Clock Frequency Tripler for Optimizing Charge Pump Rise Time in Cold-start Circuit

For energy-harvesting systems, optimizing cold-start speed ensures that the system can start up more quickly when energy becomes available, thus improving overall efficiency. In this article, a clock frequency optimization strategy is presented to optimize the voltage boosting time of the charge pump in cold-start circuit using a ring oscillator-charge pump structure. The proposed topology introduces a clock frequency multiplier based on a ring oscillator, capable of tripling the clock frequency, thereby accelerating the charging and discharging speed of the charge pump capacitors to optimize the charge pump voltage rise time. The circuit is designed and simulated using a 180-nm CMOS process. Simulation results show that after incorporating the proposed frequency tripler, the output voltage of the cross-coupled charge pump can be boosted to 755mV within 17.9ms at a cold-start voltage of 105mV, with a 700MΩ load. The addition of the clock frequency triple circuit reduces the voltage rise time of the charge pump by 66.72% and the time of the pulse generation by 45.43%, compared to the original circuit.