A MOS-Based Temperature Sensor With Inherent Inaccuracy Reduction Enabled by Time-Domain Operation

This article presents a MOS-based ON-chip temperature sensor system addressing both high-resolution and low-inaccuracy requirement, red while requiring a single temperature calibration point. Hence, the proposed temperature sensor system proves to be a low-cost solution, well addressing the requirements of the spreading market of system-on-chips (SoCs), mobile and wearable devices, and consumer electronics in general. The temperature sensor features a two-phase time-domain architecture, which employs as a sensing element a single NMOS transistor, biased alternatively with different currents, thus allowing achieving an inherent inaccuracy reduction. The proposed sensory system, fabricated in a standard 130-nm CMOS process, comprises, along the sensor core, a switched-capacitor analog interface circuit and a 1-bit second-order sigma-delta ( $\Sigma \Delta $ ) analog-to-digital converter (ADC). The proposed temperature-to-digital converter (TDC), experimentally characterized considering a batch of 16 samples, achieves 40-mK resolution at 20-kHz switching frequency and +0.75/ $- 0.92\,\,^{\circ} \text{C}$ inaccuracy across the $- 40\,\,^{\circ} \text{C}$ – $90 ^{\circ} \text{C}$ temperature range after one-point calibration at room temperature, consuming $25.4 \mu \text{W}$ , including the analog buffer added for testing purposes.