Measurement and modeling of the sensitivity of LC-VCO's to substrate noise perturbations

On-chip oscillators are very sensitive to substrate perturbations. Both low-frequency and high-frequency distortions can ruin the required spectral purity of the oscillator. This paper presents the measurement and modeling results of the sensitivity of a 900MHz LC-Voltage Controlled Oscillator (LC-VCO) to substrate perturbations in a frequency range from DC to 900MHz. Accurate measurement of the sensitivity require various measurement setups to investigate different impact phenomena. These measurements implies spectral analysis, linear vectorial network analyzer measurements and time domain measurements. The impact of substrate noise is modeled in a high Ohmic 0.18μm 1P6M CMOS technology. Below 10MHz, the impact is dominated by the on-chip resistance of the VCO ground. Above 10MHz, the bond wires, parasitics of the on-chip inductor and the off-chip decoupling capacitors determine the sensitivity to substrate perturbations.