Crystal (MHz) is a passive electronic component that uses the piezoelectric effect of quartz crystal to produce high-precision oscillation frequency. It is used to provide reference clock source.

Active devices that integrates crystal and oscillating circuit. It can output CMOS or differential frequency signal to provide reference clock source with super small sizes and high precision.

Circulator is to ensure that the signal passes forward without damage and the reverse signal is isolated. Adding a high-power load or attenuator at the third port of the circulator is the isolator.