Handling Notes
(4) Items calculated by equivalent constants and load capacitance
fs: Series resonance frequency
fp: Parallel resonance frequency
: Capacitance ratio
fL : Load resonance frequency
RL : Load resistance
CL : Load capacitance
Q : Quality factor
fs 2
1
L1
C1
fp
2
1
L1
C
C
0
0
C1
C1
C0
C1
fL fs
2
C1
(C0 CL)
1
RL R1
1
C0
CL
2
CL
C1
2
1
(f L/f s)1
C0
Q 2 fs L1
1
R1
2 fs C1 R1
The equation fL shows that fL varies as load capacitance CL connected to the crystal unit changes and that fL becomes larger
as CL becomes smaller.
The equation RL shows the change in impedance with a load capacitance connected. The impedance of crystal unit becomes
larger as CL becomes smaller.
2. Oscillation circuit and crystal unit
(1) Equivalent circuit of oscillation circuit and oscillation conditions
A simplified equivalent circuit is shown below.
Crystal unit
Oscillation circuit
Crystal unit
CL
XL
–R
RL
Oscillation circuit
C L = –X C
–R
C L : Load capacitance
–R : Negative resistance
X L : Reactance of crystal unit
–X C : Reactance of oscillation circuit
R L : Load resonance resistance
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