Temperature measurement is an increasingly important task in modern microprocessors and other digital circuits. In this paper, a ring oscillator-based CMOS temperature sensor to achieve a high thermoelectric sensitivity with nano-watt power consumption for RFID applications is introduced. A ring oscillator’s delay dependence on temperature gives a convenient way to measure temperature of a chip. Temperature dependence of the threshold voltage and carrier mobility of MOS transistors exhibits a dependence of oscillation frequency on junction temperature, and embedding this simple circuit inside any VLSI chip and in conjunction with a counter is a way for efficient and highly accurate temperature measurement. The system design as well as the circuit implementation in standard 0.18μm CMOS technology is discussed in details. A bias current generator is used to control the bias current of a high-frequency oscillator circuit, which entails maximization of temperature sensitivity and dynamic range, power consumption reduction and furthermore, by incorporation with stacked transistor insures process variation compensation. Simulated results with Cadence indicated that proposed temperature sensor at supply voltage of 0.3V has a resolution of 0.5ºC/LSB with a 10-bit digital output code over a temperature range of 0ºC to 70ºC. At 66Hz sampling rate, the proposed sensor consumes 6.3nW.
VLSI design, temperature sensor, ring oscillator, radio frequency identification, low power.