Impact of substrate perturbation on a 5 GHz VCO spectrum

This work investigates substrate coupling effects in mixed IC's, especially the perturbations on RF block. The authors present the impact of low frequency substrate noise perturbations on voltage-controlled oscillator (VCO) spectrum. A 5 GHz VCO test-chip is presented; several substrate taps have been placed inside VCO core to measure or to inject noise perturbations. The oscillation frequency sensitivity function of tuning voltage or bias current and spurious side-bands due to injected noise are measured to find out a relation between substrate noise and spectrum purity. Finally, a significant link between such device sensitivity functions and VCO spurs magnitude is demonstrated.