Conventional CMOS charge pump circuits have some current mismatching charac
teristics. The current mismatch of the charge pump in the PLLs generates a
phase offset, which increases spurs in the PLL output signals, in particula
r, 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 c
an achieve a charge pump with good current matching characteristics. It sho
ws 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 0.25<mu>m CMOS process.