Showing papers on "Band-stop filter published in 1974"

Design of digital notch filters

Abstract: It is shown that a second-order digital notch filter is uniquely characterized by two distinct parameters, the notch frequency and the 3-dB rejection bandwidth. As a result, such a filter can be realized using only two multipliers. Methods are outlined to design a notch filter for a prescribed notch frequency and a prescribed 3-dB rejection bandwidth, along with procedures for postdesign adjustment of these parameters. All two-multiplier, canonic and noncanonic, notch filter configurations are developed using the multiplier extraction approach. These networks are then compared with regard to the effect of internal multiplication roundoff errors. Results of computer simulation of the notch filter configurations are also included.

Design of Digital Notch Filters

Abstract: It is shown that a second-order digital notch filter is uniquely characterized by two distinct parameters, the notch frequency and the 3-dB rejection bandwidth. As a result, such a filter can be realized using only two multipliers. Methods are outlined to design a notch filter for a prescribed notch frequency and a prescribed 3-dB rejection bandwidth, along with procedures for postdesign adjustment of these parameters. All two-multiplier, canonic and noncanonic, notch filter configurations are developed using the multiplier extraction approach. These networks are then compared with regard to the effect of internal multiplication roundoff errors. Results of computer simulation of the notch filter configurations are also included.

Transversal frequency filter

Abstract: A charge-transfer transversal filter and method of use is provided. In one aspect of the invention a handpass filter is provided where the center frequency of the bandpass is variable responsive to the clock rate applied to the charge-transfer devices. In a different aspect of the invention a matched filter for a chirp signal is provided. The filter requires a minimum number of Nyquist samples by including the provision of a clock rate which varies responsive to the frequency sweep of the input chirp signal. A method for detecting a chirp signal is provided which includes the step of selectively varying the clock rate applied to a charge-transfer shift register responsive to the frequency variations of a selected chirp signal.

Waveguide low pass filter

Abstract: The filter may be designed from a multiple section L-C Chebyshev low pass filter prototype and is of generally ridged filter construction. The distributed shunt capacitors in the ridged section are designed to support only one mode in both the passband and primary stop band. The series inductors are calculated in accordance with evanescent mode (below cut-off) operation.

Tunable microwave notch filter

Abstract: A recursive microwave notch filter wherein each section is comprised of a pair of power dividers e.g. 3-db couplers joined by a short and a long microwave transmission line. Tuning of the frequency rejection notch is achieved by inserting an electrically controlled phase shifter having 360* of adjustment in the short transmission line. Two identical cascaded sections of the subject notch filter are required for coupling to the input of a saturated RF power amplifier, such as the output amplifier of an amplifier chain utilized in present day radar transmitters, in order to obtain the desired frequency rejection notch, due to the gain compression characteristic present in an amplifier when driven into its saturation region.

Low pass microwave filter

Abstract: A low pass microwave filter comprised of a two conductor transmission line including at least two cascaded tapered sections wherein one of the conductors in each filter section has a tapered surface, preferably linear, and having an electrical length substantially equal to one half the wavelength of the center frequency of operation. Geometrically and performance-wise the subject filter is unsymmetrical with respect to its input and output ports. The filter does not exhibit the usual rapid transition between the pass band and stop band which is a general characteristic of conventional low pass microwave filters utilizing reflective harmonic structures.

Programmable Bandpass Filter and Tone Generator Using Bucket-Brigade Delay Lines

Abstract: Bucket-brigade devices have been used to build a new type of active filter that is equivalent to a second-order digital filter without the need for complex analog-to-digital conversion. The filter response characteristics, i.e., center frequency and bandwidth, depend on the circuit parameters of gain and clock frequency, both of which may be electronically controlled. By using a variable clock signal, 1023 frequencies can be accurately selected by the proper setting of ten switches. The selected clock frequency uniquely determines the center frequency of the bucket-brigade filter. The programmable feature of the clock circuit, therefore, allows the convenient selection of the center frequency of the bandpass filter. A slight modification to the programmable bandpass filter converts it into a programmable oscillator. Thus, any one of 1023 tones can be generated by the proper setting of the switches. A device that exhibits both filter and oscillator functions has been demonstrated in the laboratory.

Distortion measurement system

Abstract: A distortion measurement system for measuring distortion as low as 0.002% includes an ultra low distortion oscillator having a relatively fast response which is achieved by switching the time constant of the control loops of the oscillator during settling. The analyzer section included in the distortion system has a unique notch filter which provides low distortion. This is achieved by adding together two 90° all pass phase shifters. In addition, automatic tuning is provided by two feedback control loops; one is responsive to out-of-phase signals which controls the RC filter circuits of the phase shifters and the other responds to the in-phase signals which controls the output summing junction of the notch filter. Finally, a feedforward type of simultaneous tuning is accomplished by ganging the oscillator frequency adjustment with the analyzer.

Low pass nonrecusine digital filter

Abstract: A digital filter having a cut-off frequency of fc to which code words of a frequency fs are applied and which supplies code words at a frequency of f's The filter comprises a first digital filter section supplying numbers having a reduced frequency fm and whose output is directly coupled to an interpolating digital filter supplying the outgoing numbers of the filter at the frequency f's The first filter section and the interpolating digital filter are each built up as a digital filter having a cut-off frequency of fm/2

Wide dynamic range voltage controlled filter for electronic musical instruments

Abstract: A voltage controlled filter for an electronic synthesizer incorporates a plurality of individual voltage controlled filter stages connected in cascade with a variable feedback interconnecting the input and output stages. Each of the stages is controlled by application of a series of pulses, with the period between successive pulses determining the cutoff frequency of the filter. Application of pulses to the filter stages at different pulse repetition rates changes the cutoff frequency of the filter and modifies the relative amplitudes of different frequency components of an audio signal to be passed by the filter. The filter is suited for use with high level signals and provides an extremely wide dynamic range through a very high signal-to-noise ratio.

CCD selective transversal filter

Abstract: A charge coupled device to provide a multi-channel selective transversal filter in which a plurality (N) of channels are sequentially processed in a common transversal filter unit to provide a desired transfer function such as a high pass filter. The analog signals from a plurality of sources or channels are fed into the selective transversal filter in serial fashion with the signal from each channel being nondestructively sampled and multiplied by appropriate weighting coefficients as provided by split electrodes separated by (N-1) charge coupled device storage bits. By having storage electrodes between the split electrodes equal to the number of input channels, the split electrodes, which provide the output signals, operate upon signal information from one channel at a time. The displacement current differences between the two halves of all of the split electrodes provide output signals having the desired filter characteristics. The transversal filter devices in accordance with the invention may be operated in a single phase clock mode or in other clock modes. The filter may have a tuning capability to modify the filter response by providing a variation of the clock frequency applied to the electrodes.

N-pole filter circuit having cascaded filter sections

Abstract: The n-pole filter preferably has four filter circuits cascaded in series. Each of the filter circuits is preferably a low-pass filter circuit and each has a controllable frequency response which is variably controlled from a common current or voltage source. Each filter circuit includes a transconductance circuit and inverting operational amplifier. A feedback resistor couples between the first and last filter circuits and is adjustable to provide different amounts of resonance.

Digital notch filter design procedure

Abstract: An analytical procedure for designing a linear digital notch filter is presented. The resultant filter is sixth-order and is implemented by cascading three second-order filters so as to avoid instability which may arise from computer coefficient truncation. The procedure outlined is straightforward, requires only simple algebraic steps, and gives filter parameter selection criteria for reducing the effects of computer coefficient truncation. Notch filters have utility in situations where a desired signal is corrupted by an additive sinusoidal pickup. One thus must process the noisy signal so as to remove the sinusoid without significantly distorting the desired signal.

Amplitude limited filter

Abstract: A filter is provided to substantially nullify the effect of process noise of less than a preset amplitude limit on the measurement of a process variable. The filter passes on to a controller or other device all signal changes greater than this amplitude. Within the amplitude limit the signal is damped by a first order lag with a filter time constant typically at least an order of magnitude greater than the average period of the noise to be filtered, but outside the amplitude limit, signal changes are passed immediately with no lag to a device such as a controller. The filter functions by generating a compensating signal essentially duplicating the process noise and then subtracting this compensating signal from the filter input signal, thus canceling this noise from the signal passed to the controller or other device. By subtracting only a limited value of this compensating signal from the filter input, changes of input greater than this limit are not compensated, and are thus immediately passed with no lag. On a sustained change of the input signal, the unlimited compensated signal will decay toward zero at the filter time constant, so that noise centering about the new sustained value of the input will be filtered.

Mass unbalance modulation pickoff attenuation and speed control in electrostatic gyroscope system

Abstract: An improved electrostatic gyro system wherein, for each of the axes of suspension of a rotor, pickoff electronics are responsive to electrode pickoff signals for developing combined mass unbalance modulation (MUM) and servo signals from which a MUM signal reconstruction circuit demodulates and reconstructs only the MUM signal. The reconstructed MUM signal is then subtracted in servo suspension electronics from the combined MUM and servo signals to substantially develop only the servo signal containing only rotor displacement information. This servo signal is then fed to a servo network which does not require a notch filter. The output of the servo network is then developed into force signals to enable an associated pair of plate charge amplifiers to electrostatically suspend the rotor properly between an associated pair of electrodes. In addition, the reconstructed MUM signals are utilized by speed control electronics to develop and add highly accurate and precise speed control signals to the output of the servo network to provide a very precise speed control of the rotor without the use of any notch filter.

Electrical current frequency filter circuit having parallel filter branches

Abstract: A filter circuit which comprises first and second parallel coupled filter branches each including a first multiplier, an intermediate frequency filter, and a second multiplier, respectively, coupled in series. A signal generator generates two output signals which are linearly independent of each other at a frequency which is equal to that of an input signal which is to be passed by the filter branches, and has a pair of output terminals coupled to the first multipliers of the filter branches for transmitting these output signals thereto. An adder is coupled to the second multipliers of the filter branches and generates an output signal which forms the output signal of the filter circuit. An adjustable signal feedback means is coupled to the output of the adder and to the inputs of the first multipliers of the filter branches for adjusting the bandwidth of the filter circuit. In an alternative embodiment of the invention, two pairs of identical filter branches are series coupled to form the filter circuit, with the adder of the second pair of filter branches generating the output signal of the filter circuit and being coupled to the signal feedback means of the circuit.

The Effects of Notch Filters on the Correlation Properties of a PN Signal

Abstract: With wideband pseudo-noise (PN) communications systems, it is sometimes desirable to supplement the inherent interference rejection capabilities by adding notch filters to attenuate relatively narrowband interference. This correspondence presents an investigation of the effects of notch filters on the performance of PN correlation receivers. A theoretical analysis of the correlation drop due to filter distortion has been conducted and confirmed by experimentation. Additional measurements and analysis have established the trade-off between correlation drop and interference suppression as a function of interference bandwidth. A typical result is that by incurring a penalty of a 1-dB drop in correlation peak, interfering signals having bandwidths of 2 to 3 percent of the PN chip rate can be attenuated by 25 dB.

A new voltage-tunable distributed RC notch filter suitable for SOS realization

Abstract: It is shown that a combination of two MOS distributed RC elements can be designed to produce a tunable notch filter in which conductance modulation as well as MOS capacitance contribute to tunability, and the conductance modulation does not de-optimize the null.

Second-order canonical active filter

Abstract: A high-pass notch filter with variable gain that may be 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 d-c gain. Three embodiments of the filter are illustrated, thus extending the available range of the gain to cover all requirements.

A Compact Channel-Dropping Filter for Stripline and Microwave Integrated Circuits

Abstract: A compact channel-dropping filter geometry is described that is particularly suited for stripline and microwave integrated circuits (MIC). The channel-dropping filter is comprised of a hairpin bandpass filter and a new bandstop filter, referred to herein as a folded-line bandstop filter. Design parameters for the latter filter for a range of bandwidths are tabulated. Analytical and experimental data for a trial channel-dropping filter are presented and discussed.

Circuitry for use with a transducer which generates a signal corresponding to a physical phenomenon

Abstract: The present circuit is primarily designed to be employed with a transducer which generates a signal in response to some physical phenomenon and said present circuit provides a direct current signal which is an excellent representation of the intensity of said physical phenomenon. In addition said circuit has excellent response over a broad frequency range as related to said physical phenomenon and has high signal to noise ratio. The present circuit principally utilizes a low pass filter which provides a relatively flat response at all frequencies below one-half of the carrier frequency as well as employing a notch filter designed to filter signals at twice the carrier frequency. The twice filtered signal is a low ripple direct current signal having the earlier described characteristics.

Pulsed doppler radar device having at least one range channel

Abstract: A pulsed Doppler radar device with variable repetition frequency, having at least one range channel operatively connectable at the pulse rate of the pulse repetition frequency, a doppler filter which suppresses clutter interference in the low Doppler frequency range, and a device for the variation of the pulse repetition frequency, in which the doppler filter of each range channel comprises at least one sampling-and-holding circuit and a following high pass or band pass filter, the switching pulse rate of the sampling-and-holding circuit being changeable with changes in the pulse repetition frequency, with the same high pass or band filter being utilized for all repetition frequency variations, the cut-off frequency of the following filter, if a high pass filter or, the lower cut-off frequency of such filter, if a band pass filter being approximately equal to the upper frequency of the clutter band width whereby the latter is suppressed, and the upper cut-off frequency, if a band pass filter is employed, being above the maximum pulse repetition frequency.

A Class of Waveguide Filters for Over-Moded Applications

Abstract: As the frequency spectrum extends to the millimeter wave range, the rapid rise in intrinsic loss and the diminishing physical dimensions greatly curtail the usefulness of conventional waveguide filters in dominant mode waveguide The incentive for designing filters in over-moded waveguide is all too apparent However, filter design in over-moded waveguide faces challenging design criteria, such as mode conversion loss and intrinsic loss, ease of being analyzed and synthesized, and feasibility for economical fabrication A filter structure is presented which fulfills all aspects of the design objectives The structure involves a type of discontinuity which is not only free from mode conversion but also extremely simple to characterize analytically The latter renders feasible the use of available filter synthesis techniques While the proposed filter structure can be designed either as a bandpass filter, a bandstop filter or a low-pass filter in an over-moded uniform waveguide of arbitrary cross section, for illustration purposes only the low-pass filter in over-moded circular waveguide is discussed in great detail Design theories are presented which allow the proposed structure to be designed either by the image method or by operating parameter filter synthesis Excellent agreement between the theory and measurements made on filter models is shown

Waveguide bandstop filter

Abstract: The filter is in the form of a resonant ring disposed inside of the waveguide which feeds microwave energy to the cooking cavity of a microwave oven. The ring is preferably disposed adjacent the magetron, can be either dielectrically or conductively supported, is rotatable for varying E vector coupling and is preferably for second harmonic suppression.

Effects of losses and parasitics on a voltage-controlled tunable distributed RC notch filter

Abstract: An evaluation is given on the effects of MIS losses and parasitic notch inductance on the tuning-range compression of a voltage-controlled tunable distributed URC notch filter.

Doppler navigation system with tracking filter for multipath discrimination

Abstract: A Doppler navigation system with tracking filter for reducing suceptibility to multipath signals. For acquisition of a Doppler ILS angle representing a signal within a spectrum also containing multipath signals, a self-tracking variable-Q filter arrangement is used, with wide band acquisition (low Q) followed by progressive steering of the filter center frequency to the desired signal frequency, together with decrease of the filter bandwidth to an equivalent of 2 beamwidths (high Q) at final balance.

Navigation receiver with doppler filter gating

Abstract: A navigation guidance receiving system for use with a Doppler navigation beacon of the type comprising a commutated linear array for producing a simulated Doppler effect. The receiving system includes a wideband Doppler beat waveform information filter and measurement circuits. Means are also provided to gate the filter output synchronously to allow dissipation of the filter transient response. The result is reduced filter frequency "pulling" and reduced measurement error due to the effect of multipath signals having beat frequencies in the filter rejection band.

Radio frequency notch filter

Abstract: A radio frequency notch filter includes a transformer secondary winding connected in series with a transmission line. The transformer primary winding is arranged with a capacitor to be parallel resonant at the filter center frequency. A reactive means is also connected in electrical shunt with the transmission line which responds at the notch frequency to drain current then traversing the secondary winding.

A Symmetric Notch Filter with two Grounded Capacitors

Abstract: A canonic symmetric notch filter with grounded capacitors is presented. It has independent controls for Q-factor and notch frequency. It also provides low-pass and band-pass response across appropriate ports. An experimental circuit was built and tested for Q-values of 1, 10 and 100 at each of the notch frequencies of 60 Hz, 1 KHz and 5 KHz. There is excellent agreement between calculated and experimental results.

Band-pass filter for frequency modulated signal transmission

Abstract: A band-pass filter comprises a delay circuit comprising a plurality of unit delay elements connected in cascade arrangement and receiving as input a signal including a frequency modulated signal and a coefficient summing circuit for carrying out coefficient summing of the outputs of specific delay units of the delay circuit and producing as output the frequency moudlated signal which has been band-pass filtered. This band-pass filter has a transmission characteristic representable by H(jω) = [ 1 - a(ω - ω.sub.o).sup.2] e - j .sup.ω.sup.τd , where: a is a constant imparting an attenuation characteristic of the filter; ω o is an angular frequency of a carrier wave of a frequency modulated signal and a center angular frequency of the band-pass filter; and τd is a delay time of the band-pass filter.