Showing papers on "Low-pass filter published in 1968"

Interference filters for the far infrared.

Abstract: Perforated metal plates (grids) of various kinds are used for the construction of transmission filters for the far ir. Examples are given of filters with low pass, high pass, bandpass, and bandstop characteristics with steep slopes. These filters are the optical equivalents of microwave waveguide filters. They can be designed by the same theoretical procedures as those to meet a wide variety of different specifications, at least in principle. Actually, losses and constructional tolerances limit the performance. Measurements at oblique incidence indicate that the filters will find useful application in light pipes too. Furthermore, they may prove advantageous in short millimeter wave systems that employ optical techniques.

Coefficient Accuracy and Digital Filter Response

Abstract: The frequency response of a digital filter realized by a finite word-length machine deviates from that which would have been obtained with an infinite word-length machine. An "ideal" or "errorless" filter is defined as a realization of the required pulse transfer function by an infinite word-length machine. This paper shows that quantization of a digital filter's coefficients in an actual realization can be represented by a "stray" transfer function in parallel with the corresponding ideal filter. Also, by making certain statistical assumptions, the statistically expected mean-square difference between the real frequency responses of the actual and ideal filters can be readily evaluated by one short computer program for all widths of quantization. Furthermore, the same computations may be used to evaluate the rms value of output noise due to data quantization and multiplicative rounding errors. Experimental measurements verify the analysis in a practical case. The application of the results to the design of the digital filters is also considered.

Optimum radar signal processing in clutter

Abstract: This paper considers the joint optimization of a class of radar signals and filters in a number of clutter-pins-noise environments. The radar signal processor in this case will be optimum in the sense that its output at the time of target detection yields the maximum ratio of peak signal power to total interference power. If the interference at the input to this signal processor is a Gaussian random process, this processor also yields the maximum probability of detection for a given value of false-alarm probability. The signals used are pulse trains and the filters are tapped delay lines. The purpose of signal design is to determine the optimum complex weighting for each pulse of the pulse train. Filter design yields the optimum complex weighting for the output taps of the delay line. Filter design for a specified signal is considered first. This is followed by combined signal and filter design and matched filter design. Constrained signal and filter design is investigated last. It should be emphasized that the optimizations require a knowledge of the clutter time-frequency distribution. For practical situations, when the clutter distribution is unknown, an adaptive filter is proposed that automatically provides the optimum filter weights for a given transmitted signal. When the clutter has a range-time extent less than the equivalent range-time extent of the signal, filter design alone yields nearly optimum performance. As the clutter becomes extended in range-time, it is necessary to consider jointly the design of signal and filter to obtain an optimum radar signal processor. In this report it is suggested that the signal be designed under the assumption of the clutter being extended over a broad range of Dopplers and that the signal processor consist of a bank of adaptive filters. Then each filter output yields the maximum ratio of peak signal to total interference power for this signal design.

Nonrecursive digital filters: Design methods for achieving specifications on frequency response

Abstract: A simple and effective method for designing a nonrecursive digital filter is described. This method is constructed so that it is convenient to implement the resulting filter by using the fast convolution application of the fast Fourier transform. For one representative example of a fast convolution implementation of a nonrecursive digital filter designed by the method in this paper, only as many multiplications (per output sample) were required by this implementation as were required by an implementation of a well-designed recursive digital filter achieving an equally effective frequency response. This method for designing nonrecursive digital filters permits the desired frequency response to be specified either numerically (at equally spaced frequencies), graphically, or analytically. Specifications are to be provided also for the permissible 1) resolution and 2) ripple. The ease with which this design method can achieve a specification on frequency response suggests the use of this method whenever the resulting nonrecursive filter can be conveniently implemented on a general-purpose digital computer. Adaptation of these methods to computing power spectra is described.

Informationsverarbeitung in homogenen Netzen von Neuronenmodellen

Abstract: The interconnection structures of the peripheral part of the nervous system, which are considered here, are two-dimensional homogeneous networks with time and space dependent inputs and outputs. The principles of connection under consideration comprise lateral inhibition and facilitation. The transfer functions of those linear networks as well as the stability problem are investigated on a digital computer using different system parameters. A closed form solution is given for an infinitely large element density which describes the network properties. In this case an inhibition system acts as high pass filter on the spatial frequencies of the input, whereas a facilitation network acts as low pass filter. The properties of the networks and the transformations in case of moving patterns are analysed using the methods of systems theory.

A Spatial Frequency Filter to Remove Zero Frequency

Abstract: A study is made of the influence of removing zero spatial frequency from an image-forming system on the characteristic of the image. The specific example of the action of the filter on the image of the edge between fields of high and low brightness is discussed in detail. Results are presented of the intensity distribution in the edge image as a function of the filter parameters. The case of two adjacent edges, with resulting mutual interference of their spread functions, is used to illustrate a practical application of the filter and to indicate the possible incidence of errors occurring in measurements taken from such images.

Generation of Digital Signaling Waveforms

Abstract: Data transmission (digital signaling) systems generally transmit continuous, essentially bandlimited signals that represent alphanumeric sequences. The transmitting apparatus in such systems must therefore convert discrete symbols-often binary pulses-into prescribed analog waveforms. Current commercial systems do this via simple filtering, gating, and conventional modulation. These practices limit the types of waveforms that can be used and they are not always amenable to variable rate signaling. This paper describes a hybrid digital-analog method for approximating closely almost any reasonable digital signaling waveform. The basic idea is very simple: a "staircase" approximation of the desired signal can be generated via a shift-register version of a transversal filter. Variations on this idea, such as derivative approximation and multirate shifting, enhance its accuracy without destroying its simplicity and time-frequency scalability.

Power system filter

Abstract: A harmonic filter for an AC power system, particularly for converter installations, which provides damping to diminish the effects of parallel resonance. The filter consists of a plurality of conventional LC shunt filters tuned to the expected harmonic frequencies. The power system may also include static capacitors for power factor correction. Since the power factor capacitors and the harmonic filters are effectively in parallel with the inherent inductance of the AC system, a parallel resonance, which may occur at one of the lower harmonic frequencies, results. In order to reduce the effects of a parallel resonance, there is provided an additional filter tuned to provide damping at the harmonic frequency at which parallel resonance may occur. This additional filter comprises an LC filter with a resistor connected in parallel with the inductance. This resistor is connected to a blocking filter which presents a high impedance to the system fundamental frequency. The effect of this resistor is to provide damping which will reduce the amplitude of oscillations under parallel resonant conditions. Since this resistor is connected through a blocking filter, it provides damping without providing excessive additional loading at the fundamental frequency.

Optimum Linear Filter for Speech Transmission

Abstract: A common speech‐communications problem is to maximize speech intelligibility over a noisy channel when the transmitter is peak‐power limited. An optimum linear solution is analytically derived, and consists of a speech‐processing filter in the transmitter. The degree of improvement due to use of the filter is derived for a number of bandwidths and signal‐to‐noise ratios. The filter was experimentally verified by articulation tests as the optimum linear configuration, and was significantly more intelligible than other filters that bounded it. Although the optimum filter depends on the noise spectrum, there is no significant difference between it and a noise‐invariant filter for white or speech‐shaped noise. The use of the filter is equivalent to raising the transmitter power between 1 and 10 dB, depending on the speech bandwidth and the signal‐to‐noise ratio.

Integrated frequency selective circuit and demodulator including phase locked loop

Abstract: AN INTEGRATED FREQUENCY SELECTIVE CIRCUIT PARTICULARLY USED FOR DEMODULATING AN FM SIGNAL WHICH INCLUDES A PHASE LOCKED LOOP HAVING A PHASE COMPARATOR COUPLED TO A LOW PASS FILTER AND AMPLIFIER WITH IN TURN HAS AN OUTPUT VOLTAGE WHICH IS THE DESIRED DEMODULATED INPUT SIGNAL AND IS COUPLED TO A VOLTAGE CONTROLLED OSCILLATOR. THE FREQUENCY OUTPUT OF THE OSCILLATOR PROVIDES THE OTHER INPUT TO THE PHASE COMPARATOR TO COMPLETE THE LOOP. WITH THE USE OF THE PHASE LOCKED LOOP, TOLERANCE VARIATIONS GREATER THAN 10% IN INTEGRAL CIRCUIT ELEMENTS CAN EASILY BE TOLERATED. BACK TO BACK DIODES MAY BE INCORPORATED IN THE CIRCUITS TO PROVIDE LIMITING ACTION FOR IMPROVED INTERFERENCE REJECTION.

Pressure wave noise filter

Abstract: AN ILLUSTRATIVE EMBODIMENT OF THE PRESENT INVENTION IN PRESSURE PULSE SIGNAL DETECTING SYSTEMS FOR USE IN DETECTING DOWNHOLE DATA TRANSMITTED TO THE SURFACE IN THE FORM OF ENCODED PRESSURE PULSES IN THE DRILLING FLUID FLOW LINES WHILE DRILLING A WELL, INCLUDES A NOISE FILTER FOR ENABLING DETECTION OF SUCH PULSES IN THE PRESENCE OF NOISE DUE TO THE MUD PUMP. THE NOISE FILTER INCLUDES A DIFFERENTIAL PRESSURE SENSOR HAVING OPPOSITE FLUID PRESSURE INPUTS CONNECTED TO SPACED POINTS IN A FLOW LINE BY MEANS PROVIDING EQUAL TRAVEL TIMES TO OPPOSITE INPUTS OF THE SENSOR FOR PRESSURE PULSES DUE TO THE PUMP, BUT PROVIDING UNEQUAL TRAVEL TIME TO OPPOSITE SENSOR INPUTS FOR PRESSURE PULSE SIGNALS ARRIVING FROM A DOWNHOLE SIGNALLING DEVICE. THIS ENABLES THE PUMP NOISE TO BE EFFECTIVELY CANCELLED WHILE THE DOWNHOLE SIGNALS ARE DETECTED.

Broad-band high-frequency low-pass filters

Abstract: Broad-band high-frequency low-pass filters formed with capacitors which have structures including multilayer and ceramic types and monolayer capacitors. A passive element such as magnetic cores are contained wholly or partially within the capacitor structure. The filter units which may themselves form complete PI filters or L filters may also be combined as the inside portion of a tubular multilayer ceramic capacitor. Rolled capacitors may be used for distributed inductance and magnetic cores in combination with wound inductors or individually may be formed as portions of the filters.

Low-pass active filter

Abstract: A LOW-PASS FILTER EMPLOYS AN ACTIVE FILTER PRECEDED BY A PASSIVE FILTER, THE ACTIVE FILTER BEING AC COUPLED IN SHUNT WITH THE PASSIVE FILTER THE PASSIVE FILTER CARRIES MOST OF THE CURRENT, THUS REDUCING THE CURRENT SUPPLIED TO THE ACTIVE FILTER AND PERMITTING THE COMPONENTS OF THE ACTIVE FILTER TO BE OF SMALLER SIZE

Low-Pass Filters with Predetermined Phase or Delay and Chebyshev Stopband Attenuation

Abstract: A method is presented for determining the transfer function of low-pass filters whose attenuation shows a Chebyshev characteristic in the stopband and whole phase or delay time can __-_2 for n even be specified independently of the aforementioned attenuation properties The transfer functions may be realized by simple ladder networks In order to obtain, as far as possible, transformerless circuits, the transfer function to be determined has a pole at infinity

Bandpass Crystal Filters by Transformation of a Low-Pass Ladder

Abstract: This correspondence describes a method by which cascade lattice crystal filters having symmetrical bandpass response may be designed by a simple transformation of LC low-pass ladder filters. An example is given of the design of a fourth order Cauer parameter filter from tabulated values.

Adaptive radar clutter rejection

Abstract: A control loop in a radar receiver is jointly responsive to range gated video and a reference potential to establish a filter control signal. A plurality of range gated filters are responsive to the filter control signal to adjust the frequency response in a manner such that clutter is rejected yet the maximum frequency bandwidth is dynamically provided for moving target detection for varying clutter conditions. Each range gated filter has a filter element which is switchable such that the effective electrical properties of the element vary in accordance with the switching to thereby effect a change in the frequency characteristics of the filter. The switching rate is much higher than the pulse repetitive frequency of the radar such that the switching rate does not interfere with signals being processed through the filter. In one embodiment, a variable duty cycle pulse generator having a fixed frequency is utilized to effect control over the frequency characteristics of a filter.

Electromagnetic Interference Reduction Filters

Abstract: This paper presents the theory and application of lumped-image parameter reactive filter networks, absorptive-type filter networks, and combined absorptive-reactive filter networks as conducted electromagnetic interference reduction circuits. A comparison of the passband characteristics by specific examples is given for filter configurations of the pi, T, absorptive, and absorptive-reactive type under implementation conditions of a fixed source impedance and a varying load impedance as encountered when filtering prime power sources feeding ac to dc converters. This paper illustrates the problem the design engineer faces when applying the usual data given in filter catalogs. The filter characteristics are presented for 50-ohm resistive source and load conditions because of MIL-STD-220A quality control testr equirements. A test configuration is recommended to determine the admittance transfer of a filter network, indicative of the networks performance characteristics under application conditions.

A Note on the Step Response of High-Pass Filters

Abstract: The existence of overshoot in the step response of a high-pass filter is shown to be dependent upon the behavior of the frequency response of the filter at the origin.

Maximally Flat Amplitude Low-Pass Filter with an Arbitrary Number of Pairs of Real Frequency Transmission Zeros

Abstract: The synthesis of a general class of filter with maximally flat passband and Chebyshev stopband attenuation characteristic is presented. The filter has an nth order voltage transfer function with m pairs of transmission zeros in the stopband, where n \geq 2 m + 1 . Butterworth and inverse Chebyshev filters are special cases of this general class with m = 0 and n = 2m + 1 , respectively.

Digital Filter Design Techniques in the Frequency Domain

Abstract: In digital filtering, the spectrum is shaped using digital components as the basic elements. Although the physical realization is different, the aims of digital filtering are, thus, the same as those for continuous filtering. It is likely that digital filtering, already in extensive use for computer simulation of analog filters, will find increasing real-time application. Real-time digital filters have several advantages over their analog counterparts: a greater degree of accuracy can be attained in their realization; a larger variety can be built since certain realization problems (akin to negative elements) do not arise; no special components are needed to realize filters with time-varying coefficients; and they are of particular utility at very low frequencies where analog components become large and unwieldy. In contrast to the linear differential equations of continuous filter theory, linear digital filter theory is based on the mathematics of linear difference equations. Using the z-transform calculus, a number of digital filter design techniques are discussed. One technique is useful in designing a digital filter whose impulse response is like that of a given analog filter, whie other techniques are suitable for designing digital filters meeting specified frequency response criteria. Another yields filters with linear phase, specified frequency response, and controlled impulse response duration. The effect of digital arithmetic on digital filter behavior is considered.

High power microwave low-pass filter of the leaky wall type

Abstract: A high power microwave low-pass filter of the ''''leaky wall'''' type is disclosed. The filter employed in the output circuit of the high power microwave source such as a klystron, magnetron, or the like between the source and the load to suppress the harmonic output from the microwave source. The microwave filter comprises a section of main waveguide which is typically rectangular provided with flanges on its opposite ends for connection to the source and the load, respectively. An array of secondary waveguides, which are dimensioned to be below cutoff for the fundamental frequency of the microwave energy to be passed by the filter are coupled through the walls of the primary waveguide to the microwave energy in the primary guide. The secondary waveguides are provided with resistive card attenuators for absorbing the microwave harmonic energy coupled from the primary waveguide to the attenuators via the secondary waveguides. The secondary waveguides are rectangular hollow waveguides having at ;east nearly equal height and width dimensions such that the seo secondary waveguides will support cross polarized microwave energy in the second harmonic range of the primary waveguide whereby attenuation of the harmonic content of the microwave energy in the primary waveguide is enhanced. The wl walls of the primary guide are defined by the inner ends of the secondary rectangular waveguides. The resistive card attenuators are disposed on a diagonal of the secondary waveguides for coupling to all the possible modes of the secondary waveguides. In one embodiment, the planes of the walls of the secondary waveguides are disposed at substantially 45* to the longitudinal axis of the primary guide to enhance coupling of the secondary waveguides to the fields in the primary waveguide.

A nonrecursive digital filter for data transmission

Abstract: High-speed digital data transmission systems often require special filter functions for spectral shaping with prescribed phase characteristics. One such filter is the cosine roll-off filter, which has applications in both serial and parallel data transmission systems. This filter is of special interest, because in such applications it is common to utilize two identical cosine roll-off filters in a cascade connection, i.e., one in the transmitter and one in the receiver. The composite response of the cascade connection has the raised-cosine roll-off characteristic, which yields low intersymbol interference. Because a linear phase characteristic is further required, the digital filter type chosen for this application is nonrecursive. The difference equation coefficients are determined from the coefficients of a Fourier series expansion of the magnitude-frequency characteristic in the form of a cosine series. The linear phase characteristic is the direct result of setting the sine terms of the Fourier series to zero. Two criteria have been selected as a measure of the digital filter performance: minimum stop-band attenuation and an RMS measure of intersymbol interference. Performance was calculated as a function of the number of terms in the cosine series used to approximate the desired function. Performance graphs, which summarize the results of this investigation, are included. The application of digital filtering techniques in the field of data transmission systems is shown to have practical value.

Variable or low pass filter

Abstract: A low pass filter for insertion between two circuits, such as a power supply and a load circuit, that blocks the passage from one circuit to the other of radio frequencies above a given pass band, and which continues to function as a satisfactory filter under the condition of reactive components in the power supply and load circuits being close to resonant values with reactive elements in the filter. The filter comprises a pi network having a series line extending between the network input and output ends that includes an inductive circuit element, and shunt lines branching from the series line that include capacitive elements with resistance to establish resistance-capacitance elements that introduce circuit losses which reduce the Q of the shunt lines to inhibit resonances that might otherwise impair the filtering function of the device.

A High-Performance Integrated Microwave Circuit Frequency Quadruple

Abstract: An S- to X-band frequency quadrupler was developed with a 4.0-dB conversion loss and 11-percent bandwidth using hybrid integrated microwave circuit techniques. The multiplier has a low-pass transforming filter on the input and a bandpass filter consisting of half-wavelength lines edge coupled over quarter wavelengths on the output. Design curves for the bandpass filter are given for ceramic microstrip. Two beam-lead varactors were used in the multiplier giving it an input power-handling capability of 3-watts peak power.

Design of Wide-Band Sampled-Data Filters

Abstract: The frequency domain of wide-band linear sampleddata filters is considered. The sampled-data filter is termed ?wideband? when the frequency range of useful approximation to its continuous counterpart approaches half the sampling frequency. Sampled-data filter representations for continuous filters can be obtained using several different design procedures.[1] A particular design method utilizing the bilinear transformation is developed. The method is especially useful in designing wide-band sampleddata filters which exhibit relatively flat frequency-magnitude characteristics in successive pass- and stop-bands. Filters of this type are widely used in network simulation and data processing problems.[2] The design method possesses two chief advantages over the standard z transform.[3] The first is that the transformation used is purely algebraic in form. This means it can be applied easily to a continuous filter having a rational transfer characteristic expressed in either polynomial or factored form. The second advantage is the elimination of aliasing[4] errors inherent in the standard z transform. Thus, the sampled-data filter obtained by this design method exhibits the same frequency response characteristics as the continuous filter, except for a nonlinear warping of the frequency scale. Compenation for this warping can be made by a suitable frequency scale modification. Some of the more common filter networks to which the design method can be applied effectively are the Butterworth, Bessel, Chebyshev, and elliptic-filter structures. The design method consists first of obtaining a rational transfer characteristic for a continuous filter that satisfies the design specifications.

Improvements relating to carrier shift telegraphy

Abstract: 1,127,451. Telegraphy. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 26 Jan., 1966 [4 Feb., 1965], No. 4895/65. Heading H4P. In a frequency shift telegraph receiver the input signals f1, f2 pass to two modulators fed also by carrier frequency f 0 . One or the other of the inputs to one modulator is 90 degrees out of phase with the corresponding input to the other modulator. The modulator outputs pass, one via a 90 degrees phase shifter, to a combiner circuit, which gives on-off keyed signals of frequency f1-f2 on a pair of output leads. Low pass filters suppress other signals at the output.