Using Analog Predistortion for Linearizing Class A–C Power Amplifiers

An analog 5th order, complex-valued polynomial predistortion IC has been built to linearize the behavior of RF power amplifiers. The predistorter can be used either at baseband or low IF frequencies and it was tested using a simple IF amplifier that could be biased to operate in classes A, AB, B and C. Intermodulation products can be reduced by 20 to 30 dB in classes A and AB over a bandwidth of several MHz. In classes B and C the shape of nonlinearity is such that a low-order polynomial predistortion function is not sufficient for linearizing them.     

An Envelope Hammerstein Model for Power Amplifiers

In this paper, an envelope Hammerstein （EH） model is introduced to describe dynamic input -output characteristics of RF power amplifiers. In the modeling approach, we use a new truncation method and an established nonlinear time series method to determine model structure. Then, we discuss the process of model parameter extraction in detailed. Finally, a 2 W WCDMA power amplifier is measured to verify the performance of EH model, and good agreement between model output and measurement result shows our model can accurately predict output characteristic of the power amplifier.     

一种新型Class AB开关电流存储单元的设计

设计了一种新型高性能Class AB开关电流(SI)第一代存储单元电路。电路由对称的电压反转跟随器(FVF)连接Class AB SI存储单元组成,输入级采用电流传输器结构,输出级采用可调共源共栅结构,电路具有误差小、功耗低、性能高等特点。基于此存储单元,设计了延时器和双线性积分器进行验证。电路采用SMIC 0.18μm工艺,在Spectre中进行仿真。结果表明,该存储单元具有较好的性能和应用价值。     

Selection of Parameters of the Primary Feed of the Luneberg Lens for the Sum–Difference Operating Mode

Excitation of the Luneberg lens by an arc antenna array of open-ended rectangular waveguides forming the H₁₀ wave is studied. Technical limitations imposed on the array of primary feeds in order to form the sum and difference operating modes of the antenna system are discussed.     

Helical antenna for satellite transmission†

The use of helical antennas for satellite transmission is proposed. The polar diagram, directivity and polarization characteristics are outlined. The advantages of circularly and elliptically polarized waves transmitted from the helical antenna for Faraday rotation experiments are discussed. The use of helical array is comparatively more compact, radiation characteristics are frequency independent and the polarization of the radiated wave is more stable. These features enable an accurate measurement of the Faraday rotation which is likely to yield a better estimate of total electron content.     

Numerical Spectral Model Based on BPM for Er-doped Waveguide Amplifiers

A spectral numerical analysis method to analyze the Er-doped waveguide amplifiers（EDWA） in wavelength division multiplexing is presented. This model is based on finite difference beam propagation method modified by Douglas scheme, which can efficiently reduce the truncation error and time consumption. By superposing the Lorentzian function for the experimental curves, the spectral properties of EDWA can be investigated. Results show that the pump efficiency of EDWA pumped at 980 nm is higher than that at 1 480 nm. Meanwhile, by rationally increasing the pump length and the erbium concentration, larger signal gains can be acquired. Taking account of the up-conversion and cross-relaxation effects of cooperation, the spectrum analysis of highly doped EDWA is carried out over a wider frequency band.     

A Novel Offset-Cancellation Technique for Low Voltage CMOS Differential Amplifiers

基于对CMOS差分放大器的非线性和元件失配理解的基础上,提出了一种应用于低电压CMOS差分放大器的失调取消技术.这种技术在不需要增加功耗的基础上,通过把输出端的失调电压转移到差分放大器的其他节点,从而达到减小输入参考的失调电压的目的.为了验证这种技术,设计了一个工作电压为1.8V的低失调的CMOS差分放大器.仿真结果表明,在负载晶体管的失配为20%,输入放大管的失配为10%时,利用这种失调转移技术,输入参考的失调可以减少40%.同已发表的失调取消技术相比,利用这种技术可以达到更低的功耗和更高的集成度.     

Frequency Variations of π-equivalent Circuit Parameters of a Junction Transistor †

One of the most useful small-signal equivalent circuit representations is based on a m-equivalent circuit representation of the transistor in a common-emitter connection. This m-equivalent circuit representation is more readily and commonly employed in circuit analysis or design in comparison with a ^'-equivalent circuit representation. The variation of equivalent circuit parameters at high frequencies in the π-equivalent circuit representation was determined by Giacoletto experimentally. Unfortunately, however, we have no example but the above, in spite of this problem being very common and important. The exact expression for π-equivalent circuit parameters is too complicated to be calculated. The result may be somewhat simplified by expanding the hyperbolic function into a Taylor series and retaining only the first few terms. Numerical values of these approximate expressions are calculated and then compared with values calculated from the corresponding exact expression. Furthermore, w-equivalent circuit parameters relative to low-frequency values are given as a function of frequency relative to f_T and f_α. The π-equivalent circuit parameters of a p-n-p germanium alloy-junction transistor of the diffusion (homogeneous base) type are obtained by measuring small-signal h parameters under the low-level injection conditions with an impedance bridge. Then, it is made clear that they are in reasonably good agreement with theoretical values. The approximate expression for α is proposed, where α is analysed in terms of magnitude and phase shift. It is shown that it is more exact and more useful than the expressions such as the Thomas-Moll expression, etc., as a result of discussing the errors in the approximations of the equations.     

Optimum Design for a Low Noise Amplifier in S-Band

An optimum design of a low noise amplifier （LNA） in S-band working at 2-4 GHz is described. Choosing FHC40LG high electronic mobility transistor （HEMT）, the noise figure of the designed amplifier simulated by Microwave Office is no more than 1.5 dB, meanwhile the gain is no less than 20 dB in the given bandwidth. The simulated results agree with the performance of the transistor itself well in consideration of its own minimum noise figure （0.3 dB） and associated gain （15.5 dB）. Simultaneously, the stability factor of the designed amplifier is no less than 1 in the given bandwidth.     

Operating System Support for High-performance Networking: a Survey

1　Introduction　Manycrucialapplicationssuchasteleconferencing ,distributedcomputingarebecomingfeasiblewithemerging high performancenetworkservices .ThesenetworkservicessuchasFDDI ,ATMandHIPPIpro videhighbandwidthandlowlatency .Forexample ,FDDIcouldoperateat 10 0Mb/s;Sonet/ATMOC 12couldoperateat 6 2 2Mb/s .Somehigh speedLANssuchasMyrinetandgigabit ethernet ,andSonet/ATMOC 4 8networkbackbonescanoperateat 1Gb/sandabove .　However,thesehigh performancenetworkservicesareyettobefully…     

Solid-state replacement for low-noise valve preamplifier†

On the basis of a previous study a transistor low-noise preamplifier has been built to replace an existing valve preamplifier. The new preamplifier has a voltage gain of approximately 50 dB over the frequency range 50 Hz to 5 MHZ and noise figure 1 to 5 dB over 10 kHz to 1 MHZ for a source resistance of 100 Ω to 100 KΩ ; those performance figures are better than with the valve preamplifier. Detailed numerical data are also given on three sets of noise parameters for the new transistor preamplifier.     

Automatic Parameters Selection for SVM Based on PSO

Motivated by the fact that automatic parameters selection for Support Vector Machine （SVM） is an important issue to make SVM practically useful and the common used Leave - One - Out （LO0） method is complex calculation and time consuming,an effective strategy for automatic parameters selection for SVM is proposed by using the Particle Swarm Optimization （PSO） in this paper. Simulation results of practice data model demonstrate the effectiveness and high efficiency of the proposed approach.     

Optimum Multiuser Detector for Multipath Slow Fading Asynchronous CDMA Channels

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Design Technologies for Silicon-Based High-Efficiency RF Power Amplifiers： A Brief Overview

This paper presents a brief overview of several promising design technologies for high efficiency silicon-based radio frequency （RF） power amplifiers （PAs） as well as the use of these technologies in mobile broadband wireless communications. Four important aspects of PA design are addressed in this paper. First, we look at class-E PA design equations and provide an example of a class-E PA that achieves efficiency of 65-70% at 2.4 GHz. Then, we discuss state-of-the-art envelope tracking （ET） design for monolithic wideband RF mobile transmitter applications. A brief overview of Doherty PA design for the next-generation wireless handset applications is then given. Towards the end of the paper, we discuss an inherently broadband and highly efficient class-J PA design targeting future multi-band multi-standard wireless communication protocols.     

The phase-plane for Langmuir's equation for space-charge limited current flow†

We consider the behaviour of the solutions of Langmuir's equation in the phase-plane and in particular we discuss the nature of the singular points and the directions of the asymptotes. It is shown that the isoclines of the equation are a family of conies passing through the singular points.     

Extremum principles for constraint problems in electrostatics †

In this paper the recently developed theory of complementary variational principles is extended to include constraints. The theory is applied to electrostatic fields where the constraint corresponds to the specification of the total charge on a conductor.     

Photovoltaic Theory for a Homogeneously Irradiated Semiconductor†

The steady-state zero-current photovoltaic effect for a semiconductor subjected to strong illumination, which is only weakly attenuated, turns out to be mathematically tractable. Spatial variation of the electrostatic potential and the associated hole-electron densities, corresponding to a surface potential established by surface states and traps, derives from a reduced Poisson-Boltzmann equation. The intrinsic or compensated semiconductor proves soluble in closed-form whereas the extrinsic case can be handled by recently developed power Beries methods; the convergence of the latter is more or less assured in the region of physical interest, becoming questionable in the overly perturbed region where large shifts in the Fermi levels for the holes and electrons occur.     

An Algorithm for Solving a Class of Transportation Problems

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Optimization of an X-band Interferometer for Plasma Diagnostics†

A 9 GHZ (3 cm) microwave free-space interferometer for measuring electron density decay over the range 2 × 10¹¹?10¹⁰ cm^?3 in a pulsed discharge afterglow is described. By using initial 90° unbalancing (instead of the conventional 180° balance) considerable improvement in sensitivity was obtained. In addition, amplitude modulation of the microwave probing signal enabled instantaneous power fluctuations to be recorded accurately as a function of time during the afterglow. Significant errors are shown to arise if the effects-of finite plasma boundaries are ignored.     

Optimum Trans–Receiver Scheme Using Cross Layer Design for Acoustic Communication

The main objective of this work is to reduce the packet loss due to packet error rate and buffer overflow for under water sensor network. In this work, a system is mapped into various states based on channel condition, buffer space, and available energy level. The set of policies are defined in terms of transmission power level, adaptive modulation scheme, and various transmission rate. We have proposed Optimum Trans–Receiver Scheme (OTRS), in which the problem is formulated as per Markov decision process model and solution is sought in terms of optimum policy identification for an individual state of the system. We have evaluated the performance of OTRS by extensive simulation with existing Adaptive Modulation Power Adaption, Power Adaption with 2 Ary Frequency Shift Keying and Power Adaption with 8 Ary Frequency Shift Keying for various performance matrices like Net Bit Rate and number of packet loss for various state of the system.