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Impedance between Two Terminals Z=R+jx

(R : Real Component, X : Impedance Component)

1. Equivalent Circuit Constants

Fig. 2-1 shows the symbol for a ceramic resonator. The

impedance and phase characteristics measured between

the terminals are shown in Fig. 2-2. This illustrates that

the resonator becomes inductive in the frequency zone

between the frequency Fr (resonant frequency), which

provides the minimum impedance, and the frequency Fa

(anti-resonant frequency), which provides the maximum

impedance.

It becomes capacitive in other frequency zones. This

means that the mechanical vibration of a two-terminal

resonator can be replaced equivalently with a

combination of series and parallel resonant circuits

consisting of an inductor : L, a capacitor : C, and a

resistor : R. In the vicinity of the specific frequency

(Refer to Note 1 on page 8), the equivalent circuit can be

expressed as shown in Fig. 2-3.

Fr and Fa frequencies are determined by the

piezoelectric ceramic material and the physical

parameters. The equivalent circuit constants can be

determined from the following formulas. (Refer to Note

2 on page 8)

Considering the limited frequency range of Fr≦F≦Fa,

inductance Le (H) having the loss Re (Ω).

(2-1)

(2-2)

(2-3)

(Qm : Mechanical Q)

Symbol

Re

Le

Re : Effective Resistance

Le : Effective Inductance

10

90

0

-90

Frequency (kHz)

Fr

Fa

2

P17E.pdf

2012.10.31