A series-parallel switched capacitor step-up DC-DC converter and its gate-control circuits for over the supply rail switches

An efficient control of the gate voltage of switches that operate outside the supply range is a problem that occurs in circuits such as step-up DC/DC converters and stimulation circuits for implantable devices. This paper proposes solutions to this problem, using as case study a 3x, ultra low-power, step-up DC/DC converter with series-parallel architecture. The proposed gate control strategy results in minimizing the gate swing of the switches and recycling of the gate charge in one of the cases, thus reducing the energy spent in driving the switch. The designed converter achieves an 84% simulated efficiency (without the control circuitry) @V_in = 400mV and 5μA load current and operates down to V_in = 200mV.