Accurate Calculation of TWT Intermodulation in the Many-Carrier Case

The formulas derived by Stette [1] permit the calculation of TWT output carrier power and intermod power when the input to the TWT consists of an infinite number of infinitesimal carriers. The formulas for these quantities involve an integration of the TWT singlecarrier characteristic over a semi-infinite range, and for most of the TWT's one considers, a simple approximation of the integration by a summation gives satisfactory answers. However, when one considers special TWT's, e.g., linearized TWT's or the piecewise linear limiter [2], simple approximations are often not good enough. To get accurate results, a multipoint Gaussian quadrature must be used.     

基于傅立叶级数法的互调产物一般特性分析

分析和讨论了非线性器件互调产物的一般行为特性.在已知传递函数的情况下,采用傅立叶级数法,推导了二载波情况下互调产物的幅度及其随阶数变化的一般表达式.针对两种典型的传递函数(分段线性软限幅器和光滑软限幅器),对二载波输入时的互调产物的幅度进行了数值计算.分析和数值结果表明:互调产物的幅度一般来说随阶数的增加而下降;高阶互调产物的下降行为本质上与传递函数的类型有关.     

AM suppression with low AM-PM conversion with the aid of avariable-gain amplifier

This paper proposes the use of a variable-gain amplifier instead of a hard limiter for amplitude modulation (AM) suppression with low AM-PM (phase modulation) conversion. A hard limiter shows phase shift variations through input-amplitude dependent changes in output waveform, combined with bandwidth limitations. It is shown that these can be kept small only for limiter bandwidths much larger than the input frequency. A linear amplifier with variable gain used for AM suppression does not suffer from this problem. A CMOS variable-gain amplifier with gain-insensitive phase shift has been designed for this purpose. The benefits and limitations of the technique are explored with reference to an experimental 2.5 μm BiCMOS chip for a television IF demodulator. Experimental and simulation results indicate that the AM-PM conversion can be kept below 0.5° at 40 MHz over an input amplitude range of 20 dB, where typical hard limiters show 3-5°. This is achieved with an amplifier bandwidth of 80 MHz, while a hard limiter would need a bandwidth of more than 600 MHz to obtain similar results     

一种ASK接收器中的中频对数放大器IC设计

一种适用于ASK接收器中的双极型对数中频放大器,具有接收信号强度指示的功能(RSSI)。这种放大器实现了对数响应的分段近似,同时作为信号解调的一部分。本文介绍了RSSI特殊的具体电路及其结构。该放大器包含五级放大,每一个放大级都由一个限幅放大器和跨导单元组成。此放大器在±1dB的线性度下实现了90dB的动态范围。     

Fault Current Limiter Based on Resonant Circuit Controlled by Power Semiconductor Devices

This work presents a resonant fault current limiter (FCL) controlled by power semiconductor devices. Initially the operation of two ideal resonant circuit topologies as fault current limiter are discussed. The analysis of these circuits is used to derive an alternative topology to the fault current limiter based on the connection of a series and a parallel resonant circuit. Digital models are implemented in the SimPowerSystem/Matlab simulation package to investigate the performance of the proposed FCL to protect transmission and distribution electric networks against short circuit currents. Transfer functions of the linear limiter models are used to identify the effect of each element of the FCL over its stability and its transient response. The developed analysis will be used to derive modifications in the FCL topology in such a way to improve their dynamic response.     

线性限幅器的设计与研究

ADC芯片广泛用于现代无线电系统,已成为大量军事装备中不可或缺的部分。复杂电磁环境可导致接收机灵敏度下降甚至失效。接收机用的ADC 芯片耐受大信号能力有限,急需一种既能保证其正常工作,又不会影响其采样灵敏度的器件,为此开发了一种新的器件,线性限幅器。为满足高线性度的限幅要求,介绍了一种基于PIN二极管的小型化线性限幅器设计方案。用ADS 仿真设计,薄膜混合工艺、一体化陶瓷管壳装配实现,开发出了一系列频率覆盖10 MHz~5 GHz,尺寸仅5 mm×5 mm×2.5 mm 的高线性度限幅器。测试结果表明,P 波段300~500 MHz产品损耗小于0.6 dB,输出P-1 大于11 dBm,输入0 dBm 信号时OIP3 大于35 dBm,输入25 dBm 信号时漏功率低于12 dBm,最大可承受功率5 W。ADC 芯片的可靠性大大提高,具有广阔应用前景。     

YIG Filters as Envelope Limiters

Envelope limiters are used in such applications as FM demodulation and power leveling. Recently, the envelope-limiting properties of yttrium-iron-garnet (YIG) filters were reported for the special cases of unmodulated and pulsed input signals. Measured data is presented hereon the response of a YIG limiter to AM carriers having modulation index of the order of 50 percent. Sinusoidal, square-wave, and low-pass noise modulating signals were used in the measurements. It was found that a YIG filter will give good envelope Iimiting for modulating frequencies in the submegacycle range. At these low frequencies the carrier and the side frequencies are not limited selectively. At higher modulating frequencies where the limiting is frequency selective, the YIG filter will not remove the variations. In fact, in the particular filter tested, the modulation index was increased, rather than decreased, at modulating frequencies greater than about 750 kc/s. A graph is given showing the measured factor of reduction (or increase) of modulation index, as a function of modulating frequency. The response of the limiter as a function of carrier frequency, modulating frequency, and input power is shown by oscilloscope displays produced by sweeping the carrier frequency or input power. In addition, selected photographs of output envelope waveforms are given.     

Electromagnetic characteristics of superquadric wire loop antennas

The analysis of antenna configurations in the form of a generalized superquadric loop, which includes circular, elliptical and rectangular loop geometries, is presented in this paper. Use of a Galerkin form of the moment method with piecewise sinusoidal subsectional basis and testing functions provides rapid numerical convergence and accurate representation of the antenna current. A convenient parametric representation for the superquadric curve is developed to allow a subsectional formulation using curved wire segments, rather than the commonly employed piecewise linear segments, to construct the geometry. Both magnetic frill and delta gap source models are implemented to allow a detailed study of input impedance, directivity, radiation pattern and current distribution as a function of various geometrical parameters. The results are shown to compare well with previous results for the special case of a circular loop antenna. Some useful curves are presented to aid in the design of practical superquadric loop antennas     

Nonlinear optical limiter and digital optical switch by cascadednonlinear couplers: analysis

In this paper, an all-optical digital switch and a limiter are proposed and analyzed, both of which consist of several nonlinear directional couplers in series. These two devices utilize the nonlinear restraining effect of the nonlinear coherent coupler on its input power. In the devices, the OFF-ON extinction ratio, the output power fluctuation and the dynamic switching range all decrease with the number of the couplers in series increasing, and the output power level can be adjusted by varying the coupling length. The characteristics of these devices with different structures are discussed, and the numerical results show that the OFF-ON extinction ratio and the dynamic switching range of the optical switches can be less than -90 dB and 0.03P_c /100, respectively, and that the fluctuation of the limiting output power of the optical limiter can be less than 10^-7P _c     

Nonlinear Techniques for the Improvement of Signal-to-Noise Ratio

We propose a novel circuit for noise rejection, which is composed mainly of a linear amplifier, a nonlinear amplifier, and a filter. The input signal is applied to a linear amplifier, a bandpass limiter, and an envelope detector followed by a low-pass filter. The output of the lowpass filter is multiplied by the output of the bandpass limiter. The difference between the output of the multiplier and linear amplifier is the output of the proposed circuit. It is then indicated that the proposed circuit rejects noise, of which amplitude is narrow-band relative to the desired signal or noise phase.     

一种脉冲功率微波限幅器的设计

在限幅器最大输入功率理论分析基础上,根据PIN限幅二极管产品手册上最大连续波输入功率和给定脉宽下最大脉冲输入功率等条件,求解得到温度时间常数及任意脉宽下最大脉冲输入功率,给出了分析模型及计算公式。研制了实验验证电路,在频率1GHz、脉宽25μs、占空比1%条件下,最大脉冲输入功率43W,与理论分析相符。     

A Practical Switching Loss Model for Buck Voltage Regulators

In this paper, a review of switching loss mechanisms for synchronous buck voltage regulators (VRs) is presented. Following the review, a new simple and accurate analytical switching loss model is proposed for synchronous buck VRs. The model includes the impact of common source inductance and switch parasitic inductances on switching loss. The proposed model uses simple equations to calculate the rise and fall times and piecewise linear approximations of the high-side MOSFET voltage and current waveforms to allow quick and accurate calculation of switching loss in a synchronous buck VR. A simulation program with integrated circuit emphasis (Spice) simulations are used to demonstrate the accuracy of the voltage source driver model operating in a 1-MHz synchronous buck VR at 12-V input, 1.3-V output. Switching loss was estimated with the proposed model and compared to Spice measurements. Experimental results are presented to demonstrate the accuracy of the proposed model.     

Evaluation of potential integral at singularity of exact kernel in thin-wire calculations

A technique is presented for calculating the potential integral of thin-wire theory at the singularity of the exact kernel in cases where the current is representable as piecewise constant and/or piecewise linear over an interval containing the singularity. The integral of the rapidly varying portion of the kernel is converted to a highly convergent power series. Examples of how one employs the results in computations are given.     

Transient response of a tunnel-diode trigger for linearly varying current pulses

The pertinent forward and reverse transient characteristics of a tunnel diode for a ramp input are analytically investigated. A comparison with the results of a step input shows that the slope of the trigger pulse greatly affects the initial development of the process. The results for a linear piecewise approximation are also presented to estimate the deviation from the actual results.     

An analytic expression for the magnitudes of the signal and intermodulation outputs of an ideal hard limiter,assuming n input signals plus gaussian noise

An expression is derived that gives the output fundamental and intermodulation product magnitudes for an ideal hard limiter, for the case of n input signals plus Gaussian noise. The expression is derived by building upon previous work by Shimbo⁴ to account for the Gaussian noise input. The expression is implemented in a computational tool. Results are generated and are compared with data generated by Jain⁵ for three-signal suppression, and by Blachman¹¹ for the functional relationship between the output and input SNR for a bandpass limiter. In all cases, the data generated agree extremely well with published results.     

The Use of Moment Space Bounds for Evaluating the Performance of a Nonlinear Digital Communication System

Certain moments of the output of a bandpass nonlinear system whose input is a stationary Gaussian random process will be used to evaluate the performance (i.e., the average probability of error) of the system. The main application of this procedure is the analysis of a frequency translating saturating satellite link. The basic analytical technique to be employed will be the use of moment space bounds, it will be shown that by using at most a two-dimensional Gaussian quadrature formula to perform a numerical integration, the bounding procedure presented in this paper can be used in a relatively straightforward manner with virtually any bounded bandpass nonlinearity. Numerical results Corresponding to a hard limiter with only an AM/AM characteristic will be presented, as well as results corresponding to a soft limiter with both AM/AM and AM/PM characteristics. In the latter model, the effects of intersymbol interference will also be included. However, computationally, the procedure is only feasible for a small number of interfering terms.     

A programmable piecewise linear large-signal CMOS amplifier

A high-speed CMOS piecewise linear approximation circuit is presented that can be programmed for correction of nonlinearity after fabrication. The basic building block generates a linear segment, for which slope and position can be adjusted. Adjustments to adapt to arbitrary functions are done with floating gate devices fabricated in standard CMOS technology. The circuit is a voltage-to-current converter with an input range of the full power-supply voltage swing. In an implementation with 18 linear segments less than 0.15% error over rail-to-rail input range was achieved for a linear transfer function. Examples of strongly nonlinear transfer functions approximated to 0.5% accuracy are shown. The large-signal 3-dB frequency is 10 MHz. The implementations are done solely with 2-μm channel length devices     

曲线分段的矩量法分析阿基米德平面螺旋天线

从混合位积分方程出发,采用矩量法结合曲线分段的三角基函数和脉冲检验函数分析了阿基米德平面螺旋天线,给出了输入阻抗,电流分布以及辐射方向图结果.从曲线形式的海伦积分方程出发结合折线分段的脉冲基函数点匹配法比较结果与文献[2～4]十分吻合.由于采用了曲线分段,在相同分段数情况下其结果的精度将比采用折线分段的高.     

Modulo sigma-delta modulation

A modulo sigma-delta modulator is introduced, and the behavior of the quantization error is derived. The system consists of a modulo limiter followed by a sigma-delta modulator. The limiter confines the input to the no-overload region of the sigma-delta modulator, and the modulo arithmetic performed by the limiter is amenable to recently developed techniques for the exact analysis of quantizer error behavior in sigma-modulators with bounded inputs. The quantization error behavior is derived for a modulator driven by a quasi-stationary random process. The limit distribution and the power of the quantization error are found. Except for some singular cases, the normalized quantization error is uniformly distributed in [-1/2, 1/2]. The power spectrum and the autocorrelation function of the quantization error with a causal ARMA ( p, q) process input are also derived. It is shown that the quantization noise is white when the input is a random process with stationary independent increments. Simulation results support the theoretical analysis     

Automatic color image contrast enhancement using Gaussian mixture modeling,piecewise linear transformation,and monotone piecewise cubic interpolant

Conventional contrast enhancement algorithms use complicated nonlinear mapping functions with parameters specified manually. In this paper, a parameter-free piecewise linear transformation and monotone piecewise cubic interpolation are used for color image contrast enhancement. The Gaussian mixture model is used to divide luminance histogram of input color image into multiple sub-histograms. Each sub-histogram is mapped linearly or nonlinearly to a portion of available output dynamic range proportional to its extent and the number of its pixels. The proposed algorithm has more controlled contrast enhancement than conventional algorithms to preserve natural outlook and local details in the input color image. This is done by considering brightness histogram preservation of input image by proposed algorithm, due to considering extent of each sub-histogram for allocating a portion of output dynamic range to it. Experimental results show that the proposed algorithm produces better or comparable contrast-enhanced images with natural outlook than several conventional algorithms on various types of images.