27.4 A BJT-Based Temperature Sensor with an 80fJ.K2 Resolution FoM

BJT-based temperature sensors are widely used because they can achieve a high accuracy after applying a low-cost 1-point trim. In terms of energy efficiency, however, they are still outperformed by resistor-based sensors [1]. Recently, significant improvements in energy efficiency have been achieved by using charge-balancing continuous-time ΔΣ-modulators (CTΔΣM) to digitize the ratio of PTAT and CTAT currents generated by BJT-based front-ends [2], [3]. In this work, an NPN-based temperature sensor is presented that uses a noise-optimized charge-balancing scheme and a current-assisted amplifier to achieve both high energy efficiency (80fJ.K² FoM) and low inaccuracy (0.1°C (3σ) from -70°C to 125°C), while occupying only 0.05mm2. Compared to the state-of-the-art [2]–[5], the proposed sensor is 2.5x more energy efficient, achieves similar accuracy, and occupies 1.5x less area.