Low Phase Noise Wide Tuning Range N-Push Cyclic-Coupled

Abstract

Cyclic-coupled ring oscillators (CCRO) provide several unique features over regular ring oscillators such as avail- ability of multiple sets of phase-shifted outputs and reduced phase noise. Furthermore, when combined with N-push frequency multi- plication low phase noise, wide t uning ranges and millimeter-wave (mm-wave) frequencies can be realized. In this work, we propose two N- p u s hC C R O sf a b r i c a t e di na9 0n md i g i t a lC M O Sp r o c e s s . First, a wideband N-Push/M-Push CCRO is presented which achieves an output frequenc y range of 3.16–12.8 GHz using a unit cell ring oscillator operating at 1–2.56 GHz. The measured phase noise at 1 MHz offset is 103.4 dBc/Hz and 101.6 dBc/Hz at 3.16 GHz and 12.8 GHz, respectively. Second, an mm-wave N-Push CCRO is presented. It generates an output frequency of 13–25 GHz with a low phase noise performance of 95 dBc/Hz at 1 MHz offset over the output fr equency range . The proposed oscillators achieve superior ph ase noise performance as well as competitive figure-of-merit compared with the state-of-the-art ring oscillators. In addition, the operation of the CCRO and its phase noise is analyzed. We con firm, analytically and experi- mentally, that the phase noise of an M-stage CCRO improves by 10 M over that of a single ring oscillator. We also show that the phase noise improvement bandwidth is a function of the coupling strength.