I. Introduction
Clock is the most important electrical signal. It is used to coordinate events inside electronic world. Clock is a key factor in time synchronization process which is the foundation for myriad applications from military, metrology, industrial, consumer, communication networks, automotive, to power grid, banking, scientific project and etc. In applications, clock signal originates from reference frequency standards that require high quality factor (Q factor) resonating element, such as micro-machined or piezoelectric crystal that acts as an electromechanical resonating module. Crystal in oscillator circuit behaves like a very high Q-tuned network, permitting vibrations at its resonant frequency.