LR1110
User Manual
Rev.1.0
UM.LR1110.W.APP
March 2020
80 of 130
Semtech
9.4 Impedance Matching Networks
The High Power PA and Low Power PAs are available on the RFO_HP_LF and RFO_LP_LF pins respectively. They are
connected to the antenna through a dedicated impedance matching network, which aims at presenting the optimized
load at the output pins when loaded with 50 Ohms at the antenna level.
9.4.1 Multi-Band Operation
It is also possible to implement a multi-band configuration using a single impedance matching network, allowing the same
set of SMD components to cover multiple sub-GHz ISM bands.
Table 9-1: Optimized Settings for LP PA with the Same
Table 9-2: Optimized Settings for HP PA with the Same Matching Network
show the optimal settings
for the PA when using the Semtech matching network. The user can fine tune the
PaDutyCycle
and
PaHpSel
according to
their requirements of matching network, efficiency, output power, and harmonic emission.
The matching network implementation proposed by Semtech is optimized for +22dBm and +15dBm for the higher ISM
bands, i.e. a 868-928 MHz operation.
9.4.2 RF Switch Implementation
The implementation examples hereafter show a combined High Power PA and High Efficiency PA operation, with the use
of a 3 ports RF switch SP3T. A single-band operation is also possible, the unused PA pin being left unconnected. In that case
a 2 ports RF switch SPDT would be necessary.
The RF switch implementation allows optimizing the impedance presented to the PA and the impedance presented to the
LNA separately. Therefore one can optimize the TX efficiency without compromising the RX sensitivity.
The RF switch can be controlled either by the host controller, or by the LR1110 itself (pins DIO5, DIO6, DIO7, DIO8 and
DIO10), using the
SetDioAsRfSwitch( )
command.
Table 9-1: Optimized Settings for LP PA with the Same Matching Network
Target Power
TxPower
PaSel
RegPASupply
PaDutyCycle
PaHPSel
+15 dBm
14
0
0
7
-
+14 dBm
14
0
0
4
-
+10 dBm
14
0
0
0
-
Table 9-2: Optimized Settings for HP PA with the Same Matching Network
Target Power
TxPower
PaSel
RegPASupply
PaDutyCycle
PaHPSel
+22 dBm
22
1
1
4
7
+20 dBm
22
1
1
2
7
+17dBm
22
1
1
4
3
1
1
1
5
+14 dBm
22
1
1
2
2
