What is the quality factor Q value of quartz crystal? | Xtalong
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