Showing papers on "Center frequency published in 1992"

Microelectromechanical filters for signal processing

Abstract: Microelectromechanical filters based on coupled lateral microresonators are demonstrated. This new class of microelectromechanical systems (MEMS) has potential signal-processing applications for filters which require narrow bandwidth (high Q), good signal-to-noise ratio, and stable temperature and aging characteristics. Microfilters presented in this paper are made by surface-micromachining technologies and tested by using an off-chip modulation technique. The frequency range of these filters is from approximately 5 kHz to on the order of 1 MHz for polysilicon microstructures with suspension beams having a 2-/spl mu/m-square cross section. A series-coupled resonator pair, designed for operation at atmospheric pressure, has a measured center frequency of 18.7 kHz and a pass bandwidth of 1.2 kHz. A planar hermetic sealing process has been developed to enable high quality factors for these mechanical filters and make possible wafer-level vacuum encapsulations. This process uses a low-stress silicon nitride shell for vacuum sealing, and experimental results show that a measured quality factor of 2200 for comb-shape microresonators can be achieved.

Signal detector employing mean energy and variance of energy content comparison for noise detection

Abstract: A signal detector discriminates between signals manifesting noise and signals manifesting information, both of which appear at an input. A analog-to-digital converter circuit samples the signals and a Fourier filter determines, for each signal sample, energy content of each of a plurality of frequency cells in the sample. A processor then determines the mean energy content and the average variance of energy content in all frequency cells in the signal sample. The mean energy content and average variance of energy content of the signal sample are then compared, and if the comparison indicates an approximate equality, the sample is declared to be noise. The processor further determines a centroid center frequency for the frequency cells in the sample which indicates, if it is on-center, that the sample is likely to be noise. The processor further determines the bandwidth of the Fourier components of the input signal, to determine if it is indicative of noise. The skew of the sample's Fourier components is also determined and if it is nearly zero (indicating the signal is symmetrical in frequency about the center frequency), a noise signal is indicated. The combined indications are then normalized and subjected to a threshold which indicates whether a signal or noise is present.

Wide bandwidth bandpass filter comprising parallel connected piezoelectric resonators

Abstract: A plurality of piezoelectric resonators (10,32,37,57,62,66,79,88,93) are utilized to form a bandpass filter (31,56,78). The resonators (10,32,37,57,62,66,79,88,93) are connected in parallel to form a plurality of parallel paths between an input (43,73,81) and an output (47,74,82) of the filter (31,56,78). A predetermined number of the piezoelectric resonators (10,32,37,57,62,66,79,88,93) provide a phase shift of approximately 180 degrees. Each parallel path has a passband and center frequency that is displaced from the passband and center frequency of other paths. Consequently, the passband of each parallel path algebraically sums and creates a filter passband that is wider than the passband of each of the filter's individual parallel paths.

Security tag for use with article having inherent capacitance

Abstract: A security tag for use with an electronic security system is used for attachment to an article having an inherent capacitance such as meat. The security system includes a transmitter for transmitting into a surveilled area electromagnetic energy having a center frequency within a predetermined detection frequency range and a receiver for detecting within the surveilled area the presence of a security tag resonating at a frequency within the detection frequency range in response to the electromagnetic energy. The tag includes a generally planar dielectric substrate having a first side and a second side. Circuitry on the substrate establishes a resonant circuit having a resonant frequency which is initially a predetermined frequency interval above the center frequency of the detection frequency range. Upon attachment of the security tag to the article, the inherent capacitance of the article interacts with the resonant circuit to shift the resonant frequency of the resonant circuit downwardly, closer to the center frequency of the detection frequency range.

Electron beams in the low corona

Abstract: Selected high-resolution spectrograms of solar fast-drift bursts in the 6.2–8.4 GHz range are presented. The bursts have similar characteristics as metric and decimetric type III bursts: rise and decay in a few thermal collision times, total bandwidth ≳3% of the center frequency, low polarization, drift rate of the order of the center frequency per second, and flare association. They appear in several groups per flare, each group consisting of some tens of single bursts. Fragmentation is also apparent in frequency; there are many narrowband bursts randomly scattered in the spectrum. The maximum frequency of the bursts is highly variable. The radiation is interpreted in terms of plasma emission of electron beams at plasma densities of more than 1011 cm−-3. At this extremely high frequency, emission from the plasma level even at the harmonic is only possible in a very anisotropic plasma. The scale lengths perpendicular and parallel to the magnetic field can be estimated. A model of the source region and its environment is presented.

System and method for acquiring an optical target

Abstract: An optical target is acquired by an optical scanning system according to an in-band target frequency in an input signal from an optical scanning device. Both the in-band energy level and the out-of-band energy level of the input signal from the optical scanning device are determined. These two energy levels are compared and a possible detection of the target is determined according to this comparison. A minimum threshold of in-band energy is required in order for the possible detection to be confirmed. The input signal may have various frequencies due to various amounts of magnification of the acquisition target as scanned by the optical scanning device. Thus the input signal may represent the target as various frequencies due to the various amounts of magnification. The various amounts of magnification of the acquisition target are due to various scanning distances between the scanning device and the acquisition target. Magnification compensation is therefore performed by providing an amount of frequency shifting of either the center frequency of a filter or the input signal frequency. The amount of frequency shifting is determined according to scanning distance. The frequency shifting is accomplished by performing digital-to-analog conversion on the digital input signal at a fiexed frequency. The output of the digital-to-analog converter is applied to an analog-to-digital converter where the analog signal is resampled at a varying resampling frequency. When the resampling frequency differs from the sampling frequency the signal is frequency shifted. Alternately, the resampled signal may be buffered and clocked out, in which case the frequency of the input signal is effectively shifted. In order to vary the amount of frequency shift according to the scanning distance, the resampling frequency applied to the analog-to-digital converter is varied according to the scanning distance. The relationship between the various resampling frequency and the varying scanning distances may be selected to cause the various input frequencies representative of a scanned acquisition target to be shifted to a single predetermined fundamental frequency.

Acoustic resonator filter with electrically variable center frequency and bandwidth

Abstract: An acoustic resonator filter having at least one of electronically variable center frequency and bandwidth has a shunt coupling consisting of an inductor and voltage variable capacitor matrix. A pair of acoustic resonators each having a parallel inductor are connected to each other and to the shunt coupling network. One of a pair of voltage variable capacitor matrixes each having a center frequency command input voltage is connected to each acoustic resonator and an associated inductor. This circuit can be extended to provide more selectivity and attenuation.

Dielectric resonator filters with wide stopbands

Abstract: Dielectric resonators used in filter networks present a model spectrum with undesired, or spurious, resonances in close proximity to the desired one Through the use of evanescent mode bandpass irises tuned to the filter center frequency, the resonator spurious modes are suppressed, resulting in N-section filters with stopbands clean to at least (N-1) times the individual iris stopband levels The problem of achieving a wide stopband is reduced to the problems of realizing the resonating capacitance required in an evanescent bandpass filter and computing the junction susceptance occurring at the interface between a larger evanescent section (the resonator enclosure) and the smaller iris opening The technique results in high-Q resonator filters with stopbands clean to at least -55 dBc, out to at least 17 times the filter center frequency >

Sonar attenuation modeling for classification of marine sediments

Abstract: An attenuation‐based model for classification of marine sediments is developed for the chirpsonar operating in the frequency range of 2–10 kHz. A relaxation‐time model is proposed that combines the various dissipative energy loss mechanisms of sound in marine sediments into a single parameter. Historical data were analyzed by converting attenuation values reported in ‘‘dB/m@kHz’’ to a single relaxation time value. Analysis of these previous attenuation measurements supports the use of a relaxation‐time model. Based on this large collection of data, an empirical equation is developed that relates relaxation time to grain size (in phi units). Using this model, very little phase dispersion is observed for a correlated chirp pulse traveling through 40 m of sand, silt, or clay. Yet, this is not so for a pulse in the ultrasonic frequency range (0.2–1.0 MHz) traveling through only 10 cm of clay. Here, significant dispersion is noted. Because of the unique Gaussian‐like shape of the correlated chirp pulse power spectrum, pulse elongation due to attenuation is minimized. Using the center frequency shift in the pulse spectrum, a new ‘‘instantaneous frequency’’ method of attenuation estimation is proposed that overcomes the problems associated with interfering reflections. Based on the relaxation‐time model, the correlated chirp pulse was synthetically attenuated to establish a relation between the relaxation time and the center frequency shift. I n s i t u sediment‐type predictions from chirpsonar data using the instantaneous frequency method and analyses of core samples taken in the Narragansett Bay, Rhode Island are in good agreement.

Multibit bandpass delta-sigma modulators using N-path structures

Abstract: Simulation results on two switched-capacitor circuits suitable for use in a multi bit bandpass sigma-delta modulator are presented. The circuits use the N-path technique to guarantee accurate placement of the noise-transfer-function zeros. A 6th-order multibit bandpass analog-to-digital converter with a sampling frequency which is four times the center frequency and with a 5.5% bandwidth relative to the center frequency (the oversampling ratio equals 36) is described as a design example. System-level simulations, reported earlier, showed that this modulator promises a 94-dB SNR as long as the DAC (digital-to-analog converter) linearity is at least 8 b. The simulation results presented show that, in order to achieve this level of performance, the integrator circuits require high op-amp gain, and so a gain-compensated version of one of them is presented. The improved circuit requires an op-amp gain of 54 dB to achieve a modulator SNR of 90 dB. >

Bandpass sigma delta converter suitable for multiple protocols

Abstract: Improved integration and simplified construction of direct conversion receivers is achieved by providing selectivity in the early stages of a sigma delta converter to reject adjacent channel signals and thereby allow greater dynamic range for the desired input signals. A bandpass sigma delta converter is taught which is suitable for use with signals having multiple protocols. In a first stage, an aliased input signal is applied to two filters having desired and preferably programmable filter characteristics which provide selectivity to the input signal. A third filter is utilized having a programmable center frequency, which receives as an input signal the sum of the filtered input signal plus the quantization noise of the first stage. This provides a first intermediate output signal of desired selectivity. Quantization noise of the first stage is also applied to a second filter stage which provides a second intermediate output signal having a first component related to the quantization noise of the first stage, and a second component which is the shaped quantization noise of the second stage. The first and second intermediate output signals are combined in order to provide a desired output signal in which the original input signal has been filtered to provide a desired selectivity and converted to a digital signal while the quantization noise of the first stage has been cancelled, and the quantization noise of the second stage has been shaped by a desired function and converted to a digital signal independent of the input signal shaping.

A 10 GHz thin film lumped element high temperature superconductor filter

Abstract: A narrowband thin-film lumped-element filter centered at 10 GHz has been fabricated using thalium-based high-temperature superconductor (HTS) technology. This filter does not suffer from the undesired spurious responses seen in thin-film distributed filters using HTS technology. The measured filter has 2.5-dB insertion loss at band center and 3% bandwidth and is within 50 MHz of the desired center frequency. Measurements were made to confirm the broad spurious free stopbands from 1 GHz to 21 GHz. Because this filter does not generate spurious modes in the substrate, it may be possible to put several filters on the same substrate in microwave systems applications. >

Time dependence of internal intensity of a dielectric sphere on and near resonance

Abstract: Transient intensities inside a large dielectric sphere (circumference/incident wavelength > 50) are computed for excitation with plane-wave pulses having a Gaussian time dependence. The center frequency of the pulse is either on or near a morphology-dependent resonance (MDR). For each internal point considered, the time dependence of the electric field is determined from the frequency spectrum of the field at that point. The frequency spectrum is the product of the incident field spectrum and the transfer function at that point. In a sphere both the internal spectrum and the associated time dependence vary with spatial location, particularly when the incident frequency is near a MDR. The time dependence of the intensity at an internal location near the surface shows an exponential tail with a time constant of 1/Δωr, where Δωr is the resonant linewidth of the MDR, so long as the incident spectrum overlaps the MDR significantly, i.e., when Δω ≤ Δω0 and Δω0 ≥ Δωr, where Δω0 is the width of the incident pulse spectrum and Δω is the detuning, the difference between the MDR frequency and the center frequency of the incident Gaussian pulse.

Optical frequency discriminator using two mach-zehnder interferometer arrangement

Abstract: An optical frequency discriminator having enhanced linearity is provided, which discriminator may be utilized in FM communications systems or in other applications. The discriminator has two interferometers with the optical path length difference for the first interferometer being ΔL and for the second interferometer being mΔL where m>1. The optical FM signal is applied in parallel to both optical interferometers with approximately m 3 times as much of the signal being applied to the first interferometer as to the second interferometer. Each interferometer has an output signal versus frequency characteristic with a substantially linear region about a center frequency, which center frequency is approximately equal to the center frequency of the input optical signal. The outputs from the interferometers are combined in a manner such as the difference in absolute value of the linear region characteristic slopes is obtained, the resulting output being a discriminated output which is substantially linear over an enhanced FM range.

Surface wave filter filtering delay transfer function

Abstract: It consists of several channels (V1, V2) in parallel, which exhibit an inter-transducer gap difference (2 1 -4 1 ; 2 2 -4 2 ) equal to an even multiple of the half-wavelength (λ) at the central frequency, from one channel to the next, so as to cancel the delay line transfer function which corresponds to the direct path between transducers.

Z-path IF-filters for mobile telephones

Abstract: IF-filters for channel selection in mobile phone systems must offer narrow bandwidths together with very steep skirts and excellent stopband rejection. Surface acoustic wave (SAW) filters fulfill these requirements. But if conventional transversal design techniques are used chip sizes become too large. The propagation path of the SAW was folded in order to make better use of the total chip length. The use of two slightly inclined reflectors results in a Z-shaped filter which conserves the temperature stability of quartz substrate. At a center frequency of 45 MHz, filters were developed on small chips with good passband characteristics and an insertion loss better than 10 dB. A filter with signal suppression of 20 dB and an ultimate relative stopband rejection of 60 dB is shown. >

Improved sigma-delta type analog-to-digital converter and method

Abstract: A multiplexed sigma delta analog-to-digital (A/D) converter for low frequency applications has a single oversampling modulator together with a relatively high cutoff lowpass filter together with individual line frequency (50 or 60 Hz) rejection filters for each output channel.

Interface having serializer including oscillator operating at first frequency and deserializer including oscillator operating at second frequency equals half first frequency for minimizing frequency interference

Abstract: A serial communication interface for sending and receiving serial data is provided including a serializer and a deserializer. The serializer is designed so that the serializer VCO has a center frequency that is one half the center frequency of the deserializer VCO. The serializer uses both edges of the clock to mix the serial bits. The deserializer design is unchanged. The two VCO's are implemented on separate chips with both chips located on the same metallized ceramic substrate with a ground plane about 40 mm apart. Near frequency interaction is significantly reduced.

Knock detection device for an internal combustion engine

Abstract: A knock detection device being provided with a plurality of digital filter units, each is designed to cover respective characteristic resonance vibration frequency components inherent to resonance vibration modes due to knocking and including first, second and third digital filters, the first digital filter being tuned to the center frequency of the characteristic resonance vibration frequency component, the second digital filter being tuned to a neighboring lower frequency and the third digital filter being tuned to a neighboring higher frequency. The maximum intensity among the three intensities determined by the first, second and third digital filters is determined as the intensity for the characteristic resonance vibration frequency component and the determined result is fed-back to the digital filter unit to correct the center frequency of the first digital filter to the frequency showing the maximum intensity, whereby the knocking is reliably detected without being affected by such factors as engine operating conditions and secular changes of the engine.

55 GHz microstrip bandpass filter made from YBa2Cu3O7−x superconductor thin film

Abstract: We report the first mm wave passive component made with high temperature superconducting thin films. Microstrip bandpass filters, with bandwidth of 2.2 GHz and a center frequency of 55 GHz, were made using YBa2Cu3O7−x filter patterns on MgO substrates with Au ground planes. The best results were obtained for a film grown with a thin SrTiO3 buffer layer and had Tc=89 K and Jc=106 A/cm2 at 84 K. The filter showed insertion loss of 1.7 db at 77 K, and 1.5 db at 70 K, compared to 7.3 db for Au filters at 77 K. Subtracting the losses in the Au ground plane, we estimated that the superconductor surface resistance is lower than one fourth that of Au at 77 K and 55 GHz.

Arrangement for compensating for temperature dependent performance characteristics of surface acoustic wave filter

Abstract: A first control circuit is provided with a temperature detector and a memory in which temperature related control data is stored. The control circuit outputs a control signal, which varies with ambient temperature, to a local oscillator which is connected with a mixer. The mixer receives an incoming radio frequency signal and a local frequency signal from the local oscillator and outputs an IF signal. The local oscillator is controlled in a manner wherein the frequency of the IF signal parallels the temperature dependent shift in center frequency of a surface acoustic wave type IF filter. The IF signal is applied to a second mixer to which a second control circuit is coupled. The second control circuit maintains the output of the second mixer at a predetermined value to compensate for the first IF's frequency shift caused by the first control circuit.

Two-octave bandwidth monolithic analog phase shifter

Abstract: The cascaded-match reflection-type phase shifter (CMRTPS) was recently introduced to utilize the full bandwidth of its 3-dB quadrature directional couplers A monolithic realization of the CMRTPS is presented that maintains a high level of performance over two octaves, while using experimental one octave bandwidth offset multilayer folded directional couplers Standard GaAs foundry processing was used to fabricate the MMIC At the 10-GHz center frequency, the measured relative phase shift varied from 0 to 98 degrees , with a decreasing bias potential from 0 to -10 V A maximum rms phase error of +or-28 degrees is maintained across the 44 to 161 GHz frequency range, for all bias levels >

Cordless telephone system

Abstract: PURPOSE:To increase a communicatable range even when transmission power in each individual frequency band is made small, to make wire tapping hard and to reduce interference and noise by controlling the center frequency of a high frequency amplifier by the control voltage of the 2nd VCO. CONSTITUTION:The high frequency amplifier 11 is set up in a narrow band and the center frequency of the amplifier 11 is controlled by voltage for controlling the 2nd VCO 22. A prescribed voltage Vc is impressed to BPFs 40, 41 until a communication line is set up and the center frequency of the BPFs 40, 41 coincides with the transmission frequency of a transmitting part held before setting up the communication line. After setting up the communication line, the output of an LPF 29 is applied to the BPFs 40, 41. Although the transmission frequency is changed after setting up the transmission line, the change appears as the output change of the LPF 29, so that the center frequency of the BPFs 40, 41 follows the transmission frequency under the control of the output from the LPF 20, the pass band width of the BPFs 40, 41 is narrowed, noise and interference is attenuated, and the transmission frequency can be always effectively received.

Data filter tuning for constant density recording applications

Abstract: An arrangement for tuning a data filter in a mass storage system. The filter cutoff frequency (low pass) may be set as a percentage above or below the incoming data rate to achieve the desired "eye opening" in read data. The frequency of a reference oscillator in a phase-locked-loop (PLL) and the cutoff frequency of the filter is controlled by a common control signal from the PLL. The PLL, locked to a scaled multiple of the data rate, determines the cutoff frequency of the filter.

Agile bandpass filter

Abstract: Two variable frequency, fixed bandwidth bandpass 10, 410 are cascaded to form a bandpass filter with variable center frequency and variable bandpass. Each filter 10, 410 includes first (16, 416) and second (24, 424) mixers separated by a fixed bandpass filter (20, 420). Each mixer includes a control input terminal 30, 32: 430, 432 which receives a control signal (f LO , f OFF ). The center frequency of the filter arrangement is controlled by the frequency of control signal f LO , and the bandwidth is controlled by the difference frequency between f LO and f OFF . A tracking arrangement 456 allows direct control of the bandpass by control of the frequency of an offset oscillator 458.

Center frequency calibration for DC coupled frequency modulation in a phase-locked loop

Abstract: A method of providing DC coupled frequency modulation without center frequency offset of a RF carrier frequency generated in a phase-locked loop circuit. The circuit is automatically calibrated to generate a feedback signal for cancelling DC offsets at the input of the coupling integrator with a digital-to-analog converter and resistor network driven by a digital counter. After removing frequency modulation, the coupling integrator's output will ramp while the offsets remain uncancelled. Incrementing or decrementing the digital counter in response to the integrator's output will adjust the feedback signal until the offsets are cancelled and the integrator ceases to ramp. The counter value is stored in a memory to allow subsequent presetting of the feedback signal to the calibrated magnitude. Holding the feedback signal constant thereafter during DC coupled frequency modulation keeps the RF carrier at center frequency.

Method for adjusting the output frequency of a frequency synthesizer

Abstract: Adjustment of the output frequency of a frequency synthesizer can be optimized in the following manner. Once a frequency adjustment request is detected, which indicates a selected frequency, a frequency difference is calculated between the selected frequency and the present frequency. A frequency scaling factor is then determined. Once the frequency difference and the frequency scaling factor are determined, a frequency adjustment time is calculated based on a proportional relationship between the frequency difference and the frequency scaling factor. The bandwidth of a multi-bandwidth filter is adjusted to a second bandwidth for the duration of the calculated frequency adjustment time. The output frequency of the frequency synthesizer is adjusted from the present frequency to the selected frequency prior to the expiration of the frequency adjustment time. Upon expiration of the frequency adjustment time, the bandwidth of the multi-bandwidth filter is adjusted from the second bandwidth to the first bandwidth.

Auto-tuned apparatus for band-pass filter

Abstract: An auto-tuned apparatus for a band-pass filter, wherein, the generated reference signals having the given frequency to be set are mixed with signals to be outputted from the band-pass filter when the reference signals have been inputted to the band-pass filter so as to multiply them for outputting the signals of the multiplied results, the signals of the direct current component from the signals of the multiplied results to be outputted are filtered, and the band-pass filter is controlled so that the center frequencies of the band-pass filter may agree with the frequencies of the reference signal in accordance with the signal of the direct current component to be outputted, whereby the center frequency of the band-pass filter can be adjusted automatically to the desired set value with simple circuit construction and precision better than in the conventional embodiment.

Method and an arrangement for measuring distances using the reflected beam principle

Abstract: For distance measurement using the reflected beam principle a transmission wave is transmitted with a periodically frequency modulated transmission frequency. The echo wave reflected at the target has a reception frequency which is periodically frequency modulated in the same manner, there being a transit time dependent frequency difference between the transmission frequency and the reception frequency, such frequency difference being the distance frequency which is determined as measure of the distance of the target from the transmission/reception location. Using a constant reference frequency the transmission frequency and the reception frequency are converted in a common mixer to give a transmission/reception intermediate frequencies mixture, which includes a transmission intermediate frequency formed by conversion of the transmission frequency using the reference frequency, and a reception intermediate frequency formed by conversion of the reception frequency using the reference frequency. The distance frequency is determined from the frequency difference between the transmission intermediate frequency and the reception intermediate frequency, and the transmission intermediate frequency comprised in the transmission reception intermediate frequencies mixture is utilized for correction of the frequency modulation of the transmission frequency. For this purpose the arrangement for implementing the method comprises a correction channel which is connected with the output of the common mixer parallel to the measurement channel.

Effects of space exposure on optical filters.

Abstract: Optical transmittance characteristics of nine optical filters were remeasured after nearly six years in space aboard the NASA Long-Duration Exposure Facility. Three different filter types were included. In general, transmittance decreased for most filters. The center frequency and bandpass of a narrow-band filter under an aluminum cover were unchanged, while narrow-band filters exposed directly to the space environment tended to show a shift in center frequency and increased bandwidth. A pair of infrared-reflecting mirrors exhibited reduced transmittance in the visible, with a mirror under an aluminum cover less degraded than a mirror exposed to space. The bandpass was unchanged for both of these mirrors. Neutral density filters showed a slight increase in transmittance for an uncovered filter; essentially no change for the filter under the aluminum cover.