A high-slope PTAT temperature sensor for frequency compensation of an RTC oscillator

Abstract

A temperature sensor used to compensate the crystal oscillator frequency instability of a real time clock (RTC) is proposed in this paper. The sensor utilizes the difference of a current proportional to the absolute temperature (PTAT) and another complementary to the absolute temperature (CTAT), generating a high-slope PTAT voltage with minimum value close to zero. The introduced approach provides a voltage signal range that reduces the power and area consumption of a 7-bit successive approximation analog-to-digital converter (SAR-ADC). The principles of the circuit topology alongside the simulation results of corners and Monte Carlo analyzes are presented. A prototype is fabricated in a 0.18 μm CMOS technology and experimental results showed a temperature inaccuracy of -0.812 to 0.266 °C, with an average resolution of 18.01 mV/°C, using a one-point calibration within the range of 0 to 40 °C. The sensor features an area of 0.08 mm2 and consumes less than 73.8 μW from a 1.8 V voltage supply.