Showing papers on "Center frequency published in 1994"

Electronic mode stirring for reverberation chambers

Abstract: A modal analysis and a uniform-field approximation are presented for the fields in an idealized two-dimensional, rectangular cavity excited by an electric line source. The model is used to evaluate the effectiveness of frequency stirring, an alternative to mechanical stirring in reverberation chamber immunity measurements. Numerical results indicate that good field uniformity (standard deviation less than 1 dB) can be obtained with a bandwidth of 10 MHz at a center frequency of 4 GHz. The bandwidth requirement is determined primarily by the number of modes excited, and higher frequencies can achieve the same field uniformity with a smaller bandwidth because of the higher mode density. Cavity excitation by two single-frequency sources is also analyzed. >

Detection of interaural delay in high-frequency sinusoidally amplitude-modulated tones, two-tone complexes, and bands of noise.

Abstract: Listeners’ ability to detect interaural temporal disparities (ITDs) was investigated for 160‐ms, sinusoidally amplitude modulated (SAM) tones, two‐tone complexes, and bands of noise at center frequencies of 4, 8, or 12 kHz. Rates of modulation for the 100%‐modulated SAM tones and frequency separation for the equal‐amplitude, two‐tone complexes ranged from 32–768 Hz, depending on center frequency. Noise bandwidths ranged from 50–2000 Hz, also depending on center frequency. The data indicate, consistent with previous results, that sensitivity to ITD with the SAM and two‐tone complexes decreases as the rate of envelope fluctuation increases beyond about 400 Hz. The decline in performance is not due simply to reduced depth of modulation produced by critical‐band‐like filtering, but is consistent with an inability to ‘‘follow’’ or encode high rates of modulation. For bands of noise, sensitivity to ITD was relatively constant as a function of bandwidth. Generally, sensitivity to ITD decreased as center frequency was increased from 4 to 8 kHz, but the relations among the data were essentially unchanged. Increasing the center frequency to 12 kHz resulted in very poor performance.

Feedback detector and suppressor

Abstract: An A/D converter converts an analog signal to a digital signal. A plurality of cascade-connected notch filters include a first notch filter which is connected to the output of the A/D converter. A D/A converter is connected to the output of the last stage notch filter for converting a digital signal to an analog signal. The output of the last stage notch filter is connected to the input of a fast Fourier transform unit for analyzing the frequency. Analysis results of the fast Fourier transform unit are supplied to a detector. A coefficient having the same center frequency as that of a peak frequency outputted from the detector is selected from a coefficient memory and it is transferred to a second coefficient memory. Thus, the frequencies of the notch filters are set to eliminate howling.

The effects of signal frequency and absolute bandwidth on gap detection in noise

Abstract: Whether temporal resolution in noisebursts is primarily determined by the highest frequency component in the signal or its absolute bandwidth remains unclear. In this study, the absolute bandwidths and upper cutoff frequencies of signal noisebursts were varied across broad frequency ranges, several times greater than previously jointly studied. The purpose was to determine how each independently affects detection, taking into consideration that bandwidth effects at one signal frequency might be very different from bandwidth effects at another. Gap detection thresholds were obtained for five subjects with normal hearing in a 2 IFC paradigm. Signals were noisebursts whose bandwidths and upper cutoff frequencies varied among 1, 2, 4, 8, and 12 kHz. Their duration was 150 ms and they were presented at an overall level of 75 dB SPL above a 45 dB SPL white noise floor. The largest mean gap detection threshold, 6.98 ms, was obtained for a noiseburst with a bandwidth of 1 kHz and upper cutoff frequency of 12 kHz. The smallest mean gap detection threshold, 2.22 ms, was found with a bandwidth and upper cutoff frequency of 12 kHz. Significant interactions were found to exist between absolute bandwidth and upper cutoff frequency. Although gap detection thresholds generally decreased with increasing signal frequency and bandwidth, the pattern was complex. When the absolute bandwidth was at least one-half the upper cutoff frequency then upper cutoff frequency and not bandwidth determined gap sensitivity; but when the absolute bandwidth was less than one-half of the upper frequency, then both determined gap thresholds.(ABSTRACT TRUNCATED AT 250 WORDS)

Analog-to-digital converters using multistage bandpass delta sigma modulators with arbitrary center frequency

Abstract: An architecture for oversampled delta-sigma (Δ--Σ) analog-to-digital (A/D) conversion of high-frequency, narrow-band signals includes multistage Δ--Σ modulators that incorporate band-reject noise shaping centered at an arbitrary center frequency F bp . These modulators cascaded with a bandpass digital filter centered at the arbitrary center frequency F bp perform A/D conversion for high-frequency, narrow-band signals having the same arbitrary frequency. The bandpass modulators are implemented by use of resonators which provide a substantially large gain at the arbitrary frequency.

Radar with adaptive range sidelobe suppression

Abstract: A method and apparatus for identifying a remote target includes a transmitter for transmitting pulses of energy toward the target for generating echo signals, and a receiver for receiving the echo signals, and for generating received signals representing the target, noise and clutter. The received signals are applied through a plurality of cascaded channels, each including a Doppler filter cascaded with a multiplier, each also including range sidelobe suppression, for, in each of the cascaded channels, narrowband filtering the signals passing therethrough about a controllable center frequency, and for, if necessary, converting the signals passing therethrough to baseband, for thereby applying one of a plurality of Doppler filtered baseband signals to the input of each of the range sidelobe suppressors of each of the cascaded channels. The power of the Doppler filtered baseband signals in each range bin is evaluated for determining the frequency at which the spectral density is greatest. The center frequency of at least one of the cascaded Doppler channels is controlled such that one of the Doppler channels has its center frequency at the maximum-power frequency.

Abnormality detecting method and apparatus for electric equipment, particularly for a rotating electric machine

Abstract: A defect detecting apparatus for monitoring an electrical equipment for defects, the electrical equipment having a resonance frequency. The defect detecting apparatus includes a sensor operatively connected to the electrical equipment for sensing a signal indicating a defect in the electrical equipment; a first bandpass filter operatively connected to the sensor, the first bandpass filter having a first bandwidth and first center frequency at substantially the resonance frequency of the electrical equipment; a second bandpass filter operatively connected to the sensor, the second bandpass filter having a second bandwidth and a second center frequency higher than the resonance frequency of the electrical equipment; a signal strength comparing circuit operatively connected to the first bandpass filter and the second bandpass filter for comparing relative strengths of signals output by the first bandpass filter and the second bandpass filter; and a partial discharge measuring circuit operatively connected to the signal strength comparing circuit for measuring an output signal of the first bandpass filter relative to an output signal of the second bandpass filter to indicate a defect in the electrical equipment.

Tracking filter and quadrature-phase reference generator

Abstract: A tracking filter has a tunable filter responsive to an input signal for producing a filtered output signal, a Hilbert transformer for producing an in-phase reference signal and a quadrature-phase reference signal from the filtered output signal, and a discriminator responsive to the input signal and the in-phase and quadrature-phase reference signals for producing a passband center frequency control signal and a passband width control signal for controlling the passband center frequency and the passband width of the tunable filter. The frequency discriminator performs complex demodulation of the input signal with the in-phase reference signals to produce respective in-phase and quadrature-phase baseband signals which are low-pass filtered. The quadrature-phase baseband signal is divided by the in-phase baseband signal. The quotient is integrated to produce the passband center frequency control signal. Preferably the baseband signals are also filtered by adjustable filters having passband center frequencies and passband widths controlled in response to the passband center frequency control signal and the passband width control signal, respectively. Preferably the tracking filter is a digital filter.

Spindle control circuit of optical disk drive

Abstract: A spindle control circuit of an optical disk drive capable of performing a high precision and high stability spindle control by preventing an off-control even if the rotation speed is shifted from a predetermined linear velocity such as when a spindle starts rotating or during a search. First and second band-pass filters are provided having a narrow band and a broad band, with the center frequency of the band being set to the center frequency of a wobble signal picked up from an optical disk, An output of the second band-pass is selectively outputted until lock state is detected, and an output of the first band-pass filter is selectively outputted after the lock state is detected. A linear velocity control is performed in accordance with a selected output of the first and second band-pass filters.

Integrated acoustooptic tunable filters using weighted coupling

Abstract: A detailed theory and experimental results are presented on weighted-coupling integrated acoustooptic tunable filters (IAOTF). A low-sidelobe-level single-stage IAOTF in which the weighted coupling was facilitated by focused surface acoustic waves along an interaction length of 6.0 mm has been realized on a Y-X LiNbO/sub 3/ substrate, 8 mm in length. The measured performances of this weighted-coupling IAOTF at the optical center wavelength of 1.31 /spl mu/m include a peak mode conversion at the acoustic center frequency of 214.6 MHz, a wavelength tuning range of 110 nm, a -3 dB optical bandwidth of 4.1 nm, and a switching rise time of 0.965 /spl mu/s. Sidelobe levels below -21.4 dB have been accomplished at the mode-conversion efficiency of 15 percent and an RF drive power of 160 mW. >

Branching filter package

Abstract: PURPOSE:To reduce the signal loss in the passing band of the filter chip of the branching filter package by specifying the characteristic impedance value of a circuit for phase matching which is formed of at least two laminated strip lines CONSTITUTION:The multi-layered branching filter package 6 contains two surface acoustic wave filter chips 7 and 8 different in center frequency of frequency band, phase matching circuits 1 and 2 for phase matching between the chips 7 and 8 which are formed of two strip lines by lamination, etc, in layers When the characteristic impedance value of the strip lines is made larger than the impedance value of an external circuit connected to the package 6, the signal loss in the passing band of the filter chip is reduced to improve characteristic deterioration of the filter, and the filter chip and strip lines are formed in layers, so the branching filter package is reduced in size The strip lines are made different in width between both their ends and the a similar result can be obtained

Coplanar MMIC active bandpass filters using negative resistance circuits

Abstract: Several active bandpass filters for 1.8 and 5.5 GHz have been developed with the coplanar line technique using negative resistance circuits. For example, a first-order active bandpass filter at 5.5 GHz and two second-order bandpass filters at 1.8 GHz are presented, where one of the 1.8 GHz filters is a fixed center frequency filter and the other a tunable one. These 1.8 GHz filters have a 3 dB bandwidth of 110 MHz. The tuning range of the center frequency is 200 MHz. >

Sonic well logging methods and apparatus for processing flexural wave in optimal frequency band

Abstract: Methods for determining an optimal frequency band for processing of flexural waves according to bias-corrected STC or QSTC are disclosed A preliminary estimate of the formation shear slowness S and a determination of the borehole diameter D are first obtained, and the flexural waves are processed in a frequency band having a center frequency f c which is a function of preliminary estimate of S and the product of that estimate of S and diameter D Where the preliminary estimate of S indicates a slow formation, f c is chosen as 06/SD Where the estimate indicates a fast formation, f c is chosen as 02/SD In other or all formations, a smooth function such as [02+((08/π) arctan ((S-100)/100))/SD] can be used to choose the center frequency Alternatively, if errors in the environmental parameters can be estimated statistically, they can be used to select an optimum center frequency Once f c is chosen, the filter parameters which define the bandwidth of the filter used in the Fourier transform of QSTC and in bias-corrected STC are preferably normalized by scaling the bandwidth BW to a specified fraction of f c ; BW=f c /Q Similarly, the window length T w used in semblance processing is preferably normalized to scale with f c so that the processing window contains the same number of cycles regardless of the frequency of the center frequency

Adaptive interference suppression for CDMA overlay systems

Abstract: It has been proposed that CDMA systems can be assigned to spectral bands which are presently occupied by narrowband users to further increase spectral capacity. Such CDMA overlay systems could provide new options for efficient utilization of the spectrum with minimal disruption to existing narrowband users, especially if adaptive interference suppression techniques are utilized in the spread spectrum receiver. Previous studies have defined the SNR improvement ratio which can be achieved for tone interferers and for narrowband interferers for which the center frequency of the interference is at the carrier frequency of the CDMA signal. In this paper the bit-error-rate (BER) performance of the mobile-to-base link of a CDMA system for a single narrowband user which occupies a significant portion of the CDMA bandwidth is evaluated. It is shown that the narrowband model used in previous studies does not apply in this case, especially for the large, effective, bandwidths which are characteristic of the interferers in the overlay system. The dependence of the BER on the filter order, the bandwidth of the interference, and its center frequency relative to the CDMA carrier frequency are defined. Additionally the increase in BER for a digital implementation of the adaptive suppression filter relative to the optimal Wiener filter is characterized with respect to the adaptive time constant and the quantization errors due to finite wordlength. It is shown that these implementation errors can be made negligible compared to the errors which are characteristic of the optimal Wiener filter. Analytic results are validated by simulation for typical system parameters. >

Internal and scattered time-dependent intensity of a dielectric sphere illuminated with a pulsed Gaussian beam

Abstract: Internal and scattered time-dependent intensities are calculated for a dielectric sphere illuminated with a pulsed Gaussian beam. The center frequency of the pulse spectrum is chosen to be on, near, or far from a morphology-dependent resonance of the sphere. The center of the beam is positioned inside, on the edge, or outside the sphere. The transfer function at a point, i.e., the electric field at each frequency of the pulse spectrum, is calculated with the plane-wave spectrum technique and the T-matrix method. The frequency spectrum of the field at a point is calculated by means of the incident field spectrum and the transfer function at that point. The time dependence of the electric field at a point inside or outside the sphere is obtained by inverse Fourier transforming the frequency spectrum. Two different decay rates in the internal and the scattered time-dependent intensity are observed: a decay rate that depends on the incident pulse spectrum and a rate that depends on the line shape of the resonant mode of the sphere.

Receive filter using frequency translation for or in cellular telephony base station

Abstract: A device for filtering wide-band signals at radio frequencies is usable either in a base station cellular telephony system or separately. The wide-band signal occupies a total frequency band comprising frequency bands allocated to that signal and a central frequency band extraneous to that wide-band signal. Within the device, the wide-band signal is mixed with a heterodyne wave to translate the signal from RF to IF. The signal at IF is then filtered by two surface acoustic wave (SAW) band-pass filters which have respective pass bands which correspond at IF to the allocated frequency bands of the wide-band signal, and which the SAW filters have the filtering effect of passing with low attenuation signals in those allocated bands while substantially attenuating signals and/or noise in the central extraneous frequency band between those allocated bands. The wide-band signal after being so filtered either remains at IF when supplied from the device or, in a subsequent stage of the device, is again mixed with the heterodyne wave to be restored back to RF. The heterodyne wave may be adjustable in frequency.

Optical Passband Filter

Abstract: An optical passband filter having a frequency transition that is several of orders of magnitude narrower than prior optical filters includes two frequency routing devices. The first frequency routing device has one input for receiving the input signal and at least N outputs, where N corresponds to the number of frequencies that compose the input signal. The N outputs of the first frequency routing device are each coupled to inputs of a second frequency routing device. The outputs of the second frequency device each correspond to one of the selected output frequency bands into which the input signal is to be divided. A multiplexed input signal containing several different frequency channels is divided into bands that are each directed to respective outputs of the second frequency routing device. The frequency transition between the various bands may be as small as the frequency resolution between adjacent outputs of the first frequency routing device.

Code Division Multiple Access Transmitter and Receiver

Abstract: A code division multiple access transmitter and receiver that makes it possible to reduce its size by designating a spreading code and a carrier frequency in a baseband. It includes a primary modulator for performing primary modulation by transmission information, thereby producing a primary modulated I signal and a primary modulated Q signal, a spreading code generator for generating a spreading code with a frequency higher than a rate of the transmission information, a secondary modulator for spread-modulating the primary modulated I signal and Q signal by using the spreading code, thereby outputting spread I-channel data and spread Q-channel data, a frequency offset circuit for offsetting the center frequency of the spread I-channel data and Q-channel data by a designated offset frequency, thereby outputting frequency offset data, and a transmitting circuit for converting the frequency offset data into a transmitted signal.

Frequency tuning system for tuning a center frequency of an analog bandpass filter

Abstract: Based on the insight that the voltage-to-current ratio or gain of a capacitor (Z) at a particular reference frequency is the product of its capacitance value with said reference frequency, a tuning system is disclosed which tunes the center frequency of an analog bandpass filter by tuning the characteristic integrator frequency (fc) of an OTA-C integrator by making the transconductance of the operational transconductance amplifier (OTA) thereof equal to the aforementioned gain at that characteristic frequency. Therefore, the tuning system includes a first tuning path in which the OTA, (or a replica thereof) is included and a second tuning path including another amplifier (B-OTA) "degenerated" by the capacitor (Z) so as to produce the required gain. The gains of both these tuning paths are then equalized by matching means (MM) generating a frequency tuning signal (VTF) which is applied to both OTA and OTA-C.

Method of tuning a ceramic duplex filter using an averaging step

Abstract: A method of tuning a duplex filter (500). First, the center frequency of at least one filter of a duplex filter (10) is measured (502). Next, the difference between the measured center frequency and a desired center frequency is determined (504). And, third the duplex filter is tuned (506) by selectively removing a substantially planar layer of dielectric material for a top surface (14) of the filter (10), whereby the frequency characteristics are modified.

Ultrasonic imager having improved bandwidth

Abstract: An ultrasonic imaging system which utilizes two summation channels to provide increased bandwidth employs two demodulation stages in each receive channel. The first demodulator receives digital signals from an analog-to-digital converter and demodulates those signals to baseband, thereby producing an in-phase component and a quadrature component. The in-phase and quadrature components are demodulated by the second demodulator, forming a total of four signals which are filtered and combined to form two sets of complex signals. One set corresponds to the upper or high frequencies and the other set corresponds to the lower frequencies. Each band is treated separately in a subsequent phase rotation. The phase changes reflect those required by the center frequency of each of the subbands. The upper band signals are coherently summed in one summation channel, while the lower band signals are coherently summed in another summation channel. The coherently summed upper and lower band signals are then reconstituted into one composite baseband signal.

Filtering coalescing binary signals: Issues concerning narrow banding, thresholds, and optimal sampling.

Abstract: When the raw output of a gravitational wave detector is correlated with the matched filter of a coalescing binary wave form the filtered output shows a periodic behavior-it rings at a certain frequency. This phenomenon could be worrisome since the signal peak in the filtered output might be reduced if it falls in the "trough" of the sinusoid. In this paper we address this question present a detailed examination of the ringing which is caused by the effective narrow banding by the matched filter of detector noise. We first solve the problem for an idealized "box" filter show that the ringing frequency is roughly the central frequency of the box if the box is not too wide. For an idealized coalescing binary filter we show that the expected value of this frequency is .7 f s where f s is the seismic noise cutoff of the detector. The ringing implies that there is some redundancy in the filtered ouput. Also the autocorrelation function of the filtered output resembles the sinc function hence adjacent sample points are correlatedi.e.the filtered output is colored. These two phenomena are relatedhave a bearing on the setting up of thresholds also suggest that we resample the filtered output at a coarser rate. We investigate the problem of thresholds when the filtered output is colored obtain relations between the false alarm probabilities threshold levels. Finally we suggest optimal sampling rates so that the resampled filtered output is uncorrelated.

Design techniques for tunable transresistance-C VHF bandpass filters

Abstract: In this paper, a tunable wideband linear transresistance (R/sub m/) amplifier is proposed and analyzed. Using the tunable R/sub m/ amplifier, a new transresistance-capacitor (R/sub m/-C) differentiator is designed. Considering the intrinsic capacitances of the MOS transistors as filter elements, this R/sub m/-C configuration can he regarded as a very high frequency (VHF) bandpass biquadratic filter. The proposed biquad has a simple structure and thus occupies a small chip area and consumes little power. Moreover, higher-order VHF bandpass filters can be realized by directly cascading the biquads. Experimental results have successfully proven the capability of the proposed new filter implementation method in realizing VHF bandpass filters with the center frequency higher than 100 MHz when C/sub d/=1 pF. The deviations of the measured center frequency f/sub o/ and quality factor Q of the fabricated bandpass filter from the simulated results are less than 8%. The deviation of the center frequency can be post-tuned by adjusting the control voltages V/sub CN/ and V/sub CP/ of the tunable R/sub m/ amplifier. With 1 pF differentiating capacitor, the center frequency of the fabricated VHF R/sub m/-C bandpass filters can be tuned in a wide range larger than 30 MHz. The measured maximum signal level is 25 mV/sub rms/ and the dynamic range is 47 dB. The chip area is 0.05 mm/sup 2/ and power consumption is 5.05 mW with /spl plusmn/2.5 V power supply. >

Method for fine tuning the resonant frequency of a filter in a combiner

Abstract: The invention relates to a method for fine tuning the resonant frequency of a filter in a combiner, which is provided for combining signals from several radio channels, to the carrier frequency of an input signal to the filter. The power of the output signal from the filter is measured in a narrow frequency band around the carrier frequency of said input signal. Furthermore, the power of the signal reflected by the filter is measured in a narrow frequency band around the carrier frequency of the input signal. Thereafter a measure of the ratio between the two power measurements is formed. The resonant frequency of the filter is adjusted so as to maximize this measure.

Balanced bridge saw filter

Abstract: The invention relates to a SAW filter comprising a first and second pair of substantially equivalent SAW transducers electrically coupled to form a bridge circuit. Each of the transducers of the first pair of transducers have a center frequency which is slightly different to the center frequency of each of the transducers of the second pair of transducers. The product of the static capacitance of the first pair is the same as the product of the static capacitance of the second pair. In use, signals input to the filter and having a frequency within the passband of the filter are coupled to the output of the bridge circuit via one or other or both arms of the bridge, as in normal bridge circuit operation. However, out of band signals are blocked since all the transducers are equivalent capacitors having the same capacitance (i.e., static capacitance). Thus, transmission of out of band signals through the filter is inhibited by the balanced nature of the bridge.

Frequency trimming of SAW devices

Abstract: This paper describes a frequency trimming technique suitable for GHz band SAW devices. A frequency shift was obtained by forming grooves on the substrate surface using an RF reactive sputter etching technique. Because the center frequency of a SAW transducer in a GHz band is very sensitive to the groove depth, a precise control of the etched amount is necessary. A very low etching rate of less than 1 nm/min. has been realized by modification of a conventional RF diode sputter etching apparatus. The low etching rate made it possible to realize precise frequency trimming for GHz band filters. Frequency trimming of more than 1000 ppm was obtained without any remarkable characteristic changes

Microstrip bandpass filters using MMIC negative resistance circuits for loss compensation

Abstract: A new bandpass filter design technique is presented which uses microstrip resonators assisted by MMIC negative resistance circuits to compensate for the resonator losses. Two filters have been designed and tested in order to demonstrate the high performance that can be achieved with this approach: One uses end-coupled resonators, and has a measured 3-dB bandwidth of only 10 MHz at a center frequency of 5.35 GHz. The second is a 4-pole filter employing dual-mode microstrip ring resonators, and this has a 70 MHz 3 dB bandwidth, centered at 5.27 GHz. These results represent some of the best selectivity performances achieved to date for miniature microwave active filters. >

Monolithic crystal strip filter

Abstract: The present invention relates to a low profile monolithic crystal strip filter and filter package. The filter includes an AT-cut rectangular strip of quartz crystal. The filter further includes input, output and ground electrodes which are formed in a symmetrical pattern on the strip. Each electrode is connected to its respective mounting or ground contact by a flag. The electrodes, contacts and flags have a predetermined size and shape, and are arranged in a predetermined configuration on the crystal strip to minimize spurious responses and insertion losses. The crystal strip is mounted to an HC-45 or HC-49 base to minimize production costs. The output signal of the filter has a center frequency of about 4 to 500 MHz, a 3 dB bandwidth of about 3 to 250 kHz, an ultimate of better than 60 dB, standard insertion losses for the number of poles in the filter and commercially acceptable spurious responses.

Apparatus for leading brain wave frequency

Abstract: Disclosed is a brain wave leading apparatus which can achieve a high brain wave leading efficiency when a human brain wave frequency is led to a desired frequency band. This brain wave leading apparatus comprises a brain wave sensor for detecting the brain wave of a person to be tested (subject) during brain wave leading, and a control unit for renewing a leading center frequency for leading the brain wave frequency therewith. The brain wave frequency of the subject is measured even during brain wave leading, and based on a weighted mean frequency f' detected in a predetermined interval, a leading center frequency F in a subsequent interval is determined. The leading of the brain wave frequency is continued with the leading center frequency F supplied from the control unit. Even if the weighted mean frequency of the subject during leading varies, therefore, the leading center frequency follows up that change, so that brain wave leading will be executed in a short period of time.