Integral function method for determination of nonlinear harmonic distortion

The analysis of harmonic distortion is of prime importance for the analog and mixed integrated circuits. Recently we presented a new integral function method (IFM), based on a completely new principle, which allows the calculation of harmonic distortion using the DC output characteristic of devices or circuits. In this work we complement the integral function method to provide direct calculation of the following distortion figures: total harmonic distortion (THD), second harmonic distortion (HD2) and third harmonic distortion (HD3), voltage intercept points (VIP) and the intermodulation distortion (IMD). The comparison with the same distortion figures calculated by the Fourier coefficients (FC), by direct AC measurements and from FFT in simulators, indicates that results obtained by IFM give an excellent agreement in the full range of the analyzed active regions. The IFM combines simplicity and computer efficiency with accuracy and with the possibility to easily analyze the distortion when varying any of the circuit or device parameters.     

线阵CCD相机镜头畸变标定方法

针对线阵CCD相机标定时镜头会产生畸变的情况,提出来一种利用交比不变的方法,考虑镜头同时存在的径向畸变和离心畸变,对畸变参数进行标定,建立畸变校正函数,并利用Matlab做出镜头畸变曲线,分析了线阵CCD相机镜头仅仅存在径向畸变时对结果的影响和径向畸变与离心畸变都存在时的影响。这种方法应用于相机标定之前,可以有效地消除线阵CCD相机镜头误差对整体标定结果的影响。     

An information criterion for likelihood selection

For a given source distribution, we establish properties of the conditional density achieving the rate distortion function lower bound as the distortion parameter varies. In the limit as the distortion tolerated goes to zero, the conditional density achieving the rate distortion function lower bound becomes degenerate in the sense that the channel it defines becomes error-free. As the permitted distortion increases to its limit, the conditional density achieving the rate distortion function lower bound defines a channel which no longer depends on the source distribution. In addition to the data compression motivation, we establish two results-one asymptotic, one nonasymptotic-showing that the the conditional densities achieving the rate distortion function lower bound make relatively weak assumptions on the dependence between the source and its representation. This corresponds, in Bayes estimation, to choosing a likelihood which makes relatively weak assumptions on the data generating mechanism if the source is regarded as a prior. Taken together, these results suggest one can use the conditional density obtained from the rate distortion function in data analysis. That is, when it is impossible to identify a “true” parametric family on the basis of physical modeling, our results provide both data compression and channel coding justification for using the conditional density achieving the rate distortion function lower bound as a likelihood     

Adaptive JPEG steganography with new distortion function

This paper presents an adaptive steganographic scheme in JPEG images by designing a novel distortion function. While some previous works employed distortion functions based on coefficient difference, we point out that the data embedding on coefficients with larger absolute values may cause less steganalytic detectability. In the proposed scheme, the distortion function is derived from both the coefficient residual and coefficient value, which measures the risks of detection due to the modification on cover data. With an exhaustive searching method, the parameters of the proposed distortion function are optimized. Then, we may employ syndrome trellis coding to embed the secret data into JPEG images when keeping a low risk. This way, the modifications are forced into high textured areas in JPEG images, and experimental results demonstrate that the steganographic security is improved by the designed distortion function.     

Source Coding With Limited-Look-Ahead Side Information at the Decoder

We characterize the rate distortion function for the source coding with decoder side information setting when the ith reconstruction symbol is allowed to depend only on the first i+lscr side information symbols, for some finite look-ahead lscr, in addition to the index from the encoder. For the case of causal side information, i.e., lscr=0, we find that the penalty of causality is the omission of the subtracted mutual information term in the Wyner-Ziv rate distortion function. For lscr>0, we derive a computable "infinite-letter" expression for the rate distortion function. When specialized to the near-lossless case, our results characterize the best achievable rate for the Slepian-Wolf source coding problem with finite side information looka-head, and have some surprising implications. We find that side information is useless for any fixed lscr when the joint probability mass function (PMF) of the source and side information satisfies the positivity condition P(x,y)>0 for all (x,y). More generally, the optimal rate depends on the distribution of the pair X,Y only through the distribution of X and the bipartite graph whose edges represent the pairs x,y for which P(x,y)>0. On the other hand, if side information look-ahead is allowed to grow faster than logarithmic in the block length, then H(X|Y) is achievable. Finally, we apply our approach to derive a computable expression for channel capacity when state information is available at the encoder with limited look-ahead     

Residual vector quantization using a multilayer competitive neuralnetwork

This paper presents a new technique for designing a jointly optimized residual vector quantizer (RVQ). In conventional stage-by-stage design procedure, each stage codebook is optimized for that particular stage distortion and does not consider the distortion from the subsequent stages. However, the overall performance can be improved if each stage codebook is optimized by minimizing the distortion from the subsequent stage quantizers as well as the distortion from the previous stage quantizers. This can only be achieved when stage codebooks are jointly designed for each other. In this paper, the proposed codebook design procedure is based on a multilayer competitive neural network where each layer of this network represents one stage of the RVQ. The weight connecting these layers form the corresponding stage codebooks of the RVQ. The joint design problem of the RVQ's codebooks (weights of the multilayer competitive neural network) is formulated as a nonlinearly constrained optimization task which is based on a Lagrangian error function. This Lagrangian error function includes all the constraints that are imposed by the joint optimization of the codebooks. The proposed procedure seeks a locally optimal solution by iteratively solving the equations for this Lagrangian error function. Simulation results show an improvement in the performance of an RVQ when designed using the proposed joint optimization technique as compared to the stage-by-stage design, where both generalized Lloyd algorithm (GLA) and the Kohonen learning algorithm (KLA) were used to design each stage codebook independently, as well as the conventional joint-optimization technique     

FM and IM intermodulation distortions in directly modulatedsingle-mode semiconductor lasers

Intermodulation distortion in directly-modulated semiconductor lasers is described with the aid of a nonlinear differential equation for the photon density. Both frequency modulation (FM) and intensity modulation (IM) have been investigated. Curves are presented of the magnitudes of the intermodulation products relative to the carriers intensity. Second order distortions are also reported. The comparison of the Bessel function analysis and the perturbation method is quite successful. Finally, laser's FM and IM modulation characteristics are compared, and these theoretical results show that distortion levels would be stronger in FM than in direct IM, when the same operating conditions are adopted     

Performance improvements using synchronous code correction inADPCM/PCM tandem connections

A sufficient condition for the existence of tandem distortion accumulation is described. The distortion for a sample time at which the sufficient condition is satisfied is studied. It is shown that the transcoding distortion is greater than the adaptive differential pulse code modulation (ADPCM) distortion when synchronous code correction is not used and less than the ADPCM distortion when synchronous code correction is used. These results are combined to show that when synchronous code correction is used, the upper bound of the single transcoding distortion is determined by the single transcoding distortion when synchronous code correction is not used. This bound cannot be generalized for multiple tandem cases     

On the asymptotic tightness of the Shannon lower bound

New results are proved on the convergence of the Shannon (1959) lower bound to the rate distortion function as the distortion decreases to zero. The key convergence result is proved using a fundamental property of informational divergence. As a corollary, it is shown that the Shannon lower bound is asymptotically tight for norm-based distortions, when the source vector has a finite differential entropy and a finite α th moment for some α>0, with respect to the given norm. Moreover, we derive a theorem of Linkov (1965) on the asymptotic tightness of the Shannon lower bound for general difference distortion measures with more relaxed conditions on the source density. We also show that the Shannon lower bound relative to a stationary source and single-letter difference distortion is asymptotically tight under very weak assumptions on the source distribution     

激光波前功率谱密度与焦斑旁瓣的关系

基于波前功率谱密度(PSD)的定义,分析了采用功率谱密度方法研究中频波前畸变与焦斑旁瓣关系的可行性。由于任意形状的波前畸变都可以由不同空间频率的正弦函数叠加组成,以正弦函数波前为例进行功率谱密度分析和远场分析。分析表明,当中频波前畸变的幅度满足一定条件时,远场二级以上的衍射非常低,可以忽略不计,此时波前功率谱密度与焦斑旁瓣具有非常好的相似性,并且这种相似性仅与中频波前畸变的幅度有关,与空间频率无关。最后还用数值模拟的方法验证了这个结论对叠加后的结果仍然成立。研究结果可以用于设计满足惯性约束聚变(ICF)驱动器打靶对焦斑旁瓣要求的光学元件中频段波前畸变指标。     

Nonlinearities of GaAlAs lasers--Harmonic distortion

Narrow stripe lasers (2-6 mum) and transverse junction lasers exhibit excellent linearity. The dependence of relative second-and third-harmonic distortion is investigated as a function of modulation frequency and modulation current. Relative second- and third-harmonic distortion of -50 and -70 dB is observed for an optical signal of 4 mW p-p (f_{m} = 60MHz). Intermodulation products are compared with the harmonic distortion and good agreement is obtained between the two quantities when the relations for a simple nonlinearity without memory are used. The measured distortion is in agreement with distortion calculated from rate equations.     

Joint Source–Channel Codes for MIMO Block-Fading Channels

We consider transmission of a continuous amplitude source over an L-block Rayleigh-fading M_t x M_r multiple-input multiple-output (MIMO) channel when the channel state information is only available at the receiver. Since the channel is not ergodic, Shannon's source-channel separation theorem becomes obsolete and the optimal performance requires a joint source-channel approach. Our goal is to minimize the expected end-to-end distortion, particularly in the high signal-to-noise ratio (SNR) regime. The figure of merit is the distortion exponent, defined as the exponential decay rate of the expected distortion with increasing SNR. We provide an upper bound and lower bounds for the distortion exponent with respect to the bandwidth ratio among the channel and source bandwidths. For the lower bounds, we analyze three different strategies based on layered source coding concatenated with progressive superposition or hybrid digital/analog transmission. In each case, by adjusting the system parameters we optimize the distortion exponent as a function of the bandwidth ratio. We prove that the distortion exponent upper bound can be achieved when the channel has only one degree of freedom, that is L = 1, and min{M_t ,M_r} =1. When we have more degrees of freedom, our achievable distortion exponents meet the upper bound for only certain ranges of the bandwidth ratio. We demonstrate that our results, which were derived for a complex Gaussian source, can be extended to more general source distributions as well.     

鱼眼镜头图像畸变的校正方法

提出了一种校正鱼眼镜头图像畸变的新方法。通过追迹光学系统的主光线,获得它在投影平面上的径向位置与它在像平面上位置之间的关系曲线;然后用傅立叶级数拟合该关系曲线;并求出该级数的逆函数,结果就可以根据畸变图像复原没有畸变的图像。用该方法数值模拟两个鱼眼镜头系统的图像畸变校正;并用其中一个鱼眼镜头（尼康16 mm/F2.8）拍摄的两张图像进行了畸变校正实验。结果表明,当设置投影平面和物平面重合时,恢复的图像相对于物体的残余径向高度误差非常小（小于0.25%）。实验证明了该方法是可行的。     

Worst sources and robust codes for difference distortion measures

It has long been known that for a mean-square error distortion measure the Gaussian distribution requires the largest rate of all sources of a given variance. It has also been stated that a code designed for the Gaussian source and yielding distortiondwhen used with a Gaussian source will yield distortionleq dwhen used with any independent-letter source of the same variance. In this paper, we extend these results in two directions: a) instead of assuming that the source has a fixed variance, we fix an arbitrary moment; b) instead of mean-square error distortion measures, we consider nearly arbitrary continuous difference distortion measures. For each moment constraint, we show that there is a given distribution that has the largest rate for (nearly) any difference distortion measure and that a code designed for this source yielding distortiondyields distortionleq dfor any ergodic source satisfying the same moment constraint. Furthermore, digital encoding of the output of this encoder may yield a lower rate when this encoder is used with a source for which it was not designed. We also extend these results to the case of a random process or random field of known correlation function under a difference distortion measure.     

Potential difference and photovoltaic effect arising from distortion of the electron wave function in a GaAs quantum well with a thin AlGaAs barrier

This paper discusses changes in the spectrum and distortion of the electron wave function of a GaAs quantum well when a thin AlGaAs barrier is introduced into it. The potential difference generated across the quantum well by distortion of the electron wave function is calculated, along with its dependence on the position of the barrier in the quantum well. The photovoltaic response of the structure to optical intersubband excitations is also calculated, along with the role of wave function and electronic spectrum distortion as well as intersubband nonradiative transitions in generating this response. The suitability of a GaAs quantum well with a thin barrier for use as an infrared detector is considered. Fiz. Tekh. Poluprovodn. 32, 1246–1250 (October 1998)     

Distortion related to polarization-mode dispersion in analoglightwave systems

Analog transmission in single-mode fiber using chirped sources gives rise to nonlinear distortion when polarization-mode dispersion (PMD) is present. We investigate experimentally and theoretically two mechanisms for this distortion: for chirped sources, PMD in the presence of polarization-mode coupling results in second-order distortion that is proportional to the square of the modulation frequency; when polarization-dependent loss is present, an additional second-order distortion term occurs that is independent of modulation frequency. Both mechanisms give rise to distortion that is time varying due to the sensitivity of PMD to ambient temperature changes. Numerical examples indicate that these effects can limit the capacity of analog systems that use directly modulated semiconductor lasers     

适用于数模混合集成的SOI MOSFET的失真分析

本文较为详细地分析了SOIMOSFET的失真行为 .利用幂级数方法对不同结构包括部分耗尽PD、全耗尽FD和体接触BC的SOI器件的谐波失真进行了对比性的实验研究 .同时 ,在实验分析的基础上提出了描述失真行为的连续的SOIMOSFET失真模型 .该模型通过引入平滑函数和主要的影响失真的物理机制 ,使得模拟计算结果能够与实验结果较好的吻合 .本文所得到的结果可用于低失真的数模混合电路的设计 ,并对低失真电路的优化提供指导方向 .     

Impact of XPM on the Performance of Microwave Photonic Switching with NOLM

The impact of XPM on the microwave photonic switching with NOLM is analyzed by the split-step Fourier method (SSFM) that can solve the coupled nonlinear Schr?dinger equation (CNLSE). The simulation results show that XPM induces the distortion of waveforms and the leak of side lobes. And the larger the modulation bandwidth is, the larger the leak of side lobes is. Furthermore, the power transmission function of NOLM Tm is distorted because of the XPM-induced nonreciprocity: Tm decreases when the splitting ratio of the coupler f ∈(0,0.5) and increases when f ∈(0.5,1.0).     

New results on coding of stationary nonergodic sources

Two results on the coding of stationary nonergodic sources are presented. The first is a source coding theorem stating that there exist variable-rate codes with performance arbitrarily close to the rate-distortion function of the stationary nonergodic source. The second is a converse information transmission theorem. It is shown that the distortion which results when the source is transmitted across a channel with capacityCis no less than the least distortion achievable by fixed-rate codes with rateC.     

High-resolution source coding for non-difference distortionmeasures: multidimensional companding

Entropy-coded vector quantization is studied using high-resolution multidimensional companding over a class of nondifference distortion measures. For distortion measures which are “locally quadratic” a rigorous derivation of the asymptotic distortion and entropy-coded rate of multidimensional companders is given along with conditions for the optimal choice of the compressor function. This optimum compressor, when it exists, depends on the distortion measure but not on the source distribution. The rate-distortion performance of the companding scheme is studied using an asymptotic expression for the rate-distortion function which parallels the Shannon lower bound for difference distortion measures. It is proved that the high-resolution performance of the scheme is arbitrarily close to the rate-distortion limit for large quantizer dimensions if the compressor function and the lattice quantizer used in the companding scheme are optimal, extending an analogous statement for entropy-coded lattice quantization and MSE distortion. The companding approach is applied to obtain a high-resolution quantizing scheme for noisy sources