A 486k S/s CMOS time-domain smart temperature sensor with −0.85°C/0.78°C voltage-calibrated error

This paper presents the first voltage-calibrated CMOS time-domain smart temperature sensor to reduce the cost of mass production. A digitally adjustable relaxation oscillator designed as the temperature sensor vibrates between CMOS-based CTAT, PTAT voltage references with mutual curvature compensation to generate linear temperature-dependent output pulses. Voltage instead of temperature calibration is adopted to alleviate the impact of process variation and TDC is used for output coding. Fabricated in a TSMC 0.18-μm standard CMOS process, the proposed sensor is able to operate at a high speed of 486k samples/sec for SoC thermal monitoring. The active area is merely 0.122 mm² and the inaccuracy is measured to be less than ±1°C for 15 test chips in a wide temperature range of -40°C to 120°C. The performance is even superior to some chips with one- or two-point temperature calibrations. A milestone is established for time-domain smart temperature sensor to get rid of the heavy burden of fixed-temperature calibration with reason error budget.