TDA5200_10 Datasheet, PDF (26/39 Pages) Infineon Technologies AG – ASK Single Conversion Receiver

TDA 5200
ASK Single Conversion Receiver
Applications
4.4
Quartz Frequency Calculation
As described in Chapter 3.4.3, the operating range of the on-chip VCO is 820 MHz to 860 MHz with a nominal
center frequency of approximately 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 down-convert the RF signals both with high- or
low-side injection at the mixer. The resulting receive frequency ranges then extend between 810 MHz and
870 MHz or between 400 MHz and 440 MHz. Low-side injection of the local oscillator has to be used for receive
frequencies between 840 MHz 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 MHz 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 MHz or 868 MHz). 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.
Therefore, the quartz frequency is calculated by using the following formula:
f _QU
=
f _RF
± 10.7
r
(5)
with
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 5
FSEL
Open
Open
GND
GND
PLL Division Ratio Dependence on States of CSEL
CSEL
Open
GND
Open
GND
Ratio r = (ƒ_LO/ƒ_QU)
64
32
128
64
Subtraction of 10.7 occurs in case the receive frequency is higher than the intended local oscillator frequency,
addition in case the receive frequency lies below the local oscillator frequency.
Example
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 −10.7 MHz)/ 32 = 13.23437MHz
(8)
Data Sheet
26
Revision 3.0, 2010-12-28