Guijie Wang

Temperature sensors and voltage references implemented in CMOS technology

This paper reviews the concepts, opportunities and limitations of temperature sensors and voltage references realized in CMOS technology. It is shown that bipolar substrate transis- tors are very suited to be applied to generate the basic and PTAT voltages. Furthermore, it is shown that dynamic element matching and auto-calibration can solve the problems related to mismatching of components and noise. The effects of mechan- ical stress are a major source of inaccuracy. In CMOS technology, the mechanical-stress effects are small, as compared to those in bipolar technology. It is concluded that, with low-cost CMOS tech- nolog, rather accurate voltage references and temperature sensors can be realized.

The temperature characteristics of bipolar transistors fabricated in CMOS technology

Abstract This paper presents the results of an experimental investigation of the temperature characteristics of bipolar transistors fabricated in CMOS technology. These results have to be known and understood to enable the design of high-performance temperature sensors and bandgap references in CMOS integrated circuits. The non-idealities of proportional to the absolute temperature voltage (VPTAT) have been studied, and the results show that we can generate accurate PTAT voltages by optimizing the operating condition and layout of the transistors (error

The piezojunction effect in NPN and PNP vertical transistors and its influence on silicon temperature sensors

Abstract This paper describes a test structure to characterize the piezojunction effect for the base-emitter voltage V BE and the PTAT voltage Δ V BE . The piezojunction effect directly affects the accuracy of temperature sensors and special types of pressure sensors. Packaging is a source of mechanical stress in electronics circuits. Measurements have been performed for two types of vertical bipolar transistors. Firstly, an NPN transistor of a BiCMOS technology and secondly, a PNP substrate transistor of a CMOS technology, both of them using a [100] silicon wafer geometry. It has been found that the sensitivity for the uniaxial stress of the V BE of the PNP is four times less than that of the NPN transistor. In both cases, the PTAT voltage appears to be hardly stress-sensitive.

Accurate DEM SC amplification of small differential voltage signal with CM level from ground to VDD

In this paper a new DEM amplifier is designed to amplify the small differential voltage signal, which CM level can be from ground to VDD, using single power supply. Using switched capacitors, the small differential voltage signal can be amplified. In order to eliminate the error caused by the mismatching, dynamic element matching technique has been applied. The simulation result shows that the error caused by mismatching of the capacitors has been significantly reduced to the second order. The DEM SC amplifier has been applied to amplify the thermocouple voltage in an interface circuit for thermocouples.

An Accurate BJT-Based CMOS Temperature Sensor With Duty-Cycle-Modulated Output

This paper describes the design of a precision bipolar junction transistor based temperature sensor implemented in standard 0.7-μm CMOS technology. It employs substrate p-n-ps as sensing elements, which makes it insensitive to the effects of mechanical (packaging) stress and facilitates the use of low-cost packaging technologies. The sensor outputs a duty-cycle-modulated signal, which can easily be interfaced to the digital world and, after low-pass filtering, to the analog world. In order to eliminate the errors caused by the component mismatch, chopping and dynamic element matching (DEM) techniques have been applied. The required component shuffling was done concurrently rather than sequentially, resulting in a fast DEM scheme that saves energy without degrading accuracy. After a single-temperature trim, the sensors inaccuracy is ±0.1 °C (−20 to 60 °C) and ±0.3 °C (−45 to 130 °C), respectively. Measurements of sensors in different packages show that the package-induced shift is less than 0.1 °C. Measurements of eight sensors over 367 days show that their output drift is less than 6 mK. While dissipating only 200 μW, the sensor achieves a resolution of 3 mK (rms) in a 1.8-ms measurement time, and a state-of-the-art resolution figure of merit of 3.2 pJK2. This combination of high accuracy, high resolution, high speed, and low-energy consumption makes this sensor suited for commercial and industrial applications.

Smart measurement system for resistive (bridge) or capacitive sensors

A low-cost smart measurement system for resistive (bridge) and capacitive sensors is presented and demonstrated. The measurement system consists of three main parts: the sensor element, a universal transducer interface (UTI) and a microcontroller. The UTI is a sensor-signal-to-time converter, based on a period-modulated oscillator, which is equipped with front-ends for many types of resistive (bridge) and capacitive sensors, and which generates a microcontroller-compatible output signal. The microcontroller performs data acquisition of the output signals from the interface UTI, controls the working status of the UTI for a specified application and communicates with a personal computer. Continuous auto-calibration of the offset and the gain of the complete system is applied to eliminate many nonidealities. Experimental results show that the accuracy and resolution are 14 bits and 16 bits, respectively, for a measurement time of about 100 ms.

12.8 A BJT-based CMOS temperature sensor with a 3.6pJ·K 2 -resolution FoM

This paper presents a precision BJT-based temperature sensor implemented in standard CMOS. Its interface electronics consists of a continuous-time duty-cycle modulator [1], whose output can be easily interfaced to a microcontroller, rather than the discrete-time ΔΣ modulators of most previous work [2-4]. This approach leads to high resolution (3mK in a 2.2ms measurement time) and high energy efficiency, as expressed by a resolution FoM of 3.6pJK2, which is a 3× improvement on the state of the art [4,5]. By employing chopping, dynamic element matching and a single room temperature trim, the sensor also achieves a spread of less than ±0.15°C (3σ) from -45 to 130°C.

The Scaling of Multiple Sensor Signals with a Wide Dynamic Voltage Range

In this paper a novel concept for scaling of multiple sensor signals with a wide dynamic voltage range is presented. With the application of Dynamic Element Matching (DEM) technique, the multiple sensor signals can be accurately pre-scaled to a limited range, which can be further processed with high performance.

A Low-Cost Smart Measurement System for Resistive (Bridge) or Capacitive Sensors

A low-cost smart measurement system for resistive (bridge) or capacitive sensors is presented. The measurement system consists of three main parts: the sensor element, a universal transducer interface (UTI) and a microcontroller. The Universal Transducer Interface (UTI) is equipped with front-ends for many types of resistive (bridge) and capacitive sensors. It is a sensor-signal-to-time converter, based on a period-modulated oscillator, which generates a microcontroller-compatible output signal. The microcontroller performs data acquisition of the output signals from the UTI, controls the operating conditions and communicates with a personal computer. Continuous auto-calibration is applied to eliminate the influences of offset and gain errors. According to the experimental results the accuracy and resolution amounts to 13 bits and 16 bits, respectively, for a measurement time of about 100 ms.