Phase Noise Analysis of Clock Generator by Using Phase Noise Sensitivity

Phase noise represents signal instabilities in the frequency domain and is assessed through power measurements at various offsets from the carrier frequency. Herein, the phase noise of a clock generator is analyzed and modeled. Sources for the phase noise of the clock output at the resonance frequency are identified, including the power supply, the heatsink, and the external crystal. Low-frequency resonance is detected and validated to be caused by the external crystal grounding design. Solutions to decrease crystal-related noise are proposed and validated. In addition, the sensitivity based on the signal-to-noise ratio is proposed and verified with measurements to numerically analyze the effects of power supply noise on clock phase noise. The proposed phase noise sensitivity is extracted from the measured phase noise results and can be used to estimate the phase noise and jitter of different power supply noises. The extraction and prediction methods are validated with different buffer types, including low-voltage differential signal, high-speed current steering logic, low-voltage positive emitter-coupled logic, and low-voltage complementary metal–oxide–semiconductor, in a device under test with the given design.