What is the Quality Factor Q Value of Quartz Crystal

What is the quality factor Q value of quartz crystal? 

Q value is also known as the "quality factor". A large Q indicates that the crystal oscillator has a small internal resistance, small loss, a small required drive level, easy vibration, and better stability. A Quartz crystal resonator is used as a resonant circuit in oscillation circuits. 

Its quality factor, namely the Q value, is a very important electrical parameter of a crystal oscillator, which is closely related to the frequency stability of the crystal oscillator. As mentioned above, the higher the Q value of the crystal oscillator, the better the frequency stability.

The quality factor of a quartz crystal is determined by its dynamic parameters, which can be clearly seen in its equivalent circuit:

R1, C1, and L1 are parameters related to quartz crystal resonators, while C0 has no relationship with quartz crystal resonator frequency. 

Definition of the quality factor of crystal oscillator resonant circuit: Q=2 π * 

energy stored in the circuit/energy consumed every cycle

The quality factor Q valueis derived from the above formula: Q=W*L1/R1

Notes:

W=2πF

F is frequency

L1 is equivalent inductance

R1 is equivalent resistance

R1 represents the loop loss. The smaller R1 is, the smaller the loss is, the higher the Q value is. 

Conversely, the larger R1 is, the lower the Q value is. If it is regarded as a free oscillation circuit, it can explain that the circuit maintains constant amplitude oscillation. When Q value is high, the oscillation attenuation slows down, and when Q value is low, the oscillation attenuation is fast.

The Q value of quartz crystal can reach millions, such as the 32.768KHz quality factor of crystal oscillator commonly used in quartz watches:

Q=w*L1/R1=2πf*L1/R1=2π*32768*107.9*100/(21*1000)=115*1000

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