## 1 Introduction  
After discovery of first and very simple fully analog chaotic system, famous Chua's oscillator, both theoretical and practical significance of research focused on the nonlinear dynamics and chaos theory has been recognized immediately. The mentioned Chua's circuit was thoroughly studied from the viewpoint of many aspects such as mechanism behind generation of strange attractors [1], geometrical interpretation of vector field [2], circuits topologically conjugated to original oscillator [3], practical implementation using modern active elements [4], and new chaos-based modulation and communication techniques [5], etc. After discovery of iconic Chua's circuit, in nearly four subsequent decades, many chaotic dynamical systems were discovered; either accidentally, during numerical investigation of mathematical model associated with real physical phenomenon, or by using numerical algorithms dedicated for chaos localization. For the latter case, fitness function could be considered as topology of evolved state attractors [6], set of one-dimensional Lyapunov exponents (LE) [7], or another. Irregular motions known as chaos and hyperchaos have several unique properties: the wideband continuous spectrum, with sensitivity to the tiny changes of the initial conditions, exhibits dense state attractors with non-integer geometrical dimension, and generated signals have increased entropy. Importantly, these kinds of behavior are not restricted to complex electronic systems and algebraically complicated dynamical flows. For example, paper [8] shows that the inductor can be removed from the circuit structure of [PERSON]'s oscillator and chaos can be generated by a fully passive ladder network composed by resistors and capacitors terminated by two-terminal piecewise-linear active resistor. Compared to that, the interesting cookbook [9] proposes methodology how to easily implement chaotic oscillators with the passive only nonlinear elements. Chaotic oscillators defined by jerk functions can be also designed by looping a low-pass frequency filter of arbitrary topology and active two-port with the prescribed polynomial transfer function [10]. Another design method is based on adopting of well-known structure of the harmonic oscillator where single nonlinear circuit component is suitably placed. For oscillator containing Wien-bridge feedback, this fact is demonstrated in several papers, such as [11]. The conventional structure of this oscillator can be made special by adopting mem-element, fractional-order device, or both [12]. Another circuit examples that show chaotic regimes of naturally harmonic oscillator can be found in paper [13; 14]. There, the so-called Colpitts and Hartley single active element-based oscillator has been addressed, respectively. Currently, the design of lumped chaotic circuits is a mature and well-established problem. To date, tens of lumped analog chaotic circuits were constructed, and existence of structurally stable chaotic behavior verified by computer-aided simulations in the time-domain or, more preferably, via laboratory measurement. Let's discuss few published examples of chaotic systems. Fully CMOS implementation of [PERSON]'s oscillator with memristor is described in this research paper [15]. Universal and straightforward design methods toward chaotic systems are presented in [16] for voltage-mode and in [17] for current-mode and mixed-mode oscillators. Both mentioned papers assume that describing set of differential equations are known. Analog computers belong to the most preferred approaches on how to design chaotic electronic systems. The application of this method is used in age-old as well as recent papers, like the work of [18] where a strongly nonlinear vector field must be implemented, or in paper [19] where the quantity detected by the inductive sensor influences the chaotic nature of the proposed circuit.