Hy,
Here is my configuration for the "LLCC68MB2BAS_868MHz" evaluation board from SEMTECH
Test equipment :
R&S FSU spectrum analyzer in SPAN = 0 mode
Oscilloscope: FLUKE 200Mhz
Battery supply 4.1V
System requirements: Output power = +14dBm
To obtain +14dBm RF output, the configuration found is :
Padc (paDutyCycle)= 3
Pahpm (hpMax)=3
Txdbm (SetTxParams)= 22
regModParam default =1 (DC-DC + LDO)
Observation of the power envelope of frames transmitted after board power-up.
Frames Pout start Pout end Deviation
View burst n° 1 7.5 dBm 11.7 dBm 4.2 dB
View burst n° 2 11.5 dBm 13.3 dBm 1.8 dB
View burst n° 3 12.6 dBm 13.96 dBm 1.36 dB
View burst n° 4 13.3 dBm 14.26 dBm 0.96 dB
View burst n° 5 13.9 dBm 14.36 dBm 0.46 dB
Battery voltage is stable and constant 3.95Volts.
Voltage Vdd = 3.3 volts (stable)
Voltage VrPA = 3.14 volts (stable)
Voltage Vref = 1.5 volts (stable)
Translated with DeepL.com (free version)
Burst n°1 :
Burst n°2
Burst n°3 :
Burst n°4 :
Burst n°5 :
VrPA voltage at 1st view :
Conclusion :
SEMTECH's "LLCC68MB2BAS_868MHz" board shows unsatisfactory behavior in terms of RF transmit power level.
This observation is observed whatever the configuration of the PA parameters (paDutyCycle, hpMax, SetTxParams), but with abnormal behavior, for example:
Padc (paDutyCycle)= 2
Pahpm (hpMax)=2
Txdbm (SetTxParams)= 22
The average power will be around +9dBm with a 3 dB variation within the frame, then with each new frame, the power drops by around 1 dB. After 10 frames, power is stable at +3 dBm and not at +14 dBm as indicated in the datasheet:
DS_LLCC68_V1.0-1.pdf table 13.21 page 71/106.
If an SEMTECH expert could respond to this problem and indicate how to eliminate this strange behavior.
The LDO or DC-DC+LDO parameter has no effect on this finding.
