A 1.35GHz All-Digital Fractional-N PLL with Adaptive Loop Gain Controller and Fractional Divider

Abstract

A 1.35GHz all-digital phase-locked loop (ADPLL) with an adaptively controlled loop filter and a 1/3rd-resolution fractional divider is presented. The adaptive loop gain controller (ALGC) effectively reduces the nonlinear characteristics of the bang-bang phase-frequency detector (BBPFD). The fractional divider partially compensates for the input phase error which is caused by the fractional-N frequency synthesis operation. A prototype ADPLL using a BBPFD with a dead zone free retimer, an ALGC, and a fractional divider is fabricated in 0.13􀈝m CMOS. The core occupies 0.19mm2 and consumes 13.7mW from a 1.2V supply. The measured RMS jitter was 4.17ps at a 1.35GHz clock output.