Semtech LR1121 - High Power PA; Figure 9-6: HP PA Output Power Vs. Txpower

LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
89 of 130
Semtech
Proprietary & Confidential
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9.2.2 High Power PA
Figure 9-6: HP PA Output Power vs. TxPower shows the output power of the high power PA with TxPower for different
PaDutyCycle settings and over the supply voltage.
For a given PaDutyCycle, the output power of the high power PA is maintained on a certain voltage range, and then
decreases with VBAT. For example:
• For the +22dBm power setting, a VR_PA of ~3.1V is required (refer to Figure 9-4). Therefore, given the 200mV drop-out
of the PA regulator, the +22dBm output power can only be obtained from a 3.3V to 3.7V supply voltage range.
• For +17dBm, VR_PA around 2V is required. Therefore the LR1121 output power will drop to +17dBm for the minimum
supply voltage 1.8V.
Therefore, the 3.3V and 3.7V plots are then superimposed for a given PaDutyCycle, and only the plots for 3.7V are visible.
For a given supply voltage, increasing the PaDutyCycle increases the output power.
For example:
• For the +22dBm power setting at 3.3V, PaDutyCycle=4 allows the high power PA to deliver +22dBm
• For the +22dBm power setting at 3.3V, PaDutyCycle=2 allows the high power PA to deliver +20dBm
Figure 9-6: HP PA Output Power vs. TxPower