Showing papers on "Low-pass filter published in 1970"

Interdigital Capacitors and Their Application to Lumped-Element Microwave Integrated Circuits

Abstract: An analysis of the frequency response of interdigital capacitors, which leads to an optimal design, is given along with an expression for their static gap capacitance. The capacitor Q is given in terms of its geometry which consists of a planar interdigital thin-filrn conductor deposited on the surface of a relatively high dielectric constant substrate. Capacitance values ranging from 0.1 to 10 pF at L band with measured Q's in excess of 400 are realizable using 2-mil line and space widths on a 99.5-percent alumina substrate with a dielectric constant of 10.3. Experimental results obtained with a lumped-constant nine-section S-band Chebyscheff low-pass filter realized using spiral inductors and optimal designed interdigital capacitors are shown to be in excellent agreement with theory. The filter had less than 0.8-dB insertion loss and greater than 25dB return loss in the passband. The filter occupies an area 6.50 by 200 roils on a 24-mil-thick substrate.

An approach to the approximation problem for nonrecursive digital filters

Abstract: A direct design procedure for nonrecursive digital filters, based primarily on the frequency-response characteristic of the desired filters, is presented. An optimization technique is used to minimize the maximum deviation of the synthesized filter from the ideal filter over some frequence range. Using this frequency-sampling technique, a wide variety of low-pass and bandpass filters have been designed, as well as several wide-band differentiators. Some experimental results on truncation of the filter coefficients are also presented. A brief discussion of the technique of nonuniform sampling is also included.

CaMoO4 ELECTRONICALLY TUNABLE OPTICAL FILTER

Abstract: The paper describes a CaMoO4 transmission‐type acousto‐optic filter. Tuning from about 6700 to 5100 A is obtained by changing an acoustic frequency from 40 to 68 MHz. The filter bandwidth is 8 A at an f/6 aperture. 95% transmission is obtained at an acoustic power density of 69 mW/mm2.

Designing digital low-pass filters--Comparison of some methods and criteria

Abstract: The problem of designing a digital low-pass filter is considered from different points of view, including two approaches which have not received sufficient attention. One approach is based on the prolate-spheroidal-function filters of Slepian, Pollak, and Landau. The other is the incompletely specified least mean-square error (LMSE) method which has been proposed by Rorabacher. We find that, compared with minimax and LSME designs, the prolate-spheroidal digital filters have very low sidelobes, at the expense of more deviation from a flat passband. If a transition band or "don't care" region of the frequency response is assumed, then the results of the minimax and LSME methods are nearly the same.

Numerical variational analysis formulated under the constraints as determined by longwave equations and a low-pass filter

Abstract: The “timewise localized” variational formalism of the numerical variational analysis method is used (1) to filter and suppress unnecessary high-frequency noises contained in initial and forecast fields and (2) to obtain dynamically sound initial values in the areas lacking data. A set of nonlinear longwave equations and a low-pass filter minimizing local changes are used in this paper as dynamical constraints. Also proposed in this study is a technique to assure the convergence of a numerical solution of the nonlinear Euler equations by an iterative process. Three applications of the method are presented. The first two examples demonstrate that the initial guess in the iterative process influences significantly the speed of convergence. The last example is an application to the 500-mb analysis of hurricane Dora, 1964, and demonstrates a reasonable analysis in the data-sparse area where the hurricane was located at 1200 GMT on Sept. 8, 1964.

Designing simple, effective digital filters

Abstract: Models for a class of narrow-band digital filters and a class of wide-band digital filters are developed and analyzed The analysis forms a basis for a computer-aided design technique for such filters. Our aim is to show that useful performance can be achieved within the constraints of very simple realizations.

A High-Current Low-Pass Filter for Magnet Power Supplies

Abstract: The majority of high-current dc power supplies for beam bending magnets have well known LCR low-pass ripple filters. To avoid prohibitive heat losses, the filter damping resistor is in series with the capacitor and not in the dc path. Such filters, when critically damped, attenuate high frequencies by 6 dB/octave. This paper analyzes an improved underdamped LCR filter which attenuates high frequencies by 12 dB/octave. Depending on the application, the improved filter can be designed to have an oscillatory or a non-oscillatory response to a step change of the input voltage. Design curves are given which show the frequency response and the time response to a unit step of a normalized improved filter for various degrees of damping.

Automatic tracking filter

Abstract: An automatic tracking filter for use in conjunction with fluid flowmeters automatically locks onto the largest signal in a given frequency spectrum. The filter comprises a narrow band-pass filter having input and output filter circuits (e.g., a low-pass and a high-pass filter) connected in series. The output of the input filter circuit is combined in a control circuit with the input signal to generate an error signal which is used to tune each of the filter circuits to the input signal. In one embodiment disclosed the filter sections are two-pole active R-C filters in which a field-effect transistor is used as a voltage variable resistor.

Coated ferrite rf filters

Abstract: In a low pass RF filter, a coating of barium titanate is applied to a ferrite substrate. In one embodiment, the RF filter is an extruded tube of ferrite coated with barium titanate. The tube is used as an RF filter for a connector pin. In another embodiment, a thin strip of ferrite is coated with barium titanate. This forms a filter strip for use on circuit boards or for use as a high capacity lossy power bus.

Corrective circuit for an active narrow notch filter

Abstract: An active narrow notch filter is adapted for connection between a power source and a load to filter out noise signals appearing on the power lines. A feedback loop having a stop-band notch filter is connected to the power lines and feeds interference signals to an amplifier which drives a correction transformer inserted in the power lines to cancel out interference signals from the power source. A corrective circuit is connected to form a feedback loop with the amplifier and notch filter to generate a feedback signal that is applied to eliminate any power line signal that passes through the notch filter. This corrective circuit has a first detector circuit producing an error signal which is fed through a first modulator to generate one component of the feedback signal that cancels out power line signals passing through the notch filter, and a second detector circuit and modulator that produces a second component of the desired feedback signal that is in quadrature with the first component.

Tuneable microelectronic active band-pass filter

Abstract: A microelectronic or integrated circuit active band-pass filter uses only resistors, capacitors, and active devices, is stable and has filter characteristics equivalent to an LC band-pass filter. A known band-pass amplifier comprises an operational amplifier and a negative feedback tuneable RC band reject network, such as a twin-T or bridged-T notch filter, or parallel high- and low-pass filters. To this is added a positive feedback circuit including an adjustable attenuator (for Q control) and a series feedback capacitor, and also a series input capacitor, that are effectively tuned to resonance at the band reject network center frequency. The positive feedback circuit thus has inductive characteristics at the passband frequencies, with resulting Q enhancement. The pass bandwidth and center frequency or high- and low-pass frequencies are tuneable independently and electronically by preferably fabricating the attenuator and band reject network in distributed RC form using insulated gate field effect transistors.

FEN filter design using tantalum and silicon integrated circuits

Abstract: An economical approach to integrated active RC filter design is described. Complex filter networks are broken down into a series of cascadable second-order filter sections consisting of tantalum thin-film RC networks and semiconductor integrated operational amplifiers. Two building blocks are available for any desired frequency within a decade and for any desired filter function (e.g., low-pass, high-pass, band-pass, band-reject, all-pass, etc.). One building block is for low Q realizations and contains one amplifier; the other is for high Q realizations and contains two. The considerable versatility of this approach is obtained by 1) a network synthesis approach based on decomposing a given second-order function into a low Q asymptotic approximation of this function in cascade with an active frequency emphasizing network and 2) by the characteristics of tantalum and silicon integrated circuits.

Dynamic noise filter having means for varying cutoff point

Abstract: A dynamic noise filter especially adapted for use in high fidelity audio reproduction systems to eliminate perceived noise. Controllable high-pass and low-pass filters are employed which respectively filter the low and high frequency portions of the audio spectrum. A very wide dynamic range of controllable cutoff points is achieved by each filter with different selectable rates of attenuation with frequency. The same attenuation characteristics are maintained throughout the range of cutoff points for each filter. In the presence of masking audio signals a fast attack, slow decay control is developed for each filter to cause the amount of filtering to decrease with increasing masking signals. The novel noise filter further features high frequency click impulse reduction, hum noise attenuation, and corner peaking and attenuation rate control.

The performance of suppressed carrier tracking loops in the presence of frequency detuning

Abstract: The extraction of a coherent reference for purposes of demodulating double-sideband suppressed carrier (DSB-SC) signals can be accomplished using either a squaring loop or a Costas loop. By means of the Fokker-Planck equation, this paper establishes the tracking performance of these two circuits in the presence of frequency detuning, and then applies the results in evaluating the performance of coherent demodulators of digital (coded or uncoded) data. The results are sufficiently general to assess the effects of a broad class of prefiltering characteristics on tracking performance, as well as the effects due to various loop filter mechanizations. An expression for the moments of the time to first loss of synchronization is also given.

Small Elliptic-Function Low-Pass Filters and Other Applications of Microwave C Sections

Abstract: A type of elliptic-function low-pass filter that is easy to design and construct, has low passband loss, and is very compact is described. With simple scaling and a limited number of standard parts, a broad range of cutoff frequencies can be obtained. Experimental results are presented for three filters with cutoff frequencies of 0.75, 1.0, and 1.5 GHz. Each filter occupies a volume of about 0.5 in/sup 3/. A physical interpretation of the conventional scaling transformation S =S'/ /spl Omega//sub c/' is given for networks containing unit elements. Use of this transformation is shown to yield scaled networks containing microwave C sections rather than unit elements. Applications to broad-band impedance transformers are given and other possible applications are suggested.

Technique for utilizing a single pulse to set the gains of a transversal filter

Abstract: A system for utilizing a single pulse having initially known characteristics to set the tap weights of a transversal filter to convert a first time function applied to the filter input into a second time function at the filter output. The pulse as it appears at the system input is converted into a first representation in the frequency domain and is mathematically operated upon, in conjunction with a generated second representation in the frequency domain of the pulse as it is desired that it appear at the output from the filter, to generate the frequency domain transfer function of the transversal filter. This transfer function is then converted into the time domain inpulse response of the filter which may be directly utilized to form the desired set of weighting factors for the transversal filter. When the first time function is a signal received over a transmission media, the system may function as a media equalizer.

Self tuning bandpass filter

Abstract: An electronic filter which simultaneously maintains a constant bandwidth and a constant center frequency gain as the input signal frequency varies, and remains self-tuning to that center frequency over a decade range. The filter utilizes a field effect transistor (FET) as a voltage variable resistance in the bandpass frequency determining circuit. The FET is responsive to a phase detector to achieve self-tuning.

Maximally flat low-pass filters with steeper slopes at cutoff

Abstract: Maximally flat rational functions with one pair of imaginary axis zeros are compared with the all pole Butterworth function for low-pass filter applications. It is shown that by using the location of the zeros as a parameter an advantageous trade between attenuation in the stopband and sharpness of the cutoff characteristic can be made. Graphs which serve as guides in the placement of these zeros and a practical design example are included.

The optical convolution of time functions.

Abstract: The ease with which an optical system can achieve an extremely large time–bandwidth product makes optical filters and cross-correlation function generators attractive for signal detection and parameter estimation when signal-to-noise ratios are very low. The principles of a new optical filter that overcomes the sometimes severe positioning requirements of conventional optical filters are described. The relationship between the signal amplitude and matched-filter impulse response amplitude is discussed, and a method for reducing a noise component that is common to all optical filters is given. A matched filter was constructed and used to detect a radar-like pulse when the signal-to-noise ratio was −40 dB. A digital computer may be used with an optical system to filter time signals with an accuracy that potentially is as good as the accuracy of an all-digital system, but with a significant reduction in computation. The theory of an optical digital filter is presented.

Data Modems with Integrated Digital Filters and Modulators

Abstract: The application of a binary transversal filter as transmitting filter and a digital circuit as modulator makes it possible to construct data transmitters consisting only of transistors and resistors. The modulation distortion, caused by the keying of a low-frequency square-wave carrier, can be compensated by a modification of the transfer function of the transmitting filter, provided the carder frequency is chosen to be a multiple of half the bit rate. This principle makes it possible to realize the whole data transmitter in one single integrated circuit. The binary transversal filter, provided with an analog-to-digital converter, can also be used to construct the data receiver for the greater part with digital circuitry.

Phase lock loop demodulator providing noise suppression

Abstract: A synchronous tone demodulator is comprised of a phase detector, a band-pass filter at the frequency of the desired tone and a low pass filter connected with a voltage-controlled oscillator in a feedback loop from the output of the phase detector to one of two inputs thereof. A carrier wave which is frequency or phase modulated by the tone is applied to the other input of the phase detector. Because the bandwidth of the feedback loop is limited by the filters, noise signals of frequencies outside of the bandpass of the filters are attenuated, thereby allowing the loop to lock even though the signal-to-noise ratio of the modulated wave is low. The desired tone signal derived by the phase detector appears at the output of the band-pass filter.

Bandpass filter including monolithic crystal elements and resistive elements

Abstract: A bandpass filter circuit includes a pair of monolithic crystal filter elements and a resistance-capacitance network, which may be a lattice network, connected between the crystal filter elements. The crystal filter elements are dual-coupled resonators which have a pair of resonator spots formed on a quartz wafer, and the resonators have relatively well defined bandpass characteristics extending above and below their resonant frequencies and provide an abrupt change in attenuation at the limits of the bandpass frequencies. The resistance-capacitance network used with the crystal filter elements acts to relocate the pole frequencies so that the characteristic curve of the complete filter closely approximates a Gaussian shape in the vicinity of the bandpass. The bandpass filter circuit thus formed is particularly adapted for use in a mobile receiver where extraneous undesired signals may occur in the crystal filter elements resulting from impulse type signals, such as that produced by spark discharge of the ignition system, and these undesired signals are greatly reduced or eliminated.

Squelch circuit having short and long time constant filters for squelch tail elimination

Abstract: A squelch filter circuit is provided having a short time constant ripple filter and a long time constant ripple filter. The long time constant ripple filter is responsive to signals just above squelch threshold in order to provide maximum sensitivity and smooth operation. At strong signal levels, where the long time constant ripple filter is not necessary, the circuit switches to a short time constant filter. The circuit reverts to the long time constant filter if the signal drops to low signal levels relatively slowly, to keep the squelch open during fade and flutter. If the signal drops very rapidly, as, for example, where the transmitter ceases transmission, only the short time constant filter is operative and the turn off of the squelch circuit is very rapid, thus eliminating the noise burst or ''''squelch tail.

Frequency-following voltage-controlled filter providing substantially constant output amplitude

Abstract: A filter arrangement for extracting the fundamental frequency from an input periodic electrical signal controlled to follow changes in frequency by the input electrical signal to provide an output sinusoidal signal whose frequency continuously follows the frequency of the input signal. This filter arrangement includes a voltage-controlled filter in combination with a feedback loop comprising an amplitude sensing circuit, a voltage comparator and an amplifier to provide an error signal related to the difference between the instantaneous output voltage of the voltagecontrolled filter and a reference voltage. This error signal is applied to the voltage-controlled filter to modify its characteristic response and, accordingly, to enable the voltagecontrolled filter to extract a fundamental frequency sinusoid which follows frequency changes by the input signal. Additionally, the instant filter arrangement inherently adjusts for variations in the amplitude of the input signal to effect automatic gain control providing a substantially constant amplitude output voltage.

Fm demodulator system

Abstract: An improved threshold performance for an FM demodulator is obtained by employing the combined features of a phase locked loop demodulator and a N-path (digital) filter. The bandwidth of the filter is adjusted to approximately two times the highest baseband frequency and its center frequency is determined by the switching frequency employed in the filter which is derived from the output signal of the phase locked loop''s voltage control oscillator (VCO). The VCO output signal is determined by the instantaneous IF input frequency resulting in an IF filter having a minimum bandwidth that tracks the input IF frequency.

Instability thresholds in digital filters due to coefficient rounding

Abstract: Asymptotic expressions are developed to determine the threshold frequency at which sine and tangent Butterworth digital low-pass recursive filters become unstable because of coefficient rounding. Both floating point and fixed point arithmetic is considered. The theoretical threshold values are compared with those obtained through actual operation of the filter on data.

Method and circuit arrangement for regulating the amplitude of the color synchronizing signal

Abstract: A method for controlling the amplitude of the color synchronizing signal in color television signals taken from a record carrier, wherein amplitude deviations from the nominal value occur which exhibit a periodically recurring component, wherein there is derived from the color synchronizing signal a control voltage corresponding to the deviation of the amplitude of the color synchronizing signal from the nominal value, such control voltage being delivered through a low pass filter, and at the same time, in respect of each of those lines for which the periodically recurring component of the deviations is substantially equal, the control voltage is averaged over a plurality of periods of the periodically recurring component, and the mean values thus obtained, and the control voltage delivered through the low pass filter is used to influence the frequency response of the taken off color television signals in the sense of reducing the deviations in the amplitude of the color synchronizing signal from the nominal value.

Transmission line filter

Abstract: A coaxial transmission line filter wherein open end cylindrical conducting elements, having equal diameters and various lengths and spacings, are provided for suppressing at least one spurious pass band in the frequency response of the filter.

Methods and aspects of active-RC filter synthesis

Abstract: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers.

Digital data transmission system

Abstract: A system for transmission of digital data on telephone-type voice circuits, which is compatible with conventional transmission equipment while being considerably smaller in size and weight. A transmitter including a multivibrator operating at two frequencies in response to mark and space signals, and a lowpass filter in the form of an operational amplifier to provide a sinusoidal output to the transmission circuit. A receiver including a band-pass amplifier, a limiter, a pulse multiplier, a multivibrator detector, a low-pass amplifier, and an output stage to produce mark and space signals corresponding to those at the input of the transmitter. The band-pass and low-pass amplifiers incorporate operational amplifiers to provide the customary filtering operation while eliminating the conventional large filter components. The multivibrator is switched to one state by the zero crossing of the input, or multiple thereof, and is switched to the other state by a precisely controlled ramp generator obtaining precision control of time and energy in the output signal.