Abstract
This study focuses on designing and analyzing the LC voltage-controlled oscillators for high substrate noise coupling immunity. The LC-VCOs with various types of the improved inductors including MEMs inductors, deep N-well (DNW) inductors, and patterned ground shield (PGS) inductors are implemented to investigate the substrate noise coupling effects. The external noise is injected to see the impacts of the proposed designs on the second-order (IM2) and third-order intermodulation (IM3) spurs of the VCOs. In addition, the equivalent circuit models are established to explain the observation trends. First, the substrate noise coupling effects in a 5-7 GHz two-switch LC-VCO using a MEMs inductor are investigated. With a frequency variation around 80 MHz, the IM2 spurs of the VCO with a MEMs inductor are about 2-3 dBm higher than that of the standard design, while smaller IM3 spurs about 2-3 dBm are observed. Then the substrate noise coupling effects in a 2.4 GHz LC-VCO with DNW and PGS inductors are studied. With a similar circuit performance, the IM3 spurs of the VCOs with DNW and PGS inductors are about 6-8 dBm and 8-15 dBm lower than that of the standard design, respectively, but the IM2 spurs are almost unchanged. Finally, physical-based equivalent circuit models are established to explain the observed trends.