面向CMOS温度传感器的低功耗数字滤波器设计

Design of Low-Power Digital Filter for CMOS Temperature Sensors

CMOS温度传感器广泛应用于物联网传感节点,功耗属性是其重要指标.数字滤波器功耗是温度传感器功耗的主要来源之一,限制数字滤波器功耗成为实现温度传感器低功耗的重要方法.基于此,开展了面向CMOS温度传感器的低功耗数字滤波器设计,提出了一种精度自适应的数字滤波器,该滤波器由递归型CIC滤波器和基于移位加法器的FIR滤波器级联而成,可根据实测温度与用户设定阈值温度区间差值自行调节CIC滤波器级数和FIR滤波器阶数.当实测温度在阈值温度区间内时,滤波器中的所有运算单元均参与运算,滤波器处于最高精度;当实测温度在阈值温度区间外时,有选择性的关断滤波器中的运算单元,使滤波器功耗下降.对于不需要重点监测的温度区间,测温精度要求通常并不高,若依旧进行高精度温度监测,将产生许多不必要功耗开销,采用精度自适应的数字滤波器可以有效解决该问题.为了进一步降低温度传感器功耗,根据温度信号变化缓慢的特点,采用单次温度转换结合闲时关断的工作模式,并对该种工作模式下单次温度转换运算进行优化,使FIR滤波器功耗降低5.5%.温度传感器采用180 nm CMOS工艺实现,测试结果表明,当实测温度处于阈值温度区间内时,传感器在-55~115℃温度范围内可以具有0.47℃的精度,在1.8 V供电电压下,传感器数字部分功耗为20.15μW.当实测温度在阈值温度区间外时,相比于实测温度处于阈值温度区间内,传感器数字部分功耗最大可降低11.3%.

The complementary metal oxide semiconductor(CMOS)temperature sensor is widely used in sensing nodes of the Internet of things,and power consumption is an important index of the sensor.Digital filter power con-sumption is one of the main sources of temperature sensor power consumption;thus,limiting digital filter power consumption is an important method to realize lower power consumption in temperature sensors.Based on this,a low-power digital filter for the CMOS temperature sensor was designed,and a precision adaptive digital filter was proposed.The precision adaptive digital filter is a two-stage structure,which consists of a recursive cascaded integrator comb(CIC)filter and a finite impulse response(FIR)filter based on a shift adder.The precision adaptive digital filter could automatically adjust the CIC filter level and the FIR filter order according to the difference between the measured temperature and the threshold temperature range set by the user.When the measured temperature was within the threshold temperature range,all arithmetic units in the filter participated in the operation,and the filter exhibited the highest precision.When the measured temperature was outside the threshold temperature range,the arithmetic units in the filter were selectively turned off to reduce the filter power consumption.For temperature ranges that did not require special monitoring,the requirement for temperature measurement accuracy was usually low.If high-precision temperature monitoring was performed,the unnecessary power consumption would occur.The use of preci-sion adaptive digital filters could effectively solve this problem.To reduce the temperature sensor power consumption further,a power mode which consists of single temperature conversion and idle shutdown,was adopted according to the characteristically gradual change of temperature signals.In this mode,the single temperature conversion arithme-tic was optimized so that the FIR filter power consumption was reduced by 5.5%.The temperature sensor chip is im-plemented with a 180 nm CMOS process.The experimental results show that,when the measured temperature is within the threshold temperature range,the sensor exhibits an accuracy of 0.47℃in the temperature range of-55℃to 115℃and the power consumption of the digital part of the temperature sensor is 20.15μW under the supply volt-age of 1.8 V.When the measured temperature is outside the threshold temperature range,the power consumption of the digital part of the temperature sensor decreases by up to 11.3%compared with that when the measured temperature is within the threshold temperature range.