An accurate CMOS time-to-digital-converter-based smart temperature sensor with negative thermal coefficient

A CMOS TDC-based smart temperature sensor with negative thermal coefficient is proposed for high-performance VLSI chips or SOC integration. Unlike the conventional intelligent temperature sensors which rely on voltage/current analog-to-digital converter (ADC) for digital output coding, the proposed temperature sensor without any bipolar transistor generates a pulse with a width inversely proportional to the measured temperature first. Then, a cyclic time-to-digital converter (TDC) is utilized to convert the pulse into the corresponding digital code. The test chips were fabricated in the TSMC CMOS 0.35-mum 2P4M digital process and have an extremely small area of 0.09 mm² , less than one-twentieth of most predecessors. Due to excellent output linearity, the achieved measurement error is merely plusmn0.6degC after two point calibration, but without any curvature correction or dynamic offset cancellation. The effective resolution is better than 0.1degC, the power consumption is about 1.5 muW at a sample rate of 5 samples/s and a measurement rate as high as 10 kHz is feasible