We derive an expression for the input complex impedance of a Sallen-Key second-order low-pass filter of twofold gain as a function of the natural frequency ωo and the quality factor . Q From this expression, it is shown that the filter behaves like a Frequency Dependent Negative Resistance (FDNR) element for low frequencies and as a single resistor at high frequencies. Furthermore, the minimum input impedance magnitude is found without using calculus. We discovered that the minimum input impedance magnitude is inversely proportional to Q and can be substantially less than its high-frequency value. Approximations to the minimum input impedance and the frequency at which it occurs are also provided. Additionally, PSpice simulations are presented which verify the theoretical derivations.
The authors present two 8-D TCM (trellis-coded modulation) schemes which use 512 points to transmit 2 b/s/Hz. The systems have constant envelope and yield asymptotic gains of 3.01 dB with only four or eight trellis states, without expanding the bandwidth over that of the equivalent uncoded system (QPSK over four consecutive time intervals). The size of the coded constellation is doubled but the minimum square Euclidean distance, the peak and average energies, and the modulation level remain identical to those of the uncoded system. The novel constellation is formed by the union of an 8-D QPSK (quadrature phase shift keying) and a rotated version of it. The present low-complexity schemes achieve small normalized redundancy, have constant envelope, and use simple and small constituent 2-D constellations.< >
The maximum and minimum gains (with respect to frequency) of third-order low-pass and high-pass filters are derived without using calculus. Our method uses the little known fact that extrema of cubic functions can easily be found by purely algebraic means. PSpice simulations are provided that verify the theoretical results.
espanolProveemos nuevas ecuaciones para la capacitancia versus la ondulacion en rectificadores de media onda y de onda entera. Demostramos que estas nuevas ecuaciones dan valores de capacitancia mas precisos que las ecuaciones convencionales presentadas en libros de texto que usan el modelo de decaimiento lineal, especialmente para fuentes con ondulacion media a muy grande. Determinamos el porcentaje de precision de nuestras ecuaciones comparandolas a la solucion numerica de las ecuaciones exactas de la relacion entre ondulacion y capacitancia EnglishWe provide new equations for capacitance vs. ripple in half-wave and full-wave rectifier circuits. We show that these new equations provide more accurate capacitance values than the conventional equations given in textbooks using the linear decay model, especially for supplies with medium to extremely large ripple. We determine the percentage accuracy of these new equations by comparing them to the numerical solution of the exact equations for the capacitance ripple relationship
The probability of symbol error (P/sub E/) performance is studied for cross-polarized M-QAM (M-ary quadrature amplitude modulation) and L-QPRS (L-ary quadrature partial response signal) systems operating in the depolarization crosstalk and differential phase shift environment. Explicit general formulas are provided and results presented for dual-channel 4-QAM (QPSK-quadrature phase-shift keying) and 9-QPRS. It is demonstrated that the P/sub E/ varies with a period of 90 degrees with differential phase shift and that L-QPRS systems are less sensitive to differential phase shift than the corresponding M-QAM systems; the sensitivity is measured by the ratio of maximum to minimum P/sub E/.< >
An evaluation of the performance of the Deep Ocean Logging Platform with Hydrographic Instrumentation and Navigation (DOLPHIN) Remotely Operated Vehicle (ROV) as a platform for collection of multibeam sonar data to produce bathymetry is presented. The DOLPHIN, equipped with an EM-100 echo sounder and NOAA's ship WHITING, carrying a Hydrochart II sonar, surveyed the Norfolk Canyon, Virginia, from August 5 through August 7, 1992; the USNS LITTLEHALES conducted its survey of the same area from August 23 through 25, 1992 with a hull-mounted EM-100. The quality of the multibeam data collected by DOLPHIN is evaluated in terms of the rms noise in each beam, the presence of spurious noise and the frequency of dropouts suffered, and is compared to data from the ships. The frequency, amplitude and distribution of heave, roll and pitch are also investigated. Results indicate the DOLPHIN is a stable survey platform for multibeam data collection which introduces negligible noise to the system, and has very infrequent dropouts. Gridded bathymetry from the three platforms are compared and show good agreement, with the bathymetry produced by the ROV and its mother ship having the least rms difference.< >
In this paper we present an approach for processing sonar signals with the ultimate goal of ocean bottom sediment classification. Work reported is based on sonar data collected by the Volume Search Sonar (VSS), one of the five sonar systems in the AN/AQS-20. Our technique is based on the Fractional Fourier Transform (FrFT), a time-frequency analysis tool which has become attractive in signal processing. Because FrFT uses linear chirps as basis functions, this approach is better suited for sonar applications. The magnitude of the bottom impulse response is given by the magnitude of the Fractional Fourier transform for optimal order applied to the bottom return signal. Joint time-frequency representations of the signal offer the possibility to determine the time-frequency configuration of the signal as its characteristic features for classification purposes. The classification is based on singular value decomposition of the Choi William distribution applied to the impulse response obtained using Fractional Fourier transform. The set of the singular values represents the desired feature vectors that describe the properties of the signal. The singular value spectrum has a high data reduction potential. It encodes the following signal features: time-bandwidth product, frequency versus time dependence, number of signal components and their spacing. The spectrum is invariant to shifts of the signal in time and frequency and is well suited for pattern recognition and classification tasks. The most relevant features (singular values) have been mapped in a reduced dimension space where an unsupervised classification has been employed for acoustic seabed sediment classification. The theoretical method is addressed and then tested on field sonar data. In our classification we used the central beams. Good agreement between the experimental results and the ground truth is shown. A performance comparison of our method to a k-means based technique is also given. Results and recommendations for future work are presented
An approach for processing sonar signals with the ultimate goal of ocean bottom sediment classification and underwater buried target classification is presented in this paper. Work reported for sediment classification is based on sonar data collected by one of the AN/AQS-20's sonars. Synthetic data, simulating data acquired by parametric sonar, is employed for target classification. The technique is based on the Fractional Fourier Transform (FrFT), which is better suited for sonar applications because FrFT uses linear chirps as basis functions. In the first stage of the algorithm, FrFT requires finding the optimum order of the transform that can be estimated based on the properties of the transmitted signal. Then, the magnitude of the Fractional Fourier transform for optimal order applied to the backscattered signal is computed in order to approximate the magnitude of the bottom impulse response. Joint time-frequency representations of the signal offer the possibility to determine the timefrequency configuration of the signal as its characteristic features for classification purposes. The classification is based on singular value decomposition of the time-frequency distributions applied to the impulse response. A set of the largest singular values provides the discriminant features in a reduced dimensional space. Various discriminant functions are employed and the performance of the classifiers is evaluated. Of particular interest for underwater under-sediment classification applications are long targets such as cables of various diameters, which need to be identified as different from other strong reflectors or point targets. Synthetic test data are used to exemplify and evaluate the proposed technique for target classification. The synthetic data simulates the impulse response of cylindrical targets buried in the seafloor sediments. Results are presented that illustrate the processing procedure. An important characteristic of this method is that good classification accuracy of an unknown target is achieved having only the response of a known target in the free field. The algorithm shows an accurate way to classify buried objects under various scenarios, with high probability of correct classification.
