A CMOS PLL using current-adjustable charge-pump and on-chip loop filter with initialization circuit

A 900MHz CMOS PLL using current-adjustable charge-pump circuit and on-chip loop filter with initialization circuit is presented. The charge-pump current is insensitive to the changes of temperature and power supply. The value of the charge-pump current can be changed by switches which are controlled by external signals. Thus the performance of the PLL, such as loop bandwidth, can be changed with the change of the charge-pump current. The loop filter initialization circuit can speed up the PLL when power on. A multi-modulus prescaler is used to fulfill the frequency division in the feedback loop. The circuit is designed in 0.18μm 1.8V 1P6M standard digital CMOS process.