Showing papers on "Band-stop filter published in 1984"

Adaptive notch filtering for the retrieval of sinusoids in noise

Abstract: In this paper, an adaptive notch filter is developed (employing a frequency domain and time domain analysis) for the enhancement and tracking of sinusoids in additive noise, colored or white. The notch filter is implemented as a constrained infinite impulse response filter with the constraint enforced by a single parameter termed the debiasing parameter. The resulting notch filter requires few parameters, facilitates the formation of the desired band rejection filter response, and also leads to various useful implementations (cascade, parallel). For the adaptation of the filter coefficients, the stochastic Gauss-Newton algorithm is used. The convergence of this updating procedure is established by studying the associated differential equation. Also, it is shown that the structure present in the problem enables truncation of the gradient, thereby reducing the complexity of adapting the filter coefficients. Simulation results are presented to substantiate the analysis, and to demonstrate the potential of the notch filtering technique.

Analysis and performance evaluation of an adaptive notch filter

Abstract: An adaptive notch filter is derived by using a general prediction error framework. The proposed infinite impulse response filler has a special structure that guarantees the desired transfer characteristics. The filter coefficients are updated by a version of the recursive maximum likelihood algorithm. The convergence properties of the algorithm and its asymptotic behavior are discussed, and its performance is evaluated by simulation results.

Digital audio amplifier having a high power output level and low distortion

Abstract: A digital amplifier having a modulator for transforming the analog audio input signal into two complimentary trains of pulse width modulated signals for driving the power switches, which modulator utilizes a precision triangular waveform to control the transformation. The modulator employs all differential processing without saturated transistors to achieve a minimal distortion modulation system. Upon the occurrence of over-modulation, pulses from the width modulated pulse train produced by the modulator are dropped, and the resulting loss of pulses is detected and fed back to a variable gain amplifier stage of the system. The distortion detection system for detecting the missing pulses utilizes a timing network to establish the missing pulse period necessary to begin input attenuation of the audio signal by the variable gain amplifier stage. A reconstruction filter includes a low-pass section for recovering the amplified audio and a notch filter section having notches centered to eliminate the fundamental of the switching frequency. A variable inductor is employed in connection with a section of the notch filter for aiding in the proper notching of the signals to maximize suppression of the switching frequency, such inductor being coupled to the feedback network, and is adjusted by the operator while observing output distortion until the distortion attains a minimum level. The reconstruction filter also includes a tapped inductor functioning as an autotransformer which introduces offsets in the output switching waveform of the power amplifier to effectively compensate for crossover distortion due to energy recovery diode overswings and power switch voltage drops.

Cardiac pacer signal detector

Abstract: A battery powered external pacer operable in fixed-rate and demand modes includes a sense amplifier having an active notch filter system for attenuating power line interference. The filter system comprises four separate data channels each including a transmission gate synchronously driven by pacer clock pulses for frequency stability. Charges developed on capacitors in each data channel are summed by an output capacitor to avoid the need for amplifiers in each channel. A detector having two comparators for detecting positive and negative directed R-wave components derives heart pulses from the amplified signal. A pulse-driven reference supply having very low power consumption provides operating bias required by the detector. A battery monitor having a single comparator simultaneously monitors supply voltage for low and unusable voltage levels.

Multinotch logic-product polarisation suppression filters: a typical design example and its performance in a rain clutter environment

Abstract: Polarisation filtering is applied in radar systems to improve target detection in adverse environments. Fluctuations of the polarisation states of unwanted incident signals dictate the need for filters that suppress such signals in the polarisation domain and cover a controllable area of polarisation space. This has led to the concept of the multinotch logic-product (MLP)polarisation filter which attempts to meet the above need. The paper describes the parameters that affect the general characteristics of the MLP filter, gives a typical design example and uses a representative set of experimentally derived rain clutter data to evaluate the performance of this MLP filter.

Wide frequency band coupling network for an active ripple and noise filter

Abstract: A ripple and noise filter for high voltage DC converters or power supplies The filter includes a common terminal, an input terminal and an output terminal A voltage sensing circuit is connected between the output and common terminals of the filter and is adapted to produce a sense signal which is proportional to the output voltage at the output terminal An active filtering circuit, preferably an amplifier having a frequency operating range which covers the frequency spectrum of the ripple and noise voltages, includes an input for receiving the sense signal and an output at which a correction signal is generated The correction signal has a magnitude and waveform such that coupling the correction signal onto the output terminal of the filter eliminates or reduces the ripple and noise A passive coupling element, preferably a capacitor, isolates the amplifier from the output terminal and couples the correction signal thereto A passive filter, also a capacitor, is connected across the output and common terminals of the filter The coupling capacitor and the passive filter capacitor have nearly identical electrical characteristics so that the correction signal is coupled onto the output terminal without distortion over the full frequency operating range of the amplifier

High frequency, wide range FIR filter

Abstract: The operating speed and dynamic input range of a digital FIR filter are markedly improved by encoding the signal by powers of two and using the thus encoded signal to shift (rather than multiply) the coefficient at each tap of the filter. A multiplexed shifter for simultaneously shifting all digits of the coefficient is also disclosed.

Multiple frequency adaptive noise filter for removing interference signals from a frequency band having a desired signal

Abstract: A multiple frequency adaptive filter system for filtering undesired periodic and/or correlated interference signals contained in the same frequency band as a desired input signal. The filter system is capable of filtering at least two sinusoidal interference signals and incorporates a negative feedback loop having a transfer function of that of narrow band-pass multiple filter. The feedback loop using interference frequencies generates a corresponding interference enhanced output signal. This enhanced output signal is combined with the input signal whereby to produce an error signal which corresponds to the desired signal contained in the input frequency band. A double or quadruple filter system is also described as examples of the present invention. The filter system is suitable for removing modulated sinusoidal interference and particularly for reducing TV co-channel interference.

Analog RC active filter

Abstract: An RC active filter device which is implemented with integrated circuit technology. Each RC filter element of the device has a distributed series resistance and a distributed shunt capacitance. The series resistance is formed by a strip of resistive material which overlies a resistive plate (or substrate) with an intervening insulating layer to form the shunt capacitance. The filter device can be designed to have a pass-band ripple response which is not affected by variation in nominal absolute resistance and capacitance values resulting from process spreads. These variations only stretch or compress the filter response along the frequency axis. The filter device comprises three RC filter elements and an operational amplifier. The RC filter elements nearest the operational amplifier determine a low pass band, while the input filter element prevents high frequency components outside the low pass band being leaked directly to the filter device output.

Constant Z bandswitched input filter

Abstract: A constant impedance (Z) bandswitched input filter for use in a wideband signal receiver includes a low pass filter, a high pass filter and a bandpass filter for reducing intermodulation distortion as well as for providing a flat input impedance characteristic. The bandpass filter resonates at the crossover frequency between the low and high pass filters for minimizing insertion loss while maintaining a constant termination impedance across the entire input signal bandwidth to reduce the input standing wave ratio (VSWR). Switching means are provided for coupling the high and low pass filters as well as the bandpass filter in circuit depending upon the frequency band tuned to. The constant Z bandswitched input filter is particularly adapted for use in a wide band cable television (CATV) system for substantially reducing intermodulation distortion and signal reflections arising from impedance mismatches, but has application in any cable operated multichannel communications system.

Dielectric Resonators Band Pass Filter with High Attenuation Rate.

Abstract: A bandpass filter with high attenuation cut off has been realized by cascading a bandpass filter containing dielectric resonators and a two dielectric resonators bandstop filter. The filter response has a higher cut off attenuation rate [26 db/10 MHz) compared to the original bandpass filter (14 db/10 MHz). The attenuation characteristics and return loss response show that the bandpass and the center frequency remain inchanged at 40 MHz and 4.015GHz respectively. The insertion losses are low (1db).

Dielectric waveguide bandpass apparatus

Abstract: A millimeter wavelength bandpass filter arrangement is produced by using a first dielectric waveguide as an input for a broadband signal to a ferrite circulator. This signal is delivered to a second dielectric waveguide having a bandstop filter formed therein. The bandstop filter reflects the desired bandpass frequency(s) back to the ferrite circulator where it is delivered to a third dielectric waveguide which is the output for the bandpass frequency(s).

Evanescent mode triple ridge lowpass harmonic filter

Abstract: A waveguide lowpass filter has successive groups of three separate ridges spaced longitudinally in said filter. A center ridge of each filter has a larger cross-sectional area than two side ridges which are the same size. All ridges are parallel to one another in a longitudinal direction. The groups are associated with shunt capacitances and the spaces between adjacent groups are associated with series inductances in an evanescent mode. In operation, the filter is capable of supporting a TE10 mode in the passband and three modes, TE10, TE20 and TE30 in the stopband. The filter has a relatively high power handling capability as compared to previous evanescent mode lowpass harmonic filters.

Band stop filter

Abstract: PURPOSE: To obtain a small sized and inexpensive filter by arranging plural structures in which a capacitor is connected to a center conductor at the open end of a coaxial resonator having a short-circuit part at its one end to adjacent capacitors via an inductor or a capacitor. CONSTITUTION: In each cylindrical ceramic dielectric substance 4 of coaxial resonators 1, 2 and 3, a center conductor 5, an outer conductor 6 and a short- circuit face 7 are formed. Each one terminal of the 1st capacitors 9, 10 and 11 is connected respectively to the center conductor 5 of the resonators 1, 2 and 3 and other terminals adjacent to each other are connected via an inductor or the 2nd capacitor formed on a base 12. Moreover, the outer conductors of the resonators 1, 2 and 3 placed side by side are connected via a conductor layer made of solder or the like. The insertion loss at a low or a high frequency band of the element formed on the base 12 is reduced by any of the inductor or the capacitor formed on the base 12, then a band block filter having an asymmetrical frequency characteristic is obtained. The structure of the element is simple and the product is made small in size and the cost is reduced. COPYRIGHT: (C)1990,JPO&Japio

Alternating-current filter circuit arrangement

Abstract: In this three-phase filter circuit system for static converter systems and particularly high-voltage direct-current short ties, at least two high-pass filters are provided which are connected in parallel. Each high-pass filter consists of a choke connected in parallel with a resistance and, in series with both, a capacitor and can be individually connected to the three-phase busbar via a switch. The filter circuits are used not only for reducing harmonics but also as compensating devices, which can be switched in steps, for the reactive power requirement of the static converters so that in the lower partial load range of the system one of the filter circuits is disconnected for reasons of reactive power balance. In order to improve the filtering effect in this lower partial load range, a bus-coupler switch connecting in each case the common junctions of capacitor, resistance and choke of the high-pass filters is closed. When the switch is closed, this widens the band width of the filter circuit which is in operation and increases the resonance frequency, and individual distortions, the total distortion and telephone interference factors on the busbar are reduced.

Switchable bandpass filter

Abstract: A bandpass filter suitable for use in modem circuitry and other applications which require the filter's center frequency to be switched is disclosed. The filter circuit has the characteristic that although the center frequency is changed the overall gain of the filter remains constant. This characteristic results from using a plurality of filter sections which each have low individual gain and providing compensating gain at the input of the filter. In addition, compensating gain elements are used in each filter section so that when the center frequency of the filter is changed, the gain of each filter stage remains constant.

Microprocessor fsk data communications module

Abstract: A microprocessor-based frequency shift keying (FSK) data communications module. The microprocessor selectively modulates and demodulates data directly in terms of a square wave pulse train in which a first frequency is used to convey a binary "1" and a second frequency to convey a binary "0". An input and an output port on the microprocessor are selectively coupled to a transmission line through a transformer, by means of electronic switches. Also included are a bandpass filter for shaping the square waves into sine waves and for filtering noise, and means including a notch filter for generating a carrier detect signal input to the microprocessor, when incoming data is detected on the transmission line. Many of the components in the module are used for both transmitting and receiving data.

Tracking filter system for use with a FM/CW radar

Abstract: A tracking filter system including a phase locked loop and a tracking filter is receptive of an input signal of frequency A and undesired frequency X from a signal source such as a frequency modulated/continuous wave radar range measuring system. The phase locked loop circuit receives the input signal and produces a control signal corresponding to a frequency intermediate frequencies A and X. The tracking filter is set by the control signal to pass frequencies above or below the intermediate frequency and thus to pass frequency A and to reject frequency X.

FM demodulator with impulse noise elimination circuit

Abstract: An apparatus for demodulating a frequency modulated input signal having a carrier signal component, including a filter for allowing only signals having frequency around the frequency of the carrier signal component and a demodulator connected to the filter for performing frequency demodulation, is provided with a noise eliminating circuit at a stage immediately before the filter. With this provision, an impulse noise having spectrum components of very wide band and which could not be rejected by the filter in prior art apparatuses, is eliminated before the demodulation.

Signal analysis apparatus including recursive filter for electromagnetic surveillance system

Abstract: The specification discloses a digital/analog signal analyzer for an electromagnetic surveillance system. Included is a notch filter having a switched capacitor filter controlled by a phase lock loop for nulling a time-varying driving frequency from the received signal. The analyzer further includes structure for digitizing the received signal and for implementing a recursive filter to enhance digital feature extraction. The recursive filter in turn includes structure for delaying a read address for subsequent use as a write address to facilitate the rapid updating of data in memory. Also included is a digital-to-analog converter assembly having a pair of piggy-backed digital-to-analog converters to produce an analog signal dependent upon both a mantissa and an exponent of a digital number in scientific notation.

Wide-band hybrid analog/Digital frequency domain adaptive filter

Abstract: This paper describes a hybrid adaptive filter which employs a cascade of analog forward and inverse Fourier transform processors interconnected via a digital interface. The interface multiplies the transformed input, sample by sample, by a set of weights stored in RAM and compares the products against a desired complex spectrum. The resulting error is used to update the RAM weights via a feedback loop, which forces the multiplied output to converge towards the desired complex spectrum. The use of frequency domain processing in the adaptive filter offers faster, more controlled convergence than conventional time domain adaptive transversal filters. We present simulations and practical results on a frequency domain adaptive filter based on 100 point surface acoustic wave chirp transform processors which give the adaptive filter a 4 MHz real-time bandwidth capability. Thus, this new processor is likely to find potential application in equalization, echo, and interference suppression in high bandwidth communications and radar systems.

Pulse width modulated inverter

Abstract: The inverter has an improved output filter (12) including a low pass filter (38, 39) for providing a sine wave output in response to a pulse width modulated waveform and a notch filter (40) coupled to the low pass filter and tuned to the frequency of the pulse width modulated waveform to eliminate that frequency from the sine wave output. The inverter also includes a series resonant circuit (54) coupled across the DC power supply (20) of the inverter and tuned to two times the frequency of the sine wave output to provide a low impedance path for AC current flowing to the power supply.

Automatic waveform equalizer

Abstract: PURPOSE:To obtain a reference waveform having a spectrum band similar to that of an input digital signal by supplying an output signal of a transversal filter to a level discriminating circuit to generate a rectangular simulated reference waveform thereby waveform-shaping by means of a band stop filter CONSTITUTION:The input digital signal 2 is led to the transversal filter 3 The filter 3 consists of an analog delay element 4 having a tap at each 1/2 of the sample interval of the signal 2, a multiplier 5 and an adder 6 The signal 2 is subjected to convolution arithmetric with a gain value at a tap gain memory 7 via the filter 3, becomes an output signal 8 reduced with waveform distortion and is outputted The output signal 8 is inputted to a reference waveform generating circuit 10 comprising a level discriminating circuit 11 and a band stop filter 13 The band stop filter 13 forms the simulated reference waveform 12 in a waveform 14 The waveform 14 is subtracted with the output signal 8 by a subtractor 15 to form an error signal 16 The interrelation between the signals 16 and 2 is calculated by a correlation operating circuit 17 so as to correct the tap gain of a memory 7

Switchable Band-Stop Filter for M.I.C.

Abstract: A switchable filter structure using transmission lines switched by means of PIN diodes permits to obtain according to the bias diode state either a transfer function band-stop or a transfer function pseudo all pass This switchable filter consists of : quarter-wave open-circuited lines separated by quarter-wave series lines, beam lead PIN diodes and biasing circuits It is well suited for M I C technology A device operating up to 18 GHz has been realized on alumina substrate using a microstrip propagation mode An application of this kind of switchable band-stop filter is the second harmonic suppression in wide band system

New digital notch filter structures with low coefficient sensitivity

Abstract: For narrow-band digital notch filters, poles are near the unit circle. Also, when the sampling rate is increased, the poles approach the point Z = + 1 . The usual realizations of digital notch filters are highly sensitive to coefficient quantization. Three new digital notch filter structures are proposed, and their coefficient sensitivities are derived.

Method and apparatus for de-ringing a switched capacitor filter

Abstract: A switched capacitor filter system is provided which is programmed to filter a predetermined sequence of tone signals. The filter system is de-rung after each selected tone signal is detected by increasing the clock frequency of the switched capacitor from the programmed value corresponding to a tone signal up to a center frequency substantially greater than that of the tone signals. Energy stored in the filter system is thus quickly dissipated. Rapid sequences of sequential tone signals are thus filtered without the problems associated with ringing of the filter.

Coupling block assembly with band-reject filter

Abstract: A band-reject filter comprises a resonator with an adjustable resonator rod which is mounted in proximity to a co-axial assembly. The coupling rod passes thru the inner conductor of the co-axial assembly and extends into the resonator. At the end of the rod inside the resonator there is a coupling disc. Means are provided to adjust the distance between the resonator rod and the disc. The frequency rejected by the filter can be adjusted by either adjusting the length of the resonator rod or by adjusting the distance between the disc and the resonator rod.

Design of recursive digital filters for the selection or rejection of a particular velocity in seismic signals

Abstract: In this paper a new type of “velocity-selecting/rejecting filter” which passes or stops a particular event in a seismic signal is proposed. The velocity-selecting filter is based on a time-space band-pass filter with sharp passband for a particular direction, and similarly, the velocity-rejecting filter is based on a time-space band-stop filter. A technique for designing such filters, in terms of an infinite-impulse-response (IIR) filter, is presented, in which a rotated version of separable filter is used. Finally, numerical examples are included to illustrate the design theory.