Low-power temperature-to-frequency converter consisting of subthreshold CMOS circuits for integrated smart temperature sensors

A low-power temperature-sensing oscillator was developed using a 0.35m standard CMOS process. This oscillator generates a clock pulse whose frequency is proportional to absolute temperature (PTAT frequency). It consists of a PTAT current generator controlled with an external reference clock and a frequency-locked loop biased with an external reference voltage. The PTAT current generator makes use MOS emperature sensor TAT requency-locked loop ubthreshold current eak inversion ow power of the exponential current characteristic of MOSFETs operated in the subthreshold region. Theoretical analyses andexperimental results showed that the circuit canbeused as a temperature sensorwith a lowpower consumptionof 10 Wor less. The temperature coefficient of the output frequencywas insensitive to variation in device parameters, so the sensor circuit can be used only with one-point calibration. Its temperature-sensing error was from−1.8 to+1 ◦ C in a temperature range of 10–80 ◦C. This temperature sensor would be suitable for use in subthreshold-operated, power-aware LSIs.