Abstract
This 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.
Highlights
With the rapid increase in the circuit density and clock speed of modern very large-scale integration (VLSI) systems, all electronic circuits and systems can be affected by problems caused by heating, which severely affects their reliability
A floorplan of the proposed thermostat fabricated in a TSMC 0.35 μm complementary metal-oxide semiconductor (CMOS) process is shown in Figure 14; as shown in the figure, the core area is 0.067 mm2
This paper presents a linearity-enhanced time-domain CMOS thermostat with process-variation calibration
Summary
With the rapid increase in the circuit density and clock speed of modern very large-scale integration (VLSI) systems, all electronic circuits and systems can be affected by problems caused by heating, which severely affects their reliability. It consists of a temperature-sensing circuit for generating a temperature-dependent time tD, a timing reference circuit for determining an adjustable set-point time tA, and a delay-time comparator for detecting the relationship between tD and tA. To reduce the cost of tests, numerous previous studies have proposed using time-domain sensors with one-point calibration [12,13,14,15,16,17,18]. Without adopting the fitting for curvature correction, a frequency-to-digital-based temperature sensor using a multiphase clock was proposed to achieve a little bit large inaccuracy of −2.8 to 2.9 °C after one-point calibration from −40 to 110 °C [15]. An oscillator-based self-calibrated temperature sensor with an on-chip process compensation circuit was proposed in [17].
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