A 4100-μm2 Wire-Metal-Based Temperature Sensor With a Fractional-Discharge FLL and a V2T Converter With ±0.2 °C Inaccuracy (3σ) From –40 °C to 125 °C and 45-fJ·K2 Resolution FoM in 28-nm CMOS

This article presents a compact wire-metal-based temperature sensor for thermal detection in advanced technologies. The key innovations include: 1) a fractional-discharge scheme originated by extracting the fractional pulse from the five-phase voltage-controlled ring oscillator (VCRO) to shrink the discharge window in the front end (FD) to 10% of a complete clock cycle, preserving the power budget while eliminating the need for bulky metal resistors; and 2) a voltage-to-time (V2T) converter with chopping implemented as an amplifying stage inside the frequency-locked loop (FLL), eliminating the undesired dc offset and 1/f-noise to safeguard the sensing accuracy and resolution. Prototyped in 28-nm CMOS process, this sensor occupies a footprint of $4100~{\mu }$ m² and consumes $10.5~{\mu }$ W under 0.8-V $V_{\mathrm {DD}}$ at room temperature. It demonstrates outstanding $3{\sigma }$ inaccuracies of ${\pm } 1.5~{^{\circ }}$ C/ ${\pm } 0.2~{^{\circ }}$ C after one-/two-point trimmings across ${-} 40~{^{\circ }}$ C to $125~{^{\circ }}$ C. The resolution figure of merit (R-FoM) achieves 45 fJ $\cdot $ K², illustrating the best-in-class performance compared to the resistor-based temperature sensors in the sub-65-nm process.