Numerical modeling of PLL jitter and the impact of its non-white spectrum on the SNR of sampled signals

The impact of PLL jitter on ADC systems is nowadays mainly investigated performing numerical simulation at system level using a Gaussian white distributed noise source. The "colored" characteristic of the jitter spectrum of PLLs is thus completely neglected. We present some practical considerations on the impact of a non-white spectrum jitter on the SNR of an analog to digital conversion. A simple numerical model is developed, which can be used for simulating the impact of non-white and "sinusoidally modulated" noise on sampling system. This model is applied to a simple ADC system and to a QAM receiver. This analysis will help to understand which is the relevant jitter specification for analog to digital conversion systems.