CMOS temperature sensor with ring oscillator for mobile DRAM self-refresh control

Abstract

This paper presents novel low-cost CMOS temperature sensor for controlling the self-refresh period of a mobile DRAM. In the proposed temperature sensor, the temperature dependency of poly resistance is used to generate a temperature-dependent bias current, and a ring oscillator driven by this bias current is employed to obtain the digital code pertaining to on-chip temperature. This method is highly area-efficient, simple and easy for IC implementation as compared to traditional temperature sensors based on bandgap reference. The proposed CMOS temperature sensor was fabricated with an 80nm 3-metal DRAM process, which occupies extremely small silicon area of only about 0.016mm2 with under 1μW power consumption for providing 0.7°C effective resolution at 1 sample/s processing rate. This result indicates that as much as 73% area reduction was obtained with improved resolution as compared to the conventional temperature sensor in mobile DRAM.