Showing papers on "Dynamic range published in 1996"

A Multiscale Retinex for Color Rendition and Dynamic Range Compression

Abstract: The human vision system performs the tasks of dynamic range compression and color constancy almost effortlessly. The same tasks pose a very challenging problem for imaging systems whose dynamic range is restricted by either the dynamic response of film, in case of analog cameras, or by the analog-to-digital converters, in the case of digital cameras. The images thus formed are unable to encompass the wide dynamic range present in most natural scenes (often < 500:1). Whereas the human visual system is quite tolerant to spectral changes in lighting conditions, these strongly affect both the film response for analog cameras and the filter responses for digital cameras, leading to incorrect color formulation in the acquired image. Our multiscale retinex, based in part on Edwin Land''s work on color constancy, provides a fast, simple, and automatic technique for simultaneous dynamic range compression and accurate color rendition. The retinex algorithm is non-linear, and global---output at a point is also a function of its surround---in extent. A comparison with conventional dynamic range compression techniques such as the application of point non-linearities, e.g. log(x,y), and global histogram equalization and/or modification shows that the multiscale retinex simultaneously provides the best dynamic range compression and color rendition. The applications of such an algorithm are many; from medical imaging to remote sensing; and from commercial photography to color transmission.

CMOS low-distortion high-frequency variable-gain amplifier

Abstract: The overall system performance of mixed-signal CMOS IC's is largely determined by the dynamic performance of the analog front-ends. System features are, in contrast, mainly set by the digital architecture. In order to optimize the dynamic range of the system and to minimize the sensitivity to substrate noise, the analog-to-digital converter (ADC) has to be preceded by a variable-gain amplifier (VGA) and a differential circuit topology for the complete front-end to be adopted. Since most of present-day applications are based on single-sided signal source definitions, the differential-input VGA must be able to perform a single-to-differential signal conversion. This paper describes the principle and design of a differential CMOS low-distortion variable-gain amplifier for high-frequency (video) applications. Experimental results of the circuit show total harmonic distortion figures better than -60 dB and a gain accuracy of 0.05 dB over the -2 to +12 dB gain range for single-sided input signals.

Tutorial compression ? Yes, but for low or high frequencies, for low or high intensities, and with what response times ?

Abstract: Several rationales for using compression in hearing aids are outlined. These rationales comprise discomfort avoidance, loudness normalization, noise reduction, short term signal dynamic range reduction, empirically determined compression, and long-term signal dynamic range reduction. The compression systems needed to implement each of these differ greatly, and these differences can be viewed as differences in the frequency range undergoing most compression, the intensity range undergoing most compression, and the speed at which the compressor(s) operate. A classification system along these lines is introduced and examples of currently available hearing aids falling into each category are given. The effects of each type of compression on speech intelligibility is investigated via a review of published research. The results of this indicate that, for speech in quiet at a comfortable level, no compression scheme yet tested offers better intelligibility than individually selected linear amplification. If input level is then decreased and the aid wearer is prevented from adjusting the volume control, many types of compression provide intelligibility superior to that available from linear amplification. In broadband noise, only one system, containing wideband compression followed by fast acting high-frequency compression, has so far been shown to provide significant intelligibility advantages.

A 128/spl times/128-pixel standard CMOS image sensor with electronic shutter

Abstract: A 128/spl times/128-pixel image sensor with a 20 s-10/sup -4/ s electronic shutter has been integrated in a 1.2-/spl mu/m digital CMOS technology. The pixel cell consists of four PMOS transistors and a photodiode with antiblooming suppression. Each pixel measures 24 /spl mu/m by 24 /spl mu/m and has a fill factor of 25%. Current is used to transfer pixel signals to the column readout amplifiers in order to minimize voltage swings on the highly capacitive column lines. Correlated double sampling is used to reduce intracolumn fixed pattern noise. The saturation voltage is 470 mV. The peak output signal to noise ratio is 45 dB, and the optical dynamic range is 56 dB. The frame transfer rate is 1.7 ms per frame.

Wavelength conversion by optimized monolithic integrated Mach-Zehnder interferometer

Abstract: Semiconductor optical amplifiers have been monolithic integrated in a passive symmetric Mach-Zehnder interferometer to form a compact polarization insensitive all-optical wavelength converter operating at up to 10 Gb/s. A simple method for reducing the impact of input power variations is proposed that increases the input power dynamic range from 4-8 dB.

A low-noise series-array Josephson junction parametric amplifier

Abstract: We have obtained parametric gain at 19 GHz from a distributed Josephson junction parametric amplifier whose active gain medium consists of a series array of 1000 Josephson junctions embedded in a coplanar waveguide. When cooled to 1.7 K the amplifier provides 16 dB gain in a mode where the internally generated double sideband noise referred to input is 0.5±0.1 K. This noise is consistent with Nyquist noise generated from the losses. An instantaneous bandwidth of 125 MHz has been observed with a peak gain of 12 dB. The 3 dB compression point with a peak gain of 14.6 dB is ‐90.5 dB and the dynamic range is 38 dB.

Image sensing apparatus which performs dynamic range expansion and image sensing method for dynamic range expansion

Abstract: An image sensing apparatus which senses an object a plurality of times in different exposures to obtain a plurality of images and makes a single image with a widened dynamic range by processing the plurality of sensed images, generates a histogram of signal levels of an image sensed in a proper exposure by using a histogram generator, automatically decides whether a dynamic range expansion processing is to be processed or not on the basis of the generated histogram by using a dynamic range expansion deciding unit, determines a parameter for sensing another image of the object in an exposure which is different from the proper exposure in accordance with a decision by the dynamic range expansion deciding unit by using a parameter determination unit, and obtains a single image of the object by processing the image sensed in the proper exposure and the image sensed by using the parameter determined by said parameter determination unit an image processing unit. When an image sensing apparatus is not equipped with a photometer, a pre-sensing operation is performed, an image sensed in the pre-sensing operation is analyzed to find a proper exposure, and this image is also used in the dynamic range expansion processing. A part or whole image data of a plurality of images which are obtained as above and necessary for the dynamic range expansion processing are compressed by a compressing unit and the compressed image data is used in the dynamic range expansion processing.

Design of an nth order Dickson voltage multiplier

Abstract: In this brief we propose a simple dynamic model of a Dickson voltage multiplier with N stages, which is obtained starting from the models previously proposed for less than 5 stages. The model allows increased insight into the dynamic behavior of these circuits and provides a valuable tool for determining a first version design.

Novel FMCW radar system concept with adaptive compensation of phase errors

Abstract: A new high-performance FMCW sensor system concept is presented The approach is based on an adaptive signal processing scheme compensating phase errors caused by VCO phase noise as well as the non-linearity of the frequency modulation The key component of the low-cost sensor is a SAW (surface acoustic wave) delay line representing a miniaturised high-precision radar reference path A correction algorithm equalises the target signal according to the phase errors simultaneously measured with the reference path Employing this method, an excellent range resolution as well as a high dynamic range and multi-target selectivlty is obtained, which has been experimentally demonstrated at millimetrewave frequencies

Dynamic range of an electro‐optic field sensor and its imaging applications

Abstract: We report the measurement of the dynamics of free‐space electro‐optic field sensors for pulsed electromagnetic wave radiation. With an optical probe power spanning six decades of linearity and excellent signal‐to‐noise ratio (SNR), it is feasible to convert a far‐infrared 2D image into an optical 2D image. A simple estimation indicates that 100 mW of optical probe power can achieve an image of 256×256 pixels with a 50 pA signal current per pixel and a SNR ≳200. We also present a comparison measurement of an ultrafast photoconductive antenna and an electro‐optic sensor crystal.

Microwave analog optical links using suboctave linearized modulators

Abstract: We report experimental links at frequencies up to 4 GHz which use two integrated optical Mach-Zehnder interferometric modulators in series to reduce third-order intermodulation distortion. This design improves the intermodulation-free dynamic range (up to 88 dB with 1 MHz noise bandwidth is demonstrated) with no noise figure penalty relative to a link using a standard modulator. Detector current is low (<2 mA), which is necessary for the detector to provide adequate linearity.

Uniform and non-uniform dynamic range remapping for optimum image display

Abstract: A contexture dependent dynamic range remapping system utilizes background estimation, mask generation, parameter estimation and dynamic range remapping of an original image to provide an optimum output image. The dynamic range remapping includes an additive algorithm or a multiplicative algorithm or a combination of both algorithms. The output from the algorithms could be filtered by an edge-preserving filter to provide a filtered output image. The system adaptively compresses the dynamic range of the DC and slow-varying signals in the original image significantly while preserving and enhancing fine structures.

Apparatus for dynamic range compression of an audio signal

Abstract: A dynamic range compression technique incorporates four novel concepts. The first is the use of a critical band multichannel structure for improved perceptual transparency. The second is the use of attack and release rates, instead of attack and release times, to affect gain control and adaptation of the compressor to changes in the input level. The third concept involves a level estimate control mode which permits increased adaptability using variable weightings of the contribution of both RMS and peak level estimates to gain control. Finally, the fourth concept involves the normalization of the level estimates to reduce or eliminate spectral distortion. These concepts provide a dynamic range compressor with improved perceptual transparency, especially with respect to music.

Highly uniform five volt CMOS image photodiode sensor array with improved contrast ratio and dynamic range

Abstract: An imager using an array of photodiodes that does not require non-standard voltages nor multiphase clocking schemes and retains good linearity with low fixed pattern and random noise generation while requiring a minimum of silicon area is described.

VERDI: an acoustically programmable and adjustable CMOS mixed-mode signal processor for hearing aid applications

Abstract: A CMOS mixed-mode fully-differential signal processor (VERDI), that constitutes the core of a hearing aid system, is introduced. Its characteristics (frequency response, compression level, and output sound pressure level) are wireless controlled by means of dual tone multi-frequency (DTMF) encoded signals transmitted by an external unit. A system description is provided, and the implementation and experimental results of the key components (preamplifier, antialiasing filter, automatic gain control, filter section, output amplifier, and DTMF receiver/decoder) are covered in more detail. The circuit has been fabricated in a conventional 1.2 /spl mu/m CMOS n-well process and operates from a single 1.3 V battery, although a dc/dc converter is required. It consumes typically less than 1 mA and occupies 28 mm/sup 2/ of silicon. The dynamic range is larger than 66 dB for the maximum input signal (54 mV/sub rms/=108 dB SPL).

Discussion on resolution and dynamic range of Se-TFT direct digital radiographic detector

Abstract: The imaging performance of a new direct digital radiographic detector based on amorphous selenium and amorphous silicon TFT array which is under development is discussed. Progress has been made on the development of a multilayer digital x-ray detector panel with a structure consisting of a thin-film transistor pixel array, selenium x-ray photoconductor, dielectric layer and top electrode. An electronic system allows the rapid readout of image data which produces high resolution and wide dynamic range images. Using a straight edge, small wires and low contrast small holes targets, we have studied the spatial resolution, contrast detectability, and dynamic range of this new detector. Digital signals obtained from each pixel of this detector are almost linear with the total x-ray energy absorbed within the pixel area over a wide range of x-ray exposures. The resultant wide dynamic range allows extended latitude of exposure conditions and the enhancement or emphasis of different gray level regions from a single set of image data. For example, from one single exposure of the head, the soft tissue of the nose, detail structure of the teeth, as well as the bone structure of the neck can be examined by displaying and emphasizing selective gray levels of the image data. Image information obtained from this detector appears to be more evenly distributed over a wide dynamic range which is different from digital data obtained from other digital modalities such as the electrometer sensing of discharged potentials on photoconductors or from film digitization. Examples of images are shown. The discrete pixel structure of this detector and the higher intrinsic spatial resolution of selenium combine to produce image sharpness greater than those produced from digital detectors of similar pixel pitch using indirect conversion method or from digitizing film-screen images. The applicability of mathematical tools, such as the MTF which was developed primarily for analog images on a continuous imaging medium, is discussed with respect to our new discrete element detector.

An image sensor with high dynamic range linear output

Abstract: Designs and operational methods to increase the dynamic range of image sensors (200) and APS devices (300) in particular by achieving more than one integration times for each pixel (302) thereof. An APS system (200) with more than one column-parallel signal chains (204, 206) for readout are described for maintaining a high frame rate in readout. Each active pixel (302) is sampled for multiple times during a single frame readout, thus resulting in multiple integration times. The operation methods can also be used to obtain multiple integration times for each pixel (302) with an APS design having a single column-parallel signal chain (104) for readout. Furthermore, analog-to-digital conversion of high speed and high resolution can be implemented.

Uncooled infrared sensors with digital focal plane array

Abstract: Loral Infrared & Imaging Systems is developing low cost, high performance, uncooled infrared imaging products for both military and commercial applications. These products are based on the microbolometer technology, a silicon micromachined sensor which combines the wafer level silicon processing with a device structure capable of yielding excellent infrared imaging performance. Here, we report on the development of an uncooled sensor, the LTC500, which incorporates an all digital focal plane array and has a measured NETD of less than 70 mK. The focal plane array and the electronics within the LTC500 have been designed as an integrated unit to meet a broad range of end user applications by providing features such as nonuniformity correction, autogain and level, NTSC video, and digital outputs. The 327 X 245 element focal plane array has a 46.25 micrometers pixel pitch and an on focal plane array 14 bit to analog to digital converter (ADC). The ADC has a measured instantaneous dynamic range of more than 76 dB at a 6.1 MHz output data rate and 60 Hz frame rate. The focal plane array consumes less than 500 mW of power, of which less than 250 mW is used in the ADC. An additional 36 dB of digital coarse offset correction in front of the ADC on the focal plane array results in a total electronic dynamic range of 112 dB. The MRT of the LTC500 camera has been measured at less 0.2 C at fo.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Dynamic range and switching speed limitations of an N/spl times/N optical packet switch based on low-gain semiconductor optical amplifiers

Abstract: Two important system performance limitations-dynamic range and switching speed-of an integrated packet switch fabric based on low-gain semiconductor optical amplifiers (SOA's) have been examined by using cascaded blocks of an SOA model, which includes transient effect, nonlinear pulse distortion effect, and amplified spontaneous emission (ASE) noise. Low-gain SOA's were used to minimize ASE noise considering that no optical filters can be integrated in an SOA-based switch fabric. The system performance with and without a narrowband optical filter at the receiver were both studied. By assuming fixed-wavelength transmitters and no optical filter can be used at the receiving end owing to the unpredictability of arriving packet wavelengths, our simulation results indicate that the dynamic ranges of 4/spl times/4 and 8/spl times/8 SOA-based packet switches at 2.5 Gb/s can only be about 3.2 and 0.8 dB, respectively. However, at 155 Mb/s, even without a receiving-end optical filter, the dynamic range of each switch size can be increased by more than 17 dB as compared to the cases of 2.5 Gb/s. Note that the dynamic ranges were estimated under the conditions of a bit error rate (BER) /spl les/10/sup -9/ and a pulse distortion ratio /spl les/30%. We have also shown that, when an optical filter with a 1 nm bandwidth was used at the receiving end to simulate (1) a circuit-switched condition where the center wavelength of the filter can be adjusted according to the established circuit, or (2) a packet-switched condition where each receiver has a wavelength demultiplexer and a detector array, the dynamic range of 4/spl times/4 and 8/spl times/8 switches can be increased to 16.3 and 14 dB, respectively, at 2.5 Gb/s.

Method and circuit arrangement for adjusting the level or dynamic range of an audio signal

Abstract: The invention relates to a method and a circuit arrangement for adjusting the level and/or dynamic range of an audio signal in a transmission system and particularly in a mobile station. According to the invention, the level of acoustic noise in the environment of a terminal (10, 12) and the level and noise level of a received signal are measured (123) and the level and/or dynamic range of the reproduced signal are adjusted (121, 122) according to the results from said measurements. The solution according to the invention helps reduce the effect of noise in the signal transmitted on the transmission channel (11) and of the acoustic noise in the environment of the terminal (12) on the intelligibility of the reproduced information.

Electrophoresis and fluorescence detection apparatus

Abstract: An improved electrophoresis and fluorescence detection apparatus has an electromagnetic radiation sensor juxtaposed with a sensing region. The output signal from the electromagnetic radiation sensor is a current signal, and the current signal is converted to a voltage signal. The voltage signal is summed with a programmable offset generated by an inexpensive eight-bit D/A converter. The offset signal is selected to establish a lower starting point for the dynamic range of the A/D conversion, and is selected to null some or all of the background electromagnetic radiation level. The summed signal is amplified and integrated in an integrator. The integrator is switchable under program control. The integrator is switched on for long and short intervals. The short intervals permit sensing over a dynamic range accommodating very high levels of fluorescence; very high peaks may be measured and features of the peaks distinguished. The long intervals permit sensing over a dynamic range that is optimized for the peaks associated with the smaller peaks of individual nucleotides. In this way, the dynamic range of the A/D convertor is set to permit the highest possible resolution over the range of interest during the time in which the sequencing of the nucleotides takes place. The sequencer is fast and economical and yields data with high resolution.

Current-mode filters using syllabic companding

Abstract: We discuss current-input current-output signal processors, the voltage state variables of which have a compressed dynamic range thanks to syllabic companding. In this way, for a wide variation of input signals, the internal signals stay well above noise, while at the same time remaining below overload levels. This results in larger dynamic range in comparison to linear processors with the same power dissipation. Theoretical, simulation, and experimental results are given. The circuits presented are an illustration of a general technique for developing nonlinear circuits which are input-output linear.

A novel, sub-harmonic pumping direct conversion receiver with high instantaneous dynamic range

Abstract: A novel sub-harmonic pumping direct conversion receiver (SHP-DCR) employing antiparallel diode pair (APDP) is proposed for high instantaneous dynamic range receivers used in mobile communications. The proposed SHP-DCR can suppress even harmonic mixing products, such as second order intermodulation (IM2) and LO noise that interfere a desired baseband signal. Moreover, the design condition of load resistance is indicated by analytical and experimental approaches for improving diode mixer disadvantages of lower conversion gain and higher LO power. A developed L-band SHP-DCR without a low noise amplifier achieves NF of 18.5 dB, IP3 at input port of 3 dBm and IM2 is below -90 dB in the actual input range.

Multi-bit DAC with noise-shaped element mismatch

Abstract: By a process similar to delta-sigma modulation, the noise caused by static mismatch in a multi-level unit-element DAC can be attenuated in a narrow frequency band. This paper explores the circuit considerations for switched-current and switched-capacitor realizations of the unit-element DAC. The switched-current DAC is found to be relatively simple and capable of high-speed operation. The switched-capacitor circuit is more complex and likely to be somewhat slower, but it is nonetheless robust and provides a simple interface. A dynamic range of 110 dB with a third-order 17-level DAC is expected, even if the DAC elements suffer from 1% mismatch.

Interrogation of low finesse optical fibre Fabry - Pérot interferometers using a four wavelength technique

Abstract: A passive signal processing technique for miniature interferometric sensors is reported It is based on phase stepping techniques and utilizes four adjacent axial modes from a multimode laser diode to provide four phase shifted intensity outputs It is shown that the effects of multiple reflections on the recovered phase are reduced by approximately two orders of magnitude compared to methods employing two and three phase shifted outputs Demultiplexing is accomplished using a monochromator and line scan CCD combined with digital processing Demonstration as a vibration and temperature sensor for a 174 m low finesse fibre Fabry - Perot cavity produced 50 dB dynamic range and 9 mrad sensitivity at 40 Hz, and 70 range and 007 resolution respectively Systematic errors are also discussed

Improvements in or relating to loudspeakers

Abstract: A loudspeaker has a digital input signal port connected to a digital interpolator to increase the effective sampling rate whose output is fed to a signal delay and magnitude detector after which the short-term dynamic range of the input signal is possibly reduced before application to a unary encoder which encodes the digital input signal into a plurality of unary signals which are then differentially delayed and pulse shaped before application to a plurality of substantially identical acoustic transducers via transducer drivers whose average power drive levels may be controlled by signals derived from the magnitude detector and from a human operator to alter the sound volume produced.

A 5 V single-chip delta-sigma audio A/D converter with 111 dB dynamic-range

Abstract: A 5V, 24 bit audio delta-sigma A/D converter has been developed. The single chip integrates stereo delta-sigma modulators, voltage reference and decimation filter. A 4th order cascaded delta-sigma with use of local feedback was employed to improve noise performance.

Test Structures for Characterization and Comparative Analysis of CMOS Image Sensors

Abstract: A set of test structures designed to characterize and compare the performance of CMOS passive and active pixel image sensors is presented. The test structures are deigned so that they can be rapidly ported from one process to another. They are also designed so that individual photodetectors and pixel circuits as well as entire image sensor arrays can be characterized and compared based on: quantum efficiency, spectral response, fixed pattern noise, sensitivity, blooming, input referred read noise, reduction of quantum efficiency caused by silicide/salicide, lag, digital switching noise sensitivity, impact ionization noise sensitivity, dynamic range, and temperature dependency of all measured parameters. Four test chips that include a variety of these structures have been built in two different 0.35 micrometer CMOS processes. The test chips include nineteen types of individual photodetectors and thirty eight types of 64 by 64 pixel arrays. The test methodology and preliminary test results from these chips are presented.

High-resolution digital quadrature detection

Abstract: We illustrate the principles of digital quadrature detection and call attention to its various benefits (ghost‐free spectra and high immunity to low‐frequency interference) and its intrinsic capability of generating data sets with different aliasing behaviors. A function describing the filtering efficiency is introduced, and the digital filters of our detector are compared with their analog counterparts of conventional nuclear magnetic resonance spectrometers. With an appropriate analog‐to‐digital converter (ADC), our digital detector has a dynamic range which is essentially limited by the analog noise, and increases when the spectral bandwidth is reduced. These nearly ideal performances are achieved through dithering, which randomizes the quantization error and oversampling, which reduces the quantization noise in the band of interest. We introduce a ‘‘figure of merit’’ for AD converters which estimates the noise performances of ADCs, and allows to compare products which achieve different compromises between speed and accuracy. The distortions due to the nonlinearities of the ADCs are analyzed through simulations. We find that the majority of the spurious signals (i.e., the errors other than noise) occur outside the band of interest, and are disposed through digital filtering. An unexpected result of the simulation is that, in some circumstances (e.g., large‐scale narrowband dithering), an increase in the number of bits of the ADC may actually reduce the distortion‐free dynamic range. In Sec. VIII we analyze practical problems like the role of the aperture jitter and the selection of the sampling frequency.