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Page 575 of 977 Results 5741 - 5750 of 9762

G. C. Giakos, S. Chowdhury, F. Russo, N. Shah
NOVEL DETECTION TRENDS FOR DIGITAL MAMMOGRAPHY

In this study, novel dual-energy detection modes for digital mammography, consisting of a combination of gas detector media with semiconductor detectors, are presented and discussed.
The purpose of this study is to measure experimentally the figure of merit (FOM) of this multimedia detector for dual-energy imaging. The experimental results indicate that the multimedia detector exhibits a high FOM. At present time, potential applications of the multimedia detector technology in several industrial areas, such as medical imaging, aerospace imaging, aviation security and surveillance, are being explored.

A. Fort, N. Machetti, S. Rocchi, N. Ulivieri, V. Vignoli
VECTORIAL IMPEDANCE METER FOR GAS CHEMICAL ANALYSIS

In this paper two digital correction techniques are presented aiming at enhancing the measurement accuracy of an electronic nose. The equipment operates as a vectorial impedance meter in the frequency range 0-15 MHz. The digital correction techniques allow compensating for the conditioning electronic response. Linear behaviour is assumed, cross-talk, amplitude and phase distortions are accounted for by a black box two-ports model. The model parameters are evaluated either with a set of measurements, spanning the whole frequency range, and by a single measurement by exploiting autoregressive (ARX) models.

J. Fischer
THE APPLICATION OF SIGMA DELTA D/A CONVERTER IN THE SIMPLE TESTING DUAL CHANNEL DDS GENERATOR

This article deals with the application of sigma delta DAC in the low cost testing dual channel generator with direct digital synthesis based on digital signal processor. The results of measurement performed by means of ADSP2181 EASY KIT are presented.

J. Fischer
PRACTICAL ASPECTS OF IMAGE PRIMARY PROCESSING AND DIGITALISATION

This paper deals with optoelectronic sensors used for optical image sensing. The basic physical principles and properties of sensors, their implementation as well as methods of signal conditioning are treated. A special attention is devoted to the properties important for digitalisation and recording of the output signal of sensors.

J. M. Dias Pereira, A. Cruz Serra, P. Girão
FLEXIBLE ADC: A DITHER AND OVERSAMPLING BASED SOLUTION TO IMPROVE THE PERFORMANCE OF ADC SYSTEMS

A well-known technique that can be used to increase the resolution of ADC digitising systems is based on dithering, oversampling and noise shaping. Dithering assures a uniform power spectral density for the quantisation error, oversampling. Followed by digital filtering, it improves signal to noise ratio and effective number of bits at the expenses of the input signal bandwidth. Noise shaping removes quantisation error power from signal bandwidth. The present paper introduces the concept of a flexible ADC that can be applied to an ordinary data acquisition board as a solution to optimise digitising systems performance for different sampling rates. Gains of ten or more effective bits can be obtained, for low frequency input signals, using always the maximum sampling rate of the ADC together with dithering, oversampling and noise shaping techniques.

Alan J. Davis ‚ Godi Fischer, Hans-Helge A1brecht, Jürgen Hess
THE 1-1-1-1 CASCADED Σ-Δ MODULATOR

The techniques to design and fabricate a cascaded sigma-delta modulator composed of 4 1st -order sections is presented. By correcting the digital outputs with estimates of the parasitic errors due to analog circuit imperfections, uncancelled quantization noise terms can be removed. Specifically, compensation for the effects of amplifier finite gain and C-ratio rnismatches allow for the realization of the 1-1-1-1 cascade. A 1-1-1-1 cascaded modulator, implemented as a fully differential switched-capacitor circuit, has been fabricated in a 1.2 µm double-poly n-well CMOS process. Measurements of the modulator verify that for an amplifier gain of 60 dB, and C-Ratio mismatch errors of approximately 0.5%-1%, the error correction offers an overall improvement in SNDR of 12-23 dB. A 12-15 µVrms sine wave can be restored with a positive SNDR for a sampling rate of 2.5 MHz and an OSR of 64.

Giovanni Chiorboli
DESIGN OF ADC HISTOGRAM TEST: A PRACTICAL CASE

In this paper, the results of the most recent studies on the sinewave histogram test are considered. Particular emphasis is dedicated to the choice of the values that the test parameters must assume for obtaining a specified measurement uncertainty. Finally, a practical example of how to organize the test of a high-speed, 12-bit converter is proposed, and some results are given which validate the theory.

S. Brigati, F. Francesconi, P. Malcovati, F. Maloberti
MODELING BAND-PASS SIGMA-DELTA MODULATORS IN SIMULINK

In this paper we present a complete set of behavioral SIMULINK models for the simulation of switched-capacitor band-pass sigma-delta (BPΣΔ) modulators. The models include most of the non-idealities which affect the performance of these circuits, such as sampling jitter, kT/C noise and operational amplifier parameters (noise, finite gain, finite bandwidth, slew-rate and saturation voltages). With the proposed models it is possible to accurately predict with fast simulations the signal-to-noise and distortion ratio and the linearity of any BPΣΔ modulator.

L. Breniuc, M. Cretu, L. Nita
POSSIBILITIES TO IMPROVE THE MEASURING PERFORMANCES OF IMPEDANCES IN A WIDE FREQUENCY RANGE

This paper presents our study regarding the possibility of using the nonlinear conversion to measure impedances in a wide range of frequencies. In this case, impedance testing is done by using a multi-frequency signal with the crest factor as low as possible. The non-linear conversion (logarithmic) has as effect measurement error reduction for low levels contained in the measurement signal. From this point of view, non-linear conversion apear to be an alternative to the problem of minimization of the crest factor of the test signal.

L. Breniuc, C.G. Haba, C. Sarmasanu
THE POSSIBILITY OF IMPLEMENTING A NONLINEAR SUCCESSIVE APPROXIMATION A/D CONVERTER USING FPGAs

This paper presents our study regarding the possibility to implement an analog to digital converter with the following capabilities: bipolar and linear analog to digital conversion with 8/12 bits resolution, bipolar non-linear (logarithmic) analog to digital converter with variable resolution 6...12 bits, bipolar and linear or non-linear analog to digital converter, depending on the measuring range. The main circuit of the converter is an FPGA (Field Programmable Gate Array). The converter has been testet using 500 kHz and 1MHz clock. The errors obtained with this converter were less than ±1 LSB.

Page 575 of 977 Results 5741 - 5750 of 9762