RF63 datasheet(25/91 Pages) ETC2

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ADVANCED COMMUNICATIONS & SENSING

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RF63

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As can be seen from Figure 17, the required bandwidth of this filter varies between the two demodulation modes.

•

FSK mode: The 99% energy bandwidth of an FSK modulated signal is approximated to be:

The bits RXParam_ButterFilt set fc, the cutoff frequency of the filter. As we are in a Zero-IF configuration, the FSK

lobes are centered around the virtual

“DC” frequency. The choice of fc should be such that the modulated signal

falls in the filter bandwidth, anticipating the Local Oscillator frequency drift over the operating temperature and

aging of the device:

Please refer to the charts in section 3.4.5 for an accurate overview of the filter bandwidth vs. setting.

•

OOK mode: The 99% energy bandwidth of an OOK modulated signal is approximated to be:

The bits RXParam_PolypFilt_center set fo, the center frequency of the polyphase filter when activated. fo should

always be chosen to be equal to the low Intermediate Frequency of the receiver (IF2). This is why, in the GUI

described in section 7.2.1 of this document, the low IF frequency of the OOK receiver denoted IF2 has been

replaced by fo.

The following setting is recommended:

The value stored in RXParam_ButterFilt determines fc, the filter cut-off frequency. So the user should set fc

according to:

Again, fc as a function of RXParam_ButterFilt is given in the section 3.4.6.

3.4.5. Channel Filters Setting in FSK Mode

Fc, the 3dB cutoff frequency of the Butterworth filter used in FSK reception, is programmed through the bit

RXParam_ButterFilt. However, the whole receiver chain influences this cutoff frequency. Thus the channel select

and resultant filter bandwidths are summarized in the following chart:

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