In the TX time slot, some RX channels can be reused as TX observation channels for PA linearization. The observation channel, in general, requires a wider bandwidth than the RX channel; this results in different decimation factors and data rates between the RX and Obs configurations.
When enabling the TDD RX/Obs sharing mode in the IP configuration, there are
two AXI4-Stream interfaces available for each
RF-ADC channel. The decimation factor, output data
rate, and FIFO configurations for each AXI4-Stream
are preserved independently, and can be switched dynamically using PL inputs (tdd_obs). Note that the RX and Obs configurations share
other function blocks in RF-ADC, such as the complex
mixer/NCO, DSA, etc. For example, choose the same real/complex mode and the same NCO
frequencies for both RX and Obs channels. The RX and Obs channels transmit data
simultaneously, yet only the data from the currently configured channel is considered
valid due to the compatibility of the data rate between the RFDC IP and the PL. The DSA
value can vary when RF-ADC switches from one mode to
another. You should set your desired DSA value each time through real time ports or RFdc
API.
For RX/Obs shared channels, when DSA values are different for RX mode and Obs mode, user should set desired DSA value for each mode before or after switching from one mode to another, the real time DSA ports enable fast DSA values updating.
Two PL clocks (AXIS_aclk, AXIS_obs_aclk) are available for different data rates.
The following diagram illustrates the TDD RX/Obs sharing mode.
An example of the timing on the observation interface is shown in the following
figure. When tdd_obs is Low the outputs are from the
FIFO1 datapath. When tdd_obs is High the outputs are
from the FIFO2 datapath. The switchover time is dependent on the settings in the
RF-ADC digital datapath.
