TDA7110F Datasheet, PDF (22/36 Pages) Infineon Technologies AG – 434 MHz ASK/FSK Transmitter in 10-pin Package

TDA7110F
3.4
Application Hints on the Crystal Oscillator
Applications
Application Hints on the crystal oscillator
The crystal oscillator achieves a turn on time less than 1 msec when the specified crystal
is used. To achieve this, a NIC oscillator type is implemented in the TDA7110F. The input
impedance of this oscillator is a negative resistance in series to an inductance. Therefore
the load capacitance of the crystal CL (specified by the crystal supplier) is transformed
to the capacitance Cv.
-R
L
f, CL Cv
IC
Figure 11 Application Hints
Formula 1:
Cv = ¹
1 _+ω2L
CL
CL:
crystal load capacitance for nominal frequency
ω:
angular frequency
L:
inductance of the crystal oscillator
Example for the ASK-Mode:
Referring to the application circuit, in ASK-Mode the capacitance C2 is replaced by a
short to ground. Assume a crystal frequency of 13.56MHz and a crystal load capacitance
of CL = 12 pF. The inductance L at 13.56MHz is about 4.6 μH. Therefore C1 is calculated
to 10 pF.
But please note that the calculated Cv value includes all parasitic. So the value of the
capacitor (except the parasitic) is a bit smaller depending on the parasitic.
Cv = ¹ = C1
1 _+ω2L
CL
Data Sheet
22
V 1.0, 2009-02-26