Distortion Generation Research Articles

Nonlinear Distortion Analysis of Polar Transmitters

This paper gives a comprehensive analysis of the major nonlinear distortion generation mechanisms present in modern wireless polar transmitters. Based on a simplified description of the physical operation of voltage supply modulated switching mode power amplifiers (PAs), it derives an analytical model of both the AM-AM and AM-PM distortions usually encountered on polar transmitters excited by the standard two-tone excitation. The predictions of this model match extensive measurement and simulation results for a real PA circuit of a polar transmitter architecture.

Functional differential equations associated to propagation

Summary. In this paper we aim to point out some problems connected to the approach of associating to propagation systems some functional differential equations. The associated models are slightly different of the standard ones in the sense that they are no longer restricted to lumped (pointwise) delays; this extension is motivated mainly by the physical and engineering significance of the basic (propagation) systems as well as by the significance of the problems. The paper will be focused around two models: the circulating fuel nuclear reactor - where the propagation is no longer lossless - and the overhead crane - where the parameters may be space varying thus inducing distortion in propagation. Basic theory and stability will be considered; in the case of the nuclear reactor a Liapunov functional of special structure is proposed which requires model reformulation.

Distortion-Free 1-Bit PWM Coding for Digital Audio Signals

Although uniformly sampled pulse width modulation (UPWM) represents a very efficient digital audio coding scheme for digital-to-analog conversion and full-digital amplification, it suffers from strong harmonic distortions, as opposed to benign nonharmonic artifacts present in analog PWM (naturally sampled PWM, NPWM). Complete elimination of these distortions usually requires excessive oversampling of the source PCM audio signal, which results to impractical realizations of digital PWM systems. In this paper, a description of digital PWM distortion generation mechanism is given and a novel principle for their minimization is proposed, based on a process having some similarity to the dithering principle employed in multibit signal quantization. This conditioning signal is termed jither and it can be applied either in the PCM amplitude or the PWM time domain. It is shown that the proposed method achieves significant decrement of the harmonic distortions, rendering digital PWM performance equivalent to that of source PCM audio, for mild oversampling (e.g., ×4) resulting to typical PWM clock rates of 90MHz.

Reducing pulse distortion in fast-light pulse propagation through an erbium-doped fiber amplifier

When a pulse superposed on a cw background propagates through an erbium-doped fiber amplifier with a negative group velocity, either pulse broadening or pulse compression can be observed. These effects can be explained in terms of two competing mechanisms: gain recovery and pulse spectrum broadening. The distortion of the pulse shape caused by these effects depends on input pulse width, pump power, and background-to-pulse power ratio. With the proper choice of these three parameters, we can obtain significant pulse advancement with minimal pulse distortion.

Interaction range and generation rate of nonlinear intrachannel signal distortion

Intrachannel cross-phase modulation and four-wave mixing are investigated in a pseudolinear transmission system. The interaction range of the nonlinear effects is studied numerically, and approximate analytical methods are used to explain the results and predict the necessary word length for general systems. The method is shown to agree with experimentally found data. The generation rate, i.e., the growth of the nonlinear distortion in different parts of the system is calculated numerically, and the possibilities for counteracting the generation of nonlinear signal distortion are discussed.

Propagation, beam geometry, and detection distortions of peak shapes in two-dimensional Fourier transform spectra

Using a solution of Maxwell's equations in the three-dimensional frequency domain, femtosecond two-dimensional Fourier transform (2DFT) spectra that include distortions due to phase matching, absorption, dispersion, and noncollinear excitation and detection of the signal are calculated for Bloch, Kubo, and Brownian oscillator relaxation models. For sample solutions longer than a wavelength, the resonant propagation distortions are larger than resonant local field distortions by a factor of approximately L/lambda, where L is the sample thickness and lambda is the optical wavelength. For the square boxcars geometry, the phase-matching distortion is usually least important, and depends on the dimensionless parameter, L sin(2)(beta)Deltaomega/(nc), where beta is the half angle between beams, n is the refractive index, c is the speed of light, and Deltaomega is the width of the spectrum. Directional filtering distortions depend on the dimensionless parameter, [(Deltaomega)w(0) sin(beta)/c](2), where w(0) is the beam waist at the focus. Qualitatively, the directional filter discriminates against off diagonal amplitude. Resonant absorption and dispersion can distort 2D spectra by 10% (20%) at a peak optical density of 0.1 (0.2). Complicated distortions of the 2DFT peak shape due to absorption and dispersion can be corrected to within 10% (15%) by simple operations that require knowledge only of the linear optical properties of the sample and the distorted two-dimensional spectrum measured at a peak optical density of up to 0.5 (1).

HTS split open-ring resonators with improved power-handling capability for reaction-type transmitting filters

Novel planar construction of high-temperature superconducting (HTS) filters that improve power-handling capability is proposed. Split open-ring resonators are developed to be used in reaction-type transmitting filters that have very sharp bandstop characteristics. Resonator structures to achieve high-unloaded Q-factors and low radiation as well as low surface current densities in the passband are numerically investigated for 5 GHz band operation. Low surface current densities reduce the generation of intermodulation distortions. Measurements confirm an unloaded Q-factor of 68 000 and third intermodulation-distortion of −82 dBc at 30 dBm input power.

The response of a low speed compressor on rotating inlet distortion

In multi-spool engines, the downstream compressor experiences a rotating inlet distortion if rotating stall occurs in upstream compressor, which may induce the instability of the whole compressor. In this paper, the compressor dynamic behavior is the major focus. The experiment was carried out on a single-stage low-speed axial-flow compressor. A rotating distortion generator equipped with different distortion sector(s) was designed to produce different rotating inlet distortion clockwise or counterclockwise with up to 100% of the compressor design speed. The distortion sector can be installed single or in some combination such as four sectors together. Three types of distortion sector/combination are used in the research work, which are single 30 degree sector, four 30 degree sectors and single 120 degree sector. It is found that the total pressure loss caused by rotating sector(s) increases when the distortion speed rises. For co-rotating distortions, all the three types of inlet distortion exhibited a peak in stall margin degradation when the distortion speed corresponded to roughly 50% of rotor speed. The two-dimensional numerical simulations of the compressor flow field clearly show the propagation of the disturbances trigged by the distortion sector(s).

Systematic Method to New Phases of Polymeric Nitrogen under High Pressure

A systematic method to unravel a large class of single-bonded (SB) polymeric phases of nitrogen under high pressure is presented. The approach is based on the combinatorial generation of different Peierls-like distortions of a given reference structure that maintain the threefold connectivity of SB nitrogen, followed by first-principles calculations. Using an eight atom simple cubic reference structure, the approach not only recovers all four SB nitrogen phases reported to date, but eight new metastable structures (confirmed by phonon density of states calculations) are found. Basic properties of the structures are computed and the trends analyzed. Extensions to the method are straightforward and should lead to the discovery of more phases of polynitrogen.

Mechanism for bandpass frequency characteristic in distortion product otoacoustic emission generation

It is commonly observed that the levels of the 2f1-f2 and the other mf1-nf2 (m = n + 1 = integer) distortion product otoacoustic emissions (DPOAEs) initially increase in level for fixed f2 as fl -->f2, starting at f1 <f2, and then begin to decrease. When these DPOAE levels are plotted as a function of either the distortion product frequency (fdp) or f2/f1 the curve has an approximate bandpass shape. It has been hypothesized that this effect is due to (1) a second filter, (2) suppression of distortion generation by the primary tones, (3) reemission of distortion products from the distortion product place (on the basilar membrane), (4) the presence of an even order nonlinearity, and (5) cancellation of the DPOAE due to the vector addition of multiple sources of distortion product. In this study distortion products were produced with f1 sweep conditions where there would be minimal vector cancellation of multiple DPOAE sources. It was observed that under this condition, there is no or minimal bandpass shape of the DPOAE generation curve. Therefore, the data support the hypothesis that the bandpass shape obtained with traditional f1 sweeps is due to vector cancellation from multiple sources.

Adaptive intra refresh for ROI video coding based on motion extrapolated error estimation

A new error estimation method based on motion extrapolation is proposed to estimate distortion propagation. The region of interest area information is combined into the end to end distortion model to improve the perceptual performance. Simulations show that this method can provide much better subjective feeling than other methods.

Spectral characteristics of gaseous media and their effects on propagation of ultra-wideband radiation in the millimeter wavelengths

Some of the principal challenges in realizing modern wireless communication links at millimeter wavelengths are the effects emerging when the electromagnetic radiation propagates through the atmosphere due its complex refractivity. Propagation of the electromagnetic radiation is studied in the frequency domain, enabling consideration of broadband modulated signals. The theory is employed for the analysis of ultra-short pulse transmission in the millimeter wave regime. The atmospheric absorptive and dispersive effects on pulse propagation delay, width and distortion are demonstrated and discussed. Using second order expansion of the propagation factors leads to the derivation of approximated analytical expressions for the delay and width as a function of distance and carrier frequency. Conditions under which pulse compression or expansion occurs were identified. The effects, predicted by the analytical solution, were compared to the results obtained from a numerical simulation, aimed at the calculation of pulse evolution while propagating in the atmospheric media.

Numerical Parametric Study of Inlet Distortion Propagation in Compressor Using Integral Approach with Taguchi Method

Due to the advancement in aircraft propulsion, there is a need to understand compressor surge and stall from the engine operational requirement. Distorted inlet conditions in axial compressors may create large oscillations of the mass flow rate, which is known as “surge,” and self-induced circumferential flow distortions rotating around the annulus, which is called “rotating stall,” or a combination of both phenomenons may exist together. Therefore, it is important to carry out analysis on the parameters that may result in either surge or stall. This study looks into the research that has been done by Kim et al. [9] (on the distorted inlet flow propagation in the axial compressors). Integral method is applied to the problems of distorted inlet flow, investigating on the relationships and the effects that some of the key parameters would have on the propagation of inlet distortion flow. The objective of this study is to justify the findings from Kim et al.'s research by using Taguchi's quality control method. The results indicate that major parameters on the inlet distortion propagation are the ratio of drag-to-lift coefficient, the inlet distorted velocity coefficient, and inlet incidence angle in influence order. This conclusion is different from that in Kim et al.'s research. Their research was carried out using only a few test cases with integral method. When integral method with Taguchi quality control method is used, the prediction of degrees of influence by the parameters on the distortion propagation becomes more reasonable and accurate.

On the effect of cyclotron emission on the spectral distortions of the cosmic microwave background

We have investigated the role of the cyclotron emission associated to cosmic magnetic fields on the evolution of CMB spectral distortions by considering the contributions by spontaneous and stimulated emission and by absorption in the computation of the photon and energy injection rates. These cyclotron emission rates have been numerically compared with those of the relevant radiative processes operating in the cosmic plasma, bremsstrahlung and double Compton scattering, for realistic CMB distorted spectra at early and late epochs. For reasonable magnetic field strengths we find that the cyclotron emission contribution is much smaller than the bremsstrahlung and double Compton contributions, because of their different frequency locations and the high bremsstrahlung and double Compton efficiency to keep the long wavelength region of the CMB spectrum close to a blackbody (at electron temperature) during the formation of the spectral distortion. Differently from previous analyses, we find that for a very large set of dissipation mechanisms the role of cyclotron emission in the evolution of CMB spectral distortions is negligible and, in particular, it cannot re-establish a blackbody spectrum after the generation of a realistic early distortion. The constraints on the energy exchanges at various cosmic times can be then derived, under quite general assumptions, by considering only Compton scattering, bremsstrahlung, and double Compton, other than, obviously, the considered dissipation process. Finally, upper limits to the CMB polarization degree induced by cyclotron emission have been estimated.

Nonlinear Space Charge Wave Theory of Distortion in a Klystron

We present a new view of nonlinear distortion in a klystron based on an analytically solvable nonlinear Eulerian model. The nonlinear contributions to the analytic solutions for the beam modulations are "nonlinear space charge waves" in the sense that they are produced by the nonlinear mixing of the linear space charge waves. For a single-frequency input, amplitude and phase distortion are shown to be results of "self-intermodulation" at the drive frequency, or mixing of harmonic distortions with the fundamental. The self-intermodulation contributions add out of phase with the linear space charge waves to produce gain compression and phase distortion. By comparing the results to a conventional large-signal Lagrangian model we find this physical picture is accurate for drive levels up to 1.2 dB of gain compression. For a two-frequency input we predict the third-order intermodulation distortion generation and suppression with the nonlinear space charge wave theory.

分子動力学法を用いたＮｉ‐Ｔｉ合金に対する相変態の観察と構造解析

An SMA (shape memory alloy) is a functional material with a unique property known as the shape memory effect, or superelasticity. Microscopically, the mechanical actuation of this effect is based on reversible transformation between different crystal phases. To clarify the atomistic mechanism in SMA, we perform molecular dynamics simulation (MDS) of phase transformations for a Ni-Ti alloy, a typical alloy used for engineering SMAs. EAM potential, which can produce both B2 and B19' structures (stable crystal phases of Ni-Ti), is adopted to model the interatomic interaction of the nickel and titanium atomic systems. Two different-sized MDS models are constructed with unit cell structures of B2 phase. These structures are surrounded by free surfaces and constrained regions so as to be subjected to uniaxial tensile loading. A series of reversible processes likely to occur in SMA, including loading, unloading, heating, and cooling, is reproduced by corresponding stages of the MDS. Phase transformation is thought to be observable by detecting the local interatomic distances and bonding angles peculiar to B19' structure (martensite). During tensile loading simulations, the martensite crystal structure is always observed, having transformed from the B2 structure. At a large strain, models exhibit a rapid propagation of local lattice distortions accompanied by the formation of martensite. In unloading simulations, the larger model contains relatively less martensite than the smaller model. The discrepancy with regards to model size may depend on a different degree of constraint strength. Reverse transformation (from B19' to B2) occurs mainly in the subsequent heating stage, in which the stress is observed to increase under constant residual strain.

Study of Ultrawide-Band Transmission in the Extremely High Frequency (EHF) Band

The growing demand for broad-band wireless communication links and the lack of wide frequency bands within the conventional spectrum, causes us to seek bandwidth in the higher microwave and millimeter-wave spectrum at extremely high frequencies (EHF) above 30 GHz. One of the principal challenges in realizing modern wireless communication links in the EHF band are phenomena occuring during electromagnetic wave propagation through the atmosphere. A space-frequency approach for analyzing wireless communication channels operating in the EHF band is presented. Propagation of the electromagnetic radiation is studied in the frequency domain, enabling consideration of ultrawide-band modulated signals. The theory is employed for the analysis of a communication channel operating at EHF which utilizes pulse amplitude modulated signals. The atmospheric absorptive and dispersive effects on pulse propagation delay, pulse width and distortion are discussed. The theory and model are demonstrated in a study of ultrashort-pulse transmission at 60 GHz.

Acoustical nonlinearities in compression chambers and horns of horn drivers

A horn driver is an essential part of sound reinforcement systems. Principles of horn driver operation are associated with generation of acoustical nonlinear distortion. Distortion is generated in a compression chamber by nonlinear compression, and by modulation of air stiffness, mass, and viscous losses, and a nonlinear relationship between particle velocity and sound pressure. Distortion is also generated in the phasing plug and horn by propagation of high amplitude waves. The effect of compression chamber air mass and viscous losses modulation and nonlinearity has not been researched previously. The analysis of modulation and nonlinear effects in the compression chamber is based on analysis of variation of the compression chamber’s air moving mass, viscous losses, and compliance as a function of the diaphragm’s instantaneous position and level of acoustical pressure. The pressure and diaphragm position-dependent parameters are incorporated into the system of nonlinear differential equations governing movement of the diaphragm and oscillation of air in compression chamber. Analysis of nonlinear propagation effects in the phasing plug and horn is based on numerical solution of an implicit nonlinear equation for propagation of finite amplitude sound waves. The work results in the methodology of simulation dynamic performance of horn drivers and provides comparative analysis of different acoustical nonlinear and parametric mechanisms.

Synapsis of recombination signal sequences located in cis and DNA underwinding in V(D)J recombination.

V(D)J recombination requires binding and synapsis of a complementary (12/23) pair of recombination signal sequences (RSSs) by the RAG1 and RAG2 proteins, aided by a high-mobility group protein, HMG1 or HMG2. Double-strand DNA cleavage within this synaptic, or paired, complex is thought to involve DNA distortion or melting near the site of cleavage. Although V(D)J recombination normally occurs between RSSs located on the same DNA molecule (in cis), all previous studies that directly assessed RSS synapsis were performed with the two DNA substrates in trans. To overcome this limitation, we have developed a facilitated circularization assay using DNA substrates of reduced length to assess synapsis of RSSs in cis. We show that a 12/23 pair of RSSs is the preferred substrate for synapsis of cis RSSs and that the efficiency of pairing is dependent upon RAG1-RAG2 stoichiometry. Synapsis in cis occurs rapidly and is kinetically favored over synapsis of RSSs located in trans. This experimental system also allowed the generation of underwound DNA substrates containing pairs of RSSs in cis. Importantly, we found that the RAG proteins cleave such substrates substantially more efficiently than relaxed substrates and that underwinding may enhance RSS synapsis as well as RAG1/2-mediated catalysis. The energy stored in such underwound substrates may be used in the generation of DNA distortion and/or protein conformational changes needed for synapsis and cleavage. We propose that this unwinding is uniquely sensed during synapsis of an appropriate 12/23 pair of RSSs.

The influence of transducer operating point on distortion generation in the cochlea.

Distortion generated by the cochlea can provide a valuable indicator of its functional state. In the present study, the dependence of distortion on the operating point of the cochlear transducer and its relevance to endolymph volume disturbances has been investigated. Calculations have suggested that as the operating point moves away from zero, second harmonic distortion would increase. Cochlear microphonic waveforms were analyzed to derive the cochlear transducer operating point and to quantify harmonic distortions. Changes in operating point and distortion were measured during endolymph manipulations that included 200-Hz tone exposures at 115-dB SPL, injections of artificial endolymph into scala media at 80, 200, or 400 nl/min, and treatment with furosemide given intravenously or locally into the cochlea. Results were compared with other functional changes that included action potential thresholds at 2.8 or 8 kHz, summating potential, endocochlear potential, and the 2 f1-f2 and f2-f1 acoustic emissions. The results demonstrated that volume disturbances caused changes in the operating point that resulted in predictable changes in distortion. Understanding the factors influencing operating point is important in the interpretation of distortion measurements and may lead to tests that can detect abnormal endolymph volume states.