Showing papers on "Band-stop filter published in 1980"

A filter family designed for use in quadrature mirror filter banks

Abstract: This paper discusses a family of filters that have been designed for Quadrature Mirror Filter (QMF) Banks. These filters provide a significant improvement over conventional optimal equiripple and window designs when used in QMF banks. The performance criterion for these filters differ from those usually used for filter design in a way which makes the usual filter design techniques difficult to apply. Two filters are actually designed simultaneously, with constraints on the stop band rejection, transition band width, and pass and transition band performance of the QMF filter structure made from those filters. Unlike most filter design problems, the behavior of the transition band is constrained, which places unusual requirements on the design algorithm. The requirement that the overall passband behavior of the QMF bank be constrained (which is a function of the passband and stop band behavior of the filter) also places very unusual requirements on the filter design. The filters were designed using a Hooke and Jeaves optimization routine with a Hanning window prototype. Theoretical results suggest that exactly flat frequency designs cannot be created for filter lengths greater than 2, however, using the discussed procedure, one can obtain QMF banks with as little as ±.0015dB ripple in their frequency response. Due to the nature of QMF filter applications, a small set of filters can be derived which will fit most applications.

Programmable multifrequency tone receiver

Abstract: A multifrequency tone receiver (100) for detecting simultaneous tone signals in a sampled digital signal. The tone receiver (100) includes a microprogrammed sequence controller (101 and Fig. 3B), a time-multiplexed digital filter (102 and Fig. 3C) and a signal processing microcomputer (103 and Fig. 3A). For each sample of the digital signal, the sequence controller (101) is programmed to time multiplex the digital filter (102) for performing three cascaded second order filtering operations (two bandpass filter operations and one low pass filter operation as shown in Fig. 2) for each of six tone signals to provide corresponding energy estimates and one additional filtering operation to provide a total energy estimate. The signal processing microcomputer (103) processes (per flowchart in Fig. 7) a number of sets of the seven energy estimates and provides an indication when a multifrequency tone pair has been detected. The digital filter (102), when enabled by a filter start signal from the sequence controller (101), asynchronously performs a signal multiplication-like filtering operation to implement each second-order filter, and provides a filter done signal upon completion of the filtering operation. Full-wave rectifying capability is provided during low pass filtering operations by logically complementing (gate 361 in Fig. 3C) the digital filter input signal. Limit cycles may be suppressed in the digital filter output signal by rounding the output signal and clamping (gates 365-368 in Fig. 3C) positive and negative overflows to the largest allowable positive and negative signals, respectively. The tone receiver (100) may be advantageously utilized in a PCM communication system for detecting multifrequency tone signalling used for dialing and supervisory control. Moreover, the inventive tone receiver (100) may be adapted to receive many different types of tone signalling simply by changing firmware (Tables I and IV) therewithin.

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.

Band stop filter and circuit arrangement for common antenna

Abstract: In a band stop filter having a plurality of series resonating circuits, and coaxial cables connected between the series resonating circuits, the length of each of the coaxial cables is made either shorter or longer than quarter wavelength at the center frequency. With this arrangement, asymmetry is introduced in the insertion loss vs frequency characteristic curve so that the curve is sharper than the symmetrical curve in a given range, resulting in a reduction of insertion loss at a transmission band which resides either above or below the center frequency. Two band stop filters may be combined to constitute an antenna coupler for connecting a transmitter and a receiver to a common antenna. Each of the series resonating circuits used in the band stop filter may be constructed of a quarter wavelength coaxial resonator, which functions as a parallel resonating circuit, and a loop-like coaxial cable, which functions as a coupling capacitor.

Tone control of the operational type

Abstract: A tone control circuit for use in audio equipments includes an attenuating high pass filter (typically, a CR filter), an attenuating low pass filter, a boosting high pass filter, a boosting low pass filter and at least an operational amplifier for tone control The high pass filters extract a treble component from an audio input signal for emphasizing or attenuating treble response, whereas the low pass filter extract a bass component of the audio input signal for emphasizing or attenuating bass response The mid-range component of the audio input signal prevented from entering the filters by virtue of a bypass circuit interposed between a source of the audio input signal and the operational amplifier

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.

Coherent noise cancelling filter

Abstract: Apparatus and method for removing coherent noise from an electrical signal, such as powerline noise, and operating in real time. An operational amplifier with digital filter and a low pass filter in the feedback loop, with the digital filter providing a feedback signal corresponding to the coherent noise in the absence of the desired signal. In the preferred embodiment, an integrating type digital filter with digital memory, and alternative embodiments with condenser memory.

Smoothing filter for digital to analog conversion

Abstract: An electronic filter comprised of three active filter sections (A, B, C) is provided to smooth the stepped signal from a digital-to-analog converter The first section has a noninverting low-pass filter transfer function, and the second has an inverting transfer function designed to pass a narrow frequency band centered at the step frequency of the stepped output signal with sharp cutoff on either side of that narrow band The third section adds the noninverted output of the first section to the inverted output of the second section This third section has a lead-lag transfer function designed to reduce the phase angle between the signal at its output terminal and the stepped signal at the input of the first section

A Low Cost Multiplexer for Channelized Receiver Front Ends at Millimeter Waves

Abstract: Work with millimeter-wave components using printed-circuit techniques has led to the successful development of multiplexers that are compatible with low-cost fabrication and packaging techniques. This paper will describe a 26 to 42-GHz multiplexer exhibiting 1.2 to 2.8 -dB insertion loss over a 4-GHz channel passband and a 45-dB rejection bandwidth of less than 8 GHz. This multiplexer uses a channel-dropping filter technique that splits the band into 4-GHz subbands (channels). Each channel-dropping filter consists of dual band-pass filters separated by a pair of 3-dB directional couplers. Fabrication costs are kept low by using chemically-milled broadwall couplers and E-plane filter resonators. A series of normalized filter design nomograph's have been generated. Measured multiplexer performance will be presented.

Method and apparatus for measuring signal to noise ratio in a TDMA communications system

Abstract: A method and apparatus for measuring signal to noise ratio in a time division multiple access (TDMA) communications system which does not require that normal communications be interrupted. The signal to noise ratio measurement is performed on the unmodulated carrier which typically occurs in the preamble of each information burst in the TDMA format. In order to perform the measurements on the carrier of the same burst in each frame, the carrier and noise powers are sampled at a predetermined time with respect to specified information which occurs at the same time in each frame, normally the frame reference burst. After being converted to the receiver intermediate frequency, the unmodulated carrier is fed to both a narrow band pass filter having a pass band at the intermediate frequency and a narrow band stop filter having a stop band at the intermediate frequency. The ratio of the band pass filter output to the band stop filter output is the signal to noise ratio within a very small error.

Phase-locked loop filter

Abstract: A tunable narrow-band filter is described incorporating a phase-locked loop that includes a phase detector, amplifier, loop filter, and voltage controlled oscillator wherein the loop filter transfer function is derived or extracted from the desired closed-loop transfer function that is of order n=3 or greater. The loop filter may furthermore have finite transmission zeros or peak attenuation at specific frequencies close to the passband which also appear in the characteristics of the narrow-band filter. The invention overcomes the problem of providing peak attenuation close to the passband of an electronically tunable narrow-band filter.

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.

Comb filter device

Abstract: A comb filter device has two operation modes, one mode being a conventional comb filter when input signals have high correlation between sequential lines, and the other mode being a simple amplifier when input signals have low or no line correlation. Therefore, this comb filter has little deterioration of vertical resolution of a television picture.

Averaging filter circuits for signal recovery applications

Abstract: The optimum filter for improving the signal-to-noise ratio in a commonly encountered signal recovery situation is the ideal averaging filter. Approximants to the averaging filter response, with averaging times between 1 ms and 100 s, are realised by RC active networks having some novel properties. The use of these filters in place of the first-order low-pass filter leads to an improvement in the measurement rate by a factor of two or greater.

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.

Selective filter for closed loop servo system

Abstract: In a closed loop servo system in which the input signal is inaccessible and not available for measurement, but the error signal and output signal are both accessible and measurable, a filter configuration is provided which can be inserted into the error signal path of the system to reduce the undesirable effects of noise or other unwanted signals without appreciably affecting the closed loop dynamics of the overall system. In the generalized system a filter having the characteristics g(s) in LaPlace notation is inserted into the error signal path of the system to filter selected components of the error signal. A second filter having the characteristics h(s) which satisfies the equation g(s)+h(s)=1, is coupled between the output signal and the output of the filter having the characteristics g(s). The signal passing through the filter having the characteristic h(s) is summed with the signal leaving the filter having the characteristics g(s) to cancel the filtering effect relative to the output signal and thus to decouple both filters from the control loop. Thus the filtering is accomplished without appreciably altering the characteristics of the control loop. In one application, the invention is utilized in connection with the proportional navigation guidance system for a homing missile. This permits extraneous signal components due to, for example, radome loop coupling and noise to be filtered from the error signal without affective the closed loop dynamics of the missile guidance.

Image frequency reflection mode filter for use in a high-frequency receiver

Abstract: A planar image reflection mode filter is provided for reflecting parasitic signal frequencies produced in the mixer of a receiver. The filter includes a reflecting quarter-wavelength filter and an adaptive circuit functioning to enable the transmission of desirable frequencies. A slot can be formed in the quarter-wavelength filter to enable odd-mode resonance and reduce the width of a transition frequency band lying between a reflection band and a transmission band.

Notch filter based on identical building-blocks with arbitrary transfer function

Abstract: A new design formula for the Multiple Frequency Notch Filter is proposed. The filter can be constructed from a finite set of identical linear sections with arbitrary transfer functions. The general transversal structure and the cascade connection of the identical linear section are considered. In contrast to the general structure, there are found three configurations which have only one adjustable element. An example illustrating the use of the proposed technique is included.

Waveguide filter employing common phase plane coupling

Abstract: Bandstop (FIGS. 1-3) and bandpass (FIGS. 4, 5) filters are presented utilizing broad and narrow wall resonator coupling in a rectangular waveguide (11 and 37) at a common cross sectional reference plane. For the bandstop filter, the resonators (12, 13) are resonant at a common frequency f 0 to provide a two-pole bandstop response in a filter of minimal longitudinal dimensions. For the compact bandpass filter, each tone rejection is provided by a pair of resonators (31, 35) coupling to the electromagnetic field signal at two points one from a broad wall and the other from a narrow wall of the waveguide (37) but displaced by some multiple of a half wavelength. Another pair of resonators (33, 34) are in common cross sectional plane relationship to the first pair but located on a wall of different width to provide rejection of a tone at the other end of the passband. The use of resonators with different resonant frequencies at a common cross sectional plane avoids possible interresonator coupling. Additional pairs of resonators (e.g., 32, 36) may be interleaved with these resonator locations. Each resonator (e.g., 13) is associated with an aperture (e.g., 19) and has its major portion extending into a housing (e.g., 18) located exterior to the waveguide (e.g., 11).

Digital filter with scaled tap coefficients

Abstract: Modem circuitry for processing data signals, featuring a digital filter whose tap coefficients are all scaled by a common factor such that the most significant bits of the filter output are indicative of the digital data.

Band-stop filter for equipment with carrier-frequency utilization of low-voltage lines

Abstract: Band-stop filter for equipment with carrier-frequency utilization of low-voltage lines, including a current-compensated choke having a closed ferrite core, two center taps, and two coil halves each of which having windings being connected to one of the center taps and wound with the same sense on the closed ferrite core, and a capacitor connected between the center taps.

Effects of Directional Coupling on the Magnetostatic Surface Wave Propagation

Abstract: In this report we describe the experimental confirmation of the directional coupling of the magnetostatic surface wave between two parallel YIG films. We also describe a theory to calculate the coupling coefficient and the over-all passband characteristics of the devices. With this technique, a bandstop filter with the minimum insertion loss of 18 dB and the rejection of at least 25 dB from the top of the passband at 7.08 GHz was demonstrated. The stopband width at 10 dEi below the top of the passband was 15 MHz. A narrow bandpass filter was also built. We observed the reduction of up to 75 of the 30 dB passband with the increase of the insertion loss of less than several decibels. This method is useful at higher frequencies because we can choose a material with the lowest intrinsic loss and control the bandwidth by the directional coupling. The experimental results agreed qualitatively well with the theoretical predictions. This will provide a new possibility to the design of magnetostatic signal processing devices.

Noise suppression circuit for two-way telephone system - has filter comprising subtractor extracting outputs of impedance transformers at outputs of two integrators

Abstract: The noise suppression circuit has the control ac voltage derived from the voice channel rectified and passed to a filter to remove the component caused by interference or background noise. The filter's output is rectified to control the gain of the channel. The filter has two input parallel integrators (I1, 12) with different time constants. Two operational amplifiers (OP1, OP2) acting as impedance converters are connected to the outputs of the integrators. A subtractor (OP3) subtracts the outputs of the operational amplifiers from one another and its output is the output of the filter. The time constants are such that the voltage at the output of the first integrator follows the amplitude variations of the LF input to the filter whilst the output voltage of the second integrator is similar to the average of the filter input voltage and is not affected by these amplitude fluctuations.

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.

An optimal design of split-electrode CCD transversal filters

Abstract: A new optimal design method is introduced for split-electrode CCD transversal filters. This method uses mixed-integer programming techniques to quantize filter parameter values consistent with actual mask dimensions. It improves filter performance over other design methods that use roundoff approximation to quantize mask parameter values. As Illustrated through examples of low-pass and notch-filter designs, our optimal design method can improve the performance significantly; in the design of a low-pass filter, it increased the stopband attenuation from 34 to 50 dB, and in the design of a notch filter, a 75-dB notch was achieved which had been completely obliterated when parameters were quantized by using roundoff approximation.

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.