A 0.0019-mm² LC-Ring Oscillator With an Ultra-Compact Transformer Achieving 175.2 dBc/Hz FoM_@1MHz and 202.4 dBc/Hz FoM_A

This brief describes an area-efficient LC-ring oscillator featuring an ultra-compact transformer resonator. The series inverters could be equivalent to the negative resistors providing gain compensation. The involved inverters and switched capacitor banks are fully integrated underneath the transformer resonator. Thus, with a comparable area of the typical ring oscillators, our oscillator shows significantly improved phase noise (PN) and figure-of-merit (FoM). Besides, we implemented the stacked coupling and distributed-coupling transformer-based LC-ring oscillators for the PN and FoM comparison. The stacked-coupling LC-ring oscillator can lower the PN with the same frequency and power budget. Fabricated in 40-nm CMOS, our stacked-coupling LC-ring oscillator scores a PN_@1MHZ of -110.4 dBc/Hz across the frequency tuning range from 3.7 to 5.1 GHz with an active area of 0.0019 mm2, corresponding to a superior FoM (FoM_A)_@1MHz of 175.2 dBc/Hz (202.4 dBc/Hz) that is 4.2 dB (6 dB) higher than the distributed-coupling LC ring oscillator.