A high swing charge pump with current mismatch reduction for PLL applications

Abstract

A charge pump (CP) is widely used in modern phase-locked loop (PLL) implementations. The CP current mismatch is a dominant source of static phase offset and reference spur in the PLL output signals. In this paper, a novel CP with small current mismatch characteristic over a wide output voltage range is proposed. The specially designed dual compensation circuits use the unity-gain feedback operational amplifier and current mirrors to reduce the current mismatch when the output voltage is closed to the supply voltage (VDD) or ground (GND). And the additional feedback transistors are used to reduce the impact from the channel length modulation effect. Post-layout simulation results demonstrate that the output current of the proposed CP in a 40 nm CMOS technology is 115 µA. Moreover, the current mismatch is less than 0.97 µA or 0.84% over the output voltage range from 0.04 to 1.07 V covering more than 93.6% of the 1.1 V supply. Thus, the proposed CP maximizes the dynamic range, and reduces the phase offset and reference spur of CP-PLLs.