A Linearity-Enhanced Time-Domain CMOS Thermostat with Process-Variation Calibration
AbstractThis study proposes a linearity-enhanced time-domain complementary metal-oxide semiconductor (CMOS) thermostat with process-variation calibration for improving the accuracy, expanding the operating temperature range, and reducing test costs. For sensing temperatures in the time domain, the large characteristic curve of a CMOS inverter markedly affects the accuracy, particularly when the operating temperature range is increased. To enhance the on-chip linearity, this study proposes a novel temperature-sensing cell comprising a simple buffer and a buffer with a thermal-compensation circuit to achieve a linearised delay. Thus, a linearity-enhanced oscillator consisting of these cells can generate an oscillation period with high linearity. To achieve one-point calibration support, an adjustable-gain time stretcher and calibration circuit were adopted for the process-variation calibration. The programmable temperature set point was determined using a reference clock and a second (identical) adjustable-gain time stretcher. A delay-time comparator with a built-in customised hysteresis circuit was used to perform a time comparison to obtain an appropriate response. Based on the proposed design, a thermostat with a small area of 0.067 mm2 was fabricated using a TSMC 0.35-μm 2P4M CMOS process, and a robust resolution of 0.05 °C and dissipation of 25 μW were achieved at a sample rate of 10 samples/s. An inaccuracy of −0.35 °C to 1.35 °C was achieved after one-point calibration at temperatures ranging from −40 °C to 120 °C. Compared with existing thermostats, the proposed thermostat substantially improves the circuit area, accuracy, operating temperature range, and test costs. View Full-Text
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Chen, C.-C.; Lin, Y. A Linearity-Enhanced Time-Domain CMOS Thermostat with Process-Variation Calibration. Sensors 2014, 14, 18784-18799.
Chen C-C, Lin Y. A Linearity-Enhanced Time-Domain CMOS Thermostat with Process-Variation Calibration. Sensors. 2014; 14(10):18784-18799.Chicago/Turabian Style
Chen, Chun-Chi; Lin, Yi. 2014. "A Linearity-Enhanced Time-Domain CMOS Thermostat with Process-Variation Calibration." Sensors 14, no. 10: 18784-18799.