TDA5100A Datasheet, PDF (22/29 Pages) Infineon Technologies AG – ASK Transmitter 434 MHz

TDA 5100 A
preliminary
Applications
4.4 Hints
1. Application Hints on the crystal oscillator
As mentioned before, the crystal oscillator achieves a turn on time less than
1 msec. To achieve this, a NIC oscillator type is implemented in the TDA 5100A.
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
IC
f, CL Cv
Cv
=
1
CL
1
+ω²L
Formula 1)
CL: crystal load capacitance for nominal frequency
ω: angular frequency
L: inductance of the crystal oscillator
Example:
Assume a crystal frequency of 13.56 MHz and a crystal load capacitance of
CL = 20 pF. The inductance L is specified within the electrical characteristics at
13.56 MHz to a value of 4.5 µH. Therefore C6 is calculated to 12 pF.
Cv
=
1
CL
1
+ω²L
=
C6
Wireless Components
4-5
Specification, March 2001