TDA5250D2 Datasheet, PDF (53/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

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TDA 5250 D2
preliminary
Applications
4.2 Crystal Oscillator
The equivalent schematic of the crystal with its parameters specified by the
crystal manufacturer can be taken from the subsequent figure.
Here also the load capacitance of the crystal C_L, which the crystal wants to see
in order to oscillate at the desired frequency, can be seen.
L₁
C₁ R₁
C_L
-R
C₀
Figure 4-14 Crystal
L₁:
C₁:
C₀:
motional inductance of the crystal
motional capacitance of the crystal
shunt capacitance of the crystal
Crystal.wmf
Therefore the Resonant Frequency f_s of the crystal is defined as:
f_S = _2π
1
L₁ *C_L
[4 – 13]
The Series Load Resonant Frequency f_S‘ of the crystal is defined as:
f_S `= _2π
1*
L₁ *C₁
1
+
C₀
C₁
+ C_L
regarding Figure 4-14
[4 – 14]
f_s’ is the nominal frequency of the crystal with a specified load when tested by
the crystal manufacturer.
Pulling Sensitivity of the crystal is defined as the magnitude of the relative
change in frequency relating to the variation of the load capacitor.
Wireless Components
4 - 13
Specification, July 2002