CMOS Integrated Time-Mode Temperature Sensor for Self-Refresh Control in DRAM Memory Cell

This paper proposes a low-power complementary metal-oxide-semiconductor (CMOS) smart temperature sensor in order to obtain self-refresh control for low-power memory cells. The multiple-block system is composed of a temperature-to-pulse generator (TPG), a time-to-digital converter (TDC), and a frequency selector. A pulse-shrinking system with an inverter-based delay line is used for feedback topology in the TDC. A temperature-independent current reference is applied for temperature compensation in the ring-oscillator and delay line in the TPG. The small-size time-mode temperature sensor is designed using a 0.35-μm CMOS process. Six different digital outputs are obtained for temperature ranging between -40°C and 100°C. Measurement shows that the proposed temperature sensor operates with a power dissipation of 0.075 μW per sample and a die area of 0.08 mm
²
. The output frequency is shown to increase exponentially with variations in temperature, while the shrinking pulse in the TDC shows linear dependence on temperature.