3.9.15 Antenna Tuning State Machine

The antenna tuning state machine tunes the antenna in TX mode by changing the capacitance values connected to the ANT_TUNE side. It steps through all 16 possible FEAT settings and measures the antenna level. Level measuring is implemented by a successive approximation algorithm that changes the FEANT value going to a DAC in the antenna tuning block and measures the antenna saturation via FESR.ANTS.

To secure the tuning process, a min/max detection is included that counts the number of antenna levels that have been measured as 0x0 or 0xF. This is an indicator for out-of-range measurement. Throughout the tuning, if a value of 0xF is measured, the antenna level detector range FEALR.RNGE is automatically increased to reduce the sensitivity for strong signals. If all measured values are at the border, the final FEAT value is set to 0x7 in the middle of the tuning range.

Before the start of the antenna tuning state machine, the antenna level detector range FEALR.RNGE can be appropriately set for the application. This specifies the lower bound of the applied range and can avoid such an out-of-range measurement. Firmware uses an EEPROM setting to set this value.

There are no user settings that influence the behavior of this state machine.