Showing papers on "Voltage-controlled filter published in 1984"

Analog input circuit with combination sample and hold and filter

Abstract: An analog input circuit, which samples and holds predetermined components sampled from input signals, has a filter and a sample and hold circuit which are formed as a unitary structure to simplify the circuit structure. For this purpose, the operational amplifier of the filter is constituted by two stages of voltage-follower circuits that are connected in series via a switch, and a holding capacitor is connected to the the switch. When the switch is closed, the holding capacitor assumes the same potential as the output of the filter and when the switch is opened, the holding capacitor maintains the output voltage of the filter.

Computer tomography system and method for operating same

Abstract: A computer tomography system has an X-ray source and a radiation receiver having an array of individual detectors each forming an electrical signal corresponding to the received radiation intensity, the X-ray source being rotated about a subject for transradiating a layer of the subject from different directions, and a measured value processing circuit to which the output signals of the individual detectors are supplied and which identifies therefrom attenuation values of predetermined points in the transradiated plane of the subject for generating a display image. The measure value processing circuit has a convolution computer, and further has an adaptive digital filter and a filter control unit to which the signals from the array are supplied before being operating on by the convolution computer. The filter control unit controls the transfer function of the filter as a function of the filter input signal so as to substantially reduce image artifacts due to quantum and electronics noise.

Wide frequency band coupling network for an active ripple and noise filter

Abstract: A ripple and noise filter for high voltage DC converters or power supplies The filter includes a common terminal, an input terminal and an output terminal A voltage sensing circuit is connected between the output and common terminals of the filter and is adapted to produce a sense signal which is proportional to the output voltage at the output terminal An active filtering circuit, preferably an amplifier having a frequency operating range which covers the frequency spectrum of the ripple and noise voltages, includes an input for receiving the sense signal and an output at which a correction signal is generated The correction signal has a magnitude and waveform such that coupling the correction signal onto the output terminal of the filter eliminates or reduces the ripple and noise A passive coupling element, preferably a capacitor, isolates the amplifier from the output terminal and couples the correction signal thereto A passive filter, also a capacitor, is connected across the output and common terminals of the filter The coupling capacitor and the passive filter capacitor have nearly identical electrical characteristics so that the correction signal is coupled onto the output terminal without distortion over the full frequency operating range of the amplifier

Adaptive acoustooptic filter

Abstract: A new adaptive filter utilizing acoustooptic devices in a space integrating architecture is described. Two configurations are presented; one of them, suitable for signal estimation, is shown to approximate the Wiener filter, while the other, suitable for detection, is shown to approximate the matched filter.

Linear phase bandpass digital filters with variable cutoff frequencies

Abstract: A low-pass-to-bandpass transformation for linear phase FIR filters is discussed. The transformed bandpass filter is implemented in a network structure in which the cutoff frequencies are controlled through two parameters. The range through which the cutoff frequencies of the transformed filter can be varied depends on the cutoff frequency and the stopband edge frequency of the prototype low-pass filter. For a given prototype filter, this range is obtained from a set of simple graphs.

Suppression of Narrow-Band Interference in a PN Spread-Spectrum Receiver Using a CTD-Based Adaptive Filter

Abstract: Analytical results have shown that adaptive filtering can be a powerful tool for the rejection of narrow-band interference in a spreadspectrum receiver. However, the complexity of adaptive filtering hardware has hindered the experimental verification of these results. This paper describes a new adaptive filter architecture for implementing the Widrow-Hoff LMS algorithm while using only two multipliers regardless of filter order. This hardware simplification is achieved through the use of a burst processing technique. A 16-tap version of this adaptive filter constructed using charge-transfer devices (CTD's) is used to suppress a single tone jammer in a direct sequence spread-spectrum receiver. Probability of error measurements demonstrating the effectiveness of the adaptive filter for suppressing the single tone jammer along with simulation results for the optimal Weiner-Hopf filter are presented and discussed.

Analog RC active filter

Abstract: An RC active filter device which is implemented with integrated circuit technology. Each RC filter element of the device has a distributed series resistance and a distributed shunt capacitance. The series resistance is formed by a strip of resistive material which overlies a resistive plate (or substrate) with an intervening insulating layer to form the shunt capacitance. The filter device can be designed to have a pass-band ripple response which is not affected by variation in nominal absolute resistance and capacitance values resulting from process spreads. These variations only stretch or compress the filter response along the frequency axis. The filter device comprises three RC filter elements and an operational amplifier. The RC filter elements nearest the operational amplifier determine a low pass band, while the input filter element prevents high frequency components outside the low pass band being leaked directly to the filter device output.

Echo correction especially for television broadcast systems

Abstract: Echo cancellation is carried out on a received demodulated analog signal. The apparatus comprises an analog transversal filter, a computing circuit for generating the direct coefficients a1 to ar and, eventually, feedback coefficients b2 to bm of an analog transversal filter. The input of a computing circuit is connected to the input of an analog transversal filter. The computing circuit is comprised of an analog-to-digital converter, whose output is connected to a self-adaptive digital transversal filter. The values of the digital transversal filter multiplication coefficients are applied, as coefficients, to the multipliers of the analog transversal filter. The optimization criterion is that of the mean quadratic error. The convergence algorithm is that of the gradient. The iterative correction may be carried out at each step on the digital transversal filter's group of coefficients. Or, it can be carried out cyclically of each of the digital transversal filter's coefficients. Variations of the self-adaptive digital transversal filter are described.

Design of wave-sc filters using building blocks

Abstract: Besides switched-capacitor (SC) filters developed for high volume production, e.g. the PCM-codec lowpass filter, numerous low volume applications exist in the area of solid-state filtering. to open up this application field for SC filters, a novel wave-SC filter structure is presented. the filter design using this concept requires only moderate design and layout skills since only a limited library of highly modular building blocks is required. It is also suitable for analogue gate array applications. As will be shown, the wave equations which are known from the theory of wave digital filters can be realized using stray-insensitive SC integrators and SC amplifiers only. Exemplary designs of a lowpass, a highpass, and a bandpass filter will be carried out with the building blocks presented. the theoretical results are verified by measurements at the breadboarded lowpass filter.

The host windowing technique for FIR digital filter design

Abstract: A detailed description is given of a technique for designing finite duration impulse response digital filters in which one portion of the impulse response sequence is identified as a "host" filter which undergoes multiplication by a simple trigonometric window in order to implement the final "object" filter. This partitioning is found to be useful, both from the viewpoint of insight into error and transition width characteristics, and from the practical implementation aspect when variation of a frequency parameter (cutoff frequency for a low-pass filter or center frequency for a bandpass filter) is desired. Design results for families of variable filters are presented under conditions where the host filter has been preoptimized to give a close approximation to minimax behavior over a whole range of values for the variable frequency parameter-all for the price of a single initial host optimization procedure for the entire family, followed by a computationally easy modification method for any one member of the family. It is seen that useful performance guarantees can be offered to the user across a range of operating conditions, and that the penalty incurred is never more than a doubling of the peak error (and often much less) over that of minimax designs specifically and laboriously computed for each condition of the variable frequency. Therefore, high speed filter coefficient variation is found to be compatible with good quality filtering in a theoretical framework which readily admits extension to non-standard filter types such as arbitrary multiband filters. A glossary of terms is included at the end of the paper.

Tuner for communications equipment

Abstract: An tuner unit is provided for communications receivers with automatic self-balancing of the individual high frequency filter circuits. An assigned frequency applied to the desired receiver channel is fed to the antenna input during the automatic balancing process. The voltage of this assigned frequency picked up at the output of the filter circuits changes according to a stepwise increase of a tuning voltage controlled by a microprocessor. The tuning voltage is applied to the filter circuit to be balanced via a digital-analog converter and via a switching means controlled by the microprocessor. The automatic balancing is provided by switching the switching means successively to connect to the individual filter sections.

Alternating-current filter circuit arrangement

Abstract: In this three-phase filter circuit system for static converter systems and particularly high-voltage direct-current short ties, at least two high-pass filters are provided which are connected in parallel. Each high-pass filter consists of a choke connected in parallel with a resistance and, in series with both, a capacitor and can be individually connected to the three-phase busbar via a switch. The filter circuits are used not only for reducing harmonics but also as compensating devices, which can be switched in steps, for the reactive power requirement of the static converters so that in the lower partial load range of the system one of the filter circuits is disconnected for reasons of reactive power balance. In order to improve the filtering effect in this lower partial load range, a bus-coupler switch connecting in each case the common junctions of capacitor, resistance and choke of the high-pass filters is closed. When the switch is closed, this widens the band width of the filter circuit which is in operation and increases the resonance frequency, and individual distortions, the total distortion and telephone interference factors on the busbar are reduced.

Switchable bandpass filter

Abstract: A bandpass filter suitable for use in modem circuitry and other applications which require the filter's center frequency to be switched is disclosed. The filter circuit has the characteristic that although the center frequency is changed the overall gain of the filter remains constant. This characteristic results from using a plurality of filter sections which each have low individual gain and providing compensating gain at the input of the filter. In addition, compensating gain elements are used in each filter section so that when the center frequency of the filter is changed, the gain of each filter stage remains constant.

Computer generation of digital filter banks

Abstract: This paper will cover a 16-channel filter bank for speech recognition and a single filter generated by computer programs from filter descriptions. The dynamic range in the filter bank (112 pole) is 68dB and the area is 32 sq. mm.

Signal analysis apparatus including recursive filter for electromagnetic surveillance system

Abstract: The specification discloses a digital/analog signal analyzer for an electromagnetic surveillance system. Included is a notch filter having a switched capacitor filter controlled by a phase lock loop for nulling a time-varying driving frequency from the received signal. The analyzer further includes structure for digitizing the received signal and for implementing a recursive filter to enhance digital feature extraction. The recursive filter in turn includes structure for delaying a read address for subsequent use as a write address to facilitate the rapid updating of data in memory. Also included is a digital-to-analog converter assembly having a pair of piggy-backed digital-to-analog converters to produce an analog signal dependent upon both a mantissa and an exponent of a digital number in scientific notation.

Self-Tuning Filter for Instrumentation

Abstract: A microprocessor-controlled filter that tunes automatically to the fundamental of the input signal is described. Hardware and software implementation are shown, and the error in maximum amplitude selection is discussed. Filter performance using a switched capacitor tunable circuit is documented.

Digital filter for video signals

Abstract: For the receiving side of a digital colour television system operating with separate coding, a digital filter is specified which meets the requirements for little circuit complexity and processes all components in time-division multiplex despite their different sampling periods. The filter consists of a first filter section (F0) and a second filter section which is an interpolating filter in parallel form with two filter branches (F1, F2). Several examples of this part-filter are specified by means of their transfer functions. Time-division multiplex processing is made possible by the fact that the delay time of the delay stages (D) contained in the digital filter is matched to the sampling period of the different components, which is achieved by building up the delay stages (D) from several switched delay elements (DFF1, DFF2, DFF3).

An Integrated 18th Order VIS-SC Pseudo-N-Path Filter

Abstract: Experimental results of an 18th order integrated bandpass filter in VIS-SC technique will be presented. This filter has been designed for use as "channel filter" e.g. in a PCM/FDM transmultiplexer.

Method and apparatus for de-ringing a switched capacitor filter

Abstract: A switched capacitor filter system is provided which is programmed to filter a predetermined sequence of tone signals. The filter system is de-rung after each selected tone signal is detected by increasing the clock frequency of the switched capacitor from the programmed value corresponding to a tone signal up to a center frequency substantially greater than that of the tone signals. Energy stored in the filter system is thus quickly dissipated. Rapid sequences of sequential tone signals are thus filtered without the problems associated with ringing of the filter.

Electrical filter comprising resonant circuits.

Abstract: A filter, such as a bandpass filter for use at intermediate frequencies in a radio transmission system, includes at least one filter stage comprising a common-emitter transistor (1) having resonant circuits (4, 5) in both its collector and emitter circuits. The ratio of the impedances of the resonant circuits (4, 5) determines the frequency response of the filter. The resonant circuits (4, 5) are isolated from one another by the transistor (1) so that they can be individually tuned. The presence of the transistor (1) also enables the input return loss of the filter to be determined independently of the tuning of the resonant circuits (4, 5). Individual filter stages can be cascaded.

Extension facilities and performance of an LSI adaptive filter

Abstract: An integrated modular solution for an audio band digital adaptive filter has been designed in LSI technology, which combines independent 240 tap adaptive and programmable FIR filters with coefficient interchange, based on a distributed normalisation architecture. Up to four filter units can be cascaded with optimum performance. Four step-sizes are provided internally with optional further external reduction for application to noisy channels.

Analogue wave filter device

Abstract: An RC active filter device which is implemeted with integrated circuit technology. Each RC filter element of the device has a distributed series resistance and a distributed shunt capacitance. The series resistance is formed by a strip of resistive material which overlies a resistive plate (or substrate) with an intervening insulating layer to form the shunt capacitance. The filter device can be designed to have a pass-band ripple response which is not affected by variation in nominal absolute resistance and capacitance values resulting from process spreads. These variations only stretch or compress the filter response along the frequency axis. The filter device shown in Figure 2 comprises three RC filter elements 1, 2 and 11, and an operational amplifier 3. The RC filter elements 1 and 2 determine a low pass band. The filter element 11 prevents high frequency components outside the low pass band being leaked directly to the filter device output.

Ground speed detector

Abstract: PURPOSE:To determine a correct ground speed removing effects of disturbance due to ruggedness or the like of ground surface, by having a Doppler signal passing through a band-pass filter which changes in the center frequency according to the speed to perform a speed display using a signal fetched. CONSTITUTION:The detection signal from a Doppler sensor 2 is fed to a low- pass filter 21 passing through an amplifier 20 and then, to band-pass filter 22 and a phase comparator 28 of a PLL circuit 27. The band-pass filter 22 employs a switched capacitor filter. The PLL circuit 27 is provided to make output frequency synchronize the frequency of an input signal and the center frequency of the band-pass filter 22 varies in the frequency of according to a reference signal (clock signal) corresponding to the vehicle speed. A signal with a fixed width fetched from the band-pass filter 22 is fed to speed display 26 passing through an F/V converter 24 and an A/D converter 25.

High-frequency GaAs transversal filter

Abstract: A transversal filter integrated circuit, fabricated using 1 μm GaAs MESFET technology, is described. The filter uses 280 MESFETs, has a clocked delay line and on-chip tap weighting to give three different filter responses. Operation has been demonstrated up to a clock frequency of 400 MHz, which is believed to be the fastest reported operation of a clocked transversal filter.

On the reconstruction of a smooth function out of its samples

Abstract: The reconstruction of smooth signals out of its samples will be considered. Using a sampling frequency higher than the Nyquist rate we are able to define a family of appropriate idealized systems for the reconstruction. They are approximated by a realizable system consisting of a digital filter followed by a D/A-converter and an analog smoothing filter. The design of the digital (nonrecursive) filter will be performed in the frequency and time domain. Some examples will demonstrate these reconstruction procedures.

High-speed single-board flexible hardware implementation of a wave digital filter

Abstract: The hardware implementation of a sixth-order wave digital filter on a single printed-circuit board has been described in the literature. In the present paper, a greatly improved hardware design is discussed. By including more parallelism into the architecture, sampling rates of over 500 kHz can be achieved for a fifthorder filter. With the aid of a microprocessor development system, the filter can be programmed for any order up to 15. Once programmed, the filter runs independently. An example is given, which illustrates the hardware performance with various coefficient wordlengths. Attention is also paid to the question of in-band noise.

Electronic filter devices

Abstract: An electronic filter device comprises a high frequency section and a low frequency section. The high frequency section has an input coupling loop connected to an input connection of the filter device, and a gyromagnetic resonance element. The low frequency section comprises at least one inductor and at least one capacitor connected to the input coupling loop of the high frequency section. The two sections of the filter device have separate output connections.

Design and Analysis of Linear Predictor-Corrector Digital Filters

Abstract: In application, it is believed that the third order linear predictor-corrector digital filter, or commonly known as the α-β-, tracking filter. can be derived from the Kaiman filter. In this paper, we characterize the values of α,β, and , so that theα-β-, tracking filter is indeed a limiting Kaiman filter, and derive the input to observation noise ratios in terms of the stochastic parameters as functions of α,β and , to allow the user to design the α-β-, filter to obtain near-optimal performancez-transform is used to uncouple the filter and to study stability.

Modified state-space filter realisation

Abstract: An active second-order bandpass filter section is derived from the state-space realisation known as the symmetric-form filter and has the same F-matrix. It is shown that this new filter section is similar to the symmetric filter insofar as it has practically the same sensitivities of `ωp' and `Q´ and has certain advantages over the symmetric filter.