A 17-mK Resolution ΣΔ-Based Temperature Sensor With an On-Chip Single-Point Calibrated Inaccuracy of ±1.5 °C (3σ)

This work presents the design of a bipolar junction transistor (BJT)-based temperature sensor with a sigma-delta analog-to-digital converter ( \Sigma \Delta ADC) fabricated in a 0.6 \mu m BiCMOS process. The sensor utilizes a proportional to absolute temperature (PTAT) current source embedding an auto-zeroing amplifier to bias the BJT core while effectively reducing offset errors. Additionally, this work achieves the combination of the temperature-sensing BJT core and the Σ∆ modulator, utilizing dynamic element matching (DEM) technique to accurately generate three different ratios (1:9, 9:1, 5:5) of BJT bias currents to cooperate with the modulator for modulation. The innovative modulation method in this work can reduce the errors caused by the operational amplifier offset voltage and BJT mismatch, completing the digitization of temperature without the need for a reference voltage source. Moreover, the sensor integrates a complete digital signal processor (DSP), allowing on-chip calibration by adjusting the operating cycle of the modulator and the initial value of the counter to obtain accurate and directly readable temperature data. It operates under a 3.3 V supply within a temperature range from −50 °C to 125 °C. Lastly, it achieves a 17 mK resolution and an inaccuracy of ±1.5 °C (3 σ ) after an on-chip single-point calibration.