Showing papers on "Band-stop filter published in 1993"

Auditory prosthesis, noise suppression apparatus and feedback suppression apparatus having focused adaptive filtering

Abstract: A noise and feedback suppression apparatus processes an audio input signal having both a desired component and an undesired component. When implemented so as to effect noise cancellation, the apparatus includes a first filter operatively coupled to the input signal. The first filter generates a focused reference signal by selectively passing an audio spectrum of the input signal which primarily contains the undesired component. The reference signal is supplied to an adaptive filter disposed to filter the input signal so as to provide an adaptive filter output signal. A combining network subtracts the adaptive filter output signal from the input signal to create an error signal. The noise suppression apparatus further includes a second filter for selectively passing to the adaptive filter an audio spectrum of the error signal substantially encompassing the spectrum of the undesired component of the input signal. This cancellation effectively removes the undesired component from the input signal without substantially affecting the desired component of the input signal. When the present apparatus is implemented so as to suppress feedback the adaptive filter output signal is employed to cancel a feedback component from the input signal.

Apparatus for NTSC signal interference cancellation through the use of digital recursive notch filters

Abstract: An NTSC interference canceler for eliminating NTSC signal interference from a HDTV signal uses recursive notch filters with adjustable center frequencies to isolate an NTSC signal's major components, i.e. the picture carrier signal, the chrominance subcarrier signal and the audio carrier signal. A single filter is used to isolate each NTSC interference signal component, with each particular filter's center frequency being adjusted to match the frequency of the particular NTSC interference signal component to be isolated by the filter. Each filter's gain may be either fixed or dynamically adjusted to match the amplitude of the NTSC interference signal component. Once isolated, these interference signal components are subtracted from the received television signal which includes both the NTSC interference signal and the HDTV signal. In this manner, the NTSC interference is removed from the HDTV signal.

On the adaptive lattice notch filter for the detection of sinusoids

Abstract: A lattice notch filter for the detection and enchancement of sinusoids in noise is presented, and the convergence properties of the algorithm are investigated using ODE (ordinary differential equation) analysis. It is shown that the frequency estimate of the algorithm for a single sinusoid is unbiased, regardless of the pole-zero contraction factor and the noise variance. An expression for the MSE (mean square error) of the frequency estimate and the output SNR of the algorithm is derived. Simulation results are presented to verify the theoretical analysis. Based on cascading the proposed second-order adaptive notch filter, three different approaches for the detection of multiple sinusoids are presented. The first approach uses a linear cascade structure, and the second and third approaches use a triangular cascade structure. The performance of the algorithms for multiple sinusoids is investigated, and computer simulation results are presented and discussed. >

Narrowband interference cancellation through the use of digital recursive notch filters

Abstract: A digital notch filter apparatus for removing narrowband interference signals from a wideband communication signal. The apparatus includes a recursive digital passband interference acquisition filter, an acquisition mode center frequency control circuit, a recursive digital passband interference tracking filter, a tracking mode center frequency control circuit and an interference detection circuit. The tracking filter has a narrower bandwidth than the acquisition filter. Both the acquisition and tracking filters are gang tuned so that the center frequencies of their passbands are adjusted in unison. During interference acquisition mode, the acquisition mode center frequency control circuit is used is to adjust the center frequency of the filters over the bandwidth covered by the interference canceler. When the interference detection circuit detects an interference signal within the passband of the tracking filter, the tracking center frequency control circuit is used to adjust the center frequency of the acquisition and tracking filters to insure that the filters remain locked onto the narrowband interference signal. Upon detection of the interference signal, the portion of the communication signal which includes the narrowband interference signal that is passed through the narrow passband tracking filter is subtracted from the communication signal to remove the narrowband interference signal. When no interference signal is detected, the communication signal is permitted to pass to the output of the notch filter circuit without attenuation.

Method and apparatus for NTSC signal interference cancellation using recursive digital notch filters

Abstract: A complex NTSC interference canceler for eliminating NTSC signal interference from in-phase and quadrature phase received television signals including both a desired HDTV signal and NTSC interference signal. The complex NTSC interference canceler uses a bank of complex recursive notch filters with adjustable center frequencies to isolate the NTSC signal's major components, i.e. the picture carrier signal, the chrominance subcarrier signal and the audio carrier signal. A single complex filter is used to isolate each NTSC interference signal component, with each particular filter's center frequency being adjusted to match the frequency of the particular NTSC interference signal component to be isolated by the filter. Each filter's gain may be either fixed or dynamically adjusted to match the amplitude of the NTSC interference signal component. Once isolated, the interference signal components are subtracted from the in-phase and quadrature phase received television signals.

Adaptive IIR notch filter based on least mean p-power error criterion

Abstract: A new second-order IIR adaptive notch filter (ANF) algorithm based on least-mean-p-power (LMP) error criterion is investigated. When the ANF is used to cancel 60-Hz interference in the recording of electrocardiograms (ECG), the performance of this adaptive algorithm with p=1 is better than that of the conventional least-mean-square (LMS, p=2) algorithm. Furthermore, when the ANF is applied to estimate the frequency of sinusoid embedded in white noise, this algorithm with p=3 has better statistical accuracy than the LMS algorithm. Simulation results are presented to demonstrate the effectiveness of the proposed ANF algorithm. >

Evaluation of digital filters for rejecting discrete spectral interference in on-site PD measurements

Abstract: A critical study of the performance of several digital filters for rejecting discrete spectral interference (DSI) in partial-discharge (PD) testing is reported. The filters are evaluated with particular reference to distortion introduced on successive PD pulses. A digital filtering method based on a cascaded second-order IIR lattice notch filter is proposed. The study shows that, for similar performance, methods based on linear prediction require longer filter orders when compared to cascaded IIR notch filters. The nonadaptive methods are found to be stable against impulsive disturbances, while adaptive methods are unstable. The method proposed gives the best performance, low distortion to a sequence of PD pulses, good stability, and fast filtering time. The performance at higher sampling rates, even with PD pulses of long widths, is also found to be superior. The method is implemented using fixed-point arithmetic leading to faster processing. Hence, the method is suitable for on-site PD measurements. >

Universal active filter

Abstract: A universal filter is provided with three inputs Vh, Vb and V1, with one output Vout, with two transconductance amplifiers Gm1, Gm2, with four capacitors mCO, (1-m)CO, CO and LCO and an amplifier K as well as a voltage follower VF. Depending on the connections of the three inputs, the universal filter takes the form of a high-pass or low-pass or band-pass filter or a trap filter or an all-pass or an otherwise active filter. Advantageously, by selection of parameters (e.g., trans-conductance, gain, scaling), the various filter characteristics like quality (Q), slope, median frequency, amplification, etc., may be adjusted. A further advantage is that the low component count of the filter provides improved reliability, reduced cost and facilitates efficient and economic fabrication in discrete or integrated circuit form.

Active vibration control system for attenuating engine generated vibrations in a vehicle

Abstract: An active vibration control (AVC) system is disclosed for attenuating vibrational frequency components generated by an engine and transferred through an engine mounting unit to vibrate a motor vehicle body. The motor vehicle is characterized by sprung mass and unsprung mass natural resonant frequencies at which the body also vibrates when the vehicle is driven over an undulating road surface. The AVC system operates by generating input signals representing different vibrational frequency components generated by the engine based upon sensed changes in engine rotation. Each input signal is filtered by an adaptive filter to produce a respective output signal. The output signals are summed to produce a canceling signal for driving an inertial mass shaker mounted on the body. The shaker inversely vibrates the body with respect to the different vibrational frequency components transferred to the body from the engine. A vibration sensor mounted to the body proximate the shaker monitors body vibration and develops a representative error signal. Vibrational components associated with the sprung and unsprung mass natural resonant frequencies are substantially removed from the error signal using a dual notch filter. The filtered error signal is then used to adjust the filtering characteristics of the adaptive filter to minimize vibration of the body caused by the different vibrational frequency components transferred to the body from the engine.

Universal active current filter with single input and three outputs using CCIIs

Abstract: A universal active filter with current gain and with single input and three outputs using second-generation current conveyors (CCIIs) is presented. The proposed circuit offers the following advantageous features: independent control of (ω0, Q and current gain through separate grounded resistors, use of only two grounded capacitors making it ideal for integration, and no requirements of critical matching condition/cancellation constraints in realising the lowpass, bandpass, highpass and notch filter responses.

Multiple-access noise rejection filter for a DS-CDMA system

Abstract: A direct-sequence multiple-access code division (DS-CDMA) communication system accommodates a multiplicity of separate transmitters (12) and at least one base-station receiver (14). Each transmitter generates a transmitted signal (16) at a common carrier frequency. Each transmitter has an assigned spreading code. Each bit time within the transmitted signal includes a unique signature waveform (21) generated from the spreading code that identifies the source of the transmitted signal. For a given transmitter, the transmitted signals from the other transmitters represent "multi-access noise" that may adversely degrade the signal-to-noise ratio (SNR) of that transmitter's signal at the receiver. Each transmitter operates using a spectrally inefficient power spectrum, i.e., a non-flat power spectrum, that simplifies the transmitter circuits. Each transmitter includes a clock source (26), a signature waveform generator (28), a data generator (30, 32), a first multiplier (42), a low pass filter (44), and RF generator (46), a second multiplier (48), a bandpass filter (50), a power amplifier (52) and a broadcast antenna (54). The receiver processes the received waveform signal on a bit-by-bit basis in the absence of knowledge of the other transmitters' spreading codes. An adaptive linear filter (66) included within the receiver (14) operates to make the SNR for the spectrally-inefficient transmitted signals approach asymptotically the SNR that would be received from a spectrally-efficient transmitted signal. Additionally, the receiver rejects narrowband interference, thereby providing superior performance over a spectrally-efficient system with no narrowband noise rejection.

Shaping of ultrashort optical pulses by using an integrated acousto-optic tunable filter.

Abstract: Reshaping of ultrashort optical pulses at 1.53 μm by using an integrated acousto-optic tunable filter is reported. Control of the optical pulse shape is accomplished by adjusting the different radio-frequency electrical signals driving the acousto-optic filter. This is to our knowledge the first demonstration of ultrashort pulse shaping using an integrated-optic device and establishes a new application area for integrated wavelength-division-multiplexed devices, namely, for manipulation of coherent, ultrafast time-domain signals.

Narrow-band MMIC filters with automatic tuning and Q-factor control

Abstract: Fully integrated, narrowband, tunable active filter monolithic microwave integrated circuits (MMICs) have been demonstrated at X-band. The three-section bandpass chip had a minimum insertion loss of less than 1.5 dB and a -3 dB bandwidth of 3% at 8.4 GHz. The notch filter chip exhibited a minimum -30 dB notch bandwidth of 20 MHz and a 2.7-GHz tuning range. A master-slave filter control circuit with fully integrated RF components was shown to track a reference signal over a frequency range greater than 2.5 GHz while maintaining the slaved filter notch depth at greater than 25 dB over that band. The same control circuit virtually eliminated the temperature dependence of the notch depth and provided a five-fold reduction in the notch frequency drift. >

Notch filters with cholesteric polarizers with birefringent film and linear polarizer

Abstract: An optical notch filter component in a color LCD display comprises an electronically controllable variable retarder interposed between circularly polarizing elements. Entering light in a particular spectral region is circularly polarized by a first of the circularly polarizing elements, and selectively retarded by zero or a half wavelength by the retarder so as to controllably yield right or left handed circular polarization. The second circular polarizer transmits only one of the circular polarizations of the light. By controlling the circular polarization of the light with the retarder, the light is either transmitted or attenuated. More uniform stopband attenuation is provided when the optical notch filter component comprises oppositely handed circular polarizing elements and a variable retarder which applies zero retardation in one of its states. A direct view display system substantially without parallax effects is formed from a stacked assembly of the notch filter components with thin substrate construction. Higher contrast is provided by doubly analyzing each color band.

Transversal filter for use in a digital subscriber line transmission interface

Abstract: A transversal filter has a transfer function for which a zero point occurs outside a unit circle on z plane and thus the output waveform has a ringing characteristic having a change from negative to positive around a precursor and before a main cursor and is associated and integrated with another transversal filter, thereby forming a waveform shaping decimation filter or a pulse shaping high-pass filter. The waveform decimation filter can eliminate a high frequency noise, changes a high frequency input data to a low frequency output data, and performs a waveform shaping operation. Therefore it cannot require a pulse shaping filter separated from the decimation filter. The pulse shaping high-pass filter includes a pulse shaping filter whose number of the taps is decreased and performs high-pass filter function. A pulse shaping filter whose number of the taps is decreased can be used separately from the high-pass filter.

Performance of a Holographic Supernotch Filter

Abstract: Results are presented of a comparative evaluation of a holographic sopernotch filter (HSNF) and a holographic notch filter (HNF) as a Rayleigh line rejection filter for Raman spectroscopy. The filter permits acquisition of both Stokes and anti-Stokes spectra down to ±200 cm−1 shift from excitation simultaneously, without filter angle adjustment. With slight angle adjustment, spectra can be recorded as close as 41 cm−1 from the excitation line. Performance of the HSNF is evaluated by measuring the low-frequency Raman spectra of Tb2(MoO4)3, water, and naphthalene.

Receiver having an adjustable matched filter

Abstract: A radio receiver's digital matched filter (52') is intended to match a pulse-shaping filter (23) in the transmitter whose signals it receives. However, the clock signal on which the matched filter's timing is based is generated by a receiver clock (58') that is independent of the transmitter clock (56) and that is subjected to no timing adjustment to bring the two clock signals into synchronism. So as to ensure that the matched and pulse-shaping filters work together as a Nyquist filter, therefore, a timing-recovery circuit (60') senses the timing offset in the matched filter's output, and a coefficient generator (80) adjusts the matched filter's coefficients in such a manner that the filter itself imposes the delay needed for the required timing relationship between the filters.

Saw notch filter for improving stop-band attenuation of a duplex filter

Abstract: When the bandwidth of a duplex filter having a certain band-width, intended for a radio telephone, is increased by affecting the coupling between the resonator circuits, the stop band of the filter is at the same time deteriorated. According to the invention, the stop-band attenuation can be improved by coupling a surface-wave filter, coupled as a notch circuit, in parallel with one of the resonator circuits of the duplex filter.

Multi-resonant electronic power converter with a wide dynamic range

Abstract: Methods and apparatus for variably converting a DC voltage to a different DC voltage level are effected by a multi-resonant electronic power converter with a wide output voltage dynamic range. The power conversion is accomplished by converting the DC voltage to an AC signal, adjusting or attenuating the AC signal to the desired amplitude, and then converting the AC signal back to a DC voltage. The output voltage may be adjusted by altering the frequency of the AC signal also known as the switching frequency. A wide dynamic range is achieved at a narrow switching frequency bandwidth by inserting either a fourth or higher order low pass filter or a notch filter at the output of the switching transistor. The high roll-off rate exhibited by either filter provides a relatively high dynamic range in a narrow frequency range.

Control method for a combined active filter system employing a current source converter and a high pass filter

Abstract: This paper describes a control method with a combined filter system which senses load current, source current and line voltage to create reference signals for an active filter. The transfer function of the active filter is identified and is used for the control system design. It is shown that the source current feedback is most effective to suppress the harmonic-enlarging effects due to parallel resonance and the harmonic current generated by source harmonic voltages. A small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results. >

Rigorous CAD of multiport coupled rectangular waveguide components

Abstract: Based on the simple mode-matching key-building block of the single double-plane step discontinuity, a general modal admittance formulation is presented for the rigorous CAD of longitudinal multi-channel or -aperture coupled rectangular waveguide structures of arbitrary size and location The theory involves an arbitrary number of rectangular coupling structures, different size and finite thickness of the coupling elements, as well as immediate higher-order mode interaction of all discontinuities The efficiency of the design method is demonstrated at two new filter examples: a metal insert Ku-band bandstop filter (12-18 GHz, WR-62) with an E-plane bypass waveguide structure, and a low-cost lowloss Ku-band four-aperture iris coupled bandpass filter The theory is verified by comparison with measured results

Device and method for tuning a band-pass filter utilizing mixing results with DC component removed

Abstract: A device and a method for adjusting a bandpass filter, especially a combiner filter. The method includes deriving an RF sample signal proportional to the power of a modulated RF signal which is one of: passing forward to the bandpass filter, reflected from the input of the bandpass filter and passed through the bandpass filter; down-converting the sample signal by another RF signal; detecting the signal strength of the mixing result; adjusting the center frequency of the passband of the bandpass filter on the basis of the detected signal strength. There is an essential frequency or modulation difference between the signals to be mixed, and so the mixing result is an AC signal of a lower frequency. No accurate adjustment of the phase relation of the signals to be mixed is required. Preferably, the frequency or phase difference between the signals to be mixed is accomplished by utilizing the phase modulation contained in the transmission when one of the signals is unmodulated. The DC component is filtered off the AC signal, which eliminates the measuring problems that otherwise would be caused by the DC offset properties of the mixer.

Variable rate digital filter

Abstract: A variable digital filter employs a variable rate sample clock with combinations of various digital filter elements such as an efficient implementation of decimation to achieve various filter realizations allowing a selectable output bandwidth. More specifically, a digital filter apparatus is coupled to receive input analog signals from a fixed anti-aliasing analog filter and optionally includes one or several stages of digital decimation filters, a low-pass filter, an optional equalizer, and an optional high-pass filter each of which may be programmed so as to configure the device with a variety of transfer characteristics. The filter device employs an input sample clock in the range of F-K*F, where, in a specific embodiment K is selected to be 2. The selectable combination of elements and stages used to form the filter needed is operative at a broad range of sample rates over a predetermined bandwidth range without loss of resolution. An extremely simple digital filter with a bandwidth of 1/4 the input sample rate is also shown.

A multitone pseudocascade, filtered-X LMS adaptive notch filter

Abstract: A filtered-X version of the LMS notch filter (FXLMS) is useful for narrowband applications where the cancelling signal cannot be directly applied to the primary signal. However, cancellation path delay limits the bandwidth performance of the filter. A cascade of FXLMS notch filters using multiple reference tones is examined for alleviating this problem. An analysis of a single-stage notch filter characterizes the response by the cancellation bandwidth and out-of-band overshoot. The results are used to synthesize a multistage cascade with offset reference tones. A pseudocascade configuration that only requires one entry point to the primary disturbance plant is also formulated. Numerical results for a three-stage FXLMS notch filter are given. Results are also presented for the cascade transient response, overshoot compensation, and extension to the multichannel case. >

Passive harmonic filter system for variable frequency drives

Abstract: A Variable Frequency Drive Power Center incorporating a new passive Harmonic Filter in an improved housing structure for Variable Frequency Drives (VFDs). The new harmonic filter improves the overall system performance by drastically reducing the line side current harmonics generated by all VFDs. The harmonic filter includes a series inductance, a parallel capacitance, and a buck transformer. The filter provides a low impedance path for the harmonic currents generated by VFD and therefore prevents them from flowing into the input ac power lines. The filter also improves the input power factor of the VFD system because of its increased inductive reactance under full-load conditions. Although the filter causes an overvoltage across the VFD terminals because of its increased capacitive reactance at the fundamental frequency this problem is overcome by using the buck transformer. The power center includes a separate section for the harmonic filter and a set of vertically-disposed compartments for mounting a plurality of VFDs on sliding assemblies. This provides a more efficient use of space and ease of maintenance, service and inspection of each individual unit.

Amplitude detection and automatic gain control of a sparsely sampled sinusoid by adjustment of a notch filter

Abstract: An accurate estimate of the amplitude of a sparsely sampled sinusoidal signal is obtained by filtering the squares of the sampled values of the sinusoidal signal with an adjustable notch filter in order to remove a double-frequency component at twice the frequency of the sinusoidal signal. This amplitude estimate, for example, is used for automatic gain control of the amplitude of the sinusoidal signal. Preferably, the notch filter is a digital filter for computing an output signal (v) from successive samples (xn, xn-1, xn-2) of an input signal (x) according to: vn =xn -βxn-1 +xn-2. The frequency control parameter (β) is computed, so as to automatically track the frequency of the sinusoidal signal, by integrating a product of a derivative (xn-1 -xn-2) of the input signal (x) and a derivative (vn -vn-1) of the filtered signal (v).

Optical filter, method of controlling transmission wavelength thereof, and optical receiver using the method

Abstract: An optical filter selectively receives a signal of a desired optical frequency from a plurality of optical-frequency-division multiplexing signals. Additionally, a transmission wavelength of the optical filter can be controlled using an optical receiver which includes the optical filter. The optical filter can perform a narrow-band optical filtering and permit, in optical communication systems using the optical filter, the transmission wavelength range of the optical filter to follow up a change in the wavelength of a light source. The optical filter selectively receives a signal of a desired optical frequency from a plurality of optical frequency-multiplexed signals. Additionally, the optical filter includes a first optical filter having a transmission band characteristic with a single peak in a desired band and a half band width of a desired amount of attenuation in the transmission band equal to or smaller than about two times a channel interval of the multiplexed light signals. A second optical filter, also in the optical filter, has a periodic transmission characteristic, an odd multiplication of a half of a free spectral range of the periodic transmission characteristic being equivalent to the channel interval of the multiplexed signals. The transmission band of the first optical filter matches with a transmission peak of the second optical filter.

Control system having signal tracking window filters

Abstract: A control system having a source of control signals and a multi-window electrical signal tracking filter. The signal tracking filter includes an operational amplifier operating in the non-inverting mode as a high impedance load, with a plurality of input stages cascaded at the input to the operational amplifier, each input stage having both a frequency determining filter portion and an amplitude determining threshold detecting portion. Each input stage defines a "window" of operation, such that the portion of a control signal or the like inputted to the filter which falls within the "window" will be filtered or attenuated thereby, while the portion of the control signal which falls outside of the "window" will pass unaffected through the filter. Cascading of the input stages allows one to customize the portions of the signal to be filtered for any particular application.

Hybrid notch filter

Abstract: A hybrid notch filter comprises an impedance inverter network connected across a two port filter network. In its simplest form, the impedance inverter network comprises impedance inverters of substantially ∑2 characteristic admittance connected between the input and output ports across which the two port filter network is connected, and impedance inverters of substantially unity characteristic admittance interconnecting the ∑2 characteristic admittance impedance inverters at their respective ends. The two port filter network may be a plurality of serially connected resonators and is connected across the output ports of the impedance inverter network. The hybrid notch filter may be formed into a switched hybrid notch filter by providing a switch between an adjacent pair of resonators in the filter network.

Multi-cavity dielectric filter

Abstract: A multi-cavity dielectric filter 30 having a single housing 32 for a plurality of resonant cavities 65. The dielectric filter 30 has a plurality of dielectric resonators 42 placed inside housing 32, instead of in individual housings, wherein the resonators 42 are spaced a quarter wave apart and are electrically isolated from one another by conductive isolation plates 44 positioned therebetween. The isolation plates 44 do not make continuous mechanical contact with the interior conducting surface of housing 32, but rather are spaced from the inner surface 77 of housing 32, thereby making assembly of the filter much simpler than if a solid RF connection had to be made. The resonators 42 are positioned inside the housing 32 between the isolation plates 44 and are supported by low loss, low dielectric constant spacers 46. End walls 59 complete the cavity formation at the termination ends 79 of housing 32. For a band reject filter, the cavities are joined by coupling loops connected to a transmission line while for a bandpass filter, apertures are placed in the isolation plates (44') so as to couple electromagnetic energy between adjacent cavities (65).