Showing papers on "Band-stop filter published in 1992"

Digital shaping filters for reducing machine vibration

Abstract: A digital shaping filter used to shape the input to digitally controlled flexible plants is derived from an input preshaping technique to reduce residual vibration in the plant output. Results from simulations show that these filters reduce plant residual vibration to zero. In addition, an arbitrary rate digital shaping filter is derived that allows the user to select any sampling rate for the digital system. The examination of these filters in the digital Z domain reveals them to be digital notch filters that are robust to vibration-mode parameter shifts. >

MRI compatible pulse oximetry system

Abstract: Magnetic resonance imaging hardware (A) defines a patient receiving region (20) that is surrounded by a bore liner (22). A socket (50) is mounted in the bore liner with an appropriate receptacle for receiving a standard plug (52) of a conventional pulse oximetry system. Conventional pulse oximetry systems include a sensor unit (54) connected with a cable (56) having the plug (52) at one end thereof. A notch filter (62) attenuates currents near the resonance frequency of the imager. A preamplifier (60) amplifies signals from the sensor unit. Within the shielding (66) of the preamplifier, a low pass filter (68) is provided to remove induced radio frequency components from the preamplified sensor unit signal. A radio frequency filter (70) mounted at the shield of the shielded room (B) prevents radio frequency signals from reaching an exterior processing and display unit (E) and prevents radio frequency signals from a clock (72) of the processing and display unit from being conveyed into the shielded room (B). The processing and display unit processes the signal received from the preamplifier to generate a pulse rate display (78) and a blood oxygen concentration display (80).

High-linearity continuous-time filter in 5-V VLSI CMOS

Abstract: High-linearity self-tuning continuous-time filters, fabricated in a standard 1.6- mu m 5-V CMOS process, are presented. Frequency control is achieved using switchable arrays of highly linear double-polysilicon capacitors in an active RC filter structure, resulting in tunable filters with very low signal distortion. One filter, a Tow-Thomas biquad, exhibits dynamic range and signal linearity of typically 91 dB. Another smaller implementation, a Sallen and Key filter, attains >or=76 dB. Cutoff frequency response is maintained to an accuracy of around +or-5%. >

Adaptive baseline wander removal in the ECG: Comparative analysis with cubic spline technique

Abstract: Baseline wandering is a classical problem in electrocardiogram (ECG) records that generally produces artifactual data when measuring ECG parameters. The authors present a cascade adaptive filter for removing the baseline wander and preserving the low-frequency components of the ECG. This cascade adaptive filter works in two stages. The first stage is an adaptive notch filter at zero frequency. The second stage is an adaptive impulse correlated filter that, using a QRS detector, estimates the ECG signal correlated with the QRS occurrence. In this way, all the signal components correlated with the QRS complex are preserved. The authors analyze the frequency response of the filter, showing that the filter can be seen as a comb filter without the DC lobe. The method was applied to ECG signals from the MIT-BIH database and its performance was compared with the cubic spline approach. The method can remove baseline wander in real time without needing to calculate the isoelectric levels, while preserving the low-frequency ECG clinical information. >

Least-mean squares adaptive digital filter havings variable size loop bandwidth

Abstract: An adaptive digital filter uses a weight adjustment unit for adjusting the weights of an adaptive digital filter according to one or more input signals to the digital filter and according to an error signal indicative of the difference between the actual and desired outputs of the digital filter. The weight adjustment unit has a first low-pass filter for low-pass filtering a signal indicative of the product of the error signal and the one or more input signals, a squarer for squaring the output of the first low-pass filter, a second low-pass filter for low-pass filtering the output of the squarer to extract the D.C. component thereof, a third low-pass filter for low-pass filtering a signal indicative of the output of the error signal squared to extract the D.C. component thereof, a dividing unit for dividing the output of the second low-pass filter by the output of the third low-pass filter to provide a loop bandwidth, and a weight calculation unit for providing values for one or more weights of the adaptive digital filter according to the previous values of the weights and the value of the loop bandwidth.

Digital multi-rate notch filter for sampled servo digital control system

Abstract: A digital servo control loop for a disk drive head position actuator implements a multi-rate notch filter in order to eliminate actuator resonances at frequencies above the sampling rate Nyquist frequency. The control loop includes circuitry responsive to the periodic digital position values sampled from embedded servo sectors which generates and puts out digital control values at the predetermined sampling rate for controlling the position of the actuator means. A digital multi-rate notch filter receives and filters the digital control values, and generates and puts out notch filtered digital control values to the actuator means at a rate comprising an integral multiple of the predetermined sampling rate.

A control theory approach to the stability and transient analysis of the filtered-x LMS adaptive notch filter

Abstract: A method is presented for analyzing the stability and transient response of the filtered-x LMS adaptive notch filter by formulating the problem in the complex weight domain and applying standard control theory. Examples are given for pure delay and second-order low-pass cancellation path transfer functions. The method is also extended to the multichannel case, where the eigenvalues of the equivalent open-loop transfer function matrix characterize the behavior. >

Adaptive filtering of ECG baseline wander

Abstract: Baseline wander removal is a classical problem in ECG signal processing. We present a cascade adaptive filter to remove the baseline wander in the ECG preserving the overlapped deterministic low frequency components of the ECG, such as ST segment components. This cascade adaptive filter works in two stages. The first stage is an adaptive notch filter at zero frequency. The second stage is an adaptive impulse correlated filter that estimates the ECG signal correlated with the QRS occurrence. In both stages the LMS algorithm is used with different gain constants μ 1 and μ 2 . We analyse the frequency response of the filter as a function of the μ 1 and μ 2 parameters, selecting those more appropriated for baseline removal. Finally, the performance of the filter is studied on an actual ECG affected by baseline drift.

Active power line conditioner with fundamental negative sequence compensation

Abstract: An improved active power line conditioner is disclosed. A series inverter is controlled by a series filter controller which performs synchronous transformations on a load current to generate a series filter feedforward signal corresponding to the fundamental components of the load current. The series filter controller also generates a series filter reference signal corresponding to a negative sequence fundamental output voltage. The series filter feedforward signal and the series filter reference signal are combined to form a series filter compensation signal. The series filter compensation signal is applied to the series inverter to generate sinusoidal input currents, with negative sequence fundamental output voltage compensation, for a non-linear load. A parallel inverter is controlled by a parallel filter controller which performs synchronous transformations to generate a parallel filter feedforward signal corresponding to the harmonic ripple components of the load current. The parallel filter controller also generates a parallel filter reference signal corresponding to a negative sequence fundamental source current. The parallel filter feedforward signal and the parallel filter reference signal are combined to form a parallel filter compensation signal. The parallel filter compensation signal is applied to the parallel inverter to generate sinusoidal voltages, with source current negative sequence fundamental compensation, for the non-linear load.

Adaptive filter using continuous cross-correlation

Abstract: Coefficients of an adaptive filter are updated continuously during the filter's normal operation. This is achieved by superimposing on the filter input signal a known noise signal. At the filter's output, a counterpart of this known noise signal is subtracted and the resultant signal is cross correlated with past samples of the noise signal. The filter coefficients are then updated in response to these correlations so as to minimize correlation of the resultant signal with the noise signal.

Pyramid processor integrated circuit

Abstract: An integrated circuit (IC) for implementing a variety of multiresolution filters in an image processor includes a programmable, symmetric, and separable two-dimensional filter (110). The input signal to the filter can be an input signal applied to the IC or a combination of two such signals. Circuitry in the IC may be programmed to imply pixel values around the edges of the two-dimensional image signals processed by the filter. The filter provides an output signal as well as each of the unfiltered signals from a tapped delay line of a filter that combines successive lines of the image. The IC also includes an arithmetic and logic unit in which the filtered output signal may be combined with an unfiltered input signal or one of the unfiltered tap signals.

Ceramic band-stop filter

Abstract: In order to provide a sufficient isolation between the resonators of a band-stop filter, prior art band-stop filters must be manufactured from separate ceramic resonator blocks. According to the invention the band-stop filter can be manufactured in a single ceramic block (1), having on one side surface strip-like areas (14; 15) of electrically conducting material extending perpendicularly from the bottom edge to the top edge and being located in the area between the resonators (A and B, B and C) and having dimensions selected so that they substantially cancel the electric and magnetic field between the resonators. If necessary, the coupling between the resonators can be adjusted by changing the width of the strip-like areas (14; 15) or by providing them with discontinuities.

Vortex flowmeter electronics

Abstract: A vortex flow transmitter (10) has a filtering circuit (20) receiving a noise contaminated input signal representative of the flow and which has a fundamental frequency varying responsively to flow. The filter (20) filters the input signal using one of a family of HP filter characteristics. Each member of the family of HP filters has varying corner frequencies, each filter having a unique switchup and a unique switchdown value assigned to it. Adaptive response means (40) select a current HP filter for use in the filter means. The adaptive means use one selection method when the flow is increasing and another selection method when the flow decreases. Output means (52) convert the signal from the filter means into a transmitter output, typically a 4-20 mA current or a frequency output representative of the flow.

Dielectric resonator filters with wide stopbands

Abstract: Dielectric resonators used in filter networks present a model spectrum with undesired, or spurious, resonances in close proximity to the desired one Through the use of evanescent mode bandpass irises tuned to the filter center frequency, the resonator spurious modes are suppressed, resulting in N-section filters with stopbands clean to at least (N-1) times the individual iris stopband levels The problem of achieving a wide stopband is reduced to the problems of realizing the resonating capacitance required in an evanescent bandpass filter and computing the junction susceptance occurring at the interface between a larger evanescent section (the resonator enclosure) and the smaller iris opening The technique results in high-Q resonator filters with stopbands clean to at least -55 dBc, out to at least 17 times the filter center frequency >

Quadrature mirror filter banks and method

Abstract: M-channel pseudo-quadrature-mirror-filter (QMF) banks using a prototype filter having a linear-phase spectral-factor of a 2Mth band filter. The overall transfer function of the analysis filter/synthesis filter system is a delay, and the aliasing cancellation has all the significant aliasing terms canceled. Consequently, the aliasing level at the output of the pseudo-QMF banks is comparable to the stopband attenuation of the prototype filter, with the error at the output of the analysis filter/synthesis filter system approximately equal to the aliasing error at the level of the stopband attenuation. The pseudo-QMF banks have the stopband attenuation of the analysis filters and thus synthesis filters of -100 dB. The resulting reconstruction error is also on the order of -100 dB. Optimization of the pseudo-QMF banks by a quadratic-constrained least-squares formulation converges very fast as both a cost function and constraints are quadratic functions with respect to unknown parameters, providing a much higher stopband attenuation compared to previous filter banks.

Combination surge and diplex filter for CATV distribution systems

Abstract: A combination surge and diplex filter is provided for a CATV distribution amplifier. In a first preferred implementation, an integrated surge and high pass filter section is provided when the CATV amplifier is used only in the forward direction. Provision is made for a plug-in low pass filter section which is matched to the high pass filter section. The plug-in low pass section is used to form a diplex filter if the reverse direction capability of the CATV system is required from the distribution amplifier. In a second preferred implementation, the integrated surge and high pass filter section is segmented into a surge filter segment which is designed as a divisible part of the high pass filter section. A plug-in module is then provided with a high pass filter segment having those components of the high pass filter section which were not necessary for surge protection and a low pass filter section matched to the high pass filter section. The plug-in module is utilized to form a diplex filter, if the reverse direction capability of the CATV system is required from the distribution amplifier.

Waveguide electroacoustical transducing

Abstract: A loudspeaker system for radiation into the passenger compartment of a vehicle has one or more elongated acoustic waveguides to efficiently transfer sound pressure energy from a loudspeaker driver outside the compartment into the compartment. Preferred embodiments feature two elongated acoustic waveguides separated by the loudspeaker driver mounted on a hard baffle panel. One waveguide has an effective length of one quarter wavelength at the lowest frequency desired to be reproduced by the loudspeaker driver, and the other waveguide has an effective length three times that of the first waveguide. One or both waveguides may be folded upon itself. The loudspeaker system is driven through circuitry providing reduced system response at frequencies that may cause the deflection of the loudspeaker to exceed its maximum limits. This circuitry includes a high pass filter for transmitting spectral components above the lowest frequency to be reproduced, and a notch filter centered at a frequency where the loudspeaker cone excursion characteristic is a maximum. Another circuit includes boosts the audio spectral components, reduced by the notch filter, into the passenger compartment through another loudspeaker system, comprising a ported enclosure having a port resonance at the notch frequency.

Method and apparatus for automatic tuning calibration of electronically tuned filters

Abstract: A method and apparatus for automatic tuning calibration of electronically tuned filters which comprises a programmable frequency generator for producing a calibration frequency signal, a filter for filtering the calibration frequency signal, a detector for producing a detector voltage, a processor for programming the frequency generator to specific test frequencies and for producing a stepped filter tuning voltage and storing the detector voltage in response to the stepped filter tuning voltage, and a converter for digital-to-analog conversion of the stepped filter tuning voltage. Calibration frequency signal versus tuning voltage responses are stored for a number of calibration iterations within the usable range of the filter and the resulting table can be used to determine the correct tuning voltage for the filter when operating at any frequency within the usable filter range.

Low aberration diffraction grating system

Abstract: A light analysis system is disclosed and comprises a source of substantially collimated light to be analyzed The source comprises a sample excited by a collimated laser light source, and further comprises a holographic notch filter having the characteristic of reflecting light at the excitation wavelenghth at which the source is excited An aberration corrected concave focusing diffraction grating receives the collimated light and focuses it at a point corresponding to its wavelength A detector detects light at a desired wavelength focused by the diffraction grating The holographic notch filter is positioned to filter the source of substantially collimated light to be filtered and the holographic notch filter is oriented substantially at an angle with respect to the collimated laser light source to result in a path length for the collimated laser light source which constrains a path length through the notch filter which causes the collimated laser light to be reflected by the filter away from the grating The grating is an aberration corrected concave focusing diffraction grating The collimated light is in the form of a bundle having a width on the order of ten millimeters

Filter utilizing a frequency selective non-conductive dielectric structure

Abstract: A filter utilizes a frequency selective, non-conductive, dielectric structure for filtering electromagnetic energy in the millimeter to far infrared frequency bands. The filter includes a non-conductive, high-dielectric, background material positioned to receive incident electromagnetic energy. A lattice structure comprised of a plurality of elongated elements formed of a non-conductive, high-dielectric material are disposed in a two-dimensional, periodic arrangement in the background material. The elements extend in parallel to one another through the background material for providing a range of frequencies over a band gap in which incident electromagnetic energy within the frequency range of the band gap is substantially prevented from propagating through the lattice structure. The dielectric structure can be adapted to operate as a band stop filter or a low pass filter.

On-chip self-tuning filter system

Abstract: An on-chip apparatus and method are provided for automatically tuning a continuous time filter in which a single filter selectively filters an information signal or, when tuning is desired, an unfiltered reference signal. During tuning, a controller determines the amplitudes of the unfiltered and filtered reference signals and their ratio. From the ratio, the controller ascertains a corresponding center or tuned frequency of the filter. If the ascertained frequency does not substantially equal a desired tuned frequency, the controller directs a bias controller to adjust the bias of the filter until the tuned frequency is substantially equal to the desired tuned frequency.

Combined UV/IR flame detection system

Abstract: A flame detector unit contains a silicon photodiode that is sensitive to UV light waves and two lead selenide photoresistors that are sensitive to IR light waves. The electromagnetic bandwidth of each sensor element is restricted by an optical wave filter to pass photons of certain wavelengths characteristic of hydrocarbon flames and to discriminate against photons of other wavelengths. Signals generated by the IR sensors are in the form of variations in electrical resistance of the sensor elements, which together with a resistor network comprise a bridge circuit which combines the two IR signals so as to discriminate against blackbody radiation sources and provide a signal which is fed through an amplifier. Amplified UV and IR signals are fed to a common analog to digital converter (ADC). Output from the ADC is fed to a digital processor through a notch filter, a cluster of weighted-moving-average filters, and into a threshold comparator/tester. Output from the comparator/tester is fed to a correlator, then through a series of alarm decision making circuits and finally into a series of alarm activation circuits. Stored wave forms relating to profiles of fire characteristics may be fed to the circuit correlator from an outside source. Data from predetermined external measurements may be fed to the alarm decision making circuits.

System and method of producing adaptive FIR digital filter with non-linear frequency resolution

Abstract: A filter and method of adapting a digital filter provides a single fixed finite impulse response (FIR) filter adaptively from measured data, in a manner whereby the filter's frequency and time resolution can be controlled. The resulting filter exhibits properties which allow it to be efficiently implemented in various multi-rate configurations. Specifically, the system and method produce an FIR filter with high resolution at low frequencies by having a large number of coefficients, but reduces resolution at higher frequencies by allowing only a fraction of the coefficients to adapt to the high frequency part of the signal. This is accomplished by using a multi-rate, segmented adaptation procedure, such that resolution and bandwidth are controlled independently at each state. If desired, the resulting filter can be made to approximate constant Q resolution. In addition, by adapting only a short part of the filter at a time, misadjustment is minimized.

Filter bank determination of discrete tone frequencies

Abstract: Specifically shaped filter responses enable power or amplitude measurements at the filter outputs to be simply transformed into accurate measurements of some desired function of the frequency (such as the frequency itself or log (frequency)) of any discrete tones within the filters' bandwidths. The invention can be used in conjunction with Fast Fourier Transform based filter banks. In cases where discrete tones are harmonically related, as in speech, the invention enables a simple determination of a weighted average of the harmonics' fundamental frequency, without having to first estimate the individual harmonics' frequencies.

Multi-passband dielectric filter construction having filter portions with dissimilarly-sized resonators

Abstract: A filter duplexer, such as a filter duplexer for a radio transceiver, of minimum dimensions is disclosed. A first filter portion of the duplexer filter includes resonators of a first geometric configuration, and a second filter circuit portion of the duplexer filter comprises resonators of a second geometric configuration. The geometric configuration of the two filter circuit portions are dissimilar such that relative characteristic admittances of the resonators of the respective filter circuit portions are dissimilar. Because the resonators of the two filter circuit portions are of dissimilar electrical characteristics, a desired frequency response of the duplexer filter may be obtained with similar resonator loading capacitances.

Tone reduction circuit for headsets

Abstract: A tone reduction circuit for headsets designed to attenuate high frequency signals while permitting low frequency signals to pass undistorted. Input signal is supplied to a low-pass filter, a high-pass filter and an automatic gain control circuit (AGC). Outputs from both filters are input to a comparator, with the comparator output connected to the gain control input of the AGC. The AGC is configured to attenuate only the higher frequency signals. Thus, the comparator output controls gain imparted to the output signal produced by the AGC. The comparator output signals no gain in the automatic gain control circuit when low-pass filter output is greater than high-pass filter output, but when the high-pass filter output is greater than the low-pass filter output the comparator controls the automatic gain generator to attenuate the higher frequency input signal in proportion to the difference between high-pass filter output and low-pass filter output. Attenuation is further enhanced by having a low-pass filter with a shifting break point which is responsive to the comparator output. The low-pass filter break point is shifted down as the comparator output increases in amplitude, thereby further attenuating the input signal.

Nulling system for constraining pulse jammer duty factors

Abstract: An adaptaive nulling antenna control system (24) which is effective in constraining pulse jammer duty factors. The system (24) accepts signals from a multibeam antenna (40) in a coded communication network (10). A band stop filter (50) removes the communication signal and analyzes the various antenna channels to form a nulling signal which is then combined with the original antenna signal to effectively null the jamming signal in those directional channels in which the jamming signal appears. The system (24) utilizes a successive over-relaxation type algorithm featuring scaling, eigenvalue shifting, and adaptive memory to give a fast attack time and slow release. The system (24) can be implemented in a pipeline architecture to further increase processing speed.

A unity power factor current-regulated SPWM rectifier with a notch feedback for stabilization and active filtering

Abstract: A stand-alone, unity power factor, current-regulated sinusoidal pulsewidth modulated (SPWM) rectifier is described. The topology is based on the series connection of three four-valve single-phase bridges, which allows the conventional two-stage logic SPWM strategy to be used without interphase interference. The problems of stability and low harmonic waveform distortion are identified. Solutions are found by using a simple local notch filter feedback circuit that fulfils the dual function of stabilizing and active filtering. From the clarification given by this more expensive but less constrained topology, the stage is set for the next step in incorporating the lessons learned to the more economical topology based on the six-valve, three phase parallel bridge, which requires a tristate logic for PWM control when operating in the current-source configuration. >

Intermediate frequency filter having a ceramic filter

Abstract: An intermediate frequency filter for an intermediate frequency used in the receiver section of a digital radio communications apparatus is composed of an amplitude-flat ceramic filter incorporating two ceramic resonators, a buffer means and a single tuning circuit having the center frequency thereof within the bandwidth of the amplitude-flat ceramic filter, all being connected in series with each other. The center frequency of the single tuning circuit and Q are adjusted to approximate the amplitude characteristic of the intermediate frequency filter to that of TBT filter (0.4≦parameter m≦1.0).