A time-domain SAR smart temperature sensor with −0.25∼+0.35°C inaccuracy for on-chip monitoring

The first time-domain successive approximation register (SAR) smart temperature sensor is proposed in this paper. Without using any bipolar transistor, a temperature sensor composed of temperature-dependent delay line is utilized to generate a delay time proportional to the measured temperature. A binary-weighted time reference delay line is adopted for set-point programming. The effective delay of the reference delay line is adjusted to approximate that of the temperature-dependent delay line for digital output coding through the help of SAR control logic. With 10 output bits, the proposed smart sensor owns a chip area of 0.6 mm² in the TSMC 0.35-mum standard digital CMOS process. The consumption current is 11.12 muA and an inaccuracy of -0.25~0.35degC over 0~90degC test temperature range is achieved for 23 test chips without any dynamic element matching, curvature correction, dynamic offset cancellation or BJT device.