A low ripple CMOS charge Pump for low-voltage application

In power supply systems, switching supplies are typically cascaded with low dropout (LDO) regulator to suppress noise and provide low noise output. By providing lower output ripple voltage from charge pump circuit, input noise level (ripple) can be reduced first before it is fed into LDO and hence a more stable supply voltage can be generated from LDO. In this paper, a low voltage CMOS charge pump which offers lower output ripple voltage is proposed. Charge transfer switch (CTS) control scheme is employed inside cross-coupled charge pump in order to suppress backward current leakage path during clock transition. Therefore, proposed charge pump circuit provides lower output ripple voltage and higher voltage pumping efficiency. The proposed circuit has been simulated in 45nm CMOS process to validate the functionality of the circuit. The measured ripple voltage is less than 60mV at 10mA load current with 60 MHz pumping frequency. The proposed charge pump circuit does not suffer gateoxide reliability and is suitable implemented in low voltage CMOS processes.