RF69 datasheet(24/81 Pages) ETC2

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RF69

Page 24

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3.4.3. Automatic Gain Control

By default (LnaGainSelect = 000), the LNA gain is controlled by a digital AGC loop in order to obtain the optimal sensitivity/

linearity trade-off.

Regardless of the data transfer mode (Packet or Continuous), the following series of events takes place when the receiver

is enabled:

 The receiver stays in WAIT mode, until RssiValue exceeds RssiThreshold for two consecutive samples. Its power

consumption is the receiver power consumption.

 When this condition is satisfied, the receiver automatically selects the most suitable LNA gain, optimizing the

sensitivity/linearity trade-off.

 The programmed LNA gain, read-accessible with LnaCurrentGain in RegLna, is carried on for the whole duration of the

packet, until one of the following conditions is fulfilled:

 Packet mode: if AutoRxRestartOn = 0, the LNA gain will remain the same for the reception of the following packet. If

AutoRxRestartOn = 1, after the controller has emptied the FIFO the receiver will re-enter the WAIT mode described

above, after a delay of InterPacketRxDelay, allowing for the distant transmitter to ramp down, hence avoiding a false

RSSI detection. In both cases (AutoRxRestartOn=0 or AutoRxRestartOn=1), the receiver can also re-enter the W AIT

mode by setting RestartRx bit to 1. The user can decide to do so, to manually launch a new AGC procedure.

 Continuous mode: upon reception of valid data, the user can decide to either leave the receiver enabled with the

same LNA gain, or to restart the procedure, by setting RestartRx bit to 1, resuming the WAIT mode of the receiver,

described above.

Notes - the AGC procedure must be performed while receiving preamble in FSK mode

- in OOK mode, the AGC will give better results if performed while receiving a constant

“1” sequence

The following figure illustrates the AGC behavior:

Towards

-125 dBm

16dB

7dB

11dB

9dB

11dB

Pin [dBm]

Higher Sensitivity

Lower Linearity

Lower Noise Figure

Lower Sensitivity

Higher Linearity

Higher Noise Figure

Figure 8. AGC Thresholds Settings

The following table summarizes the performance (typical figures) of the complete receiver:

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