Showing papers on "Butterworth filter published in 1978"

Switched-capacitor filter design using the bilinear z-transform

Abstract: A general synthesis technique is described for obtaining a switched-capacitor (SC) filter from an active RC prototype. The response of the SC filter is related to that of its prototype by the bilinear z -transform. This allows the filtering and sensitivity properties of the prototype to be preserved for the SC circuit. It also enables the designer to realize such economical and low-sensitivity circuits as the FDNR and gyrator filters. Finally, it permits the processing of signals at much higher frequencies than do previously known circuit design techniques.

Use of the Butterworth low-pass filter for oceanographic data

Abstract: The characteristics of the Butterworth low-pass filter are well known in electrical engineering. Here we discuss its use for oceanographic records and compare its characteristics with other low-pass filters now in use: the cosine-Lanczos filter, the Gaussian filter, and the ideal filter. The Butterworth filter is recursive, i.e., past values of the output are used as input, so a phase shift is introduced unless the data are filtered forward and backward through the same filter. When this is done, the filtered signal differs only slightly from that of other low-pass filters. Because the Butterworth filter uses fewer multiplicative constants for the same effect, there is a reduction in computer time over other low-pass filters; the difference becomes more pronounced as more data points are used.

High pass switched capacitor filter section

Abstract: A high-pass switched capacitor biquadratic filter based on the bilinear z-transform The filter comprises first and second integrating operational amplifiers connected in series and in combination with a third operational amplifier that serves as a sample and hold and also generates one simple pole and zero pair in the circuit transfer function thereby enabling the circuit to provide for a high degree of filter efficiency in a preselected frequency range The operational amplifiers are connected to and operate in cooperation with capacitors of a predetermined size which are switched on and off continuously by two phase clock signals supplied to the circuit The loss characteristic of the filter can be programmed by varying the clocking frequency Higher order filters can be obtained by the tandem connection of second order circuit sections followed by one or more first order pole-zero section

Filter which tracks changing frequency of input signal

Abstract: A tracking band-pass filter useful for locking onto, and passing, an input signal which changes rapidly in frequency. The filter has a frequency pass band controlled by a rectangular voltage waveform which is derived from the output signal passed by the filter. The filter output signal is translated from a sine wave to a pulse wave. The period between each two successive pulses is measured by counting the cycles of an oscillator during each respective period. The time-representing count is inverted to a frequency-representing count which controls the duty cycle of a rectangular wave used to make the filter track the changing frequency of the input signal.

Moving-average notch filter

Abstract: A moving-average notch filter with a well-defined phase characteristic for use in eliminating oscillation frequencies in a sound amplification system, wherein this moving-average filter is designed to have an output Y K in accordance with the system equation ##EQU1## where b 1 are the weighting coefficients, X K-i are input samples, and K is a constant. This filter may be designed to have a linear phase characteristic. In one embodiment, the location of the notch in the frequency response of the filter may be made to automatically track the drift of an acoustic oscillation frequency.

Variable response notch filter for machine resonance elimination in a servo control system

Abstract: This invention relates to a flexible notch filter for use in a servo system to eliminate natural mechanical resonance. The filter is an improved "twin-T" type where the "in-phase" output of the filter is fed back into the filter. Varying the feedback varies the bandwidth of the filter. The improved filter further provides for attenuation control in addition to control of the center frequency of the filter. The advantage of this filter over prior art designs is that one filter may be manufactured and adapted to be used in many servo systems since the filter can be easily adjusted to effectively eliminate the natural resonating frequency of the machine in addition to reducing phase lag at frequencies below the center frequency of the notch filter.

On the Calculation of Squaring Loss in Costas Loops with Arbitrary Arm Filters

Abstract: The calculation of the optimum performance of suppressed carrier receivers with Costas loop tracking is directly related to evaluating the loop's so-called squaring loss. Recent work by the author and others presented specific numerical results for this loss when the input data were biphase- L (Manchester coded) and the Costas loop arm filters were of the n -pole Butterworth type. These results were largely obtained by numerical integration on a digital computer. This paper presents a partial fraction expansion technique for arriving at closed form expressions for squaring loss for Costas loops with arbitary arm filters and NRZ as well as Manchester coded data. Specific closed form results are given for one and two pole Butterworth filters as examples.

Bandpass filter having low passband phase shift

Abstract: An active filter which can achieve extremely high attenuation of frequencies outside the passband while maintaining a very low phase shift of signals within the passband. A preferred embodiment is described in which two, second-order, multiple-feedback, active filter circuits are cascaded and the output of the second filter is fedback to the input of the first filter to realize a fourth-order filter which has very high attenuation of signals falling outside the passband while providing very low phase shifts of signals within the passband.

A recursive digital filter with maximally flat linear phase at an arbitrary specified frequency

Abstract: An available recursive digital low-pass filter with constant group delay cannot be spectral transformed to give, for example, a bandpass filter which also has constant group delay. This correspondence describes a technique, using Gauss-Jordan elimination, to design a recursive digital filter with maximally flat linear phase at an arbitrary specified frequency.

An estimate of the order of an optimal FIR band-pass digital filter

Abstract: The computer program of McClellan, Parks and Rabiner [1] for designing optimal (minimax) FIR filters requires the order of the filter as an input parameter. Although a reliable estimate for the lowpass case is known [2], no such estimate exists for the bandpass case. In this paper we investigate the problem of estimating the order of an optimal bandpass filter. The effects of the design specifications on filter order are studied, and a simple estimate of the filter order is presented.

Band-pass filter and gain stage

Abstract: A band-pass filter and gain stage which produces a desired passband at a preselected center frequency. The present invention can be characterized as being a very passive frequency door whose output is lightly coupled to a broad band frequency amplifier having a high gain. The present invention includes an input connected to an input impedance stage, which is connected to a monolithic filter stage, which is connected to a second impedance stage, which is connected to a gain stage, which, in turn, is connected to an output terminal. A piezoelectric quartz crystal monolithic filter or a piezoelectric ceramic monolithic filter can be employed depending on the width desired for the passband response.

Modified Butterworth filters

Abstract: A novel class of low-pass filters with zero pass-band loss at the origin and at the fixed frequency near the band-edge and satisfying (n − 2) magnitude flatness conditions at the latter are described. The magnitude characteristics of these filters are superior to those for the Butterworth filters and some other recently introduced classes of low-pass filters. They also compare favourably with Legendre monotonic pass-band filters. The all-pole filter functions of this type are discussed as well as the filter function with finite real frequency transmission zeros exhibiting Chebyshev stop-band attenuation characteristics.

Radio receiver blanker gate

Abstract: A balanced, doubly tuned gate couples between the mixer and intermediate frequency (IF) stages of a conventional radio receiver. The network is comprised of a pair of matched transformers interconnected in a balanced configuration, with the first transformer tuned to the mixer and the remaining transformer tuned to the IF stage. Capacitors interconnect the two transformers resulting in a Butterworth filter network. Two diode pairs connect in shunt across selected windings of the transformers. Direct current bias normally biases the diodes to a nonconducting state, thereby allowing the mixer signals to pass to the IF stage. A blanking signal from the receiver blanker drives the diodes to conduction thereby decoupling the mixer from the IF and blanking the receiver. Due to the doubly balanced nature of the gate, blanking is accomplished with a minimum of switching time. Moreover, the shunt diode switching scheme provides superior attenuation in the blanking mode and enhanced operation in the normal mode.

Accurate cascade synthesis

Abstract: An accurate synthesis technique for cascade networks is presented. This technique contains an adaptive accuracy-preserving procedure which dictates the order of element removal. Examples of Butterworth filter synthesis are given to show that many decades of improvement are possible with the technique.

Least-mean-square (minimum integrated power loss ratio) lowpass filters with a pair of imaginary-axis zeros

Abstract: If power is the main interest, then a class of filters with minimum integrated power loss ratio in the passband offers higher cutoff rate than the well known Butterworth filters. A technique is described to improve the cutoff rate further by introducing a pair of imaginary axis zeros, while the integrated power loss ratio in the passband is still kept at minimum. Other advantageous performances of the filters are also indicated.

Implementation of a 64-point adaptive filter using an analogue c.c.d. programmable filter

Abstract: This letter describes the construction and operation of an adaptive filter based on the Widrow least-mean-square adaption algorithm using a 64-point analogue programmable c.c.d. transversal filter as the main processing element. Initial test results are presented to confirm the principle of the system and these results may be readily compared with previously published simulation results.

Processing of seismic signals for pattern recognition

Abstract: The study describes the preparation of seismic signals in order to identify the best technique for input to a pattern recognition scheme. The signal is first filtered with zero phase shift high and low pass Butterworth filters. It is then subjected to adaptive filtering and finally moving average filtering. Spectral decomposition in terms of circular functions is done via conventional Fourier and log P maximum entropy analysis. Spectral decomposition in terms of sequency functions, Walsh, and Chebyshev, is also performed. The Walsh decomposition is done with the conventional fast operator. The Chebyshev decomposition is done with an optimization procedure. Results, based on these various operations, are presented for an underground nuclear explosion and several earthquakes.

Multirate multiplierless discrete ladder filters

Abstract: Multirate discrete ladder filter structures are proposed that, when implemented as a digital filter, achieve better passband accuracy than the corresponding uniform-rate filter and, of more importance, may be implemented without the use of digital multipliers and consequently with simpler hardware and reduced filter processing times.

Multiband FIR digital filter design algorithm for radar clutter suppression

Abstract: An algorithm is presented for designing multi-band FIR digital filters to suppress wideband or bimodal clutter in MTI radars. The technique is an iterative process in which the passband edges are varied to maximize the usable bandwidth over which a signal is detected with acceptable probability while maintaining specified clutter rejection. The clutter-bandwidth tradeoff is shown to be a function of such interrelated filter parameters as number of taps, transition widths, passband ripple, variable stopband attenuation, and stopband width. A 25-tap bandstop filter design is presented which provides 70% usable bandwidth while maintaining 20 dB wideband clutter rejection. The design is then modified to include an additional 50 dB ground clutter attenuation. The resulting 26-tap multi-band filter meets all specifications while still retaining 60% usable bandwidth. An alternative technique for bimodal clutter rejection is presented which utilizes the natural null at dc for an N-even bandstop filter to attenuate the ground component.

On the Implementation of a Two-Dimensional FIR Filter Using a Single Multiplier

Abstract: A general scheme for implementing a two-dimensional FIR filter using only one multiplier is outlined. The realization is based on sequentially multiplexing the multiplier inputs and is illustrated with the aid of a block diagram and the sequence of operations for a 3 x 3 filter.

False Lock Performance of Costas Loops with N-Pole Arm Filters

Abstract: A recent paper has been published giving the true lock and false lock behavior of conventional Costas loops. The results are in the form of an integral which has been evaluated in closed form for the case of an RC arm filter. This paper derives closed form results for the case of an arbitrary n -pole filter whose poles are all of multiplicity one. Results are plotted for Butterworth filters of several orders.

A maximally flat group delay recursive digital filter with Chebyshev stopband attenuation

Abstract: Due to the monotonically decaying nature of its magnitude response, an all-pole recursive digital filter, with its group delay approximating a prescribed constant value, does not exhibit a sharp transition band. Using transformation as the mathematical means, this correspondence describes a design technique for a recursive digital filter with a maximally flat group delay and a Chebyshev attenuation stopband.

Digital-filtering facility for computer processing

Abstract: A set of Fortran subroutines is described that enables Butterworth, Cheb?chev or elliptic filters having a lowpass, highpass or bandpass response to be designed and implemented in a form ready to filter a data sequence with only three lines of user-written program The software is modular in that separate routines are used for the functions of transfer-function computation, network synthesis and filter simulation This approach leads to several advantages, which include the ability to implement multiple filters simultaneously The existence of gerneralised algorithms for network synthesis and simulationenables this filtering facility to be used without knowledge of digital-filter theory

Monolithic, 64-Point, Programmable, Analogue CCD/MOST Transversal Filter

Abstract: A 64-point, monolithic, fully progromable, CCD/MOST transversal filter is reported. Its circuit principles and limitations are reviewed, and results for the device when used as a matched filter and a frequency filter are illustrated.

Implementation of a channel vocoder synthesizer using a fast, time-multiplexed digital filter

Abstract: This report describes the implementation of a 19-channel vocoder synthesizer, with a computer driven digital filter. The digital filter is a special purpose digital processor, which produces the transfer function of a second order section, with two poles and two zeros. Since up to 128 indipendent filter calculations can be completed during one sampling interval of the resulting speech wave, it can be time multiplexed into 128 indipendent filter sections; these can be interconnected in several ways, under computer control. The sections are used to implement the filter bank of a channel vocoder; coefficients determining both the structure of the system, and frequency response are also supplied by a computer, in this case a PDP 11/20. The basic scheme of the realized vocoder and its driving program will be discussed in detail. Possible applications include automated voice response systems in which the synthesizer is either controlled by data derived from naturally spoken sentences, or by parameters computed according to dyadic synthesis techniques.

Electronically Tunable Active-RC All-pass Filter

Abstract: A second-order active all-pass filter is realized with three op. amp. biquad circuit. The tunability of the filter is achieved by the use of periodically-switched conductances within the circuit in which the regulation of the switching parameter allows the independent adjustment of the delay characteristics. It is shown that the maximum delay time and its corresponding frequency are adjustable independently by changing the ratio of the on-duration in a period to the period of switching. The electronically tunable active all-pass filter can be used for data transmission systems because of its sufficient flexibility of adjustment.