Charge pump with perfect current matching characteristics in phase-locked loops - Electronics Letters

Conventional CMOS charge pump circuits have some current mismatching characteristics. The current mismatch of the charge pump in the PLLs generates a phase offset, which increases spurs in the PLL output signals. In particular, it reduces the locking range in wide range PLLs with a dual loop scheme. A new charge pump circuit with perfect current matching characteristics is proposed. By using an error amplifier and reference current sources, one can acheve a charge pump with good current matching characteristics. It shows nearly perfect current matching characteristics over the whole VCO input range, and the amount of the reference spur is < -75dBc in the PLL output signal. The charge pump circuit is implemented in a 0 . 2 5 ~ CMOS process.