Showing papers on "Dynamic range published in 1999"

Dynamic range improvement through multiple exposures

Abstract: This paper presents an approach for improving the effective dynamic range of cameras by using multiple photographs of the same scene taken with different exposure times. Using this method enables the photographer to accurately capture scenes that contain a high dynamic range, i.e., scenes that have both very bright and very dark regions. The approach requires an initial calibration, where the camera response function is determined. Once the response function for a camera is known, high dynamic range images can be computed easily. The high dynamic range output image consists of a weighted average of the multiply-exposed input images, and thus contains information captured by each of the input images. From a computational standpoint, the proposed algorithm is very efficient, and requires little processing time to determine a solution.

A 640/spl times/512 CMOS image sensor with ultra wide dynamic range floating-point pixel-level ADC

Abstract: Analysis results demonstrate that multiple sampling can achieve consistently higher signal-to-noise ratio at equal or higher dynamic range than using other image sensor dynamic range enhancement schemes such as well capacity adjusting. Implementing multiple sampling, however, requires much higher readout speeds than can be achieved using typical CMOS active pixel sensor (APS). This paper demonstrates, using a 640/spl times/512 CMOS image sensor with 8-b bit-serial Nyquist rate analog-to-digital converter (ADC) per 4 pixels, that pixel-level ADC enables a highly flexible and efficient implementation of multiple sampling to enhance dynamic range. Since pixel values are available to the ADC's at all times, the number and timing of the samples as well as the number of bits obtained from each sample can be freely selected and read out at fast SRAM speeds. By sampling at exponentially increasing exposure times, pixel values with binary floating-point resolution can be obtained. The 640/spl times/512 sensor is implemented in 0.35-/spl mu/m CMOS technology and achieves 10.5/spl times/10.5 /spl mu/m pixel size at 29% fill factor. Characterization techniques and measured quantum efficiency, sensitivity, ADC transfer curve, and fixed pattern noise are presented. A scene with measured dynamic range exceeding 10000:1 is sampled nine times to obtain an image with dynamic range of 65536:1. Limits on achievable dynamic range using multiple sampling are presented.

A 14-bit intrinsic accuracy Q/sup 2/ random walk CMOS DAC

Abstract: In this paper, a 14-bit, 150-MSamples/s current steering digital-to-analog converter (DAC) is presented. It uses the novel Q/sup 2/ random walk switching scheme to obtain full 14-bit accuracy without trimming or tuning. The measured integral and differential nonlinearity performances are 0.3 and 0.2 LSB, respectively; the spurious-free dynamic range is 84 dB at 500 kHz and 61 dB at 5 MHz. Running from a single 2.7-V power supply, it has a power consumption of 70 mW for an input signal of 500 kHz and 300 mW for an input signal of 15 MHz. The DAC has been integrated in a standard digital single-poly, triple-metal 0.5-/spl mu/m CMOS process. The die area is 13.1 mm/sup 2/.

CMOS imager with storage capacitor

Abstract: A CMOS imager having an improved signal to noise ratio and improved dynamic range is disclosed. The CMOS imager provides improved charge storage by fabricating a storage capacitor in parallel with the photocollection area of the imager. The storage capacitor may be a flat plate capacitor formed over the pixel, a stacked capacitor or a trench imager formed in the photosensor. The CMOS imager thus exhibits a better signal-to-noise ratio and improved dynamic range. Also disclosed are processes for forming the CMOS imager.

Recording media that exhibit high dynamic range for digital holographic data storage.

Abstract: A general strategy for fabricating thick, optically flat photopolymer recording media with high dynamic range (M/#) that exhibit low levels of recording-induced Bragg detuning for holographic data storage is presented. In particular, media with M/# values as high as 42 in 1-mm-thick formats are obtained. We believe that these results are the first demonstration of a holographic storage medium with a dynamic range of this magnitude. In addition, we report the holographic recording and recovery of high-capacity (480-kbit) digital data pages in these media, further illustrating their data-storage capabilities.

A 100-MHz, 16-b, direct digital frequency synthesizer with a 100-dBc spurious-free dynamic range

Abstract: This paper describes the architecture and the IC implementation of a direct digital frequency synthesizer (DDFS) that is based on an angle rotation algorithm (similar to CORDIC). It is shown that the architecture can be implemented as a multiplierless, feedforward, and easily pipelineable datapath. A prototype IC has been designed, fabricated in 1.0-/spl mu/m CMOS, and tested. The IC produces 16-b sine and cosine outputs with a spurious-free dynamic range of more than 100 dBc. A 36-b frequency control word gives a tuning resolution of 0.0015 Hz at a 100-MHz sampling rate.

Dynamic range of optical reflectometry with spectral interferometry

Abstract: I present an optical reflectometry (OR) technique with spectral interferometry (SIOR) that realizes high dynamic range compared with a conventional OR system using the delayed heterodyne technique (DHOR), and report on the application of this system to noninvasive in vivo measurements of the structure of the skin and the nail of an index finger. The theoretically derived dynamic range of SIOR is m/4-times superior to that of DHOR, where m is the number of independent image pixels. A dynamic range of 105 db was experimentally realized, which is comparable to the theoretically expected dynamic range of 112 db.

Broad-band linearization of a Mach-Zehnder electrooptic modulator

Abstract: Analog optical-link dynamic range in excess of 75 dB in a 1-MHz band has been achieved using specially designed electrooptic modulators that minimize one or more orders of harmonic and intermodulation distortion. To date, however, such "linearized" modulators have only enabled improved link dynamic ranges at frequencies below 1 GHz. Additionally, linearization across more than an octave bandwidth has required precise balancing of the signal voltage levels on multiple electrodes in a custom modulator, which represents a significant implementation challenge. In this paper, a link linearization technique that uses a standard Mach-Zehnder lithium-niobate modulator with only one RF and one dc-bias electrode to achieve broad-band linearization is discussed, resulting in a dynamic range of 74 dB in 1 MHz across greater than an octave bandwidth (800-2500 MHz). Instead of balancing the voltages on two RF electrodes, the modulator in this new link architecture simultaneously modulates optical carriers at two wavelengths, and it is the ratio of these optical carrier powers that is adjusted for optimum distortion canceling. The paper concludes by describing a second analogous link architecture in which it is the ratio of optical power at two modulated polarizations that is adjusted in order to achieve broad-band linearization.

Wideband radio channel measurement system at 2 GHz

Abstract: This paper describes the wideband radio channel sounding techniques for mobile radio channel measurements. Implementation of the cross-correlation method using both a sliding correlator and a matched filter detector is presented. Limitations and accuracy of radio channel measurements are discussed. Typically, delay resolution of about 20 ns is achieved with 100 MHz bandwidth. With a sliding correlator, a dynamic range of 25 dB was obtained with maximum Doppler bandwidth of 25 Hz and maximum excess delay of 19 /spl mu/s. Digital matched filtering with a maximum sampling rate of 125 MHz can be used in real-time measurements with Doppler shifts of several kilohertz and 30 dB dynamic range. Using matched filter deconvolution as a resolution enhancement technique is discussed. Examples of the time-variant complex impulse response measurements are given.

Optical coherence tomography by spectral radar: dynamic range estimation and in-vivo measurements of skin

Abstract: Spectral radar is an optical sensor for tomography, working in the Fourier domain, rather than in the time domain. The scattering amplitude a (z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. One important property of optical coherence tomography (OCT) sensors is the dynamic range. We will compare the dynamic range of spectral radar with standard OCT. The influence of the Fourier transformation on the dynamic range of spectral radar will be discussed. The clinical relevance of the in vivo measurements will be demonstrated.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Tuning Dynamic Range and Sensitivity of White-Light, Multimode, Fiber-Optic Surface Plasmon Resonance Sensors

Abstract: This paper presents the advantages of modifying the geometry of the sensing tip of a white-light, multimode optical fiber SPR sensor to optimize the dynamic range and sensitivity. By selectively beveling the distal end of the fiber probe, the wavelength of resonance can be red-shifted by more than 100 nm and blue-shifted by more than 30 nm. This increases the flexibility of a white-light SPR sensor by increasing the dynamic range of accessible RIs and by shifting the resonance to the most sensitive regions of the detector. Sensitivity, measured in wavelength shift per RI change, can be increased by a factor of 4. Also, multiple-wavelength regions of SPR activity can simultaneously be observed on the same probe, thus increasing the information content of a SPR spectrum.

User adjustable volume control that accommodates hearing

Abstract: The present invention is a method for mixing audio signals based on the preference from hearing impaired listeners, as well as non-hearing impaired listeners, without forcing hearing impaired individuals to employ special hearing-impaired equipment. A user activated controller (10, 11) controls a mixture of a preferred audio signal and a remaining audio signal across a range sufficiently wide enough to encompass all individuals. The preferred audio is recorded and maintained separated from all remaining audio and delivered to the listener in a manner that maintains this separation. The controller (10, 11) enables the user to specify a range about the ratio in which the audio may vary, which permits the listener to expand the audio across a continuous range to whatever dynamic range his hearing can accommodate. The controller (10, 11) automatically adjusts to changes in incoming audio. The controller (10, 11) can react to relatively slowly moving changes or prevent short bursts of sound in remaining audio from modifying the signal levels. The combination of the ability to control the mixing ratio and to specify the dynamic range of the ratio in which the audio may vary, coupled with the ability to automatically adjust the signal levels in response to sudden changes in incoming audio, provides a powerful user capability that truly optimizes the listening experience for any listener.

Comparative analysis of SNR for image sensors with enhanced dynamic range

Abstract: Dynamic range is a critical figure of merit for image sensors. Often a sensor with higher dynamic range is regarded as higher quality than one with lower dynamic range. For CCD and CMOS sensors operating in the integration mode the sensor SNR monotonically increases with the signal. Therefore, a sensor with higher dynamic range, generally, produces higher quality images than one with lower dynamic range. This, however, is not necessarily the case when dynamic range enhancement schemes are used. For example, suing the well capacity adjusting scheme dynamic range is enhanced but at the expense of substantial degradation in SNR. On the other hand, using multiple sampling dynamic range can be enhanced without degrading SNR. Therefore, even if both schemes achieve the same dynamic range the latter can produce higher image quality than the former. The paper provides a quantitative framework for comparing SNR for image sensors with enhanced dynamic range. We introduce a simple model to describe the sensor output response as a function of the photogenerate signal, dark signal, and noise for sensors operation in integration mode with and without dynamic range enhancement schemes. We use the model to quantify and compare dynamic range and SNR for three sensor operation modes, integration with shuttering, using the well capacity adjusting scheme, and using multiple sampling.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High sensitivity radio receiver

Abstract: The invention relates to a high sensitivity receiver installed outdoors which may be used in a base station of a mobile communication system, for example. A received radio frequency signal is converted into a signal in a desired frequency band by a reception bandpass filter RXF3, is subject to a low noise amplification to a desired level by a low noise reception amplifier LNA4, and the amplified signal is converted into an optical signal by a laser diode LD5. RXF3, LNA4 and LD5 are confined in a heat shielding box. LD5 is cooled by cooling means to the order of critical temperature where RXF3, for example, assumes a superconducting state, whereby the dynamic range is increased and stabilized.

Region-based information compaction as for digital images

Abstract: A method and apparatus for preserving the dynamic range of a relatively high dynamic range information stream (S1), illustratively a high resolution video signal, subjected to a relatively low dynamic range encoding (230, 15) and/or transport (235, 30) process(es). The invention subjects the relatively high dynamic range information stream to a segmentation and remapping process (215-225, 10) whereby each segment is remapped to the relatively low dynamic range appropriate to the encoding and/or transport process(es) utilized. An auxiliary information stream (S4) includes segment and associated remapping information such that the initial, relatively high dynamic range information stream (S1) may be recovered in a post-encoding (i.e. decoding) or post-transport (i.e., receiving) process.

Extended dynamic range image sensor system

Abstract: The invention relates to an extended dynamic range imager (100). An array of pixels (120) provides an output signal for each pixel related to an amount of light captured for each pixel during an integration period. A row of extended dynamic range (XDR) sample and hold circuits (132) having an XDR sample and hold circuit for each column of the array captures an XDR signal related to a difference between the output signal and an XDR clamp level to which the pixel is reset at a predetermined time before the end of the integration period. A row of linear sample and hold circuits (131) having a linear sample and hold circuit for each column of the array captures a linear signal related to a difference between the output signal and an initial output signal to which the pixel is reset at the beginning of the integration period.

Digital image display improvement system and method

Abstract: A technique is disclosed for enhancing discrete pixel images in accordance with a desired dynamic range, such as the dynamic range of a softcopy display. Adaptive equalization is first performed on the image data to reduce overall differences between high and low intensity values, while maintaining the overall appearance of light and dark regions of the reconstructed image. Adaptive contrast boosting or enhancement is then performed on the equalized values to bring out details visible by virtue of the enhanced local contrast. The contrast enhancement may include non-linear mapping of a mid-frequency boosted image onto the dynamic range of the softcopy display.

Active pixel cmos sensor with multiple storage capacitors

Abstract: An apparatus and method for improving dynamic rays and motion representation in digital imaging (60). A light sensitive element (10) such as a photo diode is employed to sense a light level at a surface during a period of time. A plurality of storage elements (C1-CN) are associated with the light sensitive element but electrically segregated therefrom by a plurality of sampling transistors (34, 44, 54) by enabling the sampling transistors between the particular storage element and the light sensitive element in a predetermined way. Its dynamic range can be extended and since readout between exposures is not required, exposure may be taken in closer temporal proximity thereby improving motion representation.

Apparatus and method for measuring optical tomographic image

Abstract: PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring an optical tomographic image capable of enhancing the dynamic range of the electric signal of the interference light of the signal light reflected from an object to be measured irradiated with light and the reference light reflected by a reference light reflecting mirror by removing noise contained in the electric signal and capable of rapidly measuring the optical tomographic image free from a virtual image with high sensitivity. SOLUTION: A noise removing means 45 for removing noise contained in the electric signal of interference light dispersed at every wavelength by a wavelength dispersing means 41 and detected by a detection means 43 is provided.

Dynamic range extension of wideband receiver

Abstract: A digitizer with increased dynamic range is provided by applying varying gains/attenuations to an input signal and feeding the resulting scaled signals to several conventional analog-to-digital converters to be digitized. The digitized version of the largest scaled signal which does not result in its respective analog-to-digital converter from saturating is selected by a multiplexer to be fed through as the digitizer output. Each of the gains(attenuations) differ by multiples of approximately 6 dB, since one bit in an ADC represents this value. The multiplexer outputs a digital sample size which is larger than that of the analog-to-digital converters and with the selected digitized version being output as the appropriate subset of the larger sample size to account for the gain(attenuation) of the selected signal. Preferably, this is used in a wideband receiver to increase the dynamic range of the receiver.

Method for scanning gene probe array to produce data having dynamic range that exceeds that of scanner

Abstract: A genetic sample is analyzed by providing a gene probe array including a plurality of genetic probes having different receptors. The sample is processed to include at least one fluorescently tagged ligand. The array is hybridized by exposing the probes to the processed sample such that ligands can bind to complementary receptors. Composite data having a data dynamic range is obtained from the array using an optical scanner which has a scanner dynamic range that is smaller than the data dynamic range. The scanner optically irradiates and scans the probes and detects fluorescent emissions at a first wavelength which is selected such that the scanner produces valid first data in a low intensity portion of the data dynamic range and is in saturation in at least part of a high intensity portion of the data dynamic range. The scanner then optically irradiates and scans the probes with light and detects fluorescent emissions at a second wavelength which is selected such that the scanner produces valid second data in a high intensity portion of the data dynamic range and is in cutoff in at least part of a low intensity portion of the data dynamic range. A scale factor correlation function is calculated between the first data and the second data, and is applied to convert the second data to have a same scale factor as the first data. The first data for the first portion of the data dynamic range is combined with the converted second data for the second portion of the data dynamic range to obtain the composite data.

A novel fiber-optic sensor array based on the Sagnac interferometer

Abstract: We propose a novel design for a fiber-optic acoustic sensor array that is based on the Sagnac interferometer. The performance of this Sagnac sensor array (SSA) design is analyzed and compared to acoustic sensor arrays based on the Mach-Zehnder (MZ) interferometer. It is found that the SSA exhibits several decisive advantages, including a stable bias point, a reduced conversion of source phase noise into intensity noise, and a frequency response that matches the ambient ocean noise. It is also shown that the SSA can be easily designed to have a much larger dynamic range than an MZ-based sensor array. Potential noise sources are analyzed and shown to be manageable. A means for eliminating polarization-induced signal fading is presented. The applicability of time-division, frequency-division, and code-division multiplexing schemes for the proposed design is presented.

Optical imager using a method for adaptive real-time expanding of the dynamic range

Abstract: Method and apparatus for expanding the dynamic range of an optical imager, comprising individually controlling the integration time of each pixel of a sensor array, and providing a corresponding scaling factor for the electrical output of each individual pixel during the frame time. The integration time of each pixel is controlled as a function of light intensity received by each individual pixel, by resetting the pixel after a predetermined threshold for the output signal, has been reached.

Synchronous amplitude and time control for an optimum dynamic range variable photonic delay line

Abstract: A synchronous-amplitude-controlled and time-delay-controlled photonic controller for phased-array antenna applications is proposed and demonstrated. Amplitude control is based on a variable optical attenuator system that operates in synchronism with the photonic delay line (PDL). This amplitude control system can provide both the signal calibration for the different PDL channels and settings required for driving the antenna elements of a phased-array radar and the optimum optical power levels that impinge on the photodetector for optimum fiber-optic-link performance. Various variable amplitude control modules based on ferroelectric liquid crystals, polymer-dispersed liquid crystals, and photoconductive devices are proposed. We show that the dynamic range loss due to a switched-PDL inherent structure loss can be compensated when we control the optical power from the laser, using the synchronous optical attenuation system. For the first time to our knowledge, full dynamic range loss compensation is demonstrated for an external-modulation-fed 3-bit switched PDL with a structure optical insertion loss of 5.5 dB. A compression dynamic range of 158 dB·Hz was measured at 6 GHz, and a spurious free dynamic range of 111 dB·Hz2/3 was estimated. Feasibility of the dynamic range compensation technique for multichannel, higher-insertion-loss PDL systems is discussed.

Dynamic range extender apparatus, system, and method for digital image receiver system

Abstract: A dynamic range enhancement system (DRES) receives input signals from an imager device connected to a correlated double sampling (CDS) circuit for receiving the video signal from the CCD imaging device. The dynamic range enhancement system includes a variable gain amplifier (VGA), and a limited bit-width analog-to-digital converter (ADC) which digitizes the analog signal received from the VGA. The output of the ADC is provided to an initial bit range position of a wider bit-width shifter connected to the output of the ADC. The DRES system includes a 2-bit ADC for extending the dynamic range of the imager device, which enhances the dynamic range of a 10 bit ADC to 13 bits.

Self-referenced reflective intensity modulated fiber optic displacement sensor

Abstract: A simple referencing technique is presented for a fiber optic reflective displacement sensor. Two receiving fibers are arranged side by side to operate in the negative and positive slopes of the output sig- nal. The ratio of the two outputs provides common mode rejection. A theoretical model of the new referencing technique is developed and verified experimentally. The linear operating range of the sensor de- pends on the numerical aperture of the fibers and the diameter of the second receiving fiber. The minimum detectable displacement of a rep- resentative sensor is 1.57 nm/AHz in the audio frequency range, which agrees well with the theoretical value. The measured dynamic range of the sensor is 111 dB. Alternative sensor structures to reduce the size and to increase linear range and resolution are discussed. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)02402-2)

Method and apparatus for increasing the low frequency dynamic range of a digital ECG measuring system

Abstract: An ECG signal measuring system uses low frequency compression/enhancement techniques combined with dither techniques to effectively increase the dynamic range while maintaining resolution. This aspect of the present invention is achieved without increasing the number of bits of the ADC. The system includes a HPF, an ADC, a decimation filter (DF), and a compensation filter (CF). The HPF receives an input signal (i.e., the bias current combined with ECG input signal) and attenuates the low frequency components of the input signal, including a portion of the frequency band within the desired ECG frequency band. The ADC oversamples the output signal of the HPF. The DF receives the output samples of the ADC and generates output samples at rate that is at least twice the maximum frequency of the desired ECG output signal. The CF amplifies the low frequency end of the DF output samples. The gain and cutoff frequency of the CF are set to offset the HPF's attenuation of those low frequency components of the input signal below the minimum frequency of the desired ECG output signal. System noise can be used as the dither. Consequently, the ECG output signal remains within the dynamic range of the system.

Air-coupled nondestructive evaluation using micromachined ultrasonic transducers

Abstract: Nondestructive evaluation techniques which use conventional piezoelectric transducers typically require liquid coupling fluids to improve the impedance mismatch between piezoelectric materials and air. Air-coupled ultrasonic systems can eliminate this requirement if the dynamic range of the system is large enough such that the losses at the air-solid interfaces are tolerable. Capacitive micromachined ultrasonic transducers (cMUTs) have been shown to have more than 100 dB dynamic range when used in bistatic transmission mode. This dynamic range, along with the ability to transmit ultrasound efficiently into air, makes cMUTs ideally suited for air-coupled nondestructive evaluation applications. These transducers can be used either in through transmission experiments at normal incidence to the sample or to excite and detect guided waves in aluminum and composite plates. In this paper, we present results of a pitch-catch transmission system using cMUTs that achieves a dynamic range in excess of 100 dB. The pair of transducers is modeled with an equivalent electrical circuit which predicts the transmission system's insertion loss and dynamic range. We also demonstrate the feasibility of Lamb wave defect detection for one-sided nondestructive evaluation applications. A pair of cMUTs excites and detects the so mode in a 1.2 mm-thick aluminum plate with a received signal-to-noise ratio of 28 dB without signal averaging.

Camera with spatially adjustable variable density optical filter and method for controlling the same

Abstract: A camera is provided that includes an array of optical detectors and an optical filter placed adjacent the array. The optical detectors output detection signals that are used to form control signals. The filter includes spatial sections of individually adjustable optical density. The optical densities are controlled by the individual control signals. The camera outputs the combined control signals and detection signals, thus effectively providing an output with a larger dynamic range than would be provided by the detection signals of the detectors alone. An objective lens and a housing form a stand alone unit. The detectors can have different responses to different wavelengths to achieve color specific effects. Methods are further provided for controlling the filter. The detection signals are scanned to ensure that a predefined filtering condition is met. If not, control signals are iteratively generated and applied to the filter until the condition has been met. Then the detection signals are combined with the control signals to form composite signals that encode the intensity distribution of the beam. Control methods ensure greater dynamic range and accuracy. Image processing methods enhance viewability.