Showing papers on "Dynamic range published in 1997"

Wide intrascene dynamic range CMOS APS using dual sampling

Abstract: A CMOS active pixel sensor (APS) that achieves wide intrascene dynamic range using dual sampling is reported. A 64/spl times/64 element prototype sensor with dual output architecture was fabricated using a 1.2 /spl mu/m n-well CMOS process with 20.4 /spl mu/m pitch photodiode-type active pixels. The sensor achieves an intrascene dynamic range of 109 dB without nonlinear companding.

Ultra wideband receiver with high speed noise and interference tracking threshold

Abstract: An UWB receiver utilizing a microwave tunnel diode as a single pulse detector for short pulse, impulse, baseband or ultra wideband signals. The tunnel diode detector's bias point is set at system start-up, through an automatic calibration procedure to its highest sensitivity point relative to the desired bit error rate performance (based upon internal noise only) and remains there during the entire reception process. High noise immunity is achieved through the use of a high speed, adaptive dynamic range extension process using a high speed, Gallium Arsenide (GaAs) voltage variable attenuator (VVA) whose instantaneous attenuation level is determined by a periodic sampling of the ambient noise environment. Microprocessor-controlled detector time-gating is performed to switch the tunnel diode detector to the receiver front end circuitry for reception of an incoming UWB pulse, and alternately to ground through a resistor to discharge stored charge on the tunnel diode detector. In a second embodiment, two tunnel diode detectors are utilized in parallel, one biased for data detection and the other biased for noise detection, such that data detection can be interpreted based on simultaneous comparison to both a data threshold and a noise threshold.

Method and apparatus for area selective exposure adjustment

Abstract: A digital image having a dynamic range representing a brightness in an original scene greater than the dynamic range of an output medium, is processed to fit the dynamic range of the output medium by dividing the image into first and second portions, the first portion of the image representing a brightness range extending from a minimum brightness up to a distance equal to the dynamic range of the output medium, the second portion of the image representing a brightness range extending from a maximum brightness down to a distance equal to the dynamic range of the output medium. First and second transformations are determined for the first and second portions of the image respectively that map the first and second portions onto the dynamic range of the output medium using a exposure determination algorithm of the type used in photographic printers. The digital image is then thresholded at a brightness level that divides the image into a first region having the lowest levels of brightness and a second region having the highest levels of brightness. Finally, the first transformation is applied to the first region of the image and the second transformation is applied to the second region of the image to produce a digital image having a dynamic range that matches the dynamic range of the output medium while maintaining natural contrast within objects in the image.

Use of a charge coupled device camera for low-angle elastic light scattering

Abstract: A charge coupled device (CCD) camera has been successfully used to implement a low-angle elastic light scattering setup. A novel optical detection layout brings all the light scattered by the sample directly onto the CCD, optimizing the instrument sensitivity. The detectable angular range covers ∼2 decades, from ∼0.1° to ∼10°. The calibration of the instrument, as well as the estimate of its sensitivity, accuracy, dynamic range and linearity, can be carried out by using single pinholes. Experimental results from pinholes and diluted suspensions of polystyrene spheres are presented.

Thermoelectric power sensor for microwave applications by commercial CMOS fabrication

Abstract: This work describes an implementation of a thermoelectric microwave power sensor fabricated through commercial CMOS process with additional maskless etching. The sensor combines micromachined coplanar waveguide and contact pads, a microwave termination which dissipates heat proportionally to input microwave power, and many aluminum-polysilicon thermocouples. The device was designed and fabricated in standard CMOS technology, including the appropriate superimposed dielectric openings for post-fabrication micromachining. By removing the bulk silicon located beneath the device through micromachining, thermal and electromagnetic losses are minimized. The sensor measures signal true RMS power in the frequency range up to 20 GHz with input power in the -30 dBm to +10 dBm range. Over this 40 dB dynamic range, output voltage versus input power is linear within less than /spl plusmn/0.16%. Automatic network analyzer data show an acceptable input return loss of less than -30 dB over the entire frequency range.

CCD camera with adaptive compression control mechanism

Abstract: A charge coupled device (CCD) camera includes a CCD imager circuit, a compression engine, and a control circuit coupled to both the CCD imager circuit and the compression engine. The CCD imager circuit is characterized by an integration time defined by clock pulses from the control circuit. The compression engine generates successive frame requests. The control circuit generates the clock pulses to define the integration time based on a time between the sucessive frame requests. The camera further includes a histogram accumulator and an automatic gain controlled (AGC) amplifier coupled between the CCD imager circuit and the histogram accumulator. The CCD imager circuit is characterized by a predetermined maximum imager dynamic range and generates successive frames of imager data values, each successive frame of imager data values being characterized by an imager data value dynamic range and each frame of imager data values being generated based on a corresponding integration time. The AGC amplifier is characterized by an AGC gain defined by a gain control signal and characterized by a maximum output dynamic range. The AGC amplifier processes the successive frames of imager data values into corresponding successive frames of gain controlled data values, each successive frame of gain controlled data values being characterized by a gain controlled data value dynamic range. The histogram accumulator processes a first frame of gain controlled data values to determine a first frame result. The control circuit generates the clock pulses based on the first frame results to define the integration time that corresponds to a second frame of imager data values so that the integration time is maximized while the imager data value dynamic range is less than the maximum imager dynamic range, and the control circuit further generates the gain control signal based on the first frame results and the maximum imager dynamic range to minimize the AGC gain required so that the gain controlled data value dynamic range is equal to a predetermined range within the maximum output dynamic range.

Multiresolution image sensor

Abstract: The development of the CMOS active pixel sensor (APS) has, for the first time, permitted large scale integration of supporting circuitry and smart camera-functions on the same chip as a high-performance image sensor. This paper reports on the demonstration of a new 128/spl times/128 CMOS APS with programmable multiresolution readout capability. By placing signal processing circuitry on the imaging focal plane, the image sensor can output data at varying resolutions which can decrease the computational load of downstream image processing. For instance, software intensive image pyramid reconstruction can be eliminated. The circuit uses a passive switched capacitor network to average arbitrarily large neighborhoods of pixels which can then be read out at any user-defined resolution by configuring a set of digital shift registers. The full resolution frame rate is 30 Hz with higher rates for all other image resolutions. The sensor achieved 80 dB of dynamic range while dissipating only 5 mW of power. Circuit error was less than -34 dB and introduced no objectionable fixed pattern noise or other artifacts into the image.

A Two-Path Bandpass Modulator for Digital IF Extraction at 20 MHz

Abstract: Oversampled bandpass A/D converters based on sigma-delta modulation can be used to robustly digitize the types of narrowband intermediate frequency (IF) signals that arise in radios and cellular systems. This paper proposes a two- path architecture for a fourth-order, bandpass modulator that is more tolerant of analog circuit limitations at high sampling speeds than conventional implementations based on the use of switched-capacitor biquadratic filters. An experimental prototype employing the two-path topology has been integrated in a 0.6- m, single-poly, triple-metal CMOS technology with capacitors syn- thesized from a stacked metal structure. Two interleaved paths clocked at 40 MHz digitize a 200-kHz bandwidth signal centered at 20 MHz with 75 dB of dynamic range while suppressing the undesired mirror image signal by 42 dB. At low input signal levels, the mixing of spurious tones at dc and /2 with the input appears to degrade the performance of the modulator; out- of-band sinusoidal dither is shown to be an effective means of avoiding this degradation. The experimental modulator dissipates 72 mW from a 3.3-V supply.

Programmable dynamic range receiver with adjustable dynamic range analog to digital converter

Abstract: A programmable dynamic range receiver which provides the requisite level of performance at reduced power consumption. The ΣΔ ADC within the receiver is designed with one or more loops. Each loop provides a predetermined dynamic range performance. The loops can be enabled or disabled based on the required dynamic range and a set of dynamic range thresholds. The ΣΔ ADC is also designed with adjustable bias current. The dynamic range of the ΣΔ ADC varies approximately proportional to the bias current. By adjusting the bias current, the required dynamic range can be provided by the ΣΔ ADC with minimal power consumption. A reference voltage of the ΣΔ ADC can be descreased when high dynamic range is not required, thereby allowing for less bias current in the ΣΔ ADC and supporting circuitry. The dynamic range of the ΣΔ ADC is a also function of the oversampling ratio which is proportional to the sampling frequency. High dynamic range requires a high oversampling ratio. When high dynamic range is not required, the sampling frequency can be lowered.

Error analysis in acoustic elastography. II. Strain estimation and SNR analysis.

Abstract: Accurate displacement estimates are required to obtain high-quality strain estimates in elastography. In this paper the strain variance is derived from the statistical properties of the displacement field to define a point signal-to-noise ratio for elastography (SNR0). Displacements caused by compressional forces applied along the axis of the transducer beam are modeled by scaling and shifting the axial reflectivity profile of the tissue. The strain variance is given as a function of essential experimental parameters, such as the amount of tissue compression, echo waveform window length, and the amount of window overlap. SNR0 is defined in terms of applied compression and strain variance and normalized by the input signal-to-noise ratio (SNRi) for echo signals, to formulate the performance metric SNR0/SNRi. This quantity characterizes the noise properties, dynamic range, and sensitivity of strain images based on the spatial resolution requirements. The results indicate that low noise, high sensitivity, and limited dynamic range strain images are obtained for high-frequency bandpass signals when the applied strain is small. For large strains, however, one strategy for low-noise strain imaging employs base-band signals to obtain images with large dynamic range but limited peak sensitivity and noise figure. A better strategy includes companding, which eliminates the average strain in the echo signal before cross-correlation to reduce the dynamic range requirement and increase peak sensitivity for strain estimates.

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

Abstract: A 5-V 24-b audio delta-sigma A/D converter has been developed. The single chip integrates stereo delta-sigma modulators, a voltage reference, and a decimation filter. A fourth-order cascaded delta-sigma modulator using a local feedback technique was employed to avoid overload without sacrifice in noise performance. A two-stage decimation filter architecture which reduces digital noise was developed. A new multistage comb filter was used for the first-stage, and a bit-serial finite impulse response (FIR) filter was used for the second stage. The 25.8 mm/sup 2/ chip was fabricated in 0.7-/spl mu/m CMOS with low threshold MOS devices. Measured results show 111 dB dynamic range and 103 dB peak signal-to-(noise plus distortion)S/(N+D).

System, device, and method for evaluating dynamic range in a communication system

Abstract: A system, device, and method for evaluating dynamic range in a communication system utilizes a narrow band multiple tone test signal for emulating a wide band composite signal equivalent to the symbol rate bandwidth of a digitally modulated carrier. The multiple tone test signal is constructed such that a significant portion of the third order intermodulation distortion products fall within the channels adjacent to the test channel so that the dynamic range can be evaluated with a commercially available industry standard CATV analyzer using a standard adjacent channel power measurement technique.

Application of Bragg grating sensors in the characterization of scaled marine vehicle models

Abstract: Experiments using two different fiber-optic Bragg grating strain sensor systems to measure dynamic loads, slamming forces, and bending moments on a scaled catamaran model are reported. The system designed to measure slamming forces is based on dynamic locking of the laser diode wavelength to the peak wavelength of a Bragg grating mounted in a force cell. The sensor system has a dynamic range of 27 dB (1-550 N) and a bandwidth in excess of 1 kHz. For the measurement of bending moments, a time-domain multiplexing system, which used a unique pulsed rf modulation technique, of two Bragg grating sensors mounted on a steel beam was designed. The dynamic range of this system was also 27 dB [17 Nm (Newton meter) with a 0.03-Nm resolution]. The bandwidth was limited to approximately 50 Hz.

System and method for enhancing dynamic range in images

Abstract: A system and method of enhancing dynamic range in images is disclosed that increases the contrast in the resulting image without requiring an increase in the dynamic range of the analog-to-digital converter used to convert the analog image signals to digital information The system and method disclosed achieve this advantageous result by providing per-pixel gain control circuitry and per-pixel gain selection circuitry The analog image signal range is segmented into a number (N) of multiple levels, where N is selected to be the desired level of enhancement Multiple analog gain (G1) levels and multiple digital gain (G2) levels are also provided The analog gain (G1) is selected for each image pixel based upon the segment in which that pixel falls so that the signal levels may be increased for each segment to utilize the full range (R) of the analog-to-digital converter Once digitized, a digital gain (G2) is selected for the same pixel so that on a per-pixel basis, the total gain (G1*G2) is kept substantially constant In this way, the dynamic range of the system is increased without needing to increase the dynamic range of the ADC The resulting digital information is enhanced by (Log 2 N) bits, and it may be companded down into a smaller bit range for a video output device by any desired transfer function during digital signal processing

A multichannel compression strategy for a digital hearing aid

Abstract: Multi-channel compression schemes are a practical methods of mapping the wide dynamic range of speech signals into the reduced dynamic range of hearing impaired listeners. These systems address two of the shortcomings of single-channel compression systems: (1) the reduction of gain as a result of narrow-band non-speech stimuli and (2) the reduction of gain that often occurs when high-frequency speech components are followed by intense low-frequency speech components. They also provide frequency-dependent compression ratios that are needed by many newer supra-threshold fitting strategies (e.g., DSL I/O). This paper presents a multichannel compression scheme that employs an oversampled, polyphase DFT filterbank. In each compressor channel, the gain is controlled by an adjustable combination of a overall, dual time-constant input signal level and the individual channel signal level that is measured with a short time-constant RMS detector. Informal listening tests have demonstrated that the design has very good audio quality and performs well in real-world listening situations. The design is suited for low-power, real-time operation.

The multitap lock-in CCD with offset subtraction

Abstract: An image sensor for the two-dimensional (2-D) synchronous detection of temporal properties of modulated optical wave fields is presented. Each pixel of this multitap lock-in CCD is capable of acquiring all optical data for the extraction of modulation amplitude, relative phase, background level, and higher order Fourier coefficients. By employing the pixels' offset subtraction stages, a dynamic range of >100 dB was obtained experimentally.

Bias-free high-dynamic-range phase-modulated fiber-optic link

Abstract: Bias-free optical phase demodulation using an optical delay line filter is analyzed and experimentally demonstrated. A spur-free dynamic range of 114 dB/Hz/sup 2/3/ is measured at a frequency of 12.5 GHz using optical carrier suppression. The method is shown to have the same dynamic range, noise figure, and link gain compared to a Mach-Zehnder link over a limited bandwidth.

The source-gated amorphous silicon photo-transistor

Abstract: We discuss the effect of scaling the thickness of the a-Si:H layer on the performance of photo-transistors. We show that reducing the a-Si:H layer thickness to 0.05 /spl mu/m, in order to increase the speed of pixel-switching thin-film transistors (TFTs), causes a large drop in the photo-transistor's dynamic range. We then propose, fabricate and test the Source-Gated Photo-Transistor, a new a-Si:H photo-transistor which allows the use of thin a-Si:H layers while boosting the dynamic range of the phototransistor. Our experimental results show that the source-gated photo-transistor improves the dynamic range of photo-transistors with thin a-Si:H layers (0.05 /spl mu/m) by more than 30 times. This increased dynamic range is obtained by increasing the illumination current and reducing the dark current. Illumination current is improved by doubling the optical path and increasing the photo-generated carriers lifetime within the a-Si:H layer. Dark current is reduced by pinning the gap-region to a constant potential. Finally, we confirm the principle of photo-generated carriers separation in our source-gated photo-transistor by conducting optical and bias stress measurements on conventional and source-gated photo-transistors.

Instrumental Resolution Considerations for Fourier Transform Infrared Gas-Phase Spectroscopy

Abstract: Instrumental resolution has a significant effect on the performance of Fourier transform infrared (FT-IR) spectrometers used for gasphase analysis. Low-resolution FT-IR spectroscopy offers some valuable advantages compared with the traditional high-resolution FT-IR gas-phase spectroscopy, especially in nonlaboratory environments. First, high signal-to-noise ratio (SNR) spectra can be acquired in field conditions without the use of traditional liquid nitrogen-cooled detectors. Second, the dynamic range for quantitative analysis is larger for low-resolution spectroscopy than for high-resolution due to the lower absorbance values and lower noise levels. Third, spectral analysis speed is increased and data storage requirements are substantially reduced. The purpose of this study was to investigate the effect of instrumental resolution on FT-IR gas-phase analysis. The effects of spectral resolution on sensitivity, selectivity, accuracy, precision, spectral overlap, dynamic range, and nonlinearity are separately discussed.

Intensified CCD (ICCD) dynamic range and noise performance

Abstract: This paper presents recent experimental and theoretical results regarding the dynamic range and noise performance of ICCD cameras which use micro-channel plate (MCP) image intensifiers. Vendor specifications for image intensifiers using these devices suggest that the noise factor is in the range of 1.6 to 2.2 for Gen II intensifiers and 3.5-4.2 for Gen III intensifiers which use filmed MCPs to extend the GaAs photo cathode lifetime. Our experimental results suggest that the ICCD noise factor increases dramatically as the gain is reduced to accommodate higher background light levels. Noise factors in excess of 60 have been observed. For most applications where the MCP is operated at high gain, this behavior is never encountered. However, for applications which use the MCP as a low-gain device, such as active laser range-gated systems operated in high background reflectance conditions, the imaging performance can be severely degraded. A model for the gain dependent ICCD noise factor has been developed which will be compared with the experimentally observed effects. Keywords: Micro-channel Plate, MCP, Noise Factor, Intensified CCD, ICCD, Dynamic Range, Range-Gating, Laser LineScan.

Method and apparatus for high efficiency high dynamic range power amplification

Abstract: A method and apparatus for efficient power amplification of a high dynamic range signal includes an envelope detector (220), a multi-range modulator (270), and a power amplifier (260). The multi-range modulator (270) efficiently amplifies the envelope of the input signal by selecting a power source as a function of the amplitude of the input signal. Multi-range modulator (200) produces a pulsewidth modulated signal with a duty cycle and an amplitude. When the amplitude of the input signal rises above a reference, the duty cycle and the amplitude are modified so as to keep the multi-range modulator in an operating region of high efficiency.

Multi-anode time to digital converter

Abstract: An apparatus (82) for extending the dynamic range of a data acquisition. Multiple anode detectors (80) and microchannel plates (83) are used to increase the dynamic range of a time-to-digital converter (82). Multiple anodes (80) determine characteristics of a signal without distortion which normally occurs with large signals, or obscuring by noise which normally occurs with small signals. The data from the multi-anode detectors (80) can be summed during selectable time frames (100, 102) and made multiple bit words.

Dynamic range expanding apparatus of a video image

Abstract: The present invention relates to a dynamic range expanding apparatus. The dynamic range expanding apparatus realizes a wide dynamic range for a video image while reducing the quantization noise, by determining the brightness transform function based on the combined results of the differential and the integral operation with respect to a brightness distribution function. Moreover, the dynamic range expanding apparatus transforms the color difference signal by using the brightness transform ratio without losing the valance in a color tone.

Noise Sources in Step-Scan FT-IR Spectrometry

Abstract: Step-scan Fourier transform infrared (FT-IR) spectrometry has been accepted as a useful tool for obtaining vibrational spectra of a variety of time-dependent systems. Unfortunately, a significant signal-to-noise ratio (SNR) disadvantage has been associated with the step-scan mode of data collection relative to the same data collection time with conventional rapid-scan FT-IR spectrometry. The key difference between the two methods is the average mirror velocity, which alters the dynamic range of the detector signal, as well as the frequencies of its components. The SNR disadvantage is shown to be related to low-frequency multiplicative fluctuations, caused in part by temperature variations, which convolve noise with measured spectra. Refractive index variations of air or purge gas in the paths of the infrared- and reference-laser radiation can be a particularly serious temperature-induced problem. The various noise sources are described, and experiments confirming that some are related to temperature variations are reported.

A 1.2 V BiCMOS class AB log-domain filter

Abstract: Companding improves dynamic range in situations with restricted signal swing, such as in low-voltage circuits, without the need to reduce noise at the cost of increased power dissipation. The log-domain filter principle achieves instantaneous signal companding by taking advantage of exponential device characteristics. Thanks to the high compression ratio, voltage swing and frequency tuning become almost independent of supply voltage, which can be reduced to the minimum required for proper operation. The combination of instantaneous companding with class AB operation permits processing of signals much larger than the bias level and hence increases dynamic range substantially. Class AB log-domain filters are suited to low-voltage and low power applications with moderate signal-to-noise ratio (SNR) and linearity requirements. The authors present a 3/sup rd/-order Chebyshev filter which is based on an integrator and implemented in a 1 /spl mu/m BiCMOS process. The filter can be tuned over more than 3 decades with cut-off frequencies ranging from 10 kHz to 15 MHz at supply voltages between 0.9 V and 2 V. For a 1.2 V supply, cut-off frequencies up to about 1 MHz are achieved.

Large-scale interferometric fiber sensor arrays with multiple optical amplifiers

Abstract: We report what we believe to be the first laboratory prototype of a fiber sensor array using multiple low-gain (5dB) remotely pumped amplifiers in a 10-rung ladder structure. Incorporating amplifiers improves the system noise figure to less than 20dB, compared with 32dB in an optimized passive array of the same size. Scalability to more than 300sensors per fiber pair while a high dynamic range (1microrad/ sensitivity) is maintained is demonstrated.

Improving the Dynamic Range of Real-Time X-Ray Imaging Systems via Bayesian Fusion

Abstract: The performance and reliability of detecting flaws using X-ray techniques are largely conditioned by the dynamic range of the real-time X-ray imaging systems. This paper proposes a software solution to the problem of dynamic range improvement. The idea is to acquire two images of the same object under two different acquisition conditions, and to integrate these two images in order to obtain a more accurate range measurement of signal levels. To do this, a data fusion technique is developed that is based on the Bayesian theory. The Bayesian fusion method is illustrated with the aid of both simulations and examples on real images. The study demonstrates the possibility of improving significantly the dynamic range of real-time X-ray imaging systems using data fusion techniques.

Dynamic range of Ronchi test with a phase-shifted sinusoidal grating.

Abstract: The dynamic range of a Ronchi test with a phase-shifted sinusoidal grating was investigated theoretically and experimentally As the number of fringes in a Ronchi interferogram increases, the fringe visibility decreases, which results in a decrease of phase-measurement resolution It is shown that in order to optimize the dynamic range the effective wavelength of the interferogram should be tuned to the characteristic wavelength of the object wave front The maximum dynamic range achievable is estimated to be 16 times larger than that of a Fizeau interferometer Suppressing higher-order diffraction components has achieved sheared interferograms with a signal-to-noise ratio in excess of 60:1 The effects of nonsinusoidal transmittance of the grating and the phase-shift errors were minimized by a seven-sample phase-shifting algorithm, and a phase measurement uncertainty of less than 1/700 has been achieved

Improving the range/time sidelobes of large bandwidth discontinuous spectra HF radar waveforms

Abstract: Due to heavy user congestion, many over-the-horizon (OTH) HF radars are restricted to operating within narrow frequency bands. As a result the achievable range resolution with such radars is poor. In order to operate a wideband HF radar, the signal spectrum must be made discontinuous, which gives rise to high range sidelobes and thus a low signal dynamic range. We introduce a new signal processing technique to lower the range sidelobes associated with discontinuous spectra signals. Results are presented for a repeated linear FM test case and show significant range sidelobe reduction using the new algorithm.