Contributions to the evaluation of ensembles of combinational logic gates

This work presents an effective way for evaluating and validating ensembles of combinational CMOS gates and logic cell libraries. The major contributions include an innovative design methodology for such a kind of test vehicle, as well as a simple and flexible multi-operating mode circuit architecture. The resulting circuit is quite useful for cell library verification at different levels: in the EDA environment and on silicon prototyping. The proposed methodology can be applied for analysis taking into account the logic gate functionality, timing performance, power consumption and circuit operating impact of nanometer aging effects. Simulation results demonstrate the circuit operation, features and facilities described herein.     

Guarded vector voltmeter for AC ratio standard calibration

A new setup for the calibration of the ratio of inductive voltage dividers against a ratio standard is under development at IEN. The setup is based on the direct measurement of voltage vector differences between the device under test and the standard, with a purposely built vector voltmeter described here. The uniqueness of the voltmeter is the extremely high common-mode-rejection-ratio, greater than 180 dB at 1 kHz, obtained with a bootstrapping-guarding technique. The voltmeter is battery-operated, has variable gain and a dual-channel synchronous demodulating stage with high harmonic rejection, and is operated with a personal computer through an optical-fiber interface.     

Novel impedance cell for low conductive liquids: determination of bulk and interface contributions

A plane capacitor cell with variable gap has been designed in order to detect the complex permittivity of low conductive liquids (up to 500 microS/cm) and the impedance of the sample-electrode interface. The novelty of the cell consists of the simultaneous presence of the field uniformity ensured by a guard ring, an adjustable gap between 300 microm and 6.75 mm (the electrode axial motion avoiding any rotation), and the immersion of the capacitor in the sample reservoir. The size of the capacitor electrodes and the gap values have been tested via the capacitance detection of the in-air cell at 1 kHz. The sample measurements have been performed by scanning the frequency range between 15 Hz and 2 MHz at four different capacitor gap values. In the paper a method to directly extract the bulk complex permittivity and the interface impedance versus frequency is presented. It is based on the assumption that the interface contribution is independent of the electrode gap, as confirmed (within the measurement accuracy) from measurements on all samples investigated. As samples of interest, we have chosen two certified electrolytic conductivity standards, KCl aqueous solutions having conductivity traceable to SI units; and two polymer latex aqueous dispersions of microspheres. Regarding KCl solutions, the conductivity measurements are compatible with the reference values within the specified uncertainty; the measured permittivities are consistent with the literature. For all samples, we have recovered the expected result that the interface impedance mainly affects the low frequency range (f<10 kHz).     

Short Communication: Improvements to INRIM Johnson Noise Thermometer

This paper presents a progress report for the Johnson noise thermometry experiment which is under development at the Istituto Nazionale di Ricerca Metrologica. In order to aim at an uncertainty level better than 10⁻⁵ and to reduce the measurement time, a new setup has been developed. In particular, several modifications have been applied to the experiment described by Callegaro et al. (Metrologia 46: 409, 2009) to improve the traceability to voltage, resistance and frequency standards, and new amplifiers have been designed in order to expand the working frequency range up to 20 kHz, with a sensing resistor of 1 kΩ, while maintaining amplifier induced systematic errors to an acceptable level.     

On strategies for automatic bridge balancing

Automatic balancing of coaxial AC impedance bridges asks for simple, robust and efficient strategies suitable to be easily implemented on PC controllers. The paper considers the problem of balancing a bridge with n detectors to be equivalent to the problem of finding the root of a complex-valued vector function F. To avoid electrical modeling of the bridge, F is considered generally unknown except at specific points evaluated by experiment. In this framework, efficient root-finding strategies can be employed; in particular, secant method and two generalizations of it to the case n>1 are proposed. Experimental results on a test circuit are given.     

10-nF capacitance transfer standard

New dielectric capacitance standards with a nominal value of 10 nF, suitable to be employed in the reproduction of the farad unit starting from the quantum Hall resistance, have been constructed. The standards are based on commercial chip capacitance components encased in a thermostat, and are defined as four terminal-pair impedance standards. The capacitance value is within 50/spl middot/10/sup -6/ relative to nominal; dissipation factor is about 8 /spl middot/ 10/sup -5/ at 1 kHz. The relative temperature coefficient of the capacitance value versus external ambient temperature is expected to be /spl ap/1/spl middot/10/sup -8/ K/sup -1/ near 23 /spl deg/C.     

A Current Source for Picoammeter Calibration

A current source, which is to be employed in the calibration of low-current meters (picoammeters and electrometers), is presented here. The output current range is 100 fA to 100 pA and is directly traceable to calibrated standards of dc voltage, capacitance, and time period. The source is based on a low- frequency (ap1 mHz) trapezoidal signal generator, which charges and discharges a gas-dielectric capacitor; the voltage is monitored with a voltmeter that is triggered by a precision time base. The source has been employed during March 2006 for the Italian participation to the supplementary comparison EUROMET.EM-S24 and will be part of an extension of the Italian national standard of dc current. However, being composed of low-cost electronics and common commercial instrumentation, the source can also find useful application in secondary calibration laboratories.     

Expansion Properties of Sour Cassava Starch (Polvilho Azedo): Variables Related to its Practical Application in Bakery

Sour cassava starch (polvilho azedo) is a chemically and enzymatically modified starch with the specific property of expansion in bakery products without the use of any chemical or biological leavening agents. In this work, the cumulative knowledge about sour cassava starch is presented in relation to its physicochemical characteristics, with the purpose of establishing a relation between the application properties and some structural and chemical characteristics in order to design a model of the modified structure of starch and the most important technical variables. Such approach will help to provide some quality standards for future adequate valorization of sour cassava starch, especially with respect to potential use in gluten‐free products. This work showed that a good sour cassava starch is significantly different from low expansion cassava starches with respect to pH, acid factor, swelling power, specific volume, and polymerization degree (intrinsic viscosity). These variables could be related to the maximization of sour cassava starch expansion for a future predictive decision analysis about a high quality sour cassava starch to the baking use.