Showing papers on "Voltage-controlled filter published in 1992"

Time-domain filter bank analysis: a new design theory

Abstract: The authors present a new time-domain approach for the analysis and design of a broad class of general analysis/synthesis systems based on M-band filter banks. They derive a set of time-domain conditions for reconstruction which can be used directly in a filter bank design procedure. The general and unrestricted nature of this framework allows for the design of many useful banks. In addition to the complete derivation of the time-domain conditions, they also describe the associated filter bank design procedure and a number of design examples are included. >

High-linearity continuous-time filter in 5-V VLSI CMOS

Abstract: High-linearity self-tuning continuous-time filters, fabricated in a standard 1.6- mu m 5-V CMOS process, are presented. Frequency control is achieved using switchable arrays of highly linear double-polysilicon capacitors in an active RC filter structure, resulting in tunable filters with very low signal distortion. One filter, a Tow-Thomas biquad, exhibits dynamic range and signal linearity of typically 91 dB. Another smaller implementation, a Sallen and Key filter, attains >or=76 dB. Cutoff frequency response is maintained to an accuracy of around +or-5%. >

Active power line conditioner with fundamental negative sequence compensation

Abstract: An improved active power line conditioner is disclosed. A series inverter is controlled by a series filter controller which performs synchronous transformations on a load current to generate a series filter feedforward signal corresponding to the fundamental components of the load current. The series filter controller also generates a series filter reference signal corresponding to a negative sequence fundamental output voltage. The series filter feedforward signal and the series filter reference signal are combined to form a series filter compensation signal. The series filter compensation signal is applied to the series inverter to generate sinusoidal input currents, with negative sequence fundamental output voltage compensation, for a non-linear load. A parallel inverter is controlled by a parallel filter controller which performs synchronous transformations to generate a parallel filter feedforward signal corresponding to the harmonic ripple components of the load current. The parallel filter controller also generates a parallel filter reference signal corresponding to a negative sequence fundamental source current. The parallel filter feedforward signal and the parallel filter reference signal are combined to form a parallel filter compensation signal. The parallel filter compensation signal is applied to the parallel inverter to generate sinusoidal voltages, with source current negative sequence fundamental compensation, for the non-linear load.

Adaptation and training of digital finite impulse response filter within PRML sampling data detection channel

Abstract: A digital adaptive finite impulse response filter circuit is provided for a PR4,ML sampled data channel including an analog to digital sampler for providing raw digital samples of data to the filter circuit and a sampled data detector for detecting coded data from conditioned digital samples received from the filter circuit. The filter circuit comprises a multi-tap transversal filter structure wherein each tap is connected to receive a selected coefficient, a source of a plurality of coefficients for each tap, a coefficient selector connected to the source to receive the plurality of coefficients and to provide a selected coefficient to each tap of the transversal filter structure, and a control circuit for controlling the coefficient selector and the source for providing each of the selected coefficients to a corresponding tap of the transversal filter structure. Training and adaptation methods and circuits for adapting the filter structure are also described.

Vortex flowmeter electronics

Abstract: A vortex flow transmitter (10) has a filtering circuit (20) receiving a noise contaminated input signal representative of the flow and which has a fundamental frequency varying responsively to flow. The filter (20) filters the input signal using one of a family of HP filter characteristics. Each member of the family of HP filters has varying corner frequencies, each filter having a unique switchup and a unique switchdown value assigned to it. Adaptive response means (40) select a current HP filter for use in the filter means. The adaptive means use one selection method when the flow is increasing and another selection method when the flow decreases. Output means (52) convert the signal from the filter means into a transmitter output, typically a 4-20 mA current or a frequency output representative of the flow.

Combination surge and diplex filter for CATV distribution systems

Abstract: A combination surge and diplex filter is provided for a CATV distribution amplifier. In a first preferred implementation, an integrated surge and high pass filter section is provided when the CATV amplifier is used only in the forward direction. Provision is made for a plug-in low pass filter section which is matched to the high pass filter section. The plug-in low pass section is used to form a diplex filter if the reverse direction capability of the CATV system is required from the distribution amplifier. In a second preferred implementation, the integrated surge and high pass filter section is segmented into a surge filter segment which is designed as a divisible part of the high pass filter section. A plug-in module is then provided with a high pass filter segment having those components of the high pass filter section which were not necessary for surge protection and a low pass filter section matched to the high pass filter section. The plug-in module is utilized to form a diplex filter, if the reverse direction capability of the CATV system is required from the distribution amplifier.

Method and apparatus for automatic tuning calibration of electronically tuned filters

Abstract: A method and apparatus for automatic tuning calibration of electronically tuned filters which comprises a programmable frequency generator for producing a calibration frequency signal, a filter for filtering the calibration frequency signal, a detector for producing a detector voltage, a processor for programming the frequency generator to specific test frequencies and for producing a stepped filter tuning voltage and storing the detector voltage in response to the stepped filter tuning voltage, and a converter for digital-to-analog conversion of the stepped filter tuning voltage. Calibration frequency signal versus tuning voltage responses are stored for a number of calibration iterations within the usable range of the filter and the resulting table can be used to determine the correct tuning voltage for the filter when operating at any frequency within the usable filter range.

A varactor-tuned active microwave bandpass filter

Abstract: Traditionally, microwave filters have been implemented as passive networks of waveguide, transmission-line, or discrete lumped elements. More recently, microwave active filters have also been realized. A microwave high Q-active bandpass filter is presented. using a varactor diode for tuning, and an active component giving a substantial increase in Q of the resonant sections of filter. High-Q filter elements offer low-filter insertion loss and also yield sharp passband corners, which cannot be achieved by lossy filter and amplifier combination. >

System and method of producing adaptive FIR digital filter with non-linear frequency resolution

Abstract: A filter and method of adapting a digital filter provides a single fixed finite impulse response (FIR) filter adaptively from measured data, in a manner whereby the filter's frequency and time resolution can be controlled. The resulting filter exhibits properties which allow it to be efficiently implemented in various multi-rate configurations. Specifically, the system and method produce an FIR filter with high resolution at low frequencies by having a large number of coefficients, but reduces resolution at higher frequencies by allowing only a fraction of the coefficients to adapt to the high frequency part of the signal. This is accomplished by using a multi-rate, segmented adaptation procedure, such that resolution and bandwidth are controlled independently at each state. If desired, the resulting filter can be made to approximate constant Q resolution. In addition, by adapting only a short part of the filter at a time, misadjustment is minimized.

Multi-passband dielectric filter construction having filter portions with dissimilarly-sized resonators

Abstract: A filter duplexer, such as a filter duplexer for a radio transceiver, of minimum dimensions is disclosed. A first filter portion of the duplexer filter includes resonators of a first geometric configuration, and a second filter circuit portion of the duplexer filter comprises resonators of a second geometric configuration. The geometric configuration of the two filter circuit portions are dissimilar such that 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 resonator loading capacitances.

Intermediate frequency filter having a ceramic filter

Abstract: An intermediate frequency filter for an intermediate frequency used in the receiver section of a digital radio communications apparatus is composed of an amplitude-flat ceramic filter incorporating two ceramic resonators, a buffer means and a single tuning circuit having the center frequency thereof within the bandwidth of the amplitude-flat ceramic filter, all being connected in series with each other. The center frequency of the single tuning circuit and Q are adjusted to approximate the amplitude characteristic of the intermediate frequency filter to that of TBT filter (0.4≦parameter m≦1.0).

Digital filter system with changeable cutoff frequency

Abstract: Using stored discrete samples of filter coefficients at each of a plurality of discrete operating points, a filter control (e.g., CPU) provides dynamic control of a digital filter through an interpolator in accordance with a variable input indicative of a desired operating point (e.g., cutoff frequency) of the digital filter. In response to a large change in the desired operating point, the control produces a succession of operating point subgoals progressively approaching the changed desired operating point and a corresponding succession of filter coefficient subgoals. Each filter coefficient subgoal is calculated as a function of stored discrete filter coefficient samples near each operating point subgoal. In response to a new parameter set from the filter control, containing a new subgoal of the coefficients, the interpolator starts coefficient interpolating to smoothly move the operating point of the digital filter toward the new subgoal. By starting the interpolating operations after the updating of the parameter set has been completed, synchronization may be established among the interpolating operations on the coefficients.

FSF (frequency sampling filter) bank for adaptive system identification

Abstract: Some researchers have explored the use of filter banks to improve the performance of adaptive algorithms. However, some of these approaches have shown degradation in performance. A new class of filter bank (ideal orthogonal filter bank) is defined, which enables one to avoid the degradation, even if one chooses critical subsampling in adaptive filtering. A filter bank (pseudo OFB) whose frequency response is the same as that of the ideal OFB at discrete frequency points is proposed. As a result, using the proposed filter bank, one can identify an unknown system at the discrete frequency points. >

Filter circuit and filter integrated circuit

Abstract: A filter circuit and a filter integrated circuit capable of being used in a high frequency band comprises a first resistor R 1 connected between an input signal source and an emitter of a common-base transistor TR 1 , a first capacitor C 1 connected between said input signal source and a reference voltage point, a second capacitor C 2 connected between said input signal source and a collector of the common-base transistor TR 1 , and a second resistor R 2 connected between the collector of the common-base transistor and the reference voltage point. Thus, a low-pass filter which operates in a high frequency band and suppresses the influence of characteristic parameters over the filter characteristic can be constructed.

Device and method for adjusting a bandpass filter, especially a combiner filter

Abstract: The invention relates to a frequency adjustment method for an RF bandpass filter, especially a combiner filter, wherein the center frequency of the passband of the RF bandpass filter (22) is adjusted in response to the RF power reflected from the input of the bandpass filter or passed through the bandpass filter. In the method a sample signal (Pr) proportional to the RF power reflected from the input of the bandpass filter or passed through the bandpass filter is mixed (29) with a signal of substantially the transmitting frequency, the mixing result is lowpass-filtered (24) and the bandpass filter (22) is adjusted in response to the lowpass-filtered mixing result (24a).

Microwave active filter using GaAs monolithic floating active inductor

Abstract: A broadband tunable microwave floating active inductor is proposed. Its application in the microwave active filter is presented. The design technique is to replace the passive inductor in the conventional LC ladder filter by the proposed floating active inductor. These active filters can, therefore, be implemented in full MMIC form. © 1992 John Wiley & Sons, Inc.

Data filter tuning for constant density recording applications

Abstract: An arrangement for tuning a data filter in a mass storage system. The filter cutoff frequency (low pass) may be set as a percentage above or below the incoming data rate to achieve the desired "eye opening" in read data. The frequency of a reference oscillator in a phase-locked-loop (PLL) and the cutoff frequency of the filter is controlled by a common control signal from the PLL. The PLL, locked to a scaled multiple of the data rate, determines the cutoff frequency of the filter.

Agile bandpass filter

Abstract: Two variable frequency, fixed bandwidth bandpass 10, 410 are cascaded to form a bandpass filter with variable center frequency and variable bandpass. Each filter 10, 410 includes first (16, 416) and second (24, 424) mixers separated by a fixed bandpass filter (20, 420). Each mixer includes a control input terminal 30, 32: 430, 432 which receives a control signal (f LO , f OFF ). The center frequency of the filter arrangement is controlled by the frequency of control signal f LO , and the bandwidth is controlled by the difference frequency between f LO and f OFF . A tracking arrangement 456 allows direct control of the bandpass by control of the frequency of an offset oscillator 458.

Communication system including a digital roll-off filter

Abstract: A transversal type digital roll-off filter receiving a signal n-time sampled from analog signal carrying a pulse train of symbol rate T, includes a transversal type delay line including a plurality of delay elements each having a delay time T/n. Nodes are positioned between adjacent two delay elements. The filter further includes a memory for providing first tap rating ratios to control signals of the nodes and a calculation circuit for monitoring pulse forms of the output signal of the filter, and calculating second ratios to additionally control a central node and every n-th node counted from the central node, where the second ratios are calculated to make the output pulse good in shape. The filter acts as a roll-off filter and as an automatic equalizer. In a method of diagnosing the circuits in the above system, a memory in a transmitter further has second tap rating ratios used to diagnose the system, where the first and second ratios are switchably output to a digital filter in the transmitter. The second tap rating ratios allow the first filter itself alone to output good-shape pulses. The method includes the steps of switching the first memory to output the second ratios and comparing an eye diagram with a reference level, at a point after the first filter, to determine a cause of deteriorating the pulse forms.

Method and apparatus for automatically regulating notch filter of servo system

Abstract: PURPOSE:To automatically set a coefficient of a digital notch filter for removing a vibration of a servo system in a short time. CONSTITUTION:A digital notch filter 7 formed of a modeled discrete transfer function is isolated from a servo system, a measuring command signal VCM 2 is input from a functional generator 4 to the servo system to be tested. An operation signal to be output from the system when the system is tested by a central frequency setter 9 is frequency-analyzed. An unnecessary frequency component out of a speed loop response frequency band of a signal to be assembled in the filter is detected from the analyzed result to decide the unnecessary frequency component as a central frequency. Then, coefficients of discrete transfer function of the filter 7 are obtained from a coefficient setter 10 based on the relationship between the decided central frequency and an acutance, and substituted for the function.

A 20 MHz 6th order BiCMOS programmable filter using parasitic-insensitive integrators

Abstract: A fast parasitic-insensitive continuous-time filter that uses an active integrating-capacitor is described. The filter IC consists of a sixth-order Bessel lowpass and a second-order cosine-equalizer stage. It is made up of three biquads with lowpass and bandpass outputs. Both outputs of the last stage are available with matched group-delay characteristics. The corner frequency is digitally programmable through the digital serial interface to 64 values over a 4 to 1 range. Techniques for excess-phase nulling and Gm-setting independent of supply and temperature are described. This 20 MHz, 5 V equalizer has 0.24% of total harmonic distortion with 2 Vp-p signals and is built in 1.5 mu m/4 GHz BiCMOS. >

Tunable wideband active filter

Abstract: A wideband tunable (programmable) filter includes first-order and second-order filter circuits employing bipolar transistors. The bandwidth of the filter circuits are set by the product of the dynamic emitter resistance of the transistors and directly coupled on-chip capacitances. The filter bandwidth is inversely proportional to the time constant. To adjust the resonant frequency of the filter networks, emitter currents are varied, which in turn controls the emitter resistances. As the resonant frequency of the filter network is varied, the gain and normalized frequency response of the various output nodes remain constant. In the second-order configuration, the damping ratio of the filter is set using "positive" feedback, for a Q of greater than one-half, with a loop gain of less than one. Temperature compensation is accomplished by use of a temperature "dependent" voltage network. The output of this network provides the sum of the continuous temperature compensating voltage component and the externally controlled tuning voltage for the resonant frequency. This voltage is converted to currents that control the bandwidth of the filter so as to minimize dependence of the resonant frequency upon temperature.

Lowpass filter with improved D.C. offset performance

Abstract: A lowpass filter with improved D.C. offset characteristics is disclosed. The lowpass filter includes an adjustable amplifier, an offset detecting circuit for producing an offset signal proportional to the D.C. offset between the voltage from the adjustable amplifier and the voltage to the lowpass filter, and a feedback circuit for producing a feedback signal in response to the offset signal which controls the adjustable amplifier to reduce the D.C. offset.

Tracking of a time-varying acoustic impulse response by an adaptive filter

Abstract: A simple model is set up describing roughly the change of an acoustic impulse response if an object moves through a room. From this model, specifications can be formed regarding the length and convergence rate of an adaptive filter trying to track this change. It is shown that in many practical applications an adaptive filter would not perform better than the optimal fixed filter. Next, a more accurate model is set up for the change of an acoustic impulse response if an object moves through a room. An expression is worked out for the performane of a certain type of adaptive filter, the so-called LMS adaptive filter, in tracking this change for the case of white noise as input signal to the filter. It is shown that when the nonstationaries are due to a person walking through a normal living room, and the system has the bandwidth of speech or larger, an LMS adaptive filter cannot perform substantially better than a fixed filter. This result is in agreement with the results obtained with the simple model. >

Generalized feedforward filters with complex poles

Abstract: The authors propose an extension to an existing structure, the gamma filter, replacing the real pole on the tap-to-tap transfer function with a pair of complex conjugate poles and a zero. The new structure is, like the gamma filter, an IIR filter with restricted feedback whose stability is trivial to check. While the gamma filter decouples the memory depth from the filter order for low-pass signals, the proposed structure decouples the memory depth and the central frequency from the filter order for band-pass signals. The learning equations of the model parameters are presented and shown to introduce an additive O(p) complexity to the backpropagation algorithm, where p is the filter order. The error surface for a linear filter is investigated in a system identification context, and the presence of local minima is confirmed. The performance of the proposed model was found to be better than that of the time-delay neural net in a nonlinear system identification context. >

RC filter for low and very low frequency applications

Abstract: An RC filter for low or very low frequency applications, comprising a resistor between the filter input and output, and an amplifier connected after the resistor and having an output fed back to the amplifier input through a capacitor. This simple design allows the known Miller Effect to be utilized to produce a filter having a high time constant while employing small-size components which occupy little space in integrated circuits.

Lowpass temporal filter using motion adaptive spatial filtering and its systolic realization

Abstract: A motion adaptive spatial filtering technique is discussed for a temporal filtering of video signals, and its systolic realization method is investigated. The proposed filter is based on the basic idea that a temporal filter can be implemented by means of a space-variant spatial filter, on the assumption that the motion of each pixel is known. In general, a sequence of images containing moving objects are known to have inherently temporal aliasing components. The proposed method has an important characteristic that the aliasing components can be reduced. In spite of the space-variant characteristics of the filter, a systolic architecture suitable for its hardware implementation was devised, where a processing element was composed of three delay elements, one multiplier, one adder, and one lookup table. >

Linear-phase filter having high gain selectivity

Abstract: A switched capacitor lowpass filter is disclosed having four cascaded general purpose switched capacitor active filter blocks that combine with each other to produce a particular overall transfer function that has high gain selectivity and substantially linear phase response characteristics. The filter can also include a clock input which allows a user to select the cut-off frequency of the filter. The filter's characteristics are tailored in accordance with a method which: (1) introduces a notch frequency into the filter's gain characteristics, so as to improve the filter's gain selectivity near the cut-off frequency, and (2) linearizes the phase response characteristics of the overall filter, without modifying the magnitude of the gain of the notch-containing filter.

Design concepts of a novel microwave active filter

Abstract: A novel microwave active bandpass filter structure, using a combination of microstrip line resonators and FETs, is described. The resulting filter not only produces positive gain but also has good performance regarding sharpness of skirts, rejection, and input and output return losses. Capability of constructing wider bandwidth and its superior performance at harmonic band frequencies over an end-coupled filter structure are among advantages of this design.