Journal of Circuits, Systems and Computers

When the oscillators are coupled, coupling methods are very important and influence some factors, for example, increasing or decreasing of noise and whether multi-phase synchronization phenomena can be observed or not due to the number of oscillators and so on. In this paper, multi-phase synchronization phenomena which are generated in RF CMOS LC oscillators with mutual inductor couplings and the stability of various oscillatory modes in the proposed model are investigated. In the proposed system, multi-phase synchronization phenomena can be observed regardless of the number of oscillators in RF region due to setting up the sign of the mutual inductance properly, and the each oscillatory mode is stable.

Phase models represent the ideal framework to investigate the synchronization of a nonlinear oscillator with an external forcing. While many researches focused the attention to their analysis, little work has been done about the reduction of a physical system to the corresponding phase model. In this paper we show how, resorting to averaging techniques, it is possible to obtain the phase model corresponding to a given set of state equations. As examples, we derive the phase equations and investigate the synchronization properties of two popular nonlinear oscillators.

A CMOS phase-shift oscillator that uses a phase shift in the conduction of heat is proposed. The oscillator consists of an inverting amplifier and a feedback thermal filter that are integrated on a silicon chip. The thermal filter consists of a polysilicon heater and a MOSFET thermosensor separated from each other by a S_iO₂ heat-conducting layer.¹ An input signal for the filter travels from the heater to the thermosensor through the S_iO₂ layer in the form of heat. The filter accepts the output of the inverting amplifier, produces a phase shift due to the heat conduction, and returns a 180°-shifted feedback signal to the amplifier. The oscillator produces oscillation at a specific frequency determined by the dimensions of the filter and the thermal conductivity and specific heat of Si and S_iO₂.

An RF phase-quadrature oscillator is analyzed. The designer "ensured" the phase-quadrature working condition through a suitable cross-coupled electrical connection between the two parts composing the complete oscillator. Through a detailed analysis of the dynamics of this oscillator, we show that device mismatch can lead to an unexpected stable working mode where the oscillator does not operate in a phase-quadrature condition. The proposed analysis has been first performed on a simplified model of the oscillator to allow the use of software packages for numerical continuation. The results of the analysis of the simplified oscillator dynamics have been then checked by means of accurate device models from a 65 nm RF technology library.

We present four-dimensional and five-dimensional models for classical cross-coupled LC oscillators. Using these models, sinusoidal oscillation condition, frequency and amplitude can be found. Further, undesired behaviors such as relaxation-mode oscillations and latchup can be explained and detected. A simple graphical design procedure is also described.

In this paper, we propose a Markov chain modeling of complicated phenomena observed from coupled chaotic oscillators. Once we obtain the transition probability matrix from computer simulation results, various statistical quantities can be easily calculated from the model. It is shown that various statistical quantities are easily calculated by using the Markov chain model. Various features derived from the Markov chain models of chaotic wandering of synchronization states and switching of clustering states are compared with those obtained from computer simulations of original circuit equations.

Synchronization phenomena in coupled oscillatory systems are very important models to describe various higher-dimensional nonlinear phenomena in the field of natural science. In this paper, phase synchronization in a ring of van der Pol oscillators coupled by time-varying resistors is studied. The coexistence of in-phase and anti/N-phase states and various interesting phase synchronization patterns are observed when the parameters are changed. Further, the influence of duty cycle of time-varying resistors for the observed phase synchronization patterns is investigated.

This paper presents a scalable low voltage CMOS folded-cascode quadrature voltage controlled oscillator (QVCO) design for radio-frequency (RF) applications using the TSMC 0.18 μm 6M1P CMOS process technology. The simulated startup behavior of this proposed QVCO topology indicates that, the QVCO is free from bi-modal oscillation (frequency ambiguity). The QVCO provided extended voltage swing with the supply voltage scalable in the range of 1.8 V to 0.75 V. The QVCO operates in the frequency range of 4 GHz to 3 GHz (corresponding to supply voltage scaling in the range of 1.8 V to 0.75 V) with around 11.7% tuning range and low quadrature error. The QVCO had a power consumption under 10 mW within the specified supply voltage scaling range. Phase noise simulations using the Monte Carlo analysis provide an approximate phase noise estimate of ≈ -150 dBc/Hz at an offset of 600 KHz from the center frequency (@3.7 GHz) for operation using the 1.8 V supply voltage, using moderate inductor-Q values. Monte Carlo simulations were also carried out to determine the effects of the process, voltage and temperature variations.

A higher-order oscillator, including a nonlinear unit and an 8th-order low-pass active Bessel filter is described. The Bessel unit plays the role of "three-in-one": a delay line, an amplifier and a filter. Results of hardware experiments and numerical simulation are presented. Depending on the parameters of the nonlinear unit the oscillator operates either in a one-scroll or two-scroll mode. Two positive Lyapunov exponents, found at larger values of the negative slopes of the nonlinear function, characterize the oscillations as hyperchaotic.

In this work we derive a general non-conservative model for any RC sinusoidal oscillator independent of its particular passive topology or the employed active devices. We consider an arbitrary unknown second-order passive RC network terminated at one port by a negative resistor and proceed to impose oscillation start-up and frequency constraints on a derived state-matrix.

In this paper a probabilistic feedback technique to maximize the throughput of a generic True Random Bit Generator (TRBG) circuit, under a given constraint on the entropy, is discussed. In the proposed solution, the throughput of the device is dynamically and adaptively varied by an on-line entropy detector, such to obtain, with an arbitrary confidence level, an entropy greater than a given worst-case value. The approach, which has a general validity, introduces a method for making maximum use of the TRBG random bit generation capabilities, maximizing the generation throughput while preserving its entropy. It is different from the classical "open loop" TRBG design approach, in which the circuit parameter variability determines an uncertainty about the actual entropy of the device, with the proposed techniques the TRBG generation speed is varied under a given constraint on the entropy. The method can be applied to all those integrated TRBG circuits proposed in the literature and based on the uniform sampling of, e.g., random physical processes or chaotic dynamical systems.

As faster Random Number Generators become available, the possibility to improve the accuracy of randomness tests through the analysis of a larger number of generated bits increases. In this paper we first introduce a high-performance true-random number generator designed by authors, which use a set of discrete-time piecewise-linear chaotic maps as its entropy source. Then, we present by means of suitably improved randomness tests, the validation of this generator and the comparison with other high-end solutions. We consider the NIST test suite SP 800-22 and we show that, as suggested by NIST itself, to increase the so-called power of the test, a more in-depth analysis should be performed using the outcomes of the suite over many generated sequences. With this approach we build a framework for RNG high quality testing, with which we are able to show that the designed prototype has a comparable quality with respect to the other high-quality commercial solutions, with a working speed that is one order of magnitude faster.