Showing papers on "Low-pass filter published in 1980"

A filter family designed for use in quadrature mirror filter banks

Abstract: This paper discusses a family of filters that have been designed for Quadrature Mirror Filter (QMF) Banks. These filters provide a significant improvement over conventional optimal equiripple and window designs when used in QMF banks. The performance criterion for these filters differ from those usually used for filter design in a way which makes the usual filter design techniques difficult to apply. Two filters are actually designed simultaneously, with constraints on the stop band rejection, transition band width, and pass and transition band performance of the QMF filter structure made from those filters. Unlike most filter design problems, the behavior of the transition band is constrained, which places unusual requirements on the design algorithm. The requirement that the overall passband behavior of the QMF bank be constrained (which is a function of the passband and stop band behavior of the filter) also places very unusual requirements on the filter design. The filters were designed using a Hooke and Jeaves optimization routine with a Hanning window prototype. Theoretical results suggest that exactly flat frequency designs cannot be created for filter lengths greater than 2, however, using the discussed procedure, one can obtain QMF banks with as little as ±.0015dB ripple in their frequency response. Due to the nature of QMF filter applications, a small set of filters can be derived which will fit most applications.

An analysis of multiple correlation cancellation loops with a filter in the auxiliary path

Abstract: A technique known as a "multiple correlation cancellation loop" and also as the "LMS algorithm" is widely used in adaptive arrays for radar, sonar, and communications, as well as in many other signal processing applications. In this paper an analysis of this technique is extended to the case when a linear filter appears in the auxiliary signal path. A general solution to this problem is obtained and several examples for narrow-band and broad-band signals are presented.

Fast implementations of LMS adaptive filters

Abstract: A frequency domain implementation of the LMS adaptive transversal filter is proposed. This fast LMS (FLMS) adaptive filter requires less computation than the conventional LMS adaptive filter when the filter length equals or exceeds 64 sample points.

Assessment of signal and noise in the kinematics of normal, pathological and sporting gaits.

Abstract: Cinematography is widely used to collect displacement data on human activities. Some form of smoothing or curve fitting of this raw data is necessary to reduce noise prior to analysis. The technique of low pass digital filtering (1,2) appears most appropriate, giving a simple and fast means of conditioning. The need for a well defined cutoff frequency has, in part, resulted from an increased interest in mechanical analysis of competitive sports where mechanical work costs are extremely sensitive to choice of filter cutoff frequency, especially from field study data. This paper presents a technique for assessing system noise and selecting a specific cutoff frequency for the digital filter. The application of this method to normal, pathological and sporting movements is reported.

Improved circuits for the realization of switched-capacitor filters

Abstract: New topologies for switched-capacitor filters are presented. The circuits are based on a pair of complementary integrators and have transfer functions independent of parasitic capacitances between any node and ground. Design equations are given for low-pass, bandpass, high-pass, and notch biquads, as well as ladder simulation filters. The ladder simulation filters are scaled for optimum dynamic range. Discrete prototypes of both cascade and ladder simulation filters are used to verify the theory.

General Extracted Pole Synthesis Technique with Applications to Low-Loss TE/sub011/ Mode Filters

Abstract: A novel synthesis technique is developed for two-port networks which possess finite real frequency transmission zeros. The low-pass prototype is synthesized in the form of a network with complex conjugate symmetry where the real frequency transmission zeros are extracted from both ends and realized by simple resonators separated by phase shifters. The remaining transmission zeros are realized by the central part of the filter in the form of a cross-coupled double array. This prototype is particularly suitable for designing waveguides bandpass filters and each real frequency transmission zero is independently tunable. Furthermore, in the case of the most complex transfer function with all possible types of transmission zeros, the realization requires only one type of coupling which is necessary in the important case of TE/sub011/ cylindrical mode cavity resonators. The general synthesis technique is given and the process illustrated by a nontrival example. Additionally, from the results of a computer program based upon the synthesis techniques, the important differences between the possible prototype forms for the same transfer function resulting from extracting the transmission zeros in different orders are cited.

Minimum Peak Range Sidelobe Filters for Binary Phase-Coded Waveforms

Abstract: Linear programming techniques are utilized to determine the optimal filter weights for minimizing the peak range sidelobes of a binary phase-coded waveform. The resulting filter is compared with the filter obtained by use of the least square approximation to the ideal inverse filter. For a test case using the 13-element Barker code the linear programming filter is found to have peak sidelobes as much as 5 dB lower than the least squares filter of the same length.

Cascade decimation--A technique for real time estimation of power spectra

Abstract: Cascade decimation is a technique for computing power spectra estimates for single or multi-channel time series data. It was originally developed for processing broadband, low frequency geophysical data in real time using a small digital processor. Sine and Cosine transforms are applied to sequences of data produced by successively applying a low pass digital filter and decimation by two operator to the original data. The resulting spectra are the average of estimates which are independent in time and represent constant percentage bandwidths. Thus, the technique is particularly well suited to applications where it is desireable to reject intervals of bad data or those which are naturally expressed on a log-frequency scale. Because ascade decimation is a real time process, its memory requirements are a fraction of those for techniques which operate on a stored array of data, particularly when a broad band of frequencies is being analyzed.

The generalized chebyshev low-pass prototype filter

Abstract: A synthesis method is presented for the class of low-pass prototype filters having an equiripple passband response with a single transmission zero at infinity and the remainder at a finite real frequency. To synthesize the network, the even mode or the odd mode is obtained directly using the alternating pole technique and little accuracy is lost for networks up to degree 19. Tables of element values for commonly used specifications are included. Finally, the practical advantages of this prototype when used to design certain classes of filters are discussed.

Narrow-Band Stripline or Microstrip Filters with Transmission Zeros at Real and Imaginary Frequencies

Abstract: Simple approximate design equations are derived in this paper for an even degree (n /spl ges/ 6) low-pass inverter capacitance prototype filter having single transmission zeros at both real and imaginary frecuencies. This is achieved by utilizing one or two additional couplings. The transmission zeros improve considerably the passband group delay and increase the skirt selectivity compared to those of the ordinary Chebyshev prototype. An exact and more complicated method based on the known generalized Chebyshev rational function approximation is also presented for the comparison. The prototype with one additional coupling is utilized to realize narrow-bandpass printed circuit filters consisting of half-wave resonators.

Pulsed phase locked loop strain monitor

Abstract: The RF output of a voltage controlled oscillator (VCO) 11 is periodically gated by gate 15 to a transducer 18 which produces acoustic waves in bolt 19. The reflected acoustic waves are converted to electrical signals by transducer 18 and gated by a gate 20 to mixer 31. Mixer 31 also receives the output from VCO 11 and produces an output which is filtered by low pass filter 32. The output of filter 32 is a DC signal proportional to the phase difference change from a fixed phase difference between the two input signals to mixer 32. This DC signal is sampled at an instant and held by circuit 33 in response to the "P" signal. The output of circuit 33 is integrated by integrator 34 and then applied to VCO 11 to change the frequency of VCO 11 such that the phase difference between the two inputs to mixer 31 remains at said fixed phase difference. The frequency of VCO 11 is a measure of the change in strain of bolt 19.

Photodetector array based optical measurement systems

Abstract: A method and apparatus are provided for analyzing the light pattern produced on a photodetector array. The signal produced by the array is filtered with a low pass filter and the output of the filter is differentiated to obtain either the first or second derivative of the filtered signal for one or more points in the pattern. The zero crossing of the differentiated signal is detected and the zero crossing point is timed relative to a further point, e.g., the start of the scan of the array, so as to obtain an output related to the position of the corresponding point or points in the pattern.

Switched-capacitor filter design using bilinear element modeling

Abstract: The low sensitivity of a doubly loaded reactance ladder to element-value variations is preserved in a switched-capacitor filter with the same graph if a one-to-one replacement of branch impedances is used to derive the switched filter from the reactance ladder This paper describes the design principles and some novel circuits based on this approach The frequency axes of the two filters are mapped into each other by the bilinear s{\leftrightarrow}z transformation; this results in advantageous sensitivity and selectivity properties for the resulting switched-capacitor circuit In addition, the number of active components is equal to the number of inductors replaced, and is hence small This results in very economical realization for the integrated filter

MOS switched-capacitor filters using voltage inverter switches

Abstract: Low-sensitivity switched-capacitor filters imitating LC and LC /unit-element structures can be built by means of capacitances, ordinary switches, and voltage inverter switches, the latter being quite simply realizable by electronic means (either with or even without operational amplifier). There are no restrictions on the operating rate (other than those resulting from the Nyquist theorem) nor on the location of the attenuation poles. Experimental results of an integrated third-order lowpass filter are in good agreement with theory. The effects of parasitic capacitances can be overcome by using proper design techniques.

Filter-length word-length tradeoffs in FIR digital filter design

Abstract: We give a theorem which shows that there is a lower bound on the Chebyshev approximation error for linear-phase direct-form FIR digital filters, when the coefficients are constrained to be b-bit numbers. We then investigate the tradeoff between filter-length N and coefficient word-length b, using the product Nb as a complexity measure, for both the usual direct form and the sharpening structures of Kaiser and Hamming. The sharpening structures usually provide no overall gain in Nb product, but achieve a given performance with a smaller value of b.

Equalisation of recursive digital fitters

Abstract: The purpose of this paper is to apply a recent minimax optimisation algorithm to the design of equalised recursive digital filters satisfying prescribed amplitude specifications. The technique is applied to the design of a lowpass, a highpass and a bandpass filter.

Sound signal automatic detection and display method and system

Abstract: A sound signal automatic detector used in a system with a micro computer and display for automatically detecting an input sound wave, computing from the detected sound wave the fundamental frequency of the sound and displaying its value in a number of different formats. The sound signal detector requires no attention on the part of a musician or other user while it is in operation and comprises a sound signal transducer supplying an amplifier having audio frequency bandpass characteristics compatible with the sound signal frequency spectrum over which sound signals to be analyzed extend. The bandpass characteristics of the amplifier preferably are defined by a high pass filter stage followed by an automatic gain control amplifier that in turn is followed by two stages of low pass filtering. The low pass filter stages supply their output to an alternate positive peak voltage and negative peak voltage detector circuit that functions to derive an output signal which is representative of the fundamental frequency of a input sound wave being analyzed. The output from the automatic detection circuit is supplied to a micro computer which then processes the signal and derives a number of different display formats for use by an instrumentalist, vocalist, or other musician or like person producing the sound for analysis and instruction purposes.

Zero-crossing study on dynamic properties of speckles

Abstract: The zero-crossing problem is studied for the purpose of investigating the dynamic properties of speckle produced in the diffraction field by a moving diffuse object under illumination of coherent light. The zero-crossing method is applied to the time-differentiated speckle intensity fluctuations and studied in some detail with respect to the influence of noise and the low-pass filter used for suppressing the noise. From the theoretical and experimental studies, the velocity of the moving object is found to be accurately determined by measuring the number of zero-crossings per second of the time-differentiated speckle intensity fluctuations when both the optical configuration used for producing speckles and the characteristic of the low-pass filter for suppressing the noise are known beforehand.

Sample-and-hold hybrid active RC filter

Abstract: A discrete-time analog filter for eliminating a variable frequency carrier of an amplitude-modulated signal. The filter comprises a plurality of unit delay circuits, each of which is sampled at a rate which varies in proportion to the frequency of the carrier so as to automatically tune the filter's reject band to follow the carrier frequency.

Low-sensitivity switched-capacitor ladder filters

Abstract: A switched-capacitor filter design technique based on the LDI transformation is presented which uses a novel floating inductance simulation circuit. By choosing the filter terminations properly, the circuits are shown to preserve the maximum power transfer property. A low-pass filter design example is presented to illustrate the low-sensitivity property of this technique.

Optimum design of low-pass switched-capacitor ladder filters

Abstract: A general technique for realizing Bruton's LDI transformation in low-pass switched-capacitor ladder filters is presented, which results is switched-capacitor integrators that are insensitive to parasitic capacitances. It is shown that the correct filter response may be obtained by realizing only the stable poles of the LDI transformed LC network. Realization of these "stable" poles is reduced to the problem of solving a system of nonlinear equations. The design of a third-order Chebyshev low-pass filter is presented as an example.

Explicit formula for filter function of maximally flat nonrecursive digital filters

Abstract: A general formula for the filter function of maximally flat f.i.r. digital filters using modified Krawtchouk polynomials is presented. This formula permits a direct calculation of the filter weights. It is especially advantageous for either high or low passband/stopband width ratios.

A real-time programmable switched-capacitor filter

Abstract: Four independent real-time programmable switched-capacitor filters have been fabricated on a single NMOS chip. The filters are second-order sections with digitally programmable Q and center frequency. Either low-pass or bandpass functions are available by selecting the appropriate input. The device is microprocessor compatible and includes permanent programming capability as well as an on-chip oscillator. The circuit implementation, programming capability, and operation are described.

Injection laser diode digital transmitter having signal quality monitoring arrangement

Abstract: An injection laser diode transmitter contains a detector arrangement that permits the quality of the signal transmitted over a fiber optic link of interest to be monitored for degradation and error detection, by examining the transmitted optical pulses. The transmitted signal component is extracted from the back facet of the ILD for feedback stability control purposes and is coupled to signal quality measuring circuitry from a wideband current-to-voltage converter that is coupled to the output of a fast photo diode that extracts the optical output signal from the rear facet of the ILD for the purposes of generating a feedback control voltage to be used for ILD bias control. The bias current generated through a feedback loop from the fast photo diode to the wideband current-to-voltage converter feeds reference amplifier, the output of which is coupled to a lowpass filter to remove the pulse signal component. The output of the low pass filter is a DC voltage level which is directly proportional to the average optical output of the ILD. The voltage level output of the lowpass filter is applied to a current sink coupled to the ILD. The bias current for the ILD is controlled to drive the differential to zero. Because the bias current control feedback loop is responsive to the optical output of the ILD, the bias current is automatically compensated for changes in temperature. The current-voltage converter output is further coupled to a buffer amplifier to supply an output voltage to downlink signal quality monitoring circuitry. In a repeatered, multichannel fiber optic communication system, this quality-indication signal availability facilitates a fault isolation scheme wherein the transmitter outputs are examined selectively.

Finite precision design of linear-phase fir filters

Abstract: The FIR (finite impulse response) filter is an essential tool for a large number of applications in communication. In this paper we consider the design of linear-phase FIR digital filters with finitely precise coefficients. Coefficient inaccuracy is known to degrade the frequency response of band-select FIR filters, especially in the stopband region. We derive a bound on the attainable stopband attenuation, and we also develop techniques for designing FIR filters with finitely precise coefficients. Mixed-integer programming algorithms are presented to select finitely precise coefficients for a filter that best approximates an arbitrary magnitude characteristic in the minimax sense. Our method generates a number of possible solutions including that of simple rounding or truncation and then selects the best finitely precise coefficients from this set. In this way, significant improvement in the filter performance is gained over methods that simply round or truncate the infinitely precise coefficients. We also show how integer programming can be used to design filters with powers of two coefficients. Such filters are easier to mechanize since they do not require multipliers.

Nonlinear temporal filter for television picture noise reduction

Abstract: A conventional recursive interframe lowpass filter for 625 line 5.5 MHz monochrome television is modified so that its attenuation of frame differences is instantaneously dependent on their amplitude. This results in improved rendition of motion when compared with the original design. Performance is assessed by objective measurement of noise attenuation for a range of input noise levels and nonlinear characteristics, and by subjective opinion tests on pictures containing noise and movement.

Noise generated in switched capacitor networks

Abstract: It is shown that the noise generated in a passive first-order switched-capacitor lowpass filter has its origin in the thermal noise of the m.o.s. transistors' on-resistance. The spectral description of this noise at the output of the filter is given. The measurements made on a discrete laboratory model show good correspondence with the analytical results and confirm the noise model established.

Tone control of the operational type

Abstract: A tone control circuit for use in audio equipments includes an attenuating high pass filter (typically, a CR filter), an attenuating low pass filter, a boosting high pass filter, a boosting low pass filter and at least an operational amplifier for tone control The high pass filters extract a treble component from an audio input signal for emphasizing or attenuating treble response, whereas the low pass filter extract a bass component of the audio input signal for emphasizing or attenuating bass response The mid-range component of the audio input signal prevented from entering the filters by virtue of a bypass circuit interposed between a source of the audio input signal and the operational amplifier

An optimization technique for the design of half-plane 2-D recursive digital filters

Abstract: An iterative optimization technique, based on a Modified Marquardt algorithm, is proposed for the design of asymmetric 2-D half-plane recursive digital filters with a zero-phase implementation. To illustrate the technique a fan-filter and a circular lowpass filter were designed. The technique can also be used for the design of quarter-plane filters.

Charge domain recursive filters

Abstract: A new charge-transfer device architecture has been developed for implementing recursive filters in the minority charge domain. A three pole filter using this architecture has been designed and fabricated. The measured filter characteristics are in close agreement with theoretical predictions to approximately 0.2 percent. The charge domain filter appears to retain the intrinsic CCD shift register advantages (e.g. high-speed, small output capacitance, wide linear dynamic range), while overcoming many of the disadvantages of the present CCD transversal filter architecture.