Showing papers on "Dynamic range published in 1988"

Method and apparatus for coherent imaging system

Abstract: A method and apparatus for improved digital processing of the analog echo signals in a coherent imaging system is described which simplifies the channel circuitry requirements. The analog echo signals detected with a phased array of transducer elements are first compressed in a non-linear manner then expanded non-linearly with analog-to-digital converter means to provide increased instantaneous dynamic range in the overall system. Representative phased array coherent imaging systems having the improved digital processing means are also disclosed.

A low-power stereo 16-bit CMOS D/A converter for digital audio

Abstract: A low-power 16-bit CMOS D/A (digital/analog) converter for portable digital audio is described. The converter is based on current division. To guarantee monotonicity and a good small-signal reproduction, a dynamic segmentation technique is used. A geometric averaging technique is used to minimize the harmonic distortion of the converter at high signal levels. The dynamic range is 95 dB. The circuit operates in a time-multiplex mode at a sample frequency of 44 kHz in a power supply range of 2.5-5 V and has a power consumption of 15 mW. A 2- mu m CMOS technology is used and the active chip area is 5 mm/sup 2/. >

Some remarks on the stability and performance of the noise shaper or sigma-delta modulator

Abstract: The stability constraints of the noise shaper are examined for the purpose of coder design. The author shows that the presence of a limiter in the noise shaper strongly influences the stability criteria on the loop filter of a third- or higher-order coder. A third-order coder was designed according to these results for high-fidelity audio. It performs with a dynamic range of over 100 dB, and the measured in-band noise agrees fairly well with the calculated value. The proposed design procedure also applies to the (sigma-) delta modulator, which is in essence the same device. >

Self-protecting semiconductor optical limiters.

Abstract: We present a detailed characterization of passive, picosecond optical-power-limiting devices using tightly focused beams in thick semiconductor samples. This study of limiting in ZnSe with 30-psec, 532-nm pulses shows that the resulting internal self-action (two-photon absorption plus free-carrier self-defocusing) protects the bulk material from optical damage. Simple scaling relations were determined from our results that link the limiting energy and the dynamic range to the focusing geometry and sample dimensions. These relations were used to design a monolithic optical limiter, optimized to have maximum dynamic range and minimum limiting energy. This device limits at an input energy of 10 nJ (300 W) and has a dynamic range greater than 10(4).

Sensitive, highly linear lithium niobate interferometers for electromagnetic field sensing

Abstract: An asymmetric Mach–Zehnder interferometer in Ti:LiNbO3 has been demonstrated to have a 84 dB linear dynamic range and 1.1 μV sensitivity, for a 3 kHz detection bandwidth and a 50 Ω resistance, at the 1.3 μm wavelength. This device is useful for electric and magnetic field sensing. Optimum linearity is achieved with a 90° intrinsic phase bias. The dependence of dynamic range and sensitivity on optical power, phase bias, and modulation voltage is reported. The reasons for, and magnitudes of, deviations from optimum linear behavior are described for many fabricated interferometers.

Binning spectral images in a charge-coupled device (CCD). Technical report

Abstract: A charge-coupled device (CCD) can selectively combine photogenerated charge from several detector elements into a single charge packet by a charge-readout mode called binning This article focuses on the use of charge binning in a two-dimensional CCD for increasing the sensitivity and dynamic range of spectroscopic measurements Binning allows the effective detector element size to be matched to the size of the slit image Equations describing the signal to noise ration and dynamic range of the binned readout of spectral lines are developed Results of binning to increase the sensitivity of atomic emission and molecular fluorescence measurements are presented An intraspectral dynamic range of 500,000 is achieved by mixing binned and normal readout modes of a Hg atomic emission spectrum Practical factors related to binning spectral images including spectral line orientation, readout speed, and blooming are discussed

Dynamic range compression in MRI by means of a nonlinear gradient pulse.

Abstract: In current magnetic resonance imaging (MRI), valuable information must often be discarded because the NMR signal has greater dynamic range than the analog-to-digital converter (ADC) hardware. Typically, a small set of high-intensity data points near the center of the spin echo is responsible for most of the MRI data dynamic range. We predict that it is possible to reduce the dynamic range of the MRI spin echo by incorporating an identical nonlinear gradient pulse into each repetition of the imaging pulse sequence, prior to data sampling. This pulse converts the phase distribution of the subject, ordinarily a linear function of image coordinates, into a nonlinear function. A nonlinear phase distribution can have a negligible impact on image magnitude and yet a profound impact on spin-echo magnitude. Given a nonlinear phase distribution, there will no longer be a single data point at which all of the protons have an identical phase (the echo center). Instead, the protons become phase coherent on a piecemeal basis, the echo peak is smoothed out, and its maximum amplitude and dynamic range are greatly diminished. Using gradient pulses of quadratic spatial variation, we estimate that maximum echo amplitude and dynamic range can be reduced in most cases by an order of magnitude.

Delay replacement in direct form structures

Abstract: A class of high-order low-sensitivity digital filter structures is generated by means of a direct transformation of a high-order direct-form (DF) structure. The proposed structures have low coefficient dynamic range, and exhibit low coefficient frequency-response sensitivity and roundoff noise characteristics, yet require only 3N multiplications per output sample as compared to 2N in the direct-form case. >

Digital array scanned interferometer

Abstract: An interferometer with a cylindrical lens which produces an interferogram imaging the field of view in the redundant coordinate onto a photon noise limited detector comprising a charge-coupled device or CCD having pixels aligned along two dimensions to provide spatial resolution in that dimension of the light source as well as spectral resolution. The CCD is also characterized by greater dynamic range, lower pixel response variation, and is photon noise limited, all of which enhances its use as a detector for a spectrometer.

Solid state image-pickup device with expanded dynamic range

Abstract: A solid state image-pickup device having an expanded dynamic range so that light reception from a subject having a high light intensity can be carried out without saturation of the light receiving elements of the image-pickup device.

System for simultaneous count/current measurement with a dual‐mode photon/particle detector

Abstract: A microcomputer‐based control system for a dual‐output Channeltron (TM) detector has been developed and implemented. This system is capable of collecting ion current and ion‐counting information simultaneously. Ion current and ion‐counting data are scaled in software and provide consistent ion intensity values from both outputs. Calculation of the ion current/ion count rate ratio at each peak in the mass spectrum allows the system to compensate for variations in gain from peak to peak. The data collection system maximizes the data collection rate and extends the useful dynamic range of electron multiplier‐based detection to nine orders of magnitude with no change in any of the multiplier conditions. Measurement of such a wide range of ion intensities in a single spectrum is particularly useful for applications in tandem mass spectrometry.

Wide dynamic range optical power measurement using coherent heterodyne radiometry

Abstract: A coherent heterodyne detector has a dynamic range of up to fifteen decades, as well as shot-noise-limited sensitivity. Applications of coherent heterodyne radiometry that exploit the extraordinary dynamic range include the calibration of optical filters and the measurement of scattered light from surfaces and materials.

Noise, crosstalk and distortion in mixed analog/digital integrated circuits

Abstract: In mixed analog/digital circuits, op-amp noise, aliased noise, crosstalk from digital circuits, and distortion limit the dynamic range available. Op-amp design, gain partitioning and layout are the key in achieving >25-dB signal-to-noise ratios in an analog path containing 25 op amps. The authors present methods used to maximize dynamic range and measured results obtained from ASIC (application-specific integrated-circuit) devices. >

Split dynamic range using dual array sensor chip assembly

Abstract: An infrared sensing array having a detector array, a readout circuit, and processing circuitry. The detector array includes first and second subarrays having different sensitivities associated therewith for detecting different brightness level ranges. The sensitivities of the subarrays are determined by sensing circuit elements in the readout circuit. As a result of the subarrays of different sensitivities, the composite dynamic range covered by the array is greater than the individually dynamic ranges of the subarrays.

Elimination of residual signals and reduction of noise in a low‐frequency magnetic fiber sensor

Abstract: Low‐frequency sensitivities of interferometric magnetic fiber optic sensors have been limited by the presence of a large residual signal at the dither frequency which limits the dynamic range and upconverts low‐frequency noise into sideband noise around the carrier. We present an operating regime that enables us to eliminate residual signals associated with the ac carrier. By choosing the proper carrier frequency and amplitude we obtain a nulled residual signal, strong magnetomechanical coupling, and an increase in signal‐to‐noise ratio of approximately 13 dB over previously reported results. A minimum detectable field of 45 pT/(Hz)1/2 at 0.1 Hz is demonstrated.

A method for measuring magnitude and phase of harmonics generated in nonlinear microwave two-ports

Abstract: A method for simultaneously measuring magnitude and phase of the harmonics generated by a microwave two-port is described. The measurement system has a dynamic range superior to time-domain measurements due to its reduced noise bandwidth. Sample measurements on a GaAs MESFET under large-signal operation are presented. The system allows the measurement of harmonics with a phase accuracy of about 10 degrees at 20 GHz. All types of microwave two-ports can be characterized without knowledge of their internal structure. The system can be built for any frequency less than 40 GHz where a vector generator with multiplier is available. >

An optical-feedback transimpedance receiver for high sensitivity and wide dynamic range at low bit rates

Abstract: A novel transimpedance optical receiver using optically coupled feedback rather than a conventional feedback resistor is described. The optically coupled feedback has a number of advantages, including: (1) elimination of feedback-resistor Johnson noise for higher sensitivity; (2) elimination of feedback capacitance for higher bandwidth; and (3) the capability of large feedback current with low output voltage for wide dynamic range. A theoretical analysis is presented, along with experimental results for a long-wavelength optical-feedback receiver at a bit rate of 1.5 Mb/s. The experimental receiver uses InGaAs p-i-n photodiodes and a silicon JFET preamplifier and obtains a maximum sensitivity of -63.8 dBm for an error rate of 1*10/sup -7/. When the receiver is optimized for high level signals, an optical dynamic range of 40 dB is attained with no preamplifier automatic gain control (AGC). The results of a transmission experiment over a length of 303 km of single-mode optical fiber at a wavelength of 1.55 mu m are presented. >

A wide dynamic range square-law diode detector (for radioastronomy)

Abstract: Semiconductor square-law diode detectors are frequently used in radio astronomy to recover signals immersed in the system noise. Their use is commonly restricted to narrow dynamic ranges of very low signal levels where the square-law is valid. A circuit based on operational amplifiers is proposed that would minimize temperature-drift effects within a dynamic range greater than 30 dB, with an efficiency 600 timer greater than the simple high-impedance unbiased detector. Using square-law detector theory, optimum performance is determined for a detector driving source impedance of about 14% of the dynamic resistance. >

A High Dynamic Range Acousto-Optic Image Correlator For Real-Time Pattern Recognition

Abstract: The architecture and experimental results for an incoherent acousto-optic image correlator suitable for real-time applications are presented. In the basic architecture, each time a line of the raster-scanned input image is fed into the acousto-optic device (AOD), all rows of a digitally stored reference image are read into the system using an array of light emitting diodes (LEDs). Thus, the required two-dimensional correlation is performed as a series of multi-channel 1-D time-integrations in x (performed in the AOD) combined with a multi-channel correlation in y (perpendicular to the AOD axis) using a modified CCD. The LED array and detector modifications which markedly increase the dynamic range are discussed as well as the correlator design. Further, a novel memory for storing the reference object is described for rapidly changing templates. Experimental results indicate the architecture is useful for applications in the areas of character recognition and target identification.

A floating-point A/D converter uses low resolution DAC to get wide dynamic range

Abstract: This paper describes the use of non-uniform quantizing step to realize a floating-point analogue-to-digital converter. This enables achieving wider dynamic range while using low resolution components. Main advantages of this realization are low cost, reduced hardware and better performance in terms of signal to quantizing error ratio. The main hardware components used are low resolution analogue-to-digital converter and programmable gain amplifier along with some logic elements. The algorithm can be easily implemented through software in a microprocessor-based system leading to further hardware saving.

A new high sensitivity photo-transistor for area image sensors

Abstract: A novel MOS phototransistor with a high optical gain, called a double-gate floating-surface phototransistor, has been proposed and fabricated The phototransistor realizes a 08-electron RMS noise equivalent signal over a 358-MHz-wide band It achieves a dynamic range of 75 dB with an amplification characteristic suitable for TV-camera application It is concluded that an ultra-high-sensitivity image sensor can be realized with this device >

A superconducting analog track-and-hold circuit

Abstract: A superconducting analog track-and-hold circuit has been designed, fabricated, and tested. Experimental results demonstrate a 1.2-GHz bandwidth and a 25-dB dynamic range. Model calculations indicate that an optimized circuit with a critical current density of 10000 A/cm/sup 2/ can achieve a 4-GHz bandwidth and a 35-dB dynamic range. >

A multichannel, high linearity current digitizer for digital subtraction angiography

Abstract: An experiment studying the application of synchrotron radiation for transvenous coronary angiography requires special electronics to read out a 600-element Si(Li) detector. To obtain high image quality, the electronic system must digitize the current in all 600 elements every 2 ms with a dynamic range of 40000 and a maximum nonlinearity of 0.02%. Each channel of electronics contains a current-to-voltage amplifier with computer-controlled gain and offset followed by a voltage-to-frequency converter used in the reciprocal counting mode. A high-speed digital readout method using a lookup table, digital multiplier and direct memory interface was developed. The entire system has been designed to have a low cost per channel and to be easily expanded by 1200 signal channels. >

Streak Camera Dynamic Range Optimization

Abstract: The LLNL optical streak camera is used by the Laser Fusion Program in a wide range of applications. Many of these applications require a large recorded dynamic range. Recent work has focused on maximizing the dynamic range of the streak camera recording system. For our streak cameras, image intensifier saturation limits the upper end of the dynamic range. We have developed procedures to set the image intensifier gain such that the system dynamic range is maximized. Specifically, the gain is set such that a single streak tube photoelectron is recorded with an exposure of about five times the recording system noise. This ensures detection of single photoelectrons, while not consuming intensifier or recording system dynamic range through excessive intensifier gain. The optimum intensifier gain has been determined for two types of film and for a lens-coupled CCD camera. We have determined that by recording the streak camera image with a CCD camera, the system is shot-noise limited up to the onset of image intensifier nonlinearity. When recording on film, the film determines the noise at high exposure levels. There is discussion of the effects of slit width and image intensifier saturation on dynamic range. 8 refs.

Signal Processing Requirements For A Video Rate Laser Range Finder Based Upon The Synchronized Scanner Approach

Abstract: This article presents the results of an analysis and a discussion of the signal processing requirements for a video rate laser range finder. The lateral effect photodiode is chosen as the position detector for its speed, ease of use, and cost trade-offs over other sensors. Two models are presented for this sensor: the transmission line and the lumped elements. Both are investigated for possible use in circuit analysis. The latter model is selected, although it is not as accurate as the first one. However, it can yield valuable results able to show dependences between system parameters. The results of a linear circuit analysis give some trade-offs for optimum current to voltage conversion for fast response lateral effect photodiodes. Also, a discussion of the merits of techniques for position calculation, to increase the dynamic range of the system and reduce both costs and circuit complexity, is presented.

Maximum dynamic range of clipped correlation of integrated laser speckle intensity

Abstract: The relationship between the dynamic range and the clipping threshold of a double-clipped correlation of integrated laser speckle intensity signals is discussed. In particular, the maximum dynamic range of the clipped correlation is evaluated. For α = 1 (α being the number of the integrated speckles), the maximum dynamic range occurs for the clipping threshold of In 2〈I〉, and the clipping threshold approaches the mean intensity 〈I〉 as the number of integrated speckles increases. On the other hand, the maximum dynamic range does not change and has the same value of Δ = 1/4 (Δ being defined as the dynamic range of the clipping correlation normalized by that of the nonclipping correlation), even if the number of the integrated speckles varies.

A Wide Dynamic Range Tapped Linear Array Image Sensor

Abstract: Detectors for acousto-optic signal processing applications require fast transient response as well as wide dynamic range. There are two major choices of detectors: conductive or integration mode. Conductive mode detectors have an initial transient period before they reach then' i equilibrium state. The duration of 1 his period is dependent on light level as well as detector capacitance. At low light levels a conductive mode detector is very slow; response time is typically on the order of milliseconds. Generally. to obtain fast transient response an integrating mode detector is preferred. With integrating mode detectors. the dynamic range is determined by the charge storage capability of the tran-sport shift registers and the noise level of the image sensor. The conventional net hod used to improve dynamic range is to increase the shift register charge storage capability. To achieve a dynamic range of fifty thousand assuming two hundred noise equivalent electrons, a charge storage capability of ten million electrons would be required. In order to accommodate this amount of charge. unrealistic shift registers widths would be required. Therefore, with an integrating mode detector it is difficult to achieve a dynamic range of over four orders of magnitude of input light intensity. Another alternative is to solve the problem at the photodetector aml not the shift, register. DALSA's wide dynamic range detector utilizes an optimized, ion implant doped, profiled MOSFET photodetector specifically designed for wide dynamic range. When this new detector operates at high speed and at low light levels the photons are collected and stored in an integrating fashion. However. at bright light levels where transient periods are short, the detector switches into a conductive mode. The light intensity is logarithmically compressed into small charge packets, easily carried by the CCD shift register. As a result of the logarithmic conversion, dynamic ranges of over six orders of magnitide are obtained. To achieve the short integration times necessary in acousto-optic applications. t he wide dynamic range detector has been implemented into a tapped array architecture with eight outputs and 256 photoelements. Operation of each 01)1,1)111 at 16 MHz yields detector integration times of 2 micro-seconds. Buried channel two phase CCD shift register technology is utilized to minimize image sensor noise improve video output rates and increase ease of operation.

Broadband Beamforming Via Acousto-Optics

Abstract: A novel broadband beamformer based on space-integrating, interferometric multichannel acousto-optic correlators was proposed. Both analysis and experiments were carried out to validate the concept. Simultaneous beamforming and pulse compression were demonstra'ted by an experimental simulation with a 126-bit PN coded signal of 50-MHz bandwidth. Analysis also showed that the system was suitable for multiple beamforming. The responses of the system to narrow (cw) and wideband (random noise) jammers, both on-boresight and off-bore-sight, were investigated experimentally. Results showed that, against these interferences, the system was quite robust due to the processing gain, even for the worst case where the jammers was on-boresight and its frequency coincided with the signal carrier. However, the system's sensitivity was reduced by a factor of four for the wideband jammer and a factor of ten for the narrow band jammer. The dynamic range of the system was measured to exceed 20 dB, only to be limited by detector saturation and Bragg cell non-linearity. The system could be made adaptive.© (1988) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical image processing with liquid-crystal display for image intensifier/television systems

Abstract: We have studied the effect of real‐time optical image processing (OIP) in an image intensifier/television (II–TV) radiographicimaging system by using a liquid‐crystal display (LCD) placed between the II and the TV camera. The LCD compresses the dynamic range of the transmitted image by modulating the spatial distribution of the light intensity of the image from the output phosphor of the II. The degree of dynamic‐range compression can be designed so that the dependence of the signal‐to‐noise ratio (SNR) of the LCD–TV system on x‐ray intensity matches that of the quantum noise. We measured the physical properties of an LCD and evaluated its capability for OIP. Our experimental results demonstrate that it is feasible to use an LCD to compress the dynamic range and to improve the SNR of the image. The advantages of implementing OIP with an LCD in image acquisition systems in which a TV camera is used are discussed.