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Showing papers on "Voltage-controlled filter published in 1970"


Journal ArticleDOI
TL;DR: In this paper, an improved underdamped LCR filter with an oscillatory or non-oscillatory response to a step change of the input voltage is presented. And the frequency response and the time response for a unit step of a normalized improved filter for various degrees of damping.
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.

39 citations


Patent
19 Jun 1970
TL;DR: In this article, 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, and a feedback loop has a first detector circuit producing an error signal which is fed through a first modulator that produces a second component of the desired feedback signal that is in quadrature with the first component.
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.

35 citations


Patent
James R Whitten1
18 May 1970
TL;DR: In this article, a band-pass amplifier comprises an operational amplifier and a negative feedback tuneable RC band reject network, such as a bridged-T notch filter, or parallel high-and low-pass filters.
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.

34 citations


Journal ArticleDOI
George S. Moschytz1
01 Apr 1970
TL;DR: An economical approach to integrated active RC filter design is described and 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 is obtained.
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.

34 citations


Patent
03 Nov 1970
TL;DR: In this paper, a dynamic noise filter is proposed for high fidelity audio reproduction systems to eliminate perceived noise, which is adapted for use in high fidelity Audio reproduction system to eliminating perceived noise.
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.

33 citations


Patent
13 Oct 1970
TL;DR: In this paper, 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 is presented.
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.

21 citations


Patent
C Livenick1, J Dailing1, S Malinowski1
16 Dec 1970
TL;DR: In this paper, a bandpass filter circuit is proposed 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.
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.

12 citations


Patent
John G. Neuman1
30 Nov 1970
TL;DR: In this article, an error signal related to the difference between the instantaneous output voltage of the voltage controlled filter and a reference voltage is applied to the voltage-controlled filter to modify its characteristic response and, accordingly, to enable the voltage control filter to extract a fundamental frequency sinusoid which follows frequency changes by the input signal.
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.

12 citations


Journal ArticleDOI
TL;DR: The use of a time-division multiplexed digital filter as the time-invariant part of an N -path filter is proposed and examined, and the resultant requirements for only one input modulator alleviates the problem of closely matching the transmission characteristics of the paths.
Abstract: The use of a time-division multiplexed digital filter as the time-invariant part of an N -path filter is proposed and examined. The use of a digital filter, and the resultant requirements for only one input modulator, alleviates the problem of closely matching the transmission characteristics of the paths. As a consequence of the improving matching, the time-varying modulation products in the output signal should be suppressed 10-15 dB more than in conventional implementations. The center frequency, bandwidth, and passband shape of the filter are all electronically adjustable. It is possible to time division multiplex a processor using serial arithmetic for a bandpass filter with a bandwidth of several kilohertz using high-speed bipolar logic circuits. The speed requirements for the memory are such that MOS circuitry, with its attendant size advantage, is suitable. This approach to realizing an inductorless, electronically adjustable bandpass filter should become economical in the near future because of the decreasing cost and the increasingly complex functions available in both bipolar and MOS circuitry.

9 citations


Patent
01 Jun 1970
TL;DR: In this article, a broadband composite filter circuit is disclosed which includes a plurality of filter networks, each being tuned to respond to a respective frequency bandwidth of electrical signals, and a switch is provided across the input terminals of each of the filter networks to enable each network to be selectively shorted out of the composite circuit to selectively vary the overall frequency response characteristic.
Abstract: A broadband composite filter circuit is disclosed which includes a plurality of filter networks, each being tuned to respond to a respective frequency bandwidth of electrical signals. Each of the filter networks is a four terminal filter network having a positive and a negative network input terminal and a positive and a negative network output terminal. The input terminals of all of the filter networks are connected in series with each other in a first predetermined order. The output terminals of all of the filer networks are connected in a series circuit with each other in a second predetermined order which is the opposite to the above mentioned first predetermined order. The input signal is then applied across the series input circuits and the output signal is derived from across the series output circuits. A switch is provided across the input terminals of each of the filter networks to enable each network to be selectively shorted out of the composite circuit to selectively vary the overall frequency response characteristic of the composite filter circuit.

8 citations


Patent
10 Dec 1970
TL;DR: In this paper, a phase-locked tracking filter is described, in which the input and output voltages of a band-pass filter are compared as to phase and a control voltage produced to vary the characteristics of the filter to force the filtering to ''''track'''' and provide maximum noise rejection of a desired input frequency.
Abstract: A phase-locked tracking filter in which the input and output voltages of a band-pass filter are compared as to phase and a control voltage produced to vary the characteristics of the filter to force the filter to ''''track'''' and provide maximum noise rejection of a desired input frequency. The phase comparison and feedback means includes, in the preferred version of the invention, inverting and non-inverting Schmitt triggers, a monostable multivibrator and a flip-flop phase-sensitive detector to provide a square wave voltage whose mean DC value is related to the phase difference. This voltage is used to control and vary the characteristics of the band-pass filter.

Patent
04 Dec 1970
TL;DR: In this article, an adaptive switched filter arrangement consisting of two switched filters to each of which is applied the same input signal is proposed, which minimizes phase tracking time and cancels systematic phase error.
Abstract: An adaptive switched filter arrangement formed from two switched filters to each of which is applied the same input signal. The first switched filter is switched at an independent predetermined frequency. The second switched filter, however, is tuned by the output frequency extracted by the first filter. This minimizes phase tracking time and cancels systematic phase error.

Journal ArticleDOI
TL;DR: A narrow bandpass filter which is temperature controlled to maintain optical characteristic while operating in an ambient temperature range of -20 degrees C to +70 degrees C is described.
Abstract: This paper describes a narrow bandpass filter which is temperature controlled to maintain optical characteristics while operating in an ambient temperature range of −20°C to +70°C. Pertinent sources of bandpass shift and means for their control are discussed. The analytical approach, resultant filter assembly configuration, and performance test results of the assembly are presented.

Journal ArticleDOI
01 Feb 1970
TL;DR: In this article, an active realization for a low-pass maximally flat linear amplitude filter is presented, which displays a linear amplitude rise, band-limited differentiation, with increasing frequency out to a cutoff frequency at which point the response falls off at a rate determined by the order of the filter.
Abstract: An active realization for a low-pass maximally flat linear amplitude filter is presented. The filter displays a linear amplitude rise, band-limited differentiation, with increasing frequency out to a cutoff frequency at which point the response falls off at a rate determined by the order of the filter.

Patent
Clence L Burns1
26 Oct 1970
TL;DR: In this paper, a rectifying filter is disclosed in which the amplitude of the conducted line noise generated by the rectifying process is lower and the rectifier current has fewer harmonic components than known such filters and furthermore, the operation of the disclosed filter is not decreased in quality due to changes in the loading of the filter as greatly as in known filters.
Abstract: A rectifying filter is disclosed in which the amplitude of the conducted line noise generated by the rectifying process is lower and in which the rectifier current has fewer harmonic components than known such filters and in which furthermore, the operation of the disclosed filter is not decreased in quality due to changes in the loading of the filter as greatly as in known filters. This is accomplished at least in part by inserting filter elements into the rectifying bridge comprising a part of the rectifying filter.

Journal ArticleDOI
01 May 1970
TL;DR: In this paper, an active realization for a bandpass maximally flat, linear amplitude filter is presented, which displays a linear amplitude rise with an increasing frequency change about a center point out to cutoff frequenoies beyond which the response falls off at a rate determined by the order of the filter.
Abstract: An active realization for a bandpass maximally flat, linear amplitude filter is presented. The filter displays a linear amplitude rise with an increasing frequency change about a center point out to cutoff frequenoies beyond which the response falls off at a rate determined by the order of the filter.

Journal ArticleDOI
Toby Gilsig1
TL;DR: A simple three-phase filter connection that can significantly reduce losses for high-power applications without automatic tuning is presented and it is shown that the fundamental-frequency power losses can, for some cases, be limited to those associated with the filter inductors and capacitors.
Abstract: A simple three-phase filter connection that can significantly reduce losses for high-power applications without automatic tuning is presented. It is shown that the fundamental-frequency power losses can, for some cases, be limited to those associated with the filter inductors and capacitors. Perfornance equations for the filter at the fundamental frequency and at resonance are derived, and an example is given.

Journal ArticleDOI
TL;DR: In this paper, two forms of quasi-optical filters are discussed for use at millimeter-wave frequencies and possibly for far infrared frequencies, one form consists of metallic grids with intervening dielectric support material which forms a quasioptical filter analogous to the inductively coupled waveguide bandpass filter.
Abstract: Two forms of quasi-optical filters are discussed herein for use at millimeter-wave frequencies and possibly for far infrared frequencies. One form consists of metallic grids with intervening dielectric support material which forms a quasi-optical filter analogous to the inductively coupled waveguide bandpass filter. Because of dielectric losses, the relatively weak upper stopband, and the rapidly repeating passbands, this type of structure leaves much to be desired as a bandpass quasi-optical filter. However, when designed for wide bandwidth, it makes a very good pseudo-high-pass filter. For moderate- to wide-band bandpass applications, pseudo-high-pass filters of this type can be designed to match with a form of quasi-optical low-pass filter previously treated by the authors, in order to give a bandpass filter with strong, broad stopbands on both sides of the passband. Design principles, computed performance, and experimental results are presented for both pseudo-high-pass and bandpass structures.

Patent
13 Mar 1970
TL;DR: In this paper, a null-balance system with a twin-T input filter, a high-impedance amplifier, and an output circuit having a large time constant was proposed.
Abstract: A null-balance system having a twin-T input filter, a highimpedance amplifier, and an output circuit having a large time constant. A feedback circuit between the amplifier output and the common terminal of the twin-T filter in combination with an RC circuit connected to the common terminal enhances the frequency response characteristic of the filter signal for null-balance comparison with the input is not affected by the twin-T filter. Another feedback circuit between the output circuit and the common terminal of the twin-T filter provides compensation so that the null-balance feedback circuit between the output circuit and the input of the amplifier provides a signal for null-balance comparison with an unknown input signal.

Proceedings ArticleDOI
11 May 1970
TL;DR: In this paper, the authors present recent development in active filter designs with remarkably improved filter performance, and to discuss the application of active filter techniques to microwave frequency multiplexing, where one transistor can be coupled to each filter resonator to raise its Q. The ability to divide a frequency band into large manifold of adjacent channels is a useful aid in the accurate processing of broadbandwidth signals.
Abstract: In May 1968, a new active filter technique was reported to be suitable for UHF and microwave applications. A previously unexploited transistor mechanism, associated with the transit time properties of a transistor, is found to yield stable inductance with extremely high Q, or even negative Q; thus allowing a single transistor to be substituted for an inductor in conventional filter designs. Alternately, one transistor can be coupled to each filter resonator to raise its Q. As a result, microwave active filters can be made extremely small without insertion loss or selectivity degradation. For example, the volume per resonator of recent UHF filter designs is approximately 0.1 cubic inches. Subminiature active filters have been tested at frequencies ranging from low-VHF to S-band. Accomplishing a significant reduction in filter size makes possible a number of useful systems, such as lossless multiplexer with large numbers of contiguous filter channels. The ability to divide a frequency band into a large manifold of adjacent channels is a useful aid in the accurate processing of broad-bandwidth signals. The purpose of this paper is to present recent development in active filter designs with remarkably improved filter performance, and to discuss the application of active filter techniques to microwave frequency multiplexing.

Journal ArticleDOI
TL;DR: In this article, a method for measuring low-level time-truncated signals by using narrowbandwidth synchronous time-notch filters is described, which is intended for use with ordinary narrowband receivers or field intensity meters.
Abstract: A method is described for measuring low-level time-truncated signals by using narrow-bandwidth synchronous time-notch filters. These filter systems, intended for use with ordinary narrowband receivers or field intensity meters, provide a means of isolating time-truncated signals of interest from adjacent interfering signals. In addition, the important property of near optimum sensitivity (approaching that of a matched filter) is discussed, and the laboratory results of a low-frequency time-notch filter covering the 500-Hz to 2-MHz range are given.

Journal ArticleDOI
TL;DR: In this article, the authors derived a formula for the output signal-to-noise power ratio from a limiter-discriminator that is followed by an ideal (rectangular) bandpass filter.
Abstract: A formula is derived for the output signal-to-noise power ratio from a limiter-discriminator that is followed by an ideal (rectangular) bandpass filter. This signal-to-noise ratio is shown to be inversely proportional to the difference between the cube of the upper cutoff frequency and the cube of the lower cutoff frequency. The formula commonly utilized by designers for the discriminator output signal-to-noise ratio was derived for the case of a lowpass filter on the discriminator output. The bandpass and low-pass formulas are compared to indicate 1) the advantage of bandpass filtering for the discriminator output, and 2) the error incurred if the designer employs the low-pass formula to evaluate the performance of a bandpass filter design. Finally, the accuracy of a narrow-band approximation for the bandpass formula is evaluated.