NbOx忆阻神经元的设计及其在尖峰神经网络中的应用

NbO_x忆阻器凭借其纳米尺寸、阈值切换及局部有源特性在神经形态计算领域展现出巨大的应用前景.对NbO_x忆阻器动力学特性的深入分析和研究有利于忆阻神经元电路的设计和优化.本文基于局部有源理论,采用小信号分析方法对NbO_x忆阻器物理模型展开了研究,定量分析了产生尖峰振荡的区域和条件,并确定了激励信号幅值和尖峰频率之间的定量关系.基于上述理论分析,进一步设计了NbO_x忆阻器神经元,并结合忆阻突触十字交叉阵列,构建了25×10的尖峰神经网络(spiking neuron network,SNN).最后,分别利用频率编码和时间编码两种方式,有效地实现了数字0到9模式的识别功能.     

一个超混沌Lorenz吸引子及其电路实现

通过在三阶Lorenz系统中引入一个外加的状态变量构造了一个新的超混沌系统.对系统的一些基本特性，如耗散性、平衡点、稳定性、Hopf分叉进行了详细分析，且观察到了从周期到混沌、超混沌的演化.系统超混沌的存在性通过Lyapunov指数谱得到了验证.还设计了一个模拟电子电路，从电路实验中观察到了各种超混沌吸引子. 关键词： Lorenz系统 超混沌吸引子 电路实现     

多频正弦混沌细胞神经网络及其复杂动力学特性

大量动物实验表明,生物神经系统中存在着不规则的混沌现象.混沌神经网络是一种高度非线性动力系统,它可以实现一系列复杂的动力学行为,能够优化全局搜索和神经计算,还可产生伪随机序列进行信息加密.基于脑波由不同频率的正弦信号叠加理论,为使神经网络更具生物特性,提出了一种基于多频-变频正弦函数和分段型函数的非单调激活函数.分析表明,通过调节参数可使该激活函数拥有不同状态的脑电信号,能够模拟频率不同、类型不同的脑电波同时工作时丰富多变的脑部活动.基于该激活函数设计了一种新型混沌细胞神经网络.采用基于结构复杂度的SE复杂度算法和C0复杂度算法分析了神经网络的复杂度;利用Lyapunov指数谱、分岔图和吸引盆等方法,详细分析了激活函数参数变化对其动力学特性的影响,发现此混沌神经网络模型出现了一系列的复杂现象,如多种不同类型的混沌吸引子、共存混沌吸引子、共存极限环等,提升了混沌神经网络的性能,证明了多频正弦混沌神经网络具有丰富的动力学特性,使得其在信息处理、信息加密等方面也具有较好的前景.     

Complex dynamic behaviors in hyperbolic-type memristor-based cellular neural network

This paper presents a new hyperbolic-type memristor model,whose frequency-dependent pinched hysteresis loops and equivalent circuit are tested by numerical simulations and analog integrated operational amplifier circuits.Based on the hyperbolic-type memristor model,we design a cellular neural network(CNN)with 3-neurons,whose characteristics are analyzed by bifurcations,basins of attraction,complexity analysis,and circuit simulations.We find that the memristive CNN can exhibit some complex dynamic behaviors,including multi-equilibrium points,state-dependent bifurcations,various coexisting chaotic and periodic attractors,and offset of the positions of attractors.By calculating the complexity of the memristor-based CNN system through the spectral entropy(SE)analysis,it can be seen that the complexity curve is consistent with the Lyapunov exponent spectrum,i.e.,when the system is in the chaotic state,its SE complexity is higher,while when the system is in the periodic state,its SE complexity is lower.Finally,the realizability and chaotic characteristics of the memristive CNN system are verified by an analog circuit simulation experiment.     

一个新的三维二次混沌系统及其电路实现

为了产生复杂的混沌吸引子，构造了一个新的三维二次自治混沌系统.该系统含有三个参数，每一个方程含有一个非线性乘积项.利用理论推导、数值仿真、Lyapunov指数谱和分岔图对系统的基本动力学特性进行了分析.结果表明，该系统具有五个平衡点，因而与Lorenz，Rsslor，Chen、Lü等混沌系统是非拓扑等价的；当其参数满足一定条件时，系统是混沌的.与Lorenz等混沌系统相比，该系统具有更大的正Lyapunov指数，能够产生复杂的混沌吸引子和一些有趣的动力学行为.最后，设计了实现该系统的混沌电路，电路实验结 关键词： 三维二次自治系统 混沌 混沌吸引子 电路实现     

级联混沌及其动力学特性研究

初值敏感性是混沌的本质,混沌的随机性来源于其对初始条件的高度敏感性,而Lyapunov指数又是这种初值敏感性的一种度量.本文的研究发现,混沌系统的级联可明显提高级联混沌的Lyapunov指数,改善其动力学特性.因此,本文研究了混沌系统的级联和级联混沌对动力学特性的影响,提出了混沌系统级联的定义及条件,从理论上证明了级联混沌的Lyapunov指数为各个级联子系统Lyapunov指数之和;适当的级联可增加系统参数、扩展混沌映射和满映射的参数区间,由此可提高混沌映射的初值敏感性和混沌伪随机序列的安全性.以Logistic映射、Cubic映射和Tent映射为例,研究了Logistic-Logistic级联、Logistic-Cubic级联和Logistic-Tent级联的动力学特性,验证了级联混沌动力学性能的改善.级联混沌可作为伪随机数发生器的随机信号源,用以产生初值敏感性更高、安全性更好的伪随机序列.     

A flux-controlled model of meminductor and its application in chaotic oscillator

A meminductor is a new type of memory device developed from the memristor.We present a mathematical model of a flux-controlled meminductor and its equivalent circuit model for exploring the properties of the meminductor in a nonlinear circuit.We explore the response characteristics of the meminductor under the exciting signals of sinusoidal,square,and triangular waves by using theoretical analysis and experimental tests,and design a meminductor-based oscillator based on the model.Theoretical analysis and experiments show that the meminductor-based oscillator possesses complex bifurcation behaviors and can generate periodic and chaotic oscillations.A special phenomenon called the co-existent oscillation that can generate multiple oscillations(such as chaotic,periodic oscillations as well as stable equilibrium) with the same parameters and different initial conditions occurs.We also design an analog circuit to realize the meminductor-based oscillator,and the circuit experiment results are in accordance with the theory analysis.     

蔡氏结型忆阻器的简化及其神经元电路的硬件实现

蔡氏结型忆阻器(Chua corsage memristor, CCM)属于压控型局部有源忆阻器,具有复杂的动力学行为,在神经形态计算领域具有潜在的应用价值.根据静态电压-电流特性曲线, CCM可分为二翼、四翼和六翼型.本文基于神经形态行为的产生机制,将CCM的数学模型进行简化,简化后的模型表达式中无绝对值符号,且小信号等效电路的导纳函数与简化前完全相同.进一步采用简化的CCM模型与电容和电感元件相连,构建了三阶神经元电路.利用局部有源、混沌边缘、及李雅普诺夫指数等理论分析方法,预测了该神经元电路产生神经形态行为的参数域.根据简化的CCM数学模型,采用运算放大器、乘法器、电阻和电容等常用电路元件构建了该忆阻器的电路仿真器,并连接电容和电感进一步给出了神经元电路的硬件实现.实验结果表明该神经元电路可以产生丰富的神经形态行为,包括静息状态、周期尖峰、混沌状态、双峰响应、周期振荡现象、全或无现象和尖峰簇发现象.     

N型局部有源忆阻器的神经形态行为

局部有源忆阻器(locally-active memristor,LAM)凭借其高集成度、低功耗和局部有源特性等优点,在神经形态计算领域显示出巨大的潜力.本文提出了一种简单的N型LAM数学模型,通过揭示其非线性动力特性,设计了N型LAM神经元电路.采用Hopf分岔、数值分析等方法定量研究了该电路的动力学行为,成功模拟了多种神经形态行为,包括全或无行为、尖峰、簇发、周期振荡等.并利用该神经元电路结构模拟了生物触觉神经元的频率特性.仿真结果表明:当输入信号幅值低于阈值时,神经元电路输出信号的振荡频率与输入信号强度呈正相关(即兴奋状态),并在阈值处达到最大值.随后,继续增大激励强度,振荡频率则逐渐降低(即保护性抑制状态).最后,设计了N型LAM硬件仿真器,并完成了人工神经元电路的硬件实现,实验结果与仿真结果、理论分析相一致,验证了该N型LAM具备的神经形态行为.     

Modeling random telegraph signal noise in CMOS image sensor under low light based on binomial distribution

The random telegraph signal noise in the pixel source follower MOSFET is the principle component of the noise in the CMOS image sensor under low light. In this paper, the physical and statistical model of the random telegraph signal noise in the pixel source follower based on the binomial distribution is set up. The number of electrons captured or released by the oxide traps in the unit time is described as the random variables which obey the binomial distribution. As a result,the output states and the corresponding probabilities of the first and the second samples of the correlated double sampling circuit are acquired. The standard deviation of the output states after the correlated double sampling circuit can be obtained accordingly. In the simulation section, one hundred thousand samples of the source follower MOSFET have been simulated,and the simulation results show that the proposed model has the similar statistical characteristics with the existing models under the effect of the channel length and the density of the oxide trap. Moreover, the noise histogram of the proposed model has been evaluated at different environmental temperatures.