The Nonlinear Distortions in the Oscillatory System of Generator on CFOA

In recent years, many articles came out where one could find the analysis of oscillatory systems of electric sinusoid signals generators with amplifiers called CFOA—current feedback operational amplifiers. As a rule, the analysis of such systems is made by applying mathematical modeling methods on the basis of the amplifier linear model, which does not allow estimating advantages and disadvantages of the systems realized with those amplifiers in comparison with classical systems. A nonlinear model of a current feedback operational amplifier (CFOA) is introduced in the paper; nonlinearity of “current mirror” is reflected in the form of current double limiting. The analysis of two known oscillatory systems has been carried out with the use of this non-linear model. Dependence between current limiting level, output voltage amplitude, and maximum oscillation frequency has been obtained. The paper shows that output current limiting under current output connection of capacitive load reduces frequency range and output voltage amplitude considerably and increases harmonic distortions in comparison with classical oscillatory systems. The research done has found that the application of new amplifiers does not give considerable advantages to the oscillatory systems with CFOA. 1. Introduction In the end of the last century a new operational amplifier in the monolithic form appeared in the market of electronic components. Its distinctive features, in comparison with traditional operational amplifiers, were inverting input with low input resistance, additional output with high output resistance, frequency range extension, and very fast large signal response. The amplifier was called a current feedback operational amplifier (CFOA). Typically, these amplifiers perform on the complementary bipolar technology on heterogeneous symmetric p-n-p and n-p-n transistors. Many companies have developed the manufacture of the amplifiers. The examples of the amplifiers are AD844, OPA622, and others. The description of the circuit technology of the new amplifiers is given in the materials of manufacturing companies [1, 2]. There is a detailed description of AD844 amplifier (Rybin [3]). Naturally, such amplifiers provoked great interest amidst developers of electronic devices, for example, oscillatory systems (OSs) of electric signals generators. Many works came out where different variants of OS of sinusoid oscillations were given (Abuelma’ atti [4, 5], Abuelma’ atti and Al-Shahrani [6], Soliman [7, 8], and Martínez et al. [9].) There one could find the analysis of conditions of