Showing papers on "Band-stop filter published in 2002"

A Nonlinear Adaptive Filter for Online Signal Analysis in Power Systems: Applications

Abstract: This paper presents various applications of a nonlinear adaptive notch filter which operates based on the concept of an enhanced phase-locked loop (PLL). Applications of the filter for online signal analysis for power systems protection, control and power quality enhancement are presented. The proposed scheme can be applied for signal analysis both under stationary and nonstationary conditions. Based on digital time-domain simulations, applications of the filter for (a) sinusoidal waveform peak detection, (b) harmonic identification/detection, (c) detection/extraction of individual components of a signal, (d) instantaneous reactive current extraction, (e) disturbance detection, (f) noise reduction in zero-crossings detection, and (g) amplitude (phase) demodulation for flicker estimation, are presented.

Bypass filter; multi;band antenna switch circuit; and layered module composite part and communication device using them

Abstract: A multi-band antenna switch circuit including a diplexer connected to an antenna terminal for demultiplexing signals of different passing bands, a first and a second switch circuit for switching a high frequency signal and a low frequency signal demultiplexed by the diplexer to a plurality of transmission/reception terminals, a first and a second low pass filter connected to a transmission path between the diplexer and the transmission terminal or between the first and the second switch circuit and the transmission terminal, and a notch filter provided between the diplexer and the first switch circuit or between the diplexer and the second switch circuit. The multi-band antenna switch circuit includes a high pass filter having an input terminal and an output terminal and provided at least between the diplexer and the antenna terminal and including a first inductor connected between the input terminal and the ground, a first capacitor connected between the input terminal and the output terminal, a second inductor connected to the output terminal, and a second capacitor connected between the second inductor and the ground.

Stationary frame harmonic reference generation for active filter systems

Abstract: Harmonic reference generators for active filter systems are commonly implemented in the synchronous reference frame, so that simple low- or high-pass filter functions can be used depending on the requirements of a particular application. High-pass filters in particular are used when the reference generator is required to produce an "everything but the fundamental" target waveform. This paper presents a stationary frame notch filter equivalent to a high-pass synchronous frame harmonic reference generator for such systems. The use of the stationary frame allows for quicker calculation of the reference generation in a discrete digital implementation, and also allows classical control techniques to be used to analyze the active filter system without requiring synchronous frame transformations of the outside system model. Both simulation (continuous and discrete) and experimental results showing the equivalency of the stationary and synchronous frame reference generation process are presented using both shift and delta-operator-based infinite-impulse response digital filters.

Narrowband optical filter, with a variable transmission spectrum, using stimulated Brillouin scattering in optical fiber

Abstract: A novel shape-adjustable narrowband optical filter utilizing stimulated Brillouin scattering in an optical fiber is proposed and demonstrated. In this scheme, binary-phase-shift-keying modulation is applied to the pump wave to broaden and shape the Brillouin gain spectrum. By choosing an appropriate modulation data pattern, we realized a flat-top steep-cutoff optical bandpass filter with a 3-dB bandwidth of 1.5 GHz and a 10-dB bandwidth of 2 GHz is realized. In addition, a tunable optical notch filter is also realized by deamplification of the anti-Stokes wave.

A tunable filter and method of tuning a filter

Abstract: A bandpass filter is tuned by converting the filter into an oscillator using a negative resistance circuit, tuning the oscillator by using conventional tuning techniques such as tuning a varactor via a phase locked loop, sampling and holding the tuning signal and switching off the negative resistance circuit to convert the oscillator back into a bandpass filter.

Ultra-selective 22-pole 10-transmission zero superconducting bandpass filter surpasses 50-pole Chebyshev filter

Abstract: An ultra-selective filter for third-generation (3G) and fourth-generation wireless application is presented. The demonstrated filter consists of 22 resonators and five cross couplings that produce ten transmission zeros. The filter was designed at 1950-MHz center frequency with a 20-MHz bandwidth to meet existing 3G wireless applications. The measured filter data shows excellent selectivity, better than 30-dB/100-kHz skirt slopes, and 90 dB of rejection at 350 kHz from the band edge. This filter performance surpasses the performance of a 50-pole Chebyshev filter. In order to fit a large number of resonators into a limited wafer area, a new compact resonator was developed. The filter was fabricated using a YBCO thin film on a 2-in MgO wafer.

Gain-flattening filter using long-period fiber gratings

Abstract: We propose a novel structure for a gain-flattening filter, in which a conventional long-period fiber grating (LPFG) and a phase-shifted LPFG are written closely. The transmission characteristics are investigated in the case of a closely arranged configuration. For the fabrication of a phase-shifted LPFG, a UV-trimming method to control the amount of the phase shift is examined theoretically and experimentally. Finally, a 67-mm-long LPFG gain-flattening filter designed for an erbium-doped fiber amplifier is fabricated and the measured spectrum is shown.

Ripple feedback filter suitable for analog/digital mixed-mode audio amplifier for improved efficiency and stability

Abstract: A new ripple feedback filter is presented for analog/digital mixed-mode amplifier (MMA) among audio applications. MMA is composed of two amplifiers: one is analog amplifier responsible for high fidelity and the other is digital switching amplifier in charge of high efficiency. To improve both total harmonic distortion (THD) and efficiency, a passive RLC filter is needed at the output side of the digital switching amplifier. A conventional filter, however, causes phase delay, which worsens current loop stability and makes the normal operation of MMA impossible. A ripple feedback filter is newly suggested to solve this problem, obtaining excellent efficiency and low THD.

Feedback cancellation in a hearing aid with reduced sensitivity to low-frequency tonal inputs

Abstract: A feedback cancellation system with reduced sensitivity to low-frequency tonal inputs is provided. Such a system can be used, for example, in a hearing aid to prevent cancellation of the desired tonal inputs to the hearing aid, thus improving the gain at high frequencies of the hearing aid while simultaneously preserving the desired tonal inputs at low frequencies. The feedback cancellation system comprises a first adaptive filter block for adaptively filtering an error signal to remove the low-frequency tonal components from the error signal. The first adaptive filter block is constrained so that only low-frequency tones in the error signal are cancelled, thus enabling the feedback cancellation system to still cancel “whistling” at high frequencies due to the temporary instability of the hearing aid. A second adaptive filter block adaptively filters a feedback path signal to produce an adaptively filtered feedback path signal. The first and second adaptive filter blocks are identical and filter coefficients of the first adaptive filter block are copied to those of the second adaptive filter block. Using an LMS adaptation algorithm, filter coefficients of an adaptive filer of the feedback cancellation system are controlled by the adaptively filtered error signal and the adaptively filtered feedback path signal respectively inputted from the first and second adaptive filter blocks. The adaptive filter then produces an adaptively filtered modeled feedback signal to be subtracted from an electrical audio signal input for updating the error signal of the hearing aid. The hearing aid processes the updated error signal with a digital signal processor to generate an audio output.

Digitally controlled low-harmonic rectifier having fast dynamic responses

Abstract: This paper describes a completely digitally controlled low-harmonic rectifier. It is shown that the dynamics of the outer voltage loop can be significantly improved using a digital notch filter. Low input current harmonics and fast voltage response are experimentally verified using a 200 W universal-input boost power supply operating at the switching frequency of 200 kHz.

Photonic bandpass filters with high skirt selectivity and stopband attenuation

Abstract: A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown.

Efficient excitation quantization in noise feedback coding with general noise shaping

Abstract: In a Noise Feedback Coding (NFC) system having a corresponding ZERO-STATE filter structure, the first ZERO-STATE filter structure including multiple filters, a method of producing a ZERO-STATE response error vector. The method includes: (a) transforming the first ZERO-STATE filter structure to a second ZERO-STATE filter structure including only an all-zero filter, the all-zero filter having a filter response substantially equivalent to a filter response of the ZERO-STATE filter structure including multiple filters; and (b) filtering a VQ codevector with the all-zero filter to produce the ZERO-STATE response error vector corresponding to the VQ codevector.

Low-power CSD linear phase FIR filter structure using vertical common sub-expression

Abstract: A high-speed/low-power canonic signed digit (CSD) linear phase finite impulse response (FIR) filter structure using vertical common sub-expression is proposed. In the conventional linear phase CSD filter, the horizontal common sub-expression method (see Hartley, 1996) has been widely utilised due to the inherent symmetrical filter coefficients. However, use has been made of the fact that the most significant bits of adjacent filter coefficients in the linear phase filter are also equal since they have mostly similar values. Through the example, it is shown that the proposed structure is more efficient in the case where bit precision of implementation is lower.

Consecutive mean excision algorithm

Abstract: A new adaptive excision algorithm called consecutive mean excision (CME) is presented. The CME algorithm separates iteratively the initial set of samples to two sets: outlier set and desired signal set. The initial threshold parameter required by the CME algorithm is calculated in advance based on statistical properties of the noninterfered signal. The same initial threshold parameter is shown to operate in various interference scenarios regardless of interference power and bandwidth. In this study the CME algorithm is attached to the adaptive FFT notch filter. The performance of the adaptive FFT CME notch filter is shown to overcome the basic adaptive FFT notch filter using the single mean or single median approach in various interference scenarios when attached to direct sequence communications systems.

Reducing narrowband interference in a wideband signal

Abstract: Narrowband interference in a wideband RF signal is reduced by a notch filter operating at IF between down- and up-converters supplied by a local oscillator (LO) at a frequency controlled by a control circuit The control circuit detects interference by determining power in each of a plurality of narrowband channels, also at IF via another down-converter with a controlled LO frequency, relative to power of the wideband RF signal and scaled in accordance with the wideband and narrowband bandwidths The control circuit controls the LOs for scanning the narrowband channels to determine a channel with greatest interference and to filter out this narrowband channel with the notch filter In the absence of interference, the notch is tuned outside the signal bandwidth

Stationary frame harmonic reference generation for active filter systems

Abstract: Harmonic reference generators for active power filter systems are commonly implemented in the synchronous reference frame, so that simple low or high pass filter functions can be used depending on the requirements of a particular application. High pass filters in particular are used when the reference generator is required to produce an "everything but the fundamental" target waveform. This paper presents a stationary frame notch filter equivalent to a high pass synchronous frame harmonic reference generator for such systems. The use of the stationary frame allows for quicker calculation of the reference generation in a discrete digital implementation, and also allows classical control techniques to be used to analyze the active filter system without requiring synchronous frame transformations of the outside system model. Both simulation (continuous and discrete) and experimental results showing the equivalency of the stationary and synchronous frame reference generation process are presented using both shift and delta operator based IIR digital filters.

Increased mfcc filter bandwidth for noise-robust phoneme recognition

Abstract: Many speech recognition systems use mel-frequency cepstral coefficient (mfcc) feature extraction as a front end. In the algorithm, a speech spectrum passes through a filter bank of mel-spaced triangular filters, and the filter output energies are log-compressed and transformed to the cepstral domain by the OCT. The spacing of filter bank center frequencies mimics the known warped-frequency characteristics of the human auditory system, yet the bandwidths of these filters is not chosen through biological inspiration. Instead they are set by aligning endpoints of the triangle, which is itself an arbitrary shape. It is surprising that for such a popular speech recognition front end, proper analysis or optimization of the filter bandwidths has not been performed. With complex cochlear models, realistic filter shapes that more closely approximate critical bands are used. And these filters, compared to the filters used in mfcc, are considerably wider and overlap with neighboring filters more. We have extended this filter characteristic to the mfcc algorithm and found that the increased filter bandwidth improves recognition performance in clean speech and provides added noise robustness as well.

Band switchable filter

Abstract: A ferro-electric filter and method of tuning same. The filter includes a switch for switching between quarter wave resonator and half wave resonator modes. The filter also includes a ferro-electric component for tuning the resonant frequency. The method includes applying a switching control signal to the switch for switching between resonant frequencies and applying a tuning control signal for tuning the resonant frequency.

Notch filter for DC offset reduction in radio-frequency apparatus and associated methods

Abstract: A radio-frequency (RF) receiver includes a receiver analog circuitry and a receiver digital circuitry coupled together. The receiver analog circuitry receives an RF signal. The receiver analog circuitry processes the received RF signal and generates a digital signal that it provides to the receiver digital circuitry. The receiver digital circuitry includes a digital down-converter circuitry that mixes the digital signal provided by a receiver analog circuitry with a digital intermediate frequency (IF) local oscillator signal to generate a digital down-converted signal. The receiver digital circuitry also includes a digital filter circuitry that filters the digital down-converted signal to generate a filtered digital signal. The digital filter circuitry provides a notch at a frequency that corresponds to a residual DC offset of the receiver analog circuitry.

Tunable optical add/drop multiplexer with multi-function optical amplifiers

Abstract: A photonic circuit includes a tunable drop filter arrangement that includes a plurality of resonators. The drop filter arrangement is tuned to remove a selected frequency from an input data stream from a waveguide. A wavelength sensor coupled to the drop filter to monitor the selected frequency to which the drop filter arrangement has been tuned. A tunable laser presents a new signal of a defined frequency indicative of a signal to be added to the input data stream. A modulator coupled to the tunable laser for receiving the new signal and forming a modulated signal. An add filter arrangement coupled to the modulator for receiving the modulated signal and adding the modulated signal to the data stream.

Directly tuned filter and method of directly tuning a filter

Abstract: A Method for filter tuning using direct digital sub-sampling is provided. The tuning is accomplished in the digital domain by determining the filter characteristics from the shape of the transfer function. The input signal (1) is passed through the filter (3) and is then sub-sampled by and Analog-to-digital Converter (ADC) (5). The sub-sampled signal (6) is then processed in the digital domain using a digital circuit (7) that is used to determine the center frequency (Fc) and Quality factor (Q) and/or other important filter parameters. The Fc, Q and/or other important filter parameters are then adjusted by generating digital control signals (8) that can be converted to analog signals (10) using Digital-to-analog Converters (DACs) (9).

Branching filter and communication apparatus

Abstract: A branching filter includes a receiving surface acoustic wave filter and a transmitting surface acoustic wave filter, which are provided on a multilayer ceramic substrate. The branching filter further includes at least one matching element and a low pass filter, which are provided within the multilayer ceramic substrate. The matching element is connected to the receiving surface acoustic wave filter and the low pass filter is connected to the transmitting surface acoustic wave filter. The ground of the low pass filter is separated within the multilayer ceramic substrate from the grounds of the other circuit.

Diplex circuit forming bandstop filter

Abstract: A bandstop filter for use in CATV applications is formed by a pair of diplexers, a lowpass filter and a highpass filter. Signals having a frequency range of, e.g., 0-3 GHz enter at a first node connected to the inputs of both the lowpass and highpass filters. Signals having frequencies below a first, predetermined value pass through the lowpass filter, and signals having frequencies above a second, predetermined value pass through the highpass filter with signals having frequencies between the first and second values being blocked, i.e., “stopped.” The outputs of both the lowpass and highpass filters are connected to the second diplexer at a second node which is connected to the single output.

Passband-width broadening design for WDM filter with lattice-form interleave filter and arrayed-waveguide gratings

Abstract: We successfully fabricated a high channel count and flat-top wavelength-division-multiplexing filter by integrating a waveguide-type interleave filter and two arrayed-waveguide grating on one chip. Optimizing the loss ripple of the interleave filter, we realized a 50-GHz spacing, 102-channel ports, a 1-dB passband of 30 GHz, and an insertion loss of 4 dB.

Digital de-screening of documents

Abstract: A method and a system for de-screening an image signal. The system comprises a filter bank, a control module and a blend module. The filter bank filters the image signal and produces a set of filter output signals. The control module generates at least one control signal based on the image signal and some of the filter output signals. The blend module dynamically blends the filter output signals in accordance with the control signal to produce a de-screened output signal.

Controllable broad-spectrum harmonic filter (cbf) for electrical power systems

Abstract: A broad-spectrum harmonic filter is developed. This filter is to be connected in series ahead of the load which generates harmonics. This filter basically consists of 3 fixed elements, i.e. a series reactor and a shunt reactor in series with a capacitor. It can function to completely filter out 5th harmonic current in 3 phase systems (or 3rd harmonic current in single phase systems) and to reduce other harmonic components by high percentages say, typically close to 70%. Thus the portions of various harmonics flowing toward the electrical power source can be held within acceptable limits.

An adaptively-pipelined mixed synchronous-asynchronous digital FIR filter chip operating at 1.3 GigaHertz

Abstract: A high-throughput low-latency digital finite impulse response (FIR) filter has been designed for use in partial-response maximum-likelihood (PRML) read channels of modem disk drives. The filter is a hybrid synchronous-asynchronous design. The speed critical portion of the filter is designed as a high-performance asynchronous pipeline, sandwiched between synchronous input and output portions, making it possible for the entire filter to be dropped into a clocked environment. A novel feature of the filter is that the degree of pipelining is dynamically variable, depending upon the input data rate. This feature is critical in obtaining a very low filter latency throughout the range of operating frequencies. The filter was fabricated in a 0.18 /spl mu/m CMOS process. Resulting chips were fully functional over a wide range of supply voltages, and exhibited throughputs of over 1.3 Giga items/second, and latencies as low as four clock cycles. The internal asynchronous pipeline was estimated to be capable of significantly higher throughputs, around 1.8 Giga items/second. With these performance metrics, the filter has better performance than that reported for existing digital read channel filters.

Notch filtering and multirate control for radial tracking in high-speed DVD-players

Abstract: The problem considered in this paper is the radial tracking of the optical pick-up in a DVD-ROM player. For low-speed players, it is known that this problem can be solved by means of simple lead-lag regulators. For high-speed players, the servo design problem is more tricky, and a more sophisticated control architecture is required. The control scheme here proposed is constituted by a lead-lag filter and by two adapted notch filters. This set of filters is implemented in a parallel multirate structure. The resulting controller is simple, low-cost, and adequate to meet the required tracking-error specifications. The performance of the controller is tested on a real plant; experimental results are extensively reported.

New wide-band DC-block cymbal bandpass filter

Abstract: A new low-loss dc-blocking parallel-cascaded bandpass filter is presented. The filter is much easier to use and fabricate, more compact, and simpler to design than the conventional end- or parallel-coupled line filters. The filter has a wide passband with a 2:1 voltage standing-wave ratio bandwidth of around 10% and an insertion loss of 0.5 dB at 10 GHz. Simulated results agree very well with experimental results.