RF69 datasheet(25/81 Pages) ETC2

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RF69

Page 25

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Table 13 Receiver Performance Summary

Input Power

Gain

Setting

Receiver Performance (typ)

P-1dB

[dBm]

[dB]

IIP3

[dBm]

IIP2

[dBm]

Pin < AgcThresh1

-37

-18

+35

AgcThresh1 < Pin < AgcThresh2

-31

-15

+40

AgcThresh2 < Pin < AgcThresh3

-26

-8

+48

AgcThresh3 < Pin < AgcThresh4

-14

-1

+62

AgcThresh4 < Pin < AgcThresh5

>-6

+13

+68

AgcThresh5 < Pin

+20

+75

3.4.3.1. RssiThreshold Setting

For correct operation of the AGC, RssiThreshold in RegRssiThresh must be set to the sensitivity of the receiver. The

receiver will remain in WAIT mode until RssiThreshold is exceeded.

Note

When AFC is enabled and performed automatically at the receiver startup, the channel filter used by the receiver

during the AFC and the AGC is RxBwAfc instead of the standard RxBw setting. This may impact the sensitivity of

the receiver, and the setting of RssiThreshold accordingly

3.4.3.2. AGC Reference

The AGC reference level is automatically computed in the RF69, according to:

AGC Reference [dBm] = -174 + NF + DemodSnr +10.log(2*RxBw) + FadingMargin [dBm]

With:

 NF = 7dB

: LNA

‟ s Noise Figure at maximum gain

 DemodSnr = 8 dB

: SNR needed by the demodulator

 RxBw

: Single sideband channel filter bandwidth

 FadingMargin = 5 dB : Fading margin

3.4.4. Continuous-Time DAGC

In addition to the automatic gain control described in section 3.4.3, the RF69 is capable of continuously adjusting its gain

in the digital domain, after the analog to digital conversion has occured. This feature, named DAGC, is fully transparent to

the end user. The digital gain adjustment is repeated every 2 bits, and has the following benefits:

 Fully transparent to the end user

 Improves the fading margin of the receiver during the reception of a packet, even if the gain of the LNA is frozen

 Improves the receiver robustness in fast fading signal conditions, by quickly adjusting the receiver gain (every 2 bits)

 Works in Continuous, Packet, and unlimited length Packet modes

The DAGC is enabled by setting RegTestDagc to 0x20 for low modulation index systems (i.e. when AfcLowBetaOn=1,

refer to section 3.4.16), and 0x30 for other systems. It is recommended to always enable the DAGC.

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