Second-level NIST randomness tests for improving test reliability

Testing Random Number Generators (RNGs) is as important as designing them. Here we consider the NIST test suite SF 800-22 and we show that, as suggested by NIST itself, to reveal non-perfect generators a more in-depth analysis should be performed using the outcomes of the suite over many generated sequences. Testing these second-level statistics is not trivial and, relying on a proper model that takes into account the errors due to the approximations in the first level tests, we propose a tuning of the parameters in the simplest cases. The validity of our consideration is widely supported by experimental results on several RNG currently employed by major IT players, as well as a chaos-based RNG designed by authors

Improving PA efficiency by chaos-based spreading in multicarrier DS-CDMA systems

In this paper, we investigate the effect of spreading sequences on the peak-to-average power ratio (PAPR) in order to improve the power amplifier efficiency of multicarrier direct-sequence code-division multiple access systems. Baseband shaping has been identified to have a key role in reducing PAPR by spreading and we have found that chaos-based spreading sequences give good results as compared with Gold and i.i.d. sequences behaving differently depending on the number of subcarriers

A 3 GHz spread spectrum clock generator for SATA applications using chaotic PAM modulation

This paper proposes a prototype of a Spread Spectrum Clock Generator which is the first known specifically meant for 3 GHz Serial ATA-II applications. The modulation is obtained from a fractional PLL which employs a Delta-Sigma modulator. A further innovative aspect of our work is that our prototype takes advantage of a chaotic PAM as driving signal, instead a triangular signal as in all spread spectrum generators proposed in literature for SATA-II. In this way we avoid the periodicity of the modulated clock, completely flattening the peaks in the power spectral density. The circuit prototype has been designed n 0.13 μm CMOS technology and achieves a peak reduction greater than 14 dB measured at RBW = 100 kHz. The chip active area is 0.27×0.78 mm2 and the power consumption is as low as 14.7 mW. © 2008 IEEE

On the Approximation Errors in the Frequency Test Included in the NIST SP800-22 Statistical Test Suite

In previous papers we have addressed the problem of testing Random Number Generators (RNGs) through statistical tests, with particular emphasis on the approach we called second-level testing. We have shown that this approach is capable of achieving much higher accuracy in exposing non-random generators, but may suffer from reliability issues due to approximations introduced in the test. Here we consider the NIST Frequency Test and present a mathematical expression of the error introduced by approximating the effective discrete distribution function with its continuous limit distribution. The matching against experimental data is almost perfect. © 2008 IEEE

A Zero-Transient Dual-Frequency Control for Class-E Resonant DC-DC Converters

In this paper, a dual-frequency control method for regulating the output power in class-E resonant DC-DC converters has been introduced. As in the standard ON-OFF control or other recently proposed dual-frequency controls, the approach is based on the ability of the converter to alternately operate in a high- and a low-power state. The proposed solution has a twofold advantage: on the one hand, soft-switching capabilities (i.e., Zero-Voltage and Zero-Voltage-Derivative switching) are preserved in both operating states; on the other hand, it is possible to reduce to zero the transient time required to switch from one state to the other one. The most straightforward consequence is the possibility to increase to very large values the frequency at which the two operating states are switched, up to the same order of magnitude as the main switching frequency of the converter. In this way, the additional ripple introduced by the proposed dual-frequency control can be decreased to a negligible value. The approach has been validated by measurements on a prototype operating between 4 MHz and 8 MHz and in which it has been possible to increase the control frequency up to 500 kHz

Asymptotic expressions of mismatch variance in interdigitated geometries

Performance in analog integrated circuits strongly depends on the mismatch between nominally identical devices. In this work we derive closed-form asymptotic expressions describing mismatch variance in multifinger structures, under the assumption of Gaussian autocorrelation for the mismatch-generating stochastic process. The analysis is performed on interdigitated geometries, eventually modified to make them common-centroid. Comparison with the numerical results provided by an independent model validates the theoretical expressions presented here

Stability and mismatch robustness of a leakage current cancellation technique

Leakage discharge currents represent one of the most detrimental factors for the maximum hold time in analog sample-and-hold circuits. Apart from the obvious passive solution of enlarging the sampling capacitor, alternatives based on active circuits have been proposed. We focus here on an existing solution which has proven to be effective in reducing the leakage discharge, hence extending the hold time, by a factor of 20. Being based on a feedback circuit built around the hold capacitor, it is paramount to understand its stability properties. This work tries to close the gap by analyzing the closed-loop stability of the nominal circuit. Classical control systems techniques are employed to thoroughly analyze the dynamic behaviour of the feedback circuit, highlighting the detrimental effect of device mismatches

Parameter identification for piecewise-affine fuzzy models in noisy environment

AbstractIn this paper the problem of identifying a fuzzy model from noisy data is addressed. The piecewise-affine fuzzy model structure is used as non-linear prototype for a multi–input, single–output unknown system. The consequents of the fuzzy model are identified from noisy data which are collected from experiments on the real system. The identification procedure is formulated within the Frisch scheme, well established for linear systems, which is extended so that it applies to piecewise-affine, constrained models

Subspace Energy Monitoring for Anomaly Detection @Sensor or @Edge

The amount of data generated by distributed monitoring systems that can be exploited for anomaly detection, along with real time, bandwidth, and scalability requirements leads to the abandonment of centralized approaches in favor of processing closer to where data are generated. This increases the interest in algorithms coping with the limited computational resources of gateways or sensor nodes. We here propose two dual and lightweight methods for anomaly detection based on generalized spectral analysis. We monitor the signal energy laying along with the principal and anti-principal signal subspaces, and call for an anomaly when such energy changes significantly with respect to normal conditions. A streaming approach for the online estimation of the needed subspaces is also proposed. The methods are tested by applying them to synthetic data and real-world sensor readings. The synthetic setting is used for design space exploration and highlights the tradeoff between accuracy and computational cost. The real-world example deals with structural health monitoring and shows how, despite the extremely low computations costs, our methods are able to detect permanent and transient anomalies that would classically be detected by full spectral analysis