Reduction of pump current mismatch in charge-pump PLL

A charge pump that minimises the mismatch between the charging and discharging currents and keeps the currents constant across a wide output voltage range is described. The improved current matching helps reduce the static phase offset and reference spur of a chargepump phase-locked loop (PLL) and the constant currents help control the PLL dynamics precisely. The proposed charge pump with dual compensation circuits demonstrates current mismatch of less than 3.2% and pump-current variation of 1.7% over the output voltage ranging from 0.2 to 1.0 V in the 0.13 μm CMOS process with 1.2 V supply.