7.7 Automatic Filter Tuning (FTN)

The Automatic Filter Tuning (FTN) is incorporated to compensate device tolerances for temperature and supply voltage variations, as well as part-to-part variations of the radio transceiver. The filter-tuning result is used to correct the analog baseband filter transfer function and the PLL loop-filter time constant.

An FTN calibration cycle is initiated automatically when entering the TRX_OFF state from the P_ON, SLEEP or RESET state.

Although receiver and transmitter are very robust against these variations, it is recommended to initiate the FTN manually if the radio transceiver does not use the SLEEP state. If necessary, a calibration cycle is to be initiated in states TRX_OFF, PLL_ON or RX_ON. This applies in particular for the High Data Rate modes with a much higher sensitivity against Band-Pass Filter (BPF) transfer function variations. The recommended calibration interval is five minutes or less, if the ATSAMR30M18A operates always in an active state (PLL_ON, TX_ARET_ON, RX_ON and RX_AACK_ON).