TDA5211 Datasheet, PDF (26/52 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA 5211
Applications
4.4 Quartz Frequency Calculation
Wireless Components
As described in Section 3.4.3 the operating range of the on-chip VCO is wide
enough to guarantee a receive frequency range between 310 and 350MHz. The
VCO signal is divided by 2 before applied to the mixer . This local oscillator sig-
nal can be used to downconvert the RF signals both with high- or low-side injec-
tion at the mixer. High-side injection of the local oscillator has to be used for
receive frequencies between 310 and 330 MHz. In this case the local oscillator
frequency is calculated by adding the IF frequency (10.7 MHz) to the RF fre-
quency. In this case the higher frequency of a FSK-modulated signal is
demodulated as a logical one (high).
Low-side injection has to be used for receive frequencies between 330 and
350 MHz. The local oscillator frequency is calculated by subtracting the IF fre-
quency (10.7 MHz) from the RF frequency then. Please note that in this case
sign-inversion occurs and the higher frequency of a FSK-modulated signal is
demodulated as a logical zero (low). The overall division ratios in the PLL are
64 or 32 depending on whether the CSEL-pin is left open or tied to ground.
Therefore the quartz frequency may be calculated by using the following for-
mula:
ƒ_QU = (ƒ_RF ± 10.7) / r
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 4-1 PLL Division Ratio Dependence on States of CSEL
CSEL
Ratio r = (f_LO/f_QU)
open
64
GND
32
This yields the following examples:
CSEL tied to GND:
f _QU = (315MHz + 10.7MHz )/ 32 = 10.1781 MHz
f _QU = (345MHz − 10.7MHz )/ 32 = 10.4469 MHz
CSEL open:
f _QU = (315 MHz + 10.7MHz )/ 64 = 5.0891 MHz
f _QU = (345 MHz − 10.7MHz )/ 64 = 5.2234 MHz
4-6
Specification, May 2001