Showing papers on "Voltage-controlled filter published in 1998"

A hybrid active filter for damping of harmonic resonance in industrial power systems

Abstract: This paper proposes a hybrid active filter for the damping of harmonic resonance in industrial power systems. The hybrid filter consists of a small-rated active filter and a 5th-tuned passive filter. The active filter is characterized by detecting the 5th-harmonic current flowing into the passive filter. It is controlled in such a way as to behave as a negative or positive resistor by adjusting a feedback gain from a negative to positive value, and vice versa. The negative resistor presented by the active filter cancels a positive resistor inherent in the passive filter, so that the hybrid filter acts as an ideal passive filter with infinite quality factor. This significantly improves damping the harmonic resonance, compared with the passive filter used alone. Moreover, the active filter acts as a positive resistor to prevent an excessive harmonic current from flowing into the passive filter. Experimental results obtained from a 20-kW laboratory model verify the viability and effectiveness of the hybrid active filter proposed in this paper.

Feedback cancellation apparatus and methods

Abstract: Feedback cancellation apparatus uses a cascade of two filters (114, 118) along with a short bulk delay (110). The first filter (114) is adapted when the hearing aid is turned on in the ear. This filter adapts quickly using a white noise probe signal (216), 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 (118) 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 (110) shifts the filter response to make the most effective use of the limited number of filter coefficients.

High-Q TE01 mode DR filters for PCS wireless base stations

Abstract: This paper presents the state of the art of high-Q TE01 mode DR cavity filters for PCS wireless base station applications. In order to have TE01 mode filter to be competitive with other high-Q cavity technologies, employment of nonadjacent coupling to implement advanced filter features and easy filter machining and integration are essential. The quadruplet and trisections are regarded as basic blocks to implement symmetric and asymmetric transmission zeros in filter stop band. The relative alignment of the magnetic mode field across the coupled adjacent cavities is analyzed to identify the sign of nonadjacent coupling. A direct cascading of a wide band combine filter to a TE01 mode dielectric resonator (DR) filter is proposed to suppress the spurious response of the DR cavity filter. This approach simplifies the integration between the DR filter and the spurious suppression device and has been proved to be very cost effective. Experimental eight- and six-pole quasi-elliptic function filters show the typical performances. To take advantage of the special property of magnetic mode field alignment across the adjacent cavities, a five-pole canonical asymmetric filter with three transmission zeros in low side is implemented. We believe this filter is a new design for high-Q cavity filter, while a three-pole elliptic function filter is new for DR filter technology.

On adaptive filtering in oversampled subbands

Abstract: For a number of applications like acoustic echo cancellation, adaptive filters are required to identify very long impulse responses. To reduce the computational cost in implementations, adaptive filtering in subband is known to be beneficial. Based on a review of popular fullband adaptive filtering algorithms and various subband approaches, this thesis investigates the implementation, design, and limitations of oversampled subband adaptive filter systems based on modulated complex and real valued filter banks. The main aim is to achieve a computationally efficient implementation for adaptive filter systems, for which fast methods of performing both the subband decomposition and the subband processing are researched. Therefore, a highly efficient polyphase implementation of a complex valued modulated generalized DFT (GDFT) filter bank with a judicious selection of properties for non-integer oversampling ratios is introduced. By modification, a real valued single sideband modulated filter bank is derived. Non-integer oversampling ratios are particularly important when addressing the efficiency of the subband processing. Analysis is presented to decide in which cases it is more advantageous to perform real or complex valued subband processing. Additionally, methods to adaptively adjust the filter lengths in subband adaptive filter (SAF) systems are discussed. Convergence limits for SAFs and the accuracy of the achievable equivalent fullband model based on aliasing and other distortions introduced by the employed filter banks are explicitly derived. Both an approximation of the minimum mean square error and the model accuracy can be directly linked to criteria in the design of the prototype filter for the filter bank. Together with an iterative least-squares design algorithm, it is therefore possible to construct filter banks for SAF applications with pre-defined performance limits. Simulation results are presented which demonstrate the validity and properties of the discussed SAF methods and their advantage over fullband and critically sampled SAF systems.

RF notch filter having multiple notch and variable notch frequency characteristics

Abstract: A filter network having the capability of establishing multiple, tunable notch frequencies A notch filter path is established for each notch frequency and includes a bandpass filter and inverter An input RF signal covering a wide frequency range is applied to all the notch filter paths Each notch filter path produces an output spectrum that is equal in magnitude and 180° out of phase with respect to an undesired frequency spectrum A combiner circuit combines the outputs of each notch filter path in parallel with the RF input signal to produce an RF output signal with all desired spectra unchanged and all undesired spectra attenuated

High-frequency high-Q BiCMOS current-mode bandpass filter and mobile communication application

Abstract: The design of a tunable high-frequency fully integrable current-mode bandpass filter is presented using a complementary high-performance BiCMOS process. The new architecture of this filter is based on impedance simulation and employs current controlled conveyors. The Q-factor and the center frequency can be electronically controlled with dc bias currents over a broad range of values, thus allowing easy tuning of this filter. An application to a mobile communication IF receiver channel centered at 85 MHz and with 1-MHz bandwidth based on the cascade of two identical second-order bandpass cells has been designed. Measurements show very interesting frequency performance (f/sub 0/ tunable in the range 30-120 MHz and Q from 1-140) in conjunction with low power consumption (25 mW for the fourth-order filter with /spl plusmn/2.5 V supplies).

System for digital filtering in a fixed number of clock cycles

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 modules 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 modules.

A /spl plusmn/1.5-V, 4-MHz CMOS continuous-time filter with a single-integrator based tuning

Abstract: A 4-MHz, fifth-order elliptic low-pass Gm-C filter is described whose characteristics are tuned by an on-chip automatic tuning circuit. The tuning circuit uses only one integrator as the master of tuning instead of problematic voltage controlled oscillator (VCO) and voltage controlled filter (VCF). MOS transistors in linear operation region perform the voltage-to-current conversion in an operational transconductance amplifier, and thereby we achieved /spl plusmn/1.5 V operation. A prototype filter was implemented in a 0.8-/spl mu/m double-poly, double-metal CMOS process. The filter exhibits the dynamic range of 57.6 dB and dissipates 10 mW with /spl plusmn/1.5-V supply. The stopband attenuation is better than 45.0 dB and the passband ripple is smaller than 1.0 dB.

Recursive digital filter with reset

Abstract: An integrated circuit, e.g. an Audio Codec (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 direct current (DC) buildup at internal nodes. The IIR filter performs a plurality of 2 nd order biquadratic equations in an overall average of as few as four clock cycles per 2 nd order biquad. A random access memory (RAM) is used to store the state variables for the 2 nd 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.

Programmable RF/IF bandpass filter utilizing MEM devices

Abstract: A programmable high frequency (HF) bandpass filter is disclosed. The programmable filter has a tunable bandwidth and center frequency over a large range of the radio frequency (RF) and intermediate frequency (IF) spectrum. The programmable filter incorporates micro-electro-mechanical switches (MEMS), Acoustic Charge Transport (ACT) devices, or a combination thereof, to provide tunability of the bandpass filter response characteristics.

High output impedance current-mode multifunction filter with minimum number of active and reduced number of passive elements

Abstract: A new current-mode multifunction filter with a single input and three outputs employing only three positive type CCIIs and five passive elements is presented. The proposed filter realises three filter functions simultaneously all at high impedance outputs. No component matching is required and all passive sensitivities are low.

ECG noise cancellation using digital filters

Abstract: A digital filter structure is proposed to maximally remove noise from the ECG signals. This structure is based on cascading a zero-phase bandpass, an adaptive filter, and multi-band-pass filter. It provides an efficient method for removing noise from the ECG signals. This filter structure has low implementation complexity and introduces little noise into a typical ECG. It can be applied to real-time applications particularly automatic cardiac arrhythmia classifiers.

New Universal Filter with One Input and Five Outputs Using Current-Feedback Amplifiers

Abstract: A new universal voltage-mode second-order filter circuit is presented. The circuit uses five current-feedback operational amplifiers, two grounded capacitors three grounded resistors and three floating resistors. The circuit can realize all the standard filter functions; lowpass, highpass, bandpass, notch and allpass, without changing the passive elements. The proposed circuit enjoys independent grounded-resistance-control of the natural frequency and the bandwidth, low output impedances, high input impedance as well as low active and passive sensitivities.

A New Parallel Hybrid Filter Configuration Minimizing Active Filter Size

Abstract: A conventional parallel hybrid active filter has an inherent problem of large current ratings of devices used in inverter. In general, this problem has been solved by adjust­ing turn ratio of a matching transformer. However, making the transformer with high turn ratio may be not available for high power system due to its requirement for high voltage insulation. In this paper, a new configuration is proposed for 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 for the aim of reducing the size of inverter. Through computer simulations, we have shown the outstanding performances of the proposed topology.

Radio frequency tracking filter

Abstract: A passive bandpass tracking filter tracks the frequency of an RF input signal received within a radio receiver's tracking range of RF frequencies. The bandpass filter includes parallel inductor and capacitor circuits connected in shunt between the input and output filter ports. A tracking control signal is selectively applied to change the capacitance of the LC circuits in order to shift the filter's frequency characteristics/profile as the filter tracks through the tracking band. The filter attenuates half-IF, receiver IF, and image spurious signals. In particular, the filter substantially attenuates the image spurious signal throughout the tracking frequency range by 50 dB or more below the filter output signal level. The filter also attenuates the half-IF spurious signal throughout the tracking frequency range by well over 10 dB or more below the filter output signal level. The receiver IF spurious signal is attenuated about 40 dB. The bandpass tracking filter has both a low insertion loss of about 5.0 dB or less and a substantially constant insertion loss variance at the RF receive frequency of about 1 dB or less over the entire tracking frequency range.

Operational filter building block

Abstract: A 3-terminal operational filter circuit is presented that can be used to construct various types of active filters The filter circuit can be configured to provide 2nd order low pass and band-pass frequency responses by coupling three resistors to the three filter terminals Similarly, the filter circuit can be configured to provide 2nd order band-pass and high pass frequency responses by coupling two resistors and a capacitor to the three filter terminals Furthermore, a plurality of filter circuits can be cascaded to construct various types of higher order filters The filter circuit can be manufactured to operate within a selected range of center frequencies by selecting particular values for the internal filter capacitance and resistance Users can then select a particular center frequency, quality factor, and gain of the filter circuit by selecting particular values for the circuit elements to be coupled to the three terminals

Notch filter incorporating saw devices and a delay line

Abstract: A notch filter ( 100 ) includes a parallel coupled delay line ( 104 ) and surface acoustic wave resonator ( 102 ) which provides a pole at a desired passband. The surface acoustic wave resonator ( 102 ) and the delay line ( 104 ) are configured to provide a zero at an undesired frequency or stopband. In this way, the notch filter ( 100 ) augments the stopband rejection of an associated cascaded surface acoustic wave ladder filter ( 105 ). The notch filter ( 100 ) also provides a pole at a desired frequency or passband such that losses due to the notch filter ( 100 ) at the desired passband are minimized, thereby improving overall insertion loss performance.

Harmonic suppressed microstrip multistage coupled ring bandpass filters

Abstract: Microstrip multistage coupled ring resonator bandpass filters using stepped impedance lowpass filters to suppress higher harmonics have been investigated. Two topologies based on placing the lowpass filters either into or out of the coupled rings have been considered. A harmonic suppression ratio of > 32 dB in a flat bandpass filter centred at 2.44 GHz is obtained. A practical implementation has shown very good filter characteristics with a very flat bandpass, insertion loss 32 dB.

Filter device for suppressing harmonics in radio frequency signals when dual frequencies exist

Abstract: The present invention relates to a power amplifier device (10), switchable for at least two separate basic frequency bands, for radio frequency signals with effective suppression of harmonics, where harmonics, corresponding to a first basic frequency band, can be permitted to overlap the frequency range of at least one second basic frequency band The power amplifier device (10) comprises a power amplifier (1) and an impedance matching circuit (2), switchable by means of a PIN-diode, which provides a load impedance adapted to each individual basic frequency band Furthermore, the power amplifier device comprises a filter device (3) comprising a fixed low-pass filter (3b) and a switchable filter (3b) acting as an engageable and disengageable notch filter, which comprises at least one reversible PIN-diode This switchable filter (3a) allows to pass, in a first mode, signals in the first basic frequency band and suppresses at the same time at least one order of harmonics corresponding to this basic frequency band In a second mode, the second basic frequency band is transmitted without appreciable losses, and harmonics are suppressed by the fixed low-pass filter (3a)

Magnetic storage device and filter adjusting method applied to the same

Abstract: The cut-off frequency and boost value of an analog filter on a read channel is set to initial values When the data is read from a disk, the read data is subjected to PR equalization at an FIR filter. At that time, a learning function provided on the FIR filter adjusts the tap coefficient so that an equalization error may be minimized. The cut-off frequency and boost value of the analog filter are modified until the adjusted tap coefficient has gone in a permitted range. After the tap coefficient of the FIR filter has gone in the permitted range, the cut-off frequency and boost value are stored in an EEPROM so that they can be used in a normal mode.

Multi-function active-only current-mode filter with three inputs and one output

Abstract: A new current-mode multi-function filter is proposed. The filter uses only two operational amplifiers, four operational trans-conductance amplifiers (OTAs) and one multiple-output third-generation current-conveyor (CCIII±). Without using any external passive elements, lowpass, highpass, bandpass, notch and allpass responses can be realized without changing the circuit topology and without any matching or cancellation conditions. The parameters ωo and ωo/Qo, can be electronically tuned by adjusting the bias currents of the OTAs. The proposed circuit enjoys low sensitivities.

System and method for bandpass shaping in an oversampling converter

Abstract: A digital filter in an oversampling converter is tuned to compensate for the non-ideal frequency response of a transducer coupled to the converter. In the A/D path, the filter coefficients of the decimation filter in a sigma-delta converter are tuned to compensate for the transducer. In the D/A path, the filter coefficients of the interpolation filter of a sigma-delta converter are tuned to compensate for the transducer. Filter coefficients may be statically defined in circuitry or programmable from values stored in a storage memory. Compensation may also be accomplished by tuning capacitor ratios in a switched capacitor filter, which is typically integral to the D/A path of an oversampling converter.

Noise analysis of a class of oscillators

Abstract: This paper presents noise analysis of a class of oscillators, which can be modeled by a positive feedback system with a frequency-selective Mth-order filter, an ideal comparator, and a white noise source. An explicit analytical expression for the output power spectral density is derived. A simplified expression is obtained for a special case when the Mth-order filter is replaced by a second-order bandpass filter. The general expression is shown to reduce to a well-known result if a high and-factor filter is further assumed. Theoretical results presented here are verified by experiment.

Universal current-controlled current-mode filter using the multiple-output translinear current conveyor

Abstract: A new current-mode universal filter is proposed. The filter uses three multiple-output current-controlled translinear current-conveyors (CCCII) and can simultaneously realise lowpass, highpass and bandpass responses. Realisation of notch and allpass responses is feasible. The parameters ω 0 , ω 0 /Q 0 . and the bandpass gain can be controlled by adjusting the bias currents of the CCClls. The proposed circuit enjoys low sensitivities.

High frequency switch module for multi-band

Abstract: PROBLEM TO BE SOLVED: To provide a high frequency switch module for multi-band having an excellent electric characteristics. SOLUTION: The switch module is constituted of a branching filter circuit for dividing plural transmission/reception systems of different pass bands to respective transmission/reception systems and switch circuits for switching each transmission/reception system to a transmission system and a reception system. The branching filter circuit comprises a low-pass filter circuit consisting of a distributed constant line, high-pass filter circuit comprising a capacitor, first series resonant circuit and second series resonant circuit. The low-pass filter is connected between a common terminal of the plural transmission/ reception systems and the switch circuit, at the latter step of the low-pass filter, the first resonant circuit is arranged between a terminal of the low-pass filter and a grounding point, the high pass-filter is connected between the common terminal and another switch circuit, at the latter step of the high-pass filter, the second resonant circuit is arranged between a terminal of the high- pass filter and the grounding point.

Multi-actuator system for active sound and vibration cancellation

Abstract: A multi-actuator system for active sound and vibration cancellation utilizes an LMS type algorithm having an adaptive filter. However, the error signal rather than the input is filtered through an adjoint filter of the error channel to drive an adaptive filter which in turn drives, for example, a loudspeaker to provide destructive interference for noise cancellation. The adjoint filter is realized by converting a standard filter's flow direction, such as a finite impulse response filter, swapping branching points with summing junctions and unit delays with unit advances. For multiple-input-output systems, computational complexity is significantly reduced.

Adaptive noise reduction filter with continuously variable sliding bandwidth

Abstract: An infinite impulse response (IIR) lowpass filter is placed in the audio path of an audio system wherein the upper cutoff frequency of the filter is adaptively controlled based on a comparison between the average audio signal entering the filter and the average audio signal leaving the filter. An adaptive LMS process is used to control the filter bandwidth so that the average output signal reaches a predefined percentage of the average input signal. An adaptation rate is selected depending on whether the filter bandwidth needs to increase or decrease. Adaptation is fastest for increasing bandwidth and slowest for decreasing filter bandwidth to prevent audible breathing and loss of high frequency information on sudden signal transients.

Novel MOS-C balanced-input balanced-output filter using the current feedback operational amplifier.

Abstract: A new bandpass-lowpass filter using a current feedback op.-amp. (CFOA) and MOS transistors operating in the non-saturation region is presented. The filter employs six CFOAs and realizes balanced-input balanced-output bandpasslowpass responses with independent control of Q. PSice simulation results for the proposed balanced-input balanced-output MOS-C filter are also given.