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A new scheme on the realisation of voltage-tunable immittance function (VTIF) is proposed. Here two types of grounded, high-quality (Q) resonant filters and voltage-controlled quadrature oscillators (VCQO) with a linear tuning law are presented. Analysis indicates that the filter/QO parameters are impervious to the ABB parasitic components. Experimental results exhibit a VCQO-linear tuning range of fo~14 MHz with a satisfactory phase-noise margin of immittances, viz., inductance (L) and frequency-dependent negative resistance (D) are derived using the Current Feedback Amplifier (CFA) combined with analog voltage-multiplier elements as the active building block (ABB). Subsequently, implementation of LC-bandpass and rD-band-reject selective filters, along with QO designs, is presented with low THD and phase noise of (─)104 dBc/Hz at 30 kHz offset. Experimental results of the proposed circuits had been satisfactorily verified using standard commercially available IC modules. [ABSTRACT FROM AUTHOR]

A new linear voltage-controlled oscillator (LVCO) implementation using single AD-844 CFA with a pair of AD-835 multiplier devices and a pair of grounded capacitors is proposed. The open-loop transfer function of the topology is analyzed wherein the concept of Short-Circuit Natural Frequency (SCNF) is applied to derive the sinusoid oscillator implementation. The proposed oscillator circuit is then restructured to yield a linear voltage-controlled quadrature oscillator (LVCQO) after appropriate cascade with a CFA-based active integrator. The oscillation frequency is linearly tunable ( f o ∼ 1 3. 2 MHz) by the multiplier control voltage (V). Subsequently, a high- Q selective band-pass (BP) filter is derived. Effects of the CFA port roll-off parameters and its parasitic capacitors ( C y , z) had been analyzed to be negligible. Measured oscillator response exhibited a THD ∼ 1. 8 %, a linearity error (Δ) ∼ 2. 4 % and a phase noise figure of (−) 104 dBc/Hz at 24-kHz offset. [ABSTRACT FROM AUTHOR]

Electronically tunable synthesis of immittances viz., inductor (L) and FDNR (D), using the voltage tunable current conveyor transadmittance amplifier (VTCCTA) block is presented. Design of selective LC and DR type resonators are derived. Subsequently, based on these resonators new VCO implementations, underlying the concept of short-circuit natural-frequency is proposed. According to this concept, second-order resonators yield a pair of imaginary-axis pole-pair; if Q~∞ this is amenable to sinusoid oscillator implementation without necessitating a nominal input stimulus (Vi ~0: short-circuit) to the resonator whereby the oscillation frequency (fo) is the natural pole-frequency. To this end, both the LC and DR resonators may be utilised for the VCO design using a multiplication mode current conveyor (MMCC) element, of which the LC type follows a linear tuning law variable by a control voltage (Vd.c.). Experimental results with simulation and hardware-circuit test had been satisfactorily verified using standard commercially available IC-modules. Linear range of fo-variation upto 10 MHz with satisfactory phase noise-margin had been measured. [ABSTRACT FROM AUTHOR]

Electronic transitions in the quantum confined states in the conduction band of spherical ZnO semiconductor quantum dot are studied. Photoabsorption spectra and oscillator strengths have been obtained for various sizes of quantum dot using effective mass approximation. Electric quadrupole effect has been included in addition to the electric dipole effect. The nonlinear contribution to photoabsorption spectra has also been studied. Results for transition energies of the quantum confined states are found to be in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

In this paper we study the linear and nonlinear intersubband optical properties of a nanocrystalline singly charged Si semiconductor quantum dot surrounded by an amorphous matrix of silicon dioxide, silicon nitride, and silicon carbide. A finite barrier height is considered at the interface of the dot and matrix. We also consider the effect of self-energy associated with the surface polarization due to the charging of the dot and the size dependent dielectric constant of the dot. The effect of the surrounding matrix is investigated on the linear and nonlinear absorption coefficient, refractive index changes, nonlinear susceptibility, and photoelectric cross section. Using the effective mass approximation (EMA) results are obtained for different dot radii, photon energies, and intensities. It is noted that an increase in barrier height due to the surrounding matrix leads to blueshift in peak positions of absorption coefficients and refractive index change. [ABSTRACT FROM AUTHOR]