Showing papers on "Band-stop filter published in 1990"

Gradient-based adaptive IIR notch filtering for frequency estimation

Abstract: The use of gradient-based algorithms with infinite impulse response (IIR) notch filtering for estimating sinusoids imbedded in noise is investigated. Two notch filter model structures are presented. The first is for applications where two signal sources with correlated noise components can be assessed. The second can be used in situations where only one composite signal source is available. Error surface analysis indicates that second-order modules are unimodal and result in guaranteed convergence. Higher-order modules are multimodal and require judicious choice of initial parameter estimates. Simulation results are included to demonstrate the performance characteristics of both filter structures. >

CMOS active filter design at very high frequencies

Abstract: A study of the limitations of active CMOS filters at high frequencies suggests automatic means to compensate imperfections in the filter response introduced by active devices. The effects of nonzero FET output conductance, limited frequency response and noise on the filter characteristics, and dynamic range are analyzed, particularly for filters with high Q components. These are used to demonstrate a 3- mu m CMOS realization of a fourth-order bandpass filter with a 250-kHz passband centered at 12.5 MHz. The filter demonstrates that the maximum frequency of filter operation is not as seriously limited by device f/sub T/ as was previously thought, but that automatic means may be used to tune out the imperfections introduced in the filter elements by the limited voltage gain and frequency response of transistors. >

Integral switched capacitor for filter/digital to analog converter for sigma-delta encoded digital audio

Abstract: A combined finite impulse response filter and digital-to-analog converter for converting sigma-delta over-sampled data into analog form. The filter removes out-­of-band noise energy from the reconstructed analog signal resuting from the sigma-­delta encoding process. The filter/converter is implemented in switched-capacitor technology. Further, a method of designing the optimum number of taps and the tap weight coefficients of the filter is given.

Tunable bandpass filter system and filtering method

Abstract: A tunable bandpass filter system and filtering method wherein the bandwidth of a tunable bandpass filter is adjusted as a function of the fundamental frequency of an input signal. Either a constant bandwidth or a constant quality factor tunable bandpass filter may be used. The center frequency of the tunable bandpass filter is adjusted in direct proportion to the product of the fundamental frequency and the number of a selected harmonic thereof. In the case of a constant bandwidth filter the bandwidth is adjusted in direct proportion to the quotient of the fundamental frequency divided by a selected filter quality factor. In the case of a constant quality factor filter, the bandwidth is indirectly controlled by adjusting the center frequency while adjusting the quality factor in inverse proportion to the harmonic number. The output amplitude of the filter is measured to determine the amount of distortion in the input signal. The fundamental frequency may be determined by measuring the input signal.

Frequency tracking using constrained adaptive notch filters synthesised from allpass sections

Abstract: New constrained adaptive notch filter structures are proposed. These structures are synthesised from allpass filter sections, which are realised as structurally lossless bounded real functions with a minimum number of delay elements and multipliers. Both structures admit orthogonal tuning of their notch frequency and bandwidth. Frequency tracking is achieved simply by the evaluation of a function of a filter parameter. Connections are shown with the structures used by other workers. Signal enhancement outputs are obtained from both structures and their signal-to-noise improvement ratios are given. The mirror-image pair of polynomials present in a real allpass transfer function is shown to provide a significant simplification in the generation of the necessary gradient terms used in parameter adaptation. Simulations are included to verify the performance of these structures when they are used to track both single and multiple sinusoids in additive broadband noise.

Adaptive digital filter including low-pass filter

Abstract: ADAPTIVE DIGITAL FILTER INCLUDING LOW-PASS FILTER ABSTRACT OF THE DISCLOSURE An adaptive digital filter for estimating a response characteristic of a signal path by monitoring a sampled output signal of the signal path, estimating a predetermined number of filter coefficients which represent the response characteristic of the signal path, and generating an estimated output signal of the signal path using a plurality of successive sampled input signals of the signal path and the estimated filter coefficients, where the estimation is carried out so that a difference between the output signal and the estimated output signal is reduced. Each of the filter coefficients is extracted by a low-pass filter where the low-pass filter coefficient in the low-pass filter can be set to a constant. Normalization can be carried out in either the input side or the output side of the low-pass filter. Otherwise, the low-pass filter coefficient may be set to 1-K?Xj(m)2/r, where r is set equal to a norm of the sampled input signals in the beginning, and is then set to an integrated power of the sampled input signals.

High frequency continuous time filter

Abstract: A high-frequency integrated circuit continuous time low pass filter. An on-chip oscillator is built into the filter. The filter frequency accuracy is established by trimming the frequency of the on-chip oscillator during wafer probe. The oscillator is off during normal operation of the filter. Therefore, the filter does not produce noise that will degrade the performance of the filter during normal operation. After trimming, the filter design is such that accuracy is maintained even during temperature and power supply changes. The adjustment can be made without the oscillator by direct measurement of the filter response.

Current mode allpass/notch and bandpass filters with reduced sensitivities

Abstract: A current processing filter with two transfer functions (bandpass and notch/allpass) directly available is described. It uses a first generation current conveyor and six passive components. It is demonstrated that the choice of the passive component values leads to low passive and active sensitivities. The frequency, f0, and the quality factor, Q, can be chosen independently as regards the notch/allpass configuration. Simulation results made with SPICE confirm the theoretical analysis and are given and discussed.

Adaptive filter technique for suppression of wideband or offset narrowband radio frequency interference

Abstract: The adaptive filter for frequency modulation of the present invention utilizes an audio tone multiplexed into the baseband modulation spectrum as a pilot tone to control and determine the amount of adaptation of the effective and variable bandwidth of the filter for optimum selectivity and rejection of wideband interference or narrowband offset interference. The multiplexed tone is detected and the filter is adjusted according to the signal-to-noise ratio of the detected tone. A continuous and adaptive decrease or increase in bandwidth is produced to accommodate the actual signal bandwidth to achieve rejection of interference with minimum distortion. Additionally, the filter compensates for transmitter drift of center frequency. This filter may be used at radio or intermediate frequencies.

Filter system with controlled amplitude in stopband or passband

Abstract: A filter system which may be configured either as a stopband (notch) or passband filter having controlled gain and low ripple throughout its stopband or passband. The system includes a filter network which is operative for splitting an input signal spectrum into a pair of complimentary spectrum components and a coupler for proportionately combining these spectrum components in accordance with a prescribed gain factor. The filter network may either comprise a pair of complimentary band reject and band pass filters connected to a common input terminal or a diplexer including identical filters coupled between a splitter and a combiner.

Interference detection and reduction

Abstract: Interference detection and reduction is disclosed in which an interference carrier is reduced by processing a signal of an input frequency to a demodulator such as a PSK signal appended with bit sequence for carrier recovery and bit timing recovery for use in the TDMA system, for example, a signal of the intermediate frequency (IF) band of a 140 MHz center frequency, so that the attenuation of a band-elimination filter is limited to a value smaller than a certain one, or for the frequency bands in which spectra are produced by the bit sequence, the IF signal is combined with the band-elimination filter output via a narrow band-pass filter to control the attenuation in each of these frequency bands to a value smaller than a certain one, thereby preventing the signal quality of the TDMA signal from being degraded by the insertion of the band-elimination filter. An interference detector of a multiplexer sweep system can be obtained by combining the functions of the phase-lock loop and the filter multiplexer so as to permit the estimation of the frequency of an interference carrier with a relatively simple structure.

Design and characteristics of active power filter using current source converter

Abstract: A current-source active power filter that consists of a current source active filter (AF) and second-order high-pass filters (HPFs) is described. A pulse-width-modulation (PWM) control method is described. It is shown that excellent total filter performance over a wide frequency range is obtained with a low AF switching frequency. The design criteria for AF and HPF, i.e. the carrier frequency of AF, the component values of HPF, and the inductance of a DC reactor, are presented. The compensation characteristics of the filter are derived from experimental results. >

A high‐throughput Raman notch filter set

Abstract: A chevron‐type Raman notch filter (RNF) set is described. lt combines a high signal throughput (up to 90% around 1600 cm−1 and ≳80% between and 700 and 2700 cm−1) with a laser line suppression of 108–109. The filter set can be used to replace the first two dispersion stages in triple‐stage Raman monochromators commonly employed in multichannel detection systems. This yields a gain in intensity of the detected Raman signal of a factor of 4. It is shown that in Raman spectrometers with a backscatter geometry, the filter set can also be used to optically couple the microscope and the spectrometer. This leads to a further increase in signal intensity of a factor of 3–4 as compared to the situation where a beam splitter is used. Additional advantages of the RNF set are the fact that signal throughput is almost polarization independent over a large spectral interval and that it offers the possibility to simultaneously record Stokes and anti‐Stokes spectra.

Design of linear phase FIR notch filters

Abstract: This paper investigates some approaches for designing one-dimensional linear phase finite-duration impulse-responses (FIR) notch filters, which are based on the modification of several established design techniques of linear phase FIR band-selective filters Based on extensive design examples and theoretical analysis, formulae have been developed for estimating the length of a linear phase FIR notch filter meeting the given specifications In addition, the design of two-dimensional linear phase FIR notch filters is briefly considered Illustrative examples are included

Method of controlling filter time constant and filter circuit having the time constant control function based on the method

Abstract: A method of controlling the time constant of a filter for use in a radio receiver which receives a signal, transmitted from a transmitting station at a predetermined period, intermittently at the predetermined period and demodulates and delivers the received signal, a filter circuit having the time constant control function based on the method, and a radio receiver having the filter circuit. Preferably, the filter has its time constant switchable stepwise and specifically, parallel connection of capacitors or shortcircuiting of resistors is controlled by turning on/off switches. A controller within the filter circuit or the radio receiver performs control for applying a predetermined periodical signal (or standard pulse signal) to the filter and controlling the time constant of the filter in accordance with an output signal (or triangular pulse) during a first time zone within each operation interval for the intermittent reception and for filtering the signal from the transmitting station and causing a demodulating circuit to demodulate and deliver a filtered signal.

Co-channel interference filter for digital high definition television receiver

Abstract: A high definition television system includes a transmitter and receiver pair in which the receiver includes a co-channel interference filter having a comb filter and an intersymbol interference filter. The frequency response of the comb filter is selected to attenuate NTSC co-channel interference signals. The response of the intersymbol interference signal filter is selected to provide cancellation of the intersymbol interference signals produced by the comb filter.

A varactor-tuned, active microwave band-pass filter

Abstract: A microwave tunable high-Q active bandpass filter was developed using a varactor diode for tuning and a MESFET to provide negative resistance for increasing the tank circuit Q-value. Tuning ranges of 500 MHz for the one-pole filter and 430 MHz for the two-pole filter were achieved with a center frequency of 10 GHz. A 3-dB bandwidth of 20 MHz for the one-pole filter and 80 MHz for the two-pole filter was obtained. The passband insertion loss is typically 0+or-1 dB. >

Frequency agile, dielectrically loaded resonator filter

Abstract: A frequency agile, dielectrically loaded bandpass filter is disclosed in which capacitive layers on the top surface of the filter are selectively switched to ground in order to affect a change in the center frequency of the passband response of the filiter. A PIN diode switching network, including a means for biasing the diode, is used to effectively place the capacitive layers in parallel with the quarter-wavelength transmission line resonators contained within the block of the filter.

Dynamic digital IIR audio filter and method which provides dynamic digital filtering for audio signals

Abstract: An improved dynamic digital IIR (Infinite Impulse Response) audio filter and method provides a remedy for the major problems in state of the art digital IIR filtering and dynamic digital filtering for audio. In particular, the required multiplier coefficient size is reduced, such that 16 bit coefficients are adequate for good frequency resolution. In addition, the data size of the multiplier is also reduced, to be similar to the input and output data resolution without inferior noise performance. Furthermore, the structure is easily modified to allow the fixing of the DC (Direct Current) gain of the IIR filter to unity regardless of coefficient choice, eliminating any problems with filter dynamic range at low frequency passbands. Additionally, a dynamic filter structure allows logarithmic filter sweeps and compresses the coefficients further down to as few as 8 bits with adequate resolution for audio throughout the band. The structure allows the alteration of sweep of the filter without excessive computation or the requirement to read the current sweep value.

Adaptive tracking notch filter system

Abstract: An automatic tracking notch filter system tracks a large-magnitude narrow band signal through frequency effectively eliminating it. A frequency variable notch filter is responsive to a control input at which is applied a small amplitude AC dither signal. The resulting fluctuation in frequency of the notch filter causes corresponding fluctuations in the magnitude of the notch filter output. The output signal is rectified and band pass filtered around the dither frequency before being demodulated with the dither signal to provide a DC error signal indicating the magnitude and direction in frequency of the filter misalignment. The error signal is integrated and input to the control input of the notch filter with the dither signal such that the notch filter tracks the narrow band signal in response to the feedback signal provided at its control input.

Surface acoustic wave waveguide-coupled resonator notch filter

Abstract: A surface acoustic wave (SAW) waveguide-coupled resonator filter is overcoupled to produce an essentially constant conductance and susceptance over at least the bandwidth of a desired notch filter. The SAW resonator filter is embedded in a bridged-T allpass circuit to provide the pair of equal capacitances of the circuit, and the resonator ground is connected to one terminal of the parallel inductor of the circuit having the other terminal connected to a system ground.

A nonlinear digital filter using multi-layered neural networks

Abstract: A nonlinear digital filter utilizing multilayered neural networks is proposed. This filter significantly reduces random noises superimposed on signals which contain sharp edges, while preserving their sharpness. In addition, degradation of the capability for noise reduction due to the increase of the noise power is greatly suppressed compared to previously proposed nonlinear filters. The high performance of this neural filter is demonstrated in computer simulations and actual image processing. When the noise power is small, the performance of the neural filter is almost the same as that of the epsilon -filter, which corresponds to a simplified neural filter; however, when the noise power is large, the effectiveness of the neural filter is clearly demonstrated. >

Programmable filter/equalizer for duel speed and density magnetic recording devices

Abstract: A programmable filter for the read channel of a magnetic recording device filters the sensed signals corresponding to data on magnetic media at at least two different transfer speeds of the magnetic media. The programmable filter, under microprocessor control, selectively switches its filter characteristics without affecting the quality of the filter but changing the cut-off frequency so as to correspond to the two different transfer speeds. The programmable filter of the present invention utilizes solid state switches to implement the switching of the filter characteristics to change the cut-off frequency without affecting the quality. The programmable filter is inductorless and is designed only with resistors and capacitors arranged in a filter network. The programmable filter does not use operational amplifiers, using instead low cost transistors in an emitter-follower configuration. The cut-off frequency of the filter is changed by adding resistance or capacitance in series or in parallel with existing resistances and capacitances in the resistor-capacitor network so as to change the cut-off frequency without affecting the quality. The programmable filter of the present invention provides pulse slimming thereby reducing intersymbol interference, provides sharp roll-off characteristics to minimize higher frequency noise, and produces a voltage output corresponding to the sensed data signals as well as a differentiated voltage output having the identical delay as the voltage output.

Bidirectional communication line filter and surge protector

Abstract: This invention relates to a communication line filter for use in series with communication lines. The communication line filter provides for surge protection from voltage spikes and provides frequency filtering to remove selected interference signals from other radiating sources. The communication line filter comprises: two signal conductors linked together by a fuse; a common signal ground; and two shunts for shunting a surge current between the signal conductors and the common signal ground. The shunts provide protection from short duration voltage spikes while the fuse provides protection from longer duration overvoltages. The communication line filter functions effectively, independent of the direction of current flow along the communication line with respect the line filter. The two shunts and the fuse are selected to provide the required capacitance and impedance respectively, to form a suitable frequency notch filter.

CMOS VHF transconductance-C lowpass filter

Abstract: Experimental results of a VHF CMOS transconductance-C lowpass filter are described. The filter is built with transconductors as published earlier. The cutoff frequency can be tuned from 22 to 98 MHz and the measured filter response is very close to the ideal response

Pole-zero decision feedback equalization for the digital subscriber loop

Abstract: A decision feedback equalizer (DFE) containing a feedback filter with both poles and zeros is proposed for high-speed digital communications over the subscriber loop. The feedback filter is composed of two sections; a relatively short finite-impulse-response (FIR) filter that cancels the initial part of the channel impulse response, which may contain rapid variations due to bridge taps, and a pole-zero filter than cancels the smoothly decaying tail of the impulse response. It is shown that the feedback filter can be adapted using existing infinite-impulse-response (IIR) adaptation techniques. Numerical results using a simulated subscriber loop impulse response show that a feedback filter with two poles adapted via a simplified gradient algorithm can offer significant improvement in mean squared error (MSE) (i.e., 3 to 4 dB at a signal-to-noise ratio of 20 dB) relative to a conventional DFE of the same complexity. >

Microwave frequency agile active filters for mic and mmic applications

Abstract: The purpose of this paper is to present newly developped microwave frequency agile active resonators which, in a planar structure, may be realized using MIC or MMIC technologies. Consisting of a modified Hair pin resonator feedback by an amplifier and a phase shifter, these resonators offer extremely low loss and high Q value resonators. The use of vamctors permits a tuning of the resonant frequency as well as the bandwidth. Using such resonator, a bandstop filter with a rejection of 45 dB and a lossless band pass filter with a return loss of 35 dB have been obtained at 3.1 GHz.

Light level equalizing method

Abstract: PURPOSE:To smooth the light levels of respective wavelengths or frequencies at a reception terminal by arranging a Mach-Zehnder type optical filter which has variable transmission characteristics on a transmission path and adjusting the transmission characteristics of this optical filter. CONSTITUTION:Plural optical amplifiers 1 and the Mach-Zehnder type optical filter 4 are provided on the transmission line from an optical multiplex signal transmitter 2 to a receiver 3. Then the peak wavelength and maximum-minimum transmission ratio of the optical filter 4 are adjusted. Then the opposite transmission characteristics from an original light level are obtain even for an optional light level gradient. Consequently, the optical filter 4 is connected to the optical amplifier 1 in the final stage to flatten the light level of each channel transmitted through the optical filter 4.

Gram-schmidt space-time adaptive filter using transverse orthonormal ladder filters

Abstract: A space-time adaptive filter system is provided for eliminating unwanted signals from a radar or communication system. The filter system receives a main channel and several auxiliary channels wherein the target signal is not correlated between the various signal channels. Correlated noise components are eliminated by decorrelating the signals. The adaptive filter includes a Gram-Schmidt processor for sequentially decorrelating the auxiliary signals from the main signal. Each decorrelation element of the Gram-Schmidt processor comprises a transverse orthonormal ladder filter.

A digital transmission system, an apparatus for recording and/or reproducing, and a transmitter and a receiver for use in the transmission system

Abstract: A digital transmission system has a transmitter (3,6,9) and a receiver (13,16,19). The transmitter includes a coder for subband coding of the digital signal, by dividing the digital signal band into successive subbands having approximately equal bandwidths. The receiver recontructs a replica of the digital signal by merging the subbands to the digital signal band. The transmitter includes analysis filter means (6) and receiver includes synthesis filter means (16). The filter coefficients in the analysis filter means are unequal to the filter coefficients in the synthesis filter means.