SX1231H View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SX1231H' PDF : 82 Pages View PDF
SX1231H
ADVANCED COMMUNICATIONS & SENSING
DATASHEET
Table 13 Receiver Performance Summary
Input Power
Pin
Pin < AgcThresh1
AgcThresh1 < Pin < AgcThresh2
AgcThresh2 < Pin < AgcThresh3
AgcThresh3 < Pin < AgcThresh4
AgcThresh4 < Pin < AgcThresh5
AgcThresh5 < Pin
Gain
Setting
G1
G2
G3
G4
G5
G6
Receiver Performance (typ)
P-1dB
[dBm]
NF
[dB]
IIP3
[dBm]
IIP2
[dBm]
-37
7
-18
+35
-31
13
-15
+40
-26
18
-8
+48
-14
27
-1
+62
>-6
36
+13
+68
>0
44
+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 SX1231H, 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 SX1231H 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.
Rev 1 - Oct 2011
Page 25
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