A 4H-SiC CMOS Oscillator-Based Temperature Sensor Operating from 298 K up to 573 K.

In this paper, we propose a temperature sensor based on a 4H-SiC CMOS oscillator circuit and that is able to operate in the temperature range between 298 K and 573 K. The circuit is developed on Fraunhofer IISB's 2 µm 4H-SiC CMOS technology and is designed for a bias voltage of 20 V and an oscillation frequency of 90 kHz at room temperature. The possibility to relate the absolute temperature with the oscillation frequency is due to the temperature dependency of the threshold voltage and of the channel mobility of the transistors. An analytical model of the frequency-temperature dependency has been developed and is used as a starting point for the design of the circuit. Once the circuit has been designed, numerical simulations are performed with the Verilog-A BSIM4SiC model, which has been opportunely tuned on Fraunhofer IISB's 2 µm 4H-SiC CMOS technology, and their results showed almost linear frequency-temperature characteristics with a coefficient of determination that was higher than 0.9681 for all of the bias conditions, whose maximum is 0.9992 at a VDD = 12.5 V. Moreover, we considered the effects of the fabrication process through a Monte Carlo analysis, where we varied the threshold voltage and the channel mobility with different values of the Gaussian distribution variance. For example, at VDD = 20 V, a deviation of 17.4% from the nominal characteristic is obtained for a Gaussian distribution variance of 20%. Finally, we applied the one-point calibration procedure, and temperature errors of +8.8 K and -5.8 K were observed at VDD = 15 V.

Improved workflow, sonographer productivity, and cost-effectiveness of echocardiographic service for inpatients by using miniaturized systems.

AIMS: The aim of this study was to assess the cost-effectiveness of using certified sonographers and miniaturized echocardiography systems to perform echocardiograms at bedside in comparison to moving inpatients from the admission department to the echocardiography laboratory (echo-lab). METHODS AND RESULTS: From 26 September 2005 to 27 October 2005, 112 patients admitted in six hospital wards connected through a 100 Mbit LAN to the echo-lab were scanned within the admission ward by sonographers using a miniaturized echo system. Logistical data were collected and results were compared with those obtained from 194 consecutive patients coming from the same wards and studied in the echo-lab with high-end machines between 8 March 2005 and 15 April 2005. Performing echocardiograms in the admission department avoided long waiting time of the inpatients in the echo-lab before and after the study, increased the percentage of patients studied within 3 and 5 days from request (88 vs. 77% and 100 vs. 95%, respectively; P = 0.03), increased both sonographer (by 33.9%; P < 0.001) and echo-lab productivity (by 41%; P < 0.001), and reduced costs of echocardiograms by 29%. CONCLUSION: Implementation of digital echocardiography, certified sonographers, and a miniaturized echo system allowed improvement of the cost-effectiveness of the service provided by the echo-lab for inpatients, and avoided patients' discomfort derived from prolonged waiting time before and after the exam.