Design of a low-power VLSI temperature sensor

Abstract

A low power CMOS temperature sensor with digital output is presented in this work. The sensor is current based, the combination of dependent and independent current that control the frequency of 2 ring oscillators. The difference in frequency of this two ring oscillator is converted into a digital temperature code by asynchronous counters. The reference current and the PTAT current is generated by applying a temperature dependent voltage across two resistors with different temperature coefficients. To achieve a low power consumption, the temperature voltage reference operates under 200 mV and resistors in the Mega Ohms range are utilized. In order to save area, an additional current mirror is used to reduce the current without increasing the resistor’s value. This sensor was implemented in TSMC 180nm technology and occupies an area of 0.085mm2. After post layout simulations, the sensor shows a current consumption of 1.7μA, a resolution of 0.17oC in the 0-60oC temperature range with a conversion time of 1.8ms and 3.2 nJ of energy per conversion.