Silicon Laboratories SI4421 Manual de usuario descargar pdf (Pagina 10)

RF WIRELESS FOUNDATION COURSE BOOK ONE

10 Rev. 0.1

What is Happening on the Receiver Side?

The modulated data is represented by two frequencies: and , where is the center frequency

and is the deviation. The receiver should focus on this information and should filter it out from the noise. One

of the parameters that is configurable on the RFIC is the bandwidth of the baseband filter. This circuit filters out real

information from the air, so this parameter has to be set properly. If the filter is set to too narrow, it filters out the real

data as well. If the filter is set to too wide, then it allows in too much noise, affecting the receiver sensitivity.

Figure 13. FSK Modulation

Tips & Tricks

"How does this work with EZRadio Universal ISM band FSK radio ICs?"

Silicon Labs’ EZRadio FSK transceiver chip has a zero IF architecture, so the baseband filter of them has a high

pass filter for dc cancelation. The corner frequency of it is at 10 kHz! This has to be kept in mind when defining the

deviation for the transmitter.

In raw data mode (if the FIFO is not used), the transceiver IC provides the received and demodulated data on the

DATA pin. They can also provide the recovered clock on the DCLK pin, which helps to get samples from the DATA

pin while using the right timing, according to a given data rate.

FSK





FSK





FSK



frequency [Mhz]

out

[dBm]

deviation deviation

-BBBW f

+ BBBW

± 10kHz Base band filter

characteristic

Transmitted

data

Note:

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16

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Silicon Laboratories SI4421 Manual de usuario Pagina 10