Showing papers on "Butterworth 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.

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.

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

A comparison of cascade and wave fixed-point digital-filter structures

Abstract: Three classes of digital-filter structures, namely two classes of cascade structures and one class of wave structures, are compared with regards to the number of arithmetic operations, the inherent speed capability, the output noise due to product quantization, and the sensitivity to multiplier-coefficient quantization Four types of filters are considered, namely a Butterworth low-pass filter, a Chebyshev high-pass filter, an elliptic bandstop filter, and an elliptic band-pass filter The arithmetic is assumed to be of the fixed-point type, numbers are assumed to be in two's complement representation, and number quantization is assumed to be by rounding

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.

Explicit formulas for the synthesis of optimum bandpass Butterworth and Chebyshev impedance-matching networks

Abstract: Explicit formulas for computing the optimum design parameters of the bandpass impedance-matching networks having Butterworth and Chebyshev responses of arbitrary order for a class of most practical RLC load are derived It is shown that using at most a second-order all-pass function for the equalizer back-end reflection coefficient, a bandpass impedance match is possible if and only if the series inductance of the given load does not exceed a certain critical value This is in direct contrast to the low-pass situation where we showed earlier that any given RLC load can be matched using at most the rust-order all-pass function The significance of the present results is that we reduce the design of these practical bandpass impedance-matching networks to simple arithmetic

Maximally flat f.i.r. filter with prescribed cutoff frequency

Abstract: Maximally flat f.i.r. digital filter design provides the advantage of giving a closed-form solution, but there still remains a problem of designing such a filter whose magnitude response passes through a prescribed cutoff frequency point. It is described here how to generate a class of transitional maximally flat f.i.r. digital filters to overcome such a difficulty.

Bandstop filter for very high frequency transmission lines and biassing circuit for a very high frequency transistor comprising this filter

Abstract: A bandstop filter for very high frequency transmission lines having distributed constants, having several filtering elements each intended to prevent the transmission of a specific frequency band. The first filtering element is a quarter-wave filter, the second element an assembly of two transmission paths of a length such that the signals present at the outputs have opposite phases and cancel other, the third element being a quarter-wave filter, these elements being grouped such that they form an extremely compact filter which is little sensitive to proximity effects.

Smoothing filter for digital to analog conversion

Abstract: An electronic filter comprised of three active filter sections (A, B, C) is provided to smooth the stepped signal from a digital-to-analog converter The first section has a noninverting low-pass filter transfer function, and the second has an inverting transfer function designed to pass a narrow frequency band centered at the step frequency of the stepped output signal with sharp cutoff on either side of that narrow band The third section adds the noninverted output of the first section to the inverted output of the second section This third section has a lead-lag transfer function designed to reduce the phase angle between the signal at its output terminal and the stepped signal at the input of the first section

A Low Cost Multiplexer for Channelized Receiver Front Ends at Millimeter Waves

Abstract: Work with millimeter-wave components using printed-circuit techniques has led to the successful development of multiplexers that are compatible with low-cost fabrication and packaging techniques. This paper will describe a 26 to 42-GHz multiplexer exhibiting 1.2 to 2.8 -dB insertion loss over a 4-GHz channel passband and a 45-dB rejection bandwidth of less than 8 GHz. This multiplexer uses a channel-dropping filter technique that splits the band into 4-GHz subbands (channels). Each channel-dropping filter consists of dual band-pass filters separated by a pair of 3-dB directional couplers. Fabrication costs are kept low by using chemically-milled broadwall couplers and E-plane filter resonators. A series of normalized filter design nomograph's have been generated. Measured multiplexer performance will be presented.

Phase-locked loop filter

Abstract: A tunable narrow-band filter is described incorporating a phase-locked loop that includes a phase detector, amplifier, loop filter, and voltage controlled oscillator wherein the loop filter transfer function is derived or extracted from the desired closed-loop transfer function that is of order n=3 or greater. The loop filter may furthermore have finite transmission zeros or peak attenuation at specific frequencies close to the passband which also appear in the characteristics of the narrow-band filter. The invention overcomes the problem of providing peak attenuation close to the passband of an electronically tunable narrow-band filter.

On the design of recursive low-pass digital filters

Abstract: The magnitude-squared characteristic of a low-pass filter is approximated, over the finite interval [-1, 1 ], by the ratio φ(x)/[φ(x) + P(x)] of two polynomials. For elliptic filter design, a special case, the polynomials φ(x) and P(x) (of the same order) are chosen such that the ratios P(x)/φ(x) and φ(x)/P(x) approximate, in the Chebyshev sense, the zero function over the passband [x p , 1] and stopband [-1, x s ], respectively. The passband and stopband form two disjoint intervals. The polynominals are determined by repeated applications of Darlington's technique for obtaining a rational function generalization of Chebyshev polynominals.

Averaging filter circuits for signal recovery applications

Abstract: The optimum filter for improving the signal-to-noise ratio in a commonly encountered signal recovery situation is the ideal averaging filter. Approximants to the averaging filter response, with averaging times between 1 ms and 100 s, are realised by RC active networks having some novel properties. The use of these filters in place of the first-order low-pass filter leads to an improvement in the measurement rate by a factor of two or greater.

Use of a programmable filter for inverse filtering

Abstract: A real-time deconvolution or inverse filter, operating at signal frequencies up to 5 MHz, is reported. The programmable digital filter is controlled by a computer which calculates the Wiener-filter solution using f.f.t. techniques. Deconvolved signals can be clearly discriminated after passing through a distorting medium.

OQPSK and MSK systems with bandlimiting filters in transmitter and receiver and various detector filters

Abstract: Formulas are presented for the computation of error probability of OQPSK and MSK with narrow-band filters in transmitter and receiver and various detector filters (matched filter, sampling detector, rectangular filter and half-rectangular filter) Numerical results are computed for the case when the filters in transmitter and receiver are identical Butterworth filters The error probability is presented as a function of signal/noise ratio or normalised filter bandwidth with the filter order as a parameter The conclusion is that with narrowband filters, MSK with a sampling detector or half-rectangular detector filter and OQPSK with a sampling detector are the best systems Although MSK is slightly better than OQPSK, the difference in performance is insignificant for the range of bandwidths of practical interest

Floating inductor with two current conveyors

Abstract: There have been considerable efforts towards the realization of ideal floating inductors where mostly three active blocks are required. The reduction in the number of active blocks to two was however achieved with considerable increase in the number of resistances and passive parameter constraints. The proposed scheme suggests a method to produce a floating inductor with a series negative resistance using two current conveyors, only three resistors and one capacitor, involving only one restrictive constraint. The realized inductor was also used to design a third order Butterworth filter. Experimental results confirm the applicability of the realized immittance.

A monolithic c.c.d. programmable transversal filter for analogue signal processing

Abstract: This paper describes the operational features and performance of a fully-integrated programmable transversal filter (p.t.f.), using c.c.d./m.o.s.t. technology. The choice of filter architecture for a prototype realization is discussed with particular reference to a novel multiplier array implementation using a single, time-multiplexed m.o.s. transistor. The performance characteristics of a prototype, 64-point filter design based on this approach are detailed with reference to frequency- and matched- filtering. Techniques for optimizing the performance of this analogue filter structure under microprocessor control are suggested, through the iterative adaption of the filter impulse response, and equivalent results are given to show the improvement gained. An alternative technique for improving the filter characteristics which enables it to optimize the processing of signals under certain conditions has also been demonstrated. This adaptive filter configuration is based on the linear Widrow least-mean-square (W.l.m.s.) algorithm, and has been realized using the p.t.f. with minimal additional circuitry, without the requirement for a microprocessor.A general signal-processing module of 256-points using four cascaded filters is described; and results are presented when it is used in a sonar, matched-filtering experiment. Also a 64-point adaptive filter based on a prototype p.t.f. is described and its application to inverse filtering and self-tuning filtering is demonstrated.Finally, the potential of this miniature integrated filter for sonar-type applications is reviewed against new developments. In particular, a 256-point monolithic p.t.f.currently in development, and the concept of a dedicated adaptive filter in single chip form.

Noise suppression circuit for two-way telephone system - has filter comprising subtractor extracting outputs of impedance transformers at outputs of two integrators

Abstract: The noise suppression circuit has the control ac voltage derived from the voice channel rectified and passed to a filter to remove the component caused by interference or background noise. The filter's output is rectified to control the gain of the channel. The filter has two input parallel integrators (I1, 12) with different time constants. Two operational amplifiers (OP1, OP2) acting as impedance converters are connected to the outputs of the integrators. A subtractor (OP3) subtracts the outputs of the operational amplifiers from one another and its output is the output of the filter. The time constants are such that the voltage at the output of the first integrator follows the amplitude variations of the LF input to the filter whilst the output voltage of the second integrator is similar to the average of the filter input voltage and is not affected by these amplitude fluctuations.

I.I.R. digital filter design using constrained optimisation techniques

Abstract: A new design method for all-pole infinite impulse response (i.i.r.) digital filters is introduced. The method involves minimising the area between the ideal lowpass filter response in the passhand and the actual passband response, subject to a quadratic constraint which ensures filter realisability. A unique solution is obtained to the minimisation which relates the filter weights to the eigenvector of a Toeplitz matrix. The filters are seen to have a small ripple in the passhand and a sharp cutoff in the stopband.

Equivalent circuit of a magnetic sensor coil and a simple filter for rejection of 60Hz man-made noise.

Abstract: A magnetic sensor coil is shown to behave as a 2nd order Butterworth low pass filter for induced e. m. f. if the coil's output ends are terminated with a set of parallel resistor and capacitor matched to the sensor. The conditions for matching are theoretically derived, assuming an equivalent circuit of the sensor coil. An experiment to check the Butterworth filter behavior agrees well with the theory. It demonstrates the validity of the assumed equivalent circuit of the sensor. The corner frequency of the filter can be changed, selecting different matched values of the resistor and capacitor. In the experiment, the corner frequency is set at 6Hz which rejects 60Hz man-made noise 40 db ca. without distorting magnetic pulsation signals up to the highest frequency range (Pc 1). This technique for rejection of man-made noise is more advantageous than another common practice, putting a twin-T filter between the sensor and the head amplifier. A twin-T filter used this way is shown to give rise to ringing depending on the characteristics of the sensor, the twin-T filter and the input impedance of the head amplifier.

Quarter-Wavelength Coupled Dielectric Plate Resonators for High Selectivity TE/sub 10/-Mode Filters

Abstract: An analysis of high selectivity TE/sub 10/-mode filters with quarter-wavelength coupled resonators formed by axially spaced dielectric plates is presented and shows that high-loaded quality factors of individual resonators can be obtained by placing the resonant frequency close to the waveguide cutoff frequency and by using low-loss Iow-dielectric constant materials. Design equations for Butterworth and Chebyschev filters are presented and employed in a three-cavity Butterworth filter having 30-MHz bandwidth at resonant frequency at 7250 MHz. Experimental results show that filter performance can be well predicted.

Transmission Characteristics and a Design Method of Transmission-Line Low-Pass Filters with Multiple Pairs of Coincident Zeros and Multiple Pairs of Coincident Poles

Abstract: The transmission characteristics and a design method are presented for a transmission-line Iow-pass filter with multiple pairs of coincident zeros in the finite frequency of the passband and multiple pairs of coincident poles in the finite frequency of the stopband and for a transmision-line low-pass filter with Butterworth characteristic in the passband and multiple pairs of coincident poles in the finite frequeney of the stopband. The former transmission-line low-pass filter shows an improved skirt attenuation performance and delay characteristic than a Chebyshev transmission-line low-pass filter in the same network degree. The latter type of transmission-line low-pass filter shows an improved skirt attenuation performance in comparison to a Butterworth transmission-line low-pass filter in the same network degree, it is positioned about in the middle between a Butterworth type and a Chebyshev type, the delay characteristic is improved considerably in comparison to the Chebyshev type, and the characteristic is close to that of the Butterworth type. With this design method, the connecting unit elements in addition to the stubs contribute to the attenuation response. The design example is shown on the basis of a concrete specification, and it is shown that the obtained attenuation strictly fulfills the specification.

Switch-tuned filters

Abstract: A switch-tuned filter comprises a capacitive filter and a resonant filter both receiving an input signal to be filtered. The resonant filter comprises a gyrator the frequency response of which depends on circuit parameters in two circuit paths therein. A tuning switch is arranged to select the values of the parameters in each of these circuit paths. The output signals of the gyrator and the capacitive filter are combined to form the filtered output signal. The circuit can be used as an equalizer in a magnetic tape recorder.

N-path frequency-tracking filter

Abstract: The invention relates to a tracking filter switching n switched paths, of band-pass type. This filter comprises means (M, T) for taking a prefittre signal paths of the switching timing. It is characterized in that the means (M, T) for withdrawing the prefiltered signal are constituted so tells that in said pre-filtered signal remains a part of the input signal (E) of the filter. Application to the filtering of a signal having a useful component of variable frequency associated with a high background noise.

A numerical butterworth fiber for digital data processing with applications to the analysis of track geometry

Abstract: This paper deals with the implementation of digital Butterworth filters having highpass, lowpass and bandpass characteristics. After outlining the underlying theory, examples of a sixth-order filter and a second order filter are discussed. In addition to the theoretical filter shapes, some experimental results obtained from a comparison of the Fourier transformed unfiltered and filtered records are presented. It has been concluded that these practical estimates closely fit the theoretical values, both for gain and phase shift.

Low frequency active bandpass filter.

Abstract: An active low-frequency band-pass filter is proposed which contains three operational amplifiers (13, 16, 22), one of which is connected as an inverter stage and the other two of which are connected as integrators. Of the components (C1, C2, R1...R4) determining the centre frequency of the band-pass filter, only the electrical value of one component (R3) is changed to adjust the centre frequency.

Audio signal processor for motorcycle helmets - uses bandpass, notch and active filters and amplifier with AGC

Abstract: The audio filter circuit overcomes the acoustic problems associated with ambient noise encountered by the rider of a motorcycle wearing a helmet fitted with loudspeakers. The audio signal is first fed to a band-pass filter those pass-band extends from approx. 100 Hz to an upper limit of approx. 6 kHz. This eliminates interference effects. Since only small loudspeakers can be fitted into the helmet, their resonant frequency is likely to fall within the pass-band of the filter. The band-pass filter is therefore followed by a notch filter whose effective frequency equals the loudspeaker resonant frequency. An active filter with a peak response at about 400 Hz is combined with the notch filter. The resulting signal is fed to an amplifier with a.g.c.

2-D FIR Filter design via semipolynomial approximation

Abstract: A technique is described for the design of general two-dimensional linear-phase FIR filters. It is based upon a two-step approach: (i) approximate the ideal frequency response by a semi-polynomial function, i.e., one which is a linear combination of Chebyshev basis functions in one frequency variable; then (ii) approximate this semi-polynomial by the 2-D filter response. This procedure yields 2-D filter designs which are not necessarily Chebyshev-optimal, but experience has shown them to be good designs in cases where the optimal solution is known. Furthermore, the algorithm is computationally fast and thus suited to large filter orders. Filter response specifications need not have particular topographies other than the symmetries implied by linear-phase conditions.

Least-squares low-pass filters with nonmonotonic response

Abstract: A new class of all-pole low-pass filter functions, derived from the least-squares approximation technique, is introduced. The magnitude response is compared with those of some other all-pole filters, like the Butterworth, LSM, and Chebyshev ones. The three subclasses of the new class seem to be a suitable choice for the approximation function in filter synthesis.