Showing papers on "Voltage-controlled filter published in 1990"

A new approach to harmonic compensation in power systems-a combined system of shunt passive and series active filters

Abstract: A novel approach to compensating for harmonics in power systems is presented. It is a combined system of a shunt passive filter and a small rated series active filter. The compensation principle is described, and some filtering characteristics are discussed in detail. Excellent practicability and validity to compensate for harmonics in power systems are demonstrated experimentally. Although the source harmonic voltage was only 1%, the source harmonic current reached about 10% before the series active filter was started. After it was started, no harmonic current flowed into the shunt passive filter. In addition, no harmonic voltage appeared at the terminals of the shunt passive filter, because the source harmonic voltage was applied to the series active filter. The total loss of the series active filter was less than 40 W. It is concluded that the combined system is far superior in efficiency to conventional shunt active filters. >

A practical approach to harmonic compensation in power systems-series connection of passive and active filters

Abstract: The authors present a combined system with a passive filter and a small-rated active filter, both connected in series with each other. The passive filter removes load produced harmonics just as a conventional filter does. The active filter plays a role in improving the filtering characteristics of the passive filter. This results in a great reduction of the required rating of the active filter and in eliminating all the limitations faced by using only the passive filter, leading to a practical and economical system. The active filter has a much smaller rating than a conventional active filter. Experimental results obtained from a prototype model are shown to verify the theory developed. >

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.

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.

Method and apparatus for dynamic midi synthesizer filter control

Abstract: A method and apparatus are disclosed for the dynamic control of a MIDI synthesizer filter. A digital filter controlled by a plurality of filter coefficients is preferably coupled to the output of an excitation signal source within a MIDI synthesizer. The excitation signal source is typically controlled by a MIDI data file comprising a sequential series of program control commands and matching note on and note off commands. A plurality of filter coefficient factors are stored in memory and periodically accessed in response to variations in the program control commands and matching note on and note off commands. The selected filter coefficient factors are then utilized to calculate appropriate filter coefficients so that the center frequency and filter Q of the digital filter may be dynamically and optimally controlled. In a preferred embodiment of the present invention a filter control circuit is also utilized to limit the output of the filter to a maximum level so that output stability is always maintained, independent of the initial conditions and filter coefficients of the filter.

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. >

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.

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. >

Design and DSP-chip implementation of a novel bilinear-LDI digital Jaumann filter

Abstract: The design and implementation, on a digital signal processing (DSP) chip, of a novel high-quality recursive digital filter is presented. The proposed digital filter is derived from an equally resistively terminated lossless Jaumann two-port network by using the bilinear-LDI (bilinear lossless discrete integrator) design technique. It has the important practical property that all the inductor-based states can be computed simultaneously and all the capacitor-based states can be computed simultaneously, thereby permitting a fast parallel-processing speed which is virtually independent of the order of the filter. This digital filter can be made minimal in the number of multipliers, requiring n multipliers for the realization of lowpass and bandpass filters, and n+1 multipliers for the realization of highpass and bandstop filters, where n is the order of the continuous-time prototype reference filter. It is shown that when implemented using modern DSP chips, such a filter exhibits very high-quality performance characteristics. >

A very small MMIC variable filter based on a new active filter design concept

Abstract: A novel MMIC (monolithic microwave IC) active filter is proposed for realizing a small-size variable bandpass filter with high selectivity at microwave frequencies. A second-order bandpass filter based on the proposed design concept occupies a 1.2*1.3 mm/sup 3/ area on the GaAs substrate. It is controllable for both quality factor Q, varying from 20 to 200, and a center frequency wider than 100 MHz at the 1.3 GHz band. A fourth-order bandpass filter was also fabricated by cascading two of the filter chips together. This is expected to be a key device in the future development of frequency-variable equipment. The design concept, fabrication, and measured performance of the filter are described. >

A CMOS switched-current filter technique

Abstract: Basic design techniques and considerations for switched-current (SI) circuits are presented, and experimental results from integrated filters are given. By means of analogies to switched-capacitor circuits, a five-pole lowpass Chebyshev SI filter has been integrated in a 2- mu m N-well, double-metal CMOS technology. The average die area is about 200 mil/sup 2/ per SI pole. The current mirror gain factors were derived by means of signal flow-graph techniques starting with the RLC prototype. A doubly terminated five-pole Chebyshev filter was designed for a 0.1-dB ripple bandwidth of 5 kHz with a sampling frequency of 128 kHz. The measured response is shown. The noise floor is about 70 dB down with respect to the passband. A three-pole elliptic SI filter has also been integrated to illustrate the realization of transmission zeros with SI filter techniques. >

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.

A realization of a GaAs FET microwave active filter

Abstract: A methodology for microwave active filter design has been presented by this author (see ibid., vol.37, no.9, p.1418-24, 1989). The present work serves to verify aspects of this design approach. A practical implementation of a network discussed in that work is given. First, an ideal preliminary design for a second-order bandpass filter is obtained. Next, the nonideal effects of the active devices and the lossy reactive elements are introduced, and then optimization is used to obtain the final design. Finally, the filter is constructed and tested. The measured response is found to agree quite closely with the design specifications. The filter section is constructed in hybrid form with lumped components, and uses two NEC 900100 GaAs FETs. The prototype accurately realizes a second-degree bandpass response with a center frequency of 6 GHz and a pole q of 2.5. >

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.

400 MHz switching rate GaAs switched capacitor filter

Abstract: The letter presents experimental results for a second order switched capacitor bandpass filter designed to operate with a 250 MHz switching frequency and implemented using gallium arsenide (GaAs) technology. Measurements on a chip fabricated in a 0.5 μm GaAs process confirm that the filter design, amplifier and switching components meet the desired performance specifications. The filter operates with high precision at 300 MHz and bandpass filtering at a switching frequency of 400 MHz is demonstrated.

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

Digital filter with dynamically variable filter characteristics

Abstract: Filter coefficients corresponding to a plurality of discrete cutoff frequencies are stored in advance in a memory and a filter coefficient corresponding to a specified cutoff frequency is generated by performing an interpolation referring to the filter coefficients stored in the memory, thereby saving the capacity of the memory. When a resonance index is to be specified in addition to the cutoff frequency, filter coefficients corresponding to two difference resonance indexes are acquired by the interpolation, then a new filter coefficient is acquired by executing the interpolation referring to these two filter coefficients.

2-D analog filters for real time video signal processing

Abstract: A practical hardware design of a two-dimensional (2D) analog filter proposed by M.A. Sid-Ahmed (IEEE Circ. and Syst., vol.36, p.153-4, Jan. 1989) is developed. The structure is implemented using charge coupled device (CCD) analog shift registers and wideband operational amplifiers. The operation of the filter is demonstrated by processing TV video images in real time. The 2D analog approach is evaluated by comparison with a 2D distributed arithmetic digital filter. The analog approach offers realization at lower cost, less power consumption, higher resolution, and inherent true real-time capability independent of filter order. >

Integrated filter circuit

Abstract: An integrated filter (10) having a controllable frequency response includes a pair of cascaded differential transconductance amplifiers (12, 14) with the differential outputs of the first one of the pair being coupled to the differential inputs of the second one via coupling resistors (32, 36) and the differential inputs of the first one being coupled to inputs of the filter via input coupling resistors (20, 22). The differential outputs of the second transconductance amplifier are coupled both to outputs of the filter and are fed back (50, 52 and 54, 56) to the respective differential inputs of the two amplifiers to provide multiple inputs such that the damping factor of the filter is controllable for adjusting the filter frequency transfer function by varying the ratio of the coupling resistor value to the feedback resistor value while the damping factor is independent of the natural resonant frequency of the filter. Series coupled integrating capacitors (26, 28 or 38, 40) are coupled across the differential outputs of both pairs of amplifiers with the interconnection therebetween return to ground.

A hexa-mode bandpass filter

Abstract: Practical multiple-mode degeneracies of rectangular cavities which are directly applicable to multimode bandpass filter designs are presented. A six-pole, Ku-band, pseudoelliptic, single-cavity bandpass filter has been successfully designed and built. Since all interresonator couplings were realized via tuning screws, fabrication and alignment were greatly simplified. This design offers significant savings in mass and volume compared to dual- and triple-mode, six-pole filter designs with equivalent Qs. >

Design of a quasi-planar broadside end-coupled bandpass filter

Abstract: The design method circumvents the problem of bandwidth limitation imposed on the conventional end-coupled filter realized by coplanar strips. To realize a filter with such a complicated shape, an accurate tridimensional deembedding of the filter discontinuity problem based on the quasi-TEM (transverse electromagnetic) variational spectral-domain approach is developed. This approach leads to the design of a 30% bandwidth bandpass filter which agrees favorably with the measured performance. >

Electronic musical instrument using filters for timbre control

Abstract: A filter calculating section has a plurality of basic filters formed on a time-divisional basis. The timbre of a musical tone signal is controlled by a memory section, an accumulator, a selector, an I/O assign section and a control section using the basic filters formed by the filter calculating section. A digital filter coefficient stored in a digital filter coefficient memory is read out using integer data output from a cutoff controller as an address. An interpolation circuit interpolates this digital filter coefficient on the basis of fraction data output from the cutoff controller. Based on the interpolated digital filter coefficient, the timbre of a musical tone signal is controlled.

Tunable/adaptive second-order IIR notch filter

Abstract: A modified second-order infinite impulse response (IIR) notch filter with constrained poles and zeros is presented to eliminate or retrieve sinusoids embedded in a broadband signal. Such a filter is ideally suited to either parallel or cascaded implementation. Two classes of problems are considered. The first is where the sinusoidal frequencies are known a priori. For this case a straightforward design procedure based on a set of design characteristic graphs is used to select tunable notch filter parameters. An interesting property of the notch filter model is that it can be converted to a line enhancer by interchanging the position of the poles and zeros. The second type of problem arises when the sinusoidal frequencies are unknown and possibly varying with time. This means that an adaptive solution is required and an important consideration is the parameter estimation accuracy. For this purpose, the paper derives the Cramer–Rao lower bound for the adaptive cascaded notch filter using a frequenc...

Auto-tuning circuit for an active filter used in video signal processing

Abstract: An auto-tuning circuit for automatically adjusting the transfer function of an active filter for processing video signals. A voltage-controlled filter is used as active filter, for imparting a predetermined transfer characteristic to a signal having a component related to a television signal. The transfer characteristic can be adjusted in accordance with a voltage. The auto-tuning circuit comprises PLL section connected to the voltage-controlled filter, and switching circuit. The PLL section applies to the voltage-controlled filter a control voltage corresponding to the phase difference between a reference signal and an output signal obtained by passing the reference signal through the voltage-controlled filter. The switching section allows transfer of signals between the voltage-controlled filter and the PLL section for at least one of the horizontal blanking period and vertical blanking period of the television signal.

Balanced filter circuit having a controllable balanced current multiplier

Abstract: A balanced filter circuit has a number of balanced pushpull amplifiers (10) whose inputs (11, 12) and outputs (13, 14) are coupled to filter resistors (20, 21, 22, 25, 27A/B) and filter capacitors (23, 24, 26A/B). In order to adjust the filter, the currents from the filter resistors to the inputs of the balanced amplifiers are varied by means of adjustable balanced multipliers (40).

Adaptive high pass filter having cut-off frequency controllable responsive to input signal and operating method therefor

Abstract: An adaptive high pass filter comprises a switched capacitor filter (11) operable as a high pass filter, detecting circuits (14, 15, 16) for detecting low frequency signal components included in an input signal (V i ) and control circuits (17, 18, 19) for controlling the switched capacitor filter (11) responsive to the detecting circuits. In this adaptive high pass filter, a cut-off frequency thereof is controlled responsive to low frequency signal components of the input signal. Therefore, a reproduced voice is not varied dependent upon changes in a quality of voice and surrounding environments. Thus, the reproduced voice is much closer to its original voice.