TDA7210V_10 Datasheet, PDF (21/44 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7210V
Applications
3.4
Quartz Frequency Calculation
As described in Chapter 2.4.3 the operating range of the on-chip VCO is 820 to 860 MHz with a nominal center
frequency of 840 MHz. This signal is divided by 2 before applied to the mixer in case of operation at 434 MHz. This
local oscillator signal can be used to downconvert the RF signals both with high- or low-side injection at the mixer.
The resulting receive frequency ranges then extend between 810 and 870 MHz or between 400 and 440 MHz.
Low-side injection of the local oscillator has to be used for receive frequencies between 840 and 870 MHz as well
as high-side injection for receive frequencies below 840 MHz. Corresponding to that in the 400 MHz region low-
side injection is applicable for receive frequencies above 420 MHz, high-side injection below this frequency.
Therefore for operation both in the 868 and the 434 MHz ISM bands low-side injection of the local oscillator has
to be used. Then the local oscillator frequency is calculated by subtracting the IF frequency (10.7 MHz) from the
RF frequency (434 or 868 MHz). Please note that for low-side injection no sign-inversion occurs in case of
reception and demodulation of FSK-modulated signals.
The overall division ratios in the PLL are 64 or 128 in case of operation at 868 MHz or 32 and 64 in case of
operation at 434 MHz, depending on the crystal frequency used as shown below. The quartz frequency in case of
low-side injection may be calculated by using the following formula:
f _QU
=
f _RF
±10.7
r
(5)
ƒ_RF
Receive frequency
ƒ_LO
Local oscillator (PLL) frequency (ƒ_RF ± 10.7)
ƒ_QU
Quartz oscillator frequency
r
Ratio of local oscillator (PLL) frequency and quartz, frequency as shown in the subsequent table.
Table 7
FSEL
Open
Open
GND
GND
Dependence of PLL Overall Division Ratio on FSEL and CSEL
CSEL
Ratio r = (fLO/fQU)
Open
64
GND
32
Open
128
GND
64
Example (low-side injection mode):
f_QU = (868.4MHz −10.7MHz)/ 64 = 13.40156 MHz
(6)
f_QU = (868.4MHz − 10.7MHz )/128 = 6.7008 MHz
(7)
f_QU = (434.2 MHz −10.7MHz)/ 32 = 13.23437 MHz
(8)
f_QU = (434.2 MHz − 10.7MHz )/ 64 = 6.6172 MHz
(9)
Data Sheet
21
Revision 1.1, 2010-06-18