Showing papers on "Band-stop filter published in 1999"

A globally convergent frequency estimator

Abstract: Online estimation of the frequency of a sinusoidal signal is a classical problem in systems theory that has many practical applications. In this paper the authors provide a solution to the problem of ensuring a globally convergent estimation. More specifically, they propose a new adaptive notch filter whose dynamic equations exhibit the following remarkable features: 1) all signals are globally bounded and the estimated frequency is asymptotically correct for all initial conditions and all frequency values; 2) the authors obtain a simple tuning procedure for the estimator design parameters, which trades-off the adaptation tracking capabilities with noise sensitivity, ensuring (exponential) stability of the desired orbit; and 3) transient performance is considerably enhanced, even for small or large frequencies, as witnessed by extensive simulations. To reveal some of the stability-instability mechanisms of the existing algorithms and motivate our modifications the authors make appeal to a novel nonlinear (state-dependent) time scaling. The main advantage of working in the new time scale is that they remove the coupling between the parameter update law and the filter itself, decomposing the system into a feedback form where the required modifications to ensure stability become apparent. Even though they limit their attention here to the simplest case of a single constant frequency without noise the algorithm is able to track time-varying frequencies, preserve local stability in the presence of multiple sinusoids, and is robust with respect to noise.

Feedback cancellation improvements

Abstract: Feedback cancellation apparatus uses a cascade of two filters along with a short bulk delay. The first filter is adapted when the hearing aid is turned on in the ear. This filter adapts quickly using a white noise probe signal, and then the filter coefficients are frozen. The first filter models parts of the hearing-aid feedback path that are essentially constant over the course of the day. The second filter adapts while the hearing aid is in use and does not use a separate probe signal. This filter provides a rapid correction to the feedback path model when the hearing aid goes unstable, and more slowly tracks perturbations in the feedback path that occur in daily use. The delay shifts the filter response to make the most effective use of the limited number of filter coefficients.

Electromagnetic interference (emi) filter and process for providing electromagnetic compatibility of an electronic device while in the presence of an electromagnetic emitter operating at the same frequency

Abstract: A novel electromagnetic interference (EMI) filter is designed to attenuate one or more specific frequencies in order to provide electromagnetic compatibility of an electronic device while in the presence of an electromagnetic emitter operating at the same or similar frequencies. The EMI filter of the present invention combines an EMI low pass filter with one or more “notch” EMI filters tuned to the specific frequencies of interest. When combined in this fashion, the notch EMI filter can effectively attenuate the electromagnetic field of a powerful low frequency emitter which is outside the effective attenuation frequency range of the low pass filter, which is itself effective at filtering a broad range of higher frequencies. In a preferred embodiment, the notch EMI filter capacitive element is integrated in a co-planar relationship with a ceramic feedthrough filter capacitor assembly. This combined notch and low pass filter arrangement is particularly effective in an implantable medical device such as a cardiac pacemaker or implantable cardioverter defibrillator (ICD) against passage of external interference signals, such as those caused by both digital cellular phones and electronic article surveillance systems operating at low frequencies.

A broad-band tunable CMOS channel-select filter for a low-IF wireless receiver

Abstract: Researchers agree that the active filter for channel-selection limits the dynamic range in a fully integrated wireless receiver, which uses no external components. This paper describes a filter designed for a wideband wireless LAN receiver operating in the 2.4-2.48 GHz ISM band. The receiver converts the desired channel to a low IF to enable on-chip rejection of the image. The analog filter must pass up to a 10 MHz wide single-channel centered after downconversion to IF ranging from 5 to 10 MHz. The classic requirements on all RF IC's apply to this filter, namely how to achieve the desired frequency response with the highest linearity and lowest noise at a given current consumption. For a channel-select filter, linearity is specified as out-of-band 3rd order intercept (IP3), to limit the in-band intermodulation from large interferers lying in the filter stop band. This work addresses the problem in filter architecture and circuit implementation. The achieved dynamic range surpasses all other published filter designs, except those cases where gain is favorably interleaved with filtering.

System and method for an image rejecting single conversion tuner with phase error correction

Abstract: A system and method for a single conversion tuner which generally uses phase shifted in-phase and quadrature-phase signal paths as an image rejection circuit. Through the use of broadband input LNA and mixer circuits, substantially the entire input signal bandwidth may be processed in the tuner. The broadband input LNA may pass the signal through to the mixers, which may split the signal into in-phase and quadrature terms. Then the in-phase term may be shifted by plus 45 degrees and the quadrature may be shifted by minus 45 degrees. When the terms are subsequently summed together, the desired signal components add together, while the undesired image components subtract from each other. In this way the image signal is suppressed, thus generally eliminating the need for a notch filter. A phase error correction feedback loop may be implemented to compensate for errors between the separate circuit paths. The feedback loop may use a test signal to monitor the phase error between the in-phase and quadrature circuit paths, and may correct for the phase error by shifting the phase of the LO signal sent to one or both of the broadband mixers. The feedback loop thus generally corrects for any phase errors introduced by the image rejection circuitry. The test signal preferably comprises two test tones located slightly out of band from and on either side of the image channel.

Noise control system

Abstract: A noise control system includes: a control sound generator for generating a control sound; an error detector for detecting an error signal between the control sound and noise; a noise detector for detecting a noise source signal; an adaptive filter for outputting a control signal; and a coefficient updator for updating a coefficient of the adaptive filter. The coefficient updator includes at least a first digital filter, a first coefficient update calculator, a second digital filter, a phase inverter, a third digital filter, and a second coefficient update calculator. Alternatively, the coefficient updator includes at least a first digital filter, a second digital filter, a third digital filter, a coefficient update calculator, a phase inverter, a first adder, and a second adder. In either case, the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

Infrared touch panel with improved sunlight rejection

Abstract: Ambient light can saturate the light detectors of a touch screen and cause unreliable operation. To address this concern, one or more filters may be placed proximate the detectors. A first filter may be a spatial filter, such as a microlouvre filter. A microlouvre filter is arranged so that it passes light transmitted by the light detectors and rejects off-axis light. Another filter may be a narrow band optical filter, such as a dichroic notch filter. Such an optical filter passes light having wavelengths within a narrow band selected to correspond to the spectral characteristics of the light emitters, while it rejects light of other wavelengths. The spatial filter and the narrow band optical filter may be used separately or in combination.

A novel high-Q optical microwave processor using hybrid delay-line filters

Abstract: A new hybrid active-passive photonic signal processor, which achieves high-Q microwave bandpass filtering, is presented. It overcomes the problem of achieving very high-Q values, while still operating the active stage with a large gain margin. This enables a significant increase in Q to be obtained, higher filter frequencies, and robust operation. The general synthesis procedure for the hybrid filter is described. The filter response demonstrates very high-resolution microwave signal filtering with a measured Q of 801.

Procedure for reading the data stored in a transponder and a transponder system for the execution of the procedure

Abstract: For reading the data stored in a transponder by means of an interrogation device, the interrogation device at first receives the background noise for the purpose of detecting interference frequencies present in this background noise On the basis of the interference frequencies acquired, coefficients for an adaptive filter are computed by means of which this filter may be tuned in such a way as to suppress the interference frequencies The response signal from the transponder with the superimposed background noise is received by the interrogation device and routed through the adaptive filter which acts to suppress the interference frequencies The signal available at the output of the filter can then be demodulated for the purpose of reading the data stored The transponder system for the execution of the procedure comprises a digital signal processor which computes coefficients for an adaptive filter on the basis of the interference frequencies acquired, and tunes the filter in such a way that the interference frequencies within the RF response signal received from the transponder, carrying the superimposed background noise, are suppressed The output signal from the adaptive filter may then be used for further processing

Optimum interference excision in spread spectrum communications using open-loop adaptive filters

Abstract: A generalized approach for interference suppression in PN spread spectrum communications using open-loop adaptive excision filtering is introduced. The excision filter coefficients under this technique depend on the jammer power and its instantaneous frequency (IF) information, and both values can be gained in the time-frequency domain. The dependency of the excision filter characteristics on the interference power, which was absent in past contributions in this area, is of significant importance as it allows optimum tradeoff between interference removal and the amount of self-noise generated from the induced correlation across the PN chip sequence, due to filtering. This tradeoff is bounded by the two extreme cases of no self-noise, which implies preprocessing disabled, and full interference excision, which the case previously considered. In this paper, we derive the FIR excision filters that maximize the receiver signal-to-noise ratio for narrowband interference and discuss the generalization to nonstationary jamming environment.

Notch filter tuning for resonant frequency reduction in dual inertia systems

Abstract: This paper presents a technique to measure the resonant frequency of a dual inertia spring system using an FFT. The resonant frequency measurement and anti-resonant frequency calculation are utilized to tune an infinite impulse response notch filter to reduce the torsional oscillations in both the motor and load velocities. The simplicity and easy tuning of the filter makes it practical to implement in a DSP. The baseband performance of a resonant system would greatly improve.

Method and a device for maintaining the performance quality of a code-division multiple access system in the presence of narrow band interference

Abstract: A method and device which dynamically detects, tracks and filters interfering signals with sufficient speed (i.e. within one IS-95 CDMA data. frame period, or 20 ms) and fidelity to eliminate or greatly reduce the deleterious effects of narrow band interferer signals on a CDMA link. When inserted in an RF signal path an Adaptive Notch Filter (ANF) detects narrow band interferors above a threshold level within the CDMA signal. Detection is accomplished by continuous scanning of a preset excision band, e.g. a specified narrow band associated with an AMPS system. Detected interferors are then automatically acquired and suppressed. This is achieved by electronically placing a rejection notch at the frequency of the interferors. Multiple notch filters may be used to simultaneously suppress multiple interferors. In the absence of interferors a bypass mode is selected allowing the RF signal to bypass the notch. Upon detection of an interferer, a switch is made to a suppression mode where the interferor is steered through a first notch section and suppressed. Alternatively, an external control line may be used to select the bypass mode so that the signal is allowed to pass the notch section, regardless of interferer content.

System for detecting voice activity

Abstract: A system for detection of voice activity in a communications signal, employing a nonlinear two filter voice detection algorithm, in which one filter has a low time constant (the fast filter) and one filter has a high time constant (the slow filter). The slow filter serves to provide a noise floor estimate for the incoming signal, and the fast filter serves to more closely represent the total energy in the signal. The absolute value of incoming data is presented to both filters, and the difference in filter outputs is integrated over each of a series of successive frames, thereby giving an indication of the energy level above the noise floor in each frame of the incoming signal. Voice activity is detected if the measured energy level for a frame exceeds a specified threshold level. Silence (e.g., leaving only noise) is detected if the measured energy level for each of a specified number of successive frames does not exceed a specified threshold level. The system enables voice activity to be distinguished from common noise such as pops, clicks and low level cross-talk.

Balanced filter structure utilizing bulk acoustic wave resonators having different areas

Abstract: The invention relates to resonator structures of radio communication apparatus, especially bulk acoustic wave filter structures. According to the invention, a bulk acoustic filter structure is constructed with a lattice configuration, in which two of the filters have a different area than other two for creating very steep passband edges in the frequency response of the filter. Preferably, the filter structure further comprises a second lattice structure for increasing the stopband rejection ratio of the filter structure, and for allowing the use of a simple mechanical structure. The cascaded configuration allows the construction of the filter structure in such a way, that the electrodes of the input and output port are at the same layer, thereby removing the need to make vias in the piezoelectric layer, which results in considerable simplification of the manufacturing process. Preferably, an acoustical mirror structure is used as the acoustical isolation in order to further simplify the mechanical structure of the filter structure.

Narrow-band filter including sigma-delta modulator implemented in a programmable logic device

Abstract: A narrow-band bandpass filter is implemented in a field programmable gate array (FPGA). An analog-to-digital converter quantizes an input analog signal with a high degree of precision to produce input data samples. A sigma-delta modulator re-quantizes the samples with a substantially lower degree of precision. The re-quantized samples are passed through a bandpass, lowpass, or highpass, finite impulse response (FIR) filter which operates at the lower degree of precision. The reduced degree of precision enables a substantial reduction in the number of resources required to implement the narrow-band bandpass, lowpass, or highpass filter in the FPGA. The modulator includes a predictor filter which has a center frequency coinciding with that of the FIR filter, and redistributes noise such that it is lowest within the passband of the FIR filter. The narrow-band filter design can be adapted to incorporate a single or multi-rate decimator configuration.

Switched capacitor filter circuit having reduced offsets and providing offset compensation when used in a closed feedback loop

Abstract: A switched capacitor filter circuit having reduced offsets and providing offset compensation when used in a closed feedback loop includes a chopper stabilized amplified filter circuit which amplifies and low pass filters its input data signal to produce an output signal with an out of band signal frequency component which is at the chop signal frequency and represents an offset and 1/f noise of the chopper stabilized amplified filter circuit. An output switched capacitor filter circuit which is synchronized with the chopper stabilized amplified filter circuit filters this signal with a stopband filter frequency response that virtually eliminates such out of band signal frequency component. When used in a closed feedback loop, this filtered signal is used to generate an offset compensation signal that corresponds to the residual offset within the output signal resulting from the amplifying and filtering of the input data signal. This offset compensation signal is then added to the input data signal prior to its amplification and filtering by the chopper stabilized amplified filter circuit.

LTCC-MLC duplexer for DCS-1800

Abstract: A low-temperature cofired-ceramic (LTCC) multilayer-ceramic (MLC) duplexer is presented in this paper. The duplexer is designed for a DCS-1800 handset. It is constructed using a multilayer laminated bandpass filter and a multilayer laminated bandstop filter. These two filters are capable of easy tuning after duplexer manufacture. The computer-aided design flowchart is also presented. Additionally, the tuning method and loss improvements of the duplexer are discussed. Measured results show the performance of the LTCC-MLC duplexer is acceptable for DCS-1800 applications.

Characteristics of the Vold-Kalman order tracking filter

Abstract: In this paper the filter characteristics of the Vold-Kalman Order Tracking Filter are presented. Both frequency response as well as time response and their time-frequency relationship have been investigated. Some guidelines for optimum choice of filter parameters are presented. The Vold-Kalman filter allows for the high performance simultaneous tracking of orders in systems with multiple independent shafts. With this new filter and using multiple tacho references, waveforms, as well as amplitude and phase may be extracted without the beating interactions that are associated with conventional methods. The Vold-Kalman filter provides several filter shapes for optimum resolution and stopband suppression. Orders extracted as waveforms have no phase bias, and may hence be used for playback, synthesis and tailoring.

Loop-mirror filters based on saturable-gain or -absorber gratings

Abstract: We present a novel all-fiber narrow-band filter based on pump-induced saturable-gain or -absorber gratings in a loop mirror. Our design provides built-in interferometric phase alignment of the signal to the grating for optimal filtering. Notch or bandpass functionality is determined by the choice of gain or absorption and the input ports selected for the pump and signal. The loop-mirror filter has potential bandwidths from the submegahertz to beyond the gigahertz regimes, and one can tune it optically by changing the wavelength of the pump light that establishes the grating. Such filters have potential applications to wavelength-division-multiplexed optical networks and optical rf signal processing.

Microelectromechanical accelerometer with resonance-cancelling control circuit including an idle state

Abstract: A digital feedback control circuit is disclosed for use in an accelerometer (e.g. a microelectromechanical accelerometer). The digital feedback control circuit, which periodically re-centers a proof mass in response to a sensed acceleration, is based on a sigma-delta (ΣΔ) configuration that includes a notch filter (e.g. a digital switched-capacitor filter) for rejecting signals due to mechanical resonances of the proof mass and further includes a comparator (e.g. a three-level comparator). The comparator generates one of three possible feedback states, with two of the feedback states acting to re-center the proof mass when that is needed, and with a third feedback state being an “idle” state which does not act to move the proof mass when no re-centering is needed. Additionally, the digital feedback control system includes an auto-zero trim capability for calibration of the accelerometer for accurate sensing of acceleration. The digital feedback control circuit can be fabricated using complementary metal-oxide semiconductor (CMOS) technology, bi-CMOS technology or bipolar technology and used in single- and dual-proof-mass accelerometers.

Wideband electronically tunable microwave bandstop filters using iron film-gallium arsenide waveguide structure

Abstract: A wideband electronically tunable microwave bandstop (notch) filter has been realized using ultrathin iron film-gallium arsenide (FeGaAs) material structure. A tuning range as large as 8 to 27 GHz for the peak absorption carrier frequency of a propagating microwave has been accomplished.

Current-mode and voltage-mode universal biquads using a single current-feedback amplifier

Abstract: A new current-mode universal biquad and a new voltage-mode universal biquad using a single current-feedback amplifier are proposed in this paper. Both biquads enjoy the following advantages: realization of highpass, bandpass and lowpass filtering from each configuration, avoidance of input voltage tracking error in a current-feedback amplilfier; only one active component; no requirement for match components; low passive and active sensitivities. An inverting amplifier is used to form a notch filter. Experimental results are obtained to prove the theoretical analyses.

Method and apparatus for a tunable high-resolution spectral estimator

Abstract: A tunable high resolution spectral estimator (Fig 18) method and apparatus for encoding and decoding signals, signal analysis and synthesis, and for performing high resolution spectral estimation An encoder coupled with either or both of a signal synthesizer and a spectral analyzer is used to process a frame of a time-based input signal by passing it through a bank of lower order filters and estimating a plurality of lower order covariances from which a plurality of filter parameters may be determined The signal synthesizer includes a decoder for processing the covariances and a parameter transformer for determining filter parameters for an ARMA filter

An electric assist steering system having an improved motor current controller with notch filter

Abstract: A motor controller includes a summing circuit (186) a motor current command signal (ircmd) with a motor current feedback signal (is) and for providing an error current command signal (Δicmd) having a value functionally related to the difference between the motor current command signal and the motor current feedback signal. A notch filter (200) filters the error current command signal and provides a filtered current command signal. The notch filter (200) is adapted to notch out frequencies from the error current command signal about the resonant frequency of a motor (28). A drive circuit (120, 204) energizes the motor (28) in response to the filtered current command signal. A motor current sensor (97) for sensing motor current and providing the motor current feedback signal (is).

Digital adaptive filter and acoustic echo canceller using the same

Abstract: To achieve an improved convergence behaviour for, e.g., echo cancellation there is provided a digital adaptive filter comprising a filter coefficient update means (52; 78) to successively update filter coefficience in accordance with an input signal (x), an estimated power (PI) of the input signal, and an error signal between the input signal filtered in the digital adaptive filter and the input signal propagated along an external path (16) being modelled by the digital adaptive filter. Here, an input signal power estimation means (50, 84-92) is adapted to perform recursive smoothing for an increasing input power and a decreasing input power in an asymmetric fashion with different smoothing factors. In case the estimation is carried out in the frequency domain the step size for the update of filter coefficients may be adapted frequency band selectively.

User interface for the control of an audio spectrum filter processor

Abstract: A user interface control apparatus is disclosed for the control of electronic filter parameters of audio spectrum equalizers, crossovers, and other filter processors. The user interface apparatus comprises five pushbutton keys arranged in a specific cross-shaped pattern. This single arrangement of control keys provides a common user interface control apparatus which can be used to control one or more filter types. Depression of particular keys, or particular combinations of keys can be made to electronically control multiple filter parameters, some simultaneously, and for different filter types depending on the filter type for which the invention is applied. The unique arrangement of the invention's pushbutton keys facilitates an intuitive operation of the various parameters for bell, notch, shelf, and pass-band audio filter types with a minimal number of control elements and minimal control area. The filter parameters of a bell filter that can be controlled include center frequency, amplitude, and bandwidth. The filter parameters of a notch filter that can be controlled include center frequency and bandwidth. The filter parameters of a shelf filter that can be controlled include transition frequency, shelf amplitude, and transition slope. The filter parameters of a pass-band filter that can be controlled include corner frequency, pass-band amplitude, and filter slope. Additionally, the unique arrangement of keys facilitates intuitive control of some filter parameters at two rates of continuous change. Also, the user interface allows control of a graphic equalizer, where the selection of a particular bell filter, or “band”, can be scanned at two different rates. Finally, the user interface allows the control of the corner frequencies of two adjacent pass-band filters simultaneously, such as in a crossover processor, so as to preserve the combined response of the two filters over the overlapping region.

Perceptual weighting device and method for efficient coding of wideband signals

Abstract: A perceptual weighting device for producing a perceptually weighted signal in response to a wideband signal comprises a signal preemphasis filter, a synthesis filter claculator, and a perceptual weighting filter. The signal preemphasis filter enhances high frequency content of the wideband signal to thereby produce a preemphasised signal. The signal preemphasis filter has a transfer function of the form: P(z)=1 - νz-1 wherein ν is a preemphasis factor having a value located between 0 and 1. The synthesis filter calculator is responsive to the preemphasised signal for producing synthesis filter coefficients. Finally, the perceptual weighting filter processes the preemphasised signal in relation to the synthesis filter coefficients to produce the perceptually weighted signal. The perceptual weighting filter has a transfer function, with fixed denominator, of the form: W(z) A (z/η?1?) / (1-η2z?-1?) where 0∫η?2?∫η1 ≤1 and η2 and η1 are weighting control values, whereby weighting of the wideband signal in a format region is substantially decoupled from a spectral tilt of this wideband signal.

A wideband electronically tunable microwave notch filter in yttrium iron garnet–gallium arsenide material structure

Abstract: A wideband electronically tunable microwave notch (band-stop) filter has been constructed in an yttrium iron garnet (YIG)/gallium arsenide (GaAs) material structure An incident microwave propagating along the microstrip transmission line in the GaAs substrate is coupled into and to excite the magnetostatic surface waves in the YIG layer, which is laid upon the microstrip transmission line Maximum coupling and thus the peak absorption of the output microwave power occur at the ferromagnetic resonance frequency in the YIG film as determined by a bias magnetic field A tuning range as large as 25–230 GHz in the peak absorption frequency with the corresponding magnetic field tuning range of 290–7300 Oe has been accomplished Peak absorption of 15–38 dB in the microwave output power has also been measured

Forward-backward channel interpolator

Abstract: An interpolator (40) having a linear response has a first stage implemented with an IIR filter (42) to achieve the narrow transition bandwidth with relatively few filter coefficients. Zero-stuffing and filtering are used to achieve the interpolation. A forward-backward filtering methodology is then used to achieve a linear phase response for the IIR filter (42). The input sequence to be interpolated is zero stuffed and passed through the IIR filter (42) a first time. Then the time order of the resulting sequence is reversed and then passed through the IIR filter (42) a second time. After that, the resulting output sequence is reversed again. Guard blocks are added to both ends of the input sequence and then a block of zeros is appended to the zero-stuffed guarded input sequence. The appended zero block causes the startup and ending transient effect of the IIR filter's step response (42) to be equal at both ends, which tends to improve the accuracy of the interpolation. Subsequent zero-stuffing and filtering by the FIR filter (44) stages are used to further increase the interpolation. A linear interpolator may also be included after the FIR filter (44) stages.