Experimental analysis of the effect of substrate noise on PLL performance

A novel approach is used to identify the substrate-noise sensitive components of a phase-locked loop (PLL) using a tank (LC) voltage controlled oscillator (VCO). Using passive noise injection pads capacitively connected to the substrate, continuous wave (CW) noise is injected into the substrate. The frequency response of the PLL is measured as noise is injected near dc, near the reference clock frequency, and near the VCO frequency. Analyzing the spurs seen in a spectrum analyzer leads to the conclusion that the other PLL blocks can be more sensitive to substrate noise coupling than the VCO, depending on the substrate noise frequency