
RM0453 Rev 2
159/1454
RM0453
Sub-GHz radio (SUBGHZ)
217
5.4
Sub-GHz radio clocks
5.4.1 Internal
oscillators
The following sub-GHz radio dedicated internal RC oscillators are available:
•
64 kHz RC oscillator
–
optionally used during the sub-GHz radio Sleep mode to wake up the transceiver
when performing periodic or duty cycled operations
–
used by the sub-GHz radio RTC for time based events
•
13 MHz RC oscillator, enabled for all sub-GHz radio SPI communication
The frequency of each sub-GHz radio internal oscillators is calibrated using the HSE32
clock at every sub-GHz radio transition from Deep-Sleep or Sleep-to-Standby, and after a
sub-GHz radio reset. The calibration can also be done on demand by the command
Calibrate()
.
5.4.2 HSE32
reference
clock
The high-precision 32 MHz frequency needed for the sub-GHz radio transmission and
reception is taken from HSE32. The HSE32 clock can also be used by the MCU. The use of
an external crystal (XTAL) or a temperature compensated crystal oscillator (TCXO) are
supported. The used clock source is configured in the RCC (see
for more details).
When using the HSE32 with a XTAL, the load capacitors are provided by the integrated
capacitor banks that can be trimmed. The trimming is provided by SUBGHZ_HSEINTRIMR
and SUBGHZ_HSEOUTRIMR registers. The load capacitances on OSC_IN and OSC_OUT
can be trimmed separately. Software trimming must be applied after the sub-GHz radio
entered Standby with HSE32 mode.
The TCXO regulator, integrated in the sub-GHz radio, can be used to supply an external
temperature compensated crystal oscillator (TCXO). The regulated V
DDTCXO
supply level is
controlled through
set_TcxoMode()
command.
Table 29. LoRa mode intermediate frequencies
Setting name
Bandwidth [kHz]
f
if
[kHz]
LORA_BW_500
500
0
LORA_BW_250
250
250
LORA_BW_125
125
LORA_BW_62
62.5
LORA_BW_41
41.67
167
LORA_BW_31
31.25
250
LORA_BW_20
20.83
167
LORA_BW_15
15.63
250
LORA_BW_10
10.42
167
LORA_BW_7
7.81
250