Showing papers on "Low-pass filter published in 1991"

Analysis of the properties of median and weighted median filters using threshold logic and stack filter representation

Abstract: The deterministic properties of weighted median (WM) filters are analyzed. Threshold decomposition and the stacking property together establish a unique relationship between integer and binary domain filtering. The authors present a method to find the weighted median filter which is equivalent to a stack filter defined by a positive Boolean function. Because the cascade of WM filters can always be expressed as a single stack filter this allows expression of the cascade of WM filters as a single WM filter. A direct application is the computation of the output distribution of a cascade of WM filters. The same method is used to find a nonrecursive expansion of a recursive WM filter. As applications of theoretical results, several interesting deterministic and statistical properties of WM filters are derived. >

Recursive regularization filters: design, properties, and applications

Abstract: Least squares approximation problems that are regularized with specified highpass stabilizing kernels are discussed. For each problem, there is a family of discrete regularization filters (R-filters) which allow an efficient determination of the solutions. These operators are stable symmetric lowpass filters with an adjustable scale factor. Two decomposition theorems for the z-transform of such systems are presented. One facilitates the determination of their impulse response, while the other allows an efficient implementation through successive causal and anticausal recursive filtering. A case of special interest is the design of R-filters for the first- and second-order difference operators. These results are extended for two-dimensional signals and, for illustration purposes, are applied to the problem of edge detection. This leads to a very efficient implementation (8 multiplies+10 adds per pixel) of the optimal Canny edge detector based on the use of a separable second-order R-filter. >

Spread spectrum receiver

Abstract: A spread spectrum receiver has first and second correlators which each compare a received signal with a respective reference signal. The output of each correlator is routed through a respective band pass filter and a respective AGC amplifier to a respective detector circuit which converts the output of the amplifier into a respective base band signal. The ouput of each detector circuit is supplied to a respective peak value detecting and holding section, which detects and holds for a predetermined time period peak values from the associated detector circuit. Each peak value detecting and holding circuit supplies the peak value currently held therein through a respective low pass filter which serves as an integrator to a data comparing section and to an adding section. The adding section adds the two peak values, and supplies the sum to control inputs of each of the AGC amplifiers for purposes of gain control. The data comparing circuit compares the peak values and produces an output which is demodulated data from the received signal.

On optimal infinite impulse response edge detection filters

Abstract: The authors outline the design of an optimal, computationally efficient, infinite impulse response edge detection filter. The optimal filter is computed based on Canny's high signal to noise ratio, good localization criteria, and a criterion on the spurious response of the filter to noise. An expression for the width of the filter, which is appropriate for infinite-length filters, is incorporated directly in the expression for spurious responses. The three criteria are maximized using the variational method and nonlinear constrained optimization. The optimal filter parameters are tabulated for various values of the filter performance criteria. A complete methodology for implementing the optimal filter using approximating recursive digital filtering is presented. The approximating recursive digital filter is separable into two linear filters, operating in two orthogonal directions. The implementation is very simple and computationally efficient. has a constant time of execution for different sizes of the operator, and is readily amenable to real-time hardware implementation. >

ECG muscle artifact filter system

Abstract: A filter system for removing small amplitude, high frequency signals such as muscle artifact signals from an ECG signal is provided. The filter system includes a low pass filter with variable cutoff frequencies, an electronic delay and a system for detecting the R wave in the ECG signal and determining the variable cutoff frequency in response to the detection of the R wave. A digitized input ECG signal is simultaneously presented to the electronic delay and the system for detecting the R wave. During the portion of the ECG signal exclusive of the QRS complex, the filter is operated at a low cutoff frequency to filter the muscle artifact signals for a maximum smoothing effect. At a time slightly prior to the on set of the QRS complex, the cutoff frequency is rapidly incrementally increased to a higher cutoff frequency to pass the QRS complex with a minimum reduction of amplitude of the QRS signal. At the end of the QRS signal, the cutoff frequency of the filter is rapidly incrementally returned to the low cutoff frequency.

Realization of a 1-V active filter using a linearization technique employing plurality of emitter-coupled pairs

Abstract: A low voltage (1 V), low-power (100 mu W), and low-frequency (9 kHz) fifth-order fully integrated active low-pass filter (LPF) using a bipolar technology is described. Novel highly linear transconductors consisting of N emitter-coupled pairs were designed for low-voltage operation. The linear input range is expanded to about 100 mV/sub p-p/ at 1% error with N=4, which is about twice that of the conventional linearization technique. The filter is basically a gyrator-capacitor type, in which gyrators are implemented by using the linearized transconductors. Large time constants were realized with very low current (540 nA/transconductor) owing to the high transconductance-to-operating-current ratio of the linearized transconductors. Measured results show a passband ripple of 1.5 dB, a minimum stopband rejection of 70 dB, and a dynamic range of 56 dB, despite a very high nominal impedance (400 k Omega ). Practical limitations of this approach are also discussed, such as the sensitivity of the linearized transconductors against process variations, noise, and frequency limitations. >

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. >

Current-mode allpass filter using FTFN with grounded capacitor

Abstract: A novel circuit configuration for the realisation of a current-mode first-order allpass filter using a single four-terminal floating nullor (FTFN) with a grounded capacitor, which is suitable for integrated circuit implementation, is proposed.

All-fiber filter for efficient dispersion compensation.

Abstract: A dispersive filter is proposed that is based on the coupling, with a chirped periodic perturbation, of two copropagating waveguide modes that have different group velocities. Numerical calculations show that a nearly constant dispersion can be obtained over the filter bandwidth. Pulse recompression by a factor of 10 or more is possible. The filter could be made with photoinduced refractive-index gratings in optical filters.

Activity monitoring apparatus with configurable filters

Abstract: An activity monitor adapted to be worn on the non-dominant wrist of a subject includes a bimorphous beam motion sensor. The output signal of the sensor is amplified in an amplifier circuit having a selectable amplification factor, and filtered by highpass and lowpass filter circuits having individually selectable cut-off frequencies to obtain an analog signal for processing having a bandpass and amplitude characteristic corresponding to a particular body activity under observation. A control and processing circuit within the monitor includes a microprocessor which responds to either resident internal operating instructions or to externally supplied operating instructions, or to designated data signal parameters, to provide configuration control signals to the amplifier and filter circuits, and processing of the collected data, appropriate to the particular activity being monitored. The processed data is digitally stored in an internal memory for subsequent transfer through a data port to an associated computer for display or further processing.

A continuous-time current-mode integrator

Abstract: The authors propose a continuous-time current-mode integrator that offers potential advantages for both higher frequency and lower power monolithic filtering applications. Owing to the small voltage swings inherent in current-mode circuits, the integrator time constant is determined by a small-signal transconductance and an additional MOSFET gate capacitance, while good linearity is maintained using a standard 2- mu m digital CMOS technology. Simulation results predict passband cutoff frequencies exceeding 30 MHz for a five-pole low-pass filter dissipating as little as 2 mW/pole with a 5-V power supply. >

Method of reducing block artifacts created by block transform compression algorithms

Abstract: A method of improving image quality when using block transform image compression algorithms by applying a variable lowpass filter (blur) operation on block boundaries that is based on the coefficients of the transformed data. The method of reducing block artifacts results from adaptively blurring the block boundaries based on the frequency content of the blocks. Low frequency blocks are heavily blurred, while high frequency blocks should have very little blur.

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.

Balanced low-pass common mode filter

Abstract: A balanced L-section low-pass common mode filter is connected in series with balanced data I/O lines to remove common mode signals from balanced line difference mode signals. The filter includes input and output series transformers configured so that the magnetic fields in the transformers are subtractive for out-of-phase difference mode signals and additive for in-phase common mode signals and a shunt transformer coupled to ground configured so that the magnetic fields in the transformer are additive for out-of-phase difference mode signals and subtractive for in-phase common mode signals. Accordingly, the difference mode signals are not attenuated and common mode signals react to a short circuit to ground and are thereby attenuated by the filter.

Universal active current filters using single second-generation current conveyor

Abstract: Two novel universal active current filters, one of which has multiple outputs and the other of which has a single output and high output impedance, employing a single negative second-generation current conveyor, three position-fixed capacitors and four/five position-fixed resistors are proposed. The proposed networks with the advantages of low passive sensitivities can obtain second-order lowpass, bandpass, highpass, notch and allpass current signals by adjusting the magnitudes of a grounded resistor and a grounded capacitor provided that another resistor is separable. The resonance angular frequency and quality factor are insensitive to the current tracking error of the nonideal CCII–.

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.

Electrolytic capacitor elimination in power electronic system by high frequency active filter

Abstract: The application of a high frequency current-fed type active filter for elimination of electrolytic capacitor in the DC link of an inverter is described. The active filter operation has been described, preliminary analysis and design have been made, and simulation studies have been made in detail for a three-phase inverter in PWM and square-wave modes and a single-phase inverter in PWM mode to prove the feasibility of concepts. The study indicates that it is possible to eliminate the unreliable electrolytic capacitor by high frequency active filter. >

Television signal scanning line converting apparatus

Abstract: A television signal scanning line converting apparatus, where an intra-frame average signal and inter-frame average signal are obtained by processing a progressive scanning signal in a unit of two frames with a delaying circuit and adders. A lowpass filter limits the horizontal and vertical bands of an intra-frame difference signal to reduce the field amount. If the input progressive scanning signal is a moving picture, the low vertical range of the intra-frame difference signal will be multiplexed to the high vertical range part of the intra-frame average signal and the high vertical range of the intra-frame difference signal will be transmitted separately so that the resolution of the moving picture will improve and no deterioration, caused by the turning distortion, will be produced.

Predictive FIR filters with low computational complexity

Abstract: New families of finite-impulse-response (FIR) digital filters with low computational complexity are presented. The filters are extensions of the recursive running sum. Each family of filters predicts points along a characteristic polynomial. Closed-form equations are given in both time- and frequency-domain for filters corresponding to first- and second-order polynomial models. Block diagrams for efficient implementation structures are given. The first-order predictive filters require three multipliers and five adders, and the second-order predictive filters require five multipliers and twelve adders, irrespective of the filter length. The filters exhibit low-pass characteristics with the passband shape controllable by a single parameter. The frequency and phase responses are discussed. A design example is given showing how the filters can be used as building blocks to obtain effective linear-phase low-pass filters. >

System and method employing predetermined waveforms for transmit equalization

Abstract: A data communication system employing predetermined equalized waveforms for transmit equalization is disclosed. Serial NRZ data is received from a network controller and utilized to select from memory its equivalent as predistorted and filtered Manchester encoded data. Predetermined waveforms in memory are representative of the analog waveform produced when predistorted digital Manchester encoded data is passed through a high order transmit filter. Data from memory drives a digital to analog converter (DAC) to reconstruct the waveforms into analog form. A line driver having an integrated single pole low pass filter impresses the equalized waveform on to the transmission line.

CCII-based continuous-time filters with reduced gain-bandwidth sensitivity

Abstract: Some new MOSFET-C integrators and CMOS current conveyors for realisations of the ladder filters are proposed These integrators require smaller capacitance than with those currently used The integrators also provide a better high-frequency performance in terms of gain and phase error responses A sixth-order bandpass ladder filter, with 460 KHz centre frequency, 05 dB ripple, and ripple bandwidth 120 KHz, is designed and simulated A third-order lowpass filter, with 2 dB ripple and 50 KHz ripple bandwidth, is experimentally demonstrated The results reported in the paper will be useful in the realisation of high-frequency integrated continuous-time filters

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. >

A programmable mixed-signal ASIC for power metering

Abstract: A programmable mixed analog-digital integrated circuit for use in power-metering applications is described. The IC acquires analog input signals from three pairs of voltage and current sensors and provides outputs proportional to RMS voltages and currents: real, reactive, and apparent power; and power factor, phase angle, and frequency. Combinations of two of the metering functions may be computed simultaneously and outputs are provided in both bit-serial digital and pulse-width-modulated formats. Sensor and analog-to-digital converter errors are corrected using programmable digital signal processing. To achieve accurate operation over a wide, continuous range of frequencies. the IC measures the frequency of its input signals and adjusts filter characteristics and calibration coefficients accordingly. The device has been fabricated in a 5-V 1.5- mu m CMOS process and, with gain calibration alone, has achieved an absolute metering accuracy of 0.04%. >

Method and circuit for automatic outphasing

Abstract: The invention refers to an automatic dephasing method with the phase φ= kx360 degrees/N, where k = 0,1,...N-1, in a narrow frequency band and with a dephasing circuit with 120 degrees, with application of the method for the case N=3, k=1. The method is based on an automatic control loop of the phase, where the control is made in order to maintain a constant dephasing of 0 degree between frequency multiples of order N of the inlet signal and the dephased signal.The 120-degree dephaser, achieved with a voltage controlled dephasing circuit (cell with "low pass" type transfer function and with TEC used with variable resistance), uses two identical PLL circuits for the multiplication by 3 of the frequency and the phases of the inlet and outlet signals. The correction signal from the phase sensitive detector ("with 3 states") amplified and integrated, commands the dynamic resistance of TEC and thus the dephasing inserted by the circuit, so that the frequency multiples of order 3 of the inlet and outlet signals to be in phase. The working domain of frequency of the dephaser is limited by the capture band of the PLL circuits.The circuit is not modifying the outlet signal amplitude and allows the maintenance of a constant dephasing (120 degree) between the inlet and outlet signals, independent of the frequency fluctuations of the signal or of the variation of the parameters, with temperature or in time, of the components, thus eliminating the need of control.The 120 degree dephased circuit can be used within the frame of devices which are measuring with precision the symmetrical components of voltage and current in a three-phased system with asymmetric sinusoidal magnitudes, for example in a wattmeter for three-phased alternating current in the range 35...75 Hz.

High order switched-capacitor filter with dac input.

Abstract: A digital-to-analog converter includes a delta-sigma modulator (10) that receives a digital input and converts it to a one-bit digital output stream. A fourth order switched-capacitor filter (12) is operable to receive the one-bit digital stream and convert it to an analog value int he sampled data domain. This is input to a switched-capacitor/continuous time buffer (14) which is then filtered by an active low pass filter (18) to provide an analog output. The switched-capacitor filter (12) includes four stages of integration (24), (30), (34) and (38). A one-bit DAC (20) is provided for converting the one-bit digital stream to an analog value. The one-bit DAC (20) is integral with the first stage of integration and is summed by a summing junction (22) with the output of the forth stage of integration (38). In this manner, the first stage of integration (24) is operable to influence or reduce the noise output by the fourth stage of integration (38), thus resulting in a low noise high order switched-capacitor filter.

A system identification algorithm using orthogonal functions

Abstract: An adaptive filter (ADF) structure is proposed for applications in which large-order ADFs are required. It is based on modeling the impulse response of the system to be identified as a linear combination of a set of discrete Legendre orthogonal functions. The proposed adaptive filter structure has desirable stability features and a unimodal mean-square error surface as well as a modular structure that permits an easy increase of the filter order without changing the previous stages. Computer simulations in which the proposed structure is used to identify actual acoustic echo path impulse responses show that the Legendre ADF has better convergence performance than the transversal ADF when identifying systems with long impulse response. >

Continuous-time filter tuning circuit and method

Abstract: A tuning circuit (18) for tuning an integrated circuit filter, such as a continuous-time MOSFET-C filter (12), is disclosed. The tuning circuit includes a switched-capacitor network (20) having a capacitor (I) which matches the capacitor used in the filter (12) to be tuned. Also included is a transistor (M) which matches the transistor used in the filter. The switched-capacitor network has a effective resistance which is a function of the switching rate of the network. Feedback circuitry is included which produces a control signal used to vary the small signal resistance of the transistor to match the effective resistance of the switched-capacitor network. The filter is tuned by varying the rate of which the switched capacitor network is clocked thereby changing to effective network resistance. The control voltage (Vc) responds by forcing the transistor resistance to match the new effective resistance of the switched-capacitor network. The control voltage is used to tune the filter and changes to compensate for variations in the filter capacitor and transistor, which track variations in the filter transistor and capacitor.

Harmonic and subharmonic filter

Abstract: A harmonic and subharmonic filter is coupled between a high power RF energy source and a non-linear RF load via a matching network, such as a plasma chamber. The filter passes high power RF energy in a band centered on a predetermined radio frequency, i.e., 13.56 MHz, but blocks and attenuates out-of-band energy at frequencies which are multiples of or fractions of the predetermined frequency. The harmonic and subharmonic filter comprises an input terminal, an output terminal, a series LC resonance path connected between the input and output terminals, and tuned to the predetermined radio frequency, a series resistive path formed of first and second resistors, and a parallel LC resonance path between the junction of the two resistors and ground.

2-D FIR filter design for sampling structure conversion

Abstract: The design of 2-D finite impulse response (FIR) digital filters is presented for two-dimensional sampling structure conversion Both the sampling structure model and the filter characteristics have been chosen to cover a large class of problems related to multidimensional linear processing for video signals Optimal infinite and finite precision filter design methods are proposed Experimental analysis concerning the effects of coefficient rounding on the filter frequency response was carried out, which was found to be consistent with previous theoretical results A simulation with one test picture is presented to illustrate the problem of sampling structure conversion >

Focusing filters for wide-band direction finding

Abstract: A time-domain equivalent of the coherent signal-subspace transformations (CST) is established for wideband direction finding in a possible multipath environment using general arrays. Time-domain equivalents of focusing are derived based on the least squared error approach for general transformations, and the Taylor series expansion approach for closed-form transformations. The preprocessor is realized by a multichannel digital finite impulse response filter. For diagonal transformations, the problem reduces to implementing different delays at each sensor, which in turn leads to computational simplicity. Various tapped delay line filters for realizing an arbitrary delay are proposed and compared. Simulation results reveal that low-order filter structures in the time domain achieve similar performance to the frequency domain approach, even at detection and resolution thresholds. >