TDA 5201
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 wide enough to guarantee a receive
frequency range between 310 MHz and 350 MHz. The VCO signal is divided by 2 before applied to the mixer .
This local oscillator signal can be used to down-convert the RF signals both with high- or low-side injection at the
mixer. High-side injection of the local oscillator has to be used for receive frequencies between 310 MHz and 330
MHz. In this case the local oscillator frequency is calculated by adding the IF frequency (10.7 MHz) to the RF
frequency.
Low-side injection has to be used for receive frequencies between 330 MHz and 350 MHz. The local oscillator
frequency is calculated by subtracting the IF frequency (10.7 MHz) from the RF frequency then. 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 formula:
f QU
=
f RF −10.7
r
(5)
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
CSEL
Open
GND
PLL Division Ratio Dependence on States of CSEL
Ratio r = (ƒLO/ƒQU)
64
32
Example
Addition of 10.7 is used in case of operation the device at 315 MHz, subtraction in case of operation at 345 MHz
for instance. This yields the following frequencies:
CSEL tied to GND:
f QU = (315 MHz + 10.7MHz )/ 32 = 10.1781 MHz
(6)
f QU = (345 MHz − 10.7MHz )/ 32 = 10.4469 MHz
(7)
CSEL open:
fQU = (315MHz + 10.7MHz)/ 64 = 5.0891MHz
(8)
f QU = (345 MHz − 10.7MHz )/ 64 = 5.2234 MHz
(9)
Data Sheet
25
Revision 1.6, 2010-12-21