the 70 years old master equation is indispensable.
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    Master equation for operational amplifiers: Stability of negative differential converters, crossover frequency and pass-bandwidth
    (2019-03-01) Mishonov T.M.; Danchev V.I.; Petkov E.G.; Gourev V.N.; Dimitrova I.M.; Serafimov N.S.; Stefanov A.A.; Varonov A.M.
    The time dependent master equation from the seminal article by Ragazzini, Randall and Russell (Ragazzini et al 1947 Proc. of the I.R.E. 35, 444–452) is recovered as a necessary tool for the analysis of contemporary circuits with operational amplifiers. This equation gives the relation between time dependent the output voltage U0(t) and the difference between the input voltages (U+(t ) and U-(t )). The crossover frequency f0 is represented with the time constant τ in this equation. The work of the 0 master equation is illustrated by two typical examples: a) the stability criterion of the devices with negative impedance converters, which we consider as a new result b) the frequency dependence of the amplifiers with operational amplifiers given in the technical specifications without citations of the time dependent equation. A simple circuit for determination of f0 is suggested and the method is illustrated by determination of crossover frequency for the low-noise and high speed ADA4898 operational amplifier. It is concluded that for an exact calculation of the pass bandwidth of amplifiers with active filters the 70 years old master equation is a useful technique implicitly included in the contemporary software. The frequency dependent formulae for the amplification coefficient of inverting and non-inverting amplifiers are given for the case of non-zero conductivity between the inputs of the operational amplifiers.
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    Simple do-it-yourself experimental set-up for electron charge qe measurement
    (2018-08-29) Mishonov T.M.; Petkov E.G.; Mihailova N.Z.; Stefanov A.A.; Dimitrova I.M.; Gourev V.N.; Serafimov N.S.; Danchev V.I.; Varonov A.M.
    A simple experiment for the electron charge q e measurement is described. The experimental set-up contains standard electronic equipment only and can be built in every high-school lab all around the world with several days' pocket money budget. It is concluded that it is time such a practice should be included in regular high-school education. The achieved 13% accuracy is comparable to the best student university labs. The measurement is based on Schottky noise generated by a photodiode. Using a criterion of dollar-per-accuracy for the electron charge q e measurement, this is definitely the world's best educational experiment. An industrial replica can easily be sold across the globe.