Showing papers on "Dynamic range published in 1995"

Extended depth of field through wave-front coding

Abstract: We designed an optical‐digital system that delivers near-diffraction-limited imaging performance with a large depth of field. This system is the standard incoherent optical system modified by a phase mask with digital processing of the resulting intermediate image. The phase mask alters or codes the received incoherent wave front in such a way that the point-spread function and the optical transfer function do not change appreciably as a function of misfocus. Focus-independent digital filtering of the intermediate image is used to produce a combined optical‐digital system that has a nearly diffraction limited point-spread function. This high-resolution extended depth of field is obtained through the expense of an increased dynamic range of the incoherent system. We use both the ambiguity function and the stationary-phase method to design these phase masks.

New digital detector for projection radiography

Abstract: The operational principle of a new, patented digital radiographic system using a multi-layer structure consisting of a thin-film pixel array, selenium x-ray photoconductor, dielectric layer and top electrode is described. Under an applied electric field, a diagnostic x-ray signal is obtained by the direct conversion of x-ray energy to electron-hole pairs which are collected as electrical charges by individual storage capacitor associated with each pixel element. The electronic readout sequence is initiated immediately after the x-ray exposure, and in several seconds, the image data is available for display on a video monitor, for data storage, data transmission, and hard copy generation. Signal strength of this direct conversion method is estimated to be significantly higher than that of other indirect conversion methods where light is first generated using a scintillator or phosphor and then detected by charge-coupled devices (CCDs) or thin-film-transistor (TFT) arrays in conjunction with photodiodes. In addition, since charges generated by x-ray photons move mostly along the direction of the bias electric field, images of very high spatial resolution can be obtained. The resolution limits are principally defined by the smallest pixel that can be manufactured. Recent x-ray images obtained from experimental detector panels are presented. X-ray sensitivity, dynamic range, signal-to-noise ratio, and spatial resolution are discussed.

A high resolution multibit sigma-delta modulator with individual level averaging

Abstract: A second-order sigma-delta modulator with a 3-b internal quantizer employing the individual level averaging technique has been designed and implemented in a 1.2 /spl mu/m CMOS technology. Testing results show no observable harmonic distortion components above the noise floor. Peak S/(N+D) ratio of 91 dB and dynamic range of 96 dB have been achieved at a clock rate of 2.56 MHz for a 20 kHz baseband. No tone is observed in the baseband as the amplitude of a 10 kHz input sine wave is reduced from -0.5 dB to -107 dB below the voltage reference. The active area of the prototype chip is 3.1 mm/sup 2/ and it dissipates 67.5 mW of power from a 5 V supply. >

Deemphasis and subsequent reemphasis of high-energy reversed-spectrum components of a folded video signal

Abstract: A system for reproducing a luminance signal from a medium containing a previously recorded luminance signal with a high-frequency portion thereof compressed in dynamic range includes a circuit for recovering that luminance signal from the medium. Filtering is done to separate the low-frequency and compressed-in-dynamic-range high-frequency portions of the recovered luminance signal from each other. A corer responds to the separated compressed-in-dynamic-range high-frequency portion of the recovered luminance signal to provide a cored high-frequency portion with expanded dynamic range and reduced noise. The level of the cored high-frequency portion with expanded dynamic range and reduced noise is then boosted by a predetermined amount to compensate for energy losses during the compression of the dynamic range and added back to the low-frequency portion of the recovered luminance signal to reproduce a full-band luminance signal with at least partially restored dynamic range for high-frequencies and without readily visible high-frequency noise.

The effects of switching noise on an oversampling A/D converter

Abstract: This paper presents the results of an experimental study of the effects of switching noise in a high-resolution oversampling /spl Sigma//spl Delta/ modulator. An experimental test circuit emulates the embedding of such a modulator in the same substrate as a large amount of active digital circuitry. The modulator is a third-order cascade comprising a second-order /spl Sigma//spl Delta/ stage followed by a first-order stage, both employing 1 b quantisation. A 1 /spl mu/m CMOS implementation of this design provides a dynamic range of more than 100 dB at digital audio bandwidths.

An instantaneous response CMOS optical receiver IC with wide dynamic range and extremely high sensitivity using feed-forward auto-bias adjustment

Abstract: An instantaneous response CMOS optical-receiver IC is described with wide input dynamic range and high sensitivity. In a TCM (time compression multiplexing)-TDMA (time division multiple access) fiber-optic subscriber system, a receiver should be able to handle burst-data packets with different amplitude. This requires quick response and a wide dynamic range. Instantaneous response is achieved with a new feed-forward auto-bias adjustment technique. In addition, multistaged offset compensation provides a wide dynamic range without any external elements and adjustments. Using these design techniques, an optical receiver IC was fabricated in a standard 0.8-/spl mu/m CMOS technology. The receiver has a wide dynamic range of more than 25 dB for burst-mode optical input at 29 Mb/s. It has high transimpedance gain of 150 dB/spl Omega/ and high sensitivity of -42 dBm with stable operation for FET threshold voltage and power supply voltage fluctuation. >

Adaptive gamma processing of the video cameras for the expansion of the dynamic range

Abstract: The authors have developed a new method for the expansion of the dynamic range of a video camera. A variable and nonlinear gamma characteristic is applied to the input image depending on the distribution of the luminance. The gamma characteristic is decided so as to amplify the luminance of the dark pixels and to preserve the contrast of the bright pixels for the back-lit objects. The output luminance equals the input luminance for the front-lit objects. The authors have established the decision rule of the gamma characteristic using the learning algorithms of the neural networks in order to make the decision rule coincide with the human vision. The effect of the new method is expansion of the dynamic range by 9.6 dB. The authors have developed a new structure for the implementation of the gamma decision rule. It consists of a cascade connection of RAMs and its scale is less than 1/100 than the conventional structure with a single RAM. They have implemented the adaptive gamma processing in a consumer video camera. >

Frequency-domain measurement of the millimeter wave indoor radio channel

Abstract: Coherent wideband frequency-domain measurements of the complex frequency response of millimeter wave indoor radio channels are discussed. In addition, results of measurements performed in a 2 GHz band centered around 58 GHz will be presented. It is shown that a 40 dB dynamic range and a 400 ns aliasing-free range are sufficient for a correct estimation of the rms delay spread from the measurement data. >

A 1 GHz CMOS RF Front-End IC with Wide Dynamic Range

Abstract: A 1 GHz Low Noise Amplifier and Mixer combination has been integrated in a standard 1?m CMOS process. The circuit is matched to 50? at the input, and drives a 50? load. Overall conversion gain is 22 dB, noise figure is 3.5 dB, and the IIP3 of the combination is +12 dBm. The fully balanced circuit drains 8 mA from 3V.

Amorphous Silicon Three Color Detector

Abstract: Band gap and defect engineered amorphous silicon based nipin photo diodes with bias controlled spectral response have been fabricated successfully. The devices exhibit good linearity over a wide illumination range and linearly independent spectral response curves which are required to generate a standard RGB-signal. In the bias range from -1.5 V to 1.5 V a dynamic range exceeding 90 dB for two color sensors and 80 dB for three color sensors has been observed. The general operation principle of the multispectral photo diode is discussed using a numerical simulation program. The model describes the defect state distribution of dangling bonds according to the defect-pool model and uses coherent wave propagation in the device to calculate the profile of photo generated carriers. Additionally, an analytical model has been developed to be included into standard circuit simulation programs like SPICE (Simulation Program with Integrated Circuit Emphasis). The analytical model uses linear field approximations in both i-layers of the device.

Staring IR-FPA with on-FPA adaptive dynamic range control electronics

Abstract: An adaptive dynamic range control circuit architecture is disclosed that enables an IR-FPA (10) to achieve a higher dynamic range. The circuit architecture significantly reduces a resolution required for an analog-to-digital converter (ADC 24) that converts the analog output signals of the IR-FPA to a digital representation. In a preferred embodiment of this invention a column CTIA readout integrated circuit architecture is used in conjunction with the adaptive feedback circuitry of this invention to provide pedestal suppression on a per-pixel basis for the IR-FPA. The use of the circuitry of this invention modifies the conventional column CTIA amplifier configuration to a configuration having an auto-zeroed charge ratioed gain stage (50). One advantage to this technique is that by suppressing the charge pedestal, the usable signal output from the IR-FPA can be brought off-chip to the readout integrated circuit at a much higher gain. As a result, the ADC requires fewer bits to resolve the useable signal information and dynamic range.

Method and apparatus for adjusting dynamic range and gain in an encoder/decoder for multidimensional sound fields

Abstract: An audio encoder/decoder system suitable for digital motion picture film soundtracks provides for adjusting playback signal gain and dynamic range by modifying the scale factors of scaled spectral information. In one embodiment of a transform coding system, transform coefficients are expressed in floating-point form and adjustments are made by modifying the exponents in the floating-point representation.

Improving the dynamic range of a coherent AM analog optical link using a cascaded linearized modulator

Abstract: An AM coherent analog optical link is experimentally demonstrated to achieve the highest spurious-free dynamic range reported to date for a coherent system by employing a linearized cascaded electro-optic modulator. The link gives a spurious-free dynamic range of 115 dB/spl middot/Hz/sup 2/3/, with a 34-dB reduction in third-order intermodulation distortion over conventional Mach-Zehnder modulators. With the linearized modulator, our experimental results are just 3 to 6 dB away from the fundamental limit of this link; the remaining penalty is mainly due to RF components. >

Technique for determining a compression ratio for use in processing audio signals within a telecommunications system

Abstract: A "loudness balance" procedure is used to determine the amount of dynamic range for syllabic compression loss in an individual's cochlea. In particular, an individual is asked to adjust a set of tone volumes, which are played to them, until the tone volumes sound equally loud. Based on the adjustments performed by the individual, a compression ratio is determined for that individual over at least one frequency band. The determined compression ratio is then subsequently used by a telecommunications system to provide an individual-specific sound enhancement in a telephone call. As a result, the individual-specific sound enhancement particularly compensates for an amount of hearing loss unique to that individual.

Electronic subtracter for trace-gas detection with InGaAsP diode lasers

Abstract: An electronic noise-cancellation scheme has been developed and tested for second-harmonic (2f) detection with short-external-cavity and distributed-feedback InGaAsP diode lasers and wavelength modulation. The 2f background signal and noise from, e.g., optical feedback, optical fringes, and power-supply pickup are effectively reduced by subtraction of a measure of the signal-beam photocurrent from a measure of the reference-beam photocurrent. The dynamic range required for the lock-in amplifier is also reduced because the signal owing to modulation of the laser output at the first harmonic is canceled. Reduction of the 2f background and dynamic range are important for atmospheric-pressure detection where a large wavelength modulation is necessary. The detector noise was minimized by the use of zero-biased detectors in the subtraction circuit. A beam-noise level (defined as 2× the rms value) equivalent to a line-center absorption of 1.6 × 10−6 was achieved with an equivalent-noise bandwidth of 1.25 Hz for 2f detection at 10 kHz. The electronic circuit is easy to construct and low cost.

Efficient linearisation of sigma-delta modulators using single-bit dither

Abstract: Idle tones and noise modulation in higher-order sigma-delta modulators (SDMs) can be eliminated using single-bit dither signals, with no additional reduction in dynamic range compared to multilevel dither signals. Unlike multilevel dither, single-bit dither is easily implemented in sigma-delta analogue-to-digital converters (ADCs).

A 22-kHz multibit switched-capacitor sigma-delta D/A converter with 92 dB dynamic range

Abstract: A time- and capacitor-multiplexing technique for use in a highly linear switched-capacitor multibit DAC in sigma-delta data converters is presented. The technique uses subintervals in the sample clock to deliver multiple charge packets to holding capacitors. It avoids distortion effects caused by mismatched capacitors and finite opamp gain. A five-level switched-capacitor DAC using the proposed technique was designed as part of an audio-band multibit sigma-delta D/A converter that achieved a dynamic range of 92 dB and a THD of -93 dB with a low oversampling ratio of 32. No trimming, calibration, or dynamic matching scheme was required. The five-level SC DAC has been fabricated in a 2-/spl mu/m CMOS process, and testing confirmed the anticipated theoretical results.

Optical time domain reflectometer (OTDR) with improved dynamic range and linearity

Abstract: This invention relates to a method and an apparatus for performing exceptionally linear averaging of digitized signals in an optical time domain reflectometer. Resolutions far below the quantization level of the ADC with improved linearity can be achieved without sacrificing dynamic range. Such method can be used to improve measurement accuracy on optical fibers under test.

256 x 256 CMOS active pixel image sensor

Abstract: A 256 X 256 CMOS photo-gate active pixel image sensor is presented. The image sensor uses four MOS transistors within each pixel to buffer the photo-signal, enhance sensitivity, and suppress noise. The pixel size is 20 micrometers X 20 micrometers and was implemented in a standard digital 0.9 micrometers single-polysilicon, double-metal, n-well CMOS process; leading to 25% fill-factor. Row and column decoders and counters are monolithically integrated as well as per column analog signal correlated double-sampling (CDS) processors, yielding a total chip size of approximately 4.5 mm X 5.0 mm. The image sensor features random accessibility and can be employed for electronic panning applications. It is powered from a single 5.0 V source. At 5.0 V power supply, the video signal saturation level is approximately 1,200 mV with rms read-out noise level of approximately 300 (mu) V, yielding a dynamic range of 72 dB (12 bits). The read-out sensitivity is approximately 6.75 (mu) V per electron, indicating a read-out node capacitance of approximately 24 fF which is consistent with the extracted value. The measured dark current (at room temperature) is approximately 160 mV/s, equivalent to 3.3 nA/cm 2 . The raw fixed pattern noise (exhibited as column-wise streaks) is approximately 20 mV (peak-to-peak) or approximately 1.67% of saturation level. At 15 frames per second, the power dissipation is approximately 75 mW.

A second generation charge integrator and encoder ASIC

Abstract: A second generation charge integrator and encoder ASIC (QIE5) has been designed for the KTeV experiment at Fermilab. It is intended to be used in conjunction with a FADC (typically eight bits) to digitize photomultiplier tube (PMT) current pulses at a fast rate, with variable resolution over a 16 bit dynamic range. QIE5 integrates pulses of up to 30 ma peak on eight nonoverlapping binary scaled ranges. A system clock of up to 53 MHz controls the integration period and readout rate. The device is pipelined so that there is no signal deadtime. For each clock period, one range is selected depending on the signal magnitude, and the output of that range is routed to the QIE5 analog output and fed to the FADC to form the mantissa. The selected range is encoded and output as a three bit digital exponent. With this method, the measurement resolution is a relatively constant fraction of the signal over a large dynamic range. Previous reports have described a single ended device (QIE2) which had inherent limitations. The QIE5 is a fully differential design and contains numerous other features which provide significant performance improvements. The new design philosophy and test results are presented for the first time.

Charge sensitive preamplifier and pulse shaper using CMOS process for germanium spectroscopy

Abstract: The authors have developed a low noise, low power charge sensitive amplifier and pulse shaping circuit. The application is for a double-sided germanium strip detector, nominally providing 50 independent spectroscopy channels. An array of these detectors would provide significant improvements in imaging, spectroscopy and sensitivity for space-based gamma-ray astronomy. The key features of these electronics are low noise, very low power, and a small footprint per channel. Performance of the first circuit is in good agreement with simulations, with /spl sim/205e noise rms (0 pF), and 3 mW/channel power consumption. The dynamic range is 0-3.3 MeV (germanium) with a linearity of /spl plusmn/0.6%. Performance of this prototype device is discussed. >

Multi-octave, high dynamic range operation of low-biased modulators by balanced detection

Abstract: An optical link is disclosed that is operated by a balanced detection technique so as to extend its linear dynamic range, yet substantially eliminate even-order harmonic distortion of the modulated signal. The modulator comprises two parallel arranged Mach-Zehnder interferometers that respectively have a steady state DC voltage bias applied so that the operating points of the Mach-Zehnder interferometers are selected to produce two separate modulated signals, one of which is later phase shifted by a phase shift device so as to provide an output that is combined with the other modulated signal in such a manner so as to cause a subtraction, leaving the final output signal substantially free of any unwanted even-order harmonic components in order to provide for a multi-octave response characteristic.

Introduction to high performance CCD cameras

Abstract: Scientific grade, cooled, charge coupled devices (CCDs) combined with low noise electronic design has redefined the scope of quantitative light imaging. Successful application of this technology requires a basic understanding of CCD camera operation. A brief introduction to CCD camera technology is provided as an aid to investigators interested in quantitative light measurement. Parameters used to characterize camera performance, full-well capacity, dynamic range, read noise, dark current, and linearity are defined.

A radio receiver for processing a multi-carrier signal with a large dynamic range

Abstract: A radio receiver front end is disclosed that processes a multi-carrier signal with a large dynamic range. An illustrative embodiment of the present invention incorporates both feedforward (232) and feedback (240) mechanisms to suppress the amplitude of spurious carrier signals so as to prevent those signals from flooding the dynamic range of the mixer that mixes down the multi-carrier signal.

Fiber-optic microphone based on a combination of Fabry-Perot interferometry and intensity modulation

Abstract: A fiber‐optic microphone based on a combination of Fabry–Perot interferometry and intensity modulation is described. The combination technique eliminates fringe counting ambiguity and provides a wide range measurement of optical phase change without any complicated electromechanical devices. The experimental data are compared with the result of a theoretical analysis. The microphone has a flat frequency response from 20 Hz to 10 kHz with a high sensitivity of 1.6 rad/Pa. The dynamic range is more than 65 dB. The frequency response and sensitivity can be modulated by changing the size and surface tension of the membrane. The microphone can be easily implemented and can be made very small. [Work supported by NSF.]

Automated measurement of nonlinearity of optical fiber power meters

Abstract: We have developed a system for measuring the nonlinearity of optical power meters or detectors over a dynamic range of more than 60 dB at telecommunications wavelengths. This system uses optical fiber components and is designed to accommodate common optical power meters and optical detectors. It is based on the triplet superposition method. The system also measures the range discontinuity between neighboring power ranges or scale settings of the optical power meter. We have developed an algorithm to treat both the nonlinearity and the range discontinuity in a logically consistent manner. Measurements with this system yield correction factors for powers in all ranges. The measurement system is capable of producing results which have standard deviations as low as 0.02%. With slight modification the system can operate over a 90 dB dynamic range at telecommunications wavelengths. This measurement system provides accurate determination of optical power meter or detector nonlinearity; the characterized detectors then can be used for such applications as absolute power and attenuation measurements.

Optical amplifier for amplifying a signal light and a continuous light having a wave length different from the signal light

Abstract: In an optical amplifier a signal light of a wave length λ a is coupled with a continuous light of a wave length λ b and amplified by an optical fiber amplifier. Then, the amplified output light is subjected to filtration to select the light of the wave length λ a alone, so that the ASE power is reduced and the dynamic range of the optical fiber amplifier from the minimum light receipt power to the saturation after amplification can be enlarged, and, in the case that the signal light is pulse-modulated, the deterioration of the extinction ratio is minimized.

A dynamic range enhancement technique for fiber optic microcell radio systems

Abstract: A new approach is evaluated which effectively increases the dynamic range of optical fiber links for transporting RF signals. This new approach, called the dynamic range enhancement technique (DRET), is key to connecting remotely located microcell base station antenna sites to a centralized base station via optical fiber while maintaining a good dynamic range. The cause and characteristic of distortion introduced by the optical fiber link is examined and the performance of the DRET is compared with other dynamic range enhancing techniques for a time-varying signal environment.