Showing papers on "Band-stop filter published in 1981"

Filters comprising reactive components, and a method of determining impedances thereof

Abstract: A filter comprising reactive components which define pass and stop bands has the impedances of the components selected to minimize the sum |Zin-Z2|+|Zout-Z1| in the pass band, where Zin and Zout are respectively the input and output impedances of the filter and Z1 and Z2 are nominal termination impedance at respectively the input and output of the filter. The filter characteristic in the pass band is thereby made substantially independent of the actual termination impedances of the filter in use. The design is exemplified by a 5th order low pass filter for connection in the voice signal path of a telephone subscriber line.

Diplexer for television tuning systems

Abstract: A diplexer comprises a first frequency selective filter coupled between its first input terminal and a circuit point, a second frequency selective filter coupled between the circuit point and its output terminal, and third frequency selective filter coupled between its second input terminal and the circuit point. The first filter selects frequencies higher than a first frequency and the second filter selects frequencies lower than a second frequency which is higher than the first frequency. The third filter selects frequencies lower than a third frequency which is lower than the first frequency. In a television receiver, the first and second filters serve as a bandpass filter for the UHF band, and the third filter passes the VHF and CATV bands.

Channel equalizer and method for cancelling ghosts

Abstract: A channel equalizer and ghost cancelling technique are disclosed for removing ghosts from a communications signal which includes a training signal and data. The training signal and its ghosts are processed as a finite length sequence of numbers. The equalizer includes a chain of cascaded filters, the first of which receives the training signal and its ghosts for assuming a filter condition which reduces the finite sequence by two points at the filter's output. Each successive filter in the chain receives the output of an immediately preceding filter and assumes a filter condition in which an additional two points of the finite sequence are eliminated or forced to zero. The filter conditions assumed in response to the training signal and its ghosts are maintained while the data is applied to the filter chain so that ghosts of the type experienced by the training signal are removed from the data.

Electronically tunable band reject filter

Abstract: An electronically tunable band reject filter rejects only frequencies of a signal that are in the reject band around its center frequency The band reject filter includes an input directional coupler for sampling of the signal that is to be filtered and provides a first and second signal thereby The first signal is filtered by a bandpass filter that passes only frequencies of the signal that are around the center frequency of the bandpass filter An output directional coupler combines the second signal with the filtered signal and obtains on a difference port the difference between the second signal and the filtered signal The frequencies of the signal that are centered around the center frequency of the bandpass filter are thereby rejected

Sampling filter for reducing aliasing distortion

Abstract: Sampling filter which employs fractional period displacement of samples to force additional nulls in the filter characteristic response. This sampling method and cascading antialiasing filters (501, 502, 503) provides a filter structure which minimizes the complexity of the circuit yet which provides great flexibility to implement a desired filter characteristic.

Propagation Properties of a Planar Dielectric Waveguide with Periodic Metallic Strips

Abstract: A dielectric waveguide with periodic metallic strips suitable for millimeter-wave and submillimeter-wave integrated circuits is analyzed by a rigorous formulation. The accuracy of the solution of our analysis can be systematically improved by increasing the size of the matrix associated with the eigenvalue equation. Stopband properties are numerically presented as a function of the spacing and width of metallic strips and dielectric profile. It is found that there is a difference in the stopband properties of TM and TE modes. Experimental results for the band reject filter are also presented to verify the validity of our analysis.

Switchable filter circuits

Abstract: A switchable filter circuit for use in a receiver to select a first or a second frequency band from a received signal and for providing predetermined minimum stop band attenuation at frequencies outside the selected frequency band, the second frequency band lying wholly within the first. A first filter element is provided which defines a primary pass band corresponding to the first frequency band, and a second filter element is provided which defines a secondary pass band corresponding to the second frequency band, the first filter element having an input to which the received signal is applied, and the second filter element have an input for receiving the output of the first filter element. The stop band attenuation of the first filter element is at least as great as the predetermined minimum stop band attenuation required, and the stop band attenuation of the secondary filter element within the primary pass band being that which is required by the application. Thus the first filter element significantly determines the stop band characteristics of the filter circuit as a whole outside the primary pass band.

Linear phase filter with self-equalized group delay

Abstract: In modern communication systems, it has become important to provide filters, and in particular bandpass filters, which can provide substantially uniform group delay across the bandwidth of the filter while still achieving good amplitude response. In this regard, it is particularly desirable to substantially reduce the large variations in the phase characteristics found in conventional bandpass filters at the nominal band edge of the filter. To accomplish this, a filter is provided having at least one pair of lattice arms coupled in parallel to one another between the input and output of the filter. Each of the lattice arms includes a plurality of resonant LC resonators, each of the resonators having a different resonant frequency than the center frequency of the filter. In particular, within the bandwidth of the filter, the exponential damping coefficients for the resonators in each arm are set to decay at the same rate. This desired decay can be accomplished by exponential sizing of the components.

Fabry-Perot filters used for optical preprocessing.

Abstract: A Fabry-Perot etalon placed in the object plane of a coherent optical processing system can be used as a variable bandpass preprocessing filter. Use of this filter leads to improved correlation signals in a matched spatial filter system. Experimental results are shown and compared with results obtained by two other preprocessing methods.

Microstrip bandstop filter using a dielectric resonator

Abstract: The paper presents a new analysis accurately predicting the external quality factor and scattering matrix parameters Sij of the TE01p cylindrical resonator mode, coupled with a microstrip line for arbitrary locations of the resonator and the line. The results obtained are used to ralise a Cheby?shev bandstop filter. Experimental and theoretical results are also included.

Electro-Optic Tunable Filter

Abstract: This paper describes the performance characteristics of an electronically tunable optical filter based on the electro-optic effect. Like the acousto-optic tunable filter, this device operates by selectively coupling principal polarizations in a birefringent crystal at a phase-matched wavelength by means of a spatially periodic refractive index perturbation. Instead of a traveling acoustic wave, however, the electro-optic tunable filter employs a temporally static electric field. The main advantages of this filter are its very low power consumption and its versatility of passband programming, by virtue of sepa-rately addressable voltages under microprocessor control. Two basic embodiments of the filter structure are described, one using longitudinal fields collinear with the light beam, the other using transverse fields in a "thick waveguide" configuration. Various examples of passband synthesis are described that result from apodizing the amplitude of the applied electric field perturbations. Experimental results of filter transfer characteristics at visible wavelengths are presented for the basic transfer function, for passband broadening, and for sidelobe suppression, together with theoretical computer plots showing excellent agreement. Typical driver voltages are 50 to 100 V.

Adjustable and selective electrical filters and methods of tuning them

Abstract: A notch filter is provided with an ancillary circuit including a non-inverting amplifier and a coupling which enables the filter to form part of an oscillatory loop of which the frequency of oscillation corresponds to the frequency of maximum rejection by the notch filter. Measurement of that frequency facilitates the tuning of the notch filter, which includes capacitors constituted by varactor diodes. The gain of the ancillary circuit may be adjusted to change its mode of operation from oscillation to that of a tuned amplifier so that a sweep of the center frequency of the notch filter through a range of interest facilitates a search for an unknown interfering frequency and the simultaneous tuning of the notch filter to reject that interference.

Multiple-loop adaptive delta modulator

Abstract: An adaptive delta modulator employs an additional feedback loop to produce a more accurate estimate of the input signal. The delta modulated bit stream is applied to a filter having variable filter characteristics such as bandwidth, the output of the filter being combined with the signal estimated by the prior art adaptive delta modulator. The characteristics of the incoming signal, such as bandwidth, are determined by examining the prior art estimated signal, and the filter characteristics of the additional feedback loop are varied in accordance therewith.

Hearing aid with controllable wide range of frequency response

Abstract: A hearing aid circuitry comprising a high pass filter and a low pass filter, for filtering the sound wave signals to permit adjustment of the gain of the high end of the frequency spectrum relative to its low end. The low pass filter is formed of a differential amplifier which performs a subtraction of the sound wave signal and the output signal of the high pass filter. The outputs of both filters are individually added together in proportional quantities by a single control. The use of the differential amplifier, or alternatively, a simple R-C filter of 6 dB fall off, minimizes frequency effects in the output signal in the frequency range where the high pass filter and low pass filter overlap.

Capacitive commutating filter

Abstract: A capacitive commutating filter provides a D C output voltage of amplitude responsive to the amplitude of an input waveform having a frequency substantially equal to the operating frequency of the filter The filter operating frequency is established by a digital signal The filter input is selectively and cyclically connected through N input resistances, wherein N is an integer greater than zero, to adjacently progressive N ones of (2N+1) nodes, each having one of (2N+1) capacitive filter elements connected to ground potential The equilibrium voltages across the capacitive filter elements, established during the N/(2N+1) segments of the input waveform during which each capacitor is connected to the input, are coupled to one set each of maximum-positive-polarity and maximum-negative-polarity diodes, for placing the maximum and minimum filter capacitive element voltages at respective ones of the inverting and non-inverting inputs of a differential amplifier, having the output thereof forming the filter output

Feed forward circuit

Abstract: A feed forward circuit that can be used as an isolator or filter includes a first and a second directional coupler that, depending on the application, either splits an applied signal into two paths or combines the two paths to obtain an output signal. One path includes an electronically tunable band reject filter (or notch filter) which may be bypassed by a switch in the isolator application, and an inverting amplifier. The second path includes a delay line that compensates for the time delay of the signal in the first path due to the time delay of the inverting amplifier and electronically tunable band reject filter.

Current mode biquadratic active filter

Abstract: A configuration of two transistors (Q1, Q2) and two capacitors (C1, C2) provides a current mode second-order active filter for IC implementation with low-pass, bandpass and high-pass capabilities. The filter frequency is tunable over a wide range, independently of filter Q and gain, by varying a DC bias current (Ibias1). The filter can provide one-port impedance functions, and two-port voltage, current and impedance transfer functions. With the addition of a second biasing current source (Ibias2), the filter Q can be controlled by adjusting the ratio of the two biasing current sources. Enhanced dynamic range and large signal performance can be achieved by the addition of linear resistors (R1, R2), with trade-offs in tunable frequency range and frequency linearity.

Spatial low pass filter for range finding systems

Abstract: A low pass filter for an auto focus camera system to deflect light from the main lens by a controlled angular amount and thus suppress high frequency components in the signal.

A Dielectric Resonator Bandstop Filter

Abstract: This paper presents a new analysis predicting accurately the external quality factor and scattering matrix parameters S/sub ij/ of the TE/sub 01p/ cylindrical resonator mode, coupled with a microstrip line for arbitrary locations of the resonator and the line, The results obtained are used to realize a Tchebyscheff bandstop filter. Experimental and theoretical results are also included.

Compensation apparatus for an electrohydraulic servovalve

Abstract: Electronic compensation apparatus for a drive system associated with a torque motor of an electrohydraulic servovalve. The apparatus includes means to define an open loop transfer function characteristic of the drive system, wherein the transfer function corresponds to a notch filter. Further included are means to provide the open loop characteristic with a closure rate of approximately no more than 6 db/octave with respect to a function 1/β=1-G cl (s), where G cl (s) corresponds to a closed loop transfer function of the drive system. In particular, the notch filter may be realized in a drive system that includes a series resistive-capacitive circuit connected in parallel with the torque motor. The 6 db/octave closure rate is provided by a variation of the impedance of the series resistive-capacitive circuit.

Resonant filter clipper circuit

Abstract: A circuit for peak limiting an audio signal comprises a first "M" derived filter, a first clipping circuit, a second-order low pass filter, a second clipping circuit and a second "M" derived filter. Each "M" derived filter includes a series resonant shunt leg for eliminating clipping harmonics within selected frequency ranges depending upon the resonant frequency of each shunt leg.

Notch filter device for loran c receiver

Abstract: PURPOSE:To eliminate a plurality of interference waves, by using a demultiplexer and keeping an optimum state of a lot of notch filters with one D/A converter. CONSTITUTION:Notch filter 2-4 are connected in series and interference waves included in the filters 2-4 are selected at a tuning circuit 12 and detected at a detection circuit 15. A digital voltage is supplied to a D/A converter 19 from a processor 17 and the converter 19 selectively supplies a DC voltage to the filters 2-4 through a demultiplexer 18. Further, the converter 19 and the demultiplexer 18 are controlled with the device 17 including a microcomputer so that the frequency of a wave eliminated interference is made coincident with the frequency of the interference wave at a selected notch filter.

Improvements of antijam performance of spread spectrum systems

Abstract: The present paper gives theoretical analysis and simulation tests of a proposed external circuit connection for enhancing the performance of spread-spectrum (SS) systems in the presence of continuous wave (CW) interference. This connection is an adaptive notch filter. It consists of a hard limiter, a phase-locked-loop (PLL) tracking the CW interference yielding a first estimate, an adaptive two-quadrature weighted channel, and linear combiner producing a more accurate estimate of the CW interference. The simulation tests of this connection give, in general, performances superior to previous authors' results for certain ranges of signal-to-noise ratio.

Radio frequency detection circuitry having noise discrimination capability

Abstract: In a radio frequency detector, a high pass filter is provided to attenuate any undesired low frequencies present in signals applied to the filter. The filter output serves as an input to an AND gate. A low pass filter directs power line voltage to a one-shot multivibrator which is biased to respond to the positive-going zero crossing of the power supply to produce an output of limited duration which is applied to the gate as an enabling input. The output of the gate is joined to a second one-shot multivibrator which responds to a pulse generated when the gate is fully enabled causing energization of an alarm actuator. An additional pulse detector optionally is interposed between the gate and the second one-shot to eliminate any random pulses which may occur at the gate output at a frequency below r.f. level, and an additional filter optionally is included between the high pass filter and the AND gate to eliminate the effects on the circuitry arrangement of high frequencies above a predetermined level.

Serial minimum shift keyed modulator including notch and bandpass filters

Abstract: An SMSK modulator wherein the output of a bi-phase modulator is passed through a notch filter and a band pass filter to produce an SMSK signal for transmission. The notch filter and band pass filter are constructed to simulate the output (center lobe) of an SMSK conversion filter, which is defined as a filter that converts a bi-phase shift keyed (BPSK) modulated signal into MSK.

Audio-band electro-mechanical vibration converter

Abstract: A device for giving an audio signal to a coil associated with an audio-band electromechanical converter uses a mixer, a first-stage low-pass filter, a limited and a second-stage low pass filter to correct distortion of the wave form of a signal from the limiter.

Electric filter equipment

Abstract: An electric filter, for example an harmonic filter in an HVDC convertor, has, in addition to the main filter, a low power model filter having the same frequency characteristic as the main filter. The model filter is supplied with a voltage which is a scaled-down version of the voltage appearing across the main filter. The currents in the main and model filters are sensed at corresponding places in the filters and compared. If a deviation occurs between the sensed currents in the main and model filters, an indicating signal is generated which indicates a deterioration in the performance of the main filter.

High power broadband cancellation system

Abstract: : The objective of this report is to improve the broadband cancellation technology associated with adaptive UHF (225-400 MHz) Interference Cancellation Systems (ICS) employed with tunable or hopping transmitters. More specifically, the objective is to cancel a narrowband transmitter waveform centered at a frequency f sub o plus its noise and modulation sidebands that extend over plus or minus 0.02 % of f sub o. This report describes the concept for a two-channel ICS which provides improved broadband cancellation compared to that achievable with a single-channel ICS. The input to the second-channel weight is spectrally pre-shaped by an adaptive notch filter which automatically tracks the frequency of the interference. Control of the second-channel weight utilizes a novel pilot-directed control system. A functioning unit was constructed to implement the design concept. Experimental measurements of the unit's performance across the 225 to 400 MHz band are presented which show f sub o cancellation averaging about 60 dB, and sideband cancellation (at f sub o plus or minus 85 KHz) averaging almost 55 dB. The settling time is less than 20 milliseconds. Suggestions for design refinements and for more extensive testing of the unit are discussed.