Showing papers on "Band-stop filter published in 1975"

Double layered optical low pass filter permitting improved image resolution

Abstract: A double layered optical low pass filter is provided for use in a color video system for monitoring an object scene. The optical filter is designed to optically complement a dichroic stripe filter to prevent the introduction of spurious signals by any interference between luminance and chrominance signals, while at the same time providing a transmittance of high spatial frequency luminance signal to permit an improved image resolution. The optical low pass filter includes a first phase retarding filter layer designed to provide a first spatial frequency response across the visual spectrum and a second phase retarding filter layer designed to provide a second spatial frequency response across the visual spectrum. The combined resultant optical transfer function of the filter layers disclose a cut off of the higher spatial signal components of the primary color design wavelengths of the respective first and second filter layers, while transmitting a higher spatial frequency for the luminance signal to provide the improved image resolution. The specific cut off spatial frequencies of the primary colors and the bandwidth of the luminance signals can be subjectively optimized for any applicable system.

Self-adjusting digital notch filter

Abstract: Digital filter auto-adjustment to variations in input signals is achieved by normalizing the output of the second of two substantially identical series-connected digital filter stages and subtracting the normalized output of the second filter stage from its input to provide a measure of filter signal residue power Deviations of the signal residue power from the preset limits of a signal residue power standard are detected and signals responsive thereto are used to appropriately adjust variable bandwidth constants in both filter stages

Self-tuning filter

Abstract: A self-tuning filter is provided through the employment of a voltage tunable filter circuit which simulates a series resistor-inductor-capacitor (RLC) circuit and which is tunable to vary or adjust its resonant frequency in response to the value of an input control voltage. The filter is made self-tuning through the provision of suitable circuitry, responsive to simulated inductance and capacitance voltages, to generate the input control voltage and hence render the voltage tunable filter circuit resonant at the frequency of an applied input signal.

Noise suppression filter

Abstract: A two line power filter for digital equipment or the like comprising a pair of toroidal cores on both of which both wires are wound, on one in flux adding relationship and on the other in flux opposing or cancelling relationship in reference to the primary power supply, together with capacitive shunts between the wires and from the wires to ground to filter out both common mode and differential mode noise.

Integrated feedback active filter/integrator

Abstract: An integrated feedback active filter/integrator processes electrical signals and performs bandpass and lowpass filtering or integration and double integration. The integrating and double integrating features are obtained by setting the quality factor of the bandpass filter to one half. This provides accurate integration for all frequencies greater than about ten times the center frequency of the filter. The circuit integrates the output and returns (feeds back) this value in the negative sense to the circuit input.

A novel second-order canonical RC-active realization of high-pass notch filter

Abstract: A high-pass notch filter with variable gain greater than unity is realized using a differential amplifier and only two capacitors that can be equal. The transmission zero and pole frequency are completely independent of the amplifier dc gain. Design formulas, sensitivity analysis, and measure and trim tuning process are presented. An example of a 60-Hz rejection filter is discussed, the response of which is within the required specifications even with a \pm 5-percent capacitance variation. Two modifications of the original structure can be used to realize the same filter, extending the available range of the gain to cover all requirements.

Single amplifier functionally tunable low-pass-notch filter

Abstract: The canonical network developed in this paper is an active RC negative feedback arrangement that uses a single op-amp and two capacitors to realize low-pass-notch filter characteristics. The filter parameters are adjustable through resistive trimming. This functional tuning process uses a signal generator, a dB-scale voltmeter and a phase meter. The analytical design procedure takes into account a single-pole amplifier model. The network has low-passive sensitivities and is suitable for moderate- Q applications ( Q \leq 5 ). An example is discussed giving the resistor's limits for a \pm 10 percent capacitance tolerance.

Design of a third-order single amplifier filter

Abstract: General design formulae are derived for the synthesis of a third-order low-pass filter with a finite transmission zero. The design procedure uses a unity gain positive feedback amplifier, with balanced twin-T RC networks. A design example is given for a fifth-order elliptic filter, whose performance is compared to the ideal computed response.

Electrical component failure detection apparatus

Abstract: A harmonic filter failure detection apparatus for use in a single sideband radio transmitter is disclosed. A first directional coupler measures the power delivered to the harmonic filter and a second directional coupler measures the power passed through the harmonic filter. The power measurements of the first and second directional couplers are then compared in a latch type comparator circuit and a control signal output is developed which indicates whether or not the harmonic filter is operating properly. The control signal output is used to shut down the single sideband transmitter when a filter failure has been detected.

Bidirectional constant impedance low pass/high pass filter circuit

Abstract: A bidirectional filter circuit having an input and an output and substantly constant input and output impedance characteristics over the desired frequency range. A low-pass filter network is connected between filter input and output and has identical low-pass filter half sections cascaded back-to-back with a symmetrical all-pass network interposed therebetween, the all-pass network providing isolation between the low-pass filter half sections and the desired terminating impedance therefor. First and second identical compensating networks are respectively connected to the filter input and output and have reciprocal characteristic functions with respect to the low-pass filter half sections to compensate for impedance changes in the low-pass filter half sections over the desired frequency range without affecting amplitude characteristics thereof. A high-pass filter network is connected between filter input and output and has identical high-pass filter half sections cascaded back-to-back with a symmetrical all-pass network interposed therebetween, the all-pass network providing isolation between the high-pass filter half sections and the desired terminating impedance therefor. Third and fourth identical compensating networks are respectively connected to the filter input and output and have reciprocal characteristic functions with respect to the high-pass filter half sections to compensate for impedance changes in the high-pass filter half sections over the desired frequency range without affecting amplitude characteristics thereof.

A reprogrammable filter bank using CCD discrete analog signal processing

Abstract: A multichannel filter using a 32-stage CCD analog shift register (ASR), will be described. The filter uses a recursive two-pole, one-zero network. The center frequencies, bandwidths and gains, are independently programmed using four quadrant multiplying digital-to-analog converters.

Band pass filter circuit with automatic bandwidth adjust

Abstract: Band pass filter circuit for a band pass filter which detects a phase difference between input and output signals of said band pass filter, and the detected output controls, via a low pass filter, a voltage controlled oscillator, the output of which controls first and second mixers connected respectively to an input side and an output side of the band pass filter, so that the output of the first mixer can be maintained at the center frequency of said band pass filter. Further, when an irregularly timed signal is received, before an input signal is pulled in the synchronized state, said band pass filter is provided with a wide pass band so as to pull the signal in the synchronized state in rapidly. After said input signal is pulled in said center frequency, the pass band of said band pass filter is changed to a narrow bandwidth so as to improve the quality of the noise and at the same time, a cutoff frequency of said low pass filter is changed to a lower frequency side so as to improve the stability of the band pass filter circuit.

Secam color television receivers employing tunable notch filter in luminance channel

Abstract: In the luminance signal channel, the notch filter 40 which considerably attenuates the subcarrier is a variable filter whose tuning is controlled by a signal which is a function of the instantaneous frequency of the subcarrier.

Feedback filter system

Abstract: A bandpass or band reject filter system is provided for operating on frequencies in an input signal with the filter system containing a feedback loop Quadrature components of the frequencies of interest occurring in the output signal are acted on in the feedback loop to provide a feedback signal, which can be used directly itself, to be summed with the input signal thereby effecting a cancellation of the frequencies of interest therein The frequencies of interest can be chosen by manual tuning, or by a self-tuning system which can be provided by the addition of a further feedback arrangement

Lock-in amplifier using a sampled-data synchronous filter

Abstract: A lock-in amplifier is constructed using a synchronous filter instead of a phase sensitive detector. The synchronous filter based on a signal sampling method offers an extremely narrow bandpass characteristic whose centre frequency can be easily controlled by its drive frequency. Since the filter makes smaller responses for harmonics of the signal at the tuned frequency than a phase sensitive detector, the error due to the harmonics becomes less and required performances of a prefilter are relaxed. By this lock-in amplifier the magnitude of a low-level signal affected by noise can be measured accurately without annoying phase adjustments which are required in a conventional lock-in amplifier.

Active filter with inverse option

Abstract: An electronic filter circuit comprised of summing circuits and integrating circuits is interconnected such that the filter may use the same components to serve either as a band-reject or a band-pass filter having the same natural frequency. Changing of the filter operation between the two modes is accomplished simply by the interchange of two component values.

Use of the numerical phase-difference filter for the digital channel bank

Abstract: The use of the numerical phase-difference filter in the single-sideband modulation scheme for frequency-division multiplexing is investigated and compared with the Weaver-modulator scheme proposed by Freeny et al. A simple algebraic solution to the approximation problem for arbitrary specifications in the stopband is given. The sensitivity of the stopband attenuation is the main problem that precludes the use of RC active structures; it is shown that the digital version can be implemented with a reasonable coefficients wordlength. The structure of the filter is optimised for round-off noise performance. Finally, the two modulation schemes are compared.

Precision tuning of RC parallel-T notch filter

Abstract: A new method of tuning RC parallel-T null networks has been presented. This requires trimming of only one component of the parallel-T and uses a dual input configuration for the null network.

Device for damping the tipping and yawing oscillations of the guidance system of a flying vehicle

Abstract: The guidance system for a flying vehicle having at least one guidance channel for converting an error signal to a command signal for a control surface servo of the vehicle includes means for damping oscillations at the natural frequency of the vehicle. A damping means includes a notch filter in the guidance channel which serves to damp oscillations at the notch frequency. The notch frequency is controlled and conformed to the natural frequency of the vehicle, as the natural frequency of the vehicle varies with vehicle speed, by providing the notch filter with a signal related to vehicle speed. The notch filter is arranged to vary the notch frequency in accordance with the signal provided thereto.

Power line carrier line filter

Abstract: PURPOSE:To obtain a low cost line filter with small size by constituting the bridge with two series resonant circuits, and by pciking up only commercial frequency signal with the resonant frequency signal eliminated.

Electronic filter circuit

Abstract: To eliminate the high frequency portion of an input signal while permitting low frequency and DC portions to pass, the electronic filter utilizes an n-1 order active network in combination with a capacitor to generate a shunt current, thereby providing a low pass filter having n-order operating characteristics. Included in the active network is an active element, such as an operational amplifier, which responds to an input signal by creating a voltage across the capacitor, resulting in a shunt current that in turn provides the desired filter characteristics. In certain special cases the n-order active filter can utilize a differentiating element in combination with n-2 order active network along with the capacitor to achieve n-order operating characteristics.

Voltage-controlled filter

Abstract: In a bridge circuit consisting of diodes connected in each circuit branch in a forward direction from one of a pair of opposing terminals to another with a current flowing through these diodes, impedance between a second opposing pair of terminals varies in correspondence to the magnitude of the constant current. The invention utilizes this phenomenon and provides a voltage-controlled filter employing this bridge circuit as an impedance element for determining its frequency region and thereby being capable of controlling its frequency region by voltage controlling. A primary passive low-pass filter is described as a preferred example of the invention. The invention further provides a voltage-controlled filter having the bridge circuit provided in a negative feedback loop of an amplifier in an active filter circuit and thereby being capable of controlling selectivity Q by controlling the gain of the amplifier by voltage controlling. As a preferred example of this type of filter, a secondary active low-pass filter is described.

Ganged radio frequency filter

Abstract: A three channel electronically tunable filter arrangement for selecting radio frequency signals to be processed in a monopulse receiver is disclosed. Each channel of the disclosed filter arrangement includes an yttrium-iron-garnet (YIG) filter disposed in a common structure so that the resonant frequency of each channel may be controlled by the magnetic field of a single electromagnet. Also disclosed is an alignment method whereby the response of the YIG filter in each channel may be independently adjusted to eliminate any substantial imbalance between channels as the strength of the magnetic field is changed to change the resonant frequencies of such filters.

Electromechanical branching filter

Abstract: An electromechanical branching filter capable of branching an input electrical signal into two output signals having different frequency components. It includes a wide bandpass filter section and a narrow bandpass filter section, both sections being mechanically connected to a common input transducer through coupling means including a coupler whose coupling coefficient is in the range of ±30 % of the geometric mean value of the fractional bandwidths of the two filter sections.

A tunable filter using amplifier pole

Abstract: A circuit consisting of two periodically operated switches, potentiometers, resistors, and compensated operational amplifiers, but not containing external capacitors, is proposed for the realization of a second-order bandpass and low-pass filter. The filter is electronically tunable and the natural frequency of the filter varies linearly with the width of the pulses controlling the FET switches.

Cascade synthesis of monolithic crystal filtfrs possessing finite transmission zeros

Abstract: A simple method for the synthesis of bandpass or bandstop filters possessing finite transmission zeros as a cascade of shunted double-resonator monolithic crystal filter (MCF) sections is given. The lowpass or highpass prototype transfer function is synthesized as a cascade of MCF prototype sections for which explicit expressions for the element values are given. Application of the narrow-band lowpass to bandpass frequency transformation to the prototype network then yields a physically realizable filter with the desired bandpass or bandstop response. An example of the synthesis of a bandstop filter is given to illustrate the approach.

Simple Elliptic-Function Filters Made of Rectangular Waveguide and Semi-Rigid Cables

Abstract: A semi-rigid cable makes a conventional waveguide filter into an elliptic-function filter. A four-resonator elliptic-function filter having a simple construction and a selectivity equivalent to that of a ten-resonator Butterworth filter has been developed by adding a semi-rigid cable to a conventional rectangular waveguide bandpass filter. Although using semi-rigid cable, this filter is equivalent to a rectangular waveguide bandpass filter in unloaded Q. In this filter, two signal portions having passed through different routes offset each other at attenuation poles. Also, a six-resonator filter has been constructed with two semi-rigid cables.

Delay discriminator for Coran-C radio navigation system - is able to suppress echo and scattering pulses using specified elliptic and two pole filters

Abstract: The delay discriminator, for LORAN-C and other radio navigation systems, discriminates between rapidly following pulses in the same frequency band as well as between pulses in different bands but close together is allows the suppression of echoes and scattering effects. The navigation receiver output is coupled to an elliptic filter (A) whose own output is amplified and passed to a two-pole synchronous filter (B). The latter filter consists of two one-pole filters which are separated by an amplifier. The elliptic filter has a step characteristic centered on the centre frequency whilst the two-pole filter has a continuous curve enclosing the step characteristics of the elliptical filter.