Linearization of a thermal-diffusivity-based temperature sensor

Recent work has shown that accurate temperature sensors can be realized by measuring the temperature-dependent thermal diffusivity of silicon, D. This can be done by measuring the delay of an electrothermal filter (ETF). Since D is a nonlinear function of temperature, however, such sensors generally have a nonlinear characteristic. Furthermore, the time-to-digital converter (TDC) used to digitize the ETF´s delay is also nonlinear. This paper discusses how the output characteristic of a thermal-diffusivity-based temperature sensor can be linearized by using the systematic nonlinearity of the TDC to compensate for the nonlinearity of D. Measurements on devices realized in 0.7 ¿m CMOS technology show that a nonlinearity of -1.5°C ~ 3°C can be reduced to less than ±1°C over the industrial temperature range (-45°C to 105°C).