Impact of radiated EMI in high frequency crystal oscillator

The high frequency (HF) crystal oscillator is susceptible to electromagnetic interference (EMI), which affects the stability or accuracy of reference frequency standards. The effect of radiated EMI can be both deterministic and random in nature that shows up as jitter in the time domain and phase noise in the frequency domain. In this paper, we studied the impact of radiated EMI in 155.6 MHz crystal oscillator (XO) and the design consideration for EMI and jitter insensitive signal sources for reference frequency standard applications. Experimental results and CAD simulated data provides insight into observed characteristics (mode-jumping, sub-harmonics and jitter, and validated with the design example of 155.6 MHz crystal oscillator circuits. Although, the likelihood of frequency shift in a noisy electromagnetic environment is far higher, however, this paper reports the mode-coupled phase-injected techniques to restrict the frequency shift and also minimizes the phase noise by 8–10 dB.