RFM95 Datasheet, PDF (49/121 Pages) List of Unclassifed Manufacturers – Low Power Long Range Transceiver Module

WIRELESS & SENSING
RFM95/96/97/98(W)
PRELIMINARY
DATASHEET
4.2.3.7. Image Rejection Mixer
The RFM95/96/97/98(W) employs an image rejection mixer (IRM) which, uncalibrated, 35 dB image rejection. A low phase
noise
PLL is used to perform calibration of the receiver chain. This increases the typical image rejection to 48 dB.
4.2.3.8. Image and RSSI Calibration
An automatic calibration process is used to calibrate the phase and gain of both I and Q receive paths. This calibration
allows enhanced image frequency rejection and improves the RSSI precision. This Calibration process is launched under
the following circumstances:
Š Automatically at Power On Reset or after a Manual Reset of the chip (refer to section 7.2). For applications where the
temperature remains stable, or if the Image Rejection is not a major concern, this single calibration will suffice.
Š Automatically when a pre-defined temperature change is observed.
Š Upon User request, by setting bit ImageCalStart in RegImageCal, when the device is in Standby mode. Note that in
LoRa^TM mode the calibration command is inaccessible. To perform the calibration, the radio must be returned
temporarily to FSK/OOK mode for the calibration process.
A selectable temperature change, set with TempThreshold (5, 10, 15 or 20°C), is detected and reported in TempChange, if
the temperature monitoring is turned On with TempMonitorOff=0.
This interrupt flag can be used by the application to launch a new image calibration at a convenient time if
AutoImageCalOn=0, or immediately when this temperature variation is detected, if AutoImageCalOn=1.
The calibration process takes approximately 10ms.
4.2.3.9. Timeout Function
The RFM95/96/97/98(W) includes a Timeout function, which allows it to automatically shut-down the receiver after a
receive sequence and therefore save energy.
Š Timeout interrupt is generated TimeoutRxRssi x 16 x Tbit after switching to Rx mode if the Rssi flag does not raise
within this time frame (RssiValue > RssiThreshold)
Š Timeout interrupt is generated TimeoutRxPreamble x 16 x Tbit after switching to Rx mode if the PreambleDetect flag
does not raise within this time frame
Š Timeout interrupt is generated TimeoutSignalSync x 16 x Tbit after switching to Rx mode if the SyncAddress flag does
not raise within this time frame
This timeout interrupt can be used to warn the companion processor to shut down the receiver and return to a lower power
mode. To become active, these timeouts must also be enabled by setting the correct RxTrigger parameters in
RegRxConfig:
Table 66 RxTrigger Settings to Enable Timeout Interrupts
Receiver
Triggering Event
None
Rssi Interrupt
PreambleDetect
Rssi Interrupt & PreambleDetect
RxTrigger
(2:0)
000
001
110
111
Timeout on
Rssi
Off
Active
Off
Active
Timeout on
Preamble
Off
Off
Active
Active
Timeout on
SyncAddress
Active
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