TDA7100 Datasheet, PDF (27/41 Pages) Infineon Technologies AG – 434 MHz ASK/FSK Transmitter in 10-pin Package

TDA7100
Applications
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.
Cv =
1
1 _{= C1}
+ω²L
CL
Example for the FSK-Mode:
FSK modulation is achieved by switching the load capacitance of the crystal as shown
below.
FSKDTA
FSKOUT
Csw
-R
L
COSC
f, CL Cv1
Cv2
IC
Figure 15 FSK Mode
The frequency deviation of the crystal oscillator is multiplied with the divider factor N of
the Phase Locked Loop to the output of the power amplifier. In case of small frequency
deviations (up to +/- 1000 ppm), the two desired load capacitances can be calculated
with the formula below.
CL±
=
CL
m
C0
∆f
N*
f
1
(1 +
2(C0 +
C1
CL) ₎
1±
∆f
N*
f
1
(1
+
2(C0 + CL))
C1
Data Sheet
27
V 1.0, 2007-05-02