Inductor shielding strategies to protect mmW LC-VCOs from high frequency substrate noise

This paper analyzes the impact of high-frequency substrate noise on two 60 GHz LC-VCOs that implement different strategies for inductor shielding, namely floating and grounded shields. An analytical model, which has previously shown very good accuracy up to 7 GHz, is used to identify the circuit parameters that determine the level of the spurs created by the noise. These parameters are individually evaluated for the two VCOs, identifying their relative responsibility for the observed noise effects. The analysis concludes that a floating inductor shield provides extra immunity compared to a grounded inductor shield, and that this advantage is essentially due to the improvement in the tank quality factor. The predictions of the analytical model are validated by comparing them with circuit simulations and measurements of the noise impact on the two VCOs manufactured in a 65 nm CMOS technology, proving its usefulness at mm-wave frequencies.