A CMOS based µ-power smart temperature sensor for ON-chip thermal monitoring

A low-power smart temperature-sensor has developed using a standard 0.18μm CMOS process technology. The sensor utilizes the dependency of the rising time of the output pulse of an inverter, on the drain current when triggered by a fixed frequency square wave signal. The working temperature of the proposed architecture is -40°C to +85°C with the maximum-power dissipation of 4.276μW. The occupied Si area is ≈0.4mm². The proposed architecture consists of four stages. At the first stage, the temperature is sensed in terms of voltage, using the proposed PTAT sensor. The PTAT voltage shows the measured thermal sensitivity (TS) of 2.20mV/°C with the temperature inaccuracy of ±0.35°C. The PTAT voltage is then converted into the PTAT current with the temperature coefficient (TC) of ≈3000 ppm/°C. This PTAT current is then mirrored into the current controlled inverter chain which is triggered by an external pulse. The rising time of the complementary output depends on the drain current which is proportional to the temperature. By using an inverter based comparator, the sensed temperature is expressed in terms of the duty cycle of the output pulse. It has been found by measurement that the duty-cycle varies linearly with the temperature for the given temperature range. The temperature inaccuracy of the proposed architecture after performing single point calibration is between ±1.25°C.