Understanding the Input Signal Frequency Effects on the Resistive Window of Memristors

As theoretically predicted by Prof. Chua, the input signal frequency has a major impact on the electrical behavior of memristors. According with one of the so-called fingerprints of such devices, the resistive window, <i>i.e.</i> the difference between the low and high resistance states, shrinks as the frequency increases for a given input signal amplitude. Physically, this effect stems from the incapability of ions/vacancies to follow the external electrical stimulus. In terms of the electrical behavior, the collapse of the resistive window can be ascribed to the shift of the set/reset voltages toward higher values. Moreover, for a given frequency, the resistance window increases with the signal amplitude. In this letter, we show that both phenomena are the two sides of the same coin and that can be consistently explained after considering the snapback effect and a balance model equation for the device memory state.

Understanding the Input Signal Frequency Effects on the Resistive Window of Memristors

As theoretically predicted by Prof. Chua, the input signal frequency has a major impact on the electrical behavior of memristors. According with one of the so-called fingerprints of such devices, the resistive window, <i>i.e.</i> the difference between the low and high resistance states, shrinks as the frequency increases for a given input signal amplitude. Physically, this effect stems from the incapability of ions/vacancies to follow the external electrical stimulus. In terms of the electrical behavior, the collapse of the resistive window can be ascribed to the shift of the set/reset voltages toward higher values. Moreover, for a given frequency, the resistance window increases with the signal amplitude. In this letter, we show that both phenomena are the two sides of the same coin and that can be consistently explained after considering the snapback effect and a balance model equation for the device memory state.

Analysis of structure importance of compensation capacitor in jointless track circuit

This paper models the input signal amplitude of the main track and the small track of the adjacent jointless track circuit (JTC) when JTC is idle and the track circuit reader(TCR) received signal amplitude when JTC is occupied, based on the work mechanism of JTC and TCR. Based on the models, the relative impact of compensation capacitor on signal amplitude is obtained by simulation. The paper further proposes a calculation method for structure importance of compensation capacitors. Experimental results indicate that the rankings of structure importance are not affected by ballast resistance of JTC in this method. The results also show that the compensation capacitors closer to the receiving end are more important than those closer to the sending end. In addition, C2, C6, and C3 closer to receiving end are the most important and should be paid close attention during maintenance. The second, the first and the fifth capacitor from the sending end, have less impact on the JTC and TCR signal. This paper is helpful to determine the maintenance priority of each capacitor, optimize the maintenance strategy, and make better use of JTC.

Reliability Analysis of 0.5μm CMOS Operational Amplifiers under TID Effects

Analog integrated circuits operating in radiation environments. In previous irradiation experiments performed on a switched-capacitor filter, implemented in a programmable analog array, it was observed a sudden recovery of the device performance during the irradiation, while increasing the accumulated dose. In some cases the considered performance parameters (such as the total harmonic distortion) may even be enhanced if compared to the pre-irradiation measurements, in specific accumulated dose intervals. This behavior is associated to partial inactivity windows in the internal components of the device. Spice simulations considering two complementary architectures of a simple CMOS Operational Amplifier (OpAmp) are performed, aiming to understand the origins of this effect. Results indicate that shifts on the operating point of the amplifier building blocks are responsible for the degradation and recovery of the OpAmp performance. Results also show that specific architectures, as well as, application constraints (such as the external feedback and the input signal amplitude and frequency) may result in different robustness levels related to the linear applications of the OpAmps in radiation environments.

Non-analytic at the origin, behavioral models for active or passive non-linearity

Most non-linear behavioral models of amplifiers are based on functions that are analytic at the origin and thus can be replaced by their Taylor series development around this point, e.g. polynomials of the input signal. Chebyshev Transforms can be used to compute the harmonic response of the model to a sine input signal. These responses are polynomials of the input signal amplitude. A second application of the Chebyshev transform to the first harmonic response or radio frequency (RF) characteristic will lend the carriers and intermodulation (IM) products for a two-carrier input signal, again polynomials. An important class of non-analytic non-linear behavior encountered in practice, such as hard limiters and detectors are either empirically treated or only approximated by an analytic function such as the hyperbolic tangent. This work proposes to generalize the polynomial non-linearity theory by adding non-analytic at the origin functions that, like polynomials, are invariant elements of the Chebyshev Transform. Devices modeled with these non-analytic at the origin functions exhibit intermodulation behavior significantly different from that of classical polynomial models, giving theoretical foundation to a number of important unexplained practical measurement observations.

STOCHASTIC RESONANCE IN NONLINEAR TRANSMISSION OF SPIKE SIGNALS: AN EXACT MODEL AND AN APPLICATION TO THE NEURON

Nonlinear transmission of trains of pulses enhanced by noise addition through stochastic resonance is studied. First, an exact model is presented which describes stochastic resonance in the transmission of a periodic train of pulses by a threshold system in the presence of arbitrarily distributed white noise. Second, a simulation demonstrates a novel possibility of stochastic resonance in the neuron, in the nonlinear transmission of spike trains assisted by noise. Third, it is shown that the exact model can provide a satisfactory approximation of stochastic resonance in the neuron, as the reported effect is mainly sensitive to correlations at a dominant time scale formed by the coherent period, and to the overall input signal amplitude relative to the threshold of the nonlinearity. The present results enlarge the scope of the effect of noise-enhanced transmission of signals through stochastic resonance, and also of the possible mechanisms for neural information processing.

A Nonlinear Filter for Independent Gain and Phase (With Applications)

Compensation of control systems by means of linear filters is a basic and well-known art. However, the limitations of linear compensation are also well known. In particular, the interdependence of the phase and gain characteristics of linear filters is always in conflict with the desires of the control-system designer. For example, it is impossible to introduce attenuation into a system without introducing undesirable phase lag as well. The development of a split-path nonlinear filter (SPAN filter) concept promises to yield a practical device which has independent phase and gain characteristics. These characteristics are independent of input signal amplitude. This filter can, therefore, have desirable characteristics which are unattainable with conventional linear filters. The design of the nonlinear filter to meet a desired gain-phase, describing-function specification is simplified by results given in the paper. Analysis and simulation of three sample problems has shown that a great deal of flexibility is available with this nonlinear filter. It is possible to obtain phase lead and amplitude attenuation by a proper choice of linear filtering in the two channels. Analog-computer simulation has verified the analytical work with respect to stability margins, and provided transient-response data, in the absence of analytical methods.