Showing papers on "Voltage-controlled filter published in 1980"

Sample-and-hold hybrid active RC filter

Abstract: A discrete-time analog filter for eliminating a variable frequency carrier of an amplitude-modulated signal. The filter comprises a plurality of unit delay circuits, each of which is sampled at a rate which varies in proportion to the frequency of the carrier so as to automatically tune the filter's reject band to follow the carrier frequency.

Image processing apparatus including a partitioned low pass channel

Abstract: An electronic image processing system, providing image enhancement and noise suppression, processes signals representing an array of picture elements, or pels. The system is of the kind providing a feature-enhanced output by the addition of outputs of a high-pass filter acting as an image-feature detector and a complementary low-pass filter. The low-pass filter, which also acts as an image-feature detector, includes a bandpass filter and a further low-pass filter. The latter filter (122) includes a prefilter (130 and FIG. 22) and a sub-sampling filter (132) based on a set of weighting patterns in the form of sparse matrices (FIG. 23). The bandpass filter (120) includes a similar prefilter (128) and a sub-sampling filter (134) based on a set of weighting patterns in the form of sparse matrices (FIGS. 26 and 27) that act as detectors of selected image features.

Maximally flat f.i.r. filter with prescribed cutoff frequency

Abstract: Maximally flat f.i.r. digital filter design provides the advantage of giving a closed-form solution, but there still remains a problem of designing such a filter whose magnitude response passes through a prescribed cutoff frequency point. It is described here how to generate a class of transitional maximally flat f.i.r. digital filters to overcome such a difficulty.

Bandstop filter for very high frequency transmission lines and biassing circuit for a very high frequency transistor comprising this filter

Abstract: A bandstop filter for very high frequency transmission lines having distributed constants, having several filtering elements each intended to prevent the transmission of a specific frequency band. The first filtering element is a quarter-wave filter, the second element an assembly of two transmission paths of a length such that the signals present at the outputs have opposite phases and cancel other, the third element being a quarter-wave filter, these elements being grouped such that they form an extremely compact filter which is little sensitive to proximity effects.

Frequency-phase coding device

Abstract: A doppler-tolerant pulse-compression code generator for generating a plurty of approximately orthogonal codes which will prevent radar interference and suppress jamming. These codes are generated by phase-coding the frequency-band steps and also altering the time-sequence of the frequency steps of a step-approximation to a linear FM chirp pulse. Specifically, this code generator may comprise a circuit for modulating a carrier frequency with a video pulse of bandwidth B having a length less than or equal to a desired compressed pulse length, a tapped delay line having n signal taps for sequentially delaying this video pulse, a comb filter comprising a series of n bandpass filter channels each passing different spectral bands in the bandwidth B, a switching matrix for connecting each of the n signal taps to a different one of the n bandpass filters in a controlled manner, a phase-coding circuit in each bandpass filter channel for phase coding the signal passed through the respective bandpass filter channel, and an adding circuit for adding all of the phase-coded signals from the n bandpass filter channels to form one of a set of orthogonally coded pulses.

System for reducing visible noise in television images

Abstract: A motion detector system reduces visible noise in television image signals by use of a numerical time filter. A sample memory is coupled to the output of the time filter. In the time filter, the sample of the images to be treated is combined with a corresponding and preceding sample delivered by the sample memory. A decision circuit determines whether the combination signal has a parameter of the time filter. A subtraction circuit has a first input coupled to receive the image sample which is to be treated and a second input coupled to receive the corresponding sample delivered by the sample memory. A low-pass filter has parallel inputs for receiving samples delivered by the subtracting circuit. A sign output is derived from an exclusive OR circuit coupled to a low-pass filter and a band-pass filter. A polarity reversal circuit responds to the two filters under control of the OR circuit for executing a polarity reversal when the values of the inputs of the exclusive OR circuit are different, depending on a threshold-type decision circuit.

Lowpass filter with electronic control of cutoff and resonance

Abstract: A lowpass filter circuit having an electronically controllable cutoff frequency and utilizing a feedback current mirror circuit as a variable impedance element. The filter circuit employs low noise, low distortion output circuitry and includes means for electronically controlling resonance.

IF Bandpass shaping circuits

Abstract: An IF bandpass shaping circuit for use with a television receiver having a tuner for providing intermediate frequency signals comprises a surface acoustic wave (SAW) filter coupled to the tuner. The SAW filter provides a predetermined bandpass response. A tuned circuit is coupled between the tuner and the output of the SAW filter. The tuned circuit is responsive to a frequency bandwidth which is narrow relative to the response of the SAW filter. The tuned circuit response is added to the output of the SAW filter to provide a modified SAW filter response.

Use of a programmable filter for inverse filtering

Abstract: A real-time deconvolution or inverse filter, operating at signal frequencies up to 5 MHz, is reported. The programmable digital filter is controlled by a computer which calculates the Wiener-filter solution using f.f.t. techniques. Deconvolved signals can be clearly discriminated after passing through a distorting medium.

Synthesizer for organ voices

Abstract: In an electronic musical instrument, such as an electronic organ, certain organ voices are synthesized by applying a tone signal to a voltage controlled low-pass sharp cutoff filter, the pass characteristic of which has a relatively sharp knee and a rapid rate of rolloff, thereby to sharply attenuate the harmonics contained in the tone signal which have frequencies above the cutoff frequency. The filter works on the principle that by switching one or more frequency-determining resistors in and out of the filter network at a rapid rate and varying the time on versus the time off, the effective value of the resistance varies to thereby alter the cutoff frequency and the character of the resulting sound signal. In accordance with the present invention, precise control over the switching duty cycle is achieved by establishing a reference voltage to which is added a voltage increment according to a binary weighting determined by selection of a particular organ voice. The sum of these voltages is compared with a sawtooth voltage in a comparator to produce a rectangular pulse the width of which is a function of the intersection of the ramp voltage with the sum voltage. By varying the sum voltage in digital increments in accordance with a selected voice, the width of the pulses is varied and these pulses, which are supplied to the filter, thus vary the filter characteristic to produce a sound signal simulative of the selected voice.

Design and performance evaluation of a 256-point adaptive filter

Abstract: In this paper an analogue c.c.d./m.o.s. implementation of an adaptive filter having high bandwidth and a large time-bandwidth product is described. The system demonstrates greatly improved performance characteristics in terms of size, power consumption, ease of use and increased bandwidth over previously published designs. Such a processor has many potential applications in communications signal processing, for the performance of tasks such as noise, echo and multipath cancellation and adaptive equalisation over both voice-band communications links (satellite, radio or 2– and 4-wire links) and high-bit-rate digital communication links. Possible applications in many other areas also exist. The main objective of the paper is to show that the prototype adaptive filter, which was based on a monolithic 256-point programmable transversal filter, behaves experimentally in a manner very close to that expected from theoretical models of an ideal adaptive filter, rather than to establish its efficacy for specific applications.

A monolithic c.c.d. programmable transversal filter for analogue signal processing

Abstract: This paper describes the operational features and performance of a fully-integrated programmable transversal filter (p.t.f.), using c.c.d./m.o.s.t. technology. The choice of filter architecture for a prototype realization is discussed with particular reference to a novel multiplier array implementation using a single, time-multiplexed m.o.s. transistor. The performance characteristics of a prototype, 64-point filter design based on this approach are detailed with reference to frequency- and matched- filtering. Techniques for optimizing the performance of this analogue filter structure under microprocessor control are suggested, through the iterative adaption of the filter impulse response, and equivalent results are given to show the improvement gained. An alternative technique for improving the filter characteristics which enables it to optimize the processing of signals under certain conditions has also been demonstrated. This adaptive filter configuration is based on the linear Widrow least-mean-square (W.l.m.s.) algorithm, and has been realized using the p.t.f. with minimal additional circuitry, without the requirement for a microprocessor.A general signal-processing module of 256-points using four cascaded filters is described; and results are presented when it is used in a sonar, matched-filtering experiment. Also a 64-point adaptive filter based on a prototype p.t.f. is described and its application to inverse filtering and self-tuning filtering is demonstrated.Finally, the potential of this miniature integrated filter for sonar-type applications is reviewed against new developments. In particular, a 256-point monolithic p.t.f.currently in development, and the concept of a dedicated adaptive filter in single chip form.

Integrated nonuniform thin-film bandpass filter

Abstract: A set of performance characteristics for a two-port three-terminal bandpass filter configuration of the integrated thin-film exponential distributed-parameter R-C-KR microsystem is presented. The circuit is found to have frequency response which is almost independent of the load. The bandpass filter requirements are shown to be achieved by a suitable combination of the parameters of the micro-system structure.

Vibration analyzer with digital readout

Abstract: A system for carrying out vibrational analysis of machinery and the like wherein a voltage controlled filter is combined with a phase-locked feedback loop to detect maximum amplitude within a given frequency band. A simply derived readout of frequency and amplitude is made available with the arrangement and operation over three or more decades of frequency is availed without manual switching and the like.

Automatic gain control circuit for an adaptive filter

Abstract: An adaptive filter having a delay circuit, taps of which comprise amplitude control circuits controlled by means of an error signal which indicates the difference between the output signal of the filter and a reference signal, includes a further control circuit which controls the amplitude of the reference signal such that an unwanted stable state for the filter is prevented from occurring.

Equivalent circuit of a magnetic sensor coil and a simple filter for rejection of 60Hz man-made noise.

Abstract: A magnetic sensor coil is shown to behave as a 2nd order Butterworth low pass filter for induced e. m. f. if the coil's output ends are terminated with a set of parallel resistor and capacitor matched to the sensor. The conditions for matching are theoretically derived, assuming an equivalent circuit of the sensor coil. An experiment to check the Butterworth filter behavior agrees well with the theory. It demonstrates the validity of the assumed equivalent circuit of the sensor. The corner frequency of the filter can be changed, selecting different matched values of the resistor and capacitor. In the experiment, the corner frequency is set at 6Hz which rejects 60Hz man-made noise 40 db ca. without distorting magnetic pulsation signals up to the highest frequency range (Pc 1). This technique for rejection of man-made noise is more advantageous than another common practice, putting a twin-T filter between the sensor and the head amplifier. A twin-T filter used this way is shown to give rise to ringing depending on the characteristics of the sensor, the twin-T filter and the input impedance of the head amplifier.

Linear loading for PWM filter

Abstract: An AM broadcast transmitter uses a PWM modulator that requires a pulse width filter. It has been found that the filter load varies over the modulation cycle resulting in distortion. To overcome this problem, a varying voltage is applied to an RF driver stage during portions of the modulation cycle.

Filter switching circuit

Abstract: PURPOSE:To decrease the number of parts by varying the resistance value of one optional resistance among series resistances, constituting a filter by short-circuiting it by an analog switch. CONSTITUTION:When a control voltage at a control input terminal 3 is held at a high or low level, analog switches S1, S3, S5, and S7 turn off or on and when a control voltage at a control input terminal 4 is held at a high or low level, analog switches S2, S4, S6, and S8 turn off or on. For this purpose, the control voltages applied to the control input terminals 3 and 4 are controlled to vary resisstance values, thereby varying characteristics of a filter.

N-path frequency-tracking filter

Abstract: The invention relates to a tracking filter switching n switched paths, of band-pass type. This filter comprises means (M, T) for taking a prefittre signal paths of the switching timing. It is characterized in that the means (M, T) for withdrawing the prefiltered signal are constituted so tells that in said pre-filtered signal remains a part of the input signal (E) of the filter. Application to the filtering of a signal having a useful component of variable frequency associated with a high background noise.

Filter input protection

Abstract: The invention relates to a filter input protection for a filter circuit which is connected to an a.c. or d.c. rail (R, S, T) via a switching device 1. The current flowing into the filter circuit is detected in a measurement sense by current measurement transducers (2R, 2S, 2T). The mains-frequency fundamental oscillation of the filter current is obtained by suppressing the harmonics with the aid of a low pass filter (3a, 3b, 3c) and is converted by a full-wave rectifier circuit (4) into a rectified voltage which is monitored, without previous smoothing, by a limit value detector (5), with respect to a limit value, which, if exceeded, trips the switching device (1). The filter input protection according to the invention reacts particularly quickly since there is no delay from a smoothing element.

Low frequency active bandpass filter.

Abstract: An active low-frequency band-pass filter is proposed which contains three operational amplifiers (13, 16, 22), one of which is connected as an inverter stage and the other two of which are connected as integrators. Of the components (C1, C2, R1...R4) determining the centre frequency of the band-pass filter, only the electrical value of one component (R3) is changed to adjust the centre frequency.

Audio signal processor for motorcycle helmets - uses bandpass, notch and active filters and amplifier with AGC

Abstract: The audio filter circuit overcomes the acoustic problems associated with ambient noise encountered by the rider of a motorcycle wearing a helmet fitted with loudspeakers. The audio signal is first fed to a band-pass filter those pass-band extends from approx. 100 Hz to an upper limit of approx. 6 kHz. This eliminates interference effects. Since only small loudspeakers can be fitted into the helmet, their resonant frequency is likely to fall within the pass-band of the filter. The band-pass filter is therefore followed by a notch filter whose effective frequency equals the loudspeaker resonant frequency. An active filter with a peak response at about 400 Hz is combined with the notch filter. The resulting signal is fed to an amplifier with a.g.c.

A New Computer Aid for Microwave Filter Design

Abstract: A recent development for the synthesis, as well as the analysis, of microwave filters, multiplexers, and impedance matching circuits is described in this paper. The new program offers interactive design of filter networks constructed by commensurate transmission line stubs and unit elements. Lowpass, highpass, bandpass, linear-phase lowpass and band-reject filters can be specified with maximally flat or equal-ripple passband, having monotonic, equal-minimum or arbitrary stopband specifications. If finite transmission zero locations are not known, the program can compute them by an optimization procedure. Circuit topology may also be specified by the user, or the program can generate it internally. At the command level, all the known network manipulations (Norton Transformations, Kuroda Identities including Levy's Extension, etc.) are readily available; additional unit elements may be inserted at the source or the load side to increase the complexity of an existing network. Filter size may be specified by its degree or by the appropriate stopband specifications.

Programmable Electro-Optic Tunable Filters

Abstract: An optical filter has been developed in which the operating wavelength, linewidth, line shape and peak transmission can be independently controlled. In this filter, the optical interaction is controlled electro-optically thereby requiring much less drive power than similar filters using the acousto-optic interaction. A filter has been fabricated and tuned through the visible portion of the spectrum. The programming features of the filter are described in this paper.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An Electrically Programmable Split-Electrode Charge-Coupled Transversal Filter (EPSEF)

Abstract: A CCD split-electrode transversal filter (EPSEF) with analog controlled tap weights is described. The programmable tap weighting utilizes a novel analog multiplier for sampled data, based on charge profiling underneath a resistive gate structure. The EPSEF device concept and the performance data of a prototype filter with eight programmable taps are presented. Applications of the EPSEF in several programmed filter functions and in an adaptive filter system are demonstrated.

Harmonic generator for additive synthesis of musical tones

Abstract: Each harmonic of the ten provided is represented by a pair of binary-valued signals; one having the form A ⊕ B ⊕ C, where A, B and C are octavely related square waves, and the other being a square wave like C. Each pair of signals is coupled to a resistive divider by coupling elements in an additive relation under control of an individual adjustable voltage source. The coupling elements are weighted so as to minimize distortion in the signal resulting from the mixture. The resistive divider preemphasizes the signals representing each harmonic to compensate for a voltage controlled filter in the audio output used to eliminate high order distortion components. In one embodiment a ÷3 counter followed by a binary counter provides the binary-valued signals for harmonics of order 0.5×2 n , where n is an integer, and a binary counter driven in parallel with the ÷3 counter provides the binary-valued signals for harmonics of order 1.5×2 n . A read only memory provides the binary-valued signals for harmonics whose order is prime. In a second embodiment all of the binary-valued signals are provided by a read-only memory.

High-frequency-pass metallic mesh interference filters

Abstract: High-efficiency metallic mesh high-frequency-pass interference filters have been designed and constructed for the wavenumber region 30→100 cm−1. Widebandpass filters have been fabricated using a combination of highpass and lowpass filters. The highpass filters have performed successfully at low temperatures.

A simulation‐type RC active filter using a negative impedance converter

Abstract: The LC simulation-type active RC filter has a lower element sensitivity than the cascade active RC filter This paper proposes a method of realizing the LC simulation type active RC filter which is suitable for the bandpass filter with finite number of poles The resistor is converted to a parallel circuit of -L, -C and -R by the frequency-dependent NIC composed of two resistances, two capacitances and one op-amp Then the LC filter is realized by converting all elements to negative elements The sixth-order simultaneous Chebyshev filter is constructed The test result indicates the effectiveness of the present method The present method requires smaller number of elements (particularly, active elements) than any other methods