A 1 V, 10 μW FLL-Based Time-Domain CMOS Temperature Sensor with +1.2 °C/−0.9 °C Inaccuracy from −40 °C to 125 °C

This paper presents a time-domain closed-loop resistive temperature sensor architecture. The design employs a frequency-locked loop (FLL)-based oscillator as the sensing element, generating a monotonic frequency response to temperature variations. The output frequency is digitized on-chip and converted into a temperature code. Within the oscillator core, a switched-capacitor technique converts frequency to voltage for closed-loop control, reducing charging/discharging voltage swings and significantly lowering dynamic power consumption. The FLL topology enhances frequency stability, minimizes distortion, and suppresses power supply sensitivity. Fabricated in a 180 nm CMOS process with a core area of 0.12 mm2, the sensor achieves a peak-to-peak inaccuracy of +1.2 °C/−0.9 °C from −40 °C to 125 °C. Operating at 1 V, the circuit consumes only 10 μW with a resolution of 51 mK within 12 ms.