Short-range Leakage Research Articles

A Linear-Correction Algorithm for Quasi-Synchronous DFT

Spectral leakage in the harmonic measured by quasi-synchronous DFT (QSDFT) is mainly due to short-range leakage caused by deviation in the signal frequency. By analysing the short-range-leakage characteristic of QSDFT, a linear-correction algorithm (LCQS) for QSDFT’s harmonic-analysis results is proposed. LCQS contains two linear-correction equations: an amplitude-correction equation and an initial-phase-angle-correction equation. The former is constructed by the least-squares method, whereas the latter is generated based on the linear error characteristic of the QSDFT harmonic phase. Simulation and experimental results indicate that this proposed algorithm can efficiently increase the accuracy of the harmonic parameters over a wide frequency range by minimizing the short-range spectral leakage.

The VPF Harmonic Analysis Algorithm Based on Quasi-Synchronous DFT

Background: The main source of spectral leakage in Quasi-synchronous DFT (QSDFT) harmonic analysis is the short-range leakage resulting from the fluctuating signals. Objective: The QSDFT discrete spectrum stretching theorem, as is demonstrated in this paper, shows that the peak in frequency domain changes synchronously with the signal frequency drift. Based on QSDFT, an improved algorithm—Variable Picket Fence (VPF) is proposed. Method: The VPF means the sampling position in the frequency domain will synchronously change with the signal frequency drift. In this way, we can accurately capture the spectrum peak, thereby inhibiting short-range spectral leakage. Hence signal frequency drift can be obtained by measuring the fundamental phase difference between the adjacent sample points. Results: Simulation and application results prove that this proposed algorithm increases the accuracy of harmonic analysis by inhibiting short-range spectral leakage efficiently in the range of 45 to 55HZ.

Real-Time Mitigation of Short-Range Leakage in Automotive FMCW Radar Transceivers

Frequency-modulated continuous wave radar systems suffer from permanent leakage of the transmit signal into the receive path. Besides leakage within the radar device itself, an unwanted object placed in front of the antennas causes so-called short-range (SR) leakage. In an automotive application, for instance, it originates from signal reflections of the car’s own bumper. Particularly the residual phase noise of the downconverted SR leakage signal causes a severe degradation of the achievable sensitivity. In an earlier work, we proposed an SR leakage cancellation concept that is feasible for integration in a monolithic microwave integrated circuit. In this brief, we present a hardware prototype that holistically proves our concept with discrete components. The fundamental theory and properties of the concept are proven with measurements. Further, we propose a digital design for real-time operation of the cancellation algorithm on a field programmable gate array. Ultimately, by employing measurements with a bumper mounted in front of the antennas, we show that the leakage canceller significantly improves the sensitivity of the radar.

Short-Range Leakage Cancelation in FMCW Radar Transceivers Using an Artificial On-Chip Target

A major drawback of frequency modulated continuous-wave (FMCW) radar systems is the permanent leakage from the transmit into the receive path. Besides leakage within the radar device itself, signal reflections from a fixed object in front of the antennas additionally introduce so-called short-range (SR) leakage. It causes a strong degradation of detection sensitivity due to the unpreventable phase noise of the transmit oscillator. In this work, we introduce an artificial on-chip target (OCT) to mitigate the SR leakage. The OCT consists of a delay line whose time delay is significantly smaller than the round-trip delay time of the SR leakage. This is motivated by the fact that in integrated circuits for automotive radar applications operating at 77 GHz delay lines in the range of only a few picoseconds can be realized with a reasonable amount of circuitry. Despite this constraint, we show that the proposed method achieves almost perfect cancelation of the SR leakage. The concept is based on the cross-correlation properties of the residual phase noise in the intermediate frequency (IF) domain. Further, the effectiveness of the proposed method is verified in an FMCW radar system simulation. It almost perfectly shows that a gain in sensitivity of approximately 6 dB is achieved, compensating for the performance degradation caused by the SR leakage. The novel leakage cancelation concept is carried out mainly in the digital domain enabling high flexibility and adaptivity.

Phase Difference Measurement Based on Recursive DFT with Spectrum Leakage Considered

This paper investigates spectrum leakage influence on the performance of discrete Fourier transform (DFT) based phase difference measurement and proposes a novel method with spectrum leakage considered. In the proposed method, spectrum is firstly corrected by interpolation algorithm to remove the influence of short range leakage. To avoid negative frequency interference caused by the long range leakage, real-time phase difference is calculated in succession by a recursive DFT based algorithm with negative frequency contribution. And then, precision of the proposed method is theoretically demonstrated in detail. Furthermore, the method is applied to Coriolis mass flowmeter (CMF). Simulation and experimental results show that the accuracy of phase difference measurement has largely improved, as compared with the existing method based on the sliding Goertzel algorithm.

Harmonic Analysis of Non-Sinusoidal Harmonic Signals in Electric Power System

Harmonic Analysis and control is very important for the power system because harmonics have serious harm to its normal operation. Harmonic Analysis uses fast Fourier transform (FFT) to solve this problem though it causes the spectrum leakage which Increases the calculation error. To solve this problem, the interpolation algorithm combine with tapered time windows are used. The tapered time windows solve the long-range leakage and the interpolation algorithm solves the problem of short-range leakage.

A simple interpolation algorithm for measuring multi-frequency signal based on DFT

For the multi-frequency signal under the condition of asynchronous sampling, the spectral leakages such as the negative frequency leakage, long-range leakage and short-range leakage in Fourier transform will influence the accuracy of harmonic analysis. To reduce the measurement errors caused by these effects, a new interpolated discrete Fourier transform (DFT) algorithm using three greatest spectral lines is presented. In this new algorithm, the analytical formulas for the harmonic frequency are obtained by applying the Chebyshev best approximation theory. These formulas can be easily implemented by hardware multipliers, which is convenient for real-time measurement. The simulation and experiment results show the presented algorithm has high accuracy and good anti-jamming capacity.

Extremely Flat-Top Windows for Harmonic Analysis

The window class, which is generated by multiple time-convolution of weighted-cosine windows, is presented. It is shown that after a convolution of known parent windows, the resultant convoluted (CON) window exhibits high side-lobe attenuation that is capable of suppressing long-range leakage. Moreover, using the expressions describing an error due to the short-range leakage, the optimization procedure was applied to adjust the coefficients of parent windows in order to obtain, as flat as possible, the main lobe of the CON window. As a result, the new window class having both an extremely flat-top (EFT) main lobe and high side-lobe attenuation was generated. Moreover, new windows exhibit faster decaying side lobes than parent windows. The efficiency of EFT windows in high-accuracy harmonic analysis was demonstrated through computer simulations

On the use of amplitude shaping pulses as windows for harmonic analysis

In this paper, we propose the use of shaping pulses as flat top windows for accurate amplitude and phase estimation from periodic signals in power systems. The intention is to eliminate the amplitude correction required to compensate the short-range leakage produced by nonflat-mainlobe windows in case of asynchronous sampling. The performance of the standard rise cosine filter, a generalized raised-cosine filter and a Hanning window, all of them with the same bandwidth, is compared in the simulation results. It is concluded that the accuracy of the estimates provided by the shaping pulses without amplitude compensation in the asynchronous case is relatively better than that of the amplitude compensated estimates obtained with the Hanning window. The generalized raised-cosine filter can achieve lower sidelobe levels but it does not improve the accuracy of the amplitude estimates of the standard raised-cosine filter.

An almost leakage free method for assessing Σ-Δ modulator spectra

This paper addresses the problem of spectral analysis of /spl Sigma/-/spl Delta/ modulator output spectra. Often, data containing a periodic signal are evaluated using fast-Fourier-transform (FFT) based spectral analysis. If the data set is not sampled coherently, long- and short-range leakage can hamper or prevent the frequency domain analysis, particularly if frequencies near the excitation sine frequency are of interest. Techniques such as windowing or coherent sampling help, but unfortunately may add their own effects to the spectra under scrutiny. Where coherent sampling is not easily possible, another approach to reliable spectrum analysis is a hybrid computation of the spectrum using the output bit stream from a /spl Sigma/-/spl Delta/ modulator. This will yield spectral information and an assessment of modulator performance. The method is demonstrated on MATLAB simulated /spl Sigma/-/spl Delta/ modulator bit-stream data from a single-loop, first order modulator as well as a single-loop, third order modulator, both excited by a multitone sinusoidal excitation.

Quasi-synchronous sampling algorithm and its applications

Synchronous sampling is a commonly used method with good performance. However, when perfect synchronization is impossible, or when the signal contains interharmonics, undesirable asynchronous deviations between the sampling and some components of the signal may exist. Consequently, possibly large leakage or truncation errors may occur. Consisting of a quasi-synchronous window to reduce the long-range leakage, and a compensation algorithm to reduce the short-range leakage after normal FFT, the method described in this paper will give much more accurate measurement of many electrical quantities, e.g., spectral content of signal and phase difference between two periodic signals in power networks, than the traditional one.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characterization of short-range leakage currents in undoped polycrystalline Si by means of capacitance-voltage measurement

Metal-oxide-semiconductor capacitors with undoped polycrystalline Si (polysilicon) electrodes were studied and a model was developed to explain the voltage and frequency dependence of the capacitance and serial resistance. The model assumes random distribution of leaky paths in the polycrystalline Si layer which supply the charge to the polysilicon-oxide interface.