Showing papers on "Butterworth filter published in 1993"

Input filter design for power factor correction circuits

Abstract: The issues involved in the design of power factor correction circuit input filters are significantly different than those involved in the design of input filters for DC-DC power converters. So far, there exist no guidelines for high-frequency AC power converter input filter design. This paper addresses these issues and proposes the use of a high order, actively damped filter to achieve the required EMI attenuation and power factor requirements. The new filter topology typically provides 50% filter size reduction over the standard filter designs, and simultaneously minimizes the filter-converter interaction. >

A BiCMOS low-distortion 8-MHz low-pass filter

Abstract: An 8-MHz seventh-degree elliptic-function low-pass filter is described, demonstrating an approach to low-distortion antialias filtering for high-definition video applications. The filter's performance goals are achieved through the use of circuit design principles that capitalize on the strengths of BiCMOS technology. The integrator circuits composing the filter consist of a new wideband low-distortion transconductor circuit and a unique BiCMOS Miller-stage circuit. Integrator time constants are determined by stable RC products, enabling a simplified filter calibration scheme that is insensitive to temperature-induced variations and requires no phaselock circuits. The prototype filter IC, consisting of seven integrators assembled in an active-ladder configuration, was fabricated in a 10-V, 2- mu m 2.5-GHz BiCMOS technology that also features thin-film resistors and polysilicon-plate capacitors. Measured results from the calibrated filter show passband flatness of 0.2 dB, with aberrations of less than +or-1 dB over a 100 degrees C temperature range. Stopband attenuation meets its designed goal of 60 dB. Driven by 7-V/sub pp/, differential input signals, the filter exhibits less than -72-dBc third-order intermodulation distortion products at 1 MHz. For 5-V/sub pp/ inputs at 4 MHz, third-order intermodulation spurs remain below -65 dBc. >

Design and characterization of optimal FIR filters with arbitrary phase

Abstract: An algorithm for designing a Chebyshev optimal FIR filter that approximates an arbitrary complex-valued frequency response is presented. This algorithm computes the optimal filter by solving the dual to the filter design problem. It is guaranteed to converge theoretically and requires O(N/sup 2/) computations per iteration for a filter of length N. For the first time, properties of the optimal filter are derived, and the case where the desired filter has arbitrary constant group delay is studied in detail. >

A 2.5-V active low-pass filter using all-n-p-n Gilbert cells with a 1-V/sub p-p/ range

Abstract: This paper describes the design and measured results of an all-n-p-n low-voltage (2.5 V), low-current (1 mA), large-swing (1 V/sub p-p/), low-distortion (-53 dB, 1 V/sub p-p/) active filter using a conventional bipolar process. The transconductors for the filter are composed of Gilbert cell transconductors. Distortion has been improved by feedback circuits without increasing the supply voltage and without using p-n-p transistors. The filter is a gyrator-capacitor type third-order Butterworth low-pass filter with a nominal cutoff frequency of 192 kHz. A voltage scaling technique has been applied directly to the gyrator-capacitor filter. This has improved the signal-to-noise ratio by 3 dB. Simulation results indicated that a fast operation up to tens of MHz is possible with a standard bipolar process, as the signal path is composed only of n-p-n transistors. >

Transversal filter for use in a digital subscriber line transmission interface

Abstract: A transversal filter has a transfer function for which a zero point occurs outside a unit circle on z plane and thus the output waveform has a ringing characteristic having a change from negative to positive around a precursor and before a main cursor and is associated and integrated with another transversal filter, thereby forming a waveform shaping decimation filter or a pulse shaping high-pass filter. The waveform decimation filter can eliminate a high frequency noise, changes a high frequency input data to a low frequency output data, and performs a waveform shaping operation. Therefore it cannot require a pulse shaping filter separated from the decimation filter. The pulse shaping high-pass filter includes a pulse shaping filter whose number of the taps is decreased and performs high-pass filter function. A pulse shaping filter whose number of the taps is decreased can be used separately from the high-pass filter.

Saw notch filter for improving stop-band attenuation of a duplex filter

Abstract: When the bandwidth of a duplex filter having a certain band-width, intended for a radio telephone, is increased by affecting the coupling between the resonator circuits, the stop band of the filter is at the same time deteriorated. According to the invention, the stop-band attenuation can be improved by coupling a surface-wave filter, coupled as a notch circuit, in parallel with one of the resonator circuits of the duplex filter.

Combined decimation/interpolation filter for ADC and DAC

Abstract: A COMBINED DECIMATION/INTERPOLATION FILTER FOR ADC AND DAC (analog-to-digital converter and digital-to-analog converter) provides a single filter which may be used both as a decimation filter and as an interpolation filter. It is simple and inexpensive. It gains simplicity and inexpensivenes by carefully selecting the tap weights of the filter, cascading multiple filters, time domain multiplexing the multiple filters into a single filter, and using adders instead of multipliers to provide the tap weights.

Control method for a combined active filter system employing a current source converter and a high pass filter

Abstract: This paper describes a control method with a combined filter system which senses load current, source current and line voltage to create reference signals for an active filter. The transfer function of the active filter is identified and is used for the control system design. It is shown that the source current feedback is most effective to suppress the harmonic-enlarging effects due to parallel resonance and the harmonic current generated by source harmonic voltages. A small setup controlled by a DSP was built, and the validity of the proposed method was demonstrated by experimental results. >

Cochlear filter bank with switched-capacitor circuits

Abstract: A parallel dilating-filters switched-capacitor filter bank is described in simulation of the cochlea. Area-saving is achieved by filter-sharing, effective sum-gain amplifier designs, and using area efficient nth-order filter designs, and in particular using a biquadratic filter design using charge-differencing. The structure is easily expandable to include more channels by extending with additional filters and output amplifiers, or by using several chips with different sampling frequencies in parallel connection. An offset-compensated area-efficient switched-capacitor sum-gain amplifier circuit design is described and can be used in the filter bank.

Optimal and suboptimal detection of optical fibre digital PPM

Abstract: The discrete time modulation format, known as digital PPM, has been used to exchange channel bandwidth for improved signal-to-noise ratio in optical communication systems. However, the filter that optimises signal detection is complex in that it comprises a prewhitened matched filter in cascade with a proportional-derivative-delay network. In this form, the receiver would be unrealistic for a commercial system. This paper examines the use of both optimum and suboptimum detection. Three suboptimum predetection filters are considered: a matched filter, an optimised three-pole filter and a third-order Butterworth filter. Original receiver sensitivity calculations, carried out at a bit rate of 140 Mbit/s and a wavelength of 1.3 μm, show that the optimum digital PPM system offers an 8.6 dB improvement over a typical PCM system. The suboptimum predetection filters result in sensitivity degradations of 0.4, 0.9 and 1.1 dB, respectively. This clearly illustrates that receiver complexity can be simplified without large reductions in sensitivity. In particular, the well known and simple Butterworth filter can be employed with only 1.1 dB degradation in sensitivity.

Closed form design of prototype filters for linear phase DFT polyphase filter banks

Abstract: A complex modulated subband coding filter bank with almost perfect reconstruction is discussed. It is realized by means of discrete Fourier transform (DFT) polyphase filter banks with high computational efficiency. In the analysis and the synthesis part of the filter bank, the same linear phase prototype filters are used. A closed-form design of the prototype filter is presented in the form of a square root raised-cosine function weighted by a Hamming window. This design method provides small amplitude and aliasing distortion with few filter coefficients, and enables a trade-off between the two different kinds of distortion. >

The design of nonuniform-band maximally decimated filter banks

Abstract: A design method for nonuniform-band maximally decimated filter banks is presented. It is based on the quadrature mirror filter (QMF) design method and allows the direct frequency domain design of two-band filter banks having arbitrary rational decimation ratios. The numerical design of nonuniform-band filter banks is achieved using a simple structure in which elementary modulators are used in the highpass channel to obtain almost-perfect reconstruction. >

Optimization of Butterworth filter for brain SPECT imaging.

Abstract: A method has been described to optimize the cutoff frequency of the Butterworth filter for brain SPECT imaging. Since a computer simulation study has demonstrated that separation between an object signal and the random noise in projection images in a spatial-frequency domain is influenced by the total number of counts, the cutoff frequency of the Butterworth filter should be optimized for individual subjects according to total counts in a study. To reveal the relationship between the optimal cutoff frequencies and total counts in brain SPECT study, we used a normal volunteer and 99mTc hexamethyl-propyleneamine oxime (HMPAO) to obtain projection sets with different total counts. High quality images were created from a projection set with an acquisition time of 300-seconds per projection. The filter was optimized by calculating mean square errors from high quality images visually inspecting filtered reconstructed images. Dependence between total counts and optimal cutoff frequencies was clearly demonstrated in a nonogram. Using this nomogram, the optimal cutoff frequency for each study can be estimated from total counts, maximizing visual image quality. The results suggest that the cutoff frequency of Butterworth filter should be determined by referring to total counts in each study.

Co-planar and microstrip waveguide bandpass filter

Abstract: A bandpass filter for the transmission of signals within a predetermined frequency bandwidth having a center frequency, which provides for substantial attenuation of the harmonic components of the center frequency of the filter. The bandpass filter includes at least one resonator comprising a strip conductor and a ground conductor formed on the surface of a dielectric substrate. The strip conductor is capacitively coupled to the ground conductor so as to substantially transmit the harmonic components of the center frequency of the filter to ground.

Multi-passband, dielectric filter construction

Abstract: A filter duplexer (280), such as a filter duplexer for a radio transceiver, of minimum dimensions is disclosed. A first filter portion (304, 308, 312, 316) of the duplexer filter includes resonators of at least a first geometric configuration, and a second filter circuit portion (320, 324, 328, 332, 336) of the duplexer filter comprises resonators of a second geometric configuration. The geometric configuration of the two filter circuit portions are dissimilar, and the relative characteristic admittances of the resonators of the respective filter circuit portions are dissimilar. Because the resonators of the two filter circuit portions are of dissimilar electrical characteristics, a desired frequency response of the duplexer filter may be obtained with similar loading capacitances.

A 5th order bilinear elliptic switched-current filter

Abstract: A fifth-order lowpass bilinear elliptic filter, employing second-generation regulated-cascode switched-current cells, has been integrated on a standard 1.2-/spl mu/m digital CMOS process. The filter is based on the bilinear s /spl rarr/ z transformation, which results in a simple circuit realization using switched currents. The filter occupies an area of 1.5 mm/sup 2/, has been tested up to a clock frequency of 5.75 MHz, and consumes 27 mW quiescent power. Detailed measurements were taken at a clock frequency of 2 MHz, giving a measured passband edge of 350 kHz, a stopband edge of 420 kHz, a passband ripple of 0.6 dB, and a minimum stopband attenuation of 26 dB. This integrated filter has demonstrated the level of complexity and performance achievable using switched-current techniques.

On-vehicle sound field correction device

Abstract: PURPOSE: To provide the on-vehicle sound field correction device that is able to correct a sound field of a listener into an optimum sound field optimum to a seat position corresponding to a change in the seated position. CONSTITUTION: The device is provided with a correction FIR filter arithmetic section 12 correcting an amplitude 1 phase characteristic of a digital audio input signal, a filter coefficient storage section 17 storing plural kinds of filter coefficients of the correction FIR filter arithmetic section 12, a seat position discrimination means 15 discriminating a seated position, a filter coefficient selection means 14 selecting a filter coefficient of the kind corresponding to the discriminated seat position from the filter coefficient storage device, and a filter coefficient replacement device 16 replacing the filter coefficient of the correction FIR filter arithmetic section 12 with the selected filter coefficient to correct the sound field by replacing the filter coefficient of the correction FIR filter arithmetic section 12 with the filter coefficient corresponding to the discriminated seat position. COPYRIGHT: (C)1995,JPO

Practical filter design

Abstract: Butterworth filters Chebychev filters elliptic filters active elliptic filters other ways of replacing inductors other forms of active filter special purpose filters switched capacitor filters.

Adaptive nonrecursive digital filter and method for forming filter coefficients therefor

Abstract: An adaptive nonrecursive digital filter includes a first filter unit having N controllable filter coefficients. A control unit controls the filter coefficients as a function of an input signal applied to the first filter unit at a given sampling rate and as a function of a difference between a reference signal and an output signal output by the first filter unit, in accordance with the least mean error square in each case. The first filter unit and the control unit sample the input signal and the reference signal continuously, with a cyclically varying delay, at a correspondingly increased sampling rate. A second filter unit is operated at the given sampling rate and has N controllable filter coefficients. The second filter unit receives the input signal, outputs a further output signal and has filter coefficients also being controlled by the control unit.

Least squares IIR filter design on a logarithmic frequency scale

Abstract: A technique is described for designing infinite impulse response (IIR) digital filters where the arbitrary desired frequency response is approximated with respect to the log of frequency. The technique uses the inverse of a spectral transformation to produce a prewarped specification, from which a prototype filter is designed using a suitable least-squares algorithm. The forward spectral transformation is then used on the filter to realign its frequency response with the original specification. The prewarping operation reduces the frequency resolution required in the filter design process, making it possible to use efficient, optimal design techniques that use a linear frequency scale. An algorithm is presented for the computation of the spectral transformation parameters which maximize the advantages of the prewarping operation. The error weighting function it introduces is derived and compensated for in the filter design process. The utility of the method is demonstrated with a design example. >

A low-voltage low-power current-mode high-pass leapfrog filter

Abstract: A low-power bipolar continuous-time low-frequency high-pass second-order Butterworth filter is presented that works in the current domain and operates from a single 1.3-V battery. The filter contains two adjustable in- tegrators. These integrators are realized by means of a capacitance and an adjustable transconductance amplifier with an indirect output. The complete filter, including all capacitances needed, can be integrated in an ordinary full-custom IC process. A semicustom realization is shown. The filter demonstrates operation down to 1 V with less ~:han 16 #W power consumption and a dynamic range of 50 dB. Its cutoff frequency can be exponentially tuned with a control current over a range from 100 Hz to 1 kHz.

Design and analysis of recursive filters with optimum clutter rejection using zero frequency initialization

Abstract: A novel method is described for designing optimum recursive MTI filters by using zero frequency initialization as a pre-design technique. The designed filters offer optimum clutter rejection for a given clutter power spectrum and a finite number of samples. The performance of the designed filters were studied by considering their improvement factors and frequency responses. It has been found that the new filters offer better rejection characteristic than covariance recursive filters and conventional Butterworth filters with the same pass-band.

Computation of harmonic comb filter weights

Abstract: Harmonic comb filters are characterized in the frequency domain by notches arranged at equal intervals, and centered about DC. For a finite impulse response harmonic comb filter, the characteristic polynomial has its roots on the unit circle at equal angular intervals, symmetrically about 1+j0. A simple formula for the coefficients of such a polynomial and for their derivatives with respect to the frequency interval is presented. This result is applied as well to the computation of Butterworth filter parameters. >

Design of phase equalizers for recursive filters

Abstract: A least-pth optimization method for the design of an allpass filter to act as a phase equalizer for a given recursive filter is described. The method is applied to various elliptic filters, and the combined filter/equalizer designs are compared with corresponding nonrecursive designs. An optimum equalizer-filter combination can be obtained by selecting a filter with a small passband ripple in the amplitude response. Overall, an equalized design requires substantially fewer filter coefficients, typically 15 to 75% less, than a corresponding nonrecursive design obtained using the Remez exchange algorithm. >

Filter device for transmitter-receiver antenna

Abstract: A filter device for a transmitter-receiver antenna includes a transmission side filter having resonators and a reception side filter having resonators. Each of the transmission side resonators has a first characteristic impedance ratio other than one. On the other hand, each of the reception side resonators has a second characteristic impedance ratio being set to a value which prevents spurious resonance of the reception side filter at an integral multiple of a fundamental resonance frequency of the transmission side filter, so as to avoid the situation where spurious components increase at the above-noted integral multiple in a frequency characteristic of the transmission side filter being affected by a frequency characteristic of the reception side filter.

A limiting filter for application in a GPS receiver

Abstract: The authors discuss the design of a limiting filter, a new type of microwave circuit device that is essentially a filter modified by the addition of PIN diodes or other protection devices that give the filter nonlinear limiting properties in its passband. In one potential application, for protecting the front end of a microwave receiver, a limiting filter would prevent receiver interference from out-of-band signals, as well as avoid receiver upset or damage by limiting in-band RF transients. The design specifications for the front end of a commercial global positioning system (GPS) receiver were used as a guideline for designing the limiting filter. Measurements of the prototype limiting filter are compared to theoretical calculations, and rather good agreement with measurements is observed. The measured results show that the limiting filter with diodes on the first and last resonators has characteristics that are essentially identical to those of a standard filter of the same type at low power levels, but begins limiting at 0.1 dBm and obtains greater than 30-dB isolation at power levels above 0.5 W. >

Branching filter having specific impedance and admittance characteristics

Abstract: A branching filter in which an input/output port, a first dielectric filter for use in transmission and a second dielectric filter for use in reception are coupled with each other through a branching filter circuit. The branching filter circuit includes a first line provided between the input/output port and an input port of the second dielectric filter, a second line provided between the input/output port and an output port of the first dielectric filter, and a third line provided between the input/output port and the ground. In the filter, conductor lines for use in connection between ports are used for the first and second lines.

Design of miniaturized dielectric duplexer with attenuation poles

Abstract: A design method is conceived for a miniaturized antenna duplexer with attenuation poles. Its effect is indicated by using it as an antenna duplexer for the 800-MHz portable telephone. The transmitting filter has a band-rejection filter characteristic of an elliptic function type while the receiving filter has a Chebyshev bandpass filter with attenuation poles. Previously, the design of these filters has been carried out by an optimum design using an iterative approximation from an initial design value. Hence, a large amount of computation time was required. This paper proposes a design method without an iterative approximation. In the transmission filter, resonators with a low characteristic impedance are used. In the conventional band-rejection filter design of an elliptic function type, the linearity of the reactance slope of the resonators is degraded and the insertion loss near the passband edge increases. A method of compensating for this increase is presented. In the receiving filter, the design equation for the conventional Chebyshev characteristic was modified. It is shown that a bandpass filter characteristic with attenuation poles can easily be designed. A branching circuit is added to these filters, and an antenna duplexer is constructed with a minimum number of components by the circuit transformation. The computed values of the filter characteristic agreed well with the actual example. In comparison with the optimization method based on the iterative approximation, the amount of computation for the design was about one-twentieth.

A programmable continuous-time filter

Abstract: The synthesis of a real-time programmable continuous filter in which both the cutoff frequency and the selectivity are controllable independently over a wide range is described. The approach is based on a circuit topology derived from an LC ladder, and allows the filter to be configured either as low-pass or band-pass. The filter order is easily programmed. A new MOS high-frequency differential integrator with adjustable phase characteristics is presented. >

Cascaded acoustooptic/fiber Fabry-Perot filter with finesse over 2000

Abstract: A compound optical filter consisting of an integrated acoustooptic filter in series with a fiber Fabry-Perot filter possesses a very high effective finesse of over 2000 as well as the unique multichannel passband capability of the acoustooptic filter. The fine-grain element in this pair is a narrow (0.5-AA) passband Fabry-Perot filter, and the coarse-grain element is a wide tuning range (130-nm) polarization-independent integrated acoustooptic filter. The composite device has the narrow passband of the Fabry-Perot, the wide tuning range of the acoustooptic filter and the tuning speed of the faster acoustooptic filter (5 mu s). >