Datasheet
Table Of Contents
- 1. General Description
- 2. Electrical Characteristics
- 3. SX1272/73 Features
- 4. SX1272/73 Digital Electronics
- 4.1. The LoRaTM Modem
- 4.2. FSK/OOK Modem
- 4.2.1. Bit Rate Setting
- 4.2.2. FSK/OOK Transmission
- 4.2.3. FSK/OOK Reception
- 4.2.4. Operating Modes in FSK/OOK Mode
- 4.2.5. General Overview
- 4.2.6. Startup Times
- 4.2.7. Receiver Startup Options
- 4.2.8. Receiver Restart Methods
- 4.2.9. Top Level Sequencer
- 4.2.10. Data Processing in FSK/OOK Mode
- 4.2.11. FIFO
- 4.2.12. Digital IO Pins Mapping
- 4.2.13. Continuous Mode
- 4.2.14. Packet Mode
- 4.2.15. io-homecontrol® Compatibility Mode
- 4.3. SPI Interface
- 5. SX1272/73 Analog & RF Frontend Electronics
- 6. Description of the Registers
- 7. Application Information
- 8. Packaging Information
- 9. Revision History
www.semtech.comPage 34
SX1272/73
WIRELESS, SENSING & TIMING DATASHEET
Rev. 2 - July 2014
©2014 Semtech Corporation
4.1.4. Frequency Settings
Recalling that the frequency step is given by:
In order to set LO frequency values following registers are available.
Frf is a 24-bit register which defines carrier frequency. The carrier frequency relates to the register contents by following
formula:
4.1.5. Frequency Error Indication
The SX1272 derives its RF centre frequency from a crystal reference oscillator which has a finite frequency precision.
Errors in reference frequency will manifest themselves as errors of the same proportion from the RF centre frequency.
In LoRa receive mode the SX1272 is capable of measuring the frequency offset between the receiver centre frequency and
that of an incoming LoRa signal. The image below shows the estimated frequency offset and corresponding PER for
various coding rates as a function of frequency offset. Here we can see that the modem is intolerant of frequency offsets in
the region of +/- 20% of the bandwidth and will accurately report the error over this same range.
Figure 9. Applied versus measured frequency offset and influence on PER.
The error is read by reading the three RegFei registers. The contents of which are a signed 20 bit two's compliment word,
FreqError. The frequency error is determined from the register contents by:
Where Fxtal is the crystal frequency.
Please note that the measured FEI should not be applied to the RF centre frequency to perform AFC. The FEI
measurement is provided for information only.
F
STEP
F
XOSC
2
19
----------------
=
F
RF
F
STEP
Frf 23 0(,)×=
F
Error
FreqError 2
24
×
F
xtal
------------------------------------------
=