A low-voltage charge pump starting at 135mV for thermal energy harvesting in Body Area Networks

The design of a fully integrated low-voltage charge pump for thermal electric energy harvesting is presented in this paper. The proposed circuit has a startup voltage of 135mV without the need of expensive low voltage process options. This behavior is achieved by automatic frequency adaptation in correlation to the resistance of the switches. After startup the input voltage may even drop below 100mV, therefore it is well suited for small temperature gradients appearing in Body Area Networks. A test chip was fabricated in a low cost 130nm CMOS technology with an active area of 0.8 × 0.21mm².