A digital-analog hybrid random number generator based on memristor
Authors: Yuan Ze-Shi  , Li Hong-Tao  , Zhu Xiao-Hua  ,   School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Published: December 2020

Random number generator (RNG) plays an important role in many areas including image encryption, secure communication, radar waveform generation, etc. However, existing analog methods for random number (RN) cannot satisfy the demand of bit rate. In the even worse case, system parameters from analog devices are easily distorted by surroundings, leading to a weak system robustness. As a result, researchers start to turn to digital implementation which is stabler and more efficient than analog counterpart to produce RN. However, digital methods suffer dynamical degradation due to the limited word length effect. Though some remedies, such as increasing computing precision, cascading multiple chaotic systems, pseudo-randomly perturbing the chaotic system, switching multiple chaotic systems, and error compensation method, are proposed, the limitations are even inevitable. Recently, some continuous-time chaotic oscillators combined with digital devices were used to realize RNG, and a novel approach was proposed to solve the dynamical degradation of digital chaotic system by coupling the given digital chaotic map with an analog chaotic system, where the analog chaotic system is used to anti-control the given digital chaotic map. But this method requires a whole continuous-time system realized with analog devices which restrict the performance of the integral system.#br#In this paper, a novel digital-analog hybrid chaotic system with only one analog device is constructed for the production of RN. The chosen analog device is a generalized memristor consisting of a diode bridge and a parallel RC filter.#br#Memristor is the fourth fundamental electronic component which has provoked extensive researches since the successful realization by Stan Williams's group at HP Labs in 2008.#br#The paper is arranged as follows. Firstly, a generalized memristor realized by a memristive circuit is introduced and its basic properties are given. Then the block diagram of the digital-analog hybrid system based on a single memristor feedback is depicted, and the mathematical model of the system is derived from the block diagram. Thirdly, the simple Logistic map is applied to the hybrid model and its dynamic behaviors are simulated and compared with those from the ideal Logistic before a more complex two-way coupled saw tooth map is applied to the same simulation, verifying the effectiveness of the proposed hybrid system. Finally, the complex coupled map is applied to the practical circuit producing RN which passes the NIST test suite smoothly.#br#The hybrid system has the following advantages: firstly, the introduction of the analog memristor is able to overcome the dynamical degradation in a digital system, avoiding the limited word length effect essentially. Secondly, the least analog device alleviates the sensibility to parameters and the restriction on bit rate in analog systems, ensuring that the hybrid system is robust. Thirdly, the system structure can be easily integrated into a relevant system. By designing the circuits of the system, the field programmable logic gate array of digital part can be used to realize chaotic map while the single memristor acts as a feedback to the digital part.#br#The experimental results show that the novel hybrid system is insensitive to the variations of circuit parameters and the produced RN is of great randomness, satisfying the practical applications.