Semtech LR1121 - Calibrations; Table 2-2: Calibimage Command; Table 2-3: ISM Band Values

LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
15 of 130
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2.1.3 Calibrations
During the startup sequence, the device firmware calibrates the low and high frequency RC oscillators, the PLL, the ADC,
and the image rejection of the mixer at 915MHz. After the calibration procedure the device is set in Standby RC mode.
If operating at another frequency, the image calibration procedure must be restarted using command CalibImage(...).
An image calibration is advised after large temperature variations and optimal image rejection using command
CalibImage(...).
Image calibration is necessary if there is a frequency change > 10MHz, or a temperature change > 10°C.
2.1.3.1 CalibImage
The CalibImage(...) command launches an image calibration for the given range of frequencies Freq1 and Freq2 on the
RFI_N/P_LF sub-GHz path.
By default, the image calibration is made in the band 902 - 928MHz. Nevertheless, it is possible to request the device to
perform a new image calibration at other frequencies. The frequencies are given in 4MHz steps (Ex: 900MHz -> 0xE1).
The calibration is valid for all frequencies between the two parameters. Typically, the user selects the parameters Freq1 and
Freq2 from Table 2-3: ISM Band Values. The same frequency may be provided as Freq1 and Freq2 to perform a single
calibration for the Freq1 / Freq2 value.
The command operates in any mode. At the end of the calibration procedure, the device returns to Standby RC.
For other frequency bands, Freq1 and Freq2 values can be obtained using the following formula:
• Freq1 = floor( (fmin_mhz - 1)/4)
• Freq2 = ceil( (fmax_mhz + 1)/4)
In the case of POR, or when the device is recovering from power-down or sleep mode without retention, the image
calibration is performed as part of the initial calibration process and for optimal image rejection in the band 902 - 928MHz.
If a TCXO is fitted, the calibration fails.
Table 2-2: CalibImage Command
Byte 0 1 2 3
Data from Host 0x01 0x11 Freq1 Freq2
Data to Host Stat1 Stat2 IrqStatus (31:24) IrqStatus (23:16)
Table 2-3: ISM Band Values
Frequency Band [MHz] Freq1 Freq2
430-440 0x6B 0x6E
470-510 0x75 0x81
779-787 0xC1 0xC5
863-870 0xD7 0xDB
902-928 0xE1 (default) OxE9 (default)