A new acousto-electro-optic improved resolution deflector for high frequency operation

The two main constrains on the characteristics of the acousto-optic deflector are the acoustic sound attenuation and velocity. These two parameters will determine the resolution and the radio frequency bandwidth. Due to a double degenerated phase matching condition on a specific acousto-optic deflector configuration, the possibility of an improvement on the resolution of the acousto optic deflector becomes evident. This degenerescence is the result of the action of a D.C. electric field by the electro-optic effect. This configuration presents several advantages upon the early related works based on optical activity of selected materials and enables a wideband interaction in such a way that the number of resolvable channels is kept high. This has implications on the acousto-optic spectrometers for wideband radio astronomy research.     

A new method to enhance frequency operation of CMOS ring oscillators

This article proposes a frequency-boosting method for CMOS ring oscillators. It consists of adding RC-based differentiators in delay cells to speed up their transient responses. Two novel delay cells for simple and differential versions are presented. On using MOS transistor components to implement the differentiators, the resulting increase of surface area is observed to be moderate, and this allows frequency tuning by voltage control, without inducing additional phase noise. The presented circuits are suitable for low-voltage operation. Simulation results on the proposed circuits have shown significant frequency enhancement with a competitive factor of merit.     

Pulsewidth control loop with a frequency detector for wide frequency range operation

A pulsewidth control loop (PWCL) with a frequency detector for wide frequency range operation is presented. The proposed PWCL is implemented with a duty cycle controlled circuit and frequency detector to correct the wide range frequency and duty cycle of the input clock. The duty cycle controlled circuit is able to modify the gain with different frequency and duty cycle ranges. The frequency and duty cycle of the input clock are detected by the frequency detector. The frequency detector is based on a ring oscillator and the input clock duty cycle and frequency are detected within two input clock cycles. The proposed circuit has been fabricated in a 0.35 μm CMOS technology. The proposed circuit generates the output clock of 50% duty cycle with the input range from 20% to 80% and frequency range 50–800 MHz. The measured duty cycle error is less than 1% within the frequency range from 50 MHz to 800 MHz.     

Load frequency control using Lyapunov's second method: Bang-bang control of speed changer position

This letter reports a bang-bang load frequency control policy based on the second method of Lyapunov. The proposed method is simple and practically feasible for implementation. A numerical illustration on a two-area load frequency control system is presented in order to verify the practicality of the proposed method.     

新形势下的标准组织运作机制研究

随着信息通信技术与垂直行业的深度融合,新形势下跨行业标准组织共同制定标准成为必然。知识产权对标准组织运作产生深刻影响,所以标准组织需要确保自身知识产权政策的包容性和温和性,还需要明确合作制定标准的知识产权问题的处理机制,以减少后续纠纷的发生。3GPP和IEEE的运作机制进行了对比,分析了知识产权对标准组织运作产生的重要影响。     

Direct frequency modulation of a semiconductor laser by acoustic waves

Frequency modulated signals in the output of a semiconductor laser diode are generated by applying bulk acoustic waves to the device. The mechanism involved is discussed and theoretical and experimental results are compared.     

IMPATT operation below the avalanche frequency

Very high output powers are obtained with double drift IMPATT diodes at current densities which shift the avalanche frequency above the oscillation frequency: 30-40 W pulsed around 90 GHz. This operation mode cannot be explained in terms of the conventional READ theory. A numerical large signal simulation shows that avalanche multiplication over the whole diode takes place. At high current densities the double drift device behaves like a pin diode without the unfavourable breakdown of the ionisation process in the centre of the diode.<>     

Direct frequency modulation of a semiconductor laser by surface acoustic waves

Frequency-modulated signals in the output of a semiconductor laser are generated by applying surface acoustic waves to the device. The SAW modulator is discussed and theoretical and experimental results are compared.     

新形势下电网运行维护技术的安全生产

电网运行维护的安全生产工作,关乎人们的用电以及生命财产安全,是电力行业发展中极为重要的工作内容.因此,鉴于电网运行维护安全生产工作的重要性,本文对这一工作开展中诱发问题出现的影响因素进行了分析,并提出了强化工作对策,旨在为电网运行维护安全生产工作的顺利开展提供帮助.     

GaAs---GaAlAs heterojunction transistor for high frequency operation

A bipolar transistor structure is proposed having application for either high frequency operation or integration with certain types of light emitting devices. The structure involves liquid phase epitaxially grown layers of GaAs for the collector and base regions, and of Ga_1−xAl_xAs for the heterojunction emitter. The high frequency potential of this device results primarily from the high electron mobility in GaAs and the ability to heavily dope the base region with slowly diffusing acceptors. The Ga_1−xAl_xAs emitter region provides a favorable injection efficiency and, because it is etched preferentially relative to GaAs, access to the base layer for making contact. Transistor action with d.c. common emitter current gains of 25 have been thus for observed. Calculations of the high speed capability of this transistor are presented.     

Microwave frequency operation of the heterostructure hot-electrondiode

The generation of microwave frequencies by the heterostructure hot-electron diode (H²ED) is discussed. At 77 K, self-oscillation has been produced over a broad frequency range from direct current to 10.5 GHz, limited by the parasitic series resistance and capacitance. Considerations of the bias polarity required to produce oscillations and of their high-frequency response support a model of switching from tunneling to thermionic emission     

Direct frequency demodulation with frequency-locked Gunn oscillators

The use of a frequency-locked Gunn oscillator as a frequency demodulator is described. A detection sensitivity of ?40 to ?30 dBm is obtainable with detected signals in the millivolt range.     

High relaxation oscillation frequency operation of a QW-LD at thesecond quantized level

We describe a new approach for improving the relaxation oscillation frequency characteristics of quantum-well lasers at the second quantized level. Applying an antireflection (AR) and high-reflection (HR) coating to the laser facets suppresses lasing at the first quantized transition and promotes it at the second quantized transition. The relaxation oscillation frequency for the laser emitting at the second quantized transition is twice as high as that for the laser at the first quantized transition. The increase in the relaxation oscillation frequency of the laser operated at the second quantized transition is mainly due to the increase in the differential gain. Furthermore, the differential quantum efficiency increases to 0.5 in the AR/HR-coated laser     

新型矩阵变换器安全运行策略的研究

由于矩阵式变换器（MC）没有续流回路,因而保证其安全运行也就成为了一个难点.提出了一种新型MC故障容错安全运行策略,当出现故障时,通过控制变换器双向开关的导通状态为负载提供一个可控安全的续流回路,使负载能够在短时间内释放储能,减少对变换器系统电路的损坏.并对故障情况进行分析,通过MATLAB/Simulink仿真验证该策略的正确性和可行性.     

Direct synthesis of a new class of bandstop filters

A direct synthesis technique of a new class of bandstop coupled resonator elliptic filters is presented. Two different coupling schemes, which both include source-load coupling are used. The first coupling and routing scheme is the standard folded structure used in implementing bandpass elliptic filters with N transmission zeros using N resonators. The second coupling scheme is identical to the multipath parallel structure, which was recently introduced for the synthesis of fully elliptic bandpass filters. In both cases, the source and load are directly coupled by an inverter in order to generate the required transmission zeros. It is shown that, for each coupling scheme, two distinct solutions that are not related by a similarity transformation exist. Furthermore, the two solutions both have realistic coupling coefficients in contrast to the bandpass case where only one solution, in general, is practical. It is also shown that the same coupling scheme can implement pseudoelliptic bandstop filters with N/sub z/ reflection zeros where 0/spl les/N/sub z//spl les/N.     

Dual slot-coupled microstrip antenna for dual frequency operation

A new dual slot-coupled circular antenna for dual frequency or dual polarisation operation is proposed. By optimising the placement of the two slots, high isolation between two ports is achieved. Experimentally, an isolation of more than 35 dB is obtained at L-band.<>     

Effects of diode-package cutoff frequency on TRAPATT operation

The cutoff frequency of two ideal types of package is considered, and is shown to limit the maximum rate of rise of voltage for triggering the TRAPATT mode in a commonly employed circuit. The letter also places the negative-inductance concept employed in the analysis on a mathematical foundation.     

Direct digital frequency synthesiser with high memory compressionratio

A 16 bit, 100 MHz, low-power direct digital frequency synthesiser is presented. A simple trigonometric approximation is applied to ROM compression to achieve a compact architecture. The compression ratio for the look-up table is 455:1 and the spurious-free dynamic range 96 dBc     

Stabilization of single frequency operation of coupled-cavity lasers

We present a theoretical analysis of cleaved coupled-cavity lasers. Mode selectivity arises from two mechanisms. The first is diffraction loss in the gap between the cleaved sections. The second is based on one section acting as a resonant reflector. Our analysis includes the change of refractive index with carrier density which shifts the cavity resonances and causes mode switching. Above threshold the gains g1and g2of the two cavities are not pinned, but are related for each mode in the form of a curve in the (g_{1}, g_{2}) plane. The separation of mode curves along a 45° line determines the ratio of mode intensities. Single mode operation above threshold is described by zones in the (C_{1}, C_{2}) plane where C1and C2are the currents driving the two cavities. Cases of stable, unstable, and bistable operation are discussed.