Alberto Dei, Maurizio Valle
Modeling charge injection non-linear effects in Sigma-Delta Modulators using SIMULINK

Sigma-delta (ΣΔ) modulators are the most suitable A/D converters for low to medium frequencies, high-resolution applications, in view of their inherent linearity, reduced antialiasing filtering requirements and robust analog implementation. Moreover, the growing market for asymmetrical digital subscriber line (ADSL) applications is a driving force for the development of high speed, high resolution, sigma-delta analog-to-digital converters (ADC’s). In the wider development of ADC systems, a pre-eminent role has been played by modeling techniques. Modeling of ADC allows the device behavior to be predicted with a few of preventive experiments. For this reason, in the last years a great deal of scientific interest has been directed to ADC modeling.
In this work we present a SIMULINK model, which takes into account, for the first time, the non-linear effects due to switch charge injection in Sigma-Delta modulators. These effects are non-linearly proportional to the input voltage value. This brings about offset and harmonic distortion. Therefore adequate modeling of charge injection in terms of harmonic distortion is extremely important to predict and estimate the performance of Sigma-delta modulators.

Andrea Sosso, Roberto Cerri
Compensation of Digital Voltmeters Nonlinearities by means of a Quantum Standard

The high linearity and stability of modern top-level Digital Voltmeters (DVM) can be exploited to measure voltage ratios with very low uncertainty by making two separate absolute voltage measurements. Yet, to obtain the very low uncertainties required to use a DVM as a voltage ratio standard, the intrinsic linearity of the instrument is not sufficient and techniques to determine and correct the residual non linearities must be adopted.
The Josephson Array Voltage Standard (JAVS) is well known as a voltage standard with nearly ideal accuracy. JAVS can can be also used for voltage ratio calibration, provided a source with high short- term stability is available. JAVS are then the best way to measure the very small linearities of a DVM, being the short-term requirement generally fulfilled by high quality voltmeters.
We performed several measurements for the evaluation of the linearity of DVMs in use in our laboratories, aimed at determining the performances of commercial multimeters as voltage ratio standards for the dissemination of the volt and for replacing ordinary techniques based on resistive dividers in primary metrology. The results appear to be encourag- ing for both applications: after calibration, uncertainty below 0.1 ppm can be obtained, with a stable profile of non linearity correction over time.

Dae Yong Kim, Gil Su Kim, Hoon Jae Ki, Soo Won Kim
2.5 V, 10-bit, 50-MS/s CMOS Pipeline Low Power A/D Converter

In this paper, we present A/D converter for signal processing of infrared sensor and CMOS image sensor. The A/D converter implemented in a 0.25 um CMOS process provides a resolution of 10bits at a sampling rate of 50 MS/s while dissipating 67 mW from 2.5 V supply voltage.
This A/D converter is based on a pipelined architecture in which the number of bits converted per stage and the stage number are optimized to simultaneously achieve the desired linearity and reduce power consumption as well. Simulation results show that the A/D converter using 1.5 bit per stage MDAC with switched capacitors and dynamic comparators efficiently reduces the power consumption.

Antonino S. Fiorillo , Gianni D’Angelo
A/D Convertion Error Propagation in Distance Measurement with a Sonar System based on Piezopolymer Sensors

The paper deals with the investigation on the propagation of the A/D convertion error during the distance measurement with an ultrasonic sensor aimed to emulate the behaviour of the bat bio-sonar.
In previous experiments the echo signals were processed with a 8 bit DSP and the target distance of 27 cm was evaluated with an accuracy of λ/50, but until now the nature of the measurement error was not verified.
The signal reconstruction algorithm should employ an inverse transfer characteristic with respect to that of the sensor. In the proposed application the propagation error is evaluated at different distances ranging from 27 cm to 200 cm (one-path way), by considering an ideal signal reconstruction block, which however processes the global convertion error. At the minimum distance the results are in good agreements with those one obtained in the experiments.

T. Sumimoto, T. Maruyama, Y. Azuma, S. Goto, M. Mondou, N. Furukawa, S. Okada
Image Analysis Techniques for the Detection of Defects at BGA by X-Ray

This paper deals with the development of image analysis for the detection of defects at BGA solder joints in PC boards by using X-ray imaging. We can’t detect visually defects at BGA solder joints, because they are hidden under the IC package. To improve a cost performance and the reliability of PC boards, an inspection of BGA is required in the surface mount process. Types of defects at BGA solder joints are solder bridge, missing connection, solder voids, open connection and miss-registration of parts. As we can find mostly solder bridge in these defects, we pick up this to detect solder bridge in a production line. The problems of image analysis for the detection of defects at BGA solder joints are the detection accuracy and image processing time according to a line speed of production. To get design data for the development of the inspection system, which can be used easily in the surface mount process, it is important to develop image analysis techniques based on X-ray image data. At the first step of our study, we attempt to measure the shape of BGA based on X-ray imaging.