Substrate Noise Coupling Reduction in $LC$ Voltage-Controlled Oscillators

In this letter, a substrate noise coupling effect in LC voltage-controlled oscillators (VCOs) was investigated. By 0.18-mum CMOS technology, three 2.4-GHz VCOs were designed using different types of spiral inductors to observe the substrate noise induced spurs. Compared with the design using a standard inductor, the proposed deep N-well (DNW) and patterned ground shield (PGS) VCOs demonstrated clearly reduced third-order intermodulation spurs by 6-8 and 10-15 dB, respectively. Based on the established physical-based equivalent circuit models, we found that the low-impedance paths introduced by DNW and PGS were the dominant factor for the observed substrate noise reduction in the proposed VCOs.