TDA 5210
Applications
4.4 Quartz Frequency Calculation
As described in Section 3.4.3 the operating range of the on-chip VCO is 820 to
860 MHz with a nominal center frequency of 840MHz. This signal is divided by
2 before applied to the mixer in case of operation at 434 MHz. This local oscil-
lator 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 870MHz or between 400 and 440MHz. Low-side injection of
the local oscillator has to be used for receive frequencies between 840 and
870MHz as well as high-side injection for receive frequencies below 840MHz.
Corresponding to that in the 400MHz region low-side injection is applicable for
receive frequencies above 420MHz, 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 fre-
quency is calculated by subtracting the IF frequency (10.7 MHz) from the RF
frequency (434 or 868 MHz). Please note that 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 crys-
tal frequency used as shown below. The quartz frequency in case of low-side
injection may be calculated by using the following formula:
ƒQU = (ƒRF - 10.7) / r
with ƒRF receive frequency
ƒLO local oscillator (PLL) frequency (ƒRF - 10.7)
ƒQU quartz oscillator frequency
r
ratio of local oscillator (PLL) frequency and quartz frequency as
shown in the subsequent table
Table 4-1 Dependence of PLL Overall Division Ratio on FSEL and CSEL
FSEL
open
open
GND
GND
CSEL
open
GND
open
GND
Ratio r = (fLO/fQU)
64
32
128
64
:
fQU
fQU
fQU
fQU
=
=
=
=
(
868.4MHz −10.7MHz
868.4MHz −10.7MHz
434.2MHz −10.7MHz
434.2 MHz −10.7MHz
)
/ 64 = 13.40156MHz
/128 = 6.7008 MHz
/32 = 13.23437MHz
/ 64 = 6.6172 MHz
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Wireless Components
4 - 6
Specification, May 2001
INFINEON [ Infineon ]
