SX1231-31SKB433 Semtech, SX1231-31SKB433 Datasheet - Page 25

• Manufacturer Part Number: SX1231-31SKB433
• Description: USB Kit - SX1231 433Mhz
• Manufacturer: Semtech

Table 12 Receiver Performance Summary
3.5.3.1. 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
3.5.3.2. AGC Reference
The AGC reference level is automatically computed in the SX1231, according to:
With:
3.5.4. Continuous-Time DAGC
In addition to the automatic gain control described in section 3.5.3, the SX1231 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:
The DAGC is enabled by setting RegTestDagc to 0x10 for low modulation index systems (i.e. when AfcLowBetaOn=1,
refer to section 3.5.16), and 0x30 for other systems. See section 9.6 for details. It is recommended to always enable the
DAGC.
Rev 4 - Nov 2010
ADVANCED COMMUNICATIONS & SENSING
NF = 7dB
DemodSnr = 8 dB
RxBw
FadingMargin = 5 dB : Fading margin
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
AGC Reference [dBm] = -174 + NF + DemodSnr +10.log(2*RxBw) + FadingMargin [dBm]
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
AgcThresh1 < Pin < AgcThresh2
AgcThresh2 < Pin < AgcThresh3
AgcThresh3 < Pin < AgcThresh4
AgcThresh4 < Pin < AgcThresh5
AgcThresh5 < Pin
: LNA’s Noise Figure at maximum gain
: Single sideband channel filter bandwidth
: SNR needed by the demodulator
Input Power
Pin
Pin < AgcThresh1
Setting
Gain
G2
G3
G4
G5
G1
G6
Page 25
[dBm]
P
-37
-31
-26
-14
>-6
>0
-1dB
Receiver Performance (typ)
[dB]
NF
13
18
27
36
44
7
[dBm]
IIP3
+13
+20
-18
-15
-8
-1
[dBm]
IIP2
+35
+40
+48
+62
+68
+75
DATASHEET
www.semtech.com
SX1231