Showing papers on "Band-stop filter published in 1989"

Adaptive detection and enhancement of multiple sinusoids using a cascade IIR filter

Abstract: A constrained adaptive infinite-impulse-response (IIR) filter consisting of a cascade of biquadratic notch sections is used to track multiple sinusoids. The structure can be used to isolate individual sinusoids. It is shown that for small changes around the optimum solution, the proposed update algorithm approximates the Gauss-Newton update without requiring a matrix inversion. Furthermore, the transient response is approximately independent of the number of sinusoids or their power levels. Important adaptive line enhancement performance criteria, such as signal-to-noise improvement ratio and the bias in the frequency estimate assuming white noise, are derived for the single-sinusoid case. Computer simulations are used to demonstrate the performance of the notch filter under a wide range of conditions. >

Adaptive line enhancement by using an IIR lattice notch filter

Abstract: Two simple methods for retrieving a single sinusoid corrupted with noise are proposed. They are based on the lattice form realization of an adaptive infinite-impulse-response (IIR) notch filter. The IIR filter is a cascade of second-order all-pole and all-zero filters, and the coefficients of the finite-impulse-response (FIR) section are adapted. The proposed algorithms keep the poles of the filter inside the unit circle. The computer simulation results show that the algorithms have considerable potential in adaptive notch filter applications, especially when the input signal-to-noise ratio is low. >

A parasitic-insensitive area-efficient approach to realizing very large time constants in switched-capacitor circuits

Abstract: A novel switched-capacitor technique for realizing very large time constants is presented. The technique is insensitive to parasitic capacitances and is very area-efficient. It does not require a complicated clocking scheme. The technique yields a complete family of integrators which in turn can be used to realize higher-order filtering functions based on cascaded biquadratic sections or ladder filters. These integrators have been used to implement an experimental 60-Hz notch filter working from a 128-kHz clock. >

Monolithic ceramic filter with bandstop function

Abstract: of the Disclosure A ceramic filter (144,118) includes a multiple zero bandstop filter function. The ceramic filter has a dielectric block (210) with top and bottom surfaces and at least two holes (221-227), extending from the top surface toward the bottom surface of the block. The block (210) is selectively covered with a conductive material to provide a transmission line resonator for each of the two holes. The filter also includes an input electrode (214) coupled to the dielectric means at a predetermined distance form one first hole (201), and an output electrode (216) coupled to the dielectric means at a predetermined distance from another hole (207). Finally, conductive plating (240), in the form of a transmission line, is contiguously disposed on the dielectric means adjacent the two holes and coupled thereto to provide a bandstop filter function with a zero represented at each hole.

Echo cancelling device with frequency sub-band filtering

Abstract: An echo cancelling device for use between a line receiving an incoming signal and a line transmitting an outgoing signal, for cancelling out echo, comprising a plurality of processing channels connected in parallel relation and assigned to successive mutually adjacent sub-bands of the spectral band of the outgoing signal, each channel having: a first analysis band-pass filter receiving the echo-affected signal to be transmitted, whose output is connected to the additive input of a subtractor; a second analysis band-pass filter, identical to the first filter, receiving the incoming signal and feeding an adaptive filter delivering an estimated echo value in the sub-band to the subtractive input of the subtractor; and a synthesis filter, symmetrical with the analysis filters and whose output feeds the transmission line. Each processing channel receives an estimation of the aliasing component originating from another sub-band at least and that component is eliminated by adding it to the signal originating from the filter analyzing the respective incoming signal. Estimation may be made by synthesis using at least one adaptive cross-filter fed by the output of an adjacent channel.

Normalized frequency domain LMS adaptive filter

Abstract: A normalized frequency domain Least Means Square filter. The feedback coefficient for each frequency bin is adjusted separately in the filter by use of an input power estimate. The power estimate is incorporated directly into the filter algorithm as a data-dependent, time-varying stochastic feedback coefficient. The filter is particularly useful in applications in which the input signal has large spectral variations, which could lead to filter instabilities in some frequency bins if a single feedback coefficient were employed in all frequency bins.

Feasibility study of AC- and DC-side active filters for HVDC converter terminals

Abstract: The active filter concepts are compared with the passive filters, both on the dc-side and the ac-side of the HVDC terminal. The Dickinson terminal of the CU HVDC transmission line is used as the basis for this study. Based on this study, the following conclusions are reached for the dc-side and the ac-side active filters: DC-Side Active Filters 1. The active filter is designed for filtering of the three dominant harmonics at the 12th, the 24th and the 36th harmonic frequencies. Computer simulations indicate that these three dominant harmonics can be attenuated to less than 1 % at the transmission line terminal, compared to the harmonic voltages produced by the converter. It should be noted that any other harmonic frequencies which may be troublesome can be included in the injection current to filter these harmonics. Higher order harmonics have small amplitudes; hence, the required total injection current and the total kVAs of the components in the active filter are not changed significantly by adding higher order harmonics. 2. The effective cost of the dc-side active filter is estimated to be 186 k$, which also includes the present worth of the additional 17.3 kW losses in the active filter, as compared to the passive filter. The active filter costs is lower by only 27 k$, as compared to the passivefilter cost of 213 k$. Given the uncertainty in the cost estimates, both filters are comparable in terms of cost.

Adaptive narrow-band interference rejection in a DS spread-spectrum intercept receiver using transform domain signal processing techniques

Abstract: An intercept receiver which uses a transform-domain-processing filter is described. This receiver detects direct-sequence binary-phase-shift-keyed (DS-BPSK) spread-spectrum signals in the presence of narrowband interference by employing adaptive narrowband interference rejection techniques. The improvement in the system performance over that of conventional detection techniques is shown by presenting the results of experimental measurements of probability of detection versus false alarm for an enhanced total power detector. Also presented are certain results corresponding to detection of the spectral lines generated at twice the carrier frequency, wherein the goal is often not just signal detection, but also carrier frequency estimation. The receiver uses one of two transform-domain-processing techniques for adaptive narrowband interference rejection. In the first technique, the narrowband interference is detected and excised in the transform domain by using an adaptive notch filter. In the second technique, the interference is suppressed using soft-limiting in the transform domain. >

Mean-squared error analysis of an adaptive notch filter

Abstract: A mean-square-error analysis of the steady-state coefficient fluctuation of an infinite impulse response (IIR) adaptive notch filter, whose coefficients are estimated by simple gradient and sign gradient algorithms, is presented. Regarding the magnitude and phase responses of the transfer function that is used to realize a second-order IIR adaptive notch filter, it is shown that the filter-coefficient estimation error can be studied by using first-order ordinary difference equations with stochastic input. Simple closed-form results are derived for the mean-square error of the steady-state coefficients. The results of computer experiments are presented to substantiate the analysis. >

Two cylindrical obstacles in a rectangular waveguide-resonances and filter applications

Abstract: Two metallic or lossy dielectric cylinders placed in one cross section of a rectangular waveguide are investigated by the orthogonal expansion method. Resonances are shown by frequency responses of the transmission coefficient. They are discussed by patterns of the magnetic field and diagrams of the Poynting vector. Physical explanations of the resonances are given. The structure may be used as a filter element. With two small dielectric posts, a frequency characteristic with two stopbands can be obtained. Center frequencies are tunable by moving the posts. Using one large metallic and one small dielectric post, a tunable passband characteristic can be realized. >

Servo positioning apparatus

Abstract: A notch filter, used in a servo loop, for dampening a mechanical resonance of a mechanism to be servo-controlled, including a serial T-type filter with a capacitor-resistor (CR) network having a serial connection of a first, second and third capacitors connected between an input terminal of the serial T-type filter and an output terminal of the Cr network; a first resistor connected between a return terminal of the CR network and an interconnection of the first and second capacitors; a second resistor connected between the return terminal and an interconnection of the second and third capacitors; and a third resistor connected in parallel to the three serial capacitors. A notch frequency of the notch filter is adjusted by varying the resistance values of the first and second resistors. The first and second resistors may include fixed and/or potentiometer-type variable resistors. An output from the CR network may be divided to be fed back to the return terminal to provide feedback. Amplifiers may be added to the output of the CR network and the feedback circuit to provide isolation. The first and second resistors for adjusting the notch frequency may be separately installed in a detachable disk unit which includes the mechanism to be servo-controlled. As a result, the notch frequency can be efficiently adjusted by replacing only two fixed resistors or by adjusting the variable resistor, and the cost of the disk unit can be reduced.

Infrared filter using cholesteric liquids

Abstract: A high precision optical filter includes a wideband filter element and a cholesteric liquid crystal notch filter element. In one embodiment, a wideband infrared filter (10) blocks infrared wavelengths beginning at a nearly visible corner wavelength and a cholesteric liquid crystal filter (12) blocks transmission of infrared wavelengths in a precise narrow band that includes the corner wavelength and that extends down to visible wavelengths. The liquid crystal filter may include a polymer for maintaining maximum reflectivity of the filter near the corner wavelength over an anticipated operating temperature range. The combined optical filter may be fabricated by depositing a matched pair of liquid crystal cholesteric films (15, 20) on a glass infrared filter element (10). In another embodiment, an optical filter according to the invention forms an eyepiece in a night vision goggles assembly for blocking visible light. The filter may also be mounted on a display device to block the transmission of undesirable infrared emissions at the source.

Continuously adaptive phase locked loop synthesizer

Abstract: A continuously adaptive phase locked loop synthesizer is disclosed in which error correction pulses from a phase detector are separated into narrow pulse width and wide pulse width pulses. The wide pulse width pulses are coupled to the loop filter to enable a rapid charge of the loop filter to provide a VCO control voltage on a control line connected to the output of the loop filter. The narrow pulse width pulses are filtered by a narrow bandwidth filter before being applied to the loop filter thus enabling a slow charge of the loop filter. The narrow bandwidth filter is decoupled from the control line but referenced to the control line voltage.

Optical receiver circuit including a filter network to minimize noise

Abstract: A receiver circuit for receiving a modulated optical signal and for generating a corresponding electrical signal comprises a photodiode (1) for receiving the optical signal and for generating a first modulated electrical signal. An amplification circuit (3) receives the first electrical signal or a signal related thereto via an n stage (where n is an odd-integer) filter network (2) connected between the photodiode (1) and the amplification circuit (3). The output from the amplification circuit is fed to a first equalization amd noise filter (5). The characteristics of the filter network are such that the total thermal noise power output of the first noise filter is substantially minimized.

Operational transconductance amplifier programmable filter

Abstract: A general biquadratic filter circuit is described which uses operational transconductance amplifiers. A bias current controls the transconductance (gm) of the amplifiers which in turn control the corner frequency (Wo) of the circuit. The circuit is configured with three potential sources which can be preselected to either be at a ground level or at a desired voltage level. By preselecting which of the potentials are grounded and which are at a desired voltage level, the circuit can become either a lowpass, highpass, bandpass or notch filter.

A novel technique for the reduction of capacitance spread in high-Q SC circuits

Abstract: A novel realization of a switched-capacitor (SC) integrator is proposed. The integrator attenuates the input during both clock phases, so that the time constant of the integrator is realized with the product of two capacitance ratios instead of a single capacitance ratio. The capacitance spread only increases as the square root of the time constant. This integrator is stray-insensitive. The influence of the finite DC-amplifier gain and dynamic settling is the same as in conventional SC integrators. A low-pass notch SC biquad is presented as an example to show the capacitance advantage of the integrator. The example also shows that the increase of amplifier offset is small if the total offset of the entire SC filter is considered. It is shown that the SC low-pass notch biquad reduces the total capacitance by a factor of more than three. >

Adaptive precompensators for flexible-link manipulator control

Abstract: The application of input precompensators to flexible manipulators is considered. Frequency domain compensators color the input around the flexible mode locations, resulting in a bandstop or notch filter in cascade with the system. Time domain compensators apply a sequence of impulses at prespecified times related to the modal frequencies. The resulting control corresponds to a feedforward term that convolves in real-time the desired reference input with a sequence of impulses and produces a vibration-free output. An adaptive precompensator can be implemented by combining a frequency domain identification scheme which is used to estimate online the modal frequencies and subsequently update the bandstop interval or the spacing between the impulses. The combined adaptive input preshaping scheme provides the most rapid slew that results in a vibration-free output. Experimental results are presented to verify the results. >

Band-Elimination Filter

Abstract: A band-elimination filter (BEF) that includes a coaxial dielectric resonator block, a substrate, and first, second, and third inductance elements. The coaxial dielectric resonator block includes inner conductors and an outer conductor, and forms coaxial dielectric resonators. The first inductance element is between a signal transmission path connected to one of the coaxial dielectric resonators via a series resonant capacitor and a signal transmission path connected to the other one of the coaxial dielectric resonators via a series resonant capacitor. The second inductance element is between one end of the first inductance element and the ground, and the third inductance elements is between the other end of the first inductance element and the ground.

Electrically-tunable bandpass filter

Abstract: A bandpass filter is disclosed which may be used in a superheterodyne receiver in front of the first mixer. The bandpass filter provides a narrow front end filter which is tuned automatically as the local oscillator frequency is changed. In the present exemplary embodiment, a series tuned reflective notch filter is coupled to a node of a balanced resistive bridge in such a manner that the tuned circuit presents a short circuit to the node at the filter's resonant frequency to thereby assure a maximum transfer of signal from the input to the output of the circuit at a desired frequency. At all other frequencies, the series tuned reflective notch filter will present essentially an open circuit across the node of the resistive bridge so that the node is balanced and no transmission occurs. The inclusion of the series reflective notch filter thereby produces a bandpass characteristic from the circuit input to output. By using back to back varactor diodes in the reflective notch filter, the center frequency of the passband can be changed by changing the tuning voltage applied to the varactors. In the configuration of the present invention, the varactor diodes are protected from high signal levels which are not within the narrow passband of the filter. For this reason, the filter is inherently less susceptible to the generation of intermod products than filters of a conventional design.

Tunable UHF filter for switchable VHF/UHF receiver

Abstract: A tunable/switchable notch filter adapted for use in the front end of a television receiver removes an image frequency on the low side of the UHF passband without degrading desired frequencies. The tunable/switchable notch filter can be switched out when in a VHF mode so as not to degrade VHF performance and switched in for UHF operation for filtering out a difference image frequency which varies with and is a predetermined frequency less than the desired UHF signal.

Data modem receiver

Abstract: In a data modem receiver (80) the received signal is digitized in an A/D-converter (84), the output of which is applied to notch filter means (88, 96) which eliminates secondary channel signals, and which applies an output signal to a pair of IIR filters (112, 116), responsive to the frequency components present in a training signal. The values of the IIR filter output sigals are determined and compared with a pair of threshold levels provided by a threshold setter circuit (152) responsive to the peak received signal level to detect the receipt of a training signal. In response to the detection of a training signal, DFT calculations are initiated for timing recovery and modem address identification, using samples stored in a buffer shift register (206). A gain control circuit (220) is located subsequent to a band-pass filter (212) coupled to the buffer shift register (206).

Tracking harmonic notch filter

Abstract: An electronic filter for automatically tracking and removing harmonically lated interfering electrical signals such as power line interference harmonics without attenuating other signals of interest even though the signals are frequency stable and/or near the interference signal frequencies. The filter comprises a very narrow band electronic commutated capacitor-bank comb-notch filter driven by a counter/decoder circuit which is in turn driven by a phase locked loop. The filter also comprises two narrow band analog filters tuned to the two lowest harmonics of the interfering signal. The summed output of these two filters is applied to the input of the phase locked loop. The phase locked loop locks to the proper multiple of the interfering signal and drives the comb-notch filter at a frequency which causes it to generate notches at unit multiples of the fundamental of the interference frequency. This action is continuous such that center frequencies of the notches are automatically adjusted to compensate for small variations in the interference frequency.

Multiple bandwidth filter system for phase locked loop

Abstract: A method and apparatus for combining a plurality of different filtering paths of varying bandwidth to provide selectable bandwidth signal filtering without transients caused by initialization of filter components. The signal to be filtered is applied to a plurality of parallel connected passband filters ranging from a widest passband filter to a narrowest passband filter. The bandwidth of the parallel filter combination is progressively narrowed by sequentially holding the output level of each of the filters in declining order of their passband frequency range, beginning with the widest passband filter, until all of the output levels of the filters are held constant except for the narrowest passband filter. This filter system is especially adapted for use as a loop filter in a phase locked loop control system incorporated in a data storage disc drive.

Radio receiver circuit with tuning feedback control for a tunable bandpass filter

Abstract: A zero-IF radio receiver circuit comprises an input filter (3), quadrature mixers (9,10), d.c.-blocking capacitors (24,26) and a demodulator (22). The circuit is partly integrated on a semiconductor chip and an inductive component of the input filter comprises one or more of the chip bond-wires. In order to compensate for the inevitable variation of the inductance of these bond-wires from circuit to circuit part of the signal from the local oscillator (12) is added to the input signal before its application to the input filter and the d.c. component of the resulting output from one mixer (10), which component is representative of the phase shift of the local oscillator signal produced by the input filter and hence of any tuning error of this filter, is applied to a tuning control input (30) of the filter to reduce the error. Alternatively the tuning control signal may be adjusted to maximize the sum of the squares of the d.c. components of the signals in the two IF channels and hence minimize the attenuation produced by the input filter.

Single balanced mixer with output filter

Abstract: A balanced mixer and output filter for television receivers and the like is presented. The mixer is followed by a fairly selective bandpass filter to protect the IF amplifiers from first and second adjacent channel signals.

A roll eccentricity sensor for steel-strip rolling mills

Abstract: The problem of roll eccentricity compensation in steel-strip rolling mills is examined. A novel roll eccentricity sensor is proposed for the task of retrieving the desired reference signal from the available roll-force measurement. The sensor implements a modified comb filter structure which can be arranged in either tunable or adaptive form. Simulation results based on typical experimental data indicate that the proposed sensor is appropriate and offers distinct advantages over other methods. The proposed comb filter is new in the sense that it consists of a number of second-order notch filter models with specially constrained bandwidth characteristics. An approximate gradient-based adaptive algorithm is used for the frequency estimation. The important feature of such an algorithm is that it is robust and is simple to implement. The advantages of the sensor include fast convergence and accurate parameter estimates. No extra positional sensors are required since this information can be easily obtained from the phase estimates. Finally, the sensor is not based on approximate mill models; it treats the problem as a harmonic series buried in noise. The resulting solution is based on time domain measurements that characterize the mill roll eccentricity conditions during operation. >

Frequency interpolation filter bank

Abstract: A technique is presented for designing a bank of filters with the interpolating property: given N arbitrary frequencies (f/sub m/), the mth filter has unity response at the frequency f/sub m/ and zero response at the other frequencies. The filter bank realization may be viewed either as a statistic digital filter or as an adaptive filter wherein N oscillators are summed with time-varying complex weights; the modulated weights represent the filter bank outputs. These filter banks are useful as front-end processors for telephone tone receivers, acoustic signal processing, and general spectrum analysis. >

Design of optimal FIR raised-cosine filters

Abstract: A design criterion is given to obtain square-root raisedcosine FIR filters with maximum stopband attenuation and low peak distortion. The filter coefficients can be evaluated easily and the optimal filter parameters can be obtained with tables. The design method is very simple and suited for users not oriented to filter design.

A notch-filter network for wide-band measurements of transient voltages on the power line

Abstract: A voltage probe to measure power-line disturbances in a broad frequency range in the presence of high-amplitude transients is described. Design options and experimentally verified performances are shown. The design is based on the sharp suppression of the fundamental AC power frequency by means of an RC notch filter, whereas all other frequencies are passed from a very low-3-dB limit of 300 Hz to a very high upper limit of 1 GHz. The intrinsic high-frequency limitations of the low-frequency notch circuit are overcome by means of a coordinated parallel high-frequency path. The combination of the two is capable of extremely wide frequency response (in excess of 6 decades) with excellent flatness, within fractions of a decibel in the passband. This voltage probe also satisfies requirements of high linearity and low phase distortion. The other performance parameters (such as in-band attenuation, input impedance, power frequency rejection, power dissipation, and dimensions) are equal to or better than those of the relatively narrow bandwidth voltage probes currently specified in standards and regulations. >

Hybrid form digital filter

Abstract: A hybrid form digital filter. A digital filter is provided wherein the zeros of its transfer function are provided by a direct form digital filter portion and the poles of the transfer function are provided by a normal form digital filter portion. The hybrid filter provides truncation noise and stability characteristics like those of a normal form digital filter, but its filter coefficients may be calculated more rapidly than those for a normal form digital filter having the same transfer function, thereby enabling the coefficients to be calculated in real time for tuning the filter. While the preferred embodiment is a second order hybrid digital filter, the same principles are applicable to higher order digital filters as well.