Showing papers on "Band-stop filter published in 1983"

Polyphase quadrature filters--A new subband coding technique

Abstract: A new method of implementing filter banks for subband coding of speech is presented. First, Esteban's Quadrature Mirror Filter principle is extended to allow the direct synthesis of filter banks with any number of equal size filter bands. Then, by combining the quadrature filter characteristic with the polyphase network implementation of filter banks, a new filter bank structure is obtained which requires 35% fewer computations than existing designs. In this paper the theory of operation of the Polyphase Quadrature Filter is presented and techniques for its efficient implementation are described. Then, examples of filter banks using this approach are shown and compared with other designs, and a simulation of a 16 Kbits/s coder using these filters is presented.

Low-Pass Filters to Suppress Inertial and Tidal Frequencies

Abstract: A systematic way is given to design digital filters which allow clear separation of signals with periods of a few days from noise of higher frequency, particularly tidal and inertial. Several examples are given which pass little high-frequency power and none at the principal tidal frequencies. The Lanczos–cosine filter passes too much energy near diurnal frequencies; the Godin filter is better but not optimal. A longer filter is recommended, with flat low-frequency response, a sharp cut-off and very low noise. For current meter records containing inertial motions, it appears desirable to design a filter which specifically suppresses the local inertial frequency.

Two-dimensional root structures and convergence properties of the separable median filter

Abstract: The root (signals invariant to filtering) structures of the two-dimensional separable median filter are derived and presented. In addition, it is proved that with rare exception, after repetitive passes of the separable median filter any two-dimensional signal will be reduced to a signal containing only root structures.

Birefringent-fiber polarization coupler.

Abstract: Periodically stressing a birefringent fiber once per beat length can cause coherent coupling to occur between polarization modes. Such a birefringent-fiber polarization coupler is described here. More than 30 dB of power transfer between polarizations has been achieved. The device has been used as the output coupler of an in-line Mach-Zehnder interferometer, and better than 25-dB on/off extinction has been measured. The device is wavelength selective and can be used as a multiplexer or as a notch filter. A notch of 9-nm full width at half-maximum has been achieved with a 60-period comb structure.

Digital filter for an electronic musical instrument

Abstract: A digital filter imparting a desired tone color to the tone signal is realized by the combination of a digital pole filter and a digital zero filter capable of controlling a pole and a zero in an amplitude-frequency characteristic respectively. The amplitude-frequency characteristic of the digital filter is a composite of the respective characteristics of the pole filter and the zero filter. A "peak" portion and a "valley" portion in this composite characteristic can be set independently by the pole control of the pole filter and the zero control of the zero filter, whereby the desired tone color characteristic can be readily realized. Further, the digital filter may comprise a plurality of digital filters having respective different constructions and a connection switching circuit capable of setting arbitrarily connection between these filters. The filter characteristic as a whole can be diversely altered by changing the connection, whereby diverse tone color characteristics can be realized with ease.

Analog signal translating system with automatic frequency selective signal gain adjustment

Abstract: An automatic equalizer and oscillation suppressor system utilizing phase lock loop circuits to detect oscillation candidates at identified frequencies and a low cost microprocessor to process corrective band gain action. Oscillation candidates are initially suppressed by incremental adjustment of band gains to a maximum point after which notch filters are assigned to the oscillating frequency and the band gain returned to its normal equalized value. Automatic equalization is achieved initially with a pink noise source and on an on-going real time basis with program content by use of a frequency addressable narrow band boost circuit which is selectively inserted at frequencies across the bandwidth and band gains adjusted until some oscillation has occurred in all bands or maximum master gain has been reached.

Acoustic surface-wave bandpass filter

Abstract: An acoustic surface-wave bandpass filter includes a substrate made of a piezoelectric material. Acoustic surface waves travelling on a substrate surface provided with electrically conductive narrow stripes, slits or grooves undergo interference, wherein acoustic surface waves excited at frequency in VHF and UHF range are taken out as electric signals. The number of interleaved fingers constituting input transducers and output transducers of the filter is selected greater for the transducer located at the center than those disposed at both end portions. Leakage of acoustic surface-wave energy from the end transducers can be remarkably reduced, while the number of the transducers constituting the filter can be decreased. Significant reduction of loss of the filter is thus attained.

New Narrow-Band Dual-Mode Bandstop Waveguide Filters

Abstract: A complementary relation between a dual-mode bandpass and bandstop waveguide filter is found. Then a new idea for constructing a bandstop filter is developed. Two trial samples of bandstop filters are constructed to demonstrate the principle.

Segmented transversal filter

Abstract: A segmented digital transversal filter comprising a first transversal filter 4 that eliminates all frequency components from a signal sequence above half the subsampling frequency, a second transversal filter 11 that convolutes the output of the first filter with a decimated and energy compensated lower band of filter coefficients (HI 1 '), a third transversal filter 22 that convolutes the output of the first filter and a decimated and energy-compensated upper band of filter coefficients (HI 2 '), and a fourth transversal filter 32 that convolutes the original signal sequence and the central band of filter coefficients (HI 3 ). Delays 21 and 31 are added so that the outputs of the second, third and fourth filters arrive concurrently at an adder 51, the sum being the output of the invention.

Clock-controlled filtering arrangement

Abstract: A clock-controlled filtering arrangement for suppressing a number of interference frequencies related to a clock frequency, which comprises a time-discrete comb filter included in a negative feedback loop for a selective negative feedback of the said interference frequencies, which time-discrete comb filter is connected to an output of a clock generator for controlling the frequency location of the pass ranges of the comb filter. In order to avoid on the one hand the introduction of quantizing noise and the use of additional circuits, such as A/D and D/A converters, and on the other hand the occurrence of error cumulation whilst maintaining an adequate interference suppression, the time-discrete comb filter is of the switched capacitor N-path filter type.

Analysis and performance evaluation of an adaptive notch filter

Abstract: An adaptive notch filter is derived using a general prediction error framework. The proposed infinite impulse response filter has a special structure that guarantees the desired transfer characteristics. The filter coefficients are updated by a version of the recursive maximum likelihood algorithm.

Switched capacitor filter having a reduced capacitance

Abstract: In a switched capacitor filter of a first-order responsive to a filter input signal for producing a filter output signal by carrying out sampling operation at a predetermined sampling rate by the use of switching circuit, a capacitor, and an integrating circuit, a voltage divider produces a voltage divided signal in response to the filter input signal to reduce a total capacitance determined by capacitances of the capacitor and the integrating circuit. The voltage divided signal is sampled by the switching circuit to be sent to the integrating circuit at the sampling rate through the capacitor. The integrating circuit produces the filter output signal as a result of integration. In addition, an additional switched capacitor filter of a first-order is connected in cascade to the filter to form a switched capacitor filter of a second-order. The additional filter comprises an additional voltage divider for voltage dividing an output signal of the additional filter to deliver an additional voltage divided signal to the filter and the additional filter.

Microwave-frequency response of an optical-fibre delay-line filter

Abstract: The frequency response of a single-mode fibre recirculating delay-line filter has been measured from 0 to 18 GHz using a broadband measurement system that includes an inteferometric waveguide modulator and a high-speed photodetector. An optical-fibre notch filter having a fundamental passband at 740 MHz exhibited 23 overtones that were uniform to within ±1.5 dB over the entire measurement range.

Probability of Error Measurement for an Interference Resistant Transform Domain Processing Receiver

Abstract: In this paper, the results of implementing a transform domain processing spread spectrum receiver are presented. Measured probability of error results for single tone interference conditions are compared to analytical results, and the improvement in system performance achievable by using a notch filter to attenuate the narrowband interference is demonstrated. The theoretical and experimental results agree very well. Measured probability of error results are also presented for an adaptive system where the notch filter tracks the center frequency of the interferer.

Superconducting Delay Line for Stochastic Cooling Filters

Abstract: The stochastic cooling system of the antiproton source at Fermilab uses notch filters for reducing the feedback power at frequencies corresponding to particles in the core. At the same time these filters assist in shaping the gain vs. momentum in the stack tail. These filters, therefore, must attenuate all the harmonics of the revolution frequency (629 kHz) in the operating frequency band (1-2 GHz). They require components providing delays of 1.59 microseconds with a minimum of attenuation and undesirable distortion in this passband. Transmission lines providing such delays are typically 328 m long, have a rather large diameter, and are fabricated from a high conductivity material to keep the attenuation sufficiently low. The use of superconductors allows a dramatic reduction in the diameter, total size, and cost of this component in spite of the added cryogenic requirements. The authors measured the performance of two such cables in order to demonstrate the feasibility of the superconducting cable-notch filter concept. The first cable is an 84 m long superconducting coax consisting of a solid Niobium inner conductor inside a teflon dielectric, a lead outer conductor, and an outer jacket of mylar tape. The second cable is a 1.0 km long coaxial line more » with an inner conductor of lead-plated copper wire, a FEP teflon dielectric, and an outer conductor of leadplated copper tape wrapped with mylar. This paper discusses the results of performance testing of both cables and assesses their compatibilities with notch filters. « less

Miniature 90 MHz low-loss narrowband SAW filter using new resonant configuration

Abstract: A new low-loss narrowband SAW filter that uses one pair of electrically connected IDTs with an optimum number of fingers, as well as SAW reflectors, is described. A miniature filter with a loss as low as 2 dB and a bandwidth of 0.7% at 90 MHz is presented. The filter is mounted in a TO-8 package and is usable without any outer inductors.

Noise reduction circuit arrangement of solid-state video camera

Abstract: A noise reduction circuit arrangement for video signals under low brightness condition has a high-pass filter which detects the level of a video signal to switch the amount of passage of a high-frequency band component in accordance with a magnitude of the level. The video signal, produced from an image pickup element, is supplied to a low-pass filter and the high-pass filter. The high-frequency band component produced from the high-pass filter and changed in amplitude in accordance with the level of the video signal and a low-frequency band component produced from the low-pass filter are added at an adder so as to effect aperture correction in principle. The high-frequency band to be added is so controlled as to more decrease when the brightness of the video signal is low than when the brightness is not low.

Waveguide band stop filter

Abstract: PURPOSE:To form a waveguide band stop filter having the attenuation with >=2 frequencies and a reduced length in the axial direction of a rectangular waveguide, by connecting the resonators having different resonance frequencies to >=2 side faces of the waveguide at the approximately same positions in the axial direction of the waveguide CONSTITUTION:The resonators 2, 3 and 4 having the 1st resonance frequency f1 are connected to the coupling parts 5, 6 and 7 on the side faces of a waveguide 1 At the same time, the resonators 8, 9 and 10 having the 2nd resonance frequency f2 are connected to the coupling part 11, 12, and 13 respectively The resonators 2 and 8, 3 and 9 and 4 and 10 are located at approximately same positions in the axial direction of a waveguide on the faces opposite to each other No connection is given between the resonators 2-4 and 8-10 since they have different resonance frequencies from each other Thus the frequency characteristics having the attenuation with the frequencies f1 and f2 can be obtained

Control device of magnetic bearing

Abstract: PURPOSE:To increase the rigidity of a rotary shaft in a frequency equal to its natural vibrative frequency, by selectively increasing a phase advance or a phase advance gain of a transfer function obtained from the output of a position sensor which detects a position in a radial direction of the rotary shaft. CONSTITUTION:After phase compensating an output signal from a radial sensor 19, which detects a position in the radial direction of a rotary shaft, by a phase compensating circuit 21, the signal is transmitted by removing frequencies in a prescribed range containing the natural vibrative frequency (f) of the rotary shaft 14 through a band-stop filter 22. While an output of the sensor 19, after adding a transfer function of a band-pass filter 23 to the sensor output via a gain adjuster 24 in the first adder circuit 25 to be phase advanced by a phase advance circuit 26 and converted into a suitable gain-phase characteristic by a notch filter 27, is added to an output from the band-stop filter 22 in an adder circuit 28. Then the output, being amplified by a power amplifier circuit 29, controls a radial bearing 15.

Automatic interference cancelling apparatus

Abstract: An auto notch system which automatically "notch" filters up to four interference signals (interferers) in the band from 50 KHz to 150 KHz comprises a signal detector, an adjustable notch filter, a bandpass receiver and a digital controller, plus the software that runs in the digital controller. The signal detector circuit has an antenna, a preamplifier and a group of "fixed" filters. The adjustable notch filters are four circuits, each includes an active notch type filter stage with a DAC (digital to analog converter) in series with the input resistor to allow gain control and another DAC that controls the current through a diode that is optically coupled to a light dependent resistor pair. The light resistor pair is in the filter loop and as the resistance varies the frequency response of the filter changes. Thus the frequency response is controlled by varying the diode current. The bandpass receiver is used to sense and amplify the signal output of the Loran bandpass filter or the signal output of the notch filters under control of the controller. The bandpass receiver is tuned by the controller to one 128 specific frequencies in the range from 50 KHz to 150 KHz. The controller tunes the bandpass receiver, selects its input signal source and controls the gain and frequency characteristics of the notch filters. The software commands these hardware functions.

Optical Excision In The Frequency Plane

Abstract: This paper presents recent advancements in RF filtering techniques through the use ofacousto- optics and a special purpose array of wideband photodiodes. An electronicallyprogrammable filter may be synthesized by inserting this array of photodiodes into thefrequency plane of an optical spectrum analyzer. A description of the optical system, thephotodiode array and some experimental results are presented.IntroductionThe reception and recording of wideband signals in various types of noise environmentshas been studied and analyzed for many decades. The enhancement of signal -to -noise ratiosand improvement in the dynamic range for recording and communications purposes haveincorporated such notch filter techniques as programmable digital filters, tunable L -Cfilters, and even superconducting filters for the excision of narrowband interference fromthe received information to be processed.These electronic filter techniques are very effective in enhancing the signal -to -noiseratio of an RF signal. A source of error for these filters is the phase distortion whichoccurs at the bandstop -passband edges of the filter shape. These errors, although somewhatpredictable, will add up and may severely distort the received signals when multiplefilters are stacked in series.Performing these RF filter functions in the frequency plane of an optical spectrumanalyzer1 -4 has several advantages over the current electronic techniques. First, whensome object is placed in the frequency plane of the optical spectrum analyzer, the magnitudeof the affected frequency interval is attenuated and the phase remains constant. Also, theoptical spectrum analyzer offers a high degree of parallelism which is a function of thetime -bandwidth product associated with the acousto -optic cell chosen. Many filters may berealized simply by inserting more objects into the frequency plane. With the currenttechnology, time -bandwidth products of 1000 are feasible with bandwidths ranging from 10 to1000 MHz. This time -bandwidth product of 1000 implies 1000 resolvable frequency components.Optical configurationThe optical excisor evaluated is shown in Figure 1. This configuration is a Mach -Zehnder interferometers with an acousto -optic (AO) cell operating as a spectrum analyzerinserted in one path of the interferometer.

Improvements of Antijam Performance of Spread-Spectrum Systems

Abstract: The present paper gives theoretical analysis and simulation tests of a proposed external circuit connection for enhancing the performance of spread-spectrum (SS) systems in the presence of continuous wave (CW) interference. This connection is an adaptive notch filter. It consists of a hard limiter, a phase-locked-loop (PLL) tracking the CW interference yielding a first estimate, an adaptive two-quadrature weighted channel, and linear combiner producing a more accurate estimate of the CW interference. The simulation tests of this connection give, in general, performances superior to previous authors' results for certain ranges of signal-to-noise ratio.

High-pass filter of the first order and application thereof to telephony

Abstract: A sampled first order high pass filter having a configuration that eliminates the output offset voltage normally associated with known filters of this general type. It is constructed according to the diagram of the accompanying figure with two operational amplifiers, four capacitors and eight switches actuated at each period in two separate phases a and b. The filter is particularly useful in digital telephone transmission. The filter is placed just up-stream of an analog-digital converter sampled at the same frequency as the filter and the second amplifier serves as a comparator for conversion outside the phases a and b.

Linear phase IIR filter with equiripple stopband

Abstract: A simple technique of introducing transmission zeros into a low pass all-pole filter function to make its stopband transmission equiripple is described. The zeros are introduced through a transformation which maps the stopband of the filter onto the unit circle and the passband onto a segment of the real axis in the transformed plane. The technique is used to improve the loss characteristic of all-pole constant delay filters. Examples are included to illustrate the design procedure.

System for supression of underdamped oscillations in ac power drawn by synchronous motors driving Ward-Leonard generators

Abstract: A method and apparatus for reducing oscillations in input electrical power to a Ward-Leonard drive system which is subject to variations in mechanical loading, the technique utilizing a notch filter in the feedback path to the dc generator, the notch filter being turned to match the resonant frequency of the synchronous motor.

Mechanical bandpass filter design with lumped element prototypes

Abstract: A method is presented which provides means for the design of mechanical filters by the comparison of whole "pi" sections of the filter with the corresponding sections of a simple electric prototype filter. This replaces the well-known equivalences for each filter component and reduces the accumulation of eventual comparison errors. The results are the computation of broader passbands with more accuracy and more precise narrow-band filter design. This is achieved by first splitting the shunt arms of a mechanical filter ladder in two one-ports, providing a succession of symmetrical "pi" sections, formed by two half-resonators and a coupling element in between. The calculated chain matrices of these sections which are established including more or less mechanical phenomenons of the elements, compatible with the desired approximation and bandwidth. Second, a low-pass filter is synthesized with the imposed filter characteristics, using well-known insertion loss theory. This filter is put into a form which results in a succession of symmetrical "pi" sections as well. The elements of the chain matrices of the mechanical filter sections are compared with those of the transformed electrical prototype; the comparison of the matrix coefficients yield a frequency mapping function, applicable in the same way as in the design of electrical broadband filters. The degree of approximation for each bandwidth is immediately found by comparison of the plotted matrix coefficients. Extensional, torsional, and flexural vibrations are dealt with and some commonly used combinations are calculated with their basic matrices for demonstration purposes.

Filters for Stochastic Cooling of Longitudinal Beam Emittance

Abstract: The shorted stub filter (SSF) has been used extensively to provide the electronics gain shaping for stochastic cooling of longitudinal beam emittance. The repetitive notch of this filter results from the cancellation of the incident signal by the reflected signal at frequencies where the cable electrical length equals an integer number of half wavelengths. Variations in notch depth of the SSF have been approximately compensated by a rather complicated system. Dispersion of the notch frequency resulting from variation of the phase velocity can also be approximately corrected using tuned imperfections in the shorted cable. Dispersion due to imperfections in the coaxial cable can be quite significant and can only be compensated for by costly construction techniques. This paper describes another type of notch filter. Although this filter has been mentioned previously, this analysis demonstrates the advantages of this filter in providing small notch dispersion and other properties necessary for stochastic cooling systems. Because this filter uses only forward signals, it is quite insensitive to imperfections in cables and components, and can therefore be constructed from commercially available components.

Dual mode directionally coupled band reject filter apparatus

Abstract: A dual mode directionally coupled band reject filter apparatus having coaxially aligned first and second cylindrical cavity members which are asymmetrically mounted to the broadwall of a waveguide. Both cylindrical cavity members include a plurality of tuning screws to establish elliptic-type responses.

A new independently adjustable filter using the operational amplifier pole

Abstract: A new second-order lowpass active filter, based on the single pole roll-off characteristics of the operational amplifier, with only one operational amplitier and a single external capacitor is presented. Independent control of centre frequency, frequency selectivity and passband gain by a single resistor is possible with this design. The filter has low sensitivity to all circuit active and passive parameters and is suitable for low-medium-high Q factor operations over a wide range of frequencies. The filter is suitable for integration.