A calibration-free low-cost CMOS integrated smart temperature sensor is presented that requires significantly less die area than previously published designs through the use of novel circuit technique and the 130 nm CMOS process. Uncalibrated sensor operation is achieved through the extensive use of analog dynamic element matching and chopper stabilization circuitry. A novel process-compensation circuit is presented that uses the correlation between pinch-base resistance and substrate bipolar VBE temperature gradient. Accuracy mostly within the range of ±1°C was achieved using a die area of only 0.21 sq. mm. Prototype sensor performance was found to be limited by the low β characteristics of the substrate bipolar transistors implemented in the 130 nm CMOS process.

A Calibration-Free Low-Cost Process-Compensated Temperature Sensor in 130 nm CMOS

This study presents a software application that applies the Analytic Hierarchy Process (AHP) to objectively select the best temperature sensors. Three industrial applications and seven sensor alternatives are considered. The developed application performs the selection process in a computerised, easy-to-use graphical user interface. The underlying decision method ranks temperature sensors with scores resulting from the synthesis of relative preferences of each alternative at different levels considering independent evaluation criteria. Pair-wise relative comparison matrices collected from experts are embedded and are retrieved according to user specifications. A case study is conducted which involves selecting the best sensor for an automotive catalytic converter. The thermocouple is found to be the most preferred sensor with the largest score of 0.37849, the second ranked sensor is the RTD with a score of 0.34589, and the least preferred sensor is the thermister with a score of 0.27560. Sensitivity analysis shows that the selection of the best sensor is dependent on the relative weights of the criteria as well as the chosen application. AHP is shown to provide a quantitative evaluation method which is simpler, easier and more organised than subjective opinions.

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A software application for the selection of temperature measuring sensors using the analytic hierarchy process

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Conference Proceedings I
R. P. Fisk and S. M. Hasan, “Analysis of Internally-Generated Noise in Bandgap References,” in Proc. Electronics New Zealand Conf., Christchurch, New Zealand, Nov. 2006, pp. 18-23. 

Conference Proceedings II
R. P. Fisk and S. M. Hasan, “Incremental Delta-Sigma Modulators for Temperature Sensing Applications,” in Proc. Int. Conf. Mechatronics and Machine Vision in Practice, Auckland, New Zealand, Dec. 2008, pp. 63-67.

Conference Proceedings III
R. P. Fisk and S. M. Hasan, “Low-Cost Temperature Sensor on a Modern Submicron CMOS Process,” in Proc. Electronics New Zealand Conf., Otago, New Zealand, 2009, pp. 43-48.

Accurate thermal sensing with modern CMOS integrated circuits : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Auckland, New Zealand

This work presents an incremental 2nd-order sigma delta using a single operational transconductance amplifier. This design provides a good trade-off between time conversion, high bit resolution, power consumption and area utilization for a pressure sensing reading interface. The modulator, designed in 180 nm CMOS technology, has been optimized for low area utilization, occupying only 0.058 mm2. Post-layout simulations were performed showing a resolution of 150 μV while consuming 120 μW and 460 fJ/conv. The system has a resolution of 16 bits, a bandwidth of 2 kHz, an oversampling ratio of 512 and a sampling frequency of 2 MHz.

A 16-bit Pressure Sensing Interface Integrating a 460 fJ/conv Incremental Sigma Delta ADC for Medical Devices

This paper presents a comparison of incremental delta-sigma analogue-to-digital converters for integrated temperature sensing applications. The characteristics of bipolar transistor-based temperature sensing front-ends place specific requirements on the modulator loop architecture. Single loop delta-sigma architecture that removes the input signal from the internal loop by the addition of a feedforward path to the quantiser has been investigated thoroughly. It is found that the Noise Transfer Function (NTF) implemented by the modulator can be optimised for either accuracy or integrator signal excursion, based on the requirements of the target application.

Robert P. Fisk

Papers

Incremental delta-sigma modulators for temperature sensing applications