Rainbow Electronics AT86RF230 - Manual (Page 24)

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AT86RF230
5131A-ZIGB-06/14/06
Both calibration routines will be initiated automatically when the PLL is turned on. Additionally, the center frequency
calibration is running when the PLL is programmed to a different channel (register 0x08 bits [4:0]). If the PLL is not
turned off for a long time, the control loops should be manually initiated from time to time. The calibration interval
depends on environment temperature variations but should not be longer than 5 min.
6.8. Automatic Filter Tuning
The filter-tuning unit is a separate building block within the AT86RF230. A calibration cycle is initiated automatically
when entering the TRX_OFF state from either the SLEEP, RESET or P_ON states. The result of the calibration is
the 6-bit word FTNV, and is written to the register 0x18 (FTN_CTRL).
The filter-tuning value FTNV is used to provide a stable SSBF transfer function and PLL loop-filter time constant
independent of temperature effects and part-to-part variations.
It is possible to trigger the calibration algorithm manually by setting the register bit FTN_START = 1.