TDA7110 Datasheet, PDF (26/39 Pages) Infineon Technologies AG – ASK/FSK Transmitter 868/433 MHz

TDA7110
Applications
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
IC
Cv2
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
Δf
N*
f
1
(1
+
2(C0 +
C1
CL)
)
1 ± ^Δf (1 + ^{2(C0 + CL)} )
N* f1
C1
C_L: crystal load capacitance for nominal frequency
C₀: shunt capacitance of the crystal
f: frequency
ω: ω = 2πf: angular frequency
N: division ratio of the PLL
df: peak frequency deviation
Because of the inductive part of the TDA7110, these values must be corrected
by Formula 1). The value of Cv± can be calculated.
Cv± =
1
1 _+ω2L
CL ±
Wireless Components
3-6
Data Sheet, December 2008