TDA7200 Datasheet, PDF (22/49 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7200
Applications
3.3
Crystal Load Capacitance Calculation
The value of the capacitor necessary to achieve that the crystal oscillator is operating at
the intended frequency is determined by the reactive part of the negative resistance of
the oscillator circuit as shown in Section 4.1.3 and by the crystal specifications given by
the crystal manufacturer.
Crystal
C_S
Input
impedance
Z_1-28
CRST2
28
TDA7200
1
CRST1
Figure 6 Determination of Series Capacitance Vale for the Quartz Oscillator
The required series capacitor for a crystal with specified load capacitance C_L can be
calculated as
C_S
=
1
C_L
1
+ 2π
f
X_L
C_L is the nominal load capacitance specified by the crystal manufacturer.
Example:
13.4 MHz: C_L = 12 pF
X_L=1010 Ω
C_S = 5.9 pF
This value may be obtained by putting two capacitors in series to the crystal, such as
22pF and 8.2pF for 13.4MHz.
But please note that the calculated C_S-value includes all parasitic.
3.4
Crystal Frequency Calculation
As described in Section 2.4.3 the operating range of the on-chip VCO is wide enough to
guarantee a receive frequency range between 400 and 440MHz. The VCO signal is
divided by 2 before applied to the mixer. This local oscillator signal can be used to
downconvert the RF signals both with high- or low-side injection at the mixer. High-side
Data Sheet
22
V 1.0, 2007-05-02