Showing papers on "Dynamic range published in 1991"

Encoding strategies for three‐direction phase‐contrast MR imaging of flow

Abstract: Three encoding strategies for the measurement of flow velocities in arbitrary directions with phase-contrast magnetic resonance imaging are presented; their noise and dynamic range performance are compared by means of theoretical analysis and computer simulation. A six-point measurement strategy is shown to be quite inefficient in terms of velocity variance per unit time. A simple four-point method exhibits equal dynamic range; its noise depends on flow direction but on average is equal to that of the six-point method. An alternate, balanced four-point method has noise that is direction independent and has, depending on implementation, possibly lower noise levels. Either four-point method is more efficient and is preferred over the six-point approach.

The design of high dynamic range continuous-time integratable bandpass filters

Abstract: A method to design integratable continuous-time analog high-Q bandpass filters with a prescribed dynamic range is developed. The theory accompanying this method shows the fundamental restrictions for the dynamic range. The theory is meant to determine beforehand if the desired dynamic range is realizable. The possibilities of using dynamic range optimal filter networks are discussed. The usefulness of the theories is shown by the design of a complete bandpass filter, up to the transistor level. >

Second-order sigma-delta modulation for digital-audio signal acquisition

Abstract: The authors compare the second-order sigma-delta ( Sigma Delta ) modulator to several alternative modulator architectures in the context of digital-audio signal acquisition. Design details and experimental results are presented for a 1 mu m CMOS implementation that does not require error correction or component trimming to achieve virtually ideal 16 b performance at a conversion rate of 50 kHz. The experimental modulator is a fully differential circuit that operates from a single 5 V power supply and does not require the use of precision sample-and-hold circuitry. With an oversampling ratio of 256 and a clock rate of 12.8 MHz, the modulator achieves a 98 dB dynamic range and a peak signal-to-(noise+distortion) ratio (SNDR) of 94 dB. Measurements and simulations of discrete noise peaks in the output spectrum that result from limit-cycle oscillations are also presented and discussed. >

Theory and practical implementation of a fifth-order sigma-delta A/D converter

Abstract: An 18-bit analog-to-digital converter integrated circuit has been designed which uses a fifth-order loop filter with an unusual loop topology. Implementation of the loop using differential switched-capacitor techniques is described. A one-step decimation filter with 115-dB stopband attenuation is used to remove out-of-band quantization noise. Preliminary measurements indicate a dynamic range of 105 dB, a number that is compatible with the requirements of professional digital audio

Idle channel tone and periodic noise suppression for sigma-delta modulators using high-level dither

Abstract: Technique for adding a dither signal to a sigma-delta modulator to remove low level tones and periodic noise in the desired passband of the modulator when no, or a very low, signal is present (idle). The dither signal is a high-level signal added to the imput of an quantizer in the modulator, the normalized power in the AC component thereof being at least about ##EQU1## of the square of the quantizer step, where N is the order of the modulator. No significant reduction in the dynamic range of the modulator results. The technique may also be applied to multiple order sigma-delta modulators as well as to multiple stage sigma-delta modulators. Further, the dither may be added at any point in the modulator with suitable filtering of the dither. The transfer function of the filter is proportional to the noise shaping transfer function of the modulator between the point of addition of the dither and the input to the quantizer.

System for adaptive processing of telephone voice signals

Abstract: A system for adaptively processing a telephonic speech signal performs modification in either the spectral domain or the time domain to bring the power in each frequency above the hearing threshold of the listener but below the upper limit of the listener's dynamic range.

Computed tomography apparatus using image intensifier detector

Abstract: Disclosed is a low cost computer tomographic (CT) scanner system specifically designed for radiation therapy treatment planning. A 512-channel photo-diode array (44) with digitizing electronics converts image intensifier (40) optical projection data directly into digital signals and has a dynamic range on the order of 1000,000:1. The new simulator includes a rotating gantry, an X-ray generator (30) with radiographic and fluoroscopic modes and a therapy style patient support assembly. Results on head and body size phantoms indicate that the simulator X-ray generator and image intensifier tube (IIT) (40) with multi-channel photo-detector (44) can produce photon statistic limited CT images. Software and hardware compensation methods are described which minimize geometrical distortions. Low noise, high input impedance electronics are employed which are phase locked to the line frequency. A dual sample interval method is employed which effectively increases the range of the digital signal produced by the front-end electronics by three additional bits.

A bit-stream digital-to-analog converter with 18-b resolution

Abstract: A two-channel differential 18-b bit-stream digital-to-analog converter implemented in a 2.5- mu m BiCMOS process with 7.3-mm/sup 2/ chip area is described. The circuit contains two identical 1-b D-to-A conversion channels on one single chip. Each channel consists of a digital input part, a switched-capacitor D-to-A network, and two high-performance operational amplifiers. Total harmonic distortion plus noise is better than -102 dB. The dynamic range is more than 108 dB, giving a true 18-b resolution. Output operational-amplifier distortion is below 120 dB at full-scale signal. System design considerations, implementation, and measured results of the IC are discussed. >

Digital automatic gain control

Abstract: There is provided a mechanism for Automatic Gain Control in a receiver. It comprises: determining, within a certain dynamic range, the difference in power between the desired signal and a signal received, and providing open loop gain control for the signal in response to the differential so determined, scaled by the receiver's gain characteristics, such that the signal is positioned within dynamic range so as to reduce saturation and noise.

Fiber optic pressure and temperature sensors for oil down hole application

Abstract: Detailed studies on fiber optic pressure and temperature sensors for oil down-hole applications are described in this paper. The sensor head is an interferometric based fiber optic senor in which the air-gap will change with the pressure or temperature. For high-speed applications, a novel self-calibrating interferometric/intensity-based (SCIIB) scheme, which realizes compensations for both the light source drift and the fiber loss variation, was used to demodulate the pressure (or temperature) signals. An improved white light system was developed for sensor fabrication. This system is also used as the signal demodulation system providing very high resolution. Experiment results show that the SCIIB system achieves 0.1% accuracy with a 0-8000psi working range for the pressure sensor and a 0-600 degree(s)C working range for the temperature sensor. The resolution of the white light system is about +/- 0.5 nm with a dynamic range up to 10 micrometers. The long -term testing results in the oil site are also presented in this paper.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Interfaces for high speed fiber-optic links: analysis and experiment

Abstract: An analysis of directly and externally modulated fiber-optic links is presented. The theoretical analysis is based on the signal flow diagram of the interface circuits to the laser diode, Mach-Zehnder electro-optic modulator, and p-i-n photodiode. System parameters such as gain, noise figure, two-tone intermodulation distortion, and spurious free and compression dynamic range are expressed as a function of frequency and operating point of the laser and external modulator. Two directly and externally modulated fiber-optic links were designed and fabricated to verify the analytical models. The direct modulation FO link was developed at the Ku-band (11.6-12.4 GHz), whereas the external modulation link was at L-band (875-925 MHz). Spurious-free dynamic ranges of 95.8 dB Hz/sup 2/3/ and 113 dB Hz/sup 2/3/, respectively, were achieved. The predictions based on the analytical models match the measured results. >

High dynamic range electro-optical shutter for steroscopic and other applications

Abstract: A high dynamic range electro-optical shutter for stereoscopic and other applications, and a method for increasing the dynamic range of an electro-optical shutter system The shutter of the invention is derived from an existing electro-optical shutter by adjusting the tilt angle of the plane of the shutter's surface in the optical path of the apparatus in which it is employed The invention is based upon the finding that light rays transversing an electro-optical shutter which are not perpendicularly to the plane in which a surface of the shutter lies, can have a significantly higher dynamic range than axial rays In accordance with the invention, the angle at which the shutter is mounted in an apparatus is adjusted to produce a dynamic range which is high enough for the intended application By mapping the pattern of spatial distribution of dynamic range, it is possible to design and produce shutters which are low in manufacturing cost, yet have performance which equals that of more costly shutters

Electronically enhanced x-ray detector apparatus

Abstract: The detector of the present invention is suitable for use in a radiation therapy simulator machine. The detector comprises an X-ray image intensifier tube to convert X-rays into photons, a linear array of photodiodes to convert the photons to electrical signals, optical means for coupling the photons to the linear array of photodiodes, and electronic signal processing means for conditioning the signals from the photodiodes. The conditioning includes the use of low noise, phaselocked sampling electronics, implementation of a dual sampling technique for increasing dynamic range, implementation of a linearizing technique for increasing the accuracy of the measurements, and implementation of techniques for adjusting the measurements for point spread and background noise effects.

Expansion of dynamic working range and correction for interferences in flame atomic absorption spectrometry using flow-injection gradient ratio calibration with a single standard

Abstract: Flow injection enhances the zeroth-order atomic absorption technique to a first-order technique by introducting a new predictor variable called dispersion. By use of the total information contained in the transient signal caused by this dispersion process instead of only peak height or peak area, the dynamic range of flame atomic absorption spectrometry can be substantially expanded. A straightforward algorithm, named CLAIR (c alibration graph/inearization and interfered signal reconstruction), based on gradient ratio evaluation and capable of utilizing the additional information in the transient signal for calibration and interference correction is proposed

Spatial light modulator device and a conoscopic holography system of large dynamic range including such a modulator device

Abstract: The invention relates to a spatial light modulator device comprising a photo-refractive crystal addressed by means of a write light beam and a read light beam. The crystal is placed in the cavity of an interferometer system having a transmittivity-optical path length characteristic of steep slope so as to give rise to a dynamic range of maximum transmittivity variation for minimum variation in the refractive index or optical path length of the photo-refractive crystal. The device is applicable to conoscopic holography systems of large dynamic range and to pattern recognition in real time.

Displacement response, detection limit, and dynamic range of fiber-optic lever sensors

Abstract: The authors present the evaluation of the displacement response, detection limit, and dynamic range of fiber-optic lever sensors in a general format to establish their dependence on fiber sizes, optoelectronic detector specifications, input power, and other relevant parameters. The formations for the normalized reflected optical power change are derived for the evaluation of the optimal sensor response, the linearity range, and the minimum detectable displacement. The theoretical models are verified by an experiment which determines sensor response, modulation index, reflected optical power change, and linear response range through dynamic measurement. The application of this theoretical model to the study of a fiber-optic microphone for acoustic pressure detection is considered. >

High energy X-ray computed tomography for industrial applications

Abstract: A high-energy X-ray computed tomography system with an electron linear accelerator was developed to image cross-sections of large-scale and high-density materials. An electron linear accelerator is used for the X-ray source. The maximum X-ray energy is 12 MeV and the average energy is around 4 MeV. The intensity of an X-ray fan beam passing through the test object is measured by a 15-channel detector array. CWO (CdWO/sub 4/) scintillators and photodiodes are employed for the X-ray detectors. The crosstalk noise due to scattering at X-ray photons by adjacent detectors is reduced to less than 1.6% by installing a tungsten shield between the scintillators. Extra channels are used to compensate for the baseline shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-ray transmitted in a 420 mm-thick iron block. A spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter. >

High-efficiency coding apparatus for compressing a digital video signal while controlling the coding bit rate of the compressed digital data so as to keep it constant

Abstract: Digital video signals are divided in blocks, maximum and minimum values of each block are extracted, and a frequency distribution of one frame period of a dynamic range in each block is detected. The coding condition is determined by the frequency distribution and a predetermined N kinds of characteristic tables, and by determining only one characteristic table, the signal obtained by subtracting the minimum value of each block from the digital video signals of each block is coded in variable length according to the dynamic range of each block. The characteristic table shows the relationship of the distortion or the number of quantization bits between the original signal and decoded signal after coding and decoding with respect to the dynamic range of digital video signal in each block, and the picture quality of decoded image is set as a parameter.

Electromagnetic radiation mixer based on electron heating in resistive state of superconductive Nb and YBaCuO films

Abstract: A theory of an electron-heating mixer which makes it possible to calculate all the characteristics of the device is developed. It is shown that positive conversion gain is possible for such a mixer in the millimeter to near-infrared wavelength range. The dynamic range and the optimum heterodyne power can be selected from a very wide interval by varying the mixing element volume. Measurements made for Nb within the frequency range of 120-750 GHz confirm the theory. The conversion loss obtained at T=1.6 K and normalized to the element reaches 0.3 dB in the intermediate frequency band of 40 MHz; the possible noise temperature is 50 K. The estimation of noise temperature and output band for YBaCuO at T=77 yields 200 K and more than 10 GHz, respectively.

High-dynamic-range fiber gyro with all-digital signal processing

Abstract: The paper describes a compact (50-cu cm) fiber-optic gyro (FOG) prototype with a dynamic range of +/- 1500 deg per sec and a bias stability of 1 deg per hour. The FOG uses an all-digital signal processing scheme which is intrinsically free of electronic bias drift, making it possible to work over the whole potential dynamic range of the FOG without degrading the bias performances. With a stability and a linearity of 10 ppm, this FOG is a good candidate for high-performance tactical-grade applications. A configuration scheme of the FOG prototype is presented.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Extending dynamic range of stored image data base

Abstract: The dynamic range of a digitized image database is extended to permit shifting of encoded pixel values without 'clipping', and to provide a limited window of values into which specular highlights may be encoded and stored. Digital codes into which an image scanner output has been mapped by a scene balance mechanism are converted into a set of reduced-range digital codes of the same resolution but having a smaller range of image content values than the dynamic range of the digitized image data base. The code conversion mechanism operates to convert a maximum value of 100 % white reflectance to an encoded value that is less than the upper limit of the dynamic range of the database to allow for the placement of specular highlights that are beyond the 100 % white reflectance maximum and to accommodate shifts in the digitized imagery data at both the high and low ends of the range.

Optimization of externally modulated analog optical links

Abstract: Analog fiber-optic links using an integrated-optical intensity modulator have been demonstrated and analyzed. Experimental links operate at frequencies from 40 MHz to 22 GHz with electrical gain up to 11 dB, noise figure as low as 6 dB, and intermodulation-free dynamic range of up to 113 dB-Hz2/3. The gain, noise figure, and dynamic range are shown to have a simple dependence upon a few link design parameters. Other factors affecting link performance, such as stimulated Brillouin scattering, interferometric intensity noise, modulator linearization, and addition of an optical amplifier, are also discussed briefly.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pixel by pixel offset and gain correction in analog data from scanning arrays

Abstract: Method and apparatus for a correction of photosite offset and gain in the analog domain. Correction of offset and gain in the analog domain, prior to conversion of the analog signals to digital signals, allows the use of the maximum dynamic range of the system for pixel information, once the image is converted.

An Oversampled Multi-bit CMOS D/A Converter For Digital Audio With 115dB Dynamic Range

Abstract: The analog part of a current-mode CMOS 5-b bidirectional digital/analog (D/A) converter for digital audio with 115-dB dynamic range and -90-dB distortion at 128-times oversampling is presented. The application of a multibit noise shaping approach combined with a sign-magnitude decoding in an oversampled D/A converter not only increases the dynamic range of the converter but also reduces the intermodulation sensitivity. A dynamic self-calibration technique is used to obtain the required relative accuracy and absolute linearity of the current sources. No laser or external trimming techniques are required. >

A symmetric analogue demodulator for optical fiber interferometric sensors

Abstract: Describes a form of passive homodyne demodulation for recovering a signal of interest from a Mach-Zender optical fiber interferometric sensor. The interferometer uses a 2*2 optical fiber coupler at the input, a push-pull arrangement to stretch the fibers comprising the two legs of the interferometer in a different manner, and a 3*3 optical fiber coupler at the output, generating three phase-modulated outputs. The demodulator uses all three outputs in a symmetric manner to reconstruct the signal of interest. A dynamic range of 115 dB in a 1-Hz bandwidth has been measured for a circuit implementing this scheme. The minimum detectable signal at a frequency of 600 Hz is 220 mu rad/ square root Hz. The maximum acceptable signal at 600 Hz is 140 rad, increasing linearly with decreasing frequency. A schematic diagram of an implementation of the symmetric demodulation technique in analog electronics is presented. >

Automated high precision variable aperture for spectrophotometer linearity testing

Abstract: A new automated linearity tester with a single variable aperture has been designed and built. It uses piezoelectric motors to define precisely the apertures required for application of the double aperture method of light addition. This design avoids many of the inherent shortcomings of two fixed physically separated apertures, such as interference and coherence between two separated beams and the need for an averaging sphere to compensate for beam noncoincidence at the photoreceiver. It also permits the assessment of system nonlinearity for arbitrary flux levels over an ≈70:1 dynamic range without the use of a supplementary means of optical attenuation. The tester was specifically designed for use with the National Research Council of Canada Reference spectrophotometer, but it can be adapted for use with any instrument with a large stable measurement beam. The paper discusses the correct placement and operation of this device. The performance, as evaluated by nonlinearity measurements of a known highly linear silicon photodiode, shows a reliability of <1–3 parts in 104 over a 3400:1 dynamic range at a 97% confidence level. Several applications of this linearity tester to both photomultipliers and photodiodes are described. Transmittance results for several reference materials using these linearity corrected photodetectors are compared and show a typical agreement of better than 0.025% of the value.

A highly sensitive on-chip charge detector for CCD area image sensor

Abstract: A novel on-chip charge detector for charge-coupled-device (CCD) image sensor applications was fabricated and evaluated. The device, called the double-gate floating surface detector, achieves a charge/voltage conversion gain of 220 mu V/electron, a noise equivalent electron of 0.5 electrons r.m.s. and a dynamic range of 79 dB over 3.58-MHz video bandwidth at room temperature. In the small-signal region under 20 electrons, which is the photon counting region for highly sensitive imaging devices, the device was evaluated by observing the discrete voltage levels corresponding to the number of signal electrons on an oscilloscope. This evaluation confirmed that the high charge voltage conversion gain is also maintained in this region. >

A novel optical modulator system with enhanced linearization properties

Abstract: The authors propose a novel optical modulator system that has the properties of having a null third-order intermodulation distortion (IMD); a spurious signal free dynamic range in excess of 100 dB as determined by the second-, fourth-, and fifth-order IMD; and a linear dynamic range of 2.46 radians. It is shown that a combination of a tandem of two directional couplers has the property of eliminating completely third-order IMD term, gives a large spurious signal free dynamic range, and provides a simple and practical solution to the problem of linearization of optical modulators. >

Balanced phase and polarization diversity coherent optical receiver

Abstract: A balanced phase and polarization diversity receiver employing a compact bulk optical 90 degrees hybrid and a silicon bipolar multiplier IC is described. The compact bulk optical hybrid provides all required optical signals with well-defined phase relations in a single unit and is therefore a good solution of the problems associated with the complex structure of the optical part of the receiver. The multiplier IC has a dynamic range of at least 15 dB. It guarantees that variations of the signal power in the different detection branches of the receiver cause negligible degradation in both diversity operations. The receiver has been tested in a 565-Mb/s DPSK transmission system. >