Sampled Pulse Width Research Articles

Digital inter-symbol interference mitigation method for Nyquist OTDM signal detection with coherent sampling and KNN classifier

We propose and experimentally demonstrate a digital method to mitigate inter-symbol interference (ISI) in demultiplexing Nyquist optical time-division multiplexing (N-OTDM) signal using a simple but powerfully serviceable k-nearest neighbors (KNN) classifier. The proposed method is evaluated under four types of sampling pulse-width corresponding to various extents of ISI distortion in 160 Gbaud down to 40 Gbaud demultiplexing experiments, and the mitigation performance is found to be better along with the increasement of sampling pulse-width. Compared with the traditional decision-directed least mean square (DD-LMS) equalization method, a 3.9 dB required-OSNR (at a BER of 10−4) improvement is observed under the pulse-width of 5.3 ps. Demultiplexing performance is investigated under the pulse-widths of 3.2 ps and 3.9 ps as well, in which the improvement of required-OSNR are found to be 1.33 dB and 2.95 dB, respectively. The performance improvement clearly indicates the strong ISI mitigation ability of the KNN classifier for N-OTDM signal demultiplexing. In addition, experimental results also confirm that the proposed digital ISI mitigation method could release the pulse-width requirement of the N-OTDM demultiplexing, which paves the way for future practical application of N-OTDM technique.

The temporal resolutions of the ultrafast imaging technologies based on nonlinear optics

We theoretically study some ultra-fast imaging technologies based on nonlinear optical switching effect sampling, and derive the expressions of switching functions based on nonlinear process sampling methods such as second harmonic (SH), optical Kerr effect and optical parametric amplification (OPA). For the first time, we propose a new concept, named equivalent exposure time (EET), which is used to describe accurately the actual gating time during ultrafast imaging. By using the ultra-fast rotating light fields as the targets, the simulations show that the EET of the ultrafast imaging based on SH is equivalent to the sampling laser pulse width, but the EET of the ultrafast imaging based on optical Kerr effect is 0.7 times of the sampling pulse width, while for the ultrafast imaging based on OPA, the EET depends on both the sampling pulse width and the gain. The higher the gain is, the shorter the EET, thus the higher the temporal resolution. The EET is reduced to half of the sampling pulse width when the OPA gain is 1 000. This research provides an effective way to improve the temporal resolution of the ultrafast imaging via the nonlinear optical switches.

Research on Non-uniform Interrupted Sampling Repeater Jamming for Phase Coded Radar

Because of using correlation processing technology, it is difficult for traditional jamming patterns to achieve the desired jamming effect on phase coded radar. At present, the forward deception jamming of phase coded radar is mainly realized by uniform interrupted sampling repeater jamming (UISRJ). In order to solve the problem that the UISRJ can only produce a single and delayed false target, a kind of non-uniform interrupted sampling repeater jamming (NUISRJ) is proposed. The non-uniform sampling pulse train is generated through pseudo random sequence, and then sampled and forwarded to generate jamming signal, which is processed by radar pulse compression to form dense false targets. Combining the theoretical analysis and simulation results, it can be seen that the NUISRJ has the dual effects of suppressing jamming and spoofing jamming, and the distribution of false target string is more random, including the leading and lagging false target. The amplitude and coverage area of false targets group can be controlled by adjusting sampling pulse width and forwarding times to effectively implement jamming.

Neutron-Induced Pulsewidth Distribution of Logic Gates Characterized Using a Pulse Shrinking Chain-Based Test Structure

This work presents measured data showcasing neutron-radiation induced Single Event Transient (SET) pulse widths in distinct standard logic gate types, together with a detailed analysis on the choice of design parameters impacting the corresponding sampled pulse width distributions. The SET pulse width distributions are obtained from a high density, array-based characterization-vehicle, implemented in 65nm planar CMOS and 16nm FinFET processes, featuring a tunable, high resolution pulse-shrinking chain together with a closely embedded sampling circuit to avoid width distortion effects. The proposed macro employs standard logic gate-chains in varying lengths, threshold voltages (VTH) and transistor width flavors as the Devices-Under-Test (DUTs). Measured irradiation data for a range of operating voltages from nominal down to near-threshold reveals the relative impact of the chosen design parameters such as VDD, VTH, device width and the logic chain length as well as their interplay, impacting the overall soft-error susceptibility and the sampled pulse width distributions among the different standard gate types.

Baseband Model for Uniformly Sampled RF-PWM

A baseband model for a polar RF modulator based on uniform sampling (US) pulse width modulation (PWM) is presented. RF-PWM allows to encode a complex baseband signal (amplitude and phase) into the pulse width and pulse position of a binary signal towards an efficient and fully digital RF transmitter implementation. We extend the well-known derivation of the naturally sampled (NS) RF-PWM to obtain a detailed model of the US RF-PWM which includes the intrinsic inband and side-bands distortion. In RF-PWM the carrier frequency is equal to the PWM frequency (first PWM harmonic). We develop the model such that the first or any other higher harmonic of the PWM can be used as the carrier signal. The distortion signal is analyzed in detail and a discrete-time implementation of the model which relates to previous approaches is presented. This model is key to the analysis, characterization and simulation of a fully digital transmitter.

A Multifrequency Model of Electric Locomotive for High-Frequency Instability Assessment

The high-frequency instability (HFI) issue results in serious harmonic overvoltage phenomena in the electrification railway system. This issue is rooted in the range that is not only below, but also above half the switching frequency. The commonly used small-signal averaging model is a single-frequency model in which the corresponding frequency component with perturbation frequency is considered merely. The inherent sampling nature has been neglected by the moving average operator. Therefore, it cannot reveal the effect of sideband components and may not be valid for predicting the high-frequency input admittance of a locomotive. To investigate the HFI issue, the sideband components generated by analog/data (A/D) sampling process and pulse width modulation (PWM) are taken into consideration. Then the multifrequency model of a locomotive is developed for evaluating the influences of sideband components. Meanwhile, the proposed model is validated by means of the frequency scan method, including the identification of PWM transfer functions and crossed-frequency transfer functions. Several HFI cases are summarized for comparing the accuracy between the traditional single-frequency model and the proposed multifrequency model. It denotes that the multifrequency model is more accurate to assess the high-frequency input admittance of a locomotive, especially the regions around the sampling frequency. Hardware-in-loop (HIL) results validate the theoretical analysis.

Nuisance alarm rate reduction using pulse-width multiplexing [formula omitted]-OTDR with optimized positioning accuracy

High nuisance alarm rates and missing alarm rates in phase-sensitive optical time-domain reflectometer (ϕ-OTDR) greatly restrict their practical application. In this paper, an asynchronous sampling pulse width multiplexing ϕ-OTDR is proposed to reduce both of these rates. Intersection and inclusion relationships among multiple positioning intervals are used to optimize the positioning accuracy. We construct an eight-pulse-width multiplexed ϕ-OTDR system and adopt a multisensor information fusion algorithm to verify the feasibility of the method. The experimental results show that this method can reduce the missing alarm rate by 93% and the number of nuisance alarms by 97%. The average positioning accuracy of the system is 21.4 m, which is equivalent to the spatial resolution level corresponding to the minimum pulse width in the optical pulse sequence. The positioning accuracy of some groups was as low as 6.4 m, far less than 20m. The proposed method provides a simple and feasible new approach for reducing nuisance alarm and missing alarm rates and optimizing the positioning accuracy of ϕ-OTDR.

Spectral Analysis of UPWM Signals for Filterless Digital Class D Power Amplifiers

Filterless digital class D power amplifiers usually utilize three-level uniform sampling pulse width modulation (UPWM) technique to convert the digital input signal into a UPWM signal which is used to drive the power stage. Therefore, the spectral estimation expressions for different three-level UPWM signals obtained by modulating the digital signal can be an evaluation tool for signal distortion and electromagnetic interference when filterless digital class D power amplifiers are designed. Based on the time-domain characteristics of three-level UPWM signals, the spectral estimation expressions for six types of three-level UPWM signals are proposed in this paper by using the discrete Fourier transform technique and the frequency response of the zero-order holder. According to these expressions, the relationships among the total harmonic distortion, the pulse repetition frequency and the pulse width resolution of the UPWM signal are studied. A UPWM generator test system based on field-programmable gate array is designed and implemented to measure the spectra of different UPWM signals. The measured results are compared with the calculated results obtained by the proposed expressions to verify the correctness of the proposed expressions.

An Approach to Natural Sampling Using a Digital Sampling Technique for SPWM Multilevel Inverter Modulation

This paper introduces an approach that applies a digital sampling technique for a sinusoidal pulse width modulation (SPWM) multilevel inverter modulation that reduces the total harmonic contents in the output voltage compared to that of classical regular sampling techniques. This new modulation emulates with a high degree of fidelity a natural sampling pulse width modulation (PWM). The theoretical analysis of this new digital technique compared with natural sampling has been validated by simulations and through experiments with a built prototype that performed five–level inverter modulations with vertically displaced carriers in phase disposition. Both simulation and experimental results generate a SPWM output voltage with higher fidelity than classic regular sampling techniques, allowing a reduction of the filtering demands on the inverter output, which in turn can decrease the converter size and its manufacturing costs. As the presented technique is digital, the resulting modulation is more robust against switching noise, jitter, and other system perturbations and the modulation parameters can be changed easily, even in an automated way. For this reason, the modulation introduced here can be a useful tool to perform spectral analysis for different multilevel modulations and systems.

Compensating Baseband Distortion of Regularly Sampled Pulsewidth Modulators for High-Precision Power Converters

This paper presents a straight-forward method to compensate baseband distortion for regularly sampled pulsewidth modulation, for both sawtooth and triangular carrier, aimed at high-precision power electronics applications such as medical MRI and semiconductor lithography. The method adds correction signals to the modulator input to mitigate the distortion, which is computationally lightweight, and pseudo-code is given to simplify implementation. Measurements are conducted, which confirm the improvements offered by the method. It is shown that baseband distortion can be reduced by upto 60 dB. This improves the linearity and reduces audible noise of power converters.

Analysis and Implementation of Unipolar PWM Strategies for Three Phase Cascade Multilevel Inverter Fed Induction Motor Drive

This paper presents unipolar pulse width modulation technique with sinusoidal sampling pulse width modulation are analyzed for three-phase five-level, seven-level, nine-level and eleven-level cascaded multi-level inverter. The unipolar PWM method offers a good opportunity for the realization of the Three-phase inverter control, it is better to use the unipolar PWM method with single carrier wave compared to two reference waves. In such case the motor harmonic losses will be considerably lower.The necessary calculations for generation of unipolar pulse width modulation strategies have presented in detail. The unipolar SPWM voltage switching scheme is selected in this paper because this method offers the advantages of effectively doubling the switching frequency of the inverter voltage. The cascaded multi level inverter fed induction motor is simulated and compared the total harmonic distroction for all level (five-level, seven-level, nine-level and elevel-level)of the inverter. Theoretical investigations were confirmed by the digital simulations using MATLAB/SIMULINK software.

Nonaveraged control‐oriented modeling and relative stability analysis of DC‐DC switching converters

SummaryThis paper presents a unified and exact nonaveraged approach to derive a frequency‐domain control‐oriented model for accurate prediction of the fast timescale dynamics and performances of switching converters with fixed frequency naturally sampled pulse width modulation and integrating feedback loop. Because the approach avoids averaging and approximations related to this process, a very good accuracy of the derived model is obtained. The main difference between the presented approach and the existing methodology for accurately predicting the behavior of switching converters is that, here, we break the feedback loop and we focus on analyzing the open‐loop gain and the effect of the system parameters on relative stability. This results in an approach much similar to control systems techniques rather than nonlinear dynamical system approaches. Consequently, the relative stability is tackled easily in the frequency domain. In particular, by treating the modulator as a gain depending on the operating point, the new model is formulated in such a way that standard control‐oriented tools such as Bode diagrams and root‐loci can be easily used. Therefore, the proposed approach gives some important issues like gain and phase margins that are highly useful in controller design. It is noticed that the crossover frequency, gain, and phase margins predicted by using the averaged model may deviate significantly from the actual values given by the proposed approach. The paper points out the sources of discrepancies and the theoretical results are validated by simulations using a circuit‐level switched model.

A Natural-Sampling-Based SVM Scheme for Current Source Converter With Superior Low-Order Harmonics Performance

The device switching frequency of current source converters (CSCs) in high-power medium-voltage (MV) drive applications is normally around 500 Hz. Conventional space vector modulation (SVM) features fast dynamic response but its output contains low-order harmonics with high magnitudes. In this paper, a natural-sampling-based SVM (NS-SVM) scheme is proposed to substantially suppress the low-order harmonics in practical CSC-based drives. This study proposes an equivalent discretization of NS-SVM wherein natural sampling pulse width modulation performance can be achieved with regular sampling frequency (same as a conventional SVM) instead of a high or even infinite sampling frequency. Equations for natural-sampling-based dwell time calculations for each selected vector are developed. The corresponding simplified but precise enough equations are derived on the basis of the Newton-Raphson algorithm to achieve fast online digital implementation. The proposed NS-SVM features superior low-order harmonic performance and inherits the high dynamic response and low sampling frequency of conventional SVM. Simulations and experiments are provided to verify the proposed NS-SVM scheme.

Current control with asymmetrical regular sampled pulse width modulator applied in parallel active filter

Abstract This paper presents an analysis of the properties of pulse width modulator with a single (symmetrical regular sampled PWM) and double (asymmetrical regular sampled PWM) control sampling of the input signal (low-frequency control input wave) in presence of a triangular auxiliary signal. In this paper, a comparison of the characteristics of these modulators used in the control system with a linear proportional controller is presented. The article provides the relations derived for the maximum amplification of regulators for which the control system operates stably. Analysis results have been confirmed by simulation and experimental studies of a commercial active filter installed in an industrial plant.

Effects of the photonic sampling pulse width and the photodetection bandwidth on the channel response of photonic ADCs.

We investigate the effects of the photonic sampling pulse's temporal width and the photodetection bandwidth on the channel response of time-interleaved photonic analog-to-digital converters (TIPADCs). Each sampling channel is modeled as a linear analog channel with a sampler, where the channel response is derived and analyzed theoretically. The results show that the finite temporal width of photonic sampling pulse will limit the channel analog bandwidth and the minimum feasible bandwidth of photodetection is the half of single channel sampling rate. The inter-symbol interference (ISI) induced by the finite bandwidth of photodetection will cause periodic ripples on the channel frequency response. Neither the photonic sampling with finite temporal width nor the ISI induced by the finite bandwidth of photodetection will result in excess noise. Experimental measurements on the channel responses of a TIPADC under different temporal widths and photodetection bandwidths verify the theoretical results.

Carrier-Based Pulse Width Modulation for Symmetrical Six-Phase Drives

Modulating the output of a voltage source inverter (VSI) inherently causes current distortions on the load side due to the switching behavior of the inverter. This paper describes a method to reduce these distortions for a drive setup with six phases. The setup consists of a six-phase machine connected to two three-leg two-level VSIs. The phases within the machine are symmetrically arranged and spatially shifted by $60^\circ$ . The phases are grouped so that two conventional three-phase sets are formed, each fed by one inverter. The output of each inverter leg is modulated by comparing a triangle carrier waveform with the desired fundamental wave. Arranged in this way, the drive setup offers an additional degree of freedom, the phase shift of the two carrier waveforms. It is shown that, depending on the machine parameters, there exists an optimal angle, which reduces the harmonic losses of the drive for a certain amplitude of the fundamental wave. The resulting overall current distortion can even be lower compared to a conventional three-phase drive with a two- or three-level inverter topology. For three different modulation techniques, the optimal phase shift angles are derived in an exact form, naturally, symmetrical regular and asymmetrical regular sampled pulse width modulation. An approximation with reasonable accuracy is achieved out of the exact solution. Simulations and experimental tests validate the theoretical considerations.

Small-Signal Modeling of Uniformly Sampled Phase-Shift Modulators

Phase-shift modulation (PSM) is a commonly used technique for controlling the active power flow in resonant dc–ac and dc–dc converters. Although traditionally developed as an analog modulation scheme, PSM is being increasingly implemented digitally in conjunction with advanced multivariable digital controllers and online efficiency optimization algorithms. While analog PSM is known not to introduce additional dynamics from a small-signal standpoint, the analysis disclosed in this study indicates that discrete-time, or uniformly sampled , PSM introduces a transport delay of small-signal nature. Furthermore, and in close analogy with the theory of uniformly sampled pulse width modulators, such delay depends on the modulator carrier type as well as on the converter operating point. This paper first clarifies the modeling procedure for describing the small-signal dynamics of uniformly sampled phase-shift modulators. Second, it provides an extension of the traditional phasor modeling to digital phase-controlled converters, allowing to account for the additional modulator dynamics in the design of the closed-loop compensation. Theoretical findings are validated via simulation and experimental results.

Direct Regular Sampled Pulse Width Modulation Technique for a Three-Phase Current Source Inverter

This paper proposes a new regular sampled pulse width modulation (PWM) for three-phase current source inverters. The theoretical basis of the proposed modulation strategy is described, including dwell time calculations and switching sequence selection. This strategy is well suited for digital implementation, and enjoys all the flexibilities and degree of freedoms as in space vector modulation. In addition, it ensures a minimum number of switching transitions per fundamental cycle, unlike other PWM methods. It is therefore promising for high-power medium-voltage applications. The validity of the proposed modulation strategy has been confirmed using simulation and experimentation. To furthermore substantiate the superiority of the proposed modulation strategy against other PWM methods, its performance is compared to sinusoidal PWM, selective harmonic elimination, and space vector modulation.

Super-resolution technique for CW lidar using Fourier transform reordering and Richardson-Lucy deconvolution.

An interpolation method is described for range measurements of high precision altimetry with repeating intensity modulated continuous wave (IM-CW) lidar waveforms using binary phase shift keying (BPSK), where the range profile is determined by means of a cross-correlation between the digital form of the transmitted signal and the digitized return signal collected by the lidar receiver. This method uses reordering of the array elements in the frequency domain to convert a repeating synthetic pulse signal to single highly interpolated pulse. This is then enhanced further using Richardson-Lucy deconvolution to greatly enhance the resolution of the pulse. We show the sampling resolution and pulse width can be enhanced by about two orders of magnitude using the signal processing algorithms presented, thus breaking the fundamental resolution limit for BPSK modulation of a particular bandwidth and bit rate. We demonstrate the usefulness of this technique for determining cloud and tree canopy thicknesses far beyond this fundamental limit in a lidar not designed for this purpose.

Application of Auto-Coding for Rapid and Efficient Motor Control Development

In hybrid and electric vehicles, the control of the electric motor is a critical component of vehicle functions such as motoring, generating, engine-starting and braking. The efficient and accurate control of motor torque is performed by the motor controller. It is a complex system incorporating sensor sampling, data processing, controls, diagnostics, and 3-phase Pulse Width Modulation (PWM) generation which are executed in sub-100 uSec periods. Due to the fast execution rates, care must be taken in the software coding phase to ensure the algorithms will not exceed the target processor's throughput capability. Production motor control development often still follows the path of customer requirements, component requirements, simulation, hand-code, and verification test due to the concern for processor throughput. In the case of vehicle system controls, typically executed no faster than 5-10 mSec periods, auto-coding tools are used for algorithm development as well as testing. The advantages of auto-coding to greatly speed the development process by linking the tools for simulation, code generation and testing early in the development process as well as to more easily investigate performance issues late in the process are well known. It is not uncommon, however, to lose coding efficiency with this approach. While the loss of efficiency may be tolerable for slow periods, it is not acceptable at faster periods used in motor controls as it will preclude the algorithms from executing or drive unnecessarily expensive solutions. This paper will present an auto-coding process applied to motor controls, including full implementation on a production permanent magnet motor drive. Best practices for implementing requirements into models that generate efficient code will be highlighted. An overview of the issues associated with model-based documentation will also be covered. The use of test vectors at the component, model and hardware-in-the-loop (HIL) level will be presented to show the benefits derived from using a formalized process and the natural linkage to a SPICE ® compliant process. A timing study performed during