TDA5251F1 Datasheet, PDF (50/88 Pages) Infineon Technologies AG – ASK/FSK 315MHz Wireless Transceiver

TDA5251 F1
Version 1.0
Confidential
Application
With C_L+ and C_L- the necessary C_v+ for FSK HIGH and C_v- for FSK LOW can be calculated.
Alternatively, an external AC coupled (10nF in series to 1kW) signal can be applied at pin 19 (Xout).
The drive level should be approximately 100mVpp.
3.2.1 Synthesizer Frequency setting
Generating ASK and FSK modulation 3 setable frequencies are necessary.
3.2.1.1 Possible crystal oscillator frequencies
The resulting possible crystal oscillator frequencies are shown in the following Figure 3-14
RX:
FSK
TX: FSK-
ASK
ASK
FSK+
Deviation Deviation
f₁
f₀
f₂
Nominal
Frequency
free_reg.wmf
Figure 3-14 possible crystal oscillator frequencies
In ASK receive mode the crystal oscillator is set to frequency f₂ to realize the necessary frequency
offset to receive the ASK signal at f₀*N (N: division ratio of the PLL).
To set the 3 different frequencies 3 different C_v are necessary. Via internal switches 3 external
capacitors can be combined to generate the necessary C_v in case of ASK- or FSK-modulation.
Internal banks of switchable capacitors allow the finetuning of these frequencies.
3.2.2 Transmit/Receive ASK/FSK Frequency Assignment
Depending on whether the device operates in transmit or receive mode or whether it operates in
ASK or FSK the following cases can be distinguished:
3.2.2.1 FSK-mode
In transmit mode the two frequencies representing logical HIGH and LOW data states have to be
adjusted depending on the intended frequency deviation and separately according to the following
formulas:
f_{COSC HI} = (f_RF + f_DEV) / 24
f_{COSC LOW} = (f_RF - f_DEV) / 24
[3 – 19]
Preliminary Specification
50
2003-02-18