Data Sheet

LJ1269HC
Rev1.0 Page 24 Web: www.ljelect.com
Table 13 Receiver Performance Summary
Input Power
Pin
Gain
Setting
Receiver Performance (typ)
P-1dB [dBm]
NF [dB]
IIP3 [dBm]
IIP2 [dBm]
Pin < AgcThresh1
G1
-37
7
-18
+35
AgcThresh1 < Pin < AgcThresh2
G2
-31
13
-15
+40
AgcThresh2 < Pin < AgcThresh3
G3
-26
18
-8
+48
AgcThresh4 < Pin < AgcThresh5
G4
-14
27
-1
+62
AgcThresh5 < Pin
G5
>-6
36
+13
+68
AgcThresh5 < Pin
G6
>0
44
+20
+75
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
AGC Reference
The AGC reference level is automatically computed in the LJ1269HC , 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
3.4.3. Continuous-Time DAGC
In addition to the automatic gain control described in section 3.4.3, the LJ1269HC 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)
 W orks 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.
Sub GHz FSK/OOK Transceiver Module DATASHEET