SX1231 Просмотр технического описания (PDF) - Semtech Corporation

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SX1231

Low Power Integrated UHF Transceiver

Semtech Corporation 

SX1231

ADVANCED COMMUNICATIONS & SENSING

DATASHEET

3.5.3. 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:

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

consumption is the receiver power consumption.

Š When this condition is satisfied, the receiver automatically selects the most suitable LNA gain, optimizing the sensitivity/

linearity trade-off.

Š 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:

Š 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.

Š 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

G1

7dB

11dB

G2

G3

9dB

11dB

Pin [dBm]

G4

G5

G6

Higher Sensitivity

Lower Linearity

Lower Noise Figure

Figure 7. AGC Thresholds Settings

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

Lower Sensitivity

Higher Linearity

Higher Noise Figure

Rev 3 - April 2010

Page 23

www.semtech.com

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