Showing papers on "Voltage-controlled filter published in 1999"

Feedback cancellation improvements

Abstract: Feedback cancellation apparatus uses a cascade of two filters along with a short bulk delay. The first filter is adapted when the hearing aid is turned on in the ear. This filter adapts quickly using a white noise probe signal, and then the filter coefficients are frozen. The first filter models parts of the hearing-aid feedback path that are essentially constant over the course of the day. The second filter adapts while the hearing aid is in use and does not use a separate probe signal. This filter provides a rapid correction to the feedback path model when the hearing aid goes unstable, and more slowly tracks perturbations in the feedback path that occur in daily use. The delay shifts the filter response to make the most effective use of the limited number of filter coefficients.

Electromagnetic interference (emi) filter and process for providing electromagnetic compatibility of an electronic device while in the presence of an electromagnetic emitter operating at the same frequency

Abstract: A novel electromagnetic interference (EMI) filter is designed to attenuate one or more specific frequencies in order to provide electromagnetic compatibility of an electronic device while in the presence of an electromagnetic emitter operating at the same or similar frequencies. The EMI filter of the present invention combines an EMI low pass filter with one or more “notch” EMI filters tuned to the specific frequencies of interest. When combined in this fashion, the notch EMI filter can effectively attenuate the electromagnetic field of a powerful low frequency emitter which is outside the effective attenuation frequency range of the low pass filter, which is itself effective at filtering a broad range of higher frequencies. In a preferred embodiment, the notch EMI filter capacitive element is integrated in a co-planar relationship with a ceramic feedthrough filter capacitor assembly. This combined notch and low pass filter arrangement is particularly effective in an implantable medical device such as a cardiac pacemaker or implantable cardioverter defibrillator (ICD) against passage of external interference signals, such as those caused by both digital cellular phones and electronic article surveillance systems operating at low frequencies.

A broad-band tunable CMOS channel-select filter for a low-IF wireless receiver

Abstract: Researchers agree that the active filter for channel-selection limits the dynamic range in a fully integrated wireless receiver, which uses no external components. This paper describes a filter designed for a wideband wireless LAN receiver operating in the 2.4-2.48 GHz ISM band. The receiver converts the desired channel to a low IF to enable on-chip rejection of the image. The analog filter must pass up to a 10 MHz wide single-channel centered after downconversion to IF ranging from 5 to 10 MHz. The classic requirements on all RF IC's apply to this filter, namely how to achieve the desired frequency response with the highest linearity and lowest noise at a given current consumption. For a channel-select filter, linearity is specified as out-of-band 3rd order intercept (IP3), to limit the in-band intermodulation from large interferers lying in the filter stop band. This work addresses the problem in filter architecture and circuit implementation. The achieved dynamic range surpasses all other published filter designs, except those cases where gain is favorably interleaved with filtering.

A new approach for single-phase harmonic current detecting and its application in a hybrid active power filter

Abstract: In this paper, a new approach for single-phase harmonic current detection is presented. The approach was obtained through extending ideas of three-phase instantaneous reactive power theory and constructing a two-phase system from the existing single-phase circuit. By theoretical and simulation analysis, it is shown to be a precise approach, which can be easily realized and has the merits of better steady state and dynamic performance than conventional approaches that could be used in single-phase circuits. The approach was applied into a hybrid active power filter, which combines a series active filter and a shunt passive filter together and aims at solving the harmonics problem originated by high-power single-phase nonlinear load. Following the system configuration and basic principles of the hybrid active power filter, the overall detection and control algorithm, the PWM generating technique and the DC voltage stabilizing method are introduced in detail. The detection and control algorithm were then realized by a digital control circuit with DSP processor, and successfully employed in a prototype hybrid active power filter. Experimental results on the prototype verified the effectiveness of the new detecting approach, the performance of the control circuit and the filtering characteristics of the hybrid active power filter.

Noise control system

Abstract: A noise control system includes: a control sound generator for generating a control sound; an error detector for detecting an error signal between the control sound and noise; a noise detector for detecting a noise source signal; an adaptive filter for outputting a control signal; and a coefficient updator for updating a coefficient of the adaptive filter. The coefficient updator includes at least a first digital filter, a first coefficient update calculator, a second digital filter, a phase inverter, a third digital filter, and a second coefficient update calculator. Alternatively, the coefficient updator includes at least a first digital filter, a second digital filter, a third digital filter, a coefficient update calculator, a phase inverter, a first adder, and a second adder. In either case, the coefficient updator has a function of suppressing an increase in a coefficient gain of the adaptive filter in a predetermined frequency band.

A novel high-Q optical microwave processor using hybrid delay-line filters

Abstract: A new hybrid active-passive photonic signal processor, which achieves high-Q microwave bandpass filtering, is presented. It overcomes the problem of achieving very high-Q values, while still operating the active stage with a large gain margin. This enables a significant increase in Q to be obtained, higher filter frequencies, and robust operation. The general synthesis procedure for the hybrid filter is described. The filter response demonstrates very high-resolution microwave signal filtering with a measured Q of 801.

Properties of a novel noncascaded type, easy-to-design, ripple-free optical bandpass filter

Abstract: The chief principle and properties of a novel noncascaded type optical bandpass filter with three unique general characteristics are presented. This device is based on a combination of a Michelson interferometer and a Gires-Tournois resonator (GTR). First, the filter has square-like frequency response with zero ripple, wide flat-top (0.74/spl times/bandwidth), unity contrast, sharp steepness, and infinite rejection ratio when GTR front surface mirror reflectance /spl rho/ is equal to one-third. Second, this filter possesses variable bandwidth and center wavelength tunability features with simple control mechanism and nanosecond temporal response potential. Third, the desired features of the filter can be synthesized easily by mere inspection since only three parameters are required, and their expressions are given in simple analytic forms. Numerical results showing these features are presented and other characteristics are briefly discussed.

Narrow-band filter including sigma-delta modulator implemented in a programmable logic device

Abstract: A narrow-band bandpass filter is implemented in a field programmable gate array (FPGA). An analog-to-digital converter quantizes an input analog signal with a high degree of precision to produce input data samples. A sigma-delta modulator re-quantizes the samples with a substantially lower degree of precision. The re-quantized samples are passed through a bandpass, lowpass, or highpass, finite impulse response (FIR) filter which operates at the lower degree of precision. The reduced degree of precision enables a substantial reduction in the number of resources required to implement the narrow-band bandpass, lowpass, or highpass filter in the FPGA. The modulator includes a predictor filter which has a center frequency coinciding with that of the FIR filter, and redistributes noise such that it is lowest within the passband of the FIR filter. The narrow-band filter design can be adapted to incorporate a single or multi-rate decimator configuration.

Hybrid filter for an alternating current network

Abstract: The invention relates to a hybrid filter for an alternating current network (6). The hybrid filter has a passive filter and an active filter (2,4) that are electrically connected in series, whereby the active filter (4) has a voltage source (8). According to the invention, a filter (14) adjusted to the nominal frequency of the alternating current network (6) is mounted electrically parallel to the active filter (4). This results in a hybrid filter for an alternating current network (6), whereby the active filter (4) is not subjected to fundamental frequency current component strain.

Characteristics of the Vold-Kalman order tracking filter

Abstract: In this paper the filter characteristics of the Vold-Kalman Order Tracking Filter are presented. Both frequency response as well as time response and their time-frequency relationship have been investigated. Some guidelines for optimum choice of filter parameters are presented. The Vold-Kalman filter allows for the high performance simultaneous tracking of orders in systems with multiple independent shafts. With this new filter and using multiple tacho references, waveforms, as well as amplitude and phase may be extracted without the beating interactions that are associated with conventional methods. The Vold-Kalman filter provides several filter shapes for optimum resolution and stopband suppression. Orders extracted as waveforms have no phase bias, and may hence be used for playback, synthesis and tailoring.

User interface for the control of an audio spectrum filter processor

Abstract: A user interface control apparatus is disclosed for the control of electronic filter parameters of audio spectrum equalizers, crossovers, and other filter processors. The user interface apparatus comprises five pushbutton keys arranged in a specific cross-shaped pattern. This single arrangement of control keys provides a common user interface control apparatus which can be used to control one or more filter types. Depression of particular keys, or particular combinations of keys can be made to electronically control multiple filter parameters, some simultaneously, and for different filter types depending on the filter type for which the invention is applied. The unique arrangement of the invention's pushbutton keys facilitates an intuitive operation of the various parameters for bell, notch, shelf, and pass-band audio filter types with a minimal number of control elements and minimal control area. The filter parameters of a bell filter that can be controlled include center frequency, amplitude, and bandwidth. The filter parameters of a notch filter that can be controlled include center frequency and bandwidth. The filter parameters of a shelf filter that can be controlled include transition frequency, shelf amplitude, and transition slope. The filter parameters of a pass-band filter that can be controlled include corner frequency, pass-band amplitude, and filter slope. Additionally, the unique arrangement of keys facilitates intuitive control of some filter parameters at two rates of continuous change. Also, the user interface allows control of a graphic equalizer, where the selection of a particular bell filter, or “band”, can be scanned at two different rates. Finally, the user interface allows the control of the corner frequencies of two adjacent pass-band filters simultaneously, such as in a crossover processor, so as to preserve the combined response of the two filters over the overlapping region.

Insensitive current-mode universal filter with minimum components using dual-output current conveyors

Abstract: A novel universal current-mode active filter with four inputs and one output is presented, which contains only three dual-output current conveyors. Two grounded capacitors and two grounded resistors. The circuit is very advantageous from an integration point of view. The proposed active filter realises all filter responses without any matching conditions at high impedance output and has low passive and active sensitivities.

Performance analysis of multicarrier modulation systems using cosine modulated filter banks

Abstract: We compare the performance of biorthogonal cosine modulated transmultiplexer filter banks with today's multicarrier modulation systems whose transceivers are based on DFT. In contrast to early works on transmultiplexer filter banks that concentrated on the derivation of perfect reconstruction constraints of the filter bank or prototype design, this study takes into consideration a typical twisted pair copper line transmission channel into consideration and examines the influence of different system parameters as filter length, number of channels, and the overall system delay on the distortion at the receiver. Biorthogonal filter banks have the advantage that filter length and overall system delay can be chosen independently. Restricting the equalizer at the receiver to a single scalar tap per subchannel, we show that cosine-modulated filter banks outperform DFT based multicarrier systems without a guard interval and obtain a similar performance to DFT based systems with a guard interval and time domain equalization but at a lower computational cost and a higher throughput data rate.

Dual mode mobile phone using a multiplex type filter

Abstract: The mobile phone is equipped for at least two frequency bands and includes an antenna coupled to a multiplex type filter. The multiplex type filter contains at least two disparate bandpass filters for separate reception or transmission frequency bands. A first bandpass filter of the at least two disparate bandpass filters has as a passband a first frequency band. A second bandpass filter of the at least two disparate bandpass filters has as a passband a second frequency band. An input impedance of the first bandpass filter in the second frequency band is higher than an input impedance of the second bandpass filter in the second frequency band, and an input impedance of the second bandpass filter in the first frequency band is higher that an input impedance of the first bandpass filter in the first frequency band, so that coupling of signal power at frequencies in the first frequency band to the second bandpass filter and coupling of signal power at frequencies in the second frequency band to the first bandpass filter is essentially reduced.

A new parallel hybrid filter configuration minimizing active filter size

Abstract: Conventional parallel hybrid active filters suffer from the problem of heavy current ratings of devices used in the inverter. In general, this problem has been solved by adjusting the turn ratio of a matching transformer. However, adjusting the transformer to a high turn ratio may not be possible for high voltage power systems due to their requirements for high voltage insulation. In this paper, a new configuration is proposed for a parallel hybrid active filter. In the proposed hybrid active filter, the active filter is connected to the passive filter inductor in parallel through a matching transformer with the aim of reducing the current rating of the inverter. As a result, the fundamental component of the current flowing through the passive filter is divided by the parallel paths of two inductors located at the inverter side and passive filter side, respectively. Hence, the current rating of the inverter can be reduced. Additionally, a harmonic elimination method is suggested for the proposed active filter. Through computer simulations and experiment, we have verified the effectiveness of the proposed topology.

High-Q optical microwave filter

Abstract: A new photonic signal processor topology is presented, which achieves high-Q value microwave bandpass filtering. It significantly increases the Q by means of a small free spectral range passive filter, while still operating the active stage with a large gain margin. The filter response demonstrates very high resolution microwave signal filtering with a measured Q value of 983.

Filter arrangement for shaping a pulse propagated over pots wiring, and a method of manufacturing the same

Abstract: A filter arrangement, for shaping a signal transmitted over POTS wiring, includes an input to receive a signal. The filter arrangement includes a signal path from the input to an output that is coupled to POTS wiring. The transmit path includes a high-pass filter, a low-pass filter, and a trap filter coupled between the high and the low-pass filter. The trap filter operationally introduces a filter zero at a resonant frequency of the high-pass filter.

Surface acoustic wave filter utilizing a transmission line with phase characteristics that increase filter out of band attenuation

Abstract: The present invention relates to a surface acoustic wave (SAW) filter which is used for cellular phones and other mobile communication equipment. The object of the present invention is to realize a SAW filter of which attenuation characteristics and pass characteristics can be set arbitrarily. The SAW filter of the present invention comprises comb-shaped electrodes facing each other disposed on the same piezoelectric substrate, at least two resonators with an input and output terminals, and an equivalent transmission line which is connected between an output terminal of a first resonator and an input terminal of a second resonator. The phase of the transmission line can be adjusted from 5 degrees to 175 degrees arbitrarily at the series resonance frequency of the resonators. This structure realizes a band-stop filter or a band-pass filter whose attenuation characteristics and pass characteristics can be set arbitrarily.

Apparatus and methods for tuning bandpass filters

Abstract: A signal having a substantially uniform spectral distribution, e.g., a flat noise signal such as a signal ground, is provided at the input of a bandpass filter such as an IF filter of a receiver circuit, to thereby produce an output signal at the output of the bandpass filter. The output signal is processed in a limiter to produce a limited signal. An average frequency of the limited signal is determined, and the bandpass filter is adjusted based on the determined average frequency. According to one embodiment of the present invention, the bandpass filter comprises a Gm-C filter having a transconductance, and the filter is adjusted by adjusting the transconductance of the Gm-C filter based on the determined average frequency. According to another aspect of the present invention, a desired center frequency for the bandpass filter is identified. A resolution and a desired confidence interval are also identified. The number of samples of the limited signal needed to achieve the identified desired resolution and confidence interval is determined based on the identified desired center frequency. An average frequency is determined by sampling the limited signal to obtain a plurality of samples, the number of the plurality of samples being at least as great as the determined number of samples of the limited signal to achieve the identified desired resolution and confidence level, and determining the average frequency from the plurality of samples. The bandpass filter is adjusted based on the determined average frequency to achieve a center frequency for the bandpass filter that is within a predetermined range with respect to the desired center frequency. Related apparatus are also discussed.

Bandpass filters with automatic tuning adjustment

Abstract: A method and system for tuning a tunable bandpass filter includes a bandpass filter having a passband which is dependant on the value of a tuning signal. A data signal having a dominant frequency component is applied to the filter and the power of the signal passed by the filter is determined. The tuning signal is adjusted until the passed power is maximized, indicating that the filter is tuned to the dominant frequency. The tuning signal can then be applied to other tunable circuits, including an oscillator having an output used as a clock signal to extract data from the data signal applied to the filter.

Digital implementation of a new type of hybrid filter with simplified control strategy

Abstract: A new type of hybrid active filter to compensate harmonics of a nonlinear load is presented in this paper. The proposed topology of hybrid filter combines a shunt passive filter (PF) and a shunt active filter (AF). A series inductor between both the filters is introduced to create a harmonic voltage source at the input of nonlinear load. A diode bridge rectifier with R-C load is considered as a nonlinear load. An indirect current controlled voltage source inverter (ICC-VSI) is considered as an AF. A simple control algorithm based on proportional plus integral control of a self-supporting DC bus voltage of the shunt AF is implemented on a TMS320C31 DSP. The passive filter is tuned to compensate 5/sup th/ and 7/sup th/ harmonics, while the AF compensates the rest of harmonics of the load current. A laboratory prototype model of the proposed hybrid filter is developed and its performance is examined. Experimental results are given and discussed.

Design and evaluation of an active ripple filter with Rogowski-coil current sensing

Abstract: An active ripple filter is an electronic circuit which cancels or suppresses the ripple current and EMI generated by the power stage of a power converter, thus reducing the passive filtration requirements. This paper presents the design and evaluation of a feedforward active ripple filter which employs a Rogowski coil for ripple current sensing. The design of the active filter is discussed in detail, including the advantages, tradeoffs, and limitations of the approach. Experimental results from a prototype converter system using this approach are presented, and quantitative comparisons are made between a hybrid passive/active filter and a purely passive filter. It is demonstrated that substantial improvements in filter mass and converter transient performance can be achieved using the proposed active ripple filtering method.

Distributed gain for audio codec

Abstract: An integrated circuit, e.g. an AC '97 conforming audio codec, includes a digital filter and gain module including multiple channels of gain control and multiple channels of digital filtering. A gain control module includes an overflow check of data samples requiring differing lengths of clamping. Each channel of the digital filter includes a finite impulse response (FIR) filter, and an infinite impulse response (IIR) filter. The digital filtering is implemented largely in hardware independent of the number of channels required and/or independent of the required order of the filtering. Thus, filter channels can be added or additional filtering implemented merely by increasing the clock speed without changing the digital filter design. The FIR filter is capable of being reset each frame to prevent a DC buildup at internal nodes. The IIR filter performs a plurality of 2nd order biquadratic equations in an overall average of as few as four clock cycles per 2nd order biquad. A RAM is used to store the state variables for the 2nd order biquadratic equations. The state variable RAM is reset by controlling the clear input of latches at an input and/or the output of the state variable RAM, and the state variable RAM is addressed by a delta counter which is independent of the particular number of filter channels or filter orders implemented. Test patterns may be inserted between functional blocks of an integrated circuit such as the disclosed audio codec by appropriate control of the preset and clear inputs to output latches of the functional blocks.

Filter unit comprising a wideband bandpass filter and one band-elimination filter

Abstract: A filter unit comprises a wideband bandpass filter; at least one band-elimination filter having a stop band within the passband of the bandpass filter, so that the passband is divided into a plurality of pass bands by the stop band; and the wideband bandpass filter and the band-elimination filter being disposed in a single dielectric member. Since the passband of a wideband bandpass filter is divided into a plurality of pass bands by stop bands of one or more band-elimination filters, signals having frequencies corresponding to these divided pass bands are able to pass through the filter unit simultaneously.

Method and apparatus for minimizing mismatch in a complex filter

Abstract: A complex filter minimizing mismatch error by averaging the mismatch error by integrating the real and imaginary input signals using the same integrator. A further advantage is that, as compared to known devices, the complex filter uses fewer number of components thereby reducing the consumed power. The complex filter may be used in a complex bandpass sigma-delta modulator, thereby increasing the performance of the sigma-delta modulator. The complex filter used in a sigma-delta modulator analog to digital converter increases performance of the analog to digital conversion since the mismatch noise is minimized. The complex bandpass sigma-delta modulator analog to digital converter include any number of complex filter stages.

A comparison of various low-pass filter architectures for sigma-delta demodulators

Abstract: A comparison of various low-pass filter architectures that are commonly used in Sigma-Delta(/spl Sigma/-/spl Delta/) demodulators is presented in the paper. In this comparison the conventional demodulator filter architectures such as the optimal FIR filter, Sinc/sup k/ filter and non-linear Zoomer filter are considered. It is shown that the optimum FIR filter provides the most attractive properties among the conventional demodulator low-pass filters. As an alternative to the optimal FIR filter, optimal Laguerre IIR filter architecture is then proposed in the paper. A design scheme for the optimal IIR filter is presented via the use of orthonormal Laguerre functions. In comparison with the conventional FIR filter approach, this design offers several attractive features. The proposed IIR filter design problem is easy to solve and numerically robust. Furthermore, the optimal IIR filter is easy to implement because it needs only a small number of components and therefore well suited for VLSI implementations.

An optical filter for use in or with an optical amplifier

Abstract: This invention relates to invention relates to a method for filtering and a variable slope optical filter for in-line use with an optical amplifier signal. The filter has a wavelength response that is substantially linear in slope within a band of operation wavelengths of the amplifier; the slope of the filter in an operating band of wavelengths is between zero and a only one of a positive or negative number; furthermore the filter has an amplitude response that has an opposite and counter slope as a function of wavelength to that of a gain tilt of the amplifier within the operation band of wavelengths. Relative movement between the filter and the optical amplifier signal is provided to vary the slope of the filter by means of varying the amplitude wavelength response of the filter.