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We overview the plasma properties of a two-dimensional electron gas in semiconductor heterostructures as well as new concepts and proposals of novel terahertz devices (detectors, sources utilizing plasma instabilities, and photomixers) based on these heterostructures.

Widely-tunable voltage-controlled oscillator using resonant tunneling diodes in a distributed manner is discussed. The circuit configuration and the principle of operation of the VCO are described together with several results of numerical calculations, which include necessary condition of permanent oscillation and how much the oscillation frequency is tuned by the voltage.

The feasibility of CMOS circuits operating at frequencies in the upper millimeter wave and low sub-millimeter frequency regions has been demonstrated. A 140-GHz fundamental mode VCO in 90-nm CMOS, a 410-GHz push-push VCO in 45-nm CMOS, and a 180-GHz detector circuit in 130-nm CMOS have been demonstrated. With the continued scaling of MOS transistors, 1-THz CMOS circuits will be possible. Though these results are significant, output power of signal generators must be increased and acceptable noise performance of detectors must be achieved in order to demonstrate the applicability of CMOS for implementing practical terahertz systems.

Phyllosilicate is a sheet of silicate tetrahedra bound by basal oxygens. A phyllosilicate excitable automaton is a regular network of finite state machines, which mimics structure of a silicate sheet. A node of the silicate sheet is an automaton, which takes resting, excited and refractory states, and updates its state in discrete time depending on a sum of excited states of its three (silicon automata) or six (oxygen automata) closest neighbors. Oscillator is a localized compact configuration of nonquiescent states which undergoes finite growth and modification but returns to its original state in a finite number of steps. We show that phyllosilicate excitable automata exhibit waves and oscillating localizations (oscillators) dynamics. Basic types of oscillators are classified and characterized.

Relativistic generalization of path integral Monte Carlo (PIMC) method has been proposed. The problem of relativistic oscillator has been studied in the framework of this approach. Ultra-relativistic and nonrelativistic limits have been discussed. We show that PIMC method can be effectively used for investigation of relativistic systems.

We study (1+1)-dimensional Dirac equation with non-Hermitian interactions, but real energies. In particular, we analyze the pseudoscalar and scalar interactions in detail, illustrating our observations with some examples. We also show that the relevant hidden symmetry of the Dirac equation with such an interaction is pseudo-supersymmetry.

Phase synchronization of a chaotic oscillator that is driven by two chaotic signals is investigated. The anti-biased PS in the presence of biased coupling is found, i.e., the response oscillator can be phase synchronized by the drive with a weaker coupling rather than the stronger driver. The mechanism for this behavior is explored. In the non-PS region, alternating phase-locking is observed.

The diffusion in an undamped linear oscillator driven by cross-correlated colored noises in which one of the noises is modulated by a biased periodic signal is studied. We have found the following: (1) The signal with higher frequency tends to suppress the diffusion; (2) The diffusion coefficient as a function of signal frequency Ω exhibits a pronounced resonance peak at , here denotes the oscillator frequency; (3) The noise cross-correlation results in the appearance of a minimum in the curve of diffusion coefficient as a function of noise intensity. The position and deepness of the minimum are controlled by the signal. In the case of a large signal, the minimum disappears and the diffusion coefficient increases monotonously with increasing noise intensity as usual.

Oscillators under nonlocal couplings are systematically studied. We propose functions of inverse power as mathematical realization for nonlocal couplings among oscillators in a system. Power β in a function is taken as an important parameter in our study. Since its value determines a measure of "localization" while oscillators are nonlocally coupled it is then called the "nonlocal parameter". Together with the "phase lag parameter" α, which is vital for the existence of chimera states, we are able to demonstrate a valuable phase portrait in the β-α space. System dynamics is discussed in this phase diagram analogous to phase transitions in thermodynamics.

In the last decade, many potent analytical methods have been utilized to find the approximate solution of nonlinear differential equations. Some of these methods are energy balance method (EBM), homotopy perturbation method (HPM), variational iteration method (VIM), amplitude frequency formulation (AFF), and max–min approach (MMA). Besides the methods mentioned above, the Akbari–Ganji method (AGM) is a highly efficient analytical method to solve a wide range of nonlinear equations, including heat transfer, mass transfer, and vibration problems. In this study, it was constructed the approximate analytic solution for movement of two mechanical oscillators by employing the AGM. In the derived analytical method, both oscillator motion equations and the sensitivity analysis of the frequency were included. The AGM was validated through comparison against Runge–Kutta fourth-order numerical method and an excellent agreement was achieved. Based on the results, the highest sensitivity of the oscillation frequency is related to the mass. As $\alpha$ and $\beta$ increase, the slope of the system velocity and acceleration will increase.

In this paper, a new current-mode (CM) all-pass filter employing two Dual-Output Second-Generation Current Conveyors (DO–CCIIs), one grounded resistor and one grounded capacitor is presented. The proposed circuit exhibits low input impedance and high output impedance, which makes it suitable for cascading. Moreover, adding two extra resistors to the proposed circuit, a new gain-variable voltage-mode (VM) all-pass filter is obtained. A quadrature oscillator employing minimum number of grounded passive components is derived from the developed CM filter as an application of the first-order all-pass filter. Both of the proposed all-pass filters do not require matching of passive components. The effects of the parasitic impedances of the DO–CCIIs on the transfer function (TF) of the proposed CM filter as an example are investigated. In addition, the proposed CM all-pass filter and oscillator circuit are simulated using SPICE simulation program to confirm the theory.

In this paper, we present a new method for the modeling and characterization of oscillator circuit with a Van Der Pol (VDP) model using parameter identification. We also discussed and investigated the problem of estimation in nonlinear system based on time domain data. The approach is based on an appropriate state space representation of Van der Pol oscillator that allows an optimal parameter estimation. Using sampled output voltage signal, model parameters are obtained by an iterative identification algorithm based on Output Error method. Normalization issues are fixed by an appropriate transformation allowing a quickly global minimum search. Finally, the proposed estimation method is tested and validated using simulation data from a 1 GHz oscillator circuit in GaAs technology.

This paper presents design and measurement results of a DC–DC converter, intended to harvest energy from a thermo-electric generator (TEG). The prototype chip was fabricated in 130nm CMOS technology. The designed converter can extract maximum power from a TEG, without using an input capacitor ($C_{\mathrm{\text{IN}}})$ or a closed loop maximum peak power tracking circuit to regulate the input voltage ($V_{\mathrm{\text{IN}}})$. The converter uses a low voltage oscillator coupled with charge pump to directly power the auxiliary circuits; and auxiliary circuits drives two inductors in two half cycles of a clock pulse. The measurement has been performed by using a TEG, and a voltage source (50–200mV) with a series resistance of 5ohms. The result shows that the prototype can self-starts from 70mV with 5ms startup time and can work up to a minimum of 50mV; and can extract, 57.2% (at 50mV) to 65% (at 200mV), of the available power.

In this paper, a systematic and hierarchical synthesis methodology is presented for nonlinear analog synthesis to meet the essential requirement for system automation. Behavior of nonlinear system, represented by polynomial expression, has been studied by decomposing it into linear and nonlinear sub-expression. Such sub-expressions are realized with basic building block like multiplier, adder, quadratic, etc., each of which can be represented as a network of the current mode device, operational transconductance amplifier (OTA). Polynomial series is used to represent various important functions in signal processing applications. Few nonlinear functions with their OTA representation are discussed as the applications of polynomial series. The response of all the circuits are studied through SPICE simulation validating the proposed methodology.

This paper proposes the design of a precoder in MIMO systems dedicated to JPEG Wireless (JPWL) (ISO/IEC 15444-11) image transmission which jointly takes into account the channel noise and the nonlinear distortions due to the high power amplifier (HPA) used in the transmitter. MIMO-OFDM (Orthogonal Frequency Division Multiplexing) systems dedicated to image transmission rely only on the Channel State Information (CSI) and the image content to design their precoding solutions. However, the nonlinear behavior of the HPA used at the front-end is not taken into account when designing the current precoders. In order to ensure the QoS of the transmitted image, a large level back-off is usually applied to avoid the nonlinear distortions generated by the HPA. In addition, the Input Back-off (IBO) value is statically chosen and does not depend on the other parameters of the link such as the instantaneous MIMO channel status, the modulation order and the scalability of the JPWL content. This may reduce both the global energy efficiency and the transmission quality of the Radio-Frequency (RF) link. Therefore, this work proposes a new precoding scheme to allocate the total available power while dynamically adjusting the optimal power IBO value according to the HPA parameters, the instantaneous channel status and the image content to be transmitted. Numerical results using a commercial HPA model under the IEEE 802.11n standard show that the proposed power allocation algorithm improves the visual quality of the received JPWL images compared to the state-of-the-art over a realistic radio channel model.

This paper presents an electronically tunable current-mode first-order universal filter. The proposed circuit employs only a single Extra-X Current-Controlled Conveyor (EX-CCCII) and a single grounded capacitor, which is suitable for IC implementation. The circuit can realize three current transfer functions simultaneously, namely low-pass, high-pass and all-pass. The proposed circuit exhibits low-input and high-output impedance, which is suitable for cascading. The pole frequency of the filter can be electronically tuned, by varying the bias current of EX-CCCII. The nonidealities and parasitic effects on the circuit performance are investigated in detail. Also, the Monte Carlo analysis is done to show the effect of active and passive element mismatches on the pole frequency. An eight-phase current-mode sinusoidal oscillator and current-mode second-order filter are further realized using the proposed circuit. The functionality of the proposed circuits is verified through PSPICE simulations, using 0.25-$\mu$m TSMC CMOS technology parameters.

A novel multiband impulse radio ultra-wideband (MB-IR-UWB) transmitter with an energy-efficient and low-complexity pulse generator design technique compliant with the IEEE 802.15.4a standard is investigated in this paper. This transmitter is made up of a new differential narrow triangular pulse generator, a new multiband voltage-controlled oscillator (VCO), an active mixer and a variable-gain power amplifier (PA). It operates at 14 UWB bands and generates an output signal with the duration of 3ns, more than 500MHz of channel bandwidth and more than 20dB of sidelobe suppression, while achieving an average energy efficiency of 51.36 pJ/pulse from 1.4-V supply. Improving spectral flexibility and worldwide compliance is the major contribution brought by this paper to make this circuit as a multifunction wireless device well suited for low-cost, low-power multiband applications.

A current-mode first-order filter configuration simultaneously providing noninverting and inverting low-pass (LP) and high-pass (HP) responses depending on passive element choice is proposed. In addition, all-pass filter (APF) responses can be easily obtained with interconnection of LP and HP output currents. The proposed filter employs only two differential voltage current conveyors, a grounded resistor and a grounded capacitor, so it is suitable for integrated circuit realization. It provides the feature of high output impedance. It does not need any passive element matching constraints. A voltage-mode oscillator based on the inverting APF is presented as a typical application. The performance of the proposed configuration is verified through many SPICE simulation and experimental test results.

This paper presents an independently tunable, four-input, three-output, voltage-mode (VM) biquad filter consisting of four operational transconductance amplifiers (OTAs) and two grounded capacitors. The proposed circuit can simultaneously realize three basic biquad filtering functions for single input and three outputs. All five standard biquad filtering functions can be implemented with four inputs and single output by appropriate application of input voltage signals. The developed biquad filter with high input impedances enables noninteractive control of natural angular frequency and quality factor. By slightly modifying the proposed biquad filter, the VM quadrature sinusoidal oscillator with noninteractive control for the oscillation condition and the oscillation frequency has been achieved. Simulation and experimental results are used to validate theoretical predictions.

A comprehensive resonant optimal control method is developed and discussed for suppressing homoclinic and heteroclinic bifurcations of a general one-degree-of-freedom nonlinear oscillator. Based on an adjustable phase shift, the primary resonant optimal control method is presented. By solving an optimization problem for the optimal amplitude coefficients to be used as the control parameters, the force term as the controller can be designed. Three kinds of resonant optimal control methods are compared. The control mechanism of the primary resonant optimal control method is to enlarge to the largest possible degree the control region where homoclinic and/or heteroclinic transversal intersections do not occur, and this is accomplished at lowest cost. It is shown that the primary resonant optimal control method has much better performance than the superharmonic resonant optimal control method, and it works well even when the superharmonic optimal control method fails. In particular, one new global optimal control method is presented, whose central idea is to find a frequency such that the asymmetric homoclinic bifurcations or the multiple homoclinic and heteroclinic bifurcations can attain the same critical values. On the basis of these same critical bifurcation values, chaos resulting from asymmetric homoclinic or multiple homoclinic and heteroclinic bifurcations can be effectively suppressed by the primary resonant optimal control method. This is confirmed by two illustrative examples. The theoretical analyses concerning the suppression of local and global homoclinic and heteroclinic bifurcations are in agreement with the numerical simulations, including the identification of the stable and unstable manifolds and the basins of attraction.