Integrated switched-capacitor-based cold-start circuit for DC-DC energy harvesters with wide input/output voltage range and low inductance in 40-nm CMOS

This paper outlines an integrated switched-capacitor (SC)-based cold-start circuit for dc-dc energy harvesters that uniquely combines a low cold-start voltage, wide input/output voltage and low inductance value in the boost stage. The proposed design specifically targets size-constrained, self-powered Internet-of-Things applications. The proposed design is an SC circuit built from low-threshold-voltage devices operating in the sub-threshold region and provides the drive voltage for high-threshold-voltage devices of the boost dc-dc converter. The SC circuit is an NMOS-based Dickson charge pump driven synchronously with a series of cross-coupled voltage doublers and voltage multiplying gate drivers. The SC circuit, which is integrated together with a boost converter as the dc-dc energy harvester, has been implemented in a 40-nm CMOS process for future system-on-chip integration. The measured results show that with a 4.7 μH boost converter inductance, the design can start up from typical input voltages as low as 190 mV while offering up to 2.4 V input and 5 V output voltage compatibility.