MQAM调制器的设计与实现

文中提出了一种多电平正交振幅调制器(MQAM)的设计与实现方法。该调制器由纠错编码部分、脉冲成形滤波器和混频器构成。实践证明,本设计可在单片FPGA中实现DAVIC协议中所建议的MQAM(M=16,64,256)调制器。该设计可在数字电视机顶盒(STB)内作为实现交互电视(iTV)的主体功能模块,具有较高的实用价值。     

Design of a SiGe-Si quantum-well optical modulator

A light modulator consisting of modulation-doped SiGe-Si multiple quantum wells integrated in a silicon-on-insulator waveguide is designed. The device is based on the electrorefractive effect due to the variation of holes density in the SiGe wells, induced by applying a reverse bias on a PIN diode. This mechanism is simulated by numerical calculations of the hole distribution coupled with the optical guided mode propagation characteristics. The mode effective index variation of TE-polarized light at the 1.31-/spl mu/m wavelength can then be obtained as a function of the applied bias. The influences of the structure parameters such as the thickness and the doping level of the doped barrier layers or the number of SiGe wells is analyzed thanks to a design of experiment method. The optimization gives an effective index variation of 2.10/sup -4/ for an applied bias voltage of 6 V. To obtain optical intensity modulation, this structure has to be included in a Fabry-Perot cavity. The modulation performances are analyzed.     

The higher harmonics of the electromagnetic moments of a magnetoelectric reducer

In a correctly designed magnetic reducer, the electromagnetic moments depend on the torque angles, with the dependence being near-sinusoidal. If the active zones have a nonoptimal geometry, the electromagnetic moments have high-frequency oscillations caused by the reaction moments, resulting in discrete locking or sticking of the fixed rotors. Under unfavorable conditions, the amplitudes of the pulsations may be comparable with the maximum or tilting electromagnetic moment value. The electromagnetic moments of a magnetoelectric gear reducer (MER) are calculated by the energy method based on trigonometric-series expansion of the specific magnetic conductance of the air gaps and the MMF of the magnets. For this purpose, integral expressions are found for the magnetic field energies in the air gaps which depend on the rotational positions of the rotors with respect to the fixed stator magnets. For arbitrary selected harmonics of the magnetic conductance of the air gaps and the magnets’ MMF, the conditions are determined for the orders of the above harmonics and the number of the cogs and poles at which the integrals for the magnetic field energy will be different from zero. Such an approach allowed deriving equations for the basic electromagnetic moments and the concomitant stray moments. If the found conditions are not met, the extraneous harmonics of the electromagnetic moments are eliminated. Selection of a number of modulator rods equal to a prime number is a radical means of eliminating higher harmonics of the electromagnetic moments. If a prime number of the rods cannot be selected, such numbers of the stator pole pairs should be selected at which the presence of higher harmonics of the electromagnetic moments is possible at the highest order values of the harmonics of the magnetic conductance of the air gaps and the MMF of the stator and rotor magnets.     

Fast control of current of a pulse-width modulator

A fast system of controlling a current in an active inductive load by a pulse-width modulator is proposed. For maximum fast control, a dead-beat control constructed without transformation of coordinates is used. A synthesis method of regulator parameters is given.     

Magnetic instability of ac multifilamentary superconductors in spatially distributed magnetic field

Alternating current (ac) superconducting machines such as superconducting generators, transformers, or resistive current limiters need large‐current‐capacity conductors. These conductors are generally fabricated as multistrand cables stacked with multifilamentary NbTi superconductors whose current capacity is a few tens of amperes. ac quench current degradation has often been observed in ac use of such multistrand cables. Several reasons for this degradation have been pointed out: nonuniformity of each strand current, mechanical disturbances, thermomagnetic instability, and ac losses. However, it has not as yet been overcome. Since the angle between the strand axis and the cable axis changes along the cable axis in multistrand cables, the strands are exposed to a spatially (axially) distributed magnetic field, which has longitudinal and transverse components changing periodically due to multiple cabling. This paper mainly discusses the thermomagnetic instability due to the distributed transverse magnetic field, which was compared with the self‐field instability and the longitudinal field instability experimentally and theoretically. It was confirmed that the ac quench current degradation due to the distributed transverse field could be induced by the following: nonlinear E–j characteristic, strong dependence of E–j characteristic on magnetic field in low field region, uniformity of the axial current profile inside the superconductor with the high resistive matrix, and the poor thermal diffusion of CuNi/NbTi composites. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 45–55, 2000     

Contribution to the modeling of a non-ideal Sigma-Delta modulator

One major issue facing the design and the simulation of complex circuits, such as Sigma-Delta modulators (ΣΔM), is the relatively large computing-time; required when using transistor level based simulators. Hence, high-level system modeling is suitable to achieve a time-efficient IC design. In this scope, the aim of the present work is to develop an enhanced model for a switched-capacitor second order sigma delta modulator. Besides the numerous effects, already included in the standard models, many additional non-idealities aspects have been taken into consideration. Namely, the DC nonlinearity behavior of both: the operational amplifier (OP-AMP) and the switches ON-resistance. The obtained model permits, thus, more accurate prediction of the relative signal-to-noise ratio (SNR), compared to the standard one.     

A single-phase inverter with a deadbeat regulator of a pulse-wide modulator

The structure of a control system for a pulse-wide modulator (PWM) of a single-phase voltage inverter is proposed; this control system comprises a deadbeat regulator for inducing transient processes with a finite duration in the near vicinity of an equilibrium position. A method for synthesizing the parameters of the regulator for an inverter that includes an active-inductive load with an output voltage feedback is described. Results of modeling the processes, which show a higher efficiency of the deadbeat regulator, are presented.     

Design of a phase-shifting optical feedback interferometer using anelectrooptic modulator

A laser sensor using optical feedback interferometry has been designed to measure displacements up to several micrometers. For this purpose, a lithium niobate crystal generates a phase shift in order to modulate at a frequency of 580 kHz the optical path difference between the sensor and the target. This setup has been calibrated by means of a commercial optical fiber sensor. The overall accuracy resulting is better than 65 nm for a 1-kHz sinusoidal motion of the target at 10 cm away from the sensor     

Magnetic characteristics of oxide superconductors for the application of running systems with magnetic levitation

A model vehicle is constructed which runs without contact to its magnetic rail using oxide superconductors. This paper describes the forces acting between the superconductor and the rail for such a purpose. The attractive and repulsive forces were measured at 77 K as a function of distance between the superconducting pellet and the magnetic rail. As suprconducting pellets, three kinds of materials, i.e., MPMG-Y123, BiPb2223, and Hg1223, were investigated for three kinds of permanent magnets, i.e., Nd-Fe-B, Sm-Co and ferrite.     

Simulation of a high speed interferometer optical modulator in polymer materials

In this work, the design and simulation of a high speed (300 GHz) electro-optic modulator operating at 1550-nm wavelength is presented. As electro-optic active material, a nonlinear optical polymer with highly nonlinear chromophores dispersed in an amorphous polycarbonate is used. Optimization of modulator geometrical structure and extraction of device performance parameters are obtained by 3D simulations. Finite Element Method has been exploited for the solution of Laplace equation to calculate the microwave properties of polymer-based modulator and to design its electrodes. The modeling procedure has been validated by comparison with experimental results presented in literature.     

多位数字delta-sigma调制器的设计

本文介绍了一个高信噪比的、用在24位44.1 kHz采样率的音频数/模转换器(DAC)中的4阶15级量化的delta-sigma调制器(DSM).在设计中,为了减少量化噪声,选用了奇数个量化等级;为了提高动态范围(DR),在设计噪声传输函数(NTF)时对零点进行优化,通过这些方法降低量化噪声和时钟抖动的影响.这个DSM的峰值信噪比(SNR)可以达到130 dB以上,满足0.35μmCMOS工艺设计的音频DAC的系统要求.本文给出了这个DSM的MATLAB仿真模型及仿真结果,并在此基础上给出了电路实现结构.     

Scaling the modulation bandwidth and phase efficiency of a silicon optical modulator

We present an optimized design and detailed simulation of an all-silicon optical modulator based on a silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. Based on a fully vectorial Maxwell mode solver, we analyze the modal characteristics of the silicon waveguide. We show that shrinking the waveguide size and reducing gate oxide thickness significantly enhances the phase modulation efficiency because of the optical field enhancement in the voltage induced charge layers of the MOS capacitor, which, in turn, induce refractive index modulation in silicon due to free carrier dispersion effects. We also analyze the device speed by transient semiconductor device modeling. As both optical absorption and modulation bandwidth increase with increasing doping concentration, we show that, with a nonuniform doping profile in the waveguide, balance between the device operation speed and optical loss can be realized. Our simulation suggests that a TE-polarized optical phase modulator with a bandwidth of 10 GHz and an on-chip optical loss less than 2 dB is achievable in silicon.