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Showing papers on "Low-pass filter published in 1971"


Journal ArticleDOI
TL;DR: The digital technique lends itself to the production of phase coherent or phase controlled sinusoids because of the indexing arrangement used and finer frequency steps than the READ-ONLY memory allows are available by expanding theindexing register at no increase in inaccuracy.
Abstract: A digital frequency synthesizer has been designed and constructed based on generating digital samples of \exp [j(2^{\pi}nk/N)] at time nT . The real and imaginary parts of this exponential form samples of quadrature sinusoids where the frequency index k is allowed to vary (-N/4) \leq K . The digital samples drive digital to analog converters followed by low-pass interpolating filters to produce analog sinusoids. The method is superior to digital difference equations with poles on the unit circle since the noise or numerical inaccuracy remains bounded. The digital technique used consists of factoring the exponential into two table look-ups from an efficiently organized small READ-ONLY memory table and performing a complex multiply to produce the real and imaginary components. A small array multiplier efficiently organized performs the multiplications. The technique lends itself to the production of phase coherent or phase controlled sinusoids because of the indexing arrangement used. In addition finer frequency steps than the READ-ONLY memory allows are available by expanding the indexing register at no increase in inaccuracy.

698 citations


Journal ArticleDOI
Joseph P. Kirk1, Alan L. Jones1
TL;DR: In this paper, a phase-only spatial filter was proposed for wave-front construction, in which both the amplitude and phase information necessary to construct an arbitrary image over a limited field are encoded.
Abstract: A new type of phase-only filter is described for wave-front construction, in which both the amplitude and phase information necessary to construct an arbitrary image over a limited field are encoded. It is shown that this phase-only filter can duplicate the performance of an ideal complex-valued spatial filter (a filter that controls both amplitude and phase transmittance). This phase-only filter controls the amplitude transmittance by the use of a modulated high-frequency phase carrier that diffracts a controlled amount of light into the image. This type of filter is particularly useful in the implementation of computational wave-front construction, because the maximum spatial frequency that must be plotted is associated with the image and not the carrier. The performance of the filter is examined both numerically and experimentally.

137 citations



Journal ArticleDOI
TL;DR: The SNR depends, at least, upon the contraction level, type of smoothing filter, and the amount of smoothness for the particular filter, which is important in signal communication problems of both a design and theoretical nature.
Abstract: A common method of initially processing surface-detected electromographic (EMG) activity is to differentially amplify, rectify, and then smooth (using a low-pass filter) the rectified activity. The output of the filter exhibits a mean value slightly obscured by ripple. Both the mean value and ripple increase with increasing muscle contraction. The mean value can be called the signal while the ripple, undesirable when only the signal is desired, can be called noise. The SNR depends, at least, upon the contraction level, type of smoothing filter, and the amount of smoothing for the particular filter. This defined SNR is important in signal communication problems of both a design and a theoretical nature.

65 citations


Patent
29 Oct 1971
TL;DR: In this article, a digital frequency synthesizer using modulo 10N accumulator means for receiving signals corresponding to a predetermined frequency output and for successively generating signals correspond to addresses in a storage means, each of the addresses correspond to a storage location which stores digital values corresponding to at least the magnitude of a plurality of digital samples of the output signal from the synthesizer.
Abstract: A digital frequency synthesizer using modulo 10N accumulator means for receiving signals corresponding to a predetermined frequency output and for successively generating signals corresponding to addresses in a storage means, each of the addresses corresponding to a storage location which stores digital values corresponding to at least the magnitude of a plurality of digital samples of the output signal from the synthesizer A digital-to-analog converter converts the output of the storage means into a step-type waveform which is passed through a low pass filter to generate a smooth output waveform from the system In order to reduce the size of the required storage device, sign and quadrature symmetry may be taken advantage of by making use of the redundancy of the magnitude of values in a sinusoidal signal generator

56 citations


Journal ArticleDOI
TL;DR: In this article, all-pole recursive digital low-pass filters approximating a constant group delay in an equal-ripple sense are described, where the equalripple conditions are given by a system of nonlinear equations in the poles of the transfer function.
Abstract: All-pole recursive digital low-pass filters approximating a constant group delay in an equal-ripple sense are described. The equalripple conditions are given by a system of nonlinear equations in the poles of the transfer function. The closed-form solution obtained for a particular value of the cutoff frequency yields good first approximations for the iterative procedure required in the general case. The set of approximated delays and ripples leading to realizable filters is discussed. Numerical examples illustrating the procedure are included.

53 citations


Patent
26 Jul 1971
TL;DR: In this paper, a variable bandpass filter for a dynamic noise filtering effect that reduces the perceptible noise in an audio reproduction system is proposed, where the integration response of the two paths imparts a high and low frequency filtering effect.
Abstract: A variable bandpass filter for a dynamic noise filtering effect that reduces the perceptible noise in an audio reproduction system. The variable bandpass filter responds to peak signal levels in relatively high and relatively low frequency portions of the audio spectrum to automatically and independently vary high and low frequency cutoff points for the filter in correspondence with the level of signals at those frequencies. Low distortion and wide dynamic range is achieved in a filter configuration which comprises a forward signal path and a reverse signal path, each having a variable integration response provided by temperature compensated and linearized field-effect transistor circuits. The integration response of the two paths imparts a high and low frequency filtering effect. A further constant gain feedback path establishes a uniform middle frequency amplification for the variable bandpass filter.

37 citations


Journal ArticleDOI
TL;DR: In this article, an RC active-network synthesis method described by Bruton for the realization of low-pass filters is extended to the case of bandpass filters, which use frequency-dependent negative-resistance (conductance) elements as active elements, and these can be realized by using generalized-immittance converters (GICs).
Abstract: An RC -active-network synthesis method described by Bruton for the realization of low-pass filters is extended to the case of bandpass filters. Networks are obtained which use frequency-dependent negative-resistance (conductance) elements as active elements, and these can be realized by using generalized-immittance converters (GICs). In turn, GICs can be implemented by using operational amplifiers. The method is illustrated by designing a sixth-order bandpass elliptic filter; experimental results are also given.

35 citations


Patent
15 Dec 1971
TL;DR: In this article, a voltage controlled oscillator controllable to discrete frequency outputs, which outputs are applied to a phase detector through divider circuits and compared to a reference signal of the same frequency, is controlled by variable voltages or variable width pulses, proportional to the difference in phase between the two signals.
Abstract: A voltage controlled oscillator controllable to discrete frequency outputs, which outputs are applied to a phase detector through divider circuits and compared to a reference signal of the same frequency, is controlled to discrete frequency outputs by variable voltages or variable width pulses, proportional to the difference in phase between the two signals, from the phase detector which pulses are applied to the oscillator through loop filters. Each loop filter is an RC circuit which integrates the pulses and serves as a memory to retain a relatively constant voltage thereacross. Therefore, when a specific loop filter is switched into the circuit the voltage controlled oscillator is rapidly switched to a discrete frequency output proportional to the voltage stored in the loop filter.

28 citations


Journal ArticleDOI
TL;DR: In this paper, two distinct frequency domain filters are developed in the frequency domain which represent an attempt to increase the resolution of fine structure contained in the signal whilst keeping the expected filtered noise energy within reasonable bounds.
Abstract: Two distinct filters are developed in the frequency domain which represent an attempt to increase the resolution of fine structure contained in the signal whilst keeping the expected filtered noise energy within reasonable bounds. A parameter termed the White Noise Amplification is defined and used together with a measure of the deconvolved pulse width in order to provide a more complete characterisation of the filters. Each of the two main types of frequency domain filters discussed varies in properties with respect to a single adjustable parameter. This may be contrasted with a time domain Wiener filter which in general has three variables: length, delay and an adjustable noise parameter or weight. The direct frequency domain analogue of the Wiener filter is termed a gamma-Fourier filter, and is shown to have properties which span the range from those of a spiking filter with zero least square error at one extreme, to those of a matched filter at the other extreme of its variable parameter's range. The second type of filter considered—termed the modulated Gaussian filter—is similarly shown to be a perfect spiking filter at one extreme of its parameter range, but adopts the properties of an output energy filter at the other extreme.

24 citations


Journal ArticleDOI
TL;DR: In this paper, the cutoff slope and minimum attenuation in the stopband are derived in terms of n, the number of pairs of zeros (m) and their locations, and the information required for design of finite zero filters is provided in the form of universal graphs.
Abstract: Maximally flat (MF) low-pass filters with multiple pairs of coincident or distinct imaginary axis zeros are investigated and compared with the all pole Butterworth filters. It is shown that for the same order n , finite zero filters provide much sharper cutoff than Butterworth filters, and that the cutoff slope increases with increasing number of zeros. Expressions for cutoff slope and minimum attenuation in the stopband are derived in terms of n , the number of pairs of zeros ( m ) and their locations. In the case of coincident multiple zeros, the stopband performance is found to be an optimum for a particular value of m . The information required for design of finite zero filters is provided in the form of universal graphs and use of these graphs is illustrated by a design example.

Patent
16 Apr 1971
TL;DR: In this article, a bandwidth controlled low pass filter circuit with a resistor, capacitor, voltage follower amplifier, and an insulated gate, metallic oxide semiconductor, field effect transistor utilized as a switch, in which the transistor and the resistor, together, provided the effective circuit filter resistance.
Abstract: A bandwidth controlled, low pass filter circuit having a resistor, capacitor, voltage follower amplifier, and an insulated gate, metallic oxide semiconductor, field effect transistor utilized as a switch, in which the transistor and the resistor, together, provide the effective circuit filter resistance, and the bandwidth is controlled by the transistor gate pulse frequency and pulse width. The use of several such filters as a filter bank is also disclosed.

Patent
C Harris1
28 Aug 1971
TL;DR: In this article, the transmission characteristics of an active RC filter are adjusted by digital control of passive networks included at particular points in the filter circuit, each network includes a plurlaity of passive circuit elements connected either in series or in parallel, each circuit element having a switching element in circuit relation to the associated circuit element.
Abstract: The several transmission characteristics of an active RC filter are adjusted by digital control of passive networks included at particular points in the filter circuit. Each network includes a plurlaity of passive circuit elements connected either in series or in parallel, each circuit element having a switching element in circuit relation thereto for selectively preventing current from flowing in the associated circuit element. Each switching element is uniquely controlled by the logical condition of a predetermined place of a binary control quantity. The values of the elements in a given network are related by a geometric progression such that the filter characteristic controlled by that network varies linearly with the associated binary control quantity.

Patent
30 Aug 1971
TL;DR: In this article, the frequency of the only output signal from the filter is equal to the same particular harmonic to which the phase-locked loop is locked times the difference in frequency between the reference frequency and the displaced reference frequency.
Abstract: Harmonic generator type of frequency synthesizer employing a reference frequency signal equal to the spacing between adjacent channels and a displaced reference frequency signal which differs from the reference frequency by a few hertz. The reference frequency signal is applied to a first harmonic generator which generates a spectrum of harmonics of the reference frequency. The spectrum is applied to a phase-locked loop which produces an output frequency signal equal to a particular one of the harmonics of the reference frequency. The displaced reference frequency signal is applied to a second harmonic generator which generates a spectrum of harmonics of the displaced reference frequency. The spectrum of harmonics of the displaced reference frequency is combined with the output signal of the phase-locked loop in a mixer and the output of the mixer is applied to a lowpass filter. The frequency of the only output signal from the filter is equal to the same particular harmonic to which the phase-locked loop is locked times the difference in frequency between the reference frequency and the displaced reference frequency. Since the difference between the frequencies is a known, fixed value, the signal from the filter is thus a precise measure of the particular harmonic of the reference frequency being produced by the phase-locked loop. The output frequency of the filter may be counted and compared with a preset count representing the value of a predetermined harmonic of the reference frequency to which it is desired to tune the phase-locked loop. The difference between the counts is employed to generate a voltage signal which is coupled to the phase-locked loop to change the tuning of the phase-locked loop to another harmonic of the reference frequency.

Journal ArticleDOI
TL;DR: A recently developed method of filter synthesis is proposed, which does not require high accuracy working in a computer because it operates throughout with simple factors which are never multiplied into polynomials.
Abstract: A general classification of reactive ladder filters with real transmission zeros is given which is based on the extreme frequency behavior of port impedances and on types of design polynomials of the characteristic and effective transmission functions. It is shown that this classification provides an ordered algorithm for automatic realization of ladder structures which can be used to construct a logical development of appropriate computer programs. The bilinear frequency transformation is extended to all filter classes for a synthesis procedure entirely in the transformed plane. Accuracy limitations of this method are discussed and reasons for them are pointed out. A recently developed method of filter synthesis is proposed, which does not require high accuracy working in a computer because it operates throughout with simple factors which are never multiplied into polynomials. A design example of a through-supergroup filter is offered which demonstrates limitations of standard synthesis procedures.

Patent
C Hartmann1
30 Dec 1971
TL;DR: A transducer-filter of interdigitated electrodes patterned to pass a particular wavelength of frequencies at an established center frequency is described in this article. But the authors do not specify the parameters of the transducers.
Abstract: Elastic waves propagating at the surface of a solid substrate are generated by a transducer-filter of interdigitated electrodes patterned to pass a particular wavelength of frequencies at an established center frequency. Interdigitated electrodes of the filter may be either uniformly spaced one-half wavelength apart or spaced to produce a desired function. The overlapping length of the electrode configuration for each filter varies in accordance with a weighting function usually approximating sin x/x. To generate an output signal having a desired frequency distribution between band pass and band stop regions, each filter comprises two sections of an array of three or more taps of interdigitated electrodes. These taps correspond to a fundamental, third, fifth, etc., time harmonic of the band passband stop periodicity. The two sections are arranged back to back on the substrate, that is, with the fundamental tap of each section adjacent and the highest time harmonic tap of each section at the ends of the filter. An interchange of the band pass and band stop regions is accomplished by splitting each filter and connecting the individual sections to a reversal switch. By selective programming of a plurality of filters, a particular frequency will be selected and passed through an array of such filters.

Patent
26 Oct 1971
TL;DR: In this article, the video signal is applied to a low pass filter and the filtered video signal was substracted from the original video signal, which has been suitably delayed by a delay line to produce a contour signal containing primarily high frequency video signal components.
Abstract: A television camera aperture correction system wherein the video signal is applied to a low pass filter. The filtered video signal is substracted from the original video signal, which has been suitably delayed by a delay line to produce a contour signal containing primarily high frequency video signal components. The contour signal is amplified and the low level portion of the contour signal, which is primarily high frequency noise, is removed by a coring circuit. Thereafter the cored contour signal is combined with the filtered video signal to produce a resultant video signal having enhanced high frequency components, but without the attendant high frequency noise increase conventionally associated therewith.

Journal ArticleDOI
TL;DR: In this paper, the authors calculated the ballistic deficit for proportional counter pulses shaped by different pulse shaping networks and found that networks with better signal-to-noise performance than the simplest CR-RC filter have been investigated with respect to attenuation of counter pulses.

Patent
R Willett1
08 Nov 1971
TL;DR: In this paper, a system for analyzing the frequency spectrum of an input signal includes a digital filter, the center frequency of which is varied by changing the sampling rate of the filter.
Abstract: A system for analyzing the frequency spectrum of an input signal includes a digital filter, the center frequency of which is varied by changing the sampling rate. The output signal of the digital filter is squared in a detector circuit; and the output signal of the detector circuit is fed to an integrator circuit. The integration time is varied inversely proportional to the center frequency of the digital filter to obtain a signal representative of the power spectrum of the input signal.

Patent
27 Sep 1971
TL;DR: An analog harmonic rejecting phase detector with even harmonic rejection achieved through a fundamental frequency, fr, phase detector section and rejection of the stronger odd harmonic signal content passed from the input signal through the fundamental frequency section is presented in this paper.
Abstract: An analog harmonic rejecting phase detector with even harmonic rejection achieved through a fundamental frequency, fr, phase detector section and rejection of the stronger odd harmonic signal content passed from the input signal through the fundamental frequency section. It includes a plurality of odd harmonic frequency phase detector sections such as 3fr, 5fr and possibly other odd harmonic sections up to and including a (2n 1)fr odd harmonic section. The reference signals 3fr, 5fr, etc., are square waves so phase related relative to fr as to achieve mutual cancelling with like harmonic content in the signal being passed through an invert-noninvert amplifier of the fundamental frequency section and passed to a summing amplifier. This requires an attenuator circuit after an invert-noninvert amplifier in each odd harmonic section to properly balance signal strength to the strengths of their respective counterparts passed through the fundamental frequency section. The resulting output of the summing amplifier is so integrated through a low pass filter as to present a plus or minus output voltage indicative of the input signal, fin, phase lead or lag and the magnitude of phase displacement relative to the square wave reference signal fr.

Patent
26 May 1971
TL;DR: In this paper, a digitally controlled filter comprises an operational amplifier having selectable output circuits with predetermined time constants, and a plug-in unit determines whether the filter will be a high pass filter, a low pass filter or a band-pass filter.
Abstract: A digitally controlled filter comprises an operational amplifier having selectable output circuits with predetermined time constants. A plug-in unit determines whether the filter will be a high-pass filter, a low-pass filter, or a band-pass filter. The time constants in the circuit are determined by the application of a digital word to a plurality of switching gates to connect into the circuit one or more impedance combinations having predetermined time constants.

Patent
18 Feb 1971
TL;DR: In this paper, an automatic fine tuning and modulation detection arrangement for a color television receiver for automatically obtaining optimum picture presentation and the elimination of quadrature, intermodulation distortion and other undesirable interference components in the processing of the received signal information is presented.
Abstract: An automatic fine tuning and modulation detection arrangement for a color television receiver for automatically obtaining optimum picture presentation and the elimination of quadrature, intermodulation distortion and other undesirable interference components in the processing of the received signal information. Disclosed is an automatic phase locked or control loop interconnected between a point in the intermediate frequency channel and the local oscillator of the receiver's tuner. Automatic fine tuning is obtained by electronically controlling the frequency of the tuner oscillator in relation to the output of a reference oscillator operating at the desired picture carrier frequency. A single synchronous detector is provided in lieu of the several conventional peak or envelope detectors, which synchronous detector is keyed to the action of the phase-locked or APC loop. The circuitry, with the exception of a low pass filter, is designed in integrated form for inclusion on a single monolithic chip.

Journal ArticleDOI
TL;DR: The performance of total-power and balanced Dicke-type radiometers using digital integration and the square-law device output is considered to be smoothed by an RC filter and then sampled.
Abstract: The performance of total-power and balanced Dicke-type radiometers using digital integration is considered. The square-law device output is considered to be smoothed by an RC filter and then sampled. Degradation due to finite sampling rate and quantization noise is derived.

Proceedings ArticleDOI
01 Aug 1971
TL;DR: In this article, the design of a class of impedance-transforming filters in the form of very compact and convenient mixed lumped and distributed ladder networks is presented, and the synthesis utilizes the distributed prototype technique introduced in a previous paper, but here a new approximation function appropriate to the impedance transformer problem is derived.
Abstract: The design of a class of impedance-transforming filters in the form of very compact and convenient mixed lumped and distributed ladder networks is presented. The synthesis utilizes the distributed prototype technique introduced in a previous paper, but here a new approximation function appropriate to the impedance transformer problem is derived. In addition to combining the properties of an impedance transformer and a low-pass filter, the new circuit represents a solution to the problem of short-line matching to an extreme impedance value without using extreme impedance values in the transformer. Broad-band designs are tabulated for a wide range of parameters. A discussion of the application of the technique in the design of mixed lumped and distributed broad-band matching networks is included. A 50-10-/spl Omega/ transformer was designed for the band 3.5-7.0 GHz, having a voltage standing-wave ratio of 1.15 and giving an attenuation >20 dB in the band 10.5-21.0 GHz. The length of this transformer is 0.875 in, and the experimental results showed excellent agreement with theory.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss the practical methods for finding the relevant parameters of the numerical filter and the data source by using the numerically analyzed characteristics of the least squares convolution filters.
Abstract: Numerical smoothing is one of the useful methods to extract the signal components faithfully from noisy spectroscopic data. However, the setting of the filtering parameters has been empirically done to allow the optimum operation because of its complexity. This article discusses the practical methods for finding the relevant parameters of the numerical filter and the data source by using the numerically analyzed characteristics of the least squares convolution filters. The detail procedures are demonstrated in far infrared spectroscopic applications. A result of the quantitative comparison between the numerical filter and the familiar electric RC filter is also given.

Patent
S Krauthamer1
18 Jun 1971
TL;DR: In this article, a series filter comprising a capacitor coupled in series with an inductor is used to energize an AC load from an inverter, or from other single or multi-phase power sources or combination thereof.
Abstract: A system for energizing an AC load from an inverter, or from other single- or multi-phase power sources or combination thereof, includes a series filter comprising a capacitor coupled in series with an inductor. The filter elements are resonant at the normal operating frequency of the inverter. Responsive to a large overload or a fault condition in the system, a virtual short circuit is applied across one of the filter components to detune the filter. Alternatively if a load exceeding a specified value is applied, a clamp detunes the filter. This significantly increases the effective impedance seen by the inverter or other power sources, protecting the system against excess currents.

Patent
18 Oct 1971
TL;DR: In this paper, a O - pi microwave phase shift device for operation in a wide frequency band, consisting of a filter Fm followed by a semiconductor diode, is presented. But the diode is reverse-biased.
Abstract: A O - pi microwave phase-shift device for operation in a wide frequency band, is provided. The device, connected to one end of a two-wire microwave propagation line, comprises a filter Fm followed by a semiconductor diode. The filter Fm is a series m-derived half-section low-pass filter derived from the half-section low-pass filter circuit equivalent to the diode end its output connections, the diode being reverse-biased.

Journal ArticleDOI
TL;DR: In this paper, it has been shown that when a linear process is passed through a low-pass filter, the output is approximately Gaussian, which is the case for the radar echoes from randomly dispersed scatterers.
Abstract: A random process is called a linear process if it is an infinite sum of statistically independent component random processes. A particular example of a linear process is the output of a filter driven by a sequence of impulses whose times of occurrence are the times of a Poisson process. If the filter responses are also random and the responses to impulses applied at different times are statistically independent, the filter output is still a linear process. If, however, either the impulses do not occur according to a Poisson process or the filter responses are not independent, the process is called conditionally linear. The latter situation can be used to describe the radar echoes from randomly dispersed scatterers which, however, exhibit some phase coupling.It has been shown in many special cases that when a linear process is passed through a low-pass filter, the output is approximately Gaussian. These are the well-known central limit theorems for linear processes. This paper presents a very general and w...

Patent
L Koziol1
22 Jan 1971
TL;DR: In this article, a data set capable of converting binary encoded data signals into shift keying modulated signals for transmission over telephone lines is presented, where the timing element of the data set is a voltage controlled oscillator which is responsive to the binary encoded input information.
Abstract: A data set capable of converting binary encoded data signals into shift keying modulated signals for transmission over telephone lines. The timing element of the data set is a voltage controlled oscillator which is responsive to the binary encoded input information. The oscillator is adapted to operate at one frequency for the mark or binary one level of the input information and to operate at either one of two higher frequencies for the space or binary zero level of input information. An oscillator control means is responsive to the desired bandwidth and is operable to supply either one of two control voltages to the oscillator to generate either of said space frequencies. Operational amplifiers allow elimination of the conventional inductive components in both high and low pass filters thereby making each section an active filter section instead of being a passive filter. Each active filter section provides gain control which is not available in passive sections.

Patent
21 Apr 1971
TL;DR: In this paper, a class of band-pass filters are provided, each of which comprises a plurality of low-pass active filters, and each of the filters has related resonating frequency and damping characteristics.
Abstract: A class of band-pass filters are provided, each of which comprises a plurality of low pass active filters. Each of the filters has related resonating frequency and damping characteristics. The resonating frequency and damping characteristics for each of the filters causes all of the poles of the filters to be along a line parallel to the outputs of the filter so that the output signals of the filters are summed with alternate ones of the filters having the output signal inverted with respect to the other of the filters.