MRF39RA datasheet(8/72 Pages) MICROCHIP

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MRF39RA

DS40001778B-page 8

 2015 Microchip Technology Inc.

2.4.2

AUTOMATIC GAIN CONTROL

By default (LnaGainSelect = 000) the LNA gain is

controlled by a digital AGC loop 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 remains the same for the reception of the

following packet. If AutoRxRestartOn = 1, after

the controller has emptied the FIFO the receiver

re-enters the Wait mode, after a delay of

InterPacketRxDelay, enabling 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 Wait mode by setting RestartRx

bit to ‘1’. The user can decide to do this 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.

Figure 2-3 illustrates the AGC behavior.

FIGURE 2-3:

AGC THRESHOLDS SETTINGS

Note 1: The AGC procedure must be performed

while receiving preamble in FSK mode.

2: In OOK mode, the AGC gives better

results if performed while receiving a

constant ‘1’ sequence.

Towards

-125 dBm

Pin (dBm)

16 dB

7 dB

11 dB

9 dB

11 dB

Higher Sensitivity

Lower Linearity

Lower Noise Figure

Lower Sensitivity

Higher Linearity

Higher Noise Figure

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