Showing papers on "Voltage-controlled filter published in 1971"

Phase-Only Complex-Valued Spatial Filter*

Abstract: A new type of phase-only filter is described for wave-front construction, in which both the amplitude and phase information necessary to construct an arbitrary image over a limited field are encoded. It is shown that this phase-only filter can duplicate the performance of an ideal complex-valued spatial filter (a filter that controls both amplitude and phase transmittance). This phase-only filter controls the amplitude transmittance by the use of a modulated high-frequency phase carrier that diffracts a controlled amount of light into the image. This type of filter is particularly useful in the implementation of computational wave-front construction, because the maximum spatial frequency that must be plotted is associated with the image and not the carrier. The performance of the filter is examined both numerically and experimentally.

Variable bandpass dynamic noise filter

Abstract: A variable bandpass filter for a dynamic noise filtering effect that reduces the perceptible noise in an audio reproduction system. The variable bandpass filter responds to peak signal levels in relatively high and relatively low frequency portions of the audio spectrum to automatically and independently vary high and low frequency cutoff points for the filter in correspondence with the level of signals at those frequencies. Low distortion and wide dynamic range is achieved in a filter configuration which comprises a forward signal path and a reverse signal path, each having a variable integration response provided by temperature compensated and linearized field-effect transistor circuits. The integration response of the two paths imparts a high and low frequency filtering effect. A further constant gain feedback path establishes a uniform middle frequency amplification for the variable bandpass filter.

Design of digital filter banks for speech analysis

Abstract: A bank of bandpass filters is often used in performing short-time spectrum analysis of speech signals. This paper is concerned with the analysis and design of digital filter banks composed of equally spaced bandpass filters. It is shown that significant improvement in the composite filter bank response can be achieved by proper choice of the relative phases of the bandpass filters. The results are extended to more general filter bank configurations.

Remote controlled, adjustable bandwidth low pass filter

Abstract: A bandwidth controlled, low pass filter circuit having a resistor, capacitor, voltage follower amplifier, and an insulated gate, metallic oxide semiconductor, field effect transistor utilized as a switch, in which the transistor and the resistor, together, provide the effective circuit filter resistance, and the bandwidth is controlled by the transistor gate pulse frequency and pulse width. The use of several such filters as a filter bank is also disclosed.

Digitally controlled frequency filter

Abstract: A digitally controlled filter comprises an operational amplifier having selectable output circuits with predetermined time constants. A plug-in unit determines whether the filter will be a high-pass filter, a low-pass filter, or a band-pass filter. The time constants in the circuit are determined by the application of a digital word to a plurality of switching gates to connect into the circuit one or more impedance combinations having predetermined time constants.

Electrical filter circuit

Abstract: The present electrical filter circuit has a plurality of filter paths connected in parallel to each other between an input and an output. At the input side of each path there is arranged a bandpass filter which is then followed by logic circuit and bypass means interconnected in such a manner that only one path at a time is closed to the exclusion of all other paths in response to the signal level at the output of the respective bandpass filter means.

Highly selective filter circuit

Abstract: A filter circuit providing extremely sharp attenuation at a selected frequency cutoff point. The sharp attenuation is obtained through the use of several ganged or cascaded active filter sections whose characteristics are combined in an additive fashion to provide an extremely flat passband characteristic and a sharp attenuation curve at the desired frequency cutoff value. Filter circuits of this design may be used in combination in the electrocardiograph field to isolate the R-wave of the PQRS complex of an electrocardiogram resulting in trigger signals of a high degree of accuracy for purposes of R-wave detection and evaluation.

High frequency filter apparatus

Abstract: An improved image-frequency rejection filter combines series resonant band-reject filtering at the image frequency with parallel resonant bandpass filtering at the carrier frequency.

Dual input distributed RC notch filter

Abstract: It is shown that by using the dual-input technique in the bridged distributed RC notch filter, one can (i) obtain some amount of flexibility in the choice of the bridging capacitor, or (ii) compensate for a deviation of the bridging capacitor from the design value, or (iii) obtain a low pass filter with sharper cutoff than is possible with the distributed RC network alone.

Rc active filter apparatus

Abstract: A complex filter or filter section using an amplifier with a plurality of feedback loops which may be used for bandpass filtration or for filters requiring complex transmission zeros.

Low-pass non-linear filter

Abstract: A non-linear filter for high and low frequency signals comprises means for separating and dissipating the high frequency out-ofband energy and passing the low frequency in-band energy. The filtering in a low-pass filter is achieved without phase shift both in- and out-of-band by use of conjugate high- and low-pass filters located before and after the dissipating means, respectively. A hard clipper is used to perform the dissipating function, and its reference clipping level is provided so that the maximum amplitude of the in-band signal arriving at the input to the clipper is slightly less than the clipping level. The output of the low-pass filter may be fed back to set the clipping level so that this level can track the in-band signal amplitude. A sensing resistor between the clipper and the means to set the clipping level senses the high frequency information and thus, the non-linear filter can serve as a high-pass filter with no phase shift when only the low-pass filter is used after the dissipating means.

Digital filter arrangement which alternatively filters two signals differing in frequency

Abstract: A plurality of telephone lines which convey frequency-shift signals and a corresponding plurality of data machines, which send and receive do baseband data are interconnected via a time-shared digital (filter) circuit receiver and digital circuit modulator under the supervision of a common central processor. A low-pass digital filter is arranged to filter the incoming signals to detect ringing or, alternatively, to filter the sum of the signaling frequencies to detect carrier. To detect the low frequency ringing, the response of the filter is modified by limiting the rate at which the input signals are applied thereto and by "holding" the processed signals in the filter for the prolonged interval between the input signal applications.

Electrical Design and Musical Applications of an Unconditionally Stable Combination Voltage Controlled Filter/Resonator

Abstract: A new voltage-controlled filter designed for the ARP synthesizer is a combination low-pass, high-pass, and band-reject filter capable of obtaining Q as .high as 500. The filter is unconditionally stable and the Q can be controlled from 1⁄2 to 500 by an external control voltage. The center frequency of the filter can be varied continuously over 20 octaves on a 1-volt per octave response to an external control signal.

Method of designing orthogonal filters

Abstract: A method of designing an orthogonal filter for use in a speech synthesizing system wherein the filter is constructed from a series of linear filter sections. The poles in the complex plane of any section of the filter are cancelled by the zeros of the next section.

Combined contiguous filter and acceleration and velocity analyzer for radar

Abstract: A single filter to replace a set of parallel filters in an O-T-H radar coising a prelimiting filter connected to amplifying and limiting means and quenching means for shorting out said prelimiting filter at appropriate times. The prelimiting filter is connected to receive the output of the mixer of one range bin of the velocity-and-acceleration analyzer of the radar and the predetection filter of the analyzer receives the output of the amplifying and limiting means. The quenching means also receives the output of the amplifying and limiting means and provides a quenching signal to the predetection filter.

An improved distributed RC notch filter and its application to an extremely insensitive bandpass amplifier

Abstract: A distributed RC notch filter with an improved frequency selectivity is described. An extremely insensitive bandpass amplifier can be obtained by use of such a filter.

Filter and substitute for resonant reed relay

Abstract: A monostable multivibrator is connected to a differential amplifier to perform the following functions: signal limiter, band-pass filter, low-pass filter, high-pass filter and frequency modulation detector.

An RC all-pass filter†

Abstract: An RC all-pass network with a differential input amplifier and a notch filter is described It is also shown that an appropriate choice of the notch network can introduce certain advantages in the derived network

Oscillations in active band-pass filters†

Abstract: A feedback system comprising the cascade combination of a linear amplifier, a clipper and an active band-pass filter is shown to generate both sine and square-wave oscillations. Two configurations of the active filter are considered. In both cases sinusoidal oscillation occurs, the frequency of which is variable over a wide range. Square-wave oscillation of variable frequency can also be generated in. the same system by proper choice of the system gain.

A Bandpass Filter with Switched Active Networks

Abstract: Frequency selective networks play an important role in communications and instrumentation. As present-day techniques of miniaturization do not permit the use of inductors in filters, many alternative techniques of filter realization have become important. Of these, a digital filter like the N-path filter employing switched active networks is very useful for a variety of applications. With this in view, a project was initiated to develop a four-path bandpass filter using switched RC-active networks suitable for FDM use. The special features of this project are the standardization of digital and analogue circuits for repeatable use in the filter, and facilities for easy tuning. The important design features, fabrication and performance tests on the filter are described in this paper.

A versatile active RC filter

Abstract: An active RC filter using a negative immitance converter suitable for the realization of a notch and an all-pass function is described. Two potentiometers suitably adapted in the circuit can be varied to change the notch frequency and selectivity of the filter independently. The design of the required functions with appropriate selectivity, centre frequency or delay is quite conveniently made on the complex plane. The circuit is shown to be very easily adaptable to construct a frequency selective amplifier with necessary changes in the centre frequency and the selectivity without altering the basic time constant of the circuit.

Selection of filter characteristics for phase-frequency analysis of electrical signals from the brain.

Abstract: 1 The circuit described by N I Maklyukov makes it possible to design active filters with the desired characteristics