Showing papers on "Band-stop filter published in 1985"

A minimal parameter adaptive notch filter with constrained poles and zeros

Abstract: A new algorithm is presented for adaptive notch filtering and parametric spectral estimation of multiple narrow-band or sine wave signals in an additive broad-band process. The algorithm is of recursive prediction error (RPE) form and uses a special constrained model of infinite impulse response (IIR) with a minimal number of parameters. The convergent filter is characterized by highly narrow bandwidth and uniform notches of desired shape. For sufficiently large data sets, the variances of the sine wave frequency estimates are of the same order of magnitude as the Cramer-Rao bound. Results from simulations illustrate the performance of the algorithm under a wide range of conditions.

Low-distortion switched-capacitor filter design techniques

Abstract: The distortion mechanism in switched-capacitor (SC) filters are considered, and closed-form expression relating switched-capacitors filter distortion to circuit parameters are derived. Design techniques for low-distortion applications are discussed and are applied to a sixth-order experimental filter. The filter design uses a fully differential class A/B op amp with a continuous-time common-mode feedback circuit. Distortion measurements show that for 82-dB dynamic range (relative to noise floor) the total harmonic distortion of 0.02% within the whole 4-kHz bandwidth and 0.07% within 20-kHz bandwidth.

An elliptic continuous-time CMOS filter with on-chip automatic tuning

Abstract: A voice-band continuous-time filter is described which was designed based on the technique of fully balanced networks and was fabrication in a 3.5-/spl mu/ CMOS technology. The filter implements a fifth-order elliptic low-pass transfer function with 0.05-dB passband ripple and 3.4 kHz cutoff frequency. A phase-locked loop control system fabricated on the same chip automatically references the frequency response of the filter to an external fixed clock frequency. The cutoff frequency was found to vary by less than 0.1% for an operating temperature range of 0-85/spl deg/C. The absolute value accuracy of the cutoff frequency was 0.5% (standard deviation). With /spl plusmn/5-V power supplies the measured dynamic range of the filter was approximately 100 dB.

Quadrature mirror filter design for an arbitrary number of equal bandwidth channels

Abstract: The two-channel quadrature mirror filter structure of Croisier and Esteban may be extended to an arbitrary number of equal bandwidth channels, given certain restrictions on the bandpass filters. The most serious restriction is that the stopband attenuation of eacli band-pass filter must be high for all frequencies outside twice the nominal 3 dB bandwidth of the filter. This restriction is not really a limiting factor for speech subband waveform coding since high adjacent channel attenuation is a necessity for the confinement of quantization noise. A key feature of our filter structure is that the number of multiplies, adds, and stored coefficients required for implementation is significantly less than those needed for the conventional QMF structure, given the same number of channels. Fortran code for a 16-channel filter structure is listed as an example of efficient implementation.

Adaptive signal strength and/or ambient noise driven audio shaping system

Abstract: An adaptive audio filter system is disclosed which comprises a filter means capable of producing a plurality of frequency response characteristics. A control signal generating means provides a control signal to the filter means to enable a particular frequency response. The control signal is based upon the signal to noise ratio.

Optimal design of linear phase FIR digital filters with very flat passbands and equiripple stopbands

Abstract: A new technique is presented for the design of digital FIR filters, with a prescribed degree of flatness in the passband, and a prescribed (equiripple) attenuation in the stopband. The design is based entirely on an appropriate use of the well-known Remez-exchange algorithm for the design of weighted Chebyshev FIR filters. The extreme versatility of this algorithm is combined with certain "maximally flat" FIR filter building blocks, in order to generate a wide family of filters. The design technique directly leads to structures that have low passband sensitivity properties.

A minimal parameter adaptive notch filter with constrained poles and zeros

Abstract: A new algorithm is presented for adaptive notch filtering and parametric spectral estimation of multiple narrow-band or sine wave signals in an additive broadband process. The algorithm is of recursive prediction error (RPE) form and uses a special constrained model of proper infinite impulse response (IIR) with a minimal number of parameters. The convergent filter is characterized by highly narrow bandwidth and uniform notches of desired shape. For sufficiently large data sets, the algorithm approaches the Cramer-Rao bound in estimating the frequencies of the sine wave signals.

800-MHz High-Performance SAW Filter Using New Resonant Configuration

Abstract: A new high-performance surface-acoustic-wave (SAW) filter for use in mobile telephones is presented in this paper. The design for the actual realization of the new filter is examined, from the new filter configuration to the final device operation, A low-loss weighting technique in an interdigital transducer (IDT), a new resonant structure, computer simulation procedures, and material properties are treated. Experimental results with this SAW filter included an 830-MHz center frequency, 3-percent bandwidth, insertion loss of as low as 3.5 ~ 4.0 dB, and 50-dB sidelobe suppression filter.

Speakerphone with adaptive cancellation of room echoes

Abstract: An arrangement for generating an electrical audio signal in response to a sound signal applied to a microphone in a reverberating room removes the reverberations with an adaptive filter. The filter learns or adapts so as to cancel the room echoes by receiving both the audio signal affected by reverberation and a clean audio signal from a highly directional local-acting microphone placed near the source of the sound. The signal to be filtered is applied to a transversal filter including a tapped delay line having variable taps or multipliers to produce incrementally delayed multiplied samples. The multiplied samples are summed, and the sum signal is subtracted from the clean signal to produce a difference signal. A μP is programmed to iteratively calculate the effects of changes to the tap values and to select tap values which tend to reduce the magnitude of the difference signal. When the filter is converged, the difference signal is near zero. At this time, the filtered signal and the clean signal are similar, and therefore the filter characteristic removes the effect of reverberation. The tap values are then fixed, and the signal with room reverberations can be made clean by the adapted filter.

Tunable notch filter for image frequency and conducted local oscillator leakage rejection

Abstract: A tunable notch filter for the front end of an RF receiver includes magnetically coupled input and output tunable stages each responsive to a tuning voltage provided thereto. Each of the input and output stages includes a respective series and parallel resonant circuit wherein the parallel resonant circuits are tuned to a selected RF frequency and the series resonant circuits are tuned to a frequency approximately equal to that of a local oscillator. By using the series resonant circuits to create a notch at a frequency approximating that of the local oscillator, conducted local oscillator leakage from the receiver's antenna is substantially reduced and local oscillator image frequency rejection is substantially improved.

Switched bandpass filter

Abstract: A switched bandpass filter includes a plurality of triple tuned bandpass filter sections coupled in parallel between an input and an output terminal and complemented by input and output parallel resonant circuits. Each bandpass filter section includes a switch such as a switching diode by means of which the filter section is either rendered active for passing or inactive for suppressing the frequency band to which it is tuned. Portions of the inactive bandpass filter sections contribute to the resulting frequency response with notches at frequencies outside of the passband of the active filter section. Thus, some components of the inactive bandpass filter sections are reused with the active filter section to gain steep out-of-band rejection slopes. In one embodiment, the switched bandpass filter employs only one switching diode per frequency band and, by reusing two-thirds of the filter components, provides a highly efficient switched bandpass filter arrangement.

On the Narrow-Band Microwave Filter Design Using a Dielectric Rod

Abstract: A method is presented to design bandpass or bandstop filters in the microwave region. The procedure is based on the analysis of the discontinuity problem of a circular cylindrical dielectric rod centered in a rectangular waveguide. For some special relations between the frequency, the dielectric constant, and the radius of the rod, the reflection or the transmission coefficient becomes equal to zero. This relation gives the narrow-band filter. Experimental results for filter design with the help of plastic and porcelain rods are given.

Waveguide manifold coupled multiplexer with triple mode filters

Abstract: A multiplexer has a plurality of bandpass filters coupled through E-plane or H-plane T-junctions to a waveguide manifold. Where the multiplexer has four channels and each filter is a six-pole filter, two triple mode cavities make up each filter. Where each filter is a five-pole filter, one triple cavity and one dual mode cavity makes up each filter. Two band edge channel filters are operated to produce an asymmetrical filter function response, thereby causing extra transmission zeros to be created and improving the selectivity of the filter out of the passband. The multiplexer is designed for use in satellite communication systems and can have a reduced volume and weight when compared to previous multiplexers without any sacrifice in electrical performance.

Nonlinear adaptive filter

Abstract: A nonlinear adaptive filter has an input and an output, and includes an adjustable linear filter and nonlinear filter connected serially between the input and output. The parameters for the adjustable linear filter are derived from signals on the adaptive filter output and from signals on the adaptive filter input. Preferably, the adjustable linear filter is coupled between the adaptive filter input and the nonlinear filter. A parameter computer for adjusting the parameters of the adjustable linear filter includes an input coupled to the output of the nonlinear filter, a processor for processing a signal received from the output of the nonlinear filter, and apparatus for applying the processed output signal to the parameters of the adjustable linear filter. A linear filter for shaping the spectrum of a signal received from the output of the nonlinear filter is preferably coupled between the nonlinear filter output and the parameter computer. In its preferred form, the nonlinear filter portion includes a first processor for generating from an input signal an intermediate signal having a uniform amplitude-density function, and a second processor for generating from the intermediate signal an output signal having a desired amplitude-density function.

Switched capacitor filter utilizing a differential input and output circuit

Abstract: An integrated circuit for filtering signals by having cascaded switched capacitor sampling filters. The circuit includes a transmit section which has an anti-aliasing filter, a core section filter, a highpass filter and an encoder for providing analog-to-digital conversion. Each successive filter is sampled at a lower rate to inhibit anti-aliasing. The circuit also includes a receive section which has a digital-to-analog decoder, an output buffer, a receiver core filter and a power amplifier.

Cascaded fiber optic lattice filter

Abstract: A fiber optic lattice filter having a transfer function wherein the poles and zeros are adjustable independently of each other. The filter comprises a cascaded configuration of recursive (100) and non-recursive (102) fiber optic lattice filters. In one preferred embodiment, an all-pass fiber optic filter is formed by cascading all-pole and all-zero lattice filters, and by processing the resulting filtered output signal in a subtractive detection system (104). This detection system produces a signal which represents the difference between two signal outputs provided by the all-zero filter section, and which is adjustable in magnitude, thereby providing an overall filtering function which is capable of handling both positive and negative valued input signals.

Electronic siren audio notch filter for transmitters

Abstract: A notch filter as disclosed which is adaptable to notching out a background siren from voice communications from an emergency vehicle. Two embodiments are disclosed. In the first embodiment, a frequency lock loop tracks the fundamental frequency of an electronic siren. The siren fundamental frequency is then notched out from voice transmissions using a notch filter. In the preferred transmissions using a notch filter. In the preferred embodiment, a digital ramp is generated by a first digital signal processor. This signal is input to an amplifier and a speaker thus producing an electronic siren. The digital ramp is also input to a second digital signal processor which notches out the fundamental frequency and odd harmonics thereof from the digital ramp thus acting as a comb notch filter. Analog voice is digitized by way of an analog to digital converter and input to the second digital signal processor. The second digital signal processor combs out the fundamental frequency and odd harmonics of the background siren signal from the digitized voice signal. The digitized voice signal is then converted back to an analog signal by way of a digital to analog converter.

Fourier plane recursive optical filter

Abstract: An optical recursive filtering system in which a signal beam of optical radiation is passed through the optical filtering means a multiplicity of times. The filtering system has an optical Fourier transform means, a spatial filter, optical inverse Fourier transform means and a pair of reflectors in the Fourier plane of the spatial filter. An input signal beam to be filtered is optically Fourier transformed by the transform means and is passed through the spatial filter where unwanted frequencies of the signal beam are attenuated. The filtered beam is reflected by one of the reflectors back through the filter and the second mirror reflects it back through the filter a third time. Subsequent reflections back through the filter with a consequent further filtering of the signal beam can be accomplished by appropriately positioning the reflectors. After multiple filtering passes, the filtered beam is extracted for utilization. By maintaining the recursions of the beam in the Fourier plane of the filter, which preferably is of a programmable type, the optical throw of the filter system can be significantly reduced and a flexible imaging system without the restraints of external recursion is realizable in a robust structure with fewer components. An embodiment of the system being used in a heterodyning RF optical filtering system is described.

Rapid slewing filter

Abstract: A multiplexer samples multiple analog waveform signals to provide a sequence of input signals to an active low-pass filter. The bandwidth of the filter is determined by an input RC network having series resistance and shunt capacitance elements. As the multiplexer switches state to sample a different analog signal, the resistance elements of the filter are temporarily shorted to allow the filter input signal to rapidly charge or discharge the shunt capacitance element to a steady state voltage in response to any change in input signal voltage. The resistance elements are then unshorted to permit normal low-pass filter operation. Switch means are also provided to selectively disconnect the shunt capacitance element from the network when the resistance elements are shunted, thereby selectively widening the bandwidth of the filter to pass higher frequency input signals.

Mixer controlled variable passband finite impulse response filter

Abstract: A mixer controlled, variable passband, finite impulse response filter has a plurality of individual filter function blocks which are cascaded. The filter function of each of the individual filter function blocks is represented by a fixed filter function block having a linear phase response. The junctions between successive filter function blocks form signal taps. The signal from each signal tap is delayed by a compensating delay device so that the signals from each of the plurality of signal taps have the same phase function. Signals from selected signal taps are then combined in a predetermined manner to achieve a desired filter transfer function.

Noise reduction circuit for composite color video signals

Abstract: A noise reduction circuit for eliminating the noises contained in a composite color video signal, including a high-pass filter for extracting high-frequency components from composite color video signal, an amplitude limiter responsive to the high-frequency components to limit the amplitudes of these components, a phase inverter for inverting the phase of the output from the amplitude-limiter, a mixing network receiving both of the composite color video signal and the output from the phase inverter so that the noises contained in the former are substantially cancelled by the latter, wherein a notch filter is provided to attenuate signal components of a predetermined frequency contained in the input signal to the amplitude limiter to remove the chrominance component from the signal to be supplied to the amplitude limiter. The noise reduction circuit is useful especially in a composite color video reproduction system of a constant-line-velocity video disc player having special reproduction modes such as the still-motion, fast-feed and slow-motion modes.

Digital correlation apparatus as for a television deghosting system

Abstract: A television deghosting system includes an IIR filter having programmable filter coefficients which processes the input signals to remove ghost signal components. The IIR filter may be reconfigured as an FIR filter, having its coefficient and delay values changed to operate as a matched correlation filter. In this mode the filter is used to correlate a training signal to determine the relative delays of ghost signals with respect to the direct signal. The training signal used is the sum of the squared differentials of the in-phase and quadrature-phase components of the video IF signal during an interval defined by the leading edge of the vertical sync pulse and the first equalization pulse.

Variable switched-capacitor filter capable of changing the filter characteristic thereof

Abstract: The variable switched-capacitor filter (VSCF) comprises an input terminal (101), an output terminal (104) and first and second variable switched-capacitor filter blocks (102 and 103, resp.) each having a plurality of capacitors. In each of the filter blocks (102, 103) at least one of the filters is selected in response to a control signal for changing the filter characteristic based on the selected capacitor or capacitors. A first switch (SA) delivers during a first state a first output signal from the first variable switched-capacitor filter block (102) to the output terminal (104), and during a second state, prohibits the first output signal from reaching the output terminal (104). The function of the second switch (SB) is essentially opposite to that of the first switch (SA). The selection of at least one capacitor in the first and the second variable switched-capacitor filter block (102 and 103, resp.) is performed during the second and the first state, respectively. The VSCF accomplishes automatic line equalization without being affected by waveform distortions which result from switching the filter characteristic.

Bandstop Filter Design Using a Dielectric Waveguide Grating

Abstract: Precision design techniques are obtained for dieletric waveguide (DW) bandstop filters with bandwidths up into the 5-10-percent range. Dielectric waveguide bandstop filters are realized in the form of a grating in the DW image guide which utilizes notches of varying depth and length. The grating is designed from a transmission-line prototype which has a prescribed stopband and also prescribed Chebyshev passbands. An approximate synthesis procedure for such prototypes is presented. Design data for grating notches were obtained from tests on uniform gratings, while DW dispersion is compensated for by calculations based on the "effective dielectric constant" method. Excellent agreement between computed and measured attenuation response is obtained. Two such grating structures used with loads on one end and a 3-dB coupler can be used to form a bandpass filter.

Magnetic recording and playback apparatus for teletext signals

Abstract: A magnetic recording and playback apparatus for teletext signals which accurately records and reproduces the teletext signal superposed within the vertical blanking period of television signal, includes at least one wide band filter, at least one narrow band filter, a filter selection switch which switches at least one filter for a luminance signal processing system to the wide band filter and at least one filter for a chrominance signal processing system to the narrow band filter, and a control circuit which generates a control signal for controlling the filter selection switch. The control circuit generates the control signal only during a specified period where the teletext signal is superposed. In case a comb filter is used, a switch is provided for selectively passing an output of the comb filter and an input video signal to the succeeding stages and a control circuit for producing a control signal to allow the input video signal to pass during a specified period where the teletext signal is superposed.

An integrated six-path wave-SC filter

Abstract: Experimental results of a switched capacitor (SC) N-path filter integrated in a CMOS Si-gate technology are reported, with N=6. The circuit is based on the theory of wave-flow networks and uses only fully stray-eliminating (usually referred to as stray-insensitive) SC amplifier and integrator circuits. The two main drawbacks of N-path filters, i.e. unwanted mirror frequencies due to path mismatch and clock feedthrough located in the passbands, as solved by multiplexing large filter parts and by using a third-order high-pass reference filter, respectively. The integrated six-path filter features low power consumption due to the use of dynamic amplifiers.

A single-path frequency-translated switched- capacitor bandpass filter system

Abstract: Conventional switched-capacitor (SC) filter systems have alias and image frequency-translated signal components which are regarded as undesirable and supressed by a low-pass anti-aliasing filter (AAF) and by a low-pass anti-imaging filter (AIF). In this paper, we propose a single-path frequency-translated filter system in which these frequency translations are deliberately utilized in order to realize bandpass responses with very narrow relative bandwidths. The system requires bandpass AAF and AIF which are implemented using SC techniques.

System for processing audio frequency information for frequency modulation

Abstract: In FM transmitters, particularly land mobile FM transmitters, wherein a speech signal is pre-emphasized between 300 Hz and 3 kHz, whereafter it is filtered to provide a sharp cut-off and wherein the maximum peak frequency deviation is limited in order to maintain channel integrity, the level of undistorted speech can be raised to within 90% of the transmitter peak deviation by directly connecting an amplitude limiter to a filter amplifier which behaves as a level sensitive filter when the speech signal has been limited and prevents ringing and overshoot from occurring. The output from the filter amplifier is coupled to a low pass filter, typically a fourth-order Butterworth filter, via an attenuator which reduces the amplitude of the signal to prevent the onset of further clipping.

Microwave recursive filter

Abstract: A broadband microwave recursive filter that provides sharp transitions in the frequency domain between adjacent stop and passbands comprising a signal input node; a signal output node; a filter circuit connected between the signal input node and the signal output node for providing a signal flow therebetween which has a predetermined frequency bandwidth characteristic; a microwave transistor circuit, with the microwave transistor circuit being band-limited to provide gain in only a restricted window of frequencies within the predetermined frequency bandwidth and connected for providing amplification to signals flowing in the filter circuit between the signal input node and the signal output node while suppressing out-of-window signals resulting from design approximations. The filter circuit includes a plurality of distributed feedback loop circuits, with each of the feedback loop circuits including the microwave transistor circuit therein, and wherein each of the feedback loop circuits has a different electrical length in relation to the other of the plurality of feedback loop circuits. Finally, the present filter design includes a passive filter connected in common to all of the plurality of distributed feedback loop circuits in the filter circuit for circuit for providing filter zeros on both sides of the restricted window of frequencies. In a preferred embodiment, the microwave transistor circuit includes an FET which is impedance-matched to obtain an approximately flat gain response across the window. It is preferred that the plurality of feedback loops all have amplitude weighting factors of the same sign.

Adaptive sinusoidal interference filter

Abstract: The invention relates to an adaptive filtering system for cancelling one or more sinusoidal interference signal contained with a desired signal in an incoming signal. A phase-locked loop is used to track a sinusoidal interference frequency and to synthesize various synchronous in-phase/in-quadrature square wave signals. Each of these signals is weighted in accordance with variations in the amplitude and the phase of the sinusoidal interference signal and the weighted square wave signals are combined together with the incoming signal so as to deliver the desired signal substantially free from any sinusoidal interference signal. In the case of multiple correlated signals, the instant filtering system gives a steady state performance substantially better than that of the well known Widrow-Hoff adaptive notch filter.