We have noticed that when changing by 1LSB the Tx attenuation of the AD9361, the output power momentarily (~ 1-1.5 us) changes by ~3.0dB. The problem only occurs at specific attenuation indexes. We have been able to measure that the following indexes are problematic:
- 0x77 <-> 0x78
- 0x8F <-> 0x90
- 0xA7 <-> 0xA8
- 0xBF <-> 0xC0
- 0xD7 <-> 0xD8
- 0xDF <-> 0xE0
There might be additional indexes that are problematic. It is however difficult to measure them all due to the large attenuation range.
Note that we have observed the same behavior on the ADI evaluation board. Note also that our system is FDD.
To update the Tx attenuation we use the method 2b. as originally described in the AD9361 Tx Power Control Users Guide reference document (Rev 2.1V, 10/11).
The next figures present instantaneous power when transitioning between various index.
alc_transition_0x77-0x76.tif: No problem observed
alc_transition_0x77-0x78.tif: Problem observed
alc_transition_0x78-0x77.tif: Problem observed
ADI_ref_board_alc_transition_0x78-0x77.tif: Problem observed on ADI eval board.
Do you have any suggestions to avoid such long and large Tx power glitches ?