A bipolar output voltage pulse transformer boost converter with charge pump assisted shunt regulator for thermoelectric energy harvesting

This work first generates ±1 V output via the self-startup pulse transformer boost converter. Another on-chip single-stage voltage tripler then generates 3 V output from the extra output power of boost converter, which is shunted otherwise. Higher voltage headroom is instrumental for sensor, analog and RF circuits. Charge pump clock frequency is adaptively tracking the input voltage, which is sensed using power-saving time-domain digital technique. Based on a standard CMOS 0.13-μm technology, chip measurement verified the standalone boost converter and simulation confirmed the overall system operations. The system requires minimum startup input voltage of 36 mV and input power of 5.8 μW.

I. Introduction

Thermoelectric energy harvesting is interesting due to the omnipresence and continuous operation that is time independent. The output voltage of thermoelectric generator (TEG) is in proportion to the temperature difference between its two junctions. Typically TEG is modelled as ideal voltage source with fixed source resistance . State-of-the-art thin-film TEG [1] has much smaller area size than conventional TEGs [2] [3]. Besides being compact, thin-film TEG also allows higher power to be generated per device area, which enables further miniaturization of the entire system size. Despite the newer TEG has higher output voltage than conventional TEGs, the internal resistance is higher (400 ohms vs. less than 10 ohms) and smaller output current as trade-offs. Performances of different TEGs are summarized in Table I. Table I. Comparisons of different TEGs at

TEG type				Device Area	Power/Area
Micropelt MPG-D751 [1]	1.68V	3.74mA	1.42mW	42mm × 3.3mm
Tellurex G2–30-0313 [2]	0.22V	29mA	1.58mW	30mm × 30mm
Marlow Technology TG12–2.5 [3]	0.55V	83mA	11.4mW	30mm × 30mm