A charge transfer-based high performance, ultra-low power CMOS charge pump for PLLs

Abstract

This paper presents a novel high performance, ultra-low power scalable CMOS charge pump (CP) design for analog phase-locked loops (PLLs) fabricated in all-digital nanoscale IC processes. The compact CP circuit uses four minimally-sized transistor switches and a relatively small capacitor for transferring charge within the PLL to adjust the voltage controlled oscillator frequency in the PLL control loop. Unlike the state of the art designs, the proposed CP topology does not use current mirrors, nor does it suffer from traditional mismatch errors due to its unique structure. Additionally, this charge transfer-based CP has the ability to operate at very low supply voltages well below 1 V. The fast switching action of the proposed CP allows for the use of a no-added delay D-flip flop-based phase-frequency detector resulting in a reduced PLL control loop delay and very low reference spurs in the overall PLL design. The proposed CP has been placed in a 0.5---10 GHz PLL, fabricated, and physically tested in an all-digital 40 nm TSMC CMOS process. Additionally, post-silicon measurements of the CP circuit have been completed with a variable 0.2---1.2 V supply and a 50 MHz---1 GHz reference frequency. The proposed CP has an active area of 0.0004 mm2, consumes on average 250 pW power, and has a 0.1°---0.3° phase error, dependent on the PLL frequency of operation.