Self-tracking charge pump for fast-locking PLL

Presented is a self-tracking charge pump (ST-CP) that can deliver a non-constant current over the output voltage range for a fast-locking phase-locked loop (PLL). It features a simple self-bias self-tracking architecture that can reduce, simultaneously, the PLL locking time and the current mismatch in charge and discharge phases. Experimentally verified in a 0.18 mu m CMOS process, the proposed ST-CP achieves 72% reduction of PLL locking time compared with the conventional one. The core occupies 30 x 60 mu m(2) and draws 10 mu A at 1.8 V.