Showing papers on "Band-stop filter published in 1991"

An improved lattice-based adaptive IIR notch filter

Abstract: A novel lattice-based adaptive infinite impulse response (IIR) notch filter is developed which features independent tuning of the notch frequency and attenuation bandwidth. The internal structure is based on planar rotators, ensuring reliable numerical behaviour and high processing rates in CORDIC environments. A simple update law allows a simpler implementation than previously proposed designs. Rather than minimizing an output error cost function, the algorithm is designed to achieve a stable associated differential equation, resulting in a globally convergent unbiased frequency estimator in the single sinusoid case, independent of the notch filter bandwidth. Using a second-order structure in the multiple sinusoid case, unbiased estimation of one of the input frequencies is achieved by thinning the notch bandwidth. The tracking behavior is superior to conventional output error designs, and the estimation of extremal frequencies is less prone to overflow instability than previously reported structures. >

A modified parallel-coupled filter structure that improves the upper stopband rejection and response symmetry

Abstract: A modified parallel-coupled microstrip line filter structure is presented. Using this new structure improves the filter upper stopband rejection by at least 15 dB, and the filter response symmetry is also improved. Compared with the traditional parallel-coupled filter, the modified filter used less space and is easy to lay out owing to its inline structure. Several examples show the performance improvement of the filters fabricated in both low-dielectric-constant (2.55) and high-dielectric-constant (10.2) substrates. >

An adaptive analog continuous-time CMOS biquadratic filter

Abstract: An adaptive analog continuous-time biquadratic filter is realized in a 2- mu m digital CMOS process for operation at 300 kHz. The biquad implements the notch, bandpass and low-pass transfer functions. The only parameter adapted is the resonant frequency of the biquad, which is identical to the notch frequency and the bandpass center frequency. The update method is based on a least-means-square algorithm which adapts the notch frequency to minimize the power at the notch filter output. The actual update is modified to reduce the circuit complexity to one biquad and one correlator. When the filter is tracking a sinusoid, this update generates a ripple-free gradient that decreases tracking error. Applications include phase-frequency detectors, FM demodulators (linear and frequency shift keying), clock extractors, and frequency acquisition aids for phase-locked loops and Costas loops. Measured results from experimental prototypes are presented. Nonidealities of an all-analog implementation are discussed, along with suggestions to improve performance. >

Holographic Notch Filter for Low-Wavenumber Stokes and Anti-Stokes Raman Spectroscopy

Abstract: A holographic notch filter with a 15-nm rejection band is used as a Rayleigh line filter for Raman spectroscopy with a single-stage grating spectrograph. The filter is shown to allow acquisition of Stokes and anti-Stokes spectra as close as 72 cm−1 from the exciting line.

Shifting the frequency response of switched-capacitor filters by nonuniform sampling

Abstract: A clock with nonuniformly spaced sampling times can be used to shift the frequency response of switched-capacitor filters. By using such a clock, which deviates only slightly from a uniform sampling clock, small shifts in the frequency response of a switched-capacitor filter can be realized. The nonuniform sampling generates undesired modulation sidebands which are small if the deviation from uniform sampling is small. Computer simulations and measured data are presented to support equations that predict the frequency response shift and the amplitude of the undesired sidebands. This technique can be used to correct frequency response errors in monolithic switched-capacitor filters caused by capacitor ratio inaccuracies. It may also be useful in applications such as spectrum analyzers and tone generators. >

Notch filter noise rejection system in a cardiac control device

Abstract: A physiological event signal sensing system in a cardiac control or monitoring device for detecting spontaneous cardiac electrical events which may be obscured by continuous or burst EMI line frequency noise. The noise rejecting sensing system of this invention senses and samples cardiac signals which may include a noise component which is produced by power line interference in addition to a physiological signal component. The sampling frequency is selected to be an integer multiple of at least one common power line frequency. The system notch filters the cardiac signal to remove line frequency components, using either or both lowpass and highpass notch filtering coefficients, then limits the filtered output to the amplitude of the corresponding filter input to remove filter output signals caused by the sudden termination of line frequency noise which is characteristic of burst noise.

Closed-loop feedback control system having an adaptive filter

Abstract: A closed-loop feedback control system is disclosed for controlling an operation of a load (4). An actual operation signal is subtracted from a reference operation signal to produce a resultant signal which is used to control the operation of the load (4). A filter unit, such as a notch filter, operates to suppress any machine resonance frequencies found in the operation signal due to load fluctuations, machine variations, operating environment changes, deterioration with age, etc. A filter coefficient of the filter unit is adjusted so that any fluctuation in the resonance frequency can be suppressed effectively.

A high-speed continuous-time bandpass VHF filter in MOS technology

Abstract: A very high frequency (VHF) second order bandpass filter has been developed. The filter is based on a minimal transistor-only all-MOS high-frequency generalized impedance converter (GIC) that simulates a passive RLC ladder. The filter poles are obtained using the internal lumped capacitances of the MOS transistor. Using this structure a very high frequency filter is obtained consuming a small chip area. The center frequency is controlled by an external bias current to the circuit. Using the GIC, a bandpass filter can be implemented in MOS technology with center frequencies in excess of 50 MHz. The filter is simulated for center frequencies of 47 MHz, 54 MHz and 63 MHz. >

Receiver and adaptive digital notch filter

Abstract: Adaptive IIR digital notch filters useful with RF receivers for reducing interference. One or more notch filters automatically tune, to an interferer frequency, via adapting of coefficients in the z-transform. Each notch tunes independently of any other.

Low precision finite impulse response filter for digital interpolation

Abstract: A low precision Finite Impulse Response filter (FIR) is provided for filtering in a digital interpolation operation. The interpolation operation includes two steps, a sampling rate conversion operation for interspersing zeroes between samples in an input sequence and a filtering step of filtering out images that result from this operation. The filtering operation utilizes a FIR filter that utilizes low precision filter coefficients that are selected to tune the frequency response such that the low end frequency response including the pass band, the transition band, and the portion of the stop band immediately after the transition band provides a response equivalent to that commensurate with substantially higher precision FIR filter coefficients, with the high frequency end of the stop band gradually increasing. A second, low pass filter section is provided for filtering out the image energy that exists at the output of the FIR filter in the high frequency end of the stop band to provide an overall filter response that is commensurate to that utilizing substantially higher precision FIR coefficients in the filter section. The FIR filter coefficients utilized are restricted to the set of [-1, 0, +1] such that a multiplierless FIR filter can be realized. The FIR filter coefficients are obtained by processing the infinite FIR filter coefficients through a software delta-sigma quantizer which quantizes the output to the desired low precision FIR filter coefficients.

Current mode allpass/notch and bandpass filter using single CCII

Abstract: A current mode second-order allpass notch and bandpass filter using a single CCII, two grounded capacitors and four resistors is proposed. The allpass and notch output current signals, taken out through port z of a CCII and having high output impedance, can be obtained by tuning a resistor in the proposed network. The resonance angular frequency and quality factor of the new network have the advantages of low passive sensitivities and are insensitive to the current tracking error of the nonideal CCII.

An adaptive analog continuous-time CMOS biquadratic filter

Abstract: An adaptive analog continuous-time biquadratic filter is realized in a 2- mu m digital CMOS process for operation at 300 kHz. The biquad implements the notch, bandpass, and lowpass transfer functions. The update method is based on a LMS algorithm which adapts the notch frequency to minimize the power at the notch filter output. Applications include FM demodulators (linear and frequency shift keying), clock extractors, and frequency acquisition aids for phase-locked loops and Costas loops. Measured results from experimental prototypes are presented. >

Radio transceiver with duplex and notch filter

Abstract: A transceiver for a cellular telephone, particularly a portable telephone, comprises a transmitter and a receiver coupled to a common antenna by an antenna duplex filter The duplex filter comprises two passband filters connected respectively to the transmitter and the receiver The receiver comprises a first amplifier A notch filter tuned to the transmit frequency is connected to the output of the amplifier The notch filter enables the filtering performance of the receive filter to be relaxed, and the location of the notch filter(s) at the output of amplifier means that the insertion loss is less critical The requirement for lower filtering performance enables the duplex filter to be smaller and less costly

Filter and method for filtering baseline wander

Abstract: A linear phase high pass filter having a linear phase low pass filter in parallel with an electronic delay means is disclosed to remove baseline wander from an ECG signal. The linear phase low pass filter is preferably a digital Infinite Impulse Response (IIR) filter. An input ECG signal is simultaneously presented to an IIR low pass filter and an electronic delay. The low pass filter passes the low frequency baseline signal while blocking the ECG signal comprised of higher frequency components than the cutoff frequency of the low pass filter. Thereafter, the outputs from the IIR low pass filter and delay are passed to a summer that subtracts the output of the low pass filter from the output of the delay to produce the output of the filter. The combination of the output of a low pass filter being subtracted from a delayed input signal produces a high pass filter. The resulting high pass filter has a -0.3 dB cutoff frequency of about 0.5 Hertz while providing a virtually constant group delay for the ECG signal passed through the filter.

Phonetic equalizer system

Abstract: An audio equalizer system includes a filter having a passband extending substantially continuously across the audio spectrum, with the filter having an input terminal and an output terminal. An input network is adapted to apply an input audio signal to the input terminal of the filter, and an output network is adapted to provide an output audio signal representative of the signal at the output terminal of the filter. The group delay of the filter varies continuously with frequency across the audio spectrum, with that group delay being relatively high but less than approximately 10 milliseconds at frequencies less than approximately 200 Hz and being relatively low but greater than or equal to zero at frequencies greater than approximately 8000 Hz. When configured as a hearing assistance system, an input audio transducer, or microphone, generates the audio input signal from an incident acoustic wave, and an output audio transducer, or speaker, produces an output acoustic wave from the output audio signal.

Amplitude correction of field coupled varactor tuned filters

Abstract: In a multi-stage, varactor-tuned bandpass filter utilizing electromagnetic field coupling between successive filter stages, the effective area of a coupling window provided in the RF shielding separating the filter stages is varied as a function of the varactor tune voltage to provide a flat frequency response over the filter frequency range. The bias current through a PIN diode connected across the coupling window is controlled by varactor tune voltage to effectively decrease the window area with increasing filter frequency.

Communication system for passenger vehicle

Abstract: The invention enhances the ability of rear seat passengers in a vehicle to hear the speech of a front seat occupant. Two spaced microphones in the front seat area pick up speech signals which are differentially amplified and filtered in a bandpass filter and at least one notch filter. The filter signals are reproduced through speakers in the area of the rear seat. Differential amplification of the microphone signals results in greatly reduced acoustic feedback from the speakers to the microphones. The communication system of the invention is highly integrated into other communication and audio systems in the vehicle.

A multi-tone pseudo-cascade filtered-x LMS adaptive notch filter

Abstract: Cancellation path delay limits the bandwidth performance of the FXLMS (filtered-x least-mean-square) notch filter. A cascade of FXLMS notch filters using multiple reference tones is examined in order to alleviate this problem. An analysis of a single-stage notch filter characterizes the response by the cancellation bandwidth and out-of-band overshoot, which are analytically expressed in terms of the loop gain and cancellation path delay. These results are then used to synthesize a multistage cascade with offset reference tones. A pseudocascade configuration is also formulated that only requires one entry point to the primary disturbance plant, which is a prerequisite for many applications. A numerical example of a three-stage FXLMS notch filter shows that for a 3 dB overshoot constraint, the 20 dB cancellation bandwidth is increased by a factor of 2.56. >

Bandstop filter having symmetrically altered or compensated quarter wavelength transmission line sections

Abstract: A multi-resonator notch filter incorporates a variable impedance transmission line with impedance values going from a relatively low value and increasing upward to a relatively high value then back down to a relatively low value again. A plurality of resonant cavities is coupled to the relatively high central impedance line section of the filter at odd multiples of quarter wavelength intervals. Other resonators can be coupled to lower impedance sections of the transmission line. The locations of selected resonators on the quarter wavelength intervals can be altered thereby increasing and decreasing the nominal quarter wavelength intervals of selected internal pairs by a predetermined amount thereby providing acceptable levels of performance with fewer resonators.

Anti-alias filtering apparatus for frequency domain measurements

Abstract: A filtering apparatus permits alias-free frequency domain measurement in any of a plurality of measurement bandwidths. The input signal is first passed through one of a plurality of low-pass filters. The appropriate filter is selected by a controller to provide a cut-off frequency at least as great as the selected measurement bandwidth. An analog-to-digital convertor ("ADC") samples the filtered input signal at a sample rate (f s ) set by the controller to be at least twice the measurement bandwidth. The digitized samples are then processed by a digital low-pass filter (i.e. a finite impulse response filter) to further reduce the bandwidth of the input signal to the measurement bandwidth. Operation of the digital filter is controlled by a number of filter coefficients provided by the controller as a function of the desired measurement bandwidth. A memory is provided between the ADC and the digital filter. The samples output by the ADC can be processed in real time by the digital filter if the sample rate is sufficiently low, or the samples can be stored in the memory for subsequent processing by the digital filter if a higher sample rate is required. The number of samples can be reduced by adding a decimator which outputs only one sample from each series of K samples received from the digital filter, provided f s /K is at least twice the measurement bandwidth.

Cut-off frequency automatic adjusting filter

Abstract: A cut-off frequency automatic adjusting filter includes a plurality of filters, one of them being a reference filter, and a feedback circuit for the reference filter. The feedback circuit is formed by a subtracter, a full-wave rectifier, an integrator and an error amplifier. A square wave signal is inputted to the reference filter as a reference signal instead of a sine wave signal in the conventional filter. The feedback circuit generates an electrical signal which causes the cut-off frequency of the reference filter and another filter to be constant.

Novel filter design incorporating asymmetrical stripline Y-junction circulators

Abstract: Theoretical treatments of an asymmetrical stripline Y-junction circulator have been carried out. These include a formulation of the circulation conditions of an asymmetrical circulator as well as its transmission characteristics under wide-frequency-band consideration. It is found that filter designs incorporating circulators are very plausible and give rise to a narrow transmission band around the desired transmission frequency and a wide stopband extending many times the fundamental transmission frequency. In this design, high order mode excitations inherent in other filter designs are attenuated. In addition, owing to the off-resonance operation of the ferrites, present design could be applied under higher power conditions than traditional resonant ferrite filters. >

Co-channel interference filter for television receiver

Abstract: A television signal receiver includes a comb filter having a plurality of spaced nulls for reducing undesired co-channel interference. The depth of the nulls is established in response to a control signal representing the strength of the undesired co-channel interference to provide an optimized tradeoff between interference attenuation and signal-to-noise degradation. The control signal is preferably generated in response to a received reference signal such as a pseudo random channel equalization code. The output of the comb filter is characterized by an intersymbol interference component which is canceled is an intersymbol interference filter which is also responsive to the control signal.

Electronic filters, repeated signal charge conversion apparatus, hearing aids and methods

Abstract: An electronic filter for filtering an electrical signal. Signal processing circuitry therein includes a logarithmic filter having a series of filter stages with inputs and outputs in cascade and respective circuits associated with the filter stages for storing electrical representations of filter parameters. The filter stages include circuits for respectively adding the electrical representations of the filter parameters to the electrical signal to be filtered thereby producing a set of filter sum signals. At least one of the filter stages includes circuitry for producing a filter signal in substantially logarithmic form at its output by combining a filter sum signal for that filter stage with a signal from an output of another filter stage. The signal processing circuitry produces an intermediate output signal, and a multiplexer connected to the signal processing circuit multiplexes the intermediate output signal with the electrical signal to be filtered so that the logarithmic filter operates as both a logarithmic prefilter and a logarithmic postfilter. Other electronic filters, signal conversion apparatus, electroacoustic systems, hearing aids and methods are also disclosed.

800 MHz High Power Bandpass Filter using TM Dual Mode Dielectric Resonators

Abstract: A novel high power bandpass filter using TM110 dual mode dielectric resonators was developed. TM110 dual mode is achieved with dielectric resonators physically coupled in an asymmetrically orthogonal manner and these arrayed resonators are constructed in monoblock and have high unloaded Q. By assembling these resonators, an 800 MHz high power bandpass filter was realized. Specific features achieved with this new filter are, center frequency of 840 MHz, band width of 40 MHz, and insertion loss of 0.4 dB. Physical size is 80×90×180 mm. Volume is less than 30% of conventional type high power bandpass filter using cavity resonators. This filter is useful as an antenna filter for cellular base stations.

Modular resonant cavity, modular dielectric notch resonator and modular dielectric notch filter

Abstract: Modular resonant cavities particularly for use in applications associated with high frequency electromagnetic energy each comprise a shell defining an aperture formed therethrough, and either end plates and/or divider closure plates, each having stepped-down regions for interfitting at perimeter ends of adjacent shells so as to form a resonant cavity. The modular resonant cavities include support rods passing through the corner regions of each closure plate. Fastening means at each end of the rods mechanically secure the modular resonant cavities together. The modular resonant cavities are particularly suited for forming dielectric notch resonators and in particular, such dielectric notch resonators having a centrally positioned resonators within the aperture defined by each shell and a coupling reactance mechanism formed by an inductive coupling wire and a capacitive element connected in series thereto so as to form a dielectric notch resonator with a relatively narrow bandwidth and with a small imaginary component about its operating center frequency. Dielectric notch filters using a plurality of such dielectric notch resonators further comprise a coupling transmission line which connects to each dielectric notch resonator resulting in an overall filter having a shorter overall length than comparable filters formed by prior art dielectric notch resonators. The resulting dielectric notch filter has a lower electrical loss than previous dielectric notch filters using longer coupling transmission lines.

Combined block-substrate filter

Abstract: A block-substrate dielectric filter with an a wider VHF range and better capacitive performance is set forth. A capacitive matrix situated in a dielectric substrate (102) that is operably attached to a block (104) filter provides more accurate shunt and series capacitances, and allows design of improved narrowband filters.

Multi-stage monolithic ceramic bandstop filter with isolated filter stages

Abstract: A multi-stage ceramic bandstop filter electrically isolates coupling between stages in a monolithic block of ceramic material (21) by including holes (32 and 36) between the resonator stages (30, 34, and 38) that are shorted at both the top and the bottom ends, that are coated with conductive material and that behave as electrical shields between the succeeding resonator stages electrically isolating and reducing signal coupling between stages. Isolation between stages is also provided by impedance inverting lengths of transmission line (50 and 52) that coupled the stages together.