Showing papers on "Band-stop filter published in 1998"

Multifunction optical filter with a Michelson-Gires-Tournois interferometer for wavelength-division-multiplexed network system applications.

Abstract: We propose using a novel multifunction optical filter with a Michelson–Gires–Tournois interferometer (MGTI) for future smart wavelength-division-multiplexed network system applications. The MGTI filter is a typical Michelson interferometer in which one of its reflecting mirrors is replaced with a Gires–Tournois resonator. One unique feature of this device is that it can function as a channel-passing (CP), a channel-dropping (CD), or a wide-bandpass (BP) filter, depending on the interferometer arm-length difference. Other interesting features are that (1) the linewidths of both the CP and the CD filter are twice as narrow as that of a typical Fabry–Perot filter with similar parameters, (2) theoretical visibility is always unity regardless of the mirror reflectance value, and (3) the BP filter has an excellent boxlike response function. Numerical results showing these characteristics are presented.

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.

Novel compact elliptic-function narrow-band bandpass filters using microstrip open-loop resonators with coupled and crossing lines

Abstract: Novel compact elliptic-function narrow-band bandpass filters have been designed and fabricated. This new configuration consists of two identical microstrip open-loop resonators with coupled and crossing lines. A theoretical investigation has confirmed that this novel configuration is capable of providing elliptic-function filtering. Furthermore, the feasibility of this filter is verified experimentally. Centered at 2.039 GHz, the fabricated microstrip bandpass filter shows a measured 3-dB bandwidth of 2% and two deep notches in its stopband. In addition, the main circuit of this filter occupies only 2.5 cm/spl times/1.5 cm using a substrate with dielectric constant of 10.5, making it very attractive for applications in the mobile and personal communication systems (PCS's).

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).

Performance analysis of instantaneous frequency-based interference excision techniques in spread spectrum communications

Abstract: Jammers characterized by their instantaneous frequencies can be effectively mitigated in direct sequence spread spectrum communications by using open-loop adaptive excision filters. The primary requirement for these filters is that they must possess a notch in tune with the jammer instantaneous frequency (IF) to annihilate the interference power at every time sample. The interference time-varying frequency can be obtained using existing IF estimators, including quadratic time-frequency distribution methods. Without focusing on any specific estimator, we develop expressions for the receiver performance using a general class of multiple-zero FIR excision filters and show the dependence of the bit error rate (BER) on the filter order and its group delay. The effect of inaccuracies in the jammer instantaneous frequency information on the receiver performance is considered and evaluated as a function of the filter notch bandwidth. The latter is defined by the filter zero multiplicity, which is shown to be an important factor in the analysis of the correlator signal-to-noise ratio (SNR).

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.

Acoustic wave ladder filter with effectively increased coupling coefficient and method of providing same

Abstract: An acoustic wave ladder filter with lossy inductances (42) connected in parallel with resonators (40). Shunt sections of the ladder filter include impedance inverters having pass frequencies within the stopband of series resonators (33, 34, 34). The filter additionally includes variable capacitors (44) connected in parallel with the inductances to provide adjustment capabilities. The use of lossy inductances (42) actually increases effective coupling coefficient of the filter and improves insertion loss thereby allowing improved design flexibility.

Fibre optic radio frequency notch filter with linear and continuous tuning by using a chirped fibre grating

Abstract: A method is described to construct a simple tuneable fibre optic notch filter by using a linearly-chirped fibre grating filter which offers high resolution filtering for real time signal processing in radio frequency systems. The demonstrated device will allow linear and continuous tuning of the notch frequencies.

Wavelength selectable source for wavelength division multiplexed applications

Abstract: A broadband wavelength-selectable laser includes a gain medium, an optical transmission filter, and an optical fiber with a reflective filter such as a series of fiber Bragg gratings (FBGs). The gain medium is preferably a semiconductor laser diode that generates broadband optical energy. The gain medium is optically connected to the optical transmission filter, such as a bandpass filter, a notch filter, or a periodic filter, which converts the broadband optical energy into filtered optical energy having wavelength bands of high transmissivity and wavelength bands of low transmissivity. The optical transmission filter is optically connected to the series of FBGs that reflects different wavelength bands of optical energy. Either the optical transmission filter or the FBGs are tunable over a wavelength range that includes the desired laser wavelengths. Tuning a laser to a selected wavelength requires tuning either the optical transmission filter or the FBG that corresponds to the desired wavelength so that the selected wavelength of optical energy is reflected back toward the gain medium, thereby inducing lasing at the selected wavelength. The single wavelength laser light is suitable for wavelength division multiplexed applications.

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.

Apparatus and method for filtering a digital signal

Abstract: A closed loop feedback control system operates to maintain a process variable at or near a process variable setpoint. A digital filter is implemented with the controller to filter the process variable signal input to the controller. The filter includes both an amplitude filter to clip signal spikes and glitches and low pass filter to remove higher order, noise related frequencies from the signal, that could adversely affect computational speed of the controller.

A new memoryless nonlinear gradient algorithm for a second-order adaptive IIR notch filter and its performance analysis

Abstract: Adaptive infinite impulse-response (IIR) notch filters have been widely studied for many years. However, further efforts are still to be made to pursue new algorithms which work better than the conventional plain gradient algorithm but have little increase in complexity. In this paper, we employ the gradient linearization, Taylor series expansion, and calculus of variations to derive a novel memoryless nonlinear gradient algorithm for a second-order adaptive IIR notch filter, which improves the estimation performance considerably. Approximate closed-form expressions for the stability bounds on the step size parameter and the steady-state coefficient variance are also derived. Extensive simulations indicate the significant improvement that may be achieved using the new algorithm, and verify the validity of the analytical results.

Method and apparatus for suppressing mechanical resonance in a disk drive storage device using a notch filter

Abstract: The present invention teaches the realization of a stable feedback control by selecting an optimal notch filter in an apparatus, such as a hard disk drive, that employs a positioning apparatus, such as an actuator, for positioning an object. The present invention further teaches the derivation of a frequency characteristic of a control loop excluding a notch filter by employing a method that does not damage a positioning apparatus. The present invention further teaches the method of adjusting a notch filter in accordance with a change of the resonant frequency of an actuator caused by the temperature fluctuations to prevent any deterioration of a feedback control performance.

Apparatus and method for synthesizing pseudo-stereophonic outputs from a monophonic input

Abstract: A sound enhancement system (synthesizer) disclosed. The enhancement system synthesizes pseudo-stereophonic left and right output channels output from a monophonic input channel. The monophonic input signal is applied to a perspective filter that produces a differential-mode signal and to an equalizer filter that produces a common-mode signal. The perspective filter attenuates signal components in a frequency range corresponding to the human voice. The equalizer filter attenuates signal components in a frequency range outside the frequency range of the human voice. The equalizer filter also provides a 90 degree phase shift. The differential-mode and the common-mode signals are combined to produce the output channels. The pseudo-stereo output provided by the synthesizer has relatively less ambience in the frequency range corresponding to the human voice and relatively more ambience in frequency ranges that do not correspond to the human voice.

Filter including a microstrip antenna and a frequency selective surface

Abstract: A filter including an enclosure, a dielectric material within the enclosure, at least two microstrip antennas within the enclosure, and at least one frequency selective surface including a metallic pattern. The frequency selective surface is utilized to filter an electromagnetic signal propagated within the enclosure. The geometry of the antennas and the frequency selective surfaces as well as the resonant frequencies of the frequency selective surfaces determine whether the filter is a bandpass, bandstop, notched, or combination filter. If the frequency selective surface is omitted, the combination acts as a delay circuit for delaying the electromagnetic signal, where the time delay is a function of the dielectric constant of the dielectric material.

Decimation filtering apparatus and method

Abstract: A decimation filtering apparatus using interpolated second order polynomials compensates for a droop caused by a CIC (Cascaded Integrator-Comb) filter (51). The decimation filter includes a CIC decimation filter (51) for decimation filtering the sampling signal to downconvert a sampling signal; an ISOP filter (53) for monotanically increasing an output of the CIC decimation filter (51) to compensate for a passband droop caused by the CIC decimation filter (51); a multistage halfband filter (55) including at least one modified halfband filter for 1/2 decimating a signal output from the ISOP filter (53), the multistage halfband filter (55) decimating the signal output from the ISOP filter (53) to downconvert the signal; and a programmable FIR (Finite Impulse Response) filter (57) for compensating for a passband droop of a signal output from the multistage halfband filter (55).

Estimation of power system frequency using adaptive notch filters

Abstract: A new approach for frequency relaying in power system is presented in this paper. The approach consists of passing the power system voltage signal through a two stage adaptive notch filter, which produces an estimate of the fundamental frequency of the voltage waveform and its enhanced amplitude. The adaptive of the notch filter coefficients are obtained by a recursive least mean squares algorithm. The performance of the proposed algorithm is computationally efficient and it produces an accurate estimate of the fundamental frequency in the presence of harmonics and noise, which is a prerequisite to frequency relaying in power systems. Several computer simulation results are presented in the paper to show the effectiveness of the algorithm. The algorithm is simple and suitable for real time implementation. Further the accuracy of this approach in presence of harmonics and noise is improved considerably.

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

A BiCMOS continuous-time filter for video signal processing applications

Abstract: A fully integrated BiCMOS continuous-time filter for video signal processing applications is presented. It incorporates an input clamping circuit, a third-order equalizer, a fifth-order elliptic filter with sinx/x correction, and a 75-/spl Omega/ driver. The architectures of the input and output amplifiers as well as the filter and the equalizer are chosen based on the extensive study of circuit structures and Monte Carlo simulation to meet the linearity requirement for the broadcast-quality video system. The complete chip achieves a low-pass filter response with a 5.5-MHz cutoff frequency (f/sub cc/), 0.3-dB passband ripple, 20-ns group delay variation up to 0.9 f/sub c/, and 43-dB attenuation at 1.45 f/sub c/. With a nominal 2-Vpp signal at the output, measured results show 0.2% differential gain, 0.38/spl deg/ differential phase, and 1.7-mV rms noise demonstrating 10-bit linearity in a 1.5-/spl mu/m 4-GHz BiCMOS process technology. The filter active area is 8 mm/sup 2/ and it dissipates 350 mW in a single 5-V power supply.

Optical spectrum analyzer having tunable interference filter

Abstract: An optical spectrum analyzer includes a polarization modifier that eliminates polarization-dependent wavelength spreading, enabling the analyzer to have high signal selectivity and high measurement sensitivity. The polarization modifier spatially separates orthogonal polarization components of the applied optical signal into separate optical beams and rotates the relative polarization components of the beams so that the beams are incident on a tunable interference filter in a multipass configuration at a single polarization state. The optical beams are directed through regions of the interference filter which lie on a contour of substantially equal center wavelength so that each of the multiple passes through the interference filter provides for corresponding narrowing of the filter bandwidth. Narrow bandwidth and low insertion loss are maintained over a wide tuning range by tilting the interference filter about a tilt axis intercepting the regions of the interference filter that lie on a contour of substantially equal optical thickness.

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.

Triple mode dielectric resonator hybrid reflection filters

Abstract: A new class of dielectric resonator filter is described. These devices use the triply degenerate TE/sub 11/spl delta// mode in a cubic dielectric resonator. A simple theory is used to show the similarity between this mode and the TE/sub 10/spl delta// mode in a cylindrical resonator. The cubic resonator is used in a hybrid reflection mode filter where the even and odd subnetworks of a bandpass filter are connected to two ports of a 3 dB quadrature hybrid. The transmission response through the other two ports is then the reflection coefficient of the bandpass filter. The design approach only requires the realisation of simple one port ladder networks and is ideal for realising complex filters using triple mode resonators. A design example is presented for a degree 6 elliptic function bandstop filter operating in the 850 MHz cellular radio band. A threefold size reduction is achieved when compared to single mode filters with similar electrical performance.

Method and apparatus for detecting voice activity

Abstract: A voice activity detector that implements a fast wavelet transformation using filter pairs. A quadrature high pass filter provides an output signal corresponding to the upper half of the Nyquist frequency and a quadrature low pass filter provides an output signal corresponding to the lower half of the Nyquist frequency. The quadrature high pass filter is useful for catching and isolating transients in the input signal and the quadrature low pass filter is useful for fine frequency analysis. The voice activity detector can utilize multiple decomposition levels that are arranged in a pyramid or tree formation to increase the reliability of the voice activity decision. For example, the output of the quadrature low pass filter can be further decomposed using a second pair of filters. The voice activity decision can be generated by comparing a signal power estimate for the output of the filter pairs to threshold levels that are specific for each filter or frequency range. The reliability of the voice activity decision is maximized by training the system to determine the optimum threshold levels and by basing the decision on a combination of the signal outputs. While increasing the number of decomposition levels increases the reliability of the voice activity decision, three decomposition levels is usually sufficient for detecting speech activity.

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.

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.

Adaptive filtering for selective elimination of higher harmonics from line currents of a voltage source converter

Abstract: The methods for adaptive noise canceling have been well developed and researched in digital signal processing. The task is typically accomplished by generating a reference signal with frequency that should be eliminated from the primary input signal. The reference is filtered to match the interfering sinusoid in primary input. The weights of the adaptive filter are adjusted to totally eliminate the component with undesired frequency from the primary input, creating a tunable notch filter with an infinite null at selected frequency. The above concept was used as a basis for the development of an adaptive selective harmonic canceling (ASHC) algorithm. With ASHC added to the "regular" control of the VSC, the whole VSC becomes an active adaptive infinite null power notch filter at selected frequencies. The algorithm was used for elimination of higher harmonics 5, 7, 11, 13, 17, 19 from the input utility currents.