RF65 datasheet(22/72 Pages) ETC2

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RF65

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ADVANCED COMMUNICATIONS & SENSING

DATASHEET

fc = --- ------

The default value of DccFreq cutoff frequency is typically 4% of the RxBw (channel filter BW). The cutoff frequency of the

DCC can however be increased to slightly improve the sensitivity, under wider modulation conditions. It is advised to adjust

the DCC setting while monitoring the receiver sensitivity.

3.4.8. Complex Filter - OOK

In OOK mode the RF65 is modified to a low-IF architecture. The IF frequency is automatically set to half the single side

bandwidth of the channel filter (FIF = 0.5 x RxBw). The Local Oscillator is automatically offset by the IF in the OOK receiver.

A complex filter is implemented on the chip to attenuate the resulting image frequency by typically 30 dB.

Note

this filter is automatically bypassed when receiving FSK signals (ModulationType = 00 in RegDataModul).

3.4.9. RSSI

The RSSI block evaluates the amount of energy available within the receiver channel bandwidth. Its resolution is 0.5 dB,

and it has a wide dynamic range to accommodate both small and large signal levels that may be present. Its acquisition

time is very short, taking only 2 bit periods. The RSSI sampling must occur during the reception of preamble in FSK, and

constant

“1” reception in OOK.

Note

- The receiver is capable of automatic gain calibration, in order to improve the precision of its RSSI measurements.

This function injects a known RF signal at the LNA input, and calibrates the receiver gain accordingly. This

calibration is automatically performed during the PLL start-up, making it a transparent process to the end-user.

- RssiValue can only be read when it exceeds RssiThreshold

3.4.10. Cordic

The Cordic task is to extract the phase and the amplitude of the modulation vector (I+j.Q). This information, still in the

digital domain is used:



Phase output: used by the FSK demodulator and the AFC blocks.



Amplitude output: used by the RSSI block, for FSK demodulation, AGC and automatic gain calibration purposes.

Real-time

Magnitude

Q(t)

Real-time Phase

I(t)

Figure 7. Cordic Extraction

3.4.11. Bit Rate Setting

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