TDA5212 Datasheet, PDF (26/51 Pages) Infineon Technologies AG – ASK/FSK 915MHz Single Conversion Receiver

TDA 5212
preliminary
Applications
4.3 Crystal Load Capacitance Calculation
The value of the capacitor necessary to achieve that the crystal oscillator is
operating at the intended frequency is determined by the reactive part of the
negative resistance of the oscillator circuit as shown in Section 5.1.3 and by the
crystal specifications given by the crystal manufacturer.
Crystal
C_S
Input
impedance
Z_1-28
Pin 28
TDA5212
Pin 1
Figure 4-4
Quartz_load_5212.wmf
Determination of Series Capacitance Value for the Crystal Oscillator
Crystal specified with load capacitance
1
C_S
=
1
C_l
+ 2p
f
X_L
with C_l the load capacitance (refer to the crystal specification).
Examples:
7.2 MHz:
14.5 MHz:
C_L = 12 pF
C_L = 12 pF
X_L=500 W
X_L=1050 W
C_S = 9.5 pF
C_S = 5.6 pF
These values may be obtained in high accuracy by putting two capacitors in
series to the quartz, such as 18pF and 20pF in the 7.2MHz case and 18pF and
8.2pF in the 14.5MHz case.
Wireless Components
4-5
Specification, May 2003