Showing papers on "Voltage-controlled filter published in 1995"

Single-phase active power filters for multiple nonlinear loads

Abstract: This paper presents active power filters for single-phase power systems which are comprised of multiple nonlinear loads. The paper provides background on the operation of the filter, the details of the power circuit, the details of the control design, representative waveforms, and spectral performance for a filter which supports a 384 W AC controller and a 900 W uncontrolled bridge rectifier. Experimental data indicate that the active filter typically consumes 3% or less of the average load power, suggesting that a parallel filter is an efficient compensation approach. The spectral performance shows that the active filter brings the system into compliance with IEC-555 for decision frequencies in excess of 30 kHz. A discussion is presented outlining an alternative single-phase active filter which uses two controllable switches and is based on a half-bridge topology. >

Fiber-optic tunable microwave transversal filter

Abstract: A fiber-optic finite impulse response filter with continuously tunable unit time delays is developed and studied. The filter consists of eight taps with progressively longer segments of high-dispersion fiber, but completed with dispersion-shifted fiber to nominally identical overall lengths. The time delays through each tap are tuned by varying the wavelength of the optical carrier. The constructed 8-tap filter exhibits bandpass characteristics with a Q of 30. The bandpass band is continuously tuned over a full octave from under 9 GHz to over 18 GHz with a single low-voltage control signal that demonstrates the technique's applicability to adaptive systems. >

Design and implementation of a hybrid series active filter system

Abstract: A hybrid series active filter system has been designed, built and installed at Beverly Pump Station in New England Electric Power Company utility for 765 kVA, 480 V adjustable speed drive load to comply with IEEE 519 recommended harmonic standards. The series active filter has a small rating-35 kVA which is 4% of the load kVA-and is controlled by a synchronous reference frame (SRF) based controller. The hybrid series active filter system is controlled to act as a "harmonic isolator" between the supply and load. This paper discusses the SRF controller implementation issues, design considerations of the series coupling transformer and protection issues of the small rating series active filter inverter. Operation of the series active filter under off-tuned passive filter conditions is investigated. The effectiveness of the series active filter to provide harmonic damping and the use of simpler and low cost passive filter structures such as power factor correction capacitors is demonstrated by laboratory experimental results. Field installation results demonstrate the practical and economic viability of hybrid series active filter systems for harmonic compensation of large nonlinear loads to comply with IEEE 519 recommended harmonic standards. >

Vibration/noise active control system for vehicles

Abstract: A vibration/noise active control system for automotive vehicles which generates a canceling signal for canceling vibrations and noises generated within the compartment of the vehicle, based on a reference signal related to the vibrations and noises by means of an adaptive filter. The canceling signal is converted into a canceling sound. The adaptive filter has a filter coefficient thereof changed based on the cancellation error between the canceling sound and the vibrations and noises within the compartment, detected by an error sensor, and the reference signal. A memory stores a plurality of filter coefficient values of the adaptive filter corresponding to a plurality of predetermined traveling conditions of the vehicle. A discriminator reads out a filter coefficient value of the adaptive filter corresponding to the detected predetermined traveling condition of the vehicle, supplies the read-out filter coefficient value to the adaptive filter to generate the canceling signal, and stores a filter coefficient value of the adaptive filter which has been changed based on the generated canceling signal.

Programmable two-part matched filter for spread spectrum

Abstract: A spread-spectrum-matched-filter apparatus including a code generator, a programmable-matched filter, a frame-matched filter, and a controller. The code generator generates replicas of a pilot-chip-sequence signal and a data-chip-sequence signal, which are used to set the programmable-impulse response of the programmable-matched filter. The programmable-impulse response is alternately changed between that of the pilot-chip-sequence signal and the data-chip-sequence signal so that the programmable-matched filter alternately detects the pilot-spread-spectrum channel and the data-spread-spectrum channel embedded in a received spread-spectrum signal. The frame-matched filter detects a despread-pilot-bit-sequence signal and generates a peak-pilot-correlation signal which can be used for timing of the controller as to when to trigger changing the programmable-impulse response of the programmable-matched filter.

A series active power filter which compensates current harmonics and voltage unbalance simultaneously

Abstract: An active power filter connected in series to the power distribution system is presented and analyzed in this paper. The series active power filter is implemented with a PWM voltage-source inverter and operates in conjunction with a resonant LC filter connected in parallel to the power lines and is able to compensate current harmonics and the fundamental negative and zero sequence voltage components generated by nonlinear unbalanced loads. The proposed series active power filter also compensates zero sequence current harmonic components that flow through the neutral conductor. In particular, the active power filter is discussed in terms of the principles of operations under steady-state and transient operating conditions. The design of the power and control circuits are reported. >

Filtering of harmonic currents and damping of resonances in power systems with a hybrid-active filter

Abstract: A novel hybrid-active filter topology to minimize electric utility current harmonics at high power levels is presented in this paper. The proposed topology combines both passive and active filters to obtain the lowest power converter VA rating as compared to the power converter rating in the active filter and the series-active hybrid filter configurations. This is demonstrated with experimental results from a laboratory model. Transient and steady state operation of the hybrid-active filter is also presented. The control of the proposed filter is extended to provide damping of resonances due to neighboring loads. Simulation results showing the effect of active damping are presented. >

Control method for a combined active filter system employing a current source converter and a high pass filter

Abstract: This paper describes a control method with a combined filter system which senses load current, source current, and line voltage to create reference signals for an active filter. The transfer function of the active filter is identified and is used for the control system design. It is shown that the source current feedback is most effective in suppressing the harmonic-enlarging effects due to parallel resonance and the harmonic current generated by source harmonic voltages. A small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results. >

High input impedance filters with low component spread using current-feedback amplifiers

Abstract: A new configuration for high input impedance bandpass, lowpass and highpass filters with low component spread using two current-feedback amplifiers is presented. It has the following features: orthogonal control of the natural frequency and quality factor by grounded resistors or capacitors, simple conversion into a voltage-controlled filter, minimum active components, low active and passive sensitivities, low component spread suitable for high-Q applications and low output impedance. Experimental results are given to demonstrate the feasibility of the proposed circuits. >

Universal filter using two current-feedback amplifiers

Abstract: A new universal filter using two current-feedback amplifiers is presented. This filter can realise lowpass, bandpass, highpass, notch and allpass filters from the same configuration. It has the following features: orthogonal control of the natural frequency and quality factor by grounded resistors, easy conversion into a voltage-controlled filter, minimum active components, without match components except for allpass applications, low active and passive sensitivities, and cascadability. Experimental results that confirm the theoretical analyses are obtained.

Current mode universal filter

Abstract: A low sensitvity current mode filter circuit which realises highpass, bandpass and lowpass responses is proposed.

A transfer function approach to harmonic filter design

Abstract: This paper details a new transfer function approach in passive harmonic filter design for industrial and commercial power system applications. Filter placement along with six common filter configurations are presented. Harmonic impedance, voltage division and current division transfer functions are derived and used in a practical filter design procedure which incorporates IEEE-519 distortion limits directly into the design and component specification process. A simple four step filter design procedure is outlined and used in a variable speed motor drive pumping plant application.

Universal filter using unity-gain cells

Abstract: The authors propose the use of both current and voltage followers for implementation of a universal filter. The aim is to show how, by using only unity-gain cells as active components, a universal filter can be obtained with improved performance over classical filters.

Apparatus and methods for providing combining multiple video sources

Abstract: Apparatus and methods are provided for connecting video components. In one embodiment the apparatus includes a notch filter for filtering frequencies of a first channel from a first video source, the first video source having a plurality of channels, to form a notch filter output having each of the plurality of channels except the frequencies of the first channel, a bandpass filter for filtering a second video source to pass only frequencies in a second channel in the second video source having the same frequencies as the frequencies of the first channel to form a bandpass filter output, and a summer for summing the notch filter output and the bandpass filter output to form a summed output. In another embodiment the apparatus includes a signal splitter for splitting a first input signal and providing a first and second output, the second output coupled to and providing the first video source into the notch filter.

The use of multirate notch filters in embedded-servo disk drives

Abstract: This paper explores the merits of using a discrete time multirate notch filter,in series with an FIR filter, for controlling a flexible mechanical system whose resonance is beyond one-half the servo sample rate (in other words, an aliased resonance). Through numerical optimization of the closed loop transient response, the performance of this architecture is compared to that of a single-rate notch with an FIR filter, and that of an FIR filter alone. For the specific example chosen here, it is seen that the multirate notch gives results that are far superior to either of the alternatives.

New current-feedback amplifier-based universal biquadratic filter

Abstract: A new universal biquadratic filter configuration using two current feedback amplifiers (CFA's) is presented. The proposed configuration can realize the second-order lowpass, bandpass, highpass, notch and allpass filters. Both the active and passive sensitivities are no more than unity. The natural frequency /spl omega//sub 0/ can be controlled by a grounded capacitor. The quality factor Q can also be independently controlled by a resistor. Moreover, the quality factor will be insensitive to the current tracking errors and output voltage tracking errors of the CFA's. Experimental results that confirm the theoretical analysis are obtained. The results are useful in analog filtering applications. >

A design framework for low power analog filter banks

Abstract: We detail the design of multiresolution analog filter banks, linear models of cochlear function, with power dissipation being a prime engineering constraint. We propose that a reasonable goodness criterion is the information rate through the system, per watt of power dissipated. Speech applications requiring filter banks with a wide frequency tuning range, from 20 Hz to 20 kHz, and low power consumption make the transconductance-C integrator in subthreshold CMOS the preferable integrator structure. As an example, the dynamic range of a lowpass filter is computed and subsequently used to design a filter bank that models faithfully cochlear micro-mechanics. The power consumption of the entire filter bank is computed from analytical expressions and is estimated as 355 nW, at 68 kb/s overall information rate at the output of the system.

Resonator filter with variable tuning

Abstract: An advantageous embodiment of the invention is the filter of the receiver branch of the duplex filter in a multi-channel radio transmitter/receiver having reception and transmission bands composed of plural radio-frequency channels. In the first state of the filter, when the radio transmitter/receiver is only receiving radio signals, the width of the pass band of the filter corresponds to said reception band. In the second state, in which the radio transmitter/receiver additionally transmits radio signals, the pass band of the filter is switched by current control to cover only part of the reception band. By constructing the filter in the manner proposed it is possible to use current control in the first resonator in the filter of the receiver branch. Because of its power consumption current control is otherwise unsuitable for use in e.g. the duplex filter of a portable radio-telephone.

Toward the ideal codirectional Bragg filter with an acousto-optic-filter design

Abstract: We present a novel design scheme based on the Gel'fand-Levitan-Marchenko inverse-scattering method for an acousto-optic tunable filter having an almost-ideal bandpass spectrum. We find that the ideal filter characteristics of flat-top with unity transmission and no side-lobes are in principle asymptotically possible in a properly designed codirectional Bragg filter. We propose physical schemes of achieving such characteristics in the acousto-optic tunable filter design. Filters having this desirable characteristic are of immense importance in improving the crosstalk performance in optical networks employing the wavelength-division-multiplexing scheme. We then discuss design specifics and simulated performances, and present a new optimization formula. >

Semiconductor device with a filter formed of 3-element series-and-parallel resonators

Abstract: A 3-element series parallel resonator, which performs series resonance and parallel resonance at a predetermined frequency by a combination of three elements including an inductor and a capacitor of concentrated constants, is used as a filter. This design can reduce the circuit constant and permits a filter to be formed on a semiconductor substrate. Accordingly, various micro-wave devices, such as an amplifier which requires a filter, a frequency converter, a multiplier and signal switcher, can be designed into an MMIC on a single chip.

Multi-frequency digital low pass filter for magnetic resonance imaging

Abstract: A digital lowpass filter design for filtering nuclear magnetic resonance (NMR) signals in a magnetic resonance imaging (MRI) system supports multiple frequencies and is highly configurable without sacrificing speed and performance. The first FIR filter stage of a synchronized multirate digital filter is selected from a database of filter coefficient/parameter sets which are loaded at start time and used in place. Second (and later) FIR filter stages are fixed in the example. A large number of different filter frequencies can be selected rapidly without changing the parameterized filter program reducing the amount of time to start up the MRI system and allowing "on-the-fly" filter changes in real-time between echoes and/or A/D samples. For example, filter preselection by the host can be performed in less than 100 μs, and, one of several lowpass filters can be selected by the sequencer "on-the-fly" with a latency of less than 10 μs.

Efficient digital quadrature demodulator

Abstract: A digital quadrature demodulator for an intermediate frequency (IF) input signal with an analog-to-digital (A/D) converter having a sampling frequency fs and an input to which the IF input signal is applied where the IF input signal has a bandwith B

Low power filter coefficient adaptation circuit for digital adaptive filter

Abstract: An adaptive filter for use in disk drive systems includes coefficient adaptation circuitry operating at a slower rate than the filter and consequently at a reduced power level. The adaptive filter receives input data samples corresponding to raw data read from a disk in the disk drive system and converted to digital form and provides processed output data samples. The action of the filter is defined by characteristic filter coefficients having values that are updated by adaptation circuitry during the operation of the filter. The adaptive filter is independently clocked from the adaptation circuitry, such that the input data samples and the processed output data samples are clocked through the adaptive filter at a clock rate 1/T, and the filter coefficients are updated according to a prescribed algorithm at an update rate slower than the 1/T clock rate. Filter coefficient updating occurs preferably at a rate equal to 1/J, where J is an integer greater than unity and generally in the range of 2 to 8. The coefficient update rate is achieved by providing a separate filter coefficient adaptation clock derived from the system clock by dividing that clock by a user-programmable parameter J. This process reduces the coefficient update rate, which in turn reduces the switching frequency of the logic gates, the number of pipeline latches, and, ultimately, the power consumption.

A 3V 12-55MHz BiCMOS Continuous-Time Filter with Pseudo-Differential Structure

Abstract: In this paper a 3V 2nd order lowpass continuous-time filter is presented. The filter is based on a highly linear pseudo-differential transconductor. The input common-mode signal is cancelled at the transconductor level using a feed-forward path. The output common-mode voltage is controlled at the filter level using lossy-integrators. A prototype cell has been realized in 1.2?BiCMOS technology. The pole frequency can be tuned in the range 12-55MHz. A THD of ?40dB is achieved for signals up to lVpp at 10MHz. The dynamic range is approximately 60dB.

Low component current-mode universal filter

Abstract: A low component current-conveyor based current-mode universal filter with one input and three outputs is presented. The filter can simultaneously realise lowpass, highpass and bandpass responses. Realisation of notch and allpass responses does not require additional active elements. The proposed circuit enjoys low active and passive sensitivities.

A hybrid filter for image enhancement

Abstract: We present a new hybrid filter design methodology. Our hybrid filter consists of a nonlinear impulsive noise filter and a fuzzy weighted linear filter. This hybrid filter can efficiently remove large amounts of mixed Gaussian and impulsive noise while preserving the image details. The performance and robust stability of the proposed filter are compared to linear filters and nonlinear filters theoretically and experimentally.

Loudspeaker system incorporating acoustic waveguide filters and method of construction

Abstract: A method of constructing an acoustic filter incorporates a technique in which the filter is modelled with one or more distributed two port elements. The or each distributed element is defined by a characteristic impedance and length and includes a waveguide filter which does not require damping. The or each filter section is characterized in that it has at least two resonances which are used to shape a specified response for the filter. A substantially reactive acoustic filter constructed according to the method and a loudspeaker system incorporating such an acoustic filter are also disclosed.

Method and apparatus for generating decoupled filter parameters and implementing a band decoupled filter

Abstract: A method (100) and data processing system (120) for filtering unfiltered signals (134) to produce filtered signals (136) in accordance with desired filter control parameters (124) Adjusted filter control parameters (130) are generated based upon user provided filter control parameters (124) and operational characteristics (128) of a filter (132) to be implemented The adjusted filter control parameters (130) are provided to the filter (132) which filters the unfiltered signal (134) to produce the filtered signal (136) Using the adjusted filter control parameters (130), the filter (132) has a filtering function that agrees with the desired filter control parameters (124) to effectively band decouple the filter from bands of surrounding filters A graphic equalizer (250) implements a multi-band digital filter function that substantially reduces the effects of interband coupling, producing a more accurate match to the original filter response specification

An 80-Msample/s video switched-capacitor filter using a parallel biquadratic structure

Abstract: This paper describes a fifth-order, low-pass switched capacitor filter for video applications. It has a 4-MHz cutoff frequency and uses a parallel biquadratic structure with double sampling to achieve an 80-MHz input sampling rate in a 2-/spl mu/m CMOS process. The prototype filter is fully differential, occupies an active area of 11 mm/sup 2/, and dissipates 190 mW. >

Fast adapting control system and method

Abstract: An active control system having an adaptive filter model in which the effect of transfer functions after the adaptive filter model output are eliminated from the adaption process. The adaptive control scheme inputs a reference signal to a copy of the adaptive filter model, and the copy of the adaptive filter model outputs a correction signal that drives an output transducer. The copy of the adaptive filter model does not receive an error input signal. Adaption occurs in the adaptive filter model. The model input to the adaptive filter model is a C-filtered reference signal. There are no transfer functions between the output of the adaptive filter model and the error input to the adaptive filter model. The error input to the adaptive filter model is a combination of an error signal from an error sensor, a C-filtered correction signal, and a model output signal from the adaptive filter model.