TDA5102 Datasheet, PDF (25/35 Pages) Infineon Technologies AG – ASK/FSK Transmitter 915 MHz

TDA 5102
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 5102.
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
1 _+ω2L
CL
Formula 1)
CL: crystal load capacitance for nominal frequency
ω: angular frequency
L: inductivity of the crystal oscillator
Example for the ASK-Mode:
Referring to the application circuit, in ASK-Mode the capacitance C7 is replaced
by a short to ground. Assume a crystal frequency of 14.3 MHz and a crystal load
capacitance of CL = 20 pF. The inductance L is specified within the electrical
characteristics at 14.3 MHz to a value of 11 µH. Therefore C6 is calculated to
7.2 pF.
Cv = ¹ = C6
1 _+ω2L
CL
Wireless Components
4-5
Specification, October 2001