Cd, Cg: Capacitors connected to the two pins of the crystal oscillator and the ground respectively. Generally Cd == Cg, but Cd! = Cg is also ok. Cd and Cg are called matching capacitors or external capacitors, and their function is to adjust the load capacitance to meet the requirements of crystal oscillator. It should be noted that the total capacitance of Cd and Cg in series (Cd*Cg/(Cd+Cg)) is the effective load capacitance. Assuming that Cd==Cg==30pF, the contribution of Cd and Cg to the load capacitance is 65430.

Cic: Chip pin distributed capacitance and chip internal capacitance (some chips will integrate capacitance inside the chip in order to save Cd and Cg on PCB).

△ C: PCB trace distributed capacitance, with an empirical value of 3 to 5pf.