Showing papers on "Frequency response published in 1992"

Traveling-wave polymeric optical intensity modulator with more than 40 GHz of 3-dB electrical bandwidth

Abstract: A traveling‐wave electro‐optic intensity modulator with a 3‐dB electrical bandwidth of more than 40 GHz, negligible phase distortion, low drive voltages, and an extinction ratio of better than 20 dB is reported in nonlinear optical polymers. The velocity matching between the optical and electrical waves is excellent. The frequency response of the optical modulation is in good agreement with theory.

Hard frequency-domain model error bounds from least-squares like identification techniques

Abstract: The problem of deriving so-called hard-error bounds for estimated transfer functions is addressed. A hard bound is one that is sure to be satisfied, i.e. the true system Nyquist plot will be confined with certainty to a given region, provided that the underlying assumptions are satisfied. By blending a priori knowledge and information obtained from measured data, it is shown how the uncertainty of transfer function estimates can be quantified. The emphasis is on errors due to model mismatch. The effects of unmodeled dynamics can be considered as bounded disturbances. Hence, techniques from set membership identification can be applied to this problem. The approach taken corresponds to weighted least-squares estimation, and provides hard frequency-domain transfer function error bounds. The main assumptions used in the current contribution are: that the measurement errors are bounded, that the true system is indeed linear with a certain degree of stability, and that there is some knowledge about the shape of the true frequency response. >

Applications of simulated annealing for the design of special digital filters

Abstract: The authors describe the salient features of using a simulated annealing (SA) algorithm in the context of designing digital filters with coefficient values expressed as the sum of power of two. A procedure for linear phase digital filter design, using this algorithm, is presented and tested, yielding results as good as those for known optimal methods. The algorithm is then applied to the design of Nyquist filters, optimizing at the same time both frequency response and intersymbol interference, and to the design of cascade form finite-impulse-response (FIR) filters. The drawback of using SA is that the computation time is on the order of 1-2 h for each filter design, on the Sun 3/60. However, this was more than compensated by the versatility of the new algorithm, which can be used to design filters with multiple constraints. >

Wideband low loss double mode SAW filters

Abstract: A method is discussed for achieving a wideband low-loss longitudinally coupled double mode surface acoustic wave (SAW) (DMS) filter using a leaky SAW on a 36 degrees Y-X LiTaO/sub 3/ and 64 degrees Y-X LiNbO/sub 3/ substrate with a high electromechanical coupling factor. Its characteristics are analyzed by computer simulation. With the use of the first-mode and third-mode resonance on a 64 degrees Y-X LiNbO/sub 3/ substrate and the selection of the optimum values for the distance between input and output interdigital transducers (IDTs), the electrode film thickness and the input/output IDT pair number, it is possible to achieve favorable characteristics with a 1-dB bandwidth of 33 MHz, and insertion loss of 2.1 dB, and an attenuation in the rejection band of 28 approximately 38 dB. >

Autoregressive modeling of wide-band indoor radio propagation

Abstract: Based on frequency domain measurements in the 0.9-1.1-GHz band, an autoregressive model for the frequency response of the indoor radio channel is introduced. It is shown that a second-order process is sufficient to represent the important statistical characteristics of the channel both in the frequency domain and the time domain where each pole identifies the arrival of a cluster of paths. A comparison is made between the statistical characteristics of the empirical data and of the channel responses regenerated from the second-order AR processes. Four methods to regenerate the indoor radio channel responses from a second-order AR model are proposed. The accuracy of the methods is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3-dB width of the frequency correlation function with that of the measurements performed in global, local, and mixed indoor radio propagation experiments. >

Design of quadrature mirror filters with linear phase in the frequency domain

Abstract: The design of quadrature mirror filter (QMF) banks whose analysis and synthesis filters have linear phase is considered. Because the design problem in the frequency domain is a highly nonlinear optimization problem, a linearization technique is proposed. An analytical solution formula is obtained, leading to a very efficient procedure. Computer simulations show that the design technique achieves better results in fewer iterations than conventional approaches when starting at the same preset initial guess. Moreover, the technique produces almost the same good results in six iterations if it starts at a better initial guess compared to the preset initial guess. By incorporating the technique with a weighted least squares, (WLS) algorithm, the design of QMF banks whose overall reconstruction error is minimized in the minimax sense over the entire frequency band is facilitated. Computer simulations for illustration and comparison are provided. >

A new frequency response analysis method for power transformers

Abstract: A novel frequency response analysis (FRA) method is described which is being used on power transformers at the KEMA laboratories. This frequency domain method is applied to digitally recorded time signals, is easy to use, and provides high-resolution frequency spectra for both magnitude and phase. This tailor-made FRA method uses a low voltage special impulse source to avoid aliasing. Results from several measured transformers are presented. >

Device for the coherent demodulation of time-frequency interlaced digital data, with estimation of the frequency response of the transmission channel and threshold, and corresponding transmitter

Abstract: A coherent demodulation device, for the demodulation of a digital signal of the type constituted by digital elements distributed in the time-frequency space and transmitted in the form of symbols constituted by a multiplex of N orthogonal carrier frequencies modulated by a set of the digital elements and broadcast simultaneously, the digital signal comprising reference elements, having a value and a position, in the time-frequency space, that are known to the demodulation device, comprising means for the estimation, by Fourier transform, of the frequency response of the transmission channel at any instant, carrying out the transformation of the received samples, corresponding to reference elements, from the frequency domain to the temporal domain, the multiplication in the temporal domain of the transformed samples by a rectangular temporal window (f n) and the reverse transformation, after the multiplication, of the obtained samples from the temporal domain into the frequency domain, the estimation means comprising means for the thresholding of the samples in the temporal domain, providing for the systematic elimination of the samples below a certain threshold.

Tunable BiCMOS continuous-time filter for high-frequency applications

Abstract: A BiCMOS fully differential transconductor based on MOS transistors operating in the linear region is presented. The circuit has an equivalent nondominant pole located above 1.5 GHz. This makes it suitable for high-frequency continuous-time filters. A second-order low-pass filter using the new transconductor realized in a 2- mu m BiCMOS technology is reported. The cutoff frequency f/sub 0/ of the cell is tunable in the range of 8-32 MHz and the quality factor is 2. The filter THD stays lower than -40 dB for an output signal up to 3.2 V/sub p-p/ at 5-MHz frequency. The area of the cell is 0.322 mm/sup 2/ and the power consumption (with f/sub 0/=25 MHz) is 30 mW with a single 5-V power supply. >

Design of a bipolar 10-MHz programmable continuous-time 0.05 degrees equiripple linear phase filter

Abstract: A bipolar seventh-order 0.05 degrees equiripple linear phase (constant group delay) transconductance-capacitor (g/sub m/-C) low-pass filter with a cutoff frequency (f/sub c/) tunable between 2 and 10 MHz is presented. Programmable equalization up to 9 dB at f/sub c/ is also provided. Total harmonic distortion at 2 V/sub p-p/ is less than 1%, with a dynamic range equal to 49 dB. Nominal power consumption from a single 5-V supply is 135 mW. The circuit also has a low-power mode ( >

A Spectral Element Approach to Wave Motion in Layered Solids

Abstract: A matrix methodology similar to that of the finite element method is developed for the analysis of stress waves in layered solids. Because the mass distribution is modeled exactly, the approach gives the exact frequency response of each layer. The fast Fourier transform and Fourier series are used for inversion to the time/space domain. The impact of a structured medium with multiple layers is used to demonstrate the method. Comparison with existing propagator and direct global matrix methods show the present approach to be computationally more efficient.

Resonance frequency, damping, and differential gain in 1.5 mu m multiple quantum-well lasers

Abstract: A systematic investigation is presented into the intrinsic frequency response of quantum-well lasers, using parasitic-free relative intensity noise (RIN) measurements. There is shown to be a strong dependence of the resonance frequency on the number of quantum wells in the active region, originating from variations both in internal losses and in differential gain. The differential gain is found to have values higher than in corresponding bulk lasers, but only in devices with a large number of wells. The damping is also found to vary in a manner consonant with the changes in differential gain; however, comparison with bulk lasers indicates substantially stronger gain suppression in the quantum-well lasers studied. >

Least squared error FIR filter design with transition bands

Abstract: The authors propose the use of transition bands and transition functions in the ideal amplitude frequency response to allow the analytical design of optimal least-squared-error FIR digital filters with an explicit control of the transition band edges. Design formulas are derived for approximations to ideal frequency responses which use pth-order spline transition functions. A mixed analytical and numerical method for zero-error weight in the transition bands and passband and stopband error weighting functions with an integral squared error approximation are derived. A variable-order spline transition function is developed, and a method for choosing the optimal order to minimize the integral squared approximation error is given. >

Optimal multilayer filter design using real coded genetic algorithms

Abstract: A novel approach for designing optimal multilayer filters based on a real-coded genetic algorithm is presented. Given the total number of layers in the filter, as well as the electrical properties of the materials constituting each layer, the algorithm iteratively constructs multilayers whose frequency response closely matches a desired frequency response. In contrast to existing iterative techniques, this method does not require a preliminary design using classical techniques. Also, the design procedure is independent of the nature of the multilayer as well as the characteristics of the incident and substrate media. The algorithm is applied to the design of various lowpass and high-pass optical filters, operating between practical terminal conditions. The performance of the resulting designs matches or improves on that for filters that were synthesised using semiclassical techniques.

Chirping characteristic and frequency response of MQW optical intensity modulator

Abstract: The spectral linewidth enhancement factor and frequency responses of electro-absorption-type optical-intensity modulators, especially InGaAs/InAlAs MQW modulators, are described. A method of exactly estimating the value of the alpha factor is presented under the nonlinearity of extinction-ratio characteristics. For measuring the frequency response of modulators, the sideband strength of the modulated output light with an optical spectrum analyzer, is analytically compared with the microwave power of photodiode direct detection with an electrical spectrum analyzer. >

Improved finite-difference formulation in frequency domain for three-dimensional scattering problems

Abstract: The finite-difference method in the frequency domain is a powerful tool for analyzing arbitrarily shaped transmission-line discontinuities and junctions. An improved formulation based on Maxwell's equations in integral form is presented. It corresponds to the Helmholtz equation and reduces the numerical efforts in solving the large linear equation system considerably. The method is verified by comparison to previous work on microstrip. >

Radio with fast lock phase-locked loop

Abstract: A communication device (508) for use in a Time Division Multiplex (TDM) communication system (500) includes a transmitter, a receiver, and a frequency scanner for quickly scanning the radio frequency communication channels to determine an available channel. The communication device (508) also includes a phase locked loop (100) for providing a reference signal for the communication device (508) and locking to the available channel. This phase locked loop (100) includes a Voltage Control Oscillator (VCO) (104) having a control signal input (103). The phase locked loop (100) also includes a first filter (110) and a second filter (108). The first filter (110) has a wide frequency response. The second filter (108) includes a storage element (222) and has a narrow frequency response. The phase locked loop (100) also includes a switching circuit (106) which determines which one of the two filters (110, 108) gets coupled to the voltage control oscillator (104).

Micromachined subminiature condenser microphones in silicon

Abstract: Silicon subminiature microphones can be manufactured with the methods of micromachining technology. Several condenser-type microphones have been designed and fabricated at our institute. Capacitive microphones are described, which have a structured back electrode and a membrane of silicon nitride. A smooth frequency response up to 30 kHz with a maximum open-circuit sensitivity of 10 mV/Pa is obtained. A special design of a capacitive sensor has been realized with the FET microphone. The drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane. This design represents the first suspended-gate sensor, the drain current of which is deflection controlled. Design, construction and experimental results of sensitivity and frequency response are given.

Nonparametric frequency response function estimators based on nonlinear averaging techniques

Abstract: Nonparametric frequency response function (FRF) estimators based on nonlinear averaging techniques are proposed. The suitability of such estimators for FFT based signal analyzers is studied. Under mild assumptions, it is shown that their bias is a function of the fourth-order moments of the perturbing errors on the input-output Fourier coefficients while the bias of the classical H/sub 1/ estimator is a function of the second-order moments. The performances of these estimators are analyzed in different situations: uncorrelated input-output perturbing errors (i.e., open-loop measurements), mutually correlated input-output disturbances (i.e., closed-loop measurements) and in presence of outliers. Analytical expressions are given for the bias when the input-output errors are zero-mean normal distributed (and mutually correlated). >

Observation of photodetector nonlinearities

Abstract: A heterodyne technique is used to characterise the nonlinear response behaviour of microwave pin photodetectors in terms of 3 dB bandwidth reduction and signal distortion of the sinusoidal input/output. Bandwidth reductions from 20 to 2.5 GHz (at 1.6mW) are observed.

A frequency-domain maximum likelihood estimation of synchronous machine high-order models using SSFR test data

Abstract: The authors propose a numerical scheme for processing noisy signals originating from standstill frequency response (SSFR) tests on synchronous machines. Instead of using a univariate nonlinear least-squares procedure to fit only the weighted sum of magnitude responses, they minimize a multivariate prediction error criterion based on the determinant of the residuals covariance matrix. The algorithm pertains to a large class of prediction error methods and results in a multiresponse nonlinear regression procedure related to the maximum likelihood viewpoint when the residuals distribution is Gaussian. To demonstrate the efficiency of the proposed scheme, the implementation was tested using noisy simulated data, based on the Rockport model 3.3. It is shown, using actual data from the Nanticoke turbogenerator, dating back to the EPRI-project RP-9997-2 (1980), that the frequency-domain maximum likelihood approach can be effective for direct estimation of generalized circuits with up to five equivalent windings per axis, providing satisfactory predictions of both magnitude and phase as far as the 16th harmonic. >

The Reliability of a Modified Simplex Procedure in Hearing Aid Frequency-Response Selection

Abstract: The reliability of a modified simplex procedure to select the preferred frequency response on a programmable hearing aid was studied. The effect of stimulus materials on the selected frequency resp...

A two-dimensional time-domain near-zone to far-zone transformation

Abstract: A 2D version of a time-domain transformation useful for extrapolating 3D near-zone finite-difference time-domain (FDTD) results to the far zone is outlined. While the 3D transformation produced a physically observable far-zone time-domain field, this is not convenient for the 2D case. However, a representative, 2D far-zone time-domain result can be obtained directly. This result can then be transformed to the frequency domain using a fast Fourier transform, corrected with a simple multiplicative factor, and used, for example, to calculate the complex wideband scattering width of a target. If an actual time-domain far zone result is required, it can be obtained by inverse Fourier transform of the final frequency-domain result. >

Method and apparatus for using stochastic excitation and a superconducting quantum interference device (SAUID) to perform wideband frequency response measurements

Abstract: A stochastic excitation, SQUID detection system for determining the frequency response of a sample. A pair of counterwound detection coils are adjacent to an excitation coil. The sample is selectively placed in one of the detection coils for taking measurements. The SQUID sensor is a broadband, high sensitivity device which enables the frequency response of the sample to be determined over a wide bandwidth with a single measurement.

Adjustable filter for differential microphones

Abstract: A method and apparatus for providing a differential microphone with a desired frequency response are disclosed. The desired frequency response is provided by operation of a filter, having an adjustable frequency response, coupled to the microphone. The frequency response of the filter is set by operation of a controller, also coupled to the microphone, based on signals received from the microphone. The desired frequency response may be determined based upon the distance between the microphone and a source of sound, and may comprise both a relative frequency response and absolute output level. The frequency response of the filter may comprise the substantial inverse of the frequency response of the microphone to provide a flat response. Furthermore, the filter may comprise a Butterworth filter.

System for short-range transmission of signals over the air using a high frequency carrier

Abstract: A system is provided which transmits either analog or digital data signals over the air. The system includes including a transmitter and a receiver. The transmitter and receiver are arranged to transmit signals using a carrier signal having a high frequency such as in the range of 902-928 MHz. The transmitter and receiver are configured to provide for the transmission of two channels of stereophonic signals while maintaining high signal-to-noise ratios, good frequency response, and low distortion. To provide for the proper transmission of signals between transmitter 10 and receiver 12, these devices include oscillating circuits having ceramic resonators which provide a base frequency which is readily modulated to facilitate proper transmission of either analog or digital signals between the transmitter and receiver. To further improve the transmission capability between the transmitter and receiver, the transmitter and receiver both include substantial buffering, isolation and shielding between selected circuit components to prevent unwanted areas of frequency modulation within the transmitter and receiver.

Frequency response and instantaneous temperature profile of cold-wire sensors for fluid temperature fluctuation measurements

Abstract: The information of the wire response is necessary for the estimation of corrections and uncertainty of temperature measurements. This paper describes the theoretical response of cold-wire sensors to temperature fluctuations in a fluid flow. Existing transfer functions of cold wires are approximate and implicit functions of frequency. We present the exact solutions of heat conduction equations for a cold wire and stubs taking account of the prong effect. Because the solutions have simple forms of elementary functions, we can easily calculate the frequency response of cold wires. Sample calculations are given under several typical conditions. Also, the instantaneous temperature profiles of a cold wire are obtained for the first time.

Hot carriers and the frequency response of quantum well lasers

Abstract: A simple analytical model is obtained to describe the effect of carrier heating on the frequency response of a quantum well laser. The principal factors are taken to be injection heating, recombination heating, and hot phonons. The model is applied to the GaAs/GaInAs strained layer system and is shown to qualitatively account for many of the nonideal features observed. The nonlinear effects cannot be described satisfactorily by a single phenomenological ‘‘gain suppression’’ factor. However, at low drives the conventional gain suppression factor can be expressed in terms of the phonon lifetime and the temperature‐relaxation time. The response is mediated by several time constants which, in our example, combine to give an effective time constant of about 10 ps. The modulation frequency response becomes seriously impaired when the differential gain is lowered by a factor of 2 and the time constants describing scattering and phonon lifetime are increased by a factor of 2.