The Design And Realization Of High Precision CMOS Temperature Sensors

The integrated CMOS smart temperature sensors can be used to perform the measurement of the environment temperature and the thermal protection of chips with signal processing system integrated in. The integration makes the superiority of CMOS smart temperature sensors in low cost and low power over conventional temperature sensors. But the performance of temperature sensors implemented in CMOS process is limited by variables of factors, such as process spread and so on, which result in the relative poor absolute accuracy and restricted operating range, compared to conventional temperature sensors.Based on the analysis of temperature and process characteristic, a high-precision CMOS temperature is proposed and realized. The proposed temperature sensor is composed of the PNP-based temperature sensing circuit and a low-speed high-resulosion ADC. The temperature sensing circuit is based on the traditional bandgap generation circuit. Additionally , a variety of precision techniques, such as the precision PTAT bias circuit, the chopping technique, DEM (dynamic element matching) and compensation of second order nonlinearity, are adopted to overcome the impact of non-idealities. The low-speed high-resolusion∑△ADC is composed of the∑△modulator and the decimation filter. First-order and fourth-order IA modulator are used respectively for the compromise of dissipation and resolution.The proposed CMOS temperature sensor has been fabricated in SMIC 0.18um 1P6M CMOS technology, which occupies an area of 0.5×0.6mm~2. The test result shows that the error is within±1℃in the temperature range of 0-80℃, with power dissipation of 2.5mW from a 1.8V supply. Based on the performance evaluation, measurement is taken for better performance. The post-simulation result shows that the error is within±0.3℃in the temperature range of -50-100℃, with power dissipation of 3mW from a 1.8V supply. The improved edition has also been hand over to SMIC for fabrication.The main contents and innovation of this paper is as follows:1. A moderate-precision and a high-precision integrated CMOS temperature sensor is proposed. with various of precision measurements. The test result and simulation result shows that the proposed temperature sensors is in accordance with the high-resolution low-decipation design specification.2. The temperature characteristic of bipolar transistors is analyzed. The vertical parasitic PNP transistor is adopted as the kernel temperature sensing device. Corresponding measurements are made to compensate for the impact of various of non-idealities.3. The behavior model of broadband IA modulator is upbuilt. The effect of noise, the setup characteristic of the op-amp., and so on, on the performance of the A modulator is contained in the model.4. A new two-phase, non-overlap clock generation circuit for the control of the SC integration is brought forward, which greatly reduce the sampling capacitor of the integrator.