Specifications
Page 24
WT1231H
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 RssiV
alue 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 WAIT
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:
Towa
rds
-125
dB
m
16dB 7dB 11dB 9dB
11dB
Pin
[dBm]
G1 G2 G3 G4 G5
G6
Higher
Sensitivity
Lower
Linearity
Lower Noise
Figure
Lower
Sensitivity
Higher
Linearity
Higher Noise
Figure
Figure 8. AGC Thresholds
Settings
The follo
wing table summarizes the performance (typical figures) of the complete receiver: