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 (V_DD) 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 40nm CMOS technology is 115µA. Moreover, the current mismatch is less than 0.97µA or 0.84% over the output voltage range from 0.04 to 1.07V covering more than 93.6% of the 1.1V supply. Thus, the proposed CP maximizes the dynamic range, and reduces the phase offset and reference spur of CP-PLLs.